diff --git a/doc/rfc2396.txt b/doc/rfc2396.txt deleted file mode 100644 index 5bd5211..0000000 --- a/doc/rfc2396.txt +++ /dev/null @@ -1,2243 +0,0 @@ - - - - - - -Network Working Group T. Berners-Lee -Request for Comments: 2396 MIT/LCS -Updates: 1808, 1738 R. Fielding -Category: Standards Track U.C. Irvine - L. Masinter - Xerox Corporation - August 1998 - - - Uniform Resource Identifiers (URI): Generic Syntax - -Status of this Memo - - This document specifies an Internet standards track protocol for the - Internet community, and requests discussion and suggestions for - improvements. Please refer to the current edition of the "Internet - Official Protocol Standards" (STD 1) for the standardization state - and status of this protocol. Distribution of this memo is unlimited. - -Copyright Notice - - Copyright (C) The Internet Society (1998). All Rights Reserved. - -IESG Note - - This paper describes a "superset" of operations that can be applied - to URI. It consists of both a grammar and a description of basic - functionality for URI. To understand what is a valid URI, both the - grammar and the associated description have to be studied. Some of - the functionality described is not applicable to all URI schemes, and - some operations are only possible when certain media types are - retrieved using the URI, regardless of the scheme used. - -Abstract - - A Uniform Resource Identifier (URI) is a compact string of characters - for identifying an abstract or physical resource. This document - defines the generic syntax of URI, including both absolute and - relative forms, and guidelines for their use; it revises and replaces - the generic definitions in RFC 1738 and RFC 1808. - - This document defines a grammar that is a superset of all valid URI, - such that an implementation can parse the common components of a URI - reference without knowing the scheme-specific requirements of every - possible identifier type. This document does not define a generative - grammar for URI; that task will be performed by the individual - specifications of each URI scheme. - - - - -Berners-Lee, et. al. Standards Track [Page 1] - -RFC 2396 URI Generic Syntax August 1998 - - -1. Introduction - - Uniform Resource Identifiers (URI) provide a simple and extensible - means for identifying a resource. This specification of URI syntax - and semantics is derived from concepts introduced by the World Wide - Web global information initiative, whose use of such objects dates - from 1990 and is described in "Universal Resource Identifiers in WWW" - [RFC1630]. The specification of URI is designed to meet the - recommendations laid out in "Functional Recommendations for Internet - Resource Locators" [RFC1736] and "Functional Requirements for Uniform - Resource Names" [RFC1737]. - - This document updates and merges "Uniform Resource Locators" - [RFC1738] and "Relative Uniform Resource Locators" [RFC1808] in order - to define a single, generic syntax for all URI. It excludes those - portions of RFC 1738 that defined the specific syntax of individual - URL schemes; those portions will be updated as separate documents, as - will the process for registration of new URI schemes. This document - does not discuss the issues and recommendation for dealing with - characters outside of the US-ASCII character set [ASCII]; those - recommendations are discussed in a separate document. - - All significant changes from the prior RFCs are noted in Appendix G. - -1.1 Overview of URI - - URI are characterized by the following definitions: - - Uniform - Uniformity provides several benefits: it allows different types - of resource identifiers to be used in the same context, even - when the mechanisms used to access those resources may differ; - it allows uniform semantic interpretation of common syntactic - conventions across different types of resource identifiers; it - allows introduction of new types of resource identifiers - without interfering with the way that existing identifiers are - used; and, it allows the identifiers to be reused in many - different contexts, thus permitting new applications or - protocols to leverage a pre-existing, large, and widely-used - set of resource identifiers. - - Resource - A resource can be anything that has identity. Familiar - examples include an electronic document, an image, a service - (e.g., "today's weather report for Los Angeles"), and a - collection of other resources. Not all resources are network - "retrievable"; e.g., human beings, corporations, and bound - books in a library can also be considered resources. - - - -Berners-Lee, et. al. Standards Track [Page 2] - -RFC 2396 URI Generic Syntax August 1998 - - - The resource is the conceptual mapping to an entity or set of - entities, not necessarily the entity which corresponds to that - mapping at any particular instance in time. Thus, a resource - can remain constant even when its content---the entities to - which it currently corresponds---changes over time, provided - that the conceptual mapping is not changed in the process. - - Identifier - An identifier is an object that can act as a reference to - something that has identity. In the case of URI, the object is - a sequence of characters with a restricted syntax. - - Having identified a resource, a system may perform a variety of - operations on the resource, as might be characterized by such words - as `access', `update', `replace', or `find attributes'. - -1.2. URI, URL, and URN - - A URI can be further classified as a locator, a name, or both. The - term "Uniform Resource Locator" (URL) refers to the subset of URI - that identify resources via a representation of their primary access - mechanism (e.g., their network "location"), rather than identifying - the resource by name or by some other attribute(s) of that resource. - The term "Uniform Resource Name" (URN) refers to the subset of URI - that are required to remain globally unique and persistent even when - the resource ceases to exist or becomes unavailable. - - The URI scheme (Section 3.1) defines the namespace of the URI, and - thus may further restrict the syntax and semantics of identifiers - using that scheme. This specification defines those elements of the - URI syntax that are either required of all URI schemes or are common - to many URI schemes. It thus defines the syntax and semantics that - are needed to implement a scheme-independent parsing mechanism for - URI references, such that the scheme-dependent handling of a URI can - be postponed until the scheme-dependent semantics are needed. We use - the term URL below when describing syntax or semantics that only - apply to locators. - - Although many URL schemes are named after protocols, this does not - imply that the only way to access the URL's resource is via the named - protocol. Gateways, proxies, caches, and name resolution services - might be used to access some resources, independent of the protocol - of their origin, and the resolution of some URL may require the use - of more than one protocol (e.g., both DNS and HTTP are typically used - to access an "http" URL's resource when it can't be found in a local - cache). - - - - - -Berners-Lee, et. al. Standards Track [Page 3] - -RFC 2396 URI Generic Syntax August 1998 - - - A URN differs from a URL in that it's primary purpose is persistent - labeling of a resource with an identifier. That identifier is drawn - from one of a set of defined namespaces, each of which has its own - set name structure and assignment procedures. The "urn" scheme has - been reserved to establish the requirements for a standardized URN - namespace, as defined in "URN Syntax" [RFC2141] and its related - specifications. - - Most of the examples in this specification demonstrate URL, since - they allow the most varied use of the syntax and often have a - hierarchical namespace. A parser of the URI syntax is capable of - parsing both URL and URN references as a generic URI; once the scheme - is determined, the scheme-specific parsing can be performed on the - generic URI components. In other words, the URI syntax is a superset - of the syntax of all URI schemes. - -1.3. Example URI - - The following examples illustrate URI that are in common use. - - ftp://ftp.is.co.za/rfc/rfc1808.txt - -- ftp scheme for File Transfer Protocol services - - gopher://spinaltap.micro.umn.edu/00/Weather/California/Los%20Angeles - -- gopher scheme for Gopher and Gopher+ Protocol services - - http://www.math.uio.no/faq/compression-faq/part1.html - -- http scheme for Hypertext Transfer Protocol services - - mailto:mduerst@ifi.unizh.ch - -- mailto scheme for electronic mail addresses - - news:comp.infosystems.www.servers.unix - -- news scheme for USENET news groups and articles - - telnet://melvyl.ucop.edu/ - -- telnet scheme for interactive services via the TELNET Protocol - -1.4. Hierarchical URI and Relative Forms - - An absolute identifier refers to a resource independent of the - context in which the identifier is used. In contrast, a relative - identifier refers to a resource by describing the difference within a - hierarchical namespace between the current context and an absolute - identifier of the resource. - - - - - - -Berners-Lee, et. al. Standards Track [Page 4] - -RFC 2396 URI Generic Syntax August 1998 - - - Some URI schemes support a hierarchical naming system, where the - hierarchy of the name is denoted by a "/" delimiter separating the - components in the scheme. This document defines a scheme-independent - `relative' form of URI reference that can be used in conjunction with - a `base' URI (of a hierarchical scheme) to produce another URI. The - syntax of hierarchical URI is described in Section 3; the relative - URI calculation is described in Section 5. - -1.5. URI Transcribability - - The URI syntax was designed with global transcribability as one of - its main concerns. A URI is a sequence of characters from a very - limited set, i.e. the letters of the basic Latin alphabet, digits, - and a few special characters. A URI may be represented in a variety - of ways: e.g., ink on paper, pixels on a screen, or a sequence of - octets in a coded character set. The interpretation of a URI depends - only on the characters used and not how those characters are - represented in a network protocol. - - The goal of transcribability can be described by a simple scenario. - Imagine two colleagues, Sam and Kim, sitting in a pub at an - international conference and exchanging research ideas. Sam asks Kim - for a location to get more information, so Kim writes the URI for the - research site on a napkin. Upon returning home, Sam takes out the - napkin and types the URI into a computer, which then retrieves the - information to which Kim referred. - - There are several design concerns revealed by the scenario: - - o A URI is a sequence of characters, which is not always - represented as a sequence of octets. - - o A URI may be transcribed from a non-network source, and thus - should consist of characters that are most likely to be able to - be typed into a computer, within the constraints imposed by - keyboards (and related input devices) across languages and - locales. - - o A URI often needs to be remembered by people, and it is easier - for people to remember a URI when it consists of meaningful - components. - - These design concerns are not always in alignment. For example, it - is often the case that the most meaningful name for a URI component - would require characters that cannot be typed into some systems. The - ability to transcribe the resource identifier from one medium to - another was considered more important than having its URI consist of - the most meaningful of components. In local and regional contexts - - - -Berners-Lee, et. al. Standards Track [Page 5] - -RFC 2396 URI Generic Syntax August 1998 - - - and with improving technology, users might benefit from being able to - use a wider range of characters; such use is not defined in this - document. - -1.6. Syntax Notation and Common Elements - - This document uses two conventions to describe and define the syntax - for URI. The first, called the layout form, is a general description - of the order of components and component separators, as in - - /;? - - The component names are enclosed in angle-brackets and any characters - outside angle-brackets are literal separators. Whitespace should be - ignored. These descriptions are used informally and do not define - the syntax requirements. - - The second convention is a BNF-like grammar, used to define the - formal URI syntax. The grammar is that of [RFC822], except that "|" - is used to designate alternatives. Briefly, rules are separated from - definitions by an equal "=", indentation is used to continue a rule - definition over more than one line, literals are quoted with "", - parentheses "(" and ")" are used to group elements, optional elements - are enclosed in "[" and "]" brackets, and elements may be preceded - with * to designate n or more repetitions of the following - element; n defaults to 0. - - Unlike many specifications that use a BNF-like grammar to define the - bytes (octets) allowed by a protocol, the URI grammar is defined in - terms of characters. Each literal in the grammar corresponds to the - character it represents, rather than to the octet encoding of that - character in any particular coded character set. How a URI is - represented in terms of bits and bytes on the wire is dependent upon - the character encoding of the protocol used to transport it, or the - charset of the document which contains it. - - The following definitions are common to many elements: - - alpha = lowalpha | upalpha - - lowalpha = "a" | "b" | "c" | "d" | "e" | "f" | "g" | "h" | "i" | - "j" | "k" | "l" | "m" | "n" | "o" | "p" | "q" | "r" | - "s" | "t" | "u" | "v" | "w" | "x" | "y" | "z" - - upalpha = "A" | "B" | "C" | "D" | "E" | "F" | "G" | "H" | "I" | - "J" | "K" | "L" | "M" | "N" | "O" | "P" | "Q" | "R" | - "S" | "T" | "U" | "V" | "W" | "X" | "Y" | "Z" - - - - -Berners-Lee, et. al. Standards Track [Page 6] - -RFC 2396 URI Generic Syntax August 1998 - - - digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | - "8" | "9" - - alphanum = alpha | digit - - The complete URI syntax is collected in Appendix A. - -2. URI Characters and Escape Sequences - - URI consist of a restricted set of characters, primarily chosen to - aid transcribability and usability both in computer systems and in - non-computer communications. Characters used conventionally as - delimiters around URI were excluded. The restricted set of - characters consists of digits, letters, and a few graphic symbols - were chosen from those common to most of the character encodings and - input facilities available to Internet users. - - uric = reserved | unreserved | escaped - - Within a URI, characters are either used as delimiters, or to - represent strings of data (octets) within the delimited portions. - Octets are either represented directly by a character (using the US- - ASCII character for that octet [ASCII]) or by an escape encoding. - This representation is elaborated below. - -2.1 URI and non-ASCII characters - - The relationship between URI and characters has been a source of - confusion for characters that are not part of US-ASCII. To describe - the relationship, it is useful to distinguish between a "character" - (as a distinguishable semantic entity) and an "octet" (an 8-bit - byte). There are two mappings, one from URI characters to octets, and - a second from octets to original characters: - - URI character sequence->octet sequence->original character sequence - - A URI is represented as a sequence of characters, not as a sequence - of octets. That is because URI might be "transported" by means that - are not through a computer network, e.g., printed on paper, read over - the radio, etc. - - A URI scheme may define a mapping from URI characters to octets; - whether this is done depends on the scheme. Commonly, within a - delimited component of a URI, a sequence of characters may be used to - represent a sequence of octets. For example, the character "a" - represents the octet 97 (decimal), while the character sequence "%", - "0", "a" represents the octet 10 (decimal). - - - - -Berners-Lee, et. al. Standards Track [Page 7] - -RFC 2396 URI Generic Syntax August 1998 - - - There is a second translation for some resources: the sequence of - octets defined by a component of the URI is subsequently used to - represent a sequence of characters. A 'charset' defines this mapping. - There are many charsets in use in Internet protocols. For example, - UTF-8 [UTF-8] defines a mapping from sequences of octets to sequences - of characters in the repertoire of ISO 10646. - - In the simplest case, the original character sequence contains only - characters that are defined in US-ASCII, and the two levels of - mapping are simple and easily invertible: each 'original character' - is represented as the octet for the US-ASCII code for it, which is, - in turn, represented as either the US-ASCII character, or else the - "%" escape sequence for that octet. - - For original character sequences that contain non-ASCII characters, - however, the situation is more difficult. Internet protocols that - transmit octet sequences intended to represent character sequences - are expected to provide some way of identifying the charset used, if - there might be more than one [RFC2277]. However, there is currently - no provision within the generic URI syntax to accomplish this - identification. An individual URI scheme may require a single - charset, define a default charset, or provide a way to indicate the - charset used. - - It is expected that a systematic treatment of character encoding - within URI will be developed as a future modification of this - specification. - -2.2. Reserved Characters - - Many URI include components consisting of or delimited by, certain - special characters. These characters are called "reserved", since - their usage within the URI component is limited to their reserved - purpose. If the data for a URI component would conflict with the - reserved purpose, then the conflicting data must be escaped before - forming the URI. - - reserved = ";" | "/" | "?" | ":" | "@" | "&" | "=" | "+" | - "$" | "," - - The "reserved" syntax class above refers to those characters that are - allowed within a URI, but which may not be allowed within a - particular component of the generic URI syntax; they are used as - delimiters of the components described in Section 3. - - - - - - - -Berners-Lee, et. al. Standards Track [Page 8] - -RFC 2396 URI Generic Syntax August 1998 - - - Characters in the "reserved" set are not reserved in all contexts. - The set of characters actually reserved within any given URI - component is defined by that component. In general, a character is - reserved if the semantics of the URI changes if the character is - replaced with its escaped US-ASCII encoding. - -2.3. Unreserved Characters - - Data characters that are allowed in a URI but do not have a reserved - purpose are called unreserved. These include upper and lower case - letters, decimal digits, and a limited set of punctuation marks and - symbols. - - unreserved = alphanum | mark - - mark = "-" | "_" | "." | "!" | "~" | "*" | "'" | "(" | ")" - - Unreserved characters can be escaped without changing the semantics - of the URI, but this should not be done unless the URI is being used - in a context that does not allow the unescaped character to appear. - -2.4. Escape Sequences - - Data must be escaped if it does not have a representation using an - unreserved character; this includes data that does not correspond to - a printable character of the US-ASCII coded character set, or that - corresponds to any US-ASCII character that is disallowed, as - explained below. - -2.4.1. Escaped Encoding - - An escaped octet is encoded as a character triplet, consisting of the - percent character "%" followed by the two hexadecimal digits - representing the octet code. For example, "%20" is the escaped - encoding for the US-ASCII space character. - - escaped = "%" hex hex - hex = digit | "A" | "B" | "C" | "D" | "E" | "F" | - "a" | "b" | "c" | "d" | "e" | "f" - -2.4.2. When to Escape and Unescape - - A URI is always in an "escaped" form, since escaping or unescaping a - completed URI might change its semantics. Normally, the only time - escape encodings can safely be made is when the URI is being created - from its component parts; each component may have its own set of - characters that are reserved, so only the mechanism responsible for - generating or interpreting that component can determine whether or - - - -Berners-Lee, et. al. Standards Track [Page 9] - -RFC 2396 URI Generic Syntax August 1998 - - - not escaping a character will change its semantics. Likewise, a URI - must be separated into its components before the escaped characters - within those components can be safely decoded. - - In some cases, data that could be represented by an unreserved - character may appear escaped; for example, some of the unreserved - "mark" characters are automatically escaped by some systems. If the - given URI scheme defines a canonicalization algorithm, then - unreserved characters may be unescaped according to that algorithm. - For example, "%7e" is sometimes used instead of "~" in an http URL - path, but the two are equivalent for an http URL. - - Because the percent "%" character always has the reserved purpose of - being the escape indicator, it must be escaped as "%25" in order to - be used as data within a URI. Implementers should be careful not to - escape or unescape the same string more than once, since unescaping - an already unescaped string might lead to misinterpreting a percent - data character as another escaped character, or vice versa in the - case of escaping an already escaped string. - -2.4.3. Excluded US-ASCII Characters - - Although they are disallowed within the URI syntax, we include here a - description of those US-ASCII characters that have been excluded and - the reasons for their exclusion. - - The control characters in the US-ASCII coded character set are not - used within a URI, both because they are non-printable and because - they are likely to be misinterpreted by some control mechanisms. - - control = - - The space character is excluded because significant spaces may - disappear and insignificant spaces may be introduced when URI are - transcribed or typeset or subjected to the treatment of word- - processing programs. Whitespace is also used to delimit URI in many - contexts. - - space = - - The angle-bracket "<" and ">" and double-quote (") characters are - excluded because they are often used as the delimiters around URI in - text documents and protocol fields. The character "#" is excluded - because it is used to delimit a URI from a fragment identifier in URI - references (Section 4). The percent character "%" is excluded because - it is used for the encoding of escaped characters. - - delims = "<" | ">" | "#" | "%" | <"> - - - -Berners-Lee, et. al. Standards Track [Page 10] - -RFC 2396 URI Generic Syntax August 1998 - - - Other characters are excluded because gateways and other transport - agents are known to sometimes modify such characters, or they are - used as delimiters. - - unwise = "{" | "}" | "|" | "\" | "^" | "[" | "]" | "`" - - Data corresponding to excluded characters must be escaped in order to - be properly represented within a URI. - -3. URI Syntactic Components - - The URI syntax is dependent upon the scheme. In general, absolute - URI are written as follows: - - : - - An absolute URI contains the name of the scheme being used () - followed by a colon (":") and then a string (the ) whose interpretation depends on the scheme. - - The URI syntax does not require that the scheme-specific-part have - any general structure or set of semantics which is common among all - URI. However, a subset of URI do share a common syntax for - representing hierarchical relationships within the namespace. This - "generic URI" syntax consists of a sequence of four main components: - - ://? - - each of which, except , may be absent from a particular URI. - For example, some URI schemes do not allow an component, - and others do not use a component. - - absoluteURI = scheme ":" ( hier_part | opaque_part ) - - URI that are hierarchical in nature use the slash "/" character for - separating hierarchical components. For some file systems, a "/" - character (used to denote the hierarchical structure of a URI) is the - delimiter used to construct a file name hierarchy, and thus the URI - path will look similar to a file pathname. This does NOT imply that - the resource is a file or that the URI maps to an actual filesystem - pathname. - - hier_part = ( net_path | abs_path ) [ "?" query ] - - net_path = "//" authority [ abs_path ] - - abs_path = "/" path_segments - - - - -Berners-Lee, et. al. Standards Track [Page 11] - -RFC 2396 URI Generic Syntax August 1998 - - - URI that do not make use of the slash "/" character for separating - hierarchical components are considered opaque by the generic URI - parser. - - opaque_part = uric_no_slash *uric - - uric_no_slash = unreserved | escaped | ";" | "?" | ":" | "@" | - "&" | "=" | "+" | "$" | "," - - We use the term to refer to both the and - constructs, since they are mutually exclusive for any - given URI and can be parsed as a single component. - -3.1. Scheme Component - - Just as there are many different methods of access to resources, - there are a variety of schemes for identifying such resources. The - URI syntax consists of a sequence of components separated by reserved - characters, with the first component defining the semantics for the - remainder of the URI string. - - Scheme names consist of a sequence of characters beginning with a - lower case letter and followed by any combination of lower case - letters, digits, plus ("+"), period ("."), or hyphen ("-"). For - resiliency, programs interpreting URI should treat upper case letters - as equivalent to lower case in scheme names (e.g., allow "HTTP" as - well as "http"). - - scheme = alpha *( alpha | digit | "+" | "-" | "." ) - - Relative URI references are distinguished from absolute URI in that - they do not begin with a scheme name. Instead, the scheme is - inherited from the base URI, as described in Section 5.2. - -3.2. Authority Component - - Many URI schemes include a top hierarchical element for a naming - authority, such that the namespace defined by the remainder of the - URI is governed by that authority. This authority component is - typically defined by an Internet-based server or a scheme-specific - registry of naming authorities. - - authority = server | reg_name - - The authority component is preceded by a double slash "//" and is - terminated by the next slash "/", question-mark "?", or by the end of - the URI. Within the authority component, the characters ";", ":", - "@", "?", and "/" are reserved. - - - -Berners-Lee, et. al. Standards Track [Page 12] - -RFC 2396 URI Generic Syntax August 1998 - - - An authority component is not required for a URI scheme to make use - of relative references. A base URI without an authority component - implies that any relative reference will also be without an authority - component. - -3.2.1. Registry-based Naming Authority - - The structure of a registry-based naming authority is specific to the - URI scheme, but constrained to the allowed characters for an - authority component. - - reg_name = 1*( unreserved | escaped | "$" | "," | - ";" | ":" | "@" | "&" | "=" | "+" ) - -3.2.2. Server-based Naming Authority - - URL schemes that involve the direct use of an IP-based protocol to a - specified server on the Internet use a common syntax for the server - component of the URI's scheme-specific data: - - @: - - where may consist of a user name and, optionally, scheme- - specific information about how to gain authorization to access the - server. The parts "@" and ":" may be omitted. - - server = [ [ userinfo "@" ] hostport ] - - The user information, if present, is followed by a commercial at-sign - "@". - - userinfo = *( unreserved | escaped | - ";" | ":" | "&" | "=" | "+" | "$" | "," ) - - Some URL schemes use the format "user:password" in the userinfo - field. This practice is NOT RECOMMENDED, because the passing of - authentication information in clear text (such as URI) has proven to - be a security risk in almost every case where it has been used. - - The host is a domain name of a network host, or its IPv4 address as a - set of four decimal digit groups separated by ".". Literal IPv6 - addresses are not supported. - - hostport = host [ ":" port ] - host = hostname | IPv4address - hostname = *( domainlabel "." ) toplabel [ "." ] - domainlabel = alphanum | alphanum *( alphanum | "-" ) alphanum - toplabel = alpha | alpha *( alphanum | "-" ) alphanum - - - -Berners-Lee, et. al. Standards Track [Page 13] - -RFC 2396 URI Generic Syntax August 1998 - - - IPv4address = 1*digit "." 1*digit "." 1*digit "." 1*digit - port = *digit - - Hostnames take the form described in Section 3 of [RFC1034] and - Section 2.1 of [RFC1123]: a sequence of domain labels separated by - ".", each domain label starting and ending with an alphanumeric - character and possibly also containing "-" characters. The rightmost - domain label of a fully qualified domain name will never start with a - digit, thus syntactically distinguishing domain names from IPv4 - addresses, and may be followed by a single "." if it is necessary to - distinguish between the complete domain name and any local domain. - To actually be "Uniform" as a resource locator, a URL hostname should - be a fully qualified domain name. In practice, however, the host - component may be a local domain literal. - - Note: A suitable representation for including a literal IPv6 - address as the host part of a URL is desired, but has not yet been - determined or implemented in practice. - - The port is the network port number for the server. Most schemes - designate protocols that have a default port number. Another port - number may optionally be supplied, in decimal, separated from the - host by a colon. If the port is omitted, the default port number is - assumed. - -3.3. Path Component - - The path component contains data, specific to the authority (or the - scheme if there is no authority component), identifying the resource - within the scope of that scheme and authority. - - path = [ abs_path | opaque_part ] - - path_segments = segment *( "/" segment ) - segment = *pchar *( ";" param ) - param = *pchar - - pchar = unreserved | escaped | - ":" | "@" | "&" | "=" | "+" | "$" | "," - - The path may consist of a sequence of path segments separated by a - single slash "/" character. Within a path segment, the characters - "/", ";", "=", and "?" are reserved. Each path segment may include a - sequence of parameters, indicated by the semicolon ";" character. - The parameters are not significant to the parsing of relative - references. - - - - - -Berners-Lee, et. al. Standards Track [Page 14] - -RFC 2396 URI Generic Syntax August 1998 - - -3.4. Query Component - - The query component is a string of information to be interpreted by - the resource. - - query = *uric - - Within a query component, the characters ";", "/", "?", ":", "@", - "&", "=", "+", ",", and "$" are reserved. - -4. URI References - - The term "URI-reference" is used here to denote the common usage of a - resource identifier. A URI reference may be absolute or relative, - and may have additional information attached in the form of a - fragment identifier. However, "the URI" that results from such a - reference includes only the absolute URI after the fragment - identifier (if any) is removed and after any relative URI is resolved - to its absolute form. Although it is possible to limit the - discussion of URI syntax and semantics to that of the absolute - result, most usage of URI is within general URI references, and it is - impossible to obtain the URI from such a reference without also - parsing the fragment and resolving the relative form. - - URI-reference = [ absoluteURI | relativeURI ] [ "#" fragment ] - - The syntax for relative URI is a shortened form of that for absolute - URI, where some prefix of the URI is missing and certain path - components ("." and "..") have a special meaning when, and only when, - interpreting a relative path. The relative URI syntax is defined in - Section 5. - -4.1. Fragment Identifier - - When a URI reference is used to perform a retrieval action on the - identified resource, the optional fragment identifier, separated from - the URI by a crosshatch ("#") character, consists of additional - reference information to be interpreted by the user agent after the - retrieval action has been successfully completed. As such, it is not - part of a URI, but is often used in conjunction with a URI. - - fragment = *uric - - The semantics of a fragment identifier is a property of the data - resulting from a retrieval action, regardless of the type of URI used - in the reference. Therefore, the format and interpretation of - fragment identifiers is dependent on the media type [RFC2046] of the - retrieval result. The character restrictions described in Section 2 - - - -Berners-Lee, et. al. Standards Track [Page 15] - -RFC 2396 URI Generic Syntax August 1998 - - - for URI also apply to the fragment in a URI-reference. Individual - media types may define additional restrictions or structure within - the fragment for specifying different types of "partial views" that - can be identified within that media type. - - A fragment identifier is only meaningful when a URI reference is - intended for retrieval and the result of that retrieval is a document - for which the identified fragment is consistently defined. - -4.2. Same-document References - - A URI reference that does not contain a URI is a reference to the - current document. In other words, an empty URI reference within a - document is interpreted as a reference to the start of that document, - and a reference containing only a fragment identifier is a reference - to the identified fragment of that document. Traversal of such a - reference should not result in an additional retrieval action. - However, if the URI reference occurs in a context that is always - intended to result in a new request, as in the case of HTML's FORM - element, then an empty URI reference represents the base URI of the - current document and should be replaced by that URI when transformed - into a request. - -4.3. Parsing a URI Reference - - A URI reference is typically parsed according to the four main - components and fragment identifier in order to determine what - components are present and whether the reference is relative or - absolute. The individual components are then parsed for their - subparts and, if not opaque, to verify their validity. - - Although the BNF defines what is allowed in each component, it is - ambiguous in terms of differentiating between an authority component - and a path component that begins with two slash characters. The - greedy algorithm is used for disambiguation: the left-most matching - rule soaks up as much of the URI reference string as it is capable of - matching. In other words, the authority component wins. - - Readers familiar with regular expressions should see Appendix B for a - concrete parsing example and test oracle. - -5. Relative URI References - - It is often the case that a group or "tree" of documents has been - constructed to serve a common purpose; the vast majority of URI in - these documents point to resources within the tree rather than - - - - - -Berners-Lee, et. al. Standards Track [Page 16] - -RFC 2396 URI Generic Syntax August 1998 - - - outside of it. Similarly, documents located at a particular site are - much more likely to refer to other resources at that site than to - resources at remote sites. - - Relative addressing of URI allows document trees to be partially - independent of their location and access scheme. For instance, it is - possible for a single set of hypertext documents to be simultaneously - accessible and traversable via each of the "file", "http", and "ftp" - schemes if the documents refer to each other using relative URI. - Furthermore, such document trees can be moved, as a whole, without - changing any of the relative references. Experience within the WWW - has demonstrated that the ability to perform relative referencing is - necessary for the long-term usability of embedded URI. - - The syntax for relative URI takes advantage of the syntax - of (Section 3) in order to express a reference that is - relative to the namespace of another hierarchical URI. - - relativeURI = ( net_path | abs_path | rel_path ) [ "?" query ] - - A relative reference beginning with two slash characters is termed a - network-path reference, as defined by in Section 3. Such - references are rarely used. - - A relative reference beginning with a single slash character is - termed an absolute-path reference, as defined by in - Section 3. - - A relative reference that does not begin with a scheme name or a - slash character is termed a relative-path reference. - - rel_path = rel_segment [ abs_path ] - - rel_segment = 1*( unreserved | escaped | - ";" | "@" | "&" | "=" | "+" | "$" | "," ) - - Within a relative-path reference, the complete path segments "." and - ".." have special meanings: "the current hierarchy level" and "the - level above this hierarchy level", respectively. Although this is - very similar to their use within Unix-based filesystems to indicate - directory levels, these path components are only considered special - when resolving a relative-path reference to its absolute form - (Section 5.2). - - Authors should be aware that a path segment which contains a colon - character cannot be used as the first segment of a relative URI path - (e.g., "this:that"), because it would be mistaken for a scheme name. - - - - -Berners-Lee, et. al. Standards Track [Page 17] - -RFC 2396 URI Generic Syntax August 1998 - - - It is therefore necessary to precede such segments with other - segments (e.g., "./this:that") in order for them to be referenced as - a relative path. - - It is not necessary for all URI within a given scheme to be - restricted to the syntax, since the hierarchical - properties of that syntax are only necessary when relative URI are - used within a particular document. Documents can only make use of - relative URI when their base URI fits within the syntax. - It is assumed that any document which contains a relative reference - will also have a base URI that obeys the syntax. In other words, - relative URI cannot be used within a document that has an unsuitable - base URI. - - Some URI schemes do not allow a hierarchical syntax matching the - syntax, and thus cannot use relative references. - -5.1. Establishing a Base URI - - The term "relative URI" implies that there exists some absolute "base - URI" against which the relative reference is applied. Indeed, the - base URI is necessary to define the semantics of any relative URI - reference; without it, a relative reference is meaningless. In order - for relative URI to be usable within a document, the base URI of that - document must be known to the parser. - - The base URI of a document can be established in one of four ways, - listed below in order of precedence. The order of precedence can be - thought of in terms of layers, where the innermost defined base URI - has the highest precedence. This can be visualized graphically as: - - .----------------------------------------------------------. - | .----------------------------------------------------. | - | | .----------------------------------------------. | | - | | | .----------------------------------------. | | | - | | | | .----------------------------------. | | | | - | | | | | | | | | | - | | | | `----------------------------------' | | | | - | | | | (5.1.1) Base URI embedded in the | | | | - | | | | document's content | | | | - | | | `----------------------------------------' | | | - | | | (5.1.2) Base URI of the encapsulating entity | | | - | | | (message, document, or none). | | | - | | `----------------------------------------------' | | - | | (5.1.3) URI used to retrieve the entity | | - | `----------------------------------------------------' | - | (5.1.4) Default Base URI is application-dependent | - `----------------------------------------------------------' - - - -Berners-Lee, et. al. Standards Track [Page 18] - -RFC 2396 URI Generic Syntax August 1998 - - -5.1.1. Base URI within Document Content - - Within certain document media types, the base URI of the document can - be embedded within the content itself such that it can be readily - obtained by a parser. This can be useful for descriptive documents, - such as tables of content, which may be transmitted to others through - protocols other than their usual retrieval context (e.g., E-Mail or - USENET news). - - It is beyond the scope of this document to specify how, for each - media type, the base URI can be embedded. It is assumed that user - agents manipulating such media types will be able to obtain the - appropriate syntax from that media type's specification. An example - of how the base URI can be embedded in the Hypertext Markup Language - (HTML) [RFC1866] is provided in Appendix D. - - A mechanism for embedding the base URI within MIME container types - (e.g., the message and multipart types) is defined by MHTML - [RFC2110]. Protocols that do not use the MIME message header syntax, - but which do allow some form of tagged metainformation to be included - within messages, may define their own syntax for defining the base - URI as part of a message. - -5.1.2. Base URI from the Encapsulating Entity - - If no base URI is embedded, the base URI of a document is defined by - the document's retrieval context. For a document that is enclosed - within another entity (such as a message or another document), the - retrieval context is that entity; thus, the default base URI of the - document is the base URI of the entity in which the document is - encapsulated. - -5.1.3. Base URI from the Retrieval URI - - If no base URI is embedded and the document is not encapsulated - within some other entity (e.g., the top level of a composite entity), - then, if a URI was used to retrieve the base document, that URI shall - be considered the base URI. Note that if the retrieval was the - result of a redirected request, the last URI used (i.e., that which - resulted in the actual retrieval of the document) is the base URI. - -5.1.4. Default Base URI - - If none of the conditions described in Sections 5.1.1--5.1.3 apply, - then the base URI is defined by the context of the application. - Since this definition is necessarily application-dependent, failing - - - - - -Berners-Lee, et. al. Standards Track [Page 19] - -RFC 2396 URI Generic Syntax August 1998 - - - to define the base URI using one of the other methods may result in - the same content being interpreted differently by different types of - application. - - It is the responsibility of the distributor(s) of a document - containing relative URI to ensure that the base URI for that document - can be established. It must be emphasized that relative URI cannot - be used reliably in situations where the document's base URI is not - well-defined. - -5.2. Resolving Relative References to Absolute Form - - This section describes an example algorithm for resolving URI - references that might be relative to a given base URI. - - The base URI is established according to the rules of Section 5.1 and - parsed into the four main components as described in Section 3. Note - that only the scheme component is required to be present in the base - URI; the other components may be empty or undefined. A component is - undefined if its preceding separator does not appear in the URI - reference; the path component is never undefined, though it may be - empty. The base URI's query component is not used by the resolution - algorithm and may be discarded. - - For each URI reference, the following steps are performed in order: - - 1) The URI reference is parsed into the potential four components and - fragment identifier, as described in Section 4.3. - - 2) If the path component is empty and the scheme, authority, and - query components are undefined, then it is a reference to the - current document and we are done. Otherwise, the reference URI's - query and fragment components are defined as found (or not found) - within the URI reference and not inherited from the base URI. - - 3) If the scheme component is defined, indicating that the reference - starts with a scheme name, then the reference is interpreted as an - absolute URI and we are done. Otherwise, the reference URI's - scheme is inherited from the base URI's scheme component. - - Due to a loophole in prior specifications [RFC1630], some parsers - allow the scheme name to be present in a relative URI if it is the - same as the base URI scheme. Unfortunately, this can conflict - with the correct parsing of non-hierarchical URI. For backwards - compatibility, an implementation may work around such references - by removing the scheme if it matches that of the base URI and the - scheme is known to always use the syntax. The parser - - - - -Berners-Lee, et. al. Standards Track [Page 20] - -RFC 2396 URI Generic Syntax August 1998 - - - can then continue with the steps below for the remainder of the - reference components. Validating parsers should mark such a - misformed relative reference as an error. - - 4) If the authority component is defined, then the reference is a - network-path and we skip to step 7. Otherwise, the reference - URI's authority is inherited from the base URI's authority - component, which will also be undefined if the URI scheme does not - use an authority component. - - 5) If the path component begins with a slash character ("/"), then - the reference is an absolute-path and we skip to step 7. - - 6) If this step is reached, then we are resolving a relative-path - reference. The relative path needs to be merged with the base - URI's path. Although there are many ways to do this, we will - describe a simple method using a separate string buffer. - - a) All but the last segment of the base URI's path component is - copied to the buffer. In other words, any characters after the - last (right-most) slash character, if any, are excluded. - - b) The reference's path component is appended to the buffer - string. - - c) All occurrences of "./", where "." is a complete path segment, - are removed from the buffer string. - - d) If the buffer string ends with "." as a complete path segment, - that "." is removed. - - e) All occurrences of "/../", where is a - complete path segment not equal to "..", are removed from the - buffer string. Removal of these path segments is performed - iteratively, removing the leftmost matching pattern on each - iteration, until no matching pattern remains. - - f) If the buffer string ends with "/..", where - is a complete path segment not equal to "..", that - "/.." is removed. - - g) If the resulting buffer string still begins with one or more - complete path segments of "..", then the reference is - considered to be in error. Implementations may handle this - error by retaining these components in the resolved path (i.e., - treating them as part of the final URI), by removing them from - the resolved path (i.e., discarding relative levels above the - root), or by avoiding traversal of the reference. - - - -Berners-Lee, et. al. Standards Track [Page 21] - -RFC 2396 URI Generic Syntax August 1998 - - - h) The remaining buffer string is the reference URI's new path - component. - - 7) The resulting URI components, including any inherited from the - base URI, are recombined to give the absolute form of the URI - reference. Using pseudocode, this would be - - result = "" - - if scheme is defined then - append scheme to result - append ":" to result - - if authority is defined then - append "//" to result - append authority to result - - append path to result - - if query is defined then - append "?" to result - append query to result - - if fragment is defined then - append "#" to result - append fragment to result - - return result - - Note that we must be careful to preserve the distinction between a - component that is undefined, meaning that its separator was not - present in the reference, and a component that is empty, meaning - that the separator was present and was immediately followed by the - next component separator or the end of the reference. - - The above algorithm is intended to provide an example by which the - output of implementations can be tested -- implementation of the - algorithm itself is not required. For example, some systems may find - it more efficient to implement step 6 as a pair of segment stacks - being merged, rather than as a series of string pattern replacements. - - Note: Some WWW client applications will fail to separate the - reference's query component from its path component before merging - the base and reference paths in step 6 above. This may result in - a loss of information if the query component contains the strings - "/../" or "/./". - - Resolution examples are provided in Appendix C. - - - -Berners-Lee, et. al. Standards Track [Page 22] - -RFC 2396 URI Generic Syntax August 1998 - - -6. URI Normalization and Equivalence - - In many cases, different URI strings may actually identify the - identical resource. For example, the host names used in URL are - actually case insensitive, and the URL is - equivalent to . In general, the rules for - equivalence and definition of a normal form, if any, are scheme - dependent. When a scheme uses elements of the common syntax, it will - also use the common syntax equivalence rules, namely that the scheme - and hostname are case insensitive and a URL with an explicit ":port", - where the port is the default for the scheme, is equivalent to one - where the port is elided. - -7. Security Considerations - - A URI does not in itself pose a security threat. Users should beware - that there is no general guarantee that a URL, which at one time - located a given resource, will continue to do so. Nor is there any - guarantee that a URL will not locate a different resource at some - later point in time, due to the lack of any constraint on how a given - authority apportions its namespace. Such a guarantee can only be - obtained from the person(s) controlling that namespace and the - resource in question. A specific URI scheme may include additional - semantics, such as name persistence, if those semantics are required - of all naming authorities for that scheme. - - It is sometimes possible to construct a URL such that an attempt to - perform a seemingly harmless, idempotent operation, such as the - retrieval of an entity associated with the resource, will in fact - cause a possibly damaging remote operation to occur. The unsafe URL - is typically constructed by specifying a port number other than that - reserved for the network protocol in question. The client - unwittingly contacts a site that is in fact running a different - protocol. The content of the URL contains instructions that, when - interpreted according to this other protocol, cause an unexpected - operation. An example has been the use of a gopher URL to cause an - unintended or impersonating message to be sent via a SMTP server. - - Caution should be used when using any URL that specifies a port - number other than the default for the protocol, especially when it is - a number within the reserved space. - - Care should be taken when a URL contains escaped delimiters for a - given protocol (for example, CR and LF characters for telnet - protocols) that these are not unescaped before transmission. This - might violate the protocol, but avoids the potential for such - - - - - -Berners-Lee, et. al. Standards Track [Page 23] - -RFC 2396 URI Generic Syntax August 1998 - - - characters to be used to simulate an extra operation or parameter in - that protocol, which might lead to an unexpected and possibly harmful - remote operation to be performed. - - It is clearly unwise to use a URL that contains a password which is - intended to be secret. In particular, the use of a password within - the 'userinfo' component of a URL is strongly disrecommended except - in those rare cases where the 'password' parameter is intended to be - public. - -8. Acknowledgements - - This document was derived from RFC 1738 [RFC1738] and RFC 1808 - [RFC1808]; the acknowledgements in those specifications still apply. - In addition, contributions by Gisle Aas, Martin Beet, Martin Duerst, - Jim Gettys, Martijn Koster, Dave Kristol, Daniel LaLiberte, Foteos - Macrides, James Marshall, Ryan Moats, Keith Moore, and Lauren Wood - are gratefully acknowledged. - -9. References - - [RFC2277] Alvestrand, H., "IETF Policy on Character Sets and - Languages", BCP 18, RFC 2277, January 1998. - - [RFC1630] Berners-Lee, T., "Universal Resource Identifiers in WWW: A - Unifying Syntax for the Expression of Names and Addresses - of Objects on the Network as used in the World-Wide Web", - RFC 1630, June 1994. - - [RFC1738] Berners-Lee, T., Masinter, L., and M. McCahill, Editors, - "Uniform Resource Locators (URL)", RFC 1738, December 1994. - - [RFC1866] Berners-Lee T., and D. Connolly, "HyperText Markup Language - Specification -- 2.0", RFC 1866, November 1995. - - [RFC1123] Braden, R., Editor, "Requirements for Internet Hosts -- - Application and Support", STD 3, RFC 1123, October 1989. - - [RFC822] Crocker, D., "Standard for the Format of ARPA Internet Text - Messages", STD 11, RFC 822, August 1982. - - [RFC1808] Fielding, R., "Relative Uniform Resource Locators", RFC - 1808, June 1995. - - [RFC2046] Freed, N., and N. Borenstein, "Multipurpose Internet Mail - Extensions (MIME) Part Two: Media Types", RFC 2046, - November 1996. - - - - -Berners-Lee, et. al. Standards Track [Page 24] - -RFC 2396 URI Generic Syntax August 1998 - - - [RFC1736] Kunze, J., "Functional Recommendations for Internet - Resource Locators", RFC 1736, February 1995. - - [RFC2141] Moats, R., "URN Syntax", RFC 2141, May 1997. - - [RFC1034] Mockapetris, P., "Domain Names - Concepts and Facilities", - STD 13, RFC 1034, November 1987. - - [RFC2110] Palme, J., and A. Hopmann, "MIME E-mail Encapsulation of - Aggregate Documents, such as HTML (MHTML)", RFC 2110, March - 1997. - - [RFC1737] Sollins, K., and L. Masinter, "Functional Requirements for - Uniform Resource Names", RFC 1737, December 1994. - - [ASCII] US-ASCII. "Coded Character Set -- 7-bit American Standard - Code for Information Interchange", ANSI X3.4-1986. - - [UTF-8] Yergeau, F., "UTF-8, a transformation format of ISO 10646", - RFC 2279, January 1998. - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Berners-Lee, et. al. Standards Track [Page 25] - -RFC 2396 URI Generic Syntax August 1998 - - -10. Authors' Addresses - - Tim Berners-Lee - World Wide Web Consortium - MIT Laboratory for Computer Science, NE43-356 - 545 Technology Square - Cambridge, MA 02139 - - Fax: +1(617)258-8682 - EMail: timbl@w3.org - - - Roy T. Fielding - Department of Information and Computer Science - University of California, Irvine - Irvine, CA 92697-3425 - - Fax: +1(949)824-1715 - EMail: fielding@ics.uci.edu - - - Larry Masinter - Xerox PARC - 3333 Coyote Hill Road - Palo Alto, CA 94034 - - Fax: +1(415)812-4333 - EMail: masinter@parc.xerox.com - - - - - - - - - - - - - - - - - - - - - - - -Berners-Lee, et. al. Standards Track [Page 26] - -RFC 2396 URI Generic Syntax August 1998 - - -A. Collected BNF for URI - - URI-reference = [ absoluteURI | relativeURI ] [ "#" fragment ] - absoluteURI = scheme ":" ( hier_part | opaque_part ) - relativeURI = ( net_path | abs_path | rel_path ) [ "?" query ] - - hier_part = ( net_path | abs_path ) [ "?" query ] - opaque_part = uric_no_slash *uric - - uric_no_slash = unreserved | escaped | ";" | "?" | ":" | "@" | - "&" | "=" | "+" | "$" | "," - - net_path = "//" authority [ abs_path ] - abs_path = "/" path_segments - rel_path = rel_segment [ abs_path ] - - rel_segment = 1*( unreserved | escaped | - ";" | "@" | "&" | "=" | "+" | "$" | "," ) - - scheme = alpha *( alpha | digit | "+" | "-" | "." ) - - authority = server | reg_name - - reg_name = 1*( unreserved | escaped | "$" | "," | - ";" | ":" | "@" | "&" | "=" | "+" ) - - server = [ [ userinfo "@" ] hostport ] - userinfo = *( unreserved | escaped | - ";" | ":" | "&" | "=" | "+" | "$" | "," ) - - hostport = host [ ":" port ] - host = hostname | IPv4address - hostname = *( domainlabel "." ) toplabel [ "." ] - domainlabel = alphanum | alphanum *( alphanum | "-" ) alphanum - toplabel = alpha | alpha *( alphanum | "-" ) alphanum - IPv4address = 1*digit "." 1*digit "." 1*digit "." 1*digit - port = *digit - - path = [ abs_path | opaque_part ] - path_segments = segment *( "/" segment ) - segment = *pchar *( ";" param ) - param = *pchar - pchar = unreserved | escaped | - ":" | "@" | "&" | "=" | "+" | "$" | "," - - query = *uric - - fragment = *uric - - - -Berners-Lee, et. al. Standards Track [Page 27] - -RFC 2396 URI Generic Syntax August 1998 - - - uric = reserved | unreserved | escaped - reserved = ";" | "/" | "?" | ":" | "@" | "&" | "=" | "+" | - "$" | "," - unreserved = alphanum | mark - mark = "-" | "_" | "." | "!" | "~" | "*" | "'" | - "(" | ")" - - escaped = "%" hex hex - hex = digit | "A" | "B" | "C" | "D" | "E" | "F" | - "a" | "b" | "c" | "d" | "e" | "f" - - alphanum = alpha | digit - alpha = lowalpha | upalpha - - lowalpha = "a" | "b" | "c" | "d" | "e" | "f" | "g" | "h" | "i" | - "j" | "k" | "l" | "m" | "n" | "o" | "p" | "q" | "r" | - "s" | "t" | "u" | "v" | "w" | "x" | "y" | "z" - upalpha = "A" | "B" | "C" | "D" | "E" | "F" | "G" | "H" | "I" | - "J" | "K" | "L" | "M" | "N" | "O" | "P" | "Q" | "R" | - "S" | "T" | "U" | "V" | "W" | "X" | "Y" | "Z" - digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | - "8" | "9" - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Berners-Lee, et. al. Standards Track [Page 28] - -RFC 2396 URI Generic Syntax August 1998 - - -B. Parsing a URI Reference with a Regular Expression - - As described in Section 4.3, the generic URI syntax is not sufficient - to disambiguate the components of some forms of URI. Since the - "greedy algorithm" described in that section is identical to the - disambiguation method used by POSIX regular expressions, it is - natural and commonplace to use a regular expression for parsing the - potential four components and fragment identifier of a URI reference. - - The following line is the regular expression for breaking-down a URI - reference into its components. - - ^(([^:/?#]+):)?(//([^/?#]*))?([^?#]*)(\?([^#]*))?(#(.*))? - 12 3 4 5 6 7 8 9 - - The numbers in the second line above are only to assist readability; - they indicate the reference points for each subexpression (i.e., each - paired parenthesis). We refer to the value matched for subexpression - as $. For example, matching the above expression to - - http://www.ics.uci.edu/pub/ietf/uri/#Related - - results in the following subexpression matches: - - $1 = http: - $2 = http - $3 = //www.ics.uci.edu - $4 = www.ics.uci.edu - $5 = /pub/ietf/uri/ - $6 = - $7 = - $8 = #Related - $9 = Related - - where indicates that the component is not present, as is - the case for the query component in the above example. Therefore, we - can determine the value of the four components and fragment as - - scheme = $2 - authority = $4 - path = $5 - query = $7 - fragment = $9 - - and, going in the opposite direction, we can recreate a URI reference - from its components using the algorithm in step 7 of Section 5.2. - - - - - -Berners-Lee, et. al. Standards Track [Page 29] - -RFC 2396 URI Generic Syntax August 1998 - - -C. Examples of Resolving Relative URI References - - Within an object with a well-defined base URI of - - http://a/b/c/d;p?q - - the relative URI would be resolved as follows: - -C.1. Normal Examples - - g:h = g:h - g = http://a/b/c/g - ./g = http://a/b/c/g - g/ = http://a/b/c/g/ - /g = http://a/g - //g = http://g - ?y = http://a/b/c/?y - g?y = http://a/b/c/g?y - #s = (current document)#s - g#s = http://a/b/c/g#s - g?y#s = http://a/b/c/g?y#s - ;x = http://a/b/c/;x - g;x = http://a/b/c/g;x - g;x?y#s = http://a/b/c/g;x?y#s - . = http://a/b/c/ - ./ = http://a/b/c/ - .. = http://a/b/ - ../ = http://a/b/ - ../g = http://a/b/g - ../.. = http://a/ - ../../ = http://a/ - ../../g = http://a/g - -C.2. Abnormal Examples - - Although the following abnormal examples are unlikely to occur in - normal practice, all URI parsers should be capable of resolving them - consistently. Each example uses the same base as above. - - An empty reference refers to the start of the current document. - - <> = (current document) - - Parsers must be careful in handling the case where there are more - relative path ".." segments than there are hierarchical levels in the - base URI's path. Note that the ".." syntax cannot be used to change - the authority component of a URI. - - - - -Berners-Lee, et. al. Standards Track [Page 30] - -RFC 2396 URI Generic Syntax August 1998 - - - ../../../g = http://a/../g - ../../../../g = http://a/../../g - - In practice, some implementations strip leading relative symbolic - elements (".", "..") after applying a relative URI calculation, based - on the theory that compensating for obvious author errors is better - than allowing the request to fail. Thus, the above two references - will be interpreted as "http://a/g" by some implementations. - - Similarly, parsers must avoid treating "." and ".." as special when - they are not complete components of a relative path. - - /./g = http://a/./g - /../g = http://a/../g - g. = http://a/b/c/g. - .g = http://a/b/c/.g - g.. = http://a/b/c/g.. - ..g = http://a/b/c/..g - - Less likely are cases where the relative URI uses unnecessary or - nonsensical forms of the "." and ".." complete path segments. - - ./../g = http://a/b/g - ./g/. = http://a/b/c/g/ - g/./h = http://a/b/c/g/h - g/../h = http://a/b/c/h - g;x=1/./y = http://a/b/c/g;x=1/y - g;x=1/../y = http://a/b/c/y - - All client applications remove the query component from the base URI - before resolving relative URI. However, some applications fail to - separate the reference's query and/or fragment components from a - relative path before merging it with the base path. This error is - rarely noticed, since typical usage of a fragment never includes the - hierarchy ("/") character, and the query component is not normally - used within relative references. - - g?y/./x = http://a/b/c/g?y/./x - g?y/../x = http://a/b/c/g?y/../x - g#s/./x = http://a/b/c/g#s/./x - g#s/../x = http://a/b/c/g#s/../x - - - - - - - - - - -Berners-Lee, et. al. Standards Track [Page 31] - -RFC 2396 URI Generic Syntax August 1998 - - - Some parsers allow the scheme name to be present in a relative URI if - it is the same as the base URI scheme. This is considered to be a - loophole in prior specifications of partial URI [RFC1630]. Its use - should be avoided. - - http:g = http:g ; for validating parsers - | http://a/b/c/g ; for backwards compatibility - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Berners-Lee, et. al. Standards Track [Page 32] - -RFC 2396 URI Generic Syntax August 1998 - - -D. Embedding the Base URI in HTML documents - - It is useful to consider an example of how the base URI of a document - can be embedded within the document's content. In this appendix, we - describe how documents written in the Hypertext Markup Language - (HTML) [RFC1866] can include an embedded base URI. This appendix - does not form a part of the URI specification and should not be - considered as anything more than a descriptive example. - - HTML defines a special element "BASE" which, when present in the - "HEAD" portion of a document, signals that the parser should use the - BASE element's "HREF" attribute as the base URI for resolving any - relative URI. The "HREF" attribute must be an absolute URI. Note - that, in HTML, element and attribute names are case-insensitive. For - example: - - - - An example HTML document - - - ... a hypertext anchor ... - - - A parser reading the example document should interpret the given - relative URI "../x" as representing the absolute URI - - - - regardless of the context in which the example document was obtained. - - - - - - - - - - - - - - - - - - - - - -Berners-Lee, et. al. Standards Track [Page 33] - -RFC 2396 URI Generic Syntax August 1998 - - -E. Recommendations for Delimiting URI in Context - - URI are often transmitted through formats that do not provide a clear - context for their interpretation. For example, there are many - occasions when URI are included in plain text; examples include text - sent in electronic mail, USENET news messages, and, most importantly, - printed on paper. In such cases, it is important to be able to - delimit the URI from the rest of the text, and in particular from - punctuation marks that might be mistaken for part of the URI. - - In practice, URI are delimited in a variety of ways, but usually - within double-quotes "http://test.com/", angle brackets - , or just using whitespace - - http://test.com/ - - These wrappers do not form part of the URI. - - In the case where a fragment identifier is associated with a URI - reference, the fragment would be placed within the brackets as well - (separated from the URI with a "#" character). - - In some cases, extra whitespace (spaces, linebreaks, tabs, etc.) may - need to be added to break long URI across lines. The whitespace - should be ignored when extracting the URI. - - No whitespace should be introduced after a hyphen ("-") character. - Because some typesetters and printers may (erroneously) introduce a - hyphen at the end of line when breaking a line, the interpreter of a - URI containing a line break immediately after a hyphen should ignore - all unescaped whitespace around the line break, and should be aware - that the hyphen may or may not actually be part of the URI. - - Using <> angle brackets around each URI is especially recommended as - a delimiting style for URI that contain whitespace. - - The prefix "URL:" (with or without a trailing space) was recommended - as a way to used to help distinguish a URL from other bracketed - designators, although this is not common in practice. - - For robustness, software that accepts user-typed URI should attempt - to recognize and strip both delimiters and embedded whitespace. - - For example, the text: - - - - - - - -Berners-Lee, et. al. Standards Track [Page 34] - -RFC 2396 URI Generic Syntax August 1998 - - - Yes, Jim, I found it under "http://www.w3.org/Addressing/", - but you can probably pick it up from . Note the warning in . - - contains the URI references - - http://www.w3.org/Addressing/ - ftp://ds.internic.net/rfc/ - http://www.ics.uci.edu/pub/ietf/uri/historical.html#WARNING - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -Berners-Lee, et. al. Standards Track [Page 35] - -RFC 2396 URI Generic Syntax August 1998 - - -F. Abbreviated URLs - - The URL syntax was designed for unambiguous reference to network - resources and extensibility via the URL scheme. However, as URL - identification and usage have become commonplace, traditional media - (television, radio, newspapers, billboards, etc.) have increasingly - used abbreviated URL references. That is, a reference consisting of - only the authority and path portions of the identified resource, such - as - - www.w3.org/Addressing/ - - or simply the DNS hostname on its own. Such references are primarily - intended for human interpretation rather than machine, with the - assumption that context-based heuristics are sufficient to complete - the URL (e.g., most hostnames beginning with "www" are likely to have - a URL prefix of "http://"). Although there is no standard set of - heuristics for disambiguating abbreviated URL references, many client - implementations allow them to be entered by the user and - heuristically resolved. It should be noted that such heuristics may - change over time, particularly when new URL schemes are introduced. - - Since an abbreviated URL has the same syntax as a relative URL path, - abbreviated URL references cannot be used in contexts where relative - URLs are expected. This limits the use of abbreviated URLs to places - where there is no defined base URL, such as dialog boxes and off-line - advertisements. - - - - - - - - - - - - - - - - - - - - - - - - -Berners-Lee, et. al. Standards Track [Page 36] - -RFC 2396 URI Generic Syntax August 1998 - - -G. Summary of Non-editorial Changes - -G.1. Additions - - Section 4 (URI References) was added to stem the confusion regarding - "what is a URI" and how to describe fragment identifiers given that - they are not part of the URI, but are part of the URI syntax and - parsing concerns. In addition, it provides a reference definition - for use by other IETF specifications (HTML, HTTP, etc.) that have - previously attempted to redefine the URI syntax in order to account - for the presence of fragment identifiers in URI references. - - Section 2.4 was rewritten to clarify a number of misinterpretations - and to leave room for fully internationalized URI. - - Appendix F on abbreviated URLs was added to describe the shortened - references often seen on television and magazine advertisements and - explain why they are not used in other contexts. - -G.2. Modifications from both RFC 1738 and RFC 1808 - - Changed to URI syntax instead of just URL. - - Confusion regarding the terms "character encoding", the URI - "character set", and the escaping of characters with % - equivalents has (hopefully) been reduced. Many of the BNF rule names - regarding the character sets have been changed to more accurately - describe their purpose and to encompass all "characters" rather than - just US-ASCII octets. Unless otherwise noted here, these - modifications do not affect the URI syntax. - - Both RFC 1738 and RFC 1808 refer to the "reserved" set of characters - as if URI-interpreting software were limited to a single set of - characters with a reserved purpose (i.e., as meaning something other - than the data to which the characters correspond), and that this set - was fixed by the URI scheme. However, this has not been true in - practice; any character that is interpreted differently when it is - escaped is, in effect, reserved. Furthermore, the interpreting - engine on a HTTP server is often dependent on the resource, not just - the URI scheme. The description of reserved characters has been - changed accordingly. - - The plus "+", dollar "$", and comma "," characters have been added to - those in the "reserved" set, since they are treated as reserved - within the query component. - - - - - - -Berners-Lee, et. al. Standards Track [Page 37] - -RFC 2396 URI Generic Syntax August 1998 - - - The tilde "~" character was added to those in the "unreserved" set, - since it is extensively used on the Internet in spite of the - difficulty to transcribe it with some keyboards. - - The syntax for URI scheme has been changed to require that all - schemes begin with an alpha character. - - The "user:password" form in the previous BNF was changed to a - "userinfo" token, and the possibility that it might be - "user:password" made scheme specific. In particular, the use of - passwords in the clear is not even suggested by the syntax. - - The question-mark "?" character was removed from the set of allowed - characters for the userinfo in the authority component, since testing - showed that many applications treat it as reserved for separating the - query component from the rest of the URI. - - The semicolon ";" character was added to those stated as being - reserved within the authority component, since several new schemes - are using it as a separator within userinfo to indicate the type of - user authentication. - - RFC 1738 specified that the path was separated from the authority - portion of a URI by a slash. RFC 1808 followed suit, but with a - fudge of carrying around the separator as a "prefix" in order to - describe the parsing algorithm. RFC 1630 never had this problem, - since it considered the slash to be part of the path. In writing - this specification, it was found to be impossible to accurately - describe and retain the difference between the two URI - and - without either considering the slash to be part of the path (as - corresponds to actual practice) or creating a separate component just - to hold that slash. We chose the former. - -G.3. Modifications from RFC 1738 - - The definition of specific URL schemes and their scheme-specific - syntax and semantics has been moved to separate documents. - - The URL host was defined as a fully-qualified domain name. However, - many URLs are used without fully-qualified domain names (in contexts - for which the full qualification is not necessary), without any host - (as in some file URLs), or with a host of "localhost". - - The URL port is now *digit instead of 1*digit, since systems are - expected to handle the case where the ":" separator between host and - port is supplied without a port. - - - - -Berners-Lee, et. al. Standards Track [Page 38] - -RFC 2396 URI Generic Syntax August 1998 - - - The recommendations for delimiting URI in context (Appendix E) have - been adjusted to reflect current practice. - -G.4. Modifications from RFC 1808 - - RFC 1808 (Section 4) defined an empty URL reference (a reference - containing nothing aside from the fragment identifier) as being a - reference to the base URL. Unfortunately, that definition could be - interpreted, upon selection of such a reference, as a new retrieval - action on that resource. Since the normal intent of such references - is for the user agent to change its view of the current document to - the beginning of the specified fragment within that document, not to - make an additional request of the resource, a description of how to - correctly interpret an empty reference has been added in Section 4. - - The description of the mythical Base header field has been replaced - with a reference to the Content-Location header field defined by - MHTML [RFC2110]. - - RFC 1808 described various schemes as either having or not having the - properties of the generic URI syntax. However, the only requirement - is that the particular document containing the relative references - have a base URI that abides by the generic URI syntax, regardless of - the URI scheme, so the associated description has been updated to - reflect that. - - The BNF term has been replaced with , since the - latter more accurately describes its use and purpose. Likewise, the - authority is no longer restricted to the IP server syntax. - - Extensive testing of current client applications demonstrated that - the majority of deployed systems do not use the ";" character to - indicate trailing parameter information, and that the presence of a - semicolon in a path segment does not affect the relative parsing of - that segment. Therefore, parameters have been removed as a separate - component and may now appear in any path segment. Their influence - has been removed from the algorithm for resolving a relative URI - reference. The resolution examples in Appendix C have been modified - to reflect this change. - - Implementations are now allowed to work around misformed relative - references that are prefixed by the same scheme as the base URI, but - only for schemes known to use the syntax. - - - - - - - - -Berners-Lee, et. al. Standards Track [Page 39] - -RFC 2396 URI Generic Syntax August 1998 - - -H. Full Copyright Statement - - Copyright (C) The Internet Society (1998). All Rights Reserved. - - This document and translations of it may be copied and furnished to - others, and derivative works that comment on or otherwise explain it - or assist in its implementation may be prepared, copied, published - and distributed, in whole or in part, without restriction of any - kind, provided that the above copyright notice and this paragraph are - included on all such copies and derivative works. However, this - document itself may not be modified in any way, such as by removing - the copyright notice or references to the Internet Society or other - Internet organizations, except as needed for the purpose of - developing Internet standards in which case the procedures for - copyrights defined in the Internet Standards process must be - followed, or as required to translate it into languages other than - English. - - The limited permissions granted above are perpetual and will not be - revoked by the Internet Society or its successors or assigns. - - This document and the information contained herein is provided on an - "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING - TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING - BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION - HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF - MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE. - - - - - - - - - - - - - - - - - - - - - - - - -Berners-Lee, et. al. Standards Track [Page 40] - diff --git a/doc/rfc822.txt b/doc/rfc822.txt deleted file mode 100644 index 35b09a3..0000000 --- a/doc/rfc822.txt +++ /dev/null @@ -1,2901 +0,0 @@ - - - - - - - RFC # 822 - - Obsoletes: RFC #733 (NIC #41952) - - - - - - - - - - - - - STANDARD FOR THE FORMAT OF - - ARPA INTERNET TEXT MESSAGES - - - - - - - August 13, 1982 - - - - - - - Revised by - - David H. Crocker - - - Dept. of Electrical Engineering - University of Delaware, Newark, DE 19711 - Network: DCrocker @ UDel-Relay - - - - - - - - - - - - - - - - Standard for ARPA Internet Text Messages - - - TABLE OF CONTENTS - - - PREFACE .................................................... ii - - 1. INTRODUCTION ........................................... 1 - - 1.1. Scope ............................................ 1 - 1.2. Communication Framework .......................... 2 - - 2. NOTATIONAL CONVENTIONS ................................. 3 - - 3. LEXICAL ANALYSIS OF MESSAGES ........................... 5 - - 3.1. General Description .............................. 5 - 3.2. Header Field Definitions ......................... 9 - 3.3. Lexical Tokens ................................... 10 - 3.4. Clarifications ................................... 11 - - 4. MESSAGE SPECIFICATION .................................. 17 - - 4.1. Syntax ........................................... 17 - 4.2. Forwarding ....................................... 19 - 4.3. Trace Fields ..................................... 20 - 4.4. Originator Fields ................................ 21 - 4.5. Receiver Fields .................................. 23 - 4.6. Reference Fields ................................. 23 - 4.7. Other Fields ..................................... 24 - - 5. DATE AND TIME SPECIFICATION ............................ 26 - - 5.1. Syntax ........................................... 26 - 5.2. Semantics ........................................ 26 - - 6. ADDRESS SPECIFICATION .................................. 27 - - 6.1. Syntax ........................................... 27 - 6.2. Semantics ........................................ 27 - 6.3. Reserved Address ................................. 33 - - 7. BIBLIOGRAPHY ........................................... 34 - - - APPENDIX - - A. EXAMPLES ............................................... 36 - B. SIMPLE FIELD PARSING ................................... 40 - C. DIFFERENCES FROM RFC #733 .............................. 41 - D. ALPHABETICAL LISTING OF SYNTAX RULES ................... 44 - - - August 13, 1982 - i - RFC #822 - - - - - Standard for ARPA Internet Text Messages - - - PREFACE - - - By 1977, the Arpanet employed several informal standards for - the text messages (mail) sent among its host computers. It was - felt necessary to codify these practices and provide for those - features that seemed imminent. The result of that effort was - Request for Comments (RFC) #733, "Standard for the Format of ARPA - Network Text Message", by Crocker, Vittal, Pogran, and Henderson. - The specification attempted to avoid major changes in existing - software, while permitting several new features. - - This document revises the specifications in RFC #733, in - order to serve the needs of the larger and more complex ARPA - Internet. Some of RFC #733's features failed to gain adequate - acceptance. In order to simplify the standard and the software - that follows it, these features have been removed. A different - addressing scheme is used, to handle the case of inter-network - mail; and the concept of re-transmission has been introduced. - - This specification is intended for use in the ARPA Internet. - However, an attempt has been made to free it of any dependence on - that environment, so that it can be applied to other network text - message systems. - - The specification of RFC #733 took place over the course of - one year, using the ARPANET mail environment, itself, to provide - an on-going forum for discussing the capabilities to be included. - More than twenty individuals, from across the country, partici- - pated in the original discussion. The development of this - revised specification has, similarly, utilized network mail-based - group discussion. Both specification efforts greatly benefited - from the comments and ideas of the participants. - - The syntax of the standard, in RFC #733, was originally - specified in the Backus-Naur Form (BNF) meta-language. Ken L. - Harrenstien, of SRI International, was responsible for re-coding - the BNF into an augmented BNF that makes the representation - smaller and easier to understand. - - - - - - - - - - - - - August 13, 1982 - ii - RFC #822 - - - - Standard for ARPA Internet Text Messages - - - 1. INTRODUCTION - - 1.1. SCOPE - - This standard specifies a syntax for text messages that are - sent among computer users, within the framework of "electronic - mail". The standard supersedes the one specified in ARPANET - Request for Comments #733, "Standard for the Format of ARPA Net- - work Text Messages". - - In this context, messages are viewed as having an envelope - and contents. The envelope contains whatever information is - needed to accomplish transmission and delivery. The contents - compose the object to be delivered to the recipient. This stan- - dard applies only to the format and some of the semantics of mes- - sage contents. It contains no specification of the information - in the envelope. - - However, some message systems may use information from the - contents to create the envelope. It is intended that this stan- - dard facilitate the acquisition of such information by programs. - - Some message systems may store messages in formats that - differ from the one specified in this standard. This specifica- - tion is intended strictly as a definition of what message content - format is to be passed BETWEEN hosts. - - Note: This standard is NOT intended to dictate the internal for- - mats used by sites, the specific message system features - that they are expected to support, or any of the charac- - teristics of user interface programs that create or read - messages. - - A distinction should be made between what the specification - REQUIRES and what it ALLOWS. Messages can be made complex and - rich with formally-structured components of information or can be - kept small and simple, with a minimum of such information. Also, - the standard simplifies the interpretation of differing visual - formats in messages; only the visual aspect of a message is - affected and not the interpretation of information within it. - Implementors may choose to retain such visual distinctions. - - The formal definition is divided into four levels. The bot- - tom level describes the meta-notation used in this document. The - second level describes basic lexical analyzers that feed tokens - to higher-level parsers. Next is an overall specification for - messages; it permits distinguishing individual fields. Finally, - there is definition of the contents of several structured fields. - - - - August 13, 1982 - 1 - RFC #822 - - - - Standard for ARPA Internet Text Messages - - - 1.2. COMMUNICATION FRAMEWORK - - Messages consist of lines of text. No special provisions - are made for encoding drawings, facsimile, speech, or structured - text. No significant consideration has been given to questions - of data compression or to transmission and storage efficiency, - and the standard tends to be free with the number of bits con- - sumed. For example, field names are specified as free text, - rather than special terse codes. - - A general "memo" framework is used. That is, a message con- - sists of some information in a rigid format, followed by the main - part of the message, with a format that is not specified in this - document. The syntax of several fields of the rigidly-formated - ("headers") section is defined in this specification; some of - these fields must be included in all messages. - - The syntax that distinguishes between header fields is - specified separately from the internal syntax for particular - fields. This separation is intended to allow simple parsers to - operate on the general structure of messages, without concern for - the detailed structure of individual header fields. Appendix B - is provided to facilitate construction of these parsers. - - In addition to the fields specified in this document, it is - expected that other fields will gain common use. As necessary, - the specifications for these "extension-fields" will be published - through the same mechanism used to publish this document. Users - may also wish to extend the set of fields that they use - privately. Such "user-defined fields" are permitted. - - The framework severely constrains document tone and appear- - ance and is primarily useful for most intra-organization communi- - cations and well-structured inter-organization communication. - It also can be used for some types of inter-process communica- - tion, such as simple file transfer and remote job entry. A more - robust framework might allow for multi-font, multi-color, multi- - dimension encoding of information. A less robust one, as is - present in most single-machine message systems, would more - severely constrain the ability to add fields and the decision to - include specific fields. In contrast with paper-based communica- - tion, it is interesting to note that the RECEIVER of a message - can exercise an extraordinary amount of control over the - message's appearance. The amount of actual control available to - message receivers is contingent upon the capabilities of their - individual message systems. - - - - - - August 13, 1982 - 2 - RFC #822 - - - - Standard for ARPA Internet Text Messages - - - 2. NOTATIONAL CONVENTIONS - - This specification uses an augmented Backus-Naur Form (BNF) - notation. The differences from standard BNF involve naming rules - and indicating repetition and "local" alternatives. - - 2.1. RULE NAMING - - Angle brackets ("<", ">") are not used, in general. The - name of a rule is simply the name itself, rather than "". - Quotation-marks enclose literal text (which may be upper and/or - lower case). Certain basic rules are in uppercase, such as - SPACE, TAB, CRLF, DIGIT, ALPHA, etc. Angle brackets are used in - rule definitions, and in the rest of this document, whenever - their presence will facilitate discerning the use of rule names. - - 2.2. RULE1 / RULE2: ALTERNATIVES - - Elements separated by slash ("/") are alternatives. There- - fore "foo / bar" will accept foo or bar. - - 2.3. (RULE1 RULE2): LOCAL ALTERNATIVES - - Elements enclosed in parentheses are treated as a single - element. Thus, "(elem (foo / bar) elem)" allows the token - sequences "elem foo elem" and "elem bar elem". - - 2.4. *RULE: REPETITION - - The character "*" preceding an element indicates repetition. - The full form is: - - *element - - indicating at least and at most occurrences of element. - Default values are 0 and infinity so that "*(element)" allows any - number, including zero; "1*element" requires at least one; and - "1*2element" allows one or two. - - 2.5. [RULE]: OPTIONAL - - Square brackets enclose optional elements; "[foo bar]" is - equivalent to "*1(foo bar)". - - 2.6. NRULE: SPECIFIC REPETITION - - "(element)" is equivalent to "*(element)"; that is, - exactly occurrences of (element). Thus 2DIGIT is a 2-digit - number, and 3ALPHA is a string of three alphabetic characters. - - - August 13, 1982 - 3 - RFC #822 - - - - Standard for ARPA Internet Text Messages - - - 2.7. #RULE: LISTS - - A construct "#" is defined, similar to "*", as follows: - - #element - - indicating at least and at most elements, each separated - by one or more commas (","). This makes the usual form of lists - very easy; a rule such as '(element *("," element))' can be shown - as "1#element". Wherever this construct is used, null elements - are allowed, but do not contribute to the count of elements - present. That is, "(element),,(element)" is permitted, but - counts as only two elements. Therefore, where at least one ele- - ment is required, at least one non-null element must be present. - Default values are 0 and infinity so that "#(element)" allows any - number, including zero; "1#element" requires at least one; and - "1#2element" allows one or two. - - 2.8. ; COMMENTS - - A semi-colon, set off some distance to the right of rule - text, starts a comment that continues to the end of line. This - is a simple way of including useful notes in parallel with the - specifications. - - - - - - - - - - - - - - - - - - - - - - - - - - - - August 13, 1982 - 4 - RFC #822 - - - - Standard for ARPA Internet Text Messages - - - 3. LEXICAL ANALYSIS OF MESSAGES - - 3.1. GENERAL DESCRIPTION - - A message consists of header fields and, optionally, a body. - The body is simply a sequence of lines containing ASCII charac- - ters. It is separated from the headers by a null line (i.e., a - line with nothing preceding the CRLF). - - 3.1.1. LONG HEADER FIELDS - - Each header field can be viewed as a single, logical line of - ASCII characters, comprising a field-name and a field-body. - For convenience, the field-body portion of this conceptual - entity can be split into a multiple-line representation; this - is called "folding". The general rule is that wherever there - may be linear-white-space (NOT simply LWSP-chars), a CRLF - immediately followed by AT LEAST one LWSP-char may instead be - inserted. Thus, the single line - - To: "Joe & J. Harvey" , JJV @ BBN - - can be represented as: - - To: "Joe & J. Harvey" , - JJV@BBN - - and - - To: "Joe & J. Harvey" - , JJV - @BBN - - and - - To: "Joe & - J. Harvey" , JJV @ BBN - - The process of moving from this folded multiple-line - representation of a header field to its single line represen- - tation is called "unfolding". Unfolding is accomplished by - regarding CRLF immediately followed by a LWSP-char as - equivalent to the LWSP-char. - - Note: While the standard permits folding wherever linear- - white-space is permitted, it is recommended that struc- - tured fields, such as those containing addresses, limit - folding to higher-level syntactic breaks. For address - fields, it is recommended that such folding occur - - - August 13, 1982 - 5 - RFC #822 - - - - Standard for ARPA Internet Text Messages - - - between addresses, after the separating comma. - - 3.1.2. STRUCTURE OF HEADER FIELDS - - Once a field has been unfolded, it may be viewed as being com- - posed of a field-name followed by a colon (":"), followed by a - field-body, and terminated by a carriage-return/line-feed. - The field-name must be composed of printable ASCII characters - (i.e., characters that have values between 33. and 126., - decimal, except colon). The field-body may be composed of any - ASCII characters, except CR or LF. (While CR and/or LF may be - present in the actual text, they are removed by the action of - unfolding the field.) - - Certain field-bodies of headers may be interpreted according - to an internal syntax that some systems may wish to parse. - These fields are called "structured fields". Examples - include fields containing dates and addresses. Other fields, - such as "Subject" and "Comments", are regarded simply as - strings of text. - - Note: Any field which has a field-body that is defined as - other than simply is to be treated as a struc- - tured field. - - Field-names, unstructured field bodies and structured - field bodies each are scanned by their own, independent - "lexical" analyzers. - - 3.1.3. UNSTRUCTURED FIELD BODIES - - For some fields, such as "Subject" and "Comments", no struc- - turing is assumed, and they are treated simply as s, as - in the message body. Rules of folding apply to these fields, - so that such field bodies which occupy several lines must - therefore have the second and successive lines indented by at - least one LWSP-char. - - 3.1.4. STRUCTURED FIELD BODIES - - To aid in the creation and reading of structured fields, the - free insertion of linear-white-space (which permits folding - by inclusion of CRLFs) is allowed between lexical tokens. - Rather than obscuring the syntax specifications for these - structured fields with explicit syntax for this linear-white- - space, the existence of another "lexical" analyzer is assumed. - This analyzer does not apply for unstructured field bodies - that are simply strings of text, as described above. The - analyzer provides an interpretation of the unfolded text - - - August 13, 1982 - 6 - RFC #822 - - - - Standard for ARPA Internet Text Messages - - - composing the body of the field as a sequence of lexical sym- - bols. - - These symbols are: - - - individual special characters - - quoted-strings - - domain-literals - - comments - - atoms - - The first four of these symbols are self-delimiting. Atoms - are not; they are delimited by the self-delimiting symbols and - by linear-white-space. For the purposes of regenerating - sequences of atoms and quoted-strings, exactly one SPACE is - assumed to exist, and should be used, between them. (Also, in - the "Clarifications" section on "White Space", below, note the - rules about treatment of multiple contiguous LWSP-chars.) - - So, for example, the folded body of an address field - - ":sysmail"@ Some-Group. Some-Org, - Muhammed.(I am the greatest) Ali @(the)Vegas.WBA - - - - - - - - - - - - - - - - - - - - - - - - - - - - - August 13, 1982 - 7 - RFC #822 - - - - Standard for ARPA Internet Text Messages - - - is analyzed into the following lexical symbols and types: - - :sysmail quoted string - @ special - Some-Group atom - . special - Some-Org atom - , special - Muhammed atom - . special - (I am the greatest) comment - Ali atom - @ atom - (the) comment - Vegas atom - . special - WBA atom - - The canonical representations for the data in these addresses - are the following strings: - - ":sysmail"@Some-Group.Some-Org - - and - - Muhammed.Ali@Vegas.WBA - - Note: For purposes of display, and when passing such struc- - tured information to other systems, such as mail proto- - col services, there must be NO linear-white-space - between s that are separated by period (".") or - at-sign ("@") and exactly one SPACE between all other - s. Also, headers should be in a folded form. - - - - - - - - - - - - - - - - - - - August 13, 1982 - 8 - RFC #822 - - - - Standard for ARPA Internet Text Messages - - - 3.2. HEADER FIELD DEFINITIONS - - These rules show a field meta-syntax, without regard for the - particular type or internal syntax. Their purpose is to permit - detection of fields; also, they present to higher-level parsers - an image of each field as fitting on one line. - - field = field-name ":" [ field-body ] CRLF - - field-name = 1* - - field-body = field-body-contents - [CRLF LWSP-char field-body] - - field-body-contents = - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - August 13, 1982 - 9 - RFC #822 - - - - Standard for ARPA Internet Text Messages - - - 3.3. LEXICAL TOKENS - - The following rules are used to define an underlying lexical - analyzer, which feeds tokens to higher level parsers. See the - ANSI references, in the Bibliography. - - ; ( Octal, Decimal.) - CHAR = ; ( 0-177, 0.-127.) - ALPHA = - ; (101-132, 65.- 90.) - ; (141-172, 97.-122.) - DIGIT = ; ( 60- 71, 48.- 57.) - CTL = ; ( 177, 127.) - CR = ; ( 15, 13.) - LF = ; ( 12, 10.) - SPACE = ; ( 40, 32.) - HTAB = ; ( 11, 9.) - <"> = ; ( 42, 34.) - CRLF = CR LF - - LWSP-char = SPACE / HTAB ; semantics = SPACE - - linear-white-space = 1*([CRLF] LWSP-char) ; semantics = SPACE - ; CRLF => folding - - specials = "(" / ")" / "<" / ">" / "@" ; Must be in quoted- - / "," / ";" / ":" / "\" / <"> ; string, to use - / "." / "[" / "]" ; within a word. - - delimiters = specials / linear-white-space / comment - - text = atoms, specials, - CR & bare LF, but NOT ; comments and - including CRLF> ; quoted-strings are - ; NOT recognized. - - atom = 1* - - quoted-string = <"> *(qtext/quoted-pair) <">; Regular qtext or - ; quoted chars. - - qtext = , ; => may be folded - "\" & CR, and including - linear-white-space> - - domain-literal = "[" *(dtext / quoted-pair) "]" - - - - - August 13, 1982 - 10 - RFC #822 - - - - Standard for ARPA Internet Text Messages - - - dtext = may be folded - "]", "\" & CR, & including - linear-white-space> - - comment = "(" *(ctext / quoted-pair / comment) ")" - - ctext = may be folded - ")", "\" & CR, & including - linear-white-space> - - quoted-pair = "\" CHAR ; may quote any char - - phrase = 1*word ; Sequence of words - - word = atom / quoted-string - - - 3.4. CLARIFICATIONS - - 3.4.1. QUOTING - - Some characters are reserved for special interpretation, such - as delimiting lexical tokens. To permit use of these charac- - ters as uninterpreted data, a quoting mechanism is provided. - To quote a character, precede it with a backslash ("\"). - - This mechanism is not fully general. Characters may be quoted - only within a subset of the lexical constructs. In particu- - lar, quoting is limited to use within: - - - quoted-string - - domain-literal - - comment - - Within these constructs, quoting is REQUIRED for CR and "\" - and for the character(s) that delimit the token (e.g., "(" and - ")" for a comment). However, quoting is PERMITTED for any - character. - - Note: In particular, quoting is NOT permitted within atoms. - For example when the local-part of an addr-spec must - contain a special character, a quoted string must be - used. Therefore, a specification such as: - - Full\ Name@Domain - - is not legal and must be specified as: - - "Full Name"@Domain - - - August 13, 1982 - 11 - RFC #822 - - - - Standard for ARPA Internet Text Messages - - - 3.4.2. WHITE SPACE - - Note: In structured field bodies, multiple linear space ASCII - characters (namely HTABs and SPACEs) are treated as - single spaces and may freely surround any symbol. In - all header fields, the only place in which at least one - LWSP-char is REQUIRED is at the beginning of continua- - tion lines in a folded field. - - When passing text to processes that do not interpret text - according to this standard (e.g., mail protocol servers), then - NO linear-white-space characters should occur between a period - (".") or at-sign ("@") and a . Exactly ONE SPACE should - be used in place of arbitrary linear-white-space and comment - sequences. - - Note: Within systems conforming to this standard, wherever a - member of the list of delimiters is allowed, LWSP-chars - may also occur before and/or after it. - - Writers of mail-sending (i.e., header-generating) programs - should realize that there is no network-wide definition of the - effect of ASCII HT (horizontal-tab) characters on the appear- - ance of text at another network host; therefore, the use of - tabs in message headers, though permitted, is discouraged. - - 3.4.3. COMMENTS - - A comment is a set of ASCII characters, which is enclosed in - matching parentheses and which is not within a quoted-string - The comment construct permits message originators to add text - which will be useful for human readers, but which will be - ignored by the formal semantics. Comments should be retained - while the message is subject to interpretation according to - this standard. However, comments must NOT be included in - other cases, such as during protocol exchanges with mail - servers. - - Comments nest, so that if an unquoted left parenthesis occurs - in a comment string, there must also be a matching right - parenthesis. When a comment acts as the delimiter between a - sequence of two lexical symbols, such as two atoms, it is lex- - ically equivalent with a single SPACE, for the purposes of - regenerating the sequence, such as when passing the sequence - onto a mail protocol server. Comments are detected as such - only within field-bodies of structured fields. - - If a comment is to be "folded" onto multiple lines, then the - syntax for folding must be adhered to. (See the "Lexical - - - August 13, 1982 - 12 - RFC #822 - - - - Standard for ARPA Internet Text Messages - - - Analysis of Messages" section on "Folding Long Header Fields" - above, and the section on "Case Independence" below.) Note - that the official semantics therefore do not "see" any - unquoted CRLFs that are in comments, although particular pars- - ing programs may wish to note their presence. For these pro- - grams, it would be reasonable to interpret a "CRLF LWSP-char" - as being a CRLF that is part of the comment; i.e., the CRLF is - kept and the LWSP-char is discarded. Quoted CRLFs (i.e., a - backslash followed by a CR followed by a LF) still must be - followed by at least one LWSP-char. - - 3.4.4. DELIMITING AND QUOTING CHARACTERS - - The quote character (backslash) and characters that delimit - syntactic units are not, generally, to be taken as data that - are part of the delimited or quoted unit(s). In particular, - the quotation-marks that define a quoted-string, the - parentheses that define a comment and the backslash that - quotes a following character are NOT part of the quoted- - string, comment or quoted character. A quotation-mark that is - to be part of a quoted-string, a parenthesis that is to be - part of a comment and a backslash that is to be part of either - must each be preceded by the quote-character backslash ("\"). - Note that the syntax allows any character to be quoted within - a quoted-string or comment; however only certain characters - MUST be quoted to be included as data. These characters are - the ones that are not part of the alternate text group (i.e., - ctext or qtext). - - The one exception to this rule is that a single SPACE is - assumed to exist between contiguous words in a phrase, and - this interpretation is independent of the actual number of - LWSP-chars that the creator places between the words. To - include more than one SPACE, the creator must make the LWSP- - chars be part of a quoted-string. - - Quotation marks that delimit a quoted string and backslashes - that quote the following character should NOT accompany the - quoted-string when the string is passed to processes that do - not interpret data according to this specification (e.g., mail - protocol servers). - - 3.4.5. QUOTED-STRINGS - - Where permitted (i.e., in words in structured fields) quoted- - strings are treated as a single symbol. That is, a quoted- - string is equivalent to an atom, syntactically. If a quoted- - string is to be "folded" onto multiple lines, then the syntax - for folding must be adhered to. (See the "Lexical Analysis of - - - August 13, 1982 - 13 - RFC #822 - - - - Standard for ARPA Internet Text Messages - - - Messages" section on "Folding Long Header Fields" above, and - the section on "Case Independence" below.) Therefore, the - official semantics do not "see" any bare CRLFs that are in - quoted-strings; however particular parsing programs may wish - to note their presence. For such programs, it would be rea- - sonable to interpret a "CRLF LWSP-char" as being a CRLF which - is part of the quoted-string; i.e., the CRLF is kept and the - LWSP-char is discarded. Quoted CRLFs (i.e., a backslash fol- - lowed by a CR followed by a LF) are also subject to rules of - folding, but the presence of the quoting character (backslash) - explicitly indicates that the CRLF is data to the quoted - string. Stripping off the first following LWSP-char is also - appropriate when parsing quoted CRLFs. - - 3.4.6. BRACKETING CHARACTERS - - There is one type of bracket which must occur in matched pairs - and may have pairs nested within each other: - - o Parentheses ("(" and ")") are used to indicate com- - ments. - - There are three types of brackets which must occur in matched - pairs, and which may NOT be nested: - - o Colon/semi-colon (":" and ";") are used in address - specifications to indicate that the included list of - addresses are to be treated as a group. - - o Angle brackets ("<" and ">") are generally used to - indicate the presence of a one machine-usable refer- - ence (e.g., delimiting mailboxes), possibly including - source-routing to the machine. - - o Square brackets ("[" and "]") are used to indicate the - presence of a domain-literal, which the appropriate - name-domain is to use directly, bypassing normal - name-resolution mechanisms. - - 3.4.7. CASE INDEPENDENCE - - Except as noted, alphabetic strings may be represented in any - combination of upper and lower case. The only syntactic units - - - - - - - - - August 13, 1982 - 14 - RFC #822 - - - - Standard for ARPA Internet Text Messages - - - which requires preservation of case information are: - - - text - - qtext - - dtext - - ctext - - quoted-pair - - local-part, except "Postmaster" - - When matching any other syntactic unit, case is to be ignored. - For example, the field-names "From", "FROM", "from", and even - "FroM" are semantically equal and should all be treated ident- - ically. - - When generating these units, any mix of upper and lower case - alphabetic characters may be used. The case shown in this - specification is suggested for message-creating processes. - - Note: The reserved local-part address unit, "Postmaster", is - an exception. When the value "Postmaster" is being - interpreted, it must be accepted in any mixture of - case, including "POSTMASTER", and "postmaster". - - 3.4.8. FOLDING LONG HEADER FIELDS - - Each header field may be represented on exactly one line con- - sisting of the name of the field and its body, and terminated - by a CRLF; this is what the parser sees. For readability, the - field-body portion of long header fields may be "folded" onto - multiple lines of the actual field. "Long" is commonly inter- - preted to mean greater than 65 or 72 characters. The former - length serves as a limit, when the message is to be viewed on - most simple terminals which use simple display software; how- - ever, the limit is not imposed by this standard. - - Note: Some display software often can selectively fold lines, - to suit the display terminal. In such cases, sender- - provided folding can interfere with the display - software. - - 3.4.9. BACKSPACE CHARACTERS - - ASCII BS characters (Backspace, decimal 8) may be included in - texts and quoted-strings to effect overstriking. However, any - use of backspaces which effects an overstrike to the left of - the beginning of the text or quoted-string is prohibited. - - - - - - August 13, 1982 - 15 - RFC #822 - - - - Standard for ARPA Internet Text Messages - - - 3.4.10. NETWORK-SPECIFIC TRANSFORMATIONS - - During transmission through heterogeneous networks, it may be - necessary to force data to conform to a network's local con- - ventions. For example, it may be required that a CR be fol- - lowed either by LF, making a CRLF, or by , if the CR is - to stand alone). Such transformations are reversed, when the - message exits that network. - - When crossing network boundaries, the message should be - treated as passing through two modules. It will enter the - first module containing whatever network-specific transforma- - tions that were necessary to permit migration through the - "current" network. It then passes through the modules: - - o Transformation Reversal - - The "current" network's idiosyncracies are removed and - the message is returned to the canonical form speci- - fied in this standard. - - o Transformation - - The "next" network's local idiosyncracies are imposed - on the message. - - ------------------ - From ==> | Remove Net-A | - Net-A | idiosyncracies | - ------------------ - || - \/ - Conformance - with standard - || - \/ - ------------------ - | Impose Net-B | ==> To - | idiosyncracies | Net-B - ------------------ - - - - - - - - - - - - August 13, 1982 - 16 - RFC #822 - - - - Standard for ARPA Internet Text Messages - - - 4. MESSAGE SPECIFICATION - - 4.1. SYNTAX - - Note: Due to an artifact of the notational conventions, the syn- - tax indicates that, when present, some fields, must be in - a particular order. Header fields are NOT required to - occur in any particular order, except that the message - body must occur AFTER the headers. It is recommended - that, if present, headers be sent in the order "Return- - Path", "Received", "Date", "From", "Subject", "Sender", - "To", "cc", etc. - - This specification permits multiple occurrences of most - fields. Except as noted, their interpretation is not - specified here, and their use is discouraged. - - The following syntax for the bodies of various fields should - be thought of as describing each field body as a single long - string (or line). The "Lexical Analysis of Message" section on - "Long Header Fields", above, indicates how such long strings can - be represented on more than one line in the actual transmitted - message. - - message = fields *( CRLF *text ) ; Everything after - ; first null line - ; is message body - - fields = dates ; Creation time, - source ; author id & one - 1*destination ; address required - *optional-field ; others optional - - source = [ trace ] ; net traversals - originator ; original mail - [ resent ] ; forwarded - - trace = return ; path to sender - 1*received ; receipt tags - - return = "Return-path" ":" route-addr ; return address - - received = "Received" ":" ; one per relay - ["from" domain] ; sending host - ["by" domain] ; receiving host - ["via" atom] ; physical path - *("with" atom) ; link/mail protocol - ["id" msg-id] ; receiver msg id - ["for" addr-spec] ; initial form - - - August 13, 1982 - 17 - RFC #822 - - - - Standard for ARPA Internet Text Messages - - - ";" date-time ; time received - - originator = authentic ; authenticated addr - [ "Reply-To" ":" 1#address] ) - - authentic = "From" ":" mailbox ; Single author - / ( "Sender" ":" mailbox ; Actual submittor - "From" ":" 1#mailbox) ; Multiple authors - ; or not sender - - resent = resent-authentic - [ "Resent-Reply-To" ":" 1#address] ) - - resent-authentic = - = "Resent-From" ":" mailbox - / ( "Resent-Sender" ":" mailbox - "Resent-From" ":" 1#mailbox ) - - dates = orig-date ; Original - [ resent-date ] ; Forwarded - - orig-date = "Date" ":" date-time - - resent-date = "Resent-Date" ":" date-time - - destination = "To" ":" 1#address ; Primary - / "Resent-To" ":" 1#address - / "cc" ":" 1#address ; Secondary - / "Resent-cc" ":" 1#address - / "bcc" ":" #address ; Blind carbon - / "Resent-bcc" ":" #address - - optional-field = - / "Message-ID" ":" msg-id - / "Resent-Message-ID" ":" msg-id - / "In-Reply-To" ":" *(phrase / msg-id) - / "References" ":" *(phrase / msg-id) - / "Keywords" ":" #phrase - / "Subject" ":" *text - / "Comments" ":" *text - / "Encrypted" ":" 1#2word - / extension-field ; To be defined - / user-defined-field ; May be pre-empted - - msg-id = "<" addr-spec ">" ; Unique message id - - - - - - - August 13, 1982 - 18 - RFC #822 - - - - Standard for ARPA Internet Text Messages - - - extension-field = - - - user-defined-field = - - - 4.2. FORWARDING - - Some systems permit mail recipients to forward a message, - retaining the original headers, by adding some new fields. This - standard supports such a service, through the "Resent-" prefix to - field names. - - Whenever the string "Resent-" begins a field name, the field - has the same semantics as a field whose name does not have the - prefix. However, the message is assumed to have been forwarded - by an original recipient who attached the "Resent-" field. This - new field is treated as being more recent than the equivalent, - original field. For example, the "Resent-From", indicates the - person that forwarded the message, whereas the "From" field indi- - cates the original author. - - Use of such precedence information depends upon partici- - pants' communication needs. For example, this standard does not - dictate when a "Resent-From:" address should receive replies, in - lieu of sending them to the "From:" address. - - Note: In general, the "Resent-" fields should be treated as con- - taining a set of information that is independent of the - set of original fields. Information for one set should - not automatically be taken from the other. The interpre- - tation of multiple "Resent-" fields, of the same type, is - undefined. - - In the remainder of this specification, occurrence of legal - "Resent-" fields are treated identically with the occurrence of - - - - - - - - - August 13, 1982 - 19 - RFC #822 - - - - Standard for ARPA Internet Text Messages - - - fields whose names do not contain this prefix. - - 4.3. TRACE FIELDS - - Trace information is used to provide an audit trail of mes- - sage handling. In addition, it indicates a route back to the - sender of the message. - - The list of known "via" and "with" values are registered - with the Network Information Center, SRI International, Menlo - Park, California. - - 4.3.1. RETURN-PATH - - This field is added by the final transport system that - delivers the message to its recipient. The field is intended - to contain definitive information about the address and route - back to the message's originator. - - Note: The "Reply-To" field is added by the originator and - serves to direct replies, whereas the "Return-Path" - field is used to identify a path back to the origina- - tor. - - While the syntax indicates that a route specification is - optional, every attempt should be made to provide that infor- - mation in this field. - - 4.3.2. RECEIVED - - A copy of this field is added by each transport service that - relays the message. The information in the field can be quite - useful for tracing transport problems. - - The names of the sending and receiving hosts and time-of- - receipt may be specified. The "via" parameter may be used, to - indicate what physical mechanism the message was sent over, - such as Arpanet or Phonenet, and the "with" parameter may be - used to indicate the mail-, or connection-, level protocol - that was used, such as the SMTP mail protocol, or X.25 tran- - sport protocol. - - Note: Several "with" parameters may be included, to fully - specify the set of protocols that were used. - - Some transport services queue mail; the internal message iden- - tifier that is assigned to the message may be noted, using the - "id" parameter. When the sending host uses a destination - address specification that the receiving host reinterprets, by - - - August 13, 1982 - 20 - RFC #822 - - - - Standard for ARPA Internet Text Messages - - - expansion or transformation, the receiving host may wish to - record the original specification, using the "for" parameter. - For example, when a copy of mail is sent to the member of a - distribution list, this parameter may be used to record the - original address that was used to specify the list. - - 4.4. ORIGINATOR FIELDS - - The standard allows only a subset of the combinations possi- - ble with the From, Sender, Reply-To, Resent-From, Resent-Sender, - and Resent-Reply-To fields. The limitation is intentional. - - 4.4.1. FROM / RESENT-FROM - - This field contains the identity of the person(s) who wished - this message to be sent. The message-creation process should - default this field to be a single, authenticated machine - address, indicating the AGENT (person, system or process) - entering the message. If this is not done, the "Sender" field - MUST be present. If the "From" field IS defaulted this way, - the "Sender" field is optional and is redundant with the - "From" field. In all cases, addresses in the "From" field - must be machine-usable (addr-specs) and may not contain named - lists (groups). - - 4.4.2. SENDER / RESENT-SENDER - - This field contains the authenticated identity of the AGENT - (person, system or process) that sends the message. It is - intended for use when the sender is not the author of the mes- - sage, or to indicate who among a group of authors actually - sent the message. If the contents of the "Sender" field would - be completely redundant with the "From" field, then the - "Sender" field need not be present and its use is discouraged - (though still legal). In particular, the "Sender" field MUST - be present if it is NOT the same as the "From" Field. - - The Sender mailbox specification includes a word sequence - which must correspond to a specific agent (i.e., a human user - or a computer program) rather than a standard address. This - indicates the expectation that the field will identify the - single AGENT (person, system, or process) responsible for - sending the mail and not simply include the name of a mailbox - from which the mail was sent. For example in the case of a - shared login name, the name, by itself, would not be adequate. - The local-part address unit, which refers to this agent, is - expected to be a computer system term, and not (for example) a - generalized person reference which can be used outside the - network text message context. - - - August 13, 1982 - 21 - RFC #822 - - - - Standard for ARPA Internet Text Messages - - - Since the critical function served by the "Sender" field is - identification of the agent responsible for sending mail and - since computer programs cannot be held accountable for their - behavior, it is strongly recommended that when a computer pro- - gram generates a message, the HUMAN who is responsible for - that program be referenced as part of the "Sender" field mail- - box specification. - - 4.4.3. REPLY-TO / RESENT-REPLY-TO - - This field provides a general mechanism for indicating any - mailbox(es) to which responses are to be sent. Three typical - uses for this feature can be distinguished. In the first - case, the author(s) may not have regular machine-based mail- - boxes and therefore wish(es) to indicate an alternate machine - address. In the second case, an author may wish additional - persons to be made aware of, or responsible for, replies. A - somewhat different use may be of some help to "text message - teleconferencing" groups equipped with automatic distribution - services: include the address of that service in the "Reply- - To" field of all messages submitted to the teleconference; - then participants can "reply" to conference submissions to - guarantee the correct distribution of any submission of their - own. - - Note: The "Return-Path" field is added by the mail transport - service, at the time of final deliver. It is intended - to identify a path back to the orginator of the mes- - sage. The "Reply-To" field is added by the message - originator and is intended to direct replies. - - 4.4.4. AUTOMATIC USE OF FROM / SENDER / REPLY-TO - - For systems which automatically generate address lists for - replies to messages, the following recommendations are made: - - o The "Sender" field mailbox should be sent notices of - any problems in transport or delivery of the original - messages. If there is no "Sender" field, then the - "From" field mailbox should be used. - - o The "Sender" field mailbox should NEVER be used - automatically, in a recipient's reply message. - - o If the "Reply-To" field exists, then the reply should - go to the addresses indicated in that field and not to - the address(es) indicated in the "From" field. - - - - - August 13, 1982 - 22 - RFC #822 - - - - Standard for ARPA Internet Text Messages - - - o If there is a "From" field, but no "Reply-To" field, - the reply should be sent to the address(es) indicated - in the "From" field. - - Sometimes, a recipient may actually wish to communicate with - the person that initiated the message transfer. In such - cases, it is reasonable to use the "Sender" address. - - This recommendation is intended only for automated use of - originator-fields and is not intended to suggest that replies - may not also be sent to other recipients of messages. It is - up to the respective mail-handling programs to decide what - additional facilities will be provided. - - Examples are provided in Appendix A. - - 4.5. RECEIVER FIELDS - - 4.5.1. TO / RESENT-TO - - This field contains the identity of the primary recipients of - the message. - - 4.5.2. CC / RESENT-CC - - This field contains the identity of the secondary (informa- - tional) recipients of the message. - - 4.5.3. BCC / RESENT-BCC - - This field contains the identity of additional recipients of - the message. The contents of this field are not included in - copies of the message sent to the primary and secondary reci- - pients. Some systems may choose to include the text of the - "Bcc" field only in the author(s)'s copy, while others may - also include it in the text sent to all those indicated in the - "Bcc" list. - - 4.6. REFERENCE FIELDS - - 4.6.1. MESSAGE-ID / RESENT-MESSAGE-ID - - This field contains a unique identifier (the local-part - address unit) which refers to THIS version of THIS message. - The uniqueness of the message identifier is guaranteed by the - host which generates it. This identifier is intended to be - machine readable and not necessarily meaningful to humans. A - message identifier pertains to exactly one instantiation of a - particular message; subsequent revisions to the message should - - - August 13, 1982 - 23 - RFC #822 - - - - Standard for ARPA Internet Text Messages - - - each receive new message identifiers. - - 4.6.2. IN-REPLY-TO - - The contents of this field identify previous correspon- - dence which this message answers. Note that if message iden- - tifiers are used in this field, they must use the msg-id - specification format. - - 4.6.3. REFERENCES - - The contents of this field identify other correspondence - which this message references. Note that if message identif- - iers are used, they must use the msg-id specification format. - - 4.6.4. KEYWORDS - - This field contains keywords or phrases, separated by - commas. - - 4.7. OTHER FIELDS - - 4.7.1. SUBJECT - - This is intended to provide a summary, or indicate the - nature, of the message. - - 4.7.2. COMMENTS - - Permits adding text comments onto the message without - disturbing the contents of the message's body. - - 4.7.3. ENCRYPTED - - Sometimes, data encryption is used to increase the - privacy of message contents. If the body of a message has - been encrypted, to keep its contents private, the "Encrypted" - field can be used to note the fact and to indicate the nature - of the encryption. The first parameter indicates the - software used to encrypt the body, and the second, optional - is intended to aid the recipient in selecting the - proper decryption key. This code word may be viewed as an - index to a table of keys held by the recipient. - - Note: Unfortunately, headers must contain envelope, as well - as contents, information. Consequently, it is neces- - sary that they remain unencrypted, so that mail tran- - sport services may access them. Since names, - addresses, and "Subject" field contents may contain - - - August 13, 1982 - 24 - RFC #822 - - - - Standard for ARPA Internet Text Messages - - - sensitive information, this requirement limits total - message privacy. - - Names of encryption software are registered with the Net- - work Information Center, SRI International, Menlo Park, Cali- - fornia. - - 4.7.4. EXTENSION-FIELD - - A limited number of common fields have been defined in - this document. As network mail requirements dictate, addi- - tional fields may be standardized. To provide user-defined - fields with a measure of safety, in name selection, such - extension-fields will never have names that begin with the - string "X-". - - Names of Extension-fields are registered with the Network - Information Center, SRI International, Menlo Park, California. - - 4.7.5. USER-DEFINED-FIELD - - Individual users of network mail are free to define and - use additional header fields. Such fields must have names - which are not already used in the current specification or in - any definitions of extension-fields, and the overall syntax of - these user-defined-fields must conform to this specification's - rules for delimiting and folding fields. Due to the - extension-field publishing process, the name of a user- - defined-field may be pre-empted - - Note: The prefatory string "X-" will never be used in the - names of Extension-fields. This provides user-defined - fields with a protected set of names. - - - - - - - - - - - - - - - - - - - August 13, 1982 - 25 - RFC #822 - - - - Standard for ARPA Internet Text Messages - - - 5. DATE AND TIME SPECIFICATION - - 5.1. SYNTAX - - date-time = [ day "," ] date time ; dd mm yy - ; hh:mm:ss zzz - - day = "Mon" / "Tue" / "Wed" / "Thu" - / "Fri" / "Sat" / "Sun" - - date = 1*2DIGIT month 2DIGIT ; day month year - ; e.g. 20 Jun 82 - - month = "Jan" / "Feb" / "Mar" / "Apr" - / "May" / "Jun" / "Jul" / "Aug" - / "Sep" / "Oct" / "Nov" / "Dec" - - time = hour zone ; ANSI and Military - - hour = 2DIGIT ":" 2DIGIT [":" 2DIGIT] - ; 00:00:00 - 23:59:59 - - zone = "UT" / "GMT" ; Universal Time - ; North American : UT - / "EST" / "EDT" ; Eastern: - 5/ - 4 - / "CST" / "CDT" ; Central: - 6/ - 5 - / "MST" / "MDT" ; Mountain: - 7/ - 6 - / "PST" / "PDT" ; Pacific: - 8/ - 7 - / 1ALPHA ; Military: Z = UT; - ; A:-1; (J not used) - ; M:-12; N:+1; Y:+12 - / ( ("+" / "-") 4DIGIT ) ; Local differential - ; hours+min. (HHMM) - - 5.2. SEMANTICS - - If included, day-of-week must be the day implied by the date - specification. - - Time zone may be indicated in several ways. "UT" is Univer- - sal Time (formerly called "Greenwich Mean Time"); "GMT" is per- - mitted as a reference to Universal Time. The military standard - uses a single character for each zone. "Z" is Universal Time. - "A" indicates one hour earlier, and "M" indicates 12 hours ear- - lier; "N" is one hour later, and "Y" is 12 hours later. The - letter "J" is not used. The other remaining two forms are taken - from ANSI standard X3.51-1975. One allows explicit indication of - the amount of offset from UT; the other uses common 3-character - strings for indicating time zones in North America. - - - August 13, 1982 - 26 - RFC #822 - - - - Standard for ARPA Internet Text Messages - - - 6. ADDRESS SPECIFICATION - - 6.1. SYNTAX - - address = mailbox ; one addressee - / group ; named list - - group = phrase ":" [#mailbox] ";" - - mailbox = addr-spec ; simple address - / phrase route-addr ; name & addr-spec - - route-addr = "<" [route] addr-spec ">" - - route = 1#("@" domain) ":" ; path-relative - - addr-spec = local-part "@" domain ; global address - - local-part = word *("." word) ; uninterpreted - ; case-preserved - - domain = sub-domain *("." sub-domain) - - sub-domain = domain-ref / domain-literal - - domain-ref = atom ; symbolic reference - - 6.2. SEMANTICS - - A mailbox receives mail. It is a conceptual entity which - does not necessarily pertain to file storage. For example, some - sites may choose to print mail on their line printer and deliver - the output to the addressee's desk. - - A mailbox specification comprises a person, system or pro- - cess name reference, a domain-dependent string, and a name-domain - reference. The name reference is optional and is usually used to - indicate the human name of a recipient. The name-domain refer- - ence specifies a sequence of sub-domains. The domain-dependent - string is uninterpreted, except by the final sub-domain; the rest - of the mail service merely transmits it as a literal string. - - 6.2.1. DOMAINS - - A name-domain is a set of registered (mail) names. A name- - domain specification resolves to a subordinate name-domain - specification or to a terminal domain-dependent string. - Hence, domain specification is extensible, permitting any - number of registration levels. - - - August 13, 1982 - 27 - RFC #822 - - - - Standard for ARPA Internet Text Messages - - - Name-domains model a global, logical, hierarchical addressing - scheme. The model is logical, in that an address specifica- - tion is related to name registration and is not necessarily - tied to transmission path. The model's hierarchy is a - directed graph, called an in-tree, such that there is a single - path from the root of the tree to any node in the hierarchy. - If more than one path actually exists, they are considered to - be different addresses. - - The root node is common to all addresses; consequently, it is - not referenced. Its children constitute "top-level" name- - domains. Usually, a service has access to its own full domain - specification and to the names of all top-level name-domains. - - The "top" of the domain addressing hierarchy -- a child of the - root -- is indicated by the right-most field, in a domain - specification. Its child is specified to the left, its child - to the left, and so on. - - Some groups provide formal registration services; these con- - stitute name-domains that are independent logically of - specific machines. In addition, networks and machines impli- - citly compose name-domains, since their membership usually is - registered in name tables. - - In the case of formal registration, an organization implements - a (distributed) data base which provides an address-to-route - mapping service for addresses of the form: - - person@registry.organization - - Note that "organization" is a logical entity, separate from - any particular communication network. - - A mechanism for accessing "organization" is universally avail- - able. That mechanism, in turn, seeks an instantiation of the - registry; its location is not indicated in the address specif- - ication. It is assumed that the system which operates under - the name "organization" knows how to find a subordinate regis- - try. The registry will then use the "person" string to deter- - mine where to send the mail specification. - - The latter, network-oriented case permits simple, direct, - attachment-related address specification, such as: - - user@host.network - - Once the network is accessed, it is expected that a message - will go directly to the host and that the host will resolve - - - August 13, 1982 - 28 - RFC #822 - - - - Standard for ARPA Internet Text Messages - - - the user name, placing the message in the user's mailbox. - - 6.2.2. ABBREVIATED DOMAIN SPECIFICATION - - Since any number of levels is possible within the domain - hierarchy, specification of a fully qualified address can - become inconvenient. This standard permits abbreviated domain - specification, in a special case: - - For the address of the sender, call the left-most - sub-domain Level N. In a header address, if all of - the sub-domains above (i.e., to the right of) Level N - are the same as those of the sender, then they do not - have to appear in the specification. Otherwise, the - address must be fully qualified. - - This feature is subject to approval by local sub- - domains. Individual sub-domains may require their - member systems, which originate mail, to provide full - domain specification only. When permitted, abbrevia- - tions may be present only while the message stays - within the sub-domain of the sender. - - Use of this mechanism requires the sender's sub-domain - to reserve the names of all top-level domains, so that - full specifications can be distinguished from abbrevi- - ated specifications. - - For example, if a sender's address is: - - sender@registry-A.registry-1.organization-X - - and one recipient's address is: - - recipient@registry-B.registry-1.organization-X - - and another's is: - - recipient@registry-C.registry-2.organization-X - - then ".registry-1.organization-X" need not be specified in the - the message, but "registry-C.registry-2" DOES have to be - specified. That is, the first two addresses may be abbrevi- - ated, but the third address must be fully specified. - - When a message crosses a domain boundary, all addresses must - be specified in the full format, ending with the top-level - name-domain in the right-most field. It is the responsibility - of mail forwarding services to ensure that addresses conform - - - August 13, 1982 - 29 - RFC #822 - - - - Standard for ARPA Internet Text Messages - - - with this requirement. In the case of abbreviated addresses, - the relaying service must make the necessary expansions. It - should be noted that it often is difficult for such a service - to locate all occurrences of address abbreviations. For exam- - ple, it will not be possible to find such abbreviations within - the body of the message. The "Return-Path" field can aid - recipients in recovering from these errors. - - Note: When passing any portion of an addr-spec onto a process - which does not interpret data according to this stan- - dard (e.g., mail protocol servers). There must be NO - LWSP-chars preceding or following the at-sign or any - delimiting period ("."), such as shown in the above - examples, and only ONE SPACE between contiguous - s. - - 6.2.3. DOMAIN TERMS - - A domain-ref must be THE official name of a registry, network, - or host. It is a symbolic reference, within a name sub- - domain. At times, it is necessary to bypass standard mechan- - isms for resolving such references, using more primitive - information, such as a network host address rather than its - associated host name. - - To permit such references, this standard provides the domain- - literal construct. Its contents must conform with the needs - of the sub-domain in which it is interpreted. - - Domain-literals which refer to domains within the ARPA Inter- - net specify 32-bit Internet addresses, in four 8-bit fields - noted in decimal, as described in Request for Comments #820, - "Assigned Numbers." For example: - - [10.0.3.19] - - Note: THE USE OF DOMAIN-LITERALS IS STRONGLY DISCOURAGED. It - is permitted only as a means of bypassing temporary - system limitations, such as name tables which are not - complete. - - The names of "top-level" domains, and the names of domains - under in the ARPA Internet, are registered with the Network - Information Center, SRI International, Menlo Park, California. - - 6.2.4. DOMAIN-DEPENDENT LOCAL STRING - - The local-part of an addr-spec in a mailbox specification - (i.e., the host's name for the mailbox) is understood to be - - - August 13, 1982 - 30 - RFC #822 - - - - Standard for ARPA Internet Text Messages - - - whatever the receiving mail protocol server allows. For exam- - ple, some systems do not understand mailbox references of the - form "P. D. Q. Bach", but others do. - - This specification treats periods (".") as lexical separators. - Hence, their presence in local-parts which are not quoted- - strings, is detected. However, such occurrences carry NO - semantics. That is, if a local-part has periods within it, an - address parser will divide the local-part into several tokens, - but the sequence of tokens will be treated as one uninter- - preted unit. The sequence will be re-assembled, when the - address is passed outside of the system such as to a mail pro- - tocol service. - - For example, the address: - - First.Last@Registry.Org - - is legal and does not require the local-part to be surrounded - with quotation-marks. (However, "First Last" DOES require - quoting.) The local-part of the address, when passed outside - of the mail system, within the Registry.Org domain, is - "First.Last", again without quotation marks. - - 6.2.5. BALANCING LOCAL-PART AND DOMAIN - - In some cases, the boundary between local-part and domain can - be flexible. The local-part may be a simple string, which is - used for the final determination of the recipient's mailbox. - All other levels of reference are, therefore, part of the - domain. - - For some systems, in the case of abbreviated reference to the - local and subordinate sub-domains, it may be possible to - specify only one reference within the domain part and place - the other, subordinate name-domain references within the - local-part. This would appear as: - - mailbox.sub1.sub2@this-domain - - Such a specification would be acceptable to address parsers - which conform to RFC #733, but do not support this newer - Internet standard. While contrary to the intent of this stan- - dard, the form is legal. - - Also, some sub-domains have a specification syntax which does - not conform to this standard. For example: - - sub-net.mailbox@sub-domain.domain - - - August 13, 1982 - 31 - RFC #822 - - - - Standard for ARPA Internet Text Messages - - - uses a different parsing sequence for local-part than for - domain. - - Note: As a rule, the domain specification should contain - fields which are encoded according to the syntax of - this standard and which contain generally-standardized - information. The local-part specification should con- - tain only that portion of the address which deviates - from the form or intention of the domain field. - - 6.2.6. MULTIPLE MAILBOXES - - An individual may have several mailboxes and wish to receive - mail at whatever mailbox is convenient for the sender to - access. This standard does not provide a means of specifying - "any member of" a list of mailboxes. - - A set of individuals may wish to receive mail as a single unit - (i.e., a distribution list). The construct permits - specification of such a list. Recipient mailboxes are speci- - fied within the bracketed part (":" - ";"). A copy of the - transmitted message is to be sent to each mailbox listed. - This standard does not permit recursive specification of - groups within groups. - - While a list must be named, it is not required that the con- - tents of the list be included. In this case, the
- serves only as an indication of group distribution and would - appear in the form: - - name:; - - Some mail services may provide a group-list distribution - facility, accepting a single mailbox reference, expanding it - to the full distribution list, and relaying the mail to the - list's members. This standard provides no additional syntax - for indicating such a service. Using the address - alternative, while listing one mailbox in it, can mean either - that the mailbox reference will be expanded to a list or that - there is a group with one member. - - 6.2.7. EXPLICIT PATH SPECIFICATION - - At times, a message originator may wish to indicate the - transmission path that a message should follow. This is - called source routing. The normal addressing scheme, used in - an addr-spec, is carefully separated from such information; - the portion of a route-addr is provided for such occa- - sions. It specifies the sequence of hosts and/or transmission - - - August 13, 1982 - 32 - RFC #822 - - - - Standard for ARPA Internet Text Messages - - - services that are to be traversed. Both domain-refs and - domain-literals may be used. - - Note: The use of source routing is discouraged. Unless the - sender has special need of path restriction, the choice - of transmission route should be left to the mail tran- - sport service. - - 6.3. RESERVED ADDRESS - - It often is necessary to send mail to a site, without know- - ing any of its valid addresses. For example, there may be mail - system dysfunctions, or a user may wish to find out a person's - correct address, at that site. - - This standard specifies a single, reserved mailbox address - (local-part) which is to be valid at each site. Mail sent to - that address is to be routed to a person responsible for the - site's mail system or to a person with responsibility for general - site operation. The name of the reserved local-part address is: - - Postmaster - - so that "Postmaster@domain" is required to be valid. - - Note: This reserved local-part must be matched without sensi- - tivity to alphabetic case, so that "POSTMASTER", "postmas- - ter", and even "poStmASteR" is to be accepted. - - - - - - - - - - - - - - - - - - - - - - - - August 13, 1982 - 33 - RFC #822 - - - - Standard for ARPA Internet Text Messages - - - 7. BIBLIOGRAPHY - - - ANSI. "USA Standard Code for Information Interchange," X3.4. - American National Standards Institute: New York (1968). Also - in: Feinler, E. and J. Postel, eds., "ARPANET Protocol Hand- - book", NIC 7104. - - ANSI. "Representations of Universal Time, Local Time Differen- - tials, and United States Time Zone References for Information - Interchange," X3.51-1975. American National Standards Insti- - tute: New York (1975). - - Bemer, R.W., "Time and the Computer." In: Interface Age (Feb. - 1979). - - Bennett, C.J. "JNT Mail Protocol". Joint Network Team, Ruther- - ford and Appleton Laboratory: Didcot, England. - - Bhushan, A.K., Pogran, K.T., Tomlinson, R.S., and White, J.E. - "Standardizing Network Mail Headers," ARPANET Request for - Comments No. 561, Network Information Center No. 18516; SRI - International: Menlo Park (September 1973). - - Birrell, A.D., Levin, R., Needham, R.M., and Schroeder, M.D. - "Grapevine: An Exercise in Distributed Computing," Communica- - tions of the ACM 25, 4 (April 1982), 260-274. - - Crocker, D.H., Vittal, J.J., Pogran, K.T., Henderson, D.A. - "Standard for the Format of ARPA Network Text Message," - ARPANET Request for Comments No. 733, Network Information - Center No. 41952. SRI International: Menlo Park (November - 1977). - - Feinler, E.J. and Postel, J.B. ARPANET Protocol Handbook, Net- - work Information Center No. 7104 (NTIS AD A003890). SRI - International: Menlo Park (April 1976). - - Harary, F. "Graph Theory". Addison-Wesley: Reading, Mass. - (1969). - - Levin, R. and Schroeder, M. "Transport of Electronic Messages - through a Network," TeleInformatics 79, pp. 29-33. North - Holland (1979). Also as Xerox Palo Alto Research Center - Technical Report CSL-79-4. - - Myer, T.H. and Henderson, D.A. "Message Transmission Protocol," - ARPANET Request for Comments, No. 680, Network Information - Center No. 32116. SRI International: Menlo Park (1975). - - - August 13, 1982 - 34 - RFC #822 - - - - Standard for ARPA Internet Text Messages - - - NBS. "Specification of Message Format for Computer Based Message - Systems, Recommended Federal Information Processing Standard." - National Bureau of Standards: Gaithersburg, Maryland - (October 1981). - - NIC. Internet Protocol Transition Workbook. Network Information - Center, SRI-International, Menlo Park, California (March - 1982). - - Oppen, D.C. and Dalal, Y.K. "The Clearinghouse: A Decentralized - Agent for Locating Named Objects in a Distributed Environ- - ment," OPD-T8103. Xerox Office Products Division: Palo Alto, - CA. (October 1981). - - Postel, J.B. "Assigned Numbers," ARPANET Request for Comments, - No. 820. SRI International: Menlo Park (August 1982). - - Postel, J.B. "Simple Mail Transfer Protocol," ARPANET Request - for Comments, No. 821. SRI International: Menlo Park (August - 1982). - - Shoch, J.F. "Internetwork naming, addressing and routing," in - Proc. 17th IEEE Computer Society International Conference, pp. - 72-79, Sept. 1978, IEEE Cat. No. 78 CH 1388-8C. - - Su, Z. and Postel, J. "The Domain Naming Convention for Internet - User Applications," ARPANET Request for Comments, No. 819. - SRI International: Menlo Park (August 1982). - - - - - - - - - - - - - - - - - - - - - - - - August 13, 1982 - 35 - RFC #822 - - - - Standard for ARPA Internet Text Messages - - - APPENDIX - - - A. EXAMPLES - - A.1. ADDRESSES - - A.1.1. Alfred Neuman - - A.1.2. Neuman@BBN-TENEXA - - These two "Alfred Neuman" examples have identical seman- - tics, as far as the operation of the local host's mail sending - (distribution) program (also sometimes called its "mailer") - and the remote host's mail protocol server are concerned. In - the first example, the "Alfred Neuman" is ignored by the - mailer, as "Neuman@BBN-TENEXA" completely specifies the reci- - pient. The second example contains no superfluous informa- - tion, and, again, "Neuman@BBN-TENEXA" is the intended reci- - pient. - - Note: When the message crosses name-domain boundaries, then - these specifications must be changed, so as to indicate - the remainder of the hierarchy, starting with the top - level. - - A.1.3. "George, Ted" - - This form might be used to indicate that a single mailbox - is shared by several users. The quoted string is ignored by - the originating host's mailer, because "Shared@Group.Arpanet" - completely specifies the destination mailbox. - - A.1.4. Wilt . (the Stilt) Chamberlain@NBA.US - - The "(the Stilt)" is a comment, which is NOT included in - the destination mailbox address handed to the originating - system's mailer. The local-part of the address is the string - "Wilt.Chamberlain", with NO space between the first and second - words. - - A.1.5. Address Lists - - Gourmets: Pompous Person , - Childs@WGBH.Boston, Galloping Gourmet@ - ANT.Down-Under (Australian National Television), - Cheapie@Discount-Liquors;, - Cruisers: Port@Portugal, Jones@SEA;, - Another@Somewhere.SomeOrg - - - August 13, 1982 - 36 - RFC #822 - - - - Standard for ARPA Internet Text Messages - - - This group list example points out the use of comments and the - mixing of addresses and groups. - - A.2. ORIGINATOR ITEMS - - A.2.1. Author-sent - - George Jones logs into his host as "Jones". He sends - mail himself. - - From: Jones@Group.Org - - or - - From: George Jones - - A.2.2. Secretary-sent - - George Jones logs in as Jones on his host. His secre- - tary, who logs in as Secy sends mail for him. Replies to the - mail should go to George. - - From: George Jones - Sender: Secy@Other-Group - - A.2.3. Secretary-sent, for user of shared directory - - George Jones' secretary sends mail for George. Replies - should go to George. - - From: George Jones - Sender: Secy@Other-Group - - Note that there need not be a space between "Jones" and the - "<", but adding a space enhances readability (as is the case - in other examples. - - A.2.4. Committee activity, with one author - - George is a member of a committee. He wishes to have any - replies to his message go to all committee members. - - From: George Jones - Sender: Jones@Host - Reply-To: The Committee: Jones@Host.Net, - Smith@Other.Org, - Doe@Somewhere-Else; - - Note that if George had not included himself in the - - - August 13, 1982 - 37 - RFC #822 - - - - Standard for ARPA Internet Text Messages - - - enumeration of The Committee, he would not have gotten an - implicit reply; the presence of the "Reply-to" field SUPER- - SEDES the sending of a reply to the person named in the "From" - field. - - A.2.5. Secretary acting as full agent of author - - George Jones asks his secretary (Secy@Host) to send a - message for him in his capacity as Group. He wants his secre- - tary to handle all replies. - - From: George Jones - Sender: Secy@Host - Reply-To: Secy@Host - - A.2.6. Agent for user without online mailbox - - A friend of George's, Sarah, is visiting. George's - secretary sends some mail to a friend of Sarah in computer- - land. Replies should go to George, whose mailbox is Jones at - Registry. - - From: Sarah Friendly - Sender: Secy-Name - Reply-To: Jones@Registry. - - A.2.7. Agent for member of a committee - - George's secretary sends out a message which was authored - jointly by all the members of a committee. Note that the name - of the committee cannot be specified, since names are - not permitted in the From field. - - From: Jones@Host, - Smith@Other-Host, - Doe@Somewhere-Else - Sender: Secy@SHost - - - - - - - - - - - - - - - August 13, 1982 - 38 - RFC #822 - - - - Standard for ARPA Internet Text Messages - - - A.3. COMPLETE HEADERS - - A.3.1. Minimum required - - Date: 26 Aug 76 1429 EDT Date: 26 Aug 76 1429 EDT - From: Jones@Registry.Org or From: Jones@Registry.Org - Bcc: To: Smith@Registry.Org - - Note that the "Bcc" field may be empty, while the "To" field - is required to have at least one address. - - A.3.2. Using some of the additional fields - - Date: 26 Aug 76 1430 EDT - From: George Jones - Sender: Secy@SHOST - To: "Al Neuman"@Mad-Host, - Sam.Irving@Other-Host - Message-ID: - - A.3.3. About as complex as you're going to get - - Date : 27 Aug 76 0932 PDT - From : Ken Davis - Subject : Re: The Syntax in the RFC - Sender : KSecy@Other-Host - Reply-To : Sam.Irving@Reg.Organization - To : George Jones , - Al.Neuman@MAD.Publisher - cc : Important folk: - Tom Softwood , - "Sam Irving"@Other-Host;, - Standard Distribution: - /main/davis/people/standard@Other-Host, - "standard.dist.3"@Tops-20-Host>; - Comment : Sam is away on business. He asked me to handle - his mail for him. He'll be able to provide a - more accurate explanation when he returns - next week. - In-Reply-To: , George's message - X-Special-action: This is a sample of user-defined field- - names. There could also be a field-name - "Special-action", but its name might later be - preempted - Message-ID: <4231.629.XYzi-What@Other-Host> - - - - - - - August 13, 1982 - 39 - RFC #822 - - - - Standard for ARPA Internet Text Messages - - - B. SIMPLE FIELD PARSING - - Some mail-reading software systems may wish to perform only - minimal processing, ignoring the internal syntax of structured - field-bodies and treating them the same as unstructured-field- - bodies. Such software will need only to distinguish: - - o Header fields from the message body, - - o Beginnings of fields from lines which continue fields, - - o Field-names from field-contents. - - The abbreviated set of syntactic rules which follows will - suffice for this purpose. It describes a limited view of mes- - sages and is a subset of the syntactic rules provided in the main - part of this specification. One small exception is that the con- - tents of field-bodies consist only of text: - - B.1. SYNTAX - - - message = *field *(CRLF *text) - - field = field-name ":" [field-body] CRLF - - field-name = 1* - - field-body = *text [CRLF LWSP-char field-body] - - - B.2. SEMANTICS - - Headers occur before the message body and are terminated by - a null line (i.e., two contiguous CRLFs). - - A line which continues a header field begins with a SPACE or - HTAB character, while a line beginning a field starts with a - printable character which is not a colon. - - A field-name consists of one or more printable characters - (excluding colon, space, and control-characters). A field-name - MUST be contained on one line. Upper and lower case are not dis- - tinguished when comparing field-names. - - - - - - - - August 13, 1982 - 40 - RFC #822 - - - - Standard for ARPA Internet Text Messages - - - C. DIFFERENCES FROM RFC #733 - - The following summarizes the differences between this stan- - dard and the one specified in Arpanet Request for Comments #733, - "Standard for the Format of ARPA Network Text Messages". The - differences are listed in the order of their occurrence in the - current specification. - - C.1. FIELD DEFINITIONS - - C.1.1. FIELD NAMES - - These now must be a sequence of printable characters. They - may not contain any LWSP-chars. - - C.2. LEXICAL TOKENS - - C.2.1. SPECIALS - - The characters period ("."), left-square bracket ("["), and - right-square bracket ("]") have been added. For presentation - purposes, and when passing a specification to a system that - does not conform to this standard, periods are to be contigu- - ous with their surrounding lexical tokens. No linear-white- - space is permitted between them. The presence of one LWSP- - char between other tokens is still directed. - - C.2.2. ATOM - - Atoms may not contain SPACE. - - C.2.3. SPECIAL TEXT - - ctext and qtext have had backslash ("\") added to the list of - prohibited characters. - - C.2.4. DOMAINS - - The lexical tokens and have been - added. - - C.3. MESSAGE SPECIFICATION - - C.3.1. TRACE - - The "Return-path:" and "Received:" fields have been specified. - - - - - - August 13, 1982 - 41 - RFC #822 - - - - Standard for ARPA Internet Text Messages - - - C.3.2. FROM - - The "From" field must contain machine-usable addresses (addr- - spec). Multiple addresses may be specified, but named-lists - (groups) may not. - - C.3.3. RESENT - - The meta-construct of prefacing field names with the string - "Resent-" has been added, to indicate that a message has been - forwarded by an intermediate recipient. - - C.3.4. DESTINATION - - A message must contain at least one destination address field. - "To" and "CC" are required to contain at least one address. - - C.3.5. IN-REPLY-TO - - The field-body is no longer a comma-separated list, although a - sequence is still permitted. - - C.3.6. REFERENCE - - The field-body is no longer a comma-separated list, although a - sequence is still permitted. - - C.3.7. ENCRYPTED - - A field has been specified that permits senders to indicate - that the body of a message has been encrypted. - - C.3.8. EXTENSION-FIELD - - Extension fields are prohibited from beginning with the char- - acters "X-". - - C.4. DATE AND TIME SPECIFICATION - - C.4.1. SIMPLIFICATION - - Fewer optional forms are permitted and the list of three- - letter time zones has been shortened. - - C.5. ADDRESS SPECIFICATION - - - - - - - August 13, 1982 - 42 - RFC #822 - - - - Standard for ARPA Internet Text Messages - - - C.5.1. ADDRESS - - The use of quoted-string, and the ":"-atom-":" construct, have - been removed. An address now is either a single mailbox - reference or is a named list of addresses. The latter indi- - cates a group distribution. - - C.5.2. GROUPS - - Group lists are now required to to have a name. Group lists - may not be nested. - - C.5.3. MAILBOX - - A mailbox specification may indicate a person's name, as - before. Such a named list no longer may specify multiple - mailboxes and may not be nested. - - C.5.4. ROUTE ADDRESSING - - Addresses now are taken to be absolute, global specifications, - independent of transmission paths. The construct has - been provided, to permit explicit specification of transmis- - sion path. RFC #733's use of multiple at-signs ("@") was - intended as a general syntax for indicating routing and/or - hierarchical addressing. The current standard separates these - specifications and only one at-sign is permitted. - - C.5.5. AT-SIGN - - The string " at " no longer is used as an address delimiter. - Only at-sign ("@") serves the function. - - C.5.6. DOMAINS - - Hierarchical, logical name-domains have been added. - - C.6. RESERVED ADDRESS - - The local-part "Postmaster" has been reserved, so that users can - be guaranteed at least one valid address at a site. - - - - - - - - - - - August 13, 1982 - 43 - RFC #822 - - - - Standard for ARPA Internet Text Messages - - - D. ALPHABETICAL LISTING OF SYNTAX RULES - - address = mailbox ; one addressee - / group ; named list - addr-spec = local-part "@" domain ; global address - ALPHA = - ; (101-132, 65.- 90.) - ; (141-172, 97.-122.) - atom = 1* - authentic = "From" ":" mailbox ; Single author - / ( "Sender" ":" mailbox ; Actual submittor - "From" ":" 1#mailbox) ; Multiple authors - ; or not sender - CHAR = ; ( 0-177, 0.-127.) - comment = "(" *(ctext / quoted-pair / comment) ")" - CR = ; ( 15, 13.) - CRLF = CR LF - ctext = may be folded - ")", "\" & CR, & including - linear-white-space> - CTL = ; ( 177, 127.) - date = 1*2DIGIT month 2DIGIT ; day month year - ; e.g. 20 Jun 82 - dates = orig-date ; Original - [ resent-date ] ; Forwarded - date-time = [ day "," ] date time ; dd mm yy - ; hh:mm:ss zzz - day = "Mon" / "Tue" / "Wed" / "Thu" - / "Fri" / "Sat" / "Sun" - delimiters = specials / linear-white-space / comment - destination = "To" ":" 1#address ; Primary - / "Resent-To" ":" 1#address - / "cc" ":" 1#address ; Secondary - / "Resent-cc" ":" 1#address - / "bcc" ":" #address ; Blind carbon - / "Resent-bcc" ":" #address - DIGIT = ; ( 60- 71, 48.- 57.) - domain = sub-domain *("." sub-domain) - domain-literal = "[" *(dtext / quoted-pair) "]" - domain-ref = atom ; symbolic reference - dtext = may be folded - "]", "\" & CR, & including - linear-white-space> - extension-field = - - - - August 13, 1982 - 44 - RFC #822 - - - - Standard for ARPA Internet Text Messages - - - field = field-name ":" [ field-body ] CRLF - fields = dates ; Creation time, - source ; author id & one - 1*destination ; address required - *optional-field ; others optional - field-body = field-body-contents - [CRLF LWSP-char field-body] - field-body-contents = - - field-name = 1* - group = phrase ":" [#mailbox] ";" - hour = 2DIGIT ":" 2DIGIT [":" 2DIGIT] - ; 00:00:00 - 23:59:59 - HTAB = ; ( 11, 9.) - LF = ; ( 12, 10.) - linear-white-space = 1*([CRLF] LWSP-char) ; semantics = SPACE - ; CRLF => folding - local-part = word *("." word) ; uninterpreted - ; case-preserved - LWSP-char = SPACE / HTAB ; semantics = SPACE - mailbox = addr-spec ; simple address - / phrase route-addr ; name & addr-spec - message = fields *( CRLF *text ) ; Everything after - ; first null line - ; is message body - month = "Jan" / "Feb" / "Mar" / "Apr" - / "May" / "Jun" / "Jul" / "Aug" - / "Sep" / "Oct" / "Nov" / "Dec" - msg-id = "<" addr-spec ">" ; Unique message id - optional-field = - / "Message-ID" ":" msg-id - / "Resent-Message-ID" ":" msg-id - / "In-Reply-To" ":" *(phrase / msg-id) - / "References" ":" *(phrase / msg-id) - / "Keywords" ":" #phrase - / "Subject" ":" *text - / "Comments" ":" *text - / "Encrypted" ":" 1#2word - / extension-field ; To be defined - / user-defined-field ; May be pre-empted - orig-date = "Date" ":" date-time - originator = authentic ; authenticated addr - [ "Reply-To" ":" 1#address] ) - phrase = 1*word ; Sequence of words - - - - - August 13, 1982 - 45 - RFC #822 - - - - Standard for ARPA Internet Text Messages - - - qtext = , ; => may be folded - "\" & CR, and including - linear-white-space> - quoted-pair = "\" CHAR ; may quote any char - quoted-string = <"> *(qtext/quoted-pair) <">; Regular qtext or - ; quoted chars. - received = "Received" ":" ; one per relay - ["from" domain] ; sending host - ["by" domain] ; receiving host - ["via" atom] ; physical path - *("with" atom) ; link/mail protocol - ["id" msg-id] ; receiver msg id - ["for" addr-spec] ; initial form - ";" date-time ; time received - - resent = resent-authentic - [ "Resent-Reply-To" ":" 1#address] ) - resent-authentic = - = "Resent-From" ":" mailbox - / ( "Resent-Sender" ":" mailbox - "Resent-From" ":" 1#mailbox ) - resent-date = "Resent-Date" ":" date-time - return = "Return-path" ":" route-addr ; return address - route = 1#("@" domain) ":" ; path-relative - route-addr = "<" [route] addr-spec ">" - source = [ trace ] ; net traversals - originator ; original mail - [ resent ] ; forwarded - SPACE = ; ( 40, 32.) - specials = "(" / ")" / "<" / ">" / "@" ; Must be in quoted- - / "," / ";" / ":" / "\" / <"> ; string, to use - / "." / "[" / "]" ; within a word. - sub-domain = domain-ref / domain-literal - text = atoms, specials, - CR & bare LF, but NOT ; comments and - including CRLF> ; quoted-strings are - ; NOT recognized. - time = hour zone ; ANSI and Military - trace = return ; path to sender - 1*received ; receipt tags - user-defined-field = - - word = atom / quoted-string - - - - - August 13, 1982 - 46 - RFC #822 - - - - Standard for ARPA Internet Text Messages - - - zone = "UT" / "GMT" ; Universal Time - ; North American : UT - / "EST" / "EDT" ; Eastern: - 5/ - 4 - / "CST" / "CDT" ; Central: - 6/ - 5 - / "MST" / "MDT" ; Mountain: - 7/ - 6 - / "PST" / "PDT" ; Pacific: - 8/ - 7 - / 1ALPHA ; Military: Z = UT; - <"> = ; ( 42, 34.) - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - August 13, 1982 - 47 - RFC #822 -