223 lines
8.8 KiB
TeX
223 lines
8.8 KiB
TeX
\section{Handle URIs}\label{sec:uri}
|
|
%
|
|
\begin{description}
|
|
\item[Used files:] uri.scm
|
|
\item[Name of the package:] uri
|
|
\end{description}
|
|
%
|
|
|
|
\subsection{Overview}
|
|
A URI (Uniform Resource Identifier) is of following syntax:
|
|
\begin{inset}
|
|
\ovar{scheme\/} : \semvar{path} \ovar{{\normalfont?\/} search} \ovar{{\normalfont\#} fragmentid}
|
|
\end{inset}
|
|
Parts in brackets may be ommitted. The last part is usually referred
|
|
to as fragid in this document.
|
|
|
|
As you see, the URI contains characters like \verb|:| to indicate its
|
|
different parts. But what, if the \semvar{scheme} contains \verb|:| as
|
|
part of its name? For this purpose, some special characters are
|
|
\emph{escaped} if they are a regular part of a name and not indicators
|
|
for the structure of a URI. Escape-sequences are of following scheme:
|
|
\verb|\%hh| where \verb|h| is a hexadecimal digit. The hexadecimal
|
|
number refers to the (US) ASCII code of the escaped character, e.g.\
|
|
\ex{\%20} is space (ASCII character 32) and \ex{\%61} is `a' (ASCII
|
|
character 97). This module provides procedures to escape and unescape
|
|
strings that are meant to be used in a URI.
|
|
|
|
\subsection{Procedures}
|
|
|
|
\begin{defundesc}{parse-uri} {uri-string } {scheme path search
|
|
frag-id} \label{proc:parse-uri}
|
|
|
|
Parses an \semvar{uri\=string} in the possible four fields, as
|
|
mentioned above in \emph{Overview}. These four fields are returned
|
|
as a multiple value. They are \emph{not} unescaped, as the rules for
|
|
parsing the \semvar{path} component in particular need unescaped
|
|
text, and are dependent on \semvar{scheme}. The URL parser is
|
|
responsible for doing this. If the \semvar{scheme}, \semvar{search}\
|
|
or \semvar{fragid} portions are not specified, they are \sharpf.
|
|
Otherwise, \semvar{scheme}, \semvar{search}, and \semvar{fragid} are
|
|
strings. \semvar{path} is a non-empty string list -- the path split
|
|
at slashes.
|
|
|
|
For those of you who are interested, here is a description of the
|
|
parsing technique. It is inwards from both ends.
|
|
\begin{itemize}
|
|
\item First we search forwards for the first reserved character
|
|
(\verb|=|, \verb|;|, \verb|/|, \verb|#|, \verb|?|, \verb|:| or
|
|
\verb|space|). If it's a colon, then that's the \semvar{scheme}
|
|
part, otherwise we have no \semvar{scheme} part. At all events we
|
|
remove it.
|
|
\item Then we search backwards from the end for the last reserved
|
|
char. If it's a sharp, then that's the \semvar{fragid} part --
|
|
remove it.
|
|
\item Then we search backwards from the end for the last reserved
|
|
char. If it's a question-mark, then that's the \semvar{search}
|
|
part -- remove it.
|
|
\item What's left is the path. We split at slashes. The empty string
|
|
becomes a list containing the empty string.
|
|
\end{itemize}
|
|
|
|
This scheme is tolerant of the various ways people build broken
|
|
URI's out there on the Net\footnote{So it is not absolutely conform
|
|
with RFC~1630}, e.g. \verb|=| is a reserved character, but used
|
|
unescaped in the search-part. It was given to me\footnote{That's
|
|
Olin Shivers.} by Dan Connolly of the W3C and slightly modified.
|
|
\end{defundesc}
|
|
|
|
\begin{defundesc}{unescape-uri} {string \ovar{start \ovar{end}}} {string}
|
|
Unescapes a string. This procedure should only be used \emph{after}
|
|
the URL (!) was parsed, since unescaping may introduce characters
|
|
that blow up the parse (that's why escape sequences are used in URIs
|
|
;-). Escape sequences are of the scheme as described in ``Overview''.
|
|
\end{defundesc}
|
|
|
|
|
|
%\texttt{uri-escaped-chars} \hfill
|
|
%\texttt{char-set}\index{\texttt{uri-escaped-chars}}
|
|
\defvar{uri-escaped-chars}{char-set}
|
|
\begin{desc}
|
|
A set of characters that are escaped in URIs. These are the
|
|
following characters: dollar (\verb|$|), minus (\verb|-|),%fool Xemacs$
|
|
underscore (\verb|_|), at (\verb|@|), dot (\verb|.|), and-sign
|
|
(\verb|&|), exclamation mark (\verb|!|), asterisk (\verb|*|),
|
|
backslash (\verb|\|), double quote (\verb|"|), single quote
|
|
(\verb|'|), open brace (\verb|(|), close brace (\verb|)|), comma
|
|
(\verb|,|) plus (\verb|+|) and all other characters that are neither
|
|
letters nor digits (such as space and control characters).
|
|
\end{desc}
|
|
|
|
\begin{defundesc}{escape-uri} {string \ovar{escaped-chars}} {string}
|
|
Escapes characters of \semvar{string} that are given with
|
|
\semvar{escaped\=chars}. \semvar{escaped\=chars} default to
|
|
\ex{uri\=escaped\=chars}. Be careful with using this procedure to
|
|
chunks of text with syntactically meaningful reserved characters
|
|
(e.g., paths with URI slashes or colons) -- they'll be escaped, and
|
|
lose their special meaning. E.g.\ it would be a mistake to apply
|
|
\ex{escape-uri} to
|
|
``\ex{//lcs.\ob{}mit.\ob{}edu:8001\ob/foo\ob/bar.html}'' because the
|
|
sla\-shes and co\-lons would be escaped. Note that \ex{esacpe-uri}
|
|
doesn't check this as it would lose his meaning.
|
|
\end{defundesc}
|
|
|
|
\begin{defundesc}{resolve-uri} {cscheme cp scheme p} {scheme path}
|
|
\FIXME{Sorry, I can't figure out what resolve-uri is inteded to do.
|
|
Perhaps I find it out later.}
|
|
|
|
Nobody really knows what this procedure was intended to do.
|
|
|
|
The code seems to have a bug: In the body of receive, there's a
|
|
loop. j should, according to the comment, count sequential \verb|/|.
|
|
But \ex{j} counts nothing in the body. Either zero is added \ex{((lp
|
|
(cdr cp-tail) (cons (car cp-tail) rhead) (+ j 0)))} or \ex{j} is
|
|
set to 1 \ex{((lp (cdr cp-tail) (cons (car cp-tail) rhead) 1))}.
|
|
Nevertheless, \ex{j} is expected to reach value \ex{numsl} that can
|
|
be larger than one. So what? I am confused.
|
|
\end{defundesc}
|
|
|
|
\begin{defundesc}{split-uri-path} {uri start end} {list}
|
|
Splits uri at slashes. Only the substring given with \semvar{start}
|
|
(inclusive) and \semvar{end} (exclusive) as indices is considered.
|
|
\semvar{start} and $\semvar{end} - 1$ have to be within the range of
|
|
\semvar{uri}. Otherwise an index-out-of-range exception will be
|
|
raised. Example: \codex{(split-uri-path "foo/bar/colon" 4 11)}
|
|
results to \codex{'("bar" "col")}
|
|
\end{defundesc}
|
|
|
|
\begin{defundesc}{uri-path-list->path} {plist} {string}
|
|
Generates a path out of an uri-path-list by inserting slashes
|
|
between the elements of \semvar{plist}. If you want to use the
|
|
resulting string for further operation, you should escape the
|
|
elements of \semvar{plist} in case the contain slashes. This doesn't
|
|
escape them for you, you must do that yourself like
|
|
\ex{(uri-path-list->path (map escape-uri pathlist))}.
|
|
\end{defundesc}
|
|
|
|
\begin{defundesc}{simplify-uri-path} {path} {list}
|
|
Removes `\ex{.}' and `\ex{..}' entries from path. The result is
|
|
a (maybe empty) list representing a path that does not contain any
|
|
`\ex{.}' or `\ex{..}'\,. The list can only be empty if the path
|
|
did not start with a slash (for the rare occasion someone wants to
|
|
simplify a relative path). The result is \sharpf{} if the path tries
|
|
to back up past root, for example by `\ex{/..}' or
|
|
`\ex{/foo\ob/..\ob/..}' or just `\ex{..}'\,. `\ex{//}' may occur
|
|
somewhere in the path referring to root but not being backed up.
|
|
Examples:
|
|
%FIXME: Can't we have a better environment for examples like these?
|
|
\begin{code}
|
|
(simplify-uri-path
|
|
(split-uri-path "/foo/bar/baz/.." 0 15))\end{code}
|
|
results to
|
|
\codex{'("" "foo" "bar")}
|
|
|
|
\begin{code}
|
|
(simplify-uri-path
|
|
(split-uri-path "foo/bar/baz/../../.." 0 20))\end{code}
|
|
results to
|
|
\codex{'()}
|
|
|
|
\begin{code}
|
|
(simplify-uri-path
|
|
(split-uri-path "/foo/../.." 0 10))\end{code}
|
|
results to
|
|
\codex{\sharpf ; tried to back up root}
|
|
|
|
\begin{code}
|
|
(simplify-uri-path
|
|
(split-uri-path "foo/bar//" 0 9))\end{code}
|
|
results to
|
|
\codex{'("") ; "//" refers to root}
|
|
|
|
\begin{code}
|
|
(simplify-uri-path
|
|
(split-uri-path "foo/bar/" 0 8))\end{code}
|
|
results to
|
|
\codex{'("") ; last "/" also refers to root}
|
|
|
|
\begin{code}
|
|
(simplify-uri-path
|
|
(split-uri-path "/foo/bar//baz/../.." 0 19))\end{code}
|
|
results to
|
|
\codex{\sharpf ; tries to back up root}
|
|
\end{defundesc}
|
|
|
|
\subsection*{Unexported names}
|
|
|
|
\defvar{uri-reserved}{char-set}
|
|
\begin{desc}
|
|
A list of reserved characters (semicolon, slash, hash, question
|
|
mark, double colon and space).
|
|
\end{desc}
|
|
|
|
\begin{defundesc}{hex-digit?} {character} {boolean}
|
|
Returns \sharpt{} if character is a hexadecimal digit (i.e., one of 1--9,
|
|
a--f, A--F), \sharpf{} otherwise.
|
|
\end{defundesc}
|
|
|
|
|
|
\begin{defundesc}{hexchar->int} {character} {number}
|
|
Translates the given character to an integer, e.g. \ex{(hexchar->int
|
|
\#a)} results to 10.
|
|
\end{defundesc}
|
|
|
|
\begin{defundesc}{int->hexchar} {integer} {character}
|
|
Translates the given integer from range 1--15 into an hexadecimal
|
|
character (uses uppercase letters), e.g. \ex{(int->hexchar 14)}
|
|
results to `E'.
|
|
\end{defundesc}
|
|
|
|
\begin{defundesc}{rev-append} {list-a list-b} {list}
|
|
Performs a \ex{(append (reverse list-a) list-b)}. The comment says it
|
|
should be defined in a list package but I am wondering how often
|
|
this will be used.
|
|
\end{defundesc}
|
|
|
|
%EOF
|
|
|
|
|
|
%%% Local Variables:
|
|
%%% mode: latex
|
|
%%% TeX-master: t
|
|
%%% End:
|