114 lines
4.9 KiB
Scheme
114 lines
4.9 KiB
Scheme
;;; RFC 822 field-parsing code
|
|
|
|
;;; This file is part of the Scheme Untergrund Networking package.
|
|
|
|
;;; Copyright (c) 1995 by Olin Shivers <shivers@lcs.mit.edu>
|
|
;;; Copyright (c) 2003 by Mike Sperber <sperber@informatik.uni-tuebingen.de>
|
|
;;; For copyright information, see the file COPYING which comes with
|
|
;;; the distribution.
|
|
|
|
;;; RFC 822 is the "Standard for the format of ARPA Internet text messages"
|
|
;;; -- the document that essentially tells how the fields in email headers
|
|
;;; (e.g., the Subject: and To: fields) are formatted. This code is for
|
|
;;; parsing these headers.
|
|
|
|
;;; Here is a pointer to the document:
|
|
;;; http://www.ietf.org/rfc/rfc0822.txt
|
|
|
|
;;; RFC 822 parsing is useful in other contexts as well -- the HTTP protocol
|
|
;;; uses it, and it tends to pop up here and there.
|
|
;;;
|
|
;;; RFC 822 header syntax has two levels: the general syntax for headers,
|
|
;;; and the syntax for specific headers. For example, once you have figured
|
|
;;; out which chunk of text is the To: line, there are more rules telling
|
|
;;; how to split the To: line up into a list of addresses. Another example:
|
|
;;; lines with dates, e.g., the Date: header, have a specific syntax for
|
|
;;; the time and date.
|
|
;;;
|
|
;;; This code currently *only* provides routines for parsing the gross
|
|
;;; structure -- splitting the message header into its distinct fields.
|
|
;;; It would be nice to provide the finer-detail parsers, too. You do it.
|
|
;;; -Olin
|
|
|
|
;;; A note on line-terminators:
|
|
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
|
|
;;; Line-terminating sequences are always a drag, because there's no agreement
|
|
;;; on them -- the Net protocols and DOS use cr/lf; Unix uses lf; the Mac
|
|
;;; uses cr. One one hand, you'd like to use the code for all of the above,
|
|
;;; on the other, you'd also like to use the code for strict applications
|
|
;;; that need definitely not to recognise bare cr's or lf's as terminators.
|
|
;;;
|
|
;;; RFC 822 requires a cr/lf (carriage-return/line-feed) pair to terminate
|
|
;;; lines of text. On the other hand, careful perusal of the text shows up
|
|
;;; some ambiguities (there are maybe three or four of these, and I'm too
|
|
;;; lazy to write them all down). Furthermore, it is an unfortunate fact
|
|
;;; that many Unix apps separate lines of RFC 822 text with simple linefeeds
|
|
;;; (e.g., messages kept in /usr/spool/mail). As a result, this code takes a
|
|
;;; broad-minded view of line-terminators: lines can be terminated by either
|
|
;;; cr/lf or just lf, and either terminating sequence is trimmed.
|
|
;;;
|
|
;;; If you need stricter parsing, you can pass a read-line procedure
|
|
;;; as an extra parameter. This means that you can pass in a procedure
|
|
;;; that recognizes only cr/lf's, or only cr's (for a Mac app,
|
|
;;; perhaps), and you can determine whether or not the terminators get
|
|
;;; trimmed. However, your read-line procedure must indicate the
|
|
;;; header-terminating empty line by returning *either* the empty
|
|
;;; string or the two-char string cr/lf (or the EOF object).
|
|
|
|
(define htab (ascii->char 9))
|
|
|
|
;;; Convert to a symbol using the Scheme implementation's preferred case,
|
|
;;; so we can compare these things against quoted constants.
|
|
(define string->symbol-pref
|
|
(if (char=? #\a (string-ref (symbol->string 'a) 0)) ; Is it #\a or #\A?
|
|
(lambda (s) (string->symbol (string-map char-downcase s)))
|
|
(lambda (s) (string->symbol (string-map char-upcase s)))))
|
|
|
|
(define (read-rfc822-field . args)
|
|
(receive (field body)
|
|
(apply read-rfc822-field-with-line-breaks args)
|
|
(values field
|
|
(string-concatenate body))))
|
|
|
|
(define (read-rfc822-field-with-line-breaks . args)
|
|
(let-optionals args ((port (current-input-port))
|
|
(read-line read-crlf-line))
|
|
(let ((line1 (read-line port)))
|
|
(if (or (eof-object? line1)
|
|
(zero? (string-length line1))
|
|
(string=? line1 "\r\n")) ; In case read-line doesn't trim.
|
|
(values #f #f)
|
|
(cond
|
|
((string-index line1 #\:) =>
|
|
(lambda (colon)
|
|
(let ((name (string->symbol-pref (substring line1 0 colon))))
|
|
;; Read in continuation lines.
|
|
(let lp ((lines (list (substring line1
|
|
(+ colon 1)
|
|
(string-length line1)))))
|
|
(let ((c (peek-char port)))
|
|
;; RFC822: continuous lines has to start with a space or a htab
|
|
(if (or (eqv? c #\space) (eqv? c htab))
|
|
(lp (cons (read-line port) lines))
|
|
(values name (reverse lines))))))))
|
|
(else (error "Illegal RFC 822 field syntax." line1))))))) ; No :
|
|
|
|
(define (make-read-rfc822-headers read-field)
|
|
(lambda args
|
|
(let-optionals args ((port (current-input-port))
|
|
(read-line read-crlf-line))
|
|
(let lp ((alist '()))
|
|
(receive (field val)
|
|
(read-rfc822-field port read-line)
|
|
(if field
|
|
(lp (cons (cons field val) alist))
|
|
(reverse alist)))))))
|
|
|
|
(define read-rfc822-headers
|
|
(make-read-rfc822-headers read-rfc822-field))
|
|
(define read-rfc822-headers-with-line-breaks
|
|
(make-read-rfc822-headers read-rfc822-field-with-line-breaks))
|
|
|
|
(define (rfc822-time->string time)
|
|
(format-date " ~a, ~d ~b ~Y ~H:~M:~S GMT" (date time 0)))
|