194 lines
6.4 KiB
Scheme
194 lines
6.4 KiB
Scheme
;;; -*- Scheme -*-
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;;; This file is part of the Scheme Untergrund Networking package.
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;;; Copyright (c) 1995 by Olin Shivers.
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;;; For copyright information, see the file COPYING which comes with
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;;; the distribution.
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;;; URI syntax -- [scheme] : path [? search ] [# fragmentid]
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;;; References:
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;;; - http://www.w3.org/Addressing/rfc1630.txt
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;;; Original RFC
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;;; - http://www.w3.org/hypertext/WWW/Addressing/URL/URI_Overview.html
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;;; General Web page of URI pointers.
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(define uri-reserved (string->char-set ";/#?: ="))
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(define (parse-uri s)
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(let* ((slen (string-length s))
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;; Search forwards for colon (or intervening reserved char).
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(rs1 (string-index s uri-reserved)) ; 1st reserved char
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(colon (and rs1 (char=? (string-ref s rs1) #\:) rs1))
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(path-start (if colon (+ colon 1) 0))
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;; Search backwards for # (or intervening reserved char).
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(rs-last (string-index-right s uri-reserved))
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(sharp (and rs-last (char=? (string-ref s rs-last) #\#) rs-last))
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;; Search backwards for ? (or intervening reserved char).
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;; (NB: #\= may be after #\? and before #\#)
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(rs-penult (string-index-right
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s
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(char-set-delete uri-reserved #\=)
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(or sharp slen)))
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(ques (and rs-penult (char=? (string-ref s rs-penult) #\?) rs-penult))
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(path-end (or ques sharp slen)))
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(values (and colon (substring s 0 colon))
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(split-uri s path-start path-end)
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(and ques (substring s (+ ques 1) (or sharp slen)))
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(and sharp (substring s (+ sharp 1) slen)))))
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;;; Caution:
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;;; Don't use this proc until *after* you've parsed the URL -- unescaping
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;;; might introduce reserved chars (like slashes and colons) that could
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;;; blow your parse.
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(define (unescape-uri s . maybe-start/end)
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(let-optionals maybe-start/end ((start 0)
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(end (string-length s)))
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(let* ((esc-seq? (lambda (i) (and (< (+ i 2) end)
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(char=? (string-ref s i) #\%)
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(hex-digit? (string-ref s (+ i 1)))
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(hex-digit? (string-ref s (+ i 2))))))
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(hits (let lp ((i start) (hits 0)) ; count # of esc seqs.
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(if (< i end)
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(if (esc-seq? i)
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(lp (+ i 3) (+ hits 1))
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(lp (+ i 1) hits))
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hits))))
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(if (and (zero? hits) (zero? start) (= end (string-length s))) s
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(let* ((nlen (- (- end start) (* hits 2))) ; the new
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; length of the
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; unescaped
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; string
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(ns (make-string nlen))) ; stores the result
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(let lp ((i start) (j 0)) ; sweap over the string
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(if (< j nlen)
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(lp (cond
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((esc-seq? i) ; unescape
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; escape-sequence
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(string-set! ns j
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(let ((d1 (string-ref s (+ i 1)))
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(d2 (string-ref s (+ i 2))))
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(ascii->char (+ (* 16 (hexchar->int d1))
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(hexchar->int d2)))))
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(+ i 3))
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(else (string-set! ns j (string-ref s i))
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(+ i 1)))
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(+ j 1))))
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ns)))))
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(define hex-digit?
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(let ((hex-digits (string->char-set "0123456789abcdefABCDEF")))
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(lambda (c) (char-set-contains? hex-digits c))))
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; make use of the fact that numbers and characters are in order in the ascii table
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(define (hexchar->int c)
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(- (char->ascii c)
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(if (char-numeric? c)
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(char->ascii #\0)
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(- (if (char-upper-case? c)
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(char->ascii #\A)
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(char->ascii #\a))
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10))))
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(define int->hexchar
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(let ((table '#(#\0 #\1 #\2 #\3 #\4 #\5 #\6 #\7 #\8 #\9
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#\A #\B #\C #\D #\E #\F)))
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(lambda (i) (vector-ref table i))))
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;;; Caution:
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;;; All reserved chars (e.g., slash, sharp, colon) get escaped: "=;/#?: "
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;;; So don't apply this proc to chunks of text with syntactically meaningful
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;;; reserved chars (e.g., paths with URI slashes or colons) -- they'll be
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;;; escaped, and lose their special meaning. E.g. it would be a mistake
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;;; to apply ESCAPE-URI to "//lcs.mit.edu:8001/foo/bar.html" because the
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;;; slashes and colons would be escaped.
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(define uri-escaped-chars
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(char-set-complement (char-set-union char-set:letter+digit
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(string->char-set "$-_@.&!*\"'(),+"))))
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;;; Takes a set of chars to escape. This is because we sometimes need to
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;;; escape larger sets of chars for different parts of a URI.
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(define (escape-uri s . maybe-escaped-chars)
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(let-optionals maybe-escaped-chars ((escaped-chars uri-escaped-chars))
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(let ((nlen (string-fold
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(lambda (c i)
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(+ i
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(if (char-set-contains? escaped-chars c)
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3 1)))
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0
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s))) ; new length of escaped string
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(if (= nlen (string-length s)) s
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(let ((ns (make-string nlen)))
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(string-fold
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(lambda (c i) ; replace each occurance of an
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; character to escape with %ff where ff
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; is the ascii-code in hexadecimal
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; notation
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(+ i (cond
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((char-set-contains? escaped-chars c)
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(string-set! ns i #\%)
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(let* ((d (char->ascii c))
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(dhi (bitwise-and (arithmetic-shift d -4) #xF))
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(dlo (bitwise-and d #xF)))
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(string-set! ns (+ i 1)
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(int->hexchar dhi))
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(string-set! ns (+ i 2)
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(int->hexchar dlo)))
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3)
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(else (string-set! ns i c)
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1))))
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0
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s)
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ns)))))
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;;; Cribbed from scsh's fname.scm
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(define (split-uri uri start end) ; Split at /'s (infix grammar).
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(let split ((i start)) ; "" -> ("")
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(cond
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((>= i end) '(""))
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((string-index uri #\/ i) =>
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(lambda (slash)
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(cons (substring uri i slash)
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(split (+ slash 1)))))
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(else (list (substring uri i end))))))
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;;; The elements of PLIST must be escaped in case they contain slashes.
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;;; This procedure doesn't escape them for you; you must do that yourself:
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;;; (uri-path->uri (map escape-uri pathlist))
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(define (uri-path->uri plist)
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(string-join plist "/")) ; Insert slashes between elts of PLIST.
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(define (simplify-uri-path p)
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(if (null? p) #f ; P must be non-null
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(let lp ((path-list (cdr p))
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(stack (list (car p))))
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(if (null? path-list) ; we're done
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(reverse stack)
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(cond
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((string=? (car path-list) "..") ; back up
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; neither the empty path nor root
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(if (not (or (null? stack) (string=? (car stack) "")))
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(lp (cdr path-list) (cdr stack))
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#f))
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((string=? (car path-list) ".") ; leave this
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(lp (cdr path-list) stack))
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((string=? (car path-list) "") ; back to root
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(lp (cdr path-list) '("")))
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(else ; usual segment
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(lp (cdr path-list) (cons (car path-list) stack))))))))
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