sunet/url.scm

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;;; URL parsing and unparsing -*- Scheme -*-
;;; Copyright (c) 1995 by Olin Shivers.
;;; I'm only implementing http URL's right now.
;;; References:
;;; - ftp://ftp.internic.net/rfc/rfc1738.txt
;;; Original RFC
;;; - http://www.w3.org/hypertext/WWW/Addressing/URL/Overview.html
;;; General Web page of URI pointers.
;;; Unresolved issues:
;;; - The userhost parser shouldn't substitute default values --
;;; that should happen in a separate step.
;;; Imports and non-R4RS'isms
;;; define-record Record structures
;;; receive values MV return
;;; URI support
;;; index
;;; The steps in hacking a URL are:
;;; - Take the UID, parse it, and resolve it with the context UID, if any.
;;; - Consult the UID's <scheme>. Pick the appropriate URL parser and parse.
;;; Userhost strings: //<user>:<password>@<host>:<port>/
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; A USERHOST record describes path-prefixes of the form
;;; //<user>:<password>@<host>:<port>/
;;; These are frequently used as the initial prefix of URL's describing
;;; Internet resources.
(define-record userhost ; Each slot is a decoded string or #f.
user
password
host
port)
;;; Parse a URI path (a list representing a path, not a string!) into
;;; a userhost record. Default values are taken from the userhost
;;; record DEFAULT except for the host. Returns a userhost record if
;;; it wins, and #f if it cannot parse the path. CADDR drops the
;;; userhost portion of the path. In fact, fatal-syntax-error is
;;; called, if the path doesn't start with '//'.
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(define (parse-userhost path default)
(if (and (pair? path) ; The thing better begin
(string=? (car path) "") ; with // (i.e., have two
(pair? (cdr path)) ; initial "" elements).
(string=? (cadr path) ""))
(let* ((uhs (caddr path)) ; Userhost string.
(uhs-len (string-length uhs))
; Usr:passwd at-sign,
(at (index uhs #\@)) ; if any.
(colon1 (and at (index uhs #\:))) ; Usr:passwd colon,
(colon1 (and colon1 (< colon1 at) colon1)) ; if any.
(colon2 (index uhs #\: (or at 0)))) ; Host:port colon,
; if any.
(make-userhost (if at
(unescape-uri uhs 0 (or colon1 at))
(userhost:user default))
(if colon1
(unescape-uri uhs (+ colon1 1) at)
(userhost:password default))
(unescape-uri uhs (if at (+ at 1) 0)
(or colon2 uhs-len))
(if colon2
(unescape-uri uhs (+ colon2 1) uhs-len)
(userhost:port default))))
(fatal-syntax-error "URL must begin with //..." path)))
;;; Unparser
(define userhost-escaped-chars
(char-set-union uri-escaped-chars ; @ and : are also special
(string->char-set "@:"))) ; in UH strings.
(define (userhost->string uh)
(let* ((us (userhost:user uh))
(pw (userhost:password uh))
(ho (userhost:host uh))
(po (userhost:port uh))
;; Encode before assembly in case pieces contain colons or at-signs.
(e (lambda (s) (escape-uri s userhost-escaped-chars)))
(user/passwd (if us `(,(e us) . ,(if pw `(":" ,(e pw) "@") '("@")))
'()))
(host/port (if ho `(,(e ho) . ,(if po `(":" ,(e po)) '()))
'())))
(apply string-append (append user/passwd host/port))))
;;; HTTP URL parsing
;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; The PATH slot of this record is the URL's path split at slashes,
;;; e.g., "foo/bar//baz/" => ("foo" "bar" "" "baz" "")
;;; These elements are in raw, unescaped format. To convert back to
;;; a string, use (uri-path-list->path (map escape-uri pathlist)).
(define-record http-url
userhost ; Initial //anonymous@clark.lcs.mit.edu:80/
path ; Rest of path, split at slashes & decoded.
search
frag-id)
;;; The URI parser (parse-uri in uri.scm) maps a string to four parts:
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;;; <scheme> : <path> ? <search> # <frag-id>
;;; <scheme>, <search>, and <frag-id> are strings; <path> is a non-empty
;;; string list -- the URI's path split at slashes. Optional parts of the
;;; URI, when missing, are specified as #f. If <scheme> is "http", then the
;;; other three parts can be passed to PARSE-HTTP-URL, which parses them
;;; into a HTTP-URL record (or #f if the string cannot be parsed). All strings
;;; come back from the URI parser encoded. SEARCH and FRAG-ID are left
;;; that way; this parser decodes the path elements.
;;;
;;; Return #f if the URL could not be parsed.
(define (parse-http-url path search frag-id)
(let ((uh (parse-userhost path default-http-userhost)))
(if (or (userhost:user uh) (userhost:password uh))
(fatal-syntax-error
"HTTP URL's may not specify a user or password field" path))
(make-http-url uh (map unescape-uri (cdddr path)) search frag-id)))
;;; Default http port is 80.
(define default-http-userhost (make-userhost #f #f #f "80"))
;;; Unparse.
(define (http-url->string url)
(string-append "http://"
(userhost->string (http-url:userhost url))
"/"
(uri-path-list->path (map escape-uri (http-url:path url)))
(cond ((http-url:search url) =>
(lambda (s) (string-append "?" s)))
(else ""))
(cond ((http-url:frag-id url) =>
(lambda (fi) (string-append "#" fi)))
(else ""))))