66 lines
2.7 KiB
Scheme
66 lines
2.7 KiB
Scheme
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;;; Code to parse information submitted from HTML forms. -*- Scheme -*-
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;;; Copyright (c) 1995 by Olin Shivers.
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;;; See http://www.w3.org/hypertext/WWW/MarkUp/html-spec/html-spec_toc.html
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;;; Imports and non-R4RS'isms
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;;; index (scsh)
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;;; let-optionals (let-opt package)
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;;; receive (Multiple-value return)
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;;; unescape-uri
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;;; map-string (strings package)
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;;; ? (cond)
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;;; About HTML forms
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;; The form's field data are turned into a single string, of the form
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;;; The form's field data are turned into a single string, of the form
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;;; name=val&name=val
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;;; where the <name> and <val> parts are URI encoded to hide their
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;;; &, =, and + chars, among other things. After URI encoding, the
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;;; space chars are converted to + chars, just for fun. It is important
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;;; to encode the spaces this way, because the perfectly general %xx escape
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;;; mechanism might be insufficiently confusing. This variant encoding is
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;;; called "form-url encoding."
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;;;
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;;; If the form's method is POST,
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;;; Browser sends the form's field data in the entity block, e.g.,
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;;; "button=on&ans=yes". The request's Content-type: is application/
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;;; x-www-form-urlencoded, and the request's Content-length: is the
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;;; number of bytes in the form data.
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;;;
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;;; If the form's method is GET,
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;;; Browser sends the form's field data in the URL's <search> part.
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;;; (So the server will pass to the CGI script as $QUERY_STRING,
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;;; and perhaps also on in argv[]).
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;;;
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;;; In either case, the data is "form-url encoded" (as described above).
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;;; Form-query parsing
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;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
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;;; Parse "foo=x&bar=y" into (("foo" . "x") ("bar" . "y"))
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;;; Substrings are plus-decoded and then URI-decoded. This implementation is
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;;; slightly sleazy as it will successfully parse a string like "a&b=c&d=f"
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;;; into (("a&b" . "c") ("d" . "f")) without a complaint.
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(define (parse-html-form-query q)
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(let ((qlen (string-length q)))
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(let recur ((i 0))
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(? ((index q #\= i) =>
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(lambda (j)
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(let ((k (or (index q #\& j) qlen)))
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(cons (cons (unescape-uri+ q i j)
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(unescape-uri+ q (+ j 1) k))
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(recur (+ k 1))))))
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(else '()))))) ; BOGUS STRING -- Issue a warning.
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;;; Map plus characters to spaces, then do URI decoding.
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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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(unescape-uri (string-map (lambda (c) (if (char=? c #\+) #\space c))
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(if (and (zero? start)
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(= end (string-length s)))
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s ; Gratuitous optimisation.
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(substring s start end))))))
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