;; quoted-printable.scm -- RFC2045 implementation
;; Copyright (c) 2005-2009 Alex Shinn. All rights reserved.
;; BSD-style license: http://synthcode.com/license.txt
;; Procedure: quoted-printable-encode-string str [start-col max-col]
;; Return a quoted-printable encoded representation of string
;; according to the official standard as described in RFC2045.
;;
;; ? and _ are always encoded for compatibility with RFC1522 encoding,
;; and soft newlines are inserted as necessary to keep each lines
;; length less than MAX-COL (default 76). The starting column may be
;; overridden with START-COL (default 0).
;; Procedure: quoted-printable-decode-string str [mime?]
;; Return a quoted-printable decoded representation of string. If
;; MIME? is specified and true, _ will be decoded as as space in
;; accordance with RFC1522. No errors will be raised on invalid
;; input.
;; Procedure: quoted-printable-encode [port start-col max-col]
;; Procedure: quoted-printable-decode [port start-col max-col]
;; Variations of the above which read and write to ports.
;; Procedure: quoted-printable-encode-header enc str [start-col max-col]
;; Return a quoted-printable encoded representation of string as
;; above, wrapped in =?ENC?Q?...?= as per RFC1522, split across
;; multiple MIME-header lines as needed to keep each lines length less
;; than MAX-COL. The string is encoded as is, and the encoding ENC is
;; just used for the prefix, i.e. you are responsible for ensuring STR
;; is already encoded according to ENC.
;; Example:
;; (define (mime-encode-header header value charset)
;; (let ((prefix (string-append header ": "))
;; (str (ces-convert value "UTF8" charset)))
;; (string-append
;; prefix
;; (quoted-printable-encode-header charset str (string-length prefix)))))
;; This API is backwards compatible with the Gauche library
;; rfc.quoted-printable.
(define *default-max-col* 76)
;; Allow for RFC1522 quoting for headers by always escaping ? and _
(define (qp-encode str start-col max-col separator)
(define (hex i) (integer->char (+ i (if (<= i 9) 48 55))))
(let ((end (string-length str))
(buf (make-string max-col)))
(let lp ((i 0) (col start-col) (res '()))
(cond
((= i end)
(if (pair? res)
(string-concatenate (reverse (cons (substring buf 0 col) res))
separator)
(substring buf start-col col)))
((>= col (- max-col 3))
(lp i 0 (cons (substring buf (if (pair? res) 0 start-col) col) res)))
(else
(let ((c (char->integer (string-ref str i))))
(cond
((and (<= 33 c 126) (not (memq c '(61 63 95))))
(string-set! buf col (integer->char c))
(lp (+ i 1) (+ col 1) res))
(else
(string-set! buf col #\=)
(string-set! buf (+ col 1) (hex (arithmetic-shift c -4)))
(string-set! buf (+ col 2) (hex (bitwise-and c #b1111)))
(lp (+ i 1) (+ col 3) res)))))))))
(define (quoted-printable-encode-string . o)
(let ((src (if (pair? o) (car o) (current-input-port)))
(start-col (if (and (pair? o) (pair? (cdr o))) (cadr o) 0))
(max-col (if (and (pair? o) (pair? (cdr o)) (pair? (cddr o)))
(caddr o)
*default-max-col*)))
(qp-encode (if (string? src) src (read-string #f src))
start-col max-col "=\r\n")))
(define (quoted-printable-encode . o)
(display (apply (quoted-printable-encode-string o))))
(define (quoted-printable-encode-header encoding . o)
(let ((src (if (pair? o) (car o) (current-input-port)))
(start-col (if (and (pair? o) (pair? (cdr o))) (cadr o) 0))
(max-col (if (and (pair? o) (pair? (cdr o)) (pair? (cddr o)))
(caddr o)
*default-max-col*))
(nl (if (and (pair? o) (pair? (cdr o)) (pair? (cddr o)) (pair? (cdddr o)))
(cadddr o)
"\r\n")))
(let* ((prefix (string-append "=?" encoding "?Q?"))
(prefix-length (+ 2 (string-length prefix)))
(separator (string-append "?=" nl "\t" prefix))
(effective-max-col (- max-col prefix-length)))
(string-append prefix
(qp-encode (if (string? src) src (read-string #f src))
start-col effective-max-col separator)
"?="))))
(define (quoted-printable-decode-string . o)
(define (hex? c) (or (char-numeric? c) (<= 65 (char->integer c) 70)))
(define (unhex1 c)
(let ((i (char->integer c))) (if (>= i 65) (- i 55) (- i 48))))
(define (unhex c1 c2)
(integer->char (+ (arithmetic-shift (unhex1 c1) 4) (unhex1 c2))))
(let ((src (if (pair? o) (car o) (current-input-port)))
(mime-header? (and (pair? o) (pair? (cdr o)) (car (cdr o)))))
(let* ((str (if (string? src) src (read-string #f src)))
(end (string-length str)))
(call-with-output-string
(lambda (out)
(let lp ((i 0))
(cond
((< i end)
(let ((c (string-ref str i)))
(case c
((#\=) ; = escapes
(cond
((< (+ i 2) end)
(let ((c2 (string-ref str (+ i 1))))
(cond
((eq? c2 #\newline) (lp (+ i 2)))
((eq? c2 #\return)
(lp (if (eq? (string-ref str (+ i 2)) #\newline)
(+ i 3)
(+ i 2))))
((hex? c2)
(let ((c3 (string-ref str (+ i 2))))
(if (hex? c3) (write-char (unhex c2 c3) out))
(lp (+ i 3))))
(else (lp (+ i 3))))))))
((#\_) ; maybe translate _ to space
(write-char (if mime-header? #\space c) out)
(lp (+ i 1)))
((#\space #\tab) ; strip trailing whitespace
(let lp2 ((j (+ i 1)))
(cond
((not (= j end))
(case (string-ref str j)
((#\space #\tab) (lp2 (+ j 1)))
((#\newline)
(lp (+ j 1)))
((#\return)
(let ((k (+ j 1)))
(lp (if (and (< k end)
(eqv? #\newline (string-ref str k)))
(+ k 1) k))))
(else (display (substring str i j) out) (lp j)))))))
(else ; a literal char
(write-char c out)
(lp (+ i 1)))))))))))))
(define (quoted-printable-decode . o)
(display (apply quoted-printable-decode-string o)))