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;;; guile-email --- Guile email parser
;;; Copyright © 2018, 2020 Arun Isaac <arunisaac@systemreboot.net>
;;; Copyright © 2023 Andrew Whatson <whatson@tailcall.au>
;;;
;;; This file is part of guile-email.
;;;
;;; guile-email is free software; you can redistribute it and/or modify
;;; it under the terms of the GNU Affero General Public License as
;;; published by the Free Software Foundation; either version 3 of the
;;; License, or (at your option) any later version.
;;;
;;; guile-email is distributed in the hope that it will be useful, but
;;; WITHOUT ANY WARRANTY; without even the implied warranty of
;;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
;;; Affero General Public License for more details.
;;;
;;; You should have received a copy of the GNU Affero General Public
;;; License along with guile-email. If not, see
;;; <http://www.gnu.org/licenses/>.
(define-module (email quoted-printable)
#:use-module (rnrs bytevectors)
#:use-module (rnrs io ports)
#:use-module (ice-9 format)
#:use-module (ice-9 match)
#:use-module (srfi srfi-26)
#:export (quoted-printable-decode
quoted-printable-encode
q-encoding-decode
q-encoding-encode))
;; TODO: Error out on invalid quoted-printable input
(define quoted-printable-decode
(match-lambda*
(((? string? str))
(call-with-input-string str quoted-printable-decode))
(((? port? in))
(call-with-bytevector-output-port
(cut quoted-printable-decode in <>)))
(((? port? in) (? port? out))
(let ((c (read-char in)))
(cond
((eof-object? c) out)
((char=? c #\=)
(let ((c1 (read-char in)))
;; Skip if \n was read.
(unless (char=? c1 #\Newline)
(let ((c2 (read-char in)))
;; Skip if \r\n was read.
(unless (and (char=? c1 #\Return)
(char=? c2 #\Newline))
(put-u8 out (string->number (string c1 c2) 16))))))
(quoted-printable-decode in out))
(else (put-u8 out (char->integer c))
(quoted-printable-decode in out)))))))
(define* (quoted-printable-style-encode
in out literal-char-set
#:optional (number-of-chars-left-on-this-line 76))
(let ((x (get-u8 in))
(put-into-output
(lambda (str)
(let* ((len (string-length str))
(break-line? (<= number-of-chars-left-on-this-line len)))
(put-string
out (string-append (if break-line? "=\n" "") str))
(if break-line?
(- 76 len)
(- number-of-chars-left-on-this-line len))))))
(unless (eof-object? x)
(let ((c (integer->char x)))
(quoted-printable-style-encode
in out literal-char-set
(put-into-output
(if (char-set-contains? literal-char-set c)
(string c)
(format #f "=~:@(~2,'0x~)" x))))))))
;; Character set of characters to be represented by themselves in
;; quoted-printable encoding
(define %quoted-printable-literal-char-set
(char-set-delete
(ucs-range->char-set (char->integer #\space)
(char->integer #\delete))
#\=))
;; Character set of characters to be represented by themselves in Q
;; encoding
(define %q-encoding-literal-char-set
(char-set-delete
%quoted-printable-literal-char-set
#\? #\_))
(define quoted-printable-encode
(match-lambda*
(((? bytevector? bv))
(call-with-port (open-bytevector-input-port bv)
quoted-printable-encode))
(((? port? in))
(call-with-output-string
(cut quoted-printable-encode in <>)))
(((? port? in) (? port? out))
(quoted-printable-style-encode
in out %quoted-printable-literal-char-set))))
(define (q-encoding-decode str)
(quoted-printable-decode
(string-map
(lambda (c)
(if (char=? c #\_) #\Space c))
str)))
(define (q-encoding-encode bv)
(string-map
(lambda (c)
(if (char=? c #\Space) #\_ c))
(call-with-port (open-bytevector-input-port bv)
(lambda (in)
(call-with-output-string
(cut quoted-printable-style-encode in <>
%q-encoding-literal-char-set))))))
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