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;; -*- mode: scheme; coding: utf-8 -*-
;; Copyright © 2009, 2010, 2012, 2013 Göran Weinholt <goran@weinholt.se>
;; Permission is hereby granted, free of charge, to any person obtaining a
;; copy of this software and associated documentation files (the "Software"),
;; to deal in the Software without restriction, including without limitation
;; the rights to use, copy, modify, merge, publish, distribute, sublicense,
;; and/or sell copies of the Software, and to permit persons to whom the
;; Software is furnished to do so, subject to the following conditions:
;; The above copyright notice and this permission notice shall be included in
;; all copies or substantial portions of the Software.
;; THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
;; IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
;; FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL
;; THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
;; LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
;; FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
;; DEALINGS IN THE SOFTWARE.
#!r6rs
;; RFC 4648 Base-N Encodings
(library (web socket base64)
(export base64-encode
base64-decode
base64-alphabet
base64url-alphabet
get-delimited-base64
put-delimited-base64)
(import (rnrs)
(only (srfi :13 strings)
string-index
string-prefix? string-suffix?
string-concatenate string-trim-both))
(define base64-alphabet
"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/")
(define base64url-alphabet
"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789-_")
(define base64-encode
(case-lambda
;; Simple interface. Returns a string containing the canonical
;; base64 representation of the given bytevector.
((bv)
(base64-encode bv 0 (bytevector-length bv) #f #f base64-alphabet #f))
((bv start)
(base64-encode bv start (bytevector-length bv) #f #f base64-alphabet #f))
((bv start end)
(base64-encode bv start end #f #f base64-alphabet #f))
((bv start end line-length)
(base64-encode bv start end line-length #f base64-alphabet #f))
((bv start end line-length no-padding)
(base64-encode bv start end line-length no-padding base64-alphabet #f))
((bv start end line-length no-padding alphabet)
(base64-encode bv start end line-length no-padding alphabet #f))
;; Base64 encodes the bytes [start,end[ in the given bytevector.
;; Lines are limited to line-length characters (unless #f),
;; which must be a multiple of four. To omit the padding
;; characters (#\=) set no-padding to a true value. If port is
;; #f, returns a string.
((bv start end line-length no-padding alphabet port)
(assert (or (not line-length) (zero? (mod line-length 4))))
(let-values (((p extract) (if port
(values port (lambda () (values)))
(open-string-output-port))))
(letrec ((put (if line-length
(let ((chars 0))
(lambda (p c)
(when (fx=? chars line-length)
(set! chars 0)
(put-char p #\linefeed))
(set! chars (fx+ chars 1))
(put-char p c)))
put-char)))
(let lp ((i start))
(cond ((= i end))
((<= (+ i 3) end)
(let ((x (bytevector-uint-ref bv i (endianness big) 3)))
(put p (string-ref alphabet (fxbit-field x 18 24)))
(put p (string-ref alphabet (fxbit-field x 12 18)))
(put p (string-ref alphabet (fxbit-field x 6 12)))
(put p (string-ref alphabet (fxbit-field x 0 6)))
(lp (+ i 3))))
((<= (+ i 2) end)
(let ((x (fxarithmetic-shift-left (bytevector-u16-ref bv i (endianness big)) 8)))
(put p (string-ref alphabet (fxbit-field x 18 24)))
(put p (string-ref alphabet (fxbit-field x 12 18)))
(put p (string-ref alphabet (fxbit-field x 6 12)))
(unless no-padding
(put p #\=))))
(else
(let ((x (fxarithmetic-shift-left (bytevector-u8-ref bv i) 16)))
(put p (string-ref alphabet (fxbit-field x 18 24)))
(put p (string-ref alphabet (fxbit-field x 12 18)))
(unless no-padding
(put p #\=)
(put p #\=)))))))
(extract)))))
;; Create a lookup table for the alphabet and remember the latest table.
(define get-decode-table
(let ((ascii-table #f)
(extra-table '()) ;in the unlikely case of unicode chars
(table-alphabet #f))
(lambda (alphabet)
(unless (eq? alphabet table-alphabet)
;; Rebuild the table.
(do ((ascii (make-vector 128 #f))
(extra '())
(i 0 (+ i 1)))
((= i (string-length alphabet))
(set! ascii-table ascii)
(set! extra-table extra))
(let ((c (char->integer (string-ref alphabet i))))
(if (fx<=? c 127)
(vector-set! ascii c i)
(set! extra (cons (cons c i) extra)))))
(set! table-alphabet alphabet))
(values ascii-table extra-table))))
;; Decodes a correctly padded base64 string, optionally ignoring
;; non-alphabet characters.
(define base64-decode
(case-lambda
((str)
(base64-decode str base64-alphabet #f))
((str alphabet)
(base64-decode str alphabet #f))
((str alphabet port)
(base64-decode str alphabet port #t))
((str alphabet port strict?)
(define (pad? c) (eqv? c (char->integer #\=)))
(let-values (((p extract) (if port
(values port (lambda () (values)))
(open-bytevector-output-port)))
((ascii extra) (get-decode-table alphabet)))
(define-syntax lookup
(syntax-rules ()
((_ c) (or (and (fx<=? c 127) (vector-ref ascii c))
(cond ((assv c extra) => cdr)
(else #f))))))
(let* ((len (if strict?
(string-length str)
(let lp ((i (fx- (string-length str) 1)))
;; Skip trailing invalid chars.
(cond ((fxzero? i) 0)
((let ((c (char->integer (string-ref str i))))
(or (lookup c) (pad? c)))
(fx+ i 1))
(else (lp (fx- i 1))))))))
(let lp ((i 0))
(cond
((fx=? i len)
(extract))
((fx<=? i (fx- len 4))
(let lp* ((c1 (char->integer (string-ref str i)))
(c2 (char->integer (string-ref str (fx+ i 1))))
(c3 (char->integer (string-ref str (fx+ i 2))))
(c4 (char->integer (string-ref str (fx+ i 3))))
(i i))
(let ((i1 (lookup c1)) (i2 (lookup c2))
(i3 (lookup c3)) (i4 (lookup c4)))
(cond
((and i1 i2 i3 i4)
;; All characters present and accounted for.
;; The most common case.
(let ((x (fxior (fxarithmetic-shift-left i1 18)
(fxarithmetic-shift-left i2 12)
(fxarithmetic-shift-left i3 6)
i4)))
(put-u8 p (fxbit-field x 16 24))
(put-u8 p (fxbit-field x 8 16))
(put-u8 p (fxbit-field x 0 8))
(lp (fx+ i 4))))
((and i1 i2 i3 (pad? c4) (= i (- len 4)))
;; One padding character at the end of the input.
(let ((x (fxior (fxarithmetic-shift-left i1 18)
(fxarithmetic-shift-left i2 12)
(fxarithmetic-shift-left i3 6))))
(put-u8 p (fxbit-field x 16 24))
(put-u8 p (fxbit-field x 8 16))
(lp (fx+ i 4))))
((and i1 i2 (pad? c3) (pad? c4) (= i (- len 4)))
;; Two padding characters.
(let ((x (fxior (fxarithmetic-shift-left i1 18)
(fxarithmetic-shift-left i2 12))))
(put-u8 p (fxbit-field x 16 24))
(lp (fx+ i 4))))
((not strict?)
;; Non-alphabet characters.
(let lp ((i i) (c* '()) (n 4))
(cond ((fxzero? n)
;; Found four valid characters.
(lp* (cadddr c*) (caddr c*) (cadr c*) (car c*)
(fx- i 4)))
((fx=? i len)
(error 'base64-decode
"Invalid input in non-strict mode."
i c*))
(else
;; Gather alphabetic (or valid
;; padding) characters.
(let ((c (char->integer (string-ref str i))))
(cond ((or (lookup c)
(and (pad? c)
(fx<=? n 2)
(fx=? i (fx- len n))))
(lp (fx+ i 1) (cons c c*) (fx- n 1)))
(else
(lp (fx+ i 1) c* n))))))))
(else
(error 'base64-decode
"Invalid input in strict mode."
c1 c2 c3 c4))))))
(else
(error 'base64-decode
"The input is too short, it may be missing padding."
i)))))))))
(define (get-line-comp f port)
(if (port-eof? port)
(eof-object)
(f (get-line port))))
;; Reads the common -----BEGIN/END type----- delimited format from
;; the given port. Returns two values: a string with the type and a
;; bytevector containing the base64 decoded data. The second value
;; is the eof object if there is an eof before the BEGIN delimiter.
(define get-delimited-base64
(case-lambda
((port)
(get-delimited-base64 port #t))
((port strict)
(define (get-first-data-line port)
;; Some MIME data has header fields in the same format as mail
;; or http. These are ignored.
(let ((line (get-line-comp string-trim-both port)))
(cond ((eof-object? line) line)
((string-index line #\:)
(let lp () ;read until empty line
(let ((line (get-line-comp string-trim-both port)))
(if (string=? line "")
(get-line-comp string-trim-both port)
(lp)))))
(else line))))
(let ((line (get-line-comp string-trim-both port)))
(cond ((eof-object? line)
(values "" (eof-object)))
((string=? line "")
(get-delimited-base64 port))
((and (string-prefix? "-----BEGIN " line)
(string-suffix? "-----" line))
(let* ((type (substring line 11 (- (string-length line) 5)))
(endline (string-append "-----END " type "-----")))
(let-values (((outp extract) (open-bytevector-output-port)))
(let lp ((line (get-first-data-line port)))
(cond ((eof-object? line)
(error 'get-delimited-base64
"unexpected end of file"))
((string-prefix? "-" line)
(unless (string=? line endline)
(error 'get-delimited-base64
"bad end delimiter" type line))
(values type (extract)))
(else
(unless (and (= (string-length line) 5)
(string-prefix? "=" line)) ;Skip Radix-64 checksum
(base64-decode line base64-alphabet outp))
(lp (get-line-comp string-trim-both port))))))))
(else ;skip garbage (like in openssl x509 -in foo -text output).
(get-delimited-base64 port)))))))
(define put-delimited-base64
(case-lambda
((port type bv line-length)
(display (string-append "-----BEGIN " type "-----\n") port)
(base64-encode bv 0 (bytevector-length bv)
line-length #f base64-alphabet port)
(display (string-append "\n-----END " type "-----\n") port))
((port type bv)
(put-delimited-base64 port type bv 76)))))
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