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(define-module (base64)
:use-module ((srfi srfi-71) :select (let*))
:use-module (srfi srfi-88) ; suffix keywords
:use-module ((rnrs bytevectors)
:select (bytevector-u8-ref
bytevector-u8-set!
bytevector-length
make-bytevector))
:use-module ((rnrs io ports)
:select (string->bytevector
bytevector->string
make-transcoder
latin-1-codec
native-transcoder))
:export (base64->bytevector
bytevector->base64
base64-string->bytevector
bytevector->base64-string
base64encode
base64decode
))
(define table
(list->vector
(map char->integer
(string->list
"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"))))
(define (real->encoded byte)
(vector-ref table byte))
(define (encoded->real byte)
(define A (char->integer #\A))
(define Z (char->integer #\Z))
(define a (char->integer #\a))
(define z (char->integer #\z))
(define zero (char->integer #\0))
(define nine (char->integer #\9))
(cond [(= byte (char->integer #\=)) 0]
[(= byte (char->integer #\+)) 62]
[(= byte (char->integer #\/)) 63]
[(<= A byte Z)
(- byte A)]
[(<= a byte z)
(+ 26 (- byte a))]
[(<= zero byte nine)
(+ 26 26 (- byte zero))]
[else (scm-error 'decoding-error
"encoded->real"
"Invalid character in Base64 string: ~s"
(list byte) #f)]))
(define ref
(make-procedure-with-setter
bytevector-u8-ref
bytevector-u8-set!))
(define (base64->bytevector bv)
(catch 'out-of-range
(lambda ()
(let ((len* (bytevector-length bv)))
(if (zero? len*)
(make-bytevector 0)
(let* ((rest (+ (if (= (char->integer #\=) (ref bv (- len* 1)))
1 0)
(if (= (char->integer #\=) (ref bv (- len* 2)))
1 0)))
(x (/ (- len* rest) 4))
(ret-len (floor (* 3 x))))
(define ret (make-bytevector ret-len))
(do ((i 0 (1+ i)))
((>= i (floor x)))
(let ((a (encoded->real (ref bv (+ (* i 4) 0))))
(b (encoded->real (ref bv (+ (* i 4) 1))))
(c (encoded->real (ref bv (+ (* i 4) 2))))
(d (encoded->real (ref bv (+ (* i 4) 3)))))
(let ((aa (logior (ash a 2) (ash b -4)))
(ab (logior (ash (logand b #xF) 4) (ash c -2)))
(ac (logior (ash (logand c 3) 6) d)))
(set! (ref ret (+ (* i 3) 0)) aa)
(set! (ref ret (+ (* i 3) 1)) ab)
(set! (ref ret (+ (* i 3) 2)) ac))))
(case rest
[(2)
(let ((a (encoded->real (ref bv (+ (* (floor x) 4) 0))))
(b (encoded->real (ref bv (+ (* (floor x) 4) 1)))))
(let ((aa (logior (ash a 2) (ash b -4))))
(set! (ref ret (- ret-len 1)) aa)))]
[(1)
(let ((a (encoded->real (ref bv (+ (* (floor x) 4) 0))))
(b (encoded->real (ref bv (+ (* (floor x) 4) 1))))
(c (encoded->real (ref bv (+ (* (floor x) 4) 2)))))
(let ((aa (logior (ash a 2) (ash b -4)))
(ab (logior (ash (logand b #xF) 4) (ash c -2))))
(set! (ref ret (- ret-len 2)) aa)
(set! (ref ret (- ret-len 1)) ab)))])
ret))))
(lambda (err proc fmt args data)
(scm-error 'decoding-error "base64->bytevector"
(format #f "~~a in ~~a: ~a" fmt)
(cons* err (or proc "unknown function") args)
data))))
(define (bytevector->base64 bv)
(let* ((len (bytevector-length bv))
(iterations rest (floor/ len 3)))
(define ret (make-bytevector (+ (* 4 iterations)
(if (zero? rest)
0 4))))
(do ((i 0 (1+ i)))
((>= i iterations))
(let ((a (ref bv (+ (* i 3) 0)))
(b (ref bv (+ (* i 3) 1)))
(c (ref bv (+ (* i 3) 2))))
(let ((aa (ash a -2))
(ab (logior (ash (logand #b11 a) 4) (ash b -4)))
(ac (logior (ash (logand b #b1111) 2) (ash c -6)))
(ad (logand c #x3F)))
(set! (ref ret (+ (* i 4) 0)) (real->encoded aa))
(set! (ref ret (+ (* i 4) 1)) (real->encoded ab))
(set! (ref ret (+ (* i 4) 2)) (real->encoded ac))
(set! (ref ret (+ (* i 4) 3)) (real->encoded ad)))))
(case rest
[(1)
(let ((byte (ref bv (- len 1))))
(let ((a (ash byte -2))
(b (ash (logand byte 3) 4)))
(set! (ref ret (+ 0 (* 4 iterations))) (real->encoded a))
(set! (ref ret (+ 1 (* 4 iterations))) (real->encoded b))
(set! (ref ret (+ 2 (* 4 iterations))) (char->integer #\=))
(set! (ref ret (+ 3 (* 4 iterations))) (char->integer #\=))))]
[(2)
(let ((byte1 (ref bv (- len 2)))
(byte2 (ref bv (- len 1))))
(let ((a (ash byte1 -2))
(b (logior (ash (logand byte1 3) 4) (ash byte2 -4 )))
(c (ash (logand byte2 #xF) 2)))
(set! (ref ret (+ 0 (* 4 iterations))) (real->encoded a))
(set! (ref ret (+ 1 (* 4 iterations))) (real->encoded b))
(set! (ref ret (+ 2 (* 4 iterations))) (real->encoded c))
(set! (ref ret (+ 3 (* 4 iterations))) (char->integer #\=))))])
ret))
;; string -> bv
(define (base64-string->bytevector string)
(base64->bytevector
(string->bytevector string (make-transcoder (latin-1-codec)))))
;; bv -> string
(define (bytevector->base64-string bv)
(bytevector->string (bytevector->base64 bv)
(make-transcoder (latin-1-codec))))
;; string -> string
(define* (base64encode string optional: (transcoder (native-transcoder)))
(bytevector->string
(bytevector->base64 (string->bytevector string transcoder))
(make-transcoder (latin-1-codec))))
;; string -> string
(define* (base64decode string optional: (transcoder (native-transcoder)))
(bytevector->string
(base64->bytevector
(string->bytevector string (make-transcoder (latin-1-codec))))
transcoder))
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