gcrypt/base64.scm

@@ -21,10 +21,10 @@
 ;; You should have received a copy of the GNU General Public License
 ;; along with this program.  If not, see <http://www.gnu.org/licenses/>.
 ;;
-;; This file incorporates work covered by the following copyright and  
+;; This file incorporates work covered by the following copyright and
 ;; permission notice:
 ;;
-;;   Copyright © 2009, 2010 Göran Weinholt <goran@weinholt.se>
+;;   Copyright © 2009, 2010, 2012, 2013, 2018 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"),
@@ -74,7 +74,11 @@
 (define-alias fxior logior)
 (define-alias fxxor logxor)
 (define-alias fx=? =)
+(define-alias fx<=? <=)
+(define-alias fxzero? zero?)
 (define-alias fx+ +)
+(define-alias fx- -)
+(define-alias fxmod modulo)
 (define-alias mod modulo)
 
 (define-syntax-rule (assert exp)
@@ -147,9 +151,29 @@
                       (put p #\=)))))))
        (extract)))))
 
-  ;; Decodes a base64 string. The string must contain only pure
-  ;; unpadded base64 data.
-  
+;; 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 base64 string, optionally ignoring non-alphabet
+;; characters and lack of padding.
 (define base64-decode
   (case-lambda
     ((str)
@@ -157,97 +181,166 @@
     ((str alphabet)
      (base64-decode str alphabet #f))
     ((str alphabet port)
-     (unless (zero? (mod (string-length str) 4))
-       (error 'base64-decode
-              "input string must be a multiple of four characters"))
+     (base64-decode str alphabet port #t))
+    ((str alphabet port strict?)
+     (base64-decode str alphabet port strict? #t))
+    ((str alphabet port strict? strict-padding?)
+     (define (pad? c) (eqv? c (char->integer #\=)))
      (let-values (((p extract) (if port
                                    (values port (lambda () (values)))
-                                   (open-bytevector-output-port))))
-       (do ((i 0 (+ i 4)))
-           ((= i (string-length str))
-            (extract))
-         (let ((c1 (string-ref str i))
-               (c2 (string-ref str (+ i 1)))
-               (c3 (string-ref str (+ i 2)))
-               (c4 (string-ref str (+ i 3))))
-           ;; TODO: be more clever than string-index
-           (let ((i1 (string-index alphabet c1))
-                 (i2 (string-index alphabet c2))
-                 (i3 (string-index alphabet c3))
-                 (i4 (string-index alphabet c4)))
-             (cond ((and i1 i2 i3 i4)
-                    (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))))
-                   ((and i1 i2 i3 (char=? c4 #\=)
-                         (= i (- (string-length str) 4)))
-                    (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))))
-                   ((and i1 i2 (char=? c3 #\=) (char=? c4 #\=)
-                         (= i (- (string-length str) 4)))
-                    (let ((x (fxior (fxarithmetic-shift-left i1 18)
-                                    (fxarithmetic-shift-left i2 12))))
-                      (put-u8 p (fxbit-field x 16 24))))
-                   (else
-                    (error 'base64-decode "invalid input"
-                           (list c1 c2 c3 c4)))))))))))
+                                   (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 lp-restart ((str str))
+         (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))))))
+              ((not strict-padding?)
+               ;; Append an appropriate amount of padding after the
+               ;; remaining characters.
+               (if (<= 2 (- len i) 3)
+                   (lp-restart (string-append (substring str i (string-length str))
+                                              (if (= (- len i) 2) "==" "=")))
+                   (error 'base64-decode "The input is too short." i)))
+              (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 port)
-  (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)))))
+;; 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 ((previous "") (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)))
+                          ((and (= (string-length line) 5)
+                                (string-prefix? "=" line))
+                           ;; Skip Radix-64 checksum
+                           (lp previous (get-line-comp string-trim-both port)))
+                          ((not (fxzero? (fxmod (fx+ (string-length previous)
+                                                     (string-length line))
+                                                4)))
+                           ;; OpenSSH outputs lines with a bad length
+                           (lp (string-append previous line)
+                               (get-line-comp string-trim-both port)))
+                          (else
+                           (base64-decode (string-append previous 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

tests/base64.scm

@@ -29,10 +29,22 @@
 (define (string->base64 str)
   (base64-encode (string->utf8 str)))
 
+(define (base64->string base64)
+  (utf8->string (base64-decode base64)))
+
+(define (string->base64-padding str padding)
+  (let ((bv (string->utf8 str)))
+    (base64-encode bv 0 (bytevector-length bv) #f (not padding))))
+
+(define (base64->string-padding base64 padding)
+  (utf8->string (base64-decode base64 base64url-alphabet #f #f padding)))
+
 ;;; Test vectors from <https://tools.ietf.org/rfc/rfc4648.txt>.
 
 (test-begin "base64")
 
+;; Encoding
+
 (test-equal "empty string"
   (string->base64 "")
   "")
@@ -61,4 +73,50 @@
   (string->base64 "foobar")
   "Zm9vYmFy")
 
+(test-equal "foob (no padding)"
+  (string->base64-padding "foob" #f)
+  "Zm9vYg")
+
+(test-equal "foob (padding)"
+  (string->base64-padding "foob" #t)
+  "Zm9vYg==")
+
+;; Decoding
+
+(test-equal "empty string"
+  (base64->string "")
+  "")
+
+(test-equal "f"
+  (base64->string "Zg==")
+  "f")
+
+(test-equal "fo"
+  (base64->string "Zm8=")
+  "fo")
+
+(test-equal "foo"
+  (base64->string "Zm9v")
+  "foo")
+
+(test-equal "foob"
+  (base64->string "Zm9vYg==")
+  "foob")
+
+(test-equal "fooba"
+  (base64->string "Zm9vYmE=")
+  "fooba")
+
+(test-equal "foobar"
+  (base64->string "Zm9vYmFy")
+  "foobar")
+
+(test-equal "foob (no padding)"
+  (base64->string-padding "Zm9vYg" #f)
+  "foob")
+
+(test-equal "foob (padding)"
+  (base64->string-padding "Zm9vYg==" #t)
+  "foob")
+
 (test-end "base64")