base64: Test for invalid characters when decoding.

1 files changed, 7 insertions, 3 deletions

diff --git a/chickadee/base64.scm b/chickadee/base64.scm
index 89fc4bb..c12fa39 100644
--- a/chickadee/base64.scm
+++ b/chickadee/base64.scm
@@ -45,9 +45,9 @@
   (let ((cache (make-hash-table)))
     (lambda (alphabet)
       (or (hash-ref cache alphabet)
-          (let ((bv (make-bytevector 128)))
+          (let ((bv (make-bytevector 128 -1)))
             (alphabet-for-each (lambda (i x)
-                                 (bytevector-u8-set! bv x i))
+                                 (bytevector-s8-set! bv x i))
                                alphabet)
             (hash-set! cache alphabet bv)
             bv)))))
@@ -56,7 +56,11 @@
   "Decode the base64 encoded string @var{str} using @var{alphabet} and
 return a bytevector containing the decoded data."
   (define decoder (alphabet->decoder alphabet))
-  (define (decode char) (bytevector-u8-ref decoder (char->integer char)))
+  (define (decode char)
+    (let ((x (bytevector-s8-ref decoder (char->integer char))))
+      (when (eq? x -1)
+        (error "invalid base64 character" char))
+      x))
   (call-with-input-string str
     (lambda (in)
       (call-with-output-bytevector