1 files changed, 24 insertions, 15 deletions
diff --git a/src/pkg/encoding/base64/base64.go b/src/pkg/encoding/base64/base64.go
index 85e398fd0..e38c26d0e 100644
--- a/src/pkg/encoding/base64/base64.go
+++ b/src/pkg/encoding/base64/base64.go
@@ -159,13 +159,11 @@ func (e *encoder) Write(p []byte) (n int, err error) {
 		nn := len(e.out) / 4 * 3
 		if nn > len(p) {
 			nn = len(p)
+			nn -= nn % 3
 		}
-		nn -= nn % 3
-		if nn > 0 {
-			e.enc.Encode(e.out[0:], p[0:nn])
-			if _, e.err = e.w.Write(e.out[0 : nn/3*4]); e.err != nil {
-				return n, e.err
-			}
+		e.enc.Encode(e.out[0:], p[0:nn])
+		if _, e.err = e.w.Write(e.out[0 : nn/3*4]); e.err != nil {
+			return n, e.err
 		}
 		n += nn
 		p = p[nn:]
@@ -226,21 +224,33 @@ func (enc *Encoding) decode(dst, src []byte) (n int, end bool, err error) {
 		var dbuf [4]byte
 		dlen := 4
 
-		for j := 0; j < 4; {
+		for j := range dbuf {
 			if len(src) == 0 {
 				return n, false, CorruptInputError(olen - len(src) - j)
 			}
 			in := src[0]
 			src = src[1:]
-			if in == '=' && j >= 2 && len(src) < 4 {
+			if in == '=' {
 				// We've reached the end and there's padding
-				if len(src)+j < 4-1 {
-					// not enough padding
-					return n, false, CorruptInputError(olen)
-				}
-				if len(src) > 0 && src[0] != '=' {
+				switch j {
+				case 0, 1:
 					// incorrect padding
 					return n, false, CorruptInputError(olen - len(src) - 1)
+				case 2:
+					// "==" is expected, the first "=" is already consumed.
+					if len(src) == 0 {
+						// not enough padding
+						return n, false, CorruptInputError(olen)
+					}
+					if src[0] != '=' {
+						// incorrect padding
+						return n, false, CorruptInputError(olen - len(src) - 1)
+					}
+					src = src[1:]
+				}
+				if len(src) > 0 {
+					// trailing garbage
+					err = CorruptInputError(olen - len(src))
 				}
 				dlen, end = j, true
 				break
@@ -249,7 +259,6 @@ func (enc *Encoding) decode(dst, src []byte) (n int, end bool, err error) {
 			if dbuf[j] == 0xFF {
 				return n, false, CorruptInputError(olen - len(src) - 1)
 			}
-			j++
 		}
 
 		// Pack 4x 6-bit source blocks into 3 byte destination
@@ -268,7 +277,7 @@ func (enc *Encoding) decode(dst, src []byte) (n int, end bool, err error) {
 		n += dlen - 1
 	}
 
-	return n, end, nil
+	return n, end, err
 }
 
 // Decode decodes src using the encoding enc.  It writes at most