encoding/base64: correct DecodedLen overestimate for unpadded encodings

While we're at it, add tests for EncodedLen and DecodedLen.

Fixes #14803.

Change-Id: I200c72cf11c51669b8d9f70c6e57ece359f7ae61
Reviewed-on: https://go-review.googlesource.com/20649
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

diff --git a/src/encoding/base64/base64.go b/src/encoding/base64/base64.go
index 0de9b40f85612cadca2ecf9ebae291cb2cf3e7b9..c2116d8a3436180bdc66ac8d8061d690d946ba42 100644 (file)
--- a/src/encoding/base64/base64.go
+++ b/src/encoding/base64/base64.go
@@ -459,7 +459,7 @@ func NewDecoder(enc *Encoding, r io.Reader) io.Reader {
 func (enc *Encoding) DecodedLen(n int) int {
        if enc.padChar == NoPadding {
                // Unpadded data may end with partial block of 2-3 characters.
-               return (n*6 + 7) / 8
+               return n * 6 / 8
        }
        // Padded base64 should always be a multiple of 4 characters in length.
        return n / 4 * 3

diff --git a/src/encoding/base64/base64_test.go b/src/encoding/base64/base64_test.go
index eebf113212a17122a188623dc13adbd861f2b80d..19ddb92f644b23c118a926e0cd34dff28085509d 100644 (file)
--- a/src/encoding/base64/base64_test.go
+++ b/src/encoding/base64/base64_test.go
@@ -234,6 +234,51 @@ func TestDecodeCorrupt(t *testing.T) {
        }
 }
 
+func TestEncodedLen(t *testing.T) {
+       for _, tt := range []struct {
+               enc  *Encoding
+               n    int
+               want int
+       }{
+               {RawStdEncoding, 0, 0},
+               {RawStdEncoding, 1, 2},
+               {RawStdEncoding, 2, 3},
+               {RawStdEncoding, 3, 4},
+               {RawStdEncoding, 7, 10},
+               {StdEncoding, 0, 0},
+               {StdEncoding, 1, 4},
+               {StdEncoding, 2, 4},
+               {StdEncoding, 3, 4},
+               {StdEncoding, 4, 8},
+               {StdEncoding, 7, 12},
+       } {
+               if got := tt.enc.EncodedLen(tt.n); got != tt.want {
+                       t.Errorf("EncodedLen(%d): got %d, want %d", tt.n, got, tt.want)
+               }
+       }
+}
+
+func TestDecodedLen(t *testing.T) {
+       for _, tt := range []struct {
+               enc  *Encoding
+               n    int
+               want int
+       }{
+               {RawStdEncoding, 0, 0},
+               {RawStdEncoding, 2, 1},
+               {RawStdEncoding, 3, 2},
+               {RawStdEncoding, 4, 3},
+               {RawStdEncoding, 10, 7},
+               {StdEncoding, 0, 0},
+               {StdEncoding, 4, 3},
+               {StdEncoding, 8, 6},
+       } {
+               if got := tt.enc.DecodedLen(tt.n); got != tt.want {
+                       t.Errorf("DecodedLen(%d): got %d, want %d", tt.n, got, tt.want)
+               }
+       }
+}
+
 func TestBig(t *testing.T) {
        n := 3*1000 + 1
        raw := make([]byte, n)