image/jpeg: don't assume that an ensureNBits failure implies that we can

call unreadByteStuffedByte.

If ensureNBits was due to an io.EOF that was translated to
jpeg.errShortHuffmanData, then we may have read no bytes, so there is no
byte-stuffed-byte to unread.

Fixes #10387

Change-Id: I39a3842590c6cef2aa48943288d52f603338b44d
Reviewed-on: https://go-review.googlesource.com/8841
Reviewed-by: Rob Pike <r@golang.org>

diff --git a/src/image/jpeg/reader.go b/src/image/jpeg/reader.go
index 2c3c2f72f8dbd6af93a15a782f75ed1f598adbb5..435b67a0200700e1b8291af782d3e26b4149266b 100644 (file)
--- a/src/image/jpeg/reader.go
+++ b/src/image/jpeg/reader.go
@@ -170,7 +170,7 @@ func (d *decoder) fill() error {
 // can happen when expecting to read a 0xff 0x00 byte-stuffed byte.
 func (d *decoder) unreadByteStuffedByte() {
        if d.bytes.nUnreadable == 0 {
-               panic("jpeg: unreadByteStuffedByte call cannot be fulfilled")
+               return
        }
        d.bytes.i -= d.bytes.nUnreadable
        d.bytes.nUnreadable = 0
@@ -242,12 +242,7 @@ func (d *decoder) readByteStuffedByte() (x byte, err error) {
 // stuffing.
 func (d *decoder) readFull(p []byte) error {
        // Unread the overshot bytes, if any.
-       if d.bytes.nUnreadable != 0 {
-               if d.bits.n >= 8 {
-                       d.unreadByteStuffedByte()
-               }
-               d.bytes.nUnreadable = 0
-       }
+       d.unreadByteStuffedByte()
 
        for {
                n := copy(p, d.bytes.buf[d.bytes.i:d.bytes.j])
@@ -269,12 +264,7 @@ func (d *decoder) readFull(p []byte) error {
 // ignore ignores the next n bytes.
 func (d *decoder) ignore(n int) error {
        // Unread the overshot bytes, if any.
-       if d.bytes.nUnreadable != 0 {
-               if d.bits.n >= 8 {
-                       d.unreadByteStuffedByte()
-               }
-               d.bytes.nUnreadable = 0
-       }
+       d.unreadByteStuffedByte()
 
        for {
                m := d.bytes.j - d.bytes.i

diff --git a/src/image/jpeg/reader_test.go b/src/image/jpeg/reader_test.go
index c5a36cba21273e69d4064f9addcccf8d2fc51b9e..5964b92aacc9f59f0b259cf4fe54ec66a68ac6ff 100644 (file)
--- a/src/image/jpeg/reader_test.go
+++ b/src/image/jpeg/reader_test.go
@@ -186,6 +186,26 @@ func pixString(pix []byte, stride, x, y int) string {
        return s.String()
 }
 
+func TestTruncatedSOSDataDoesntPanic(t *testing.T) {
+       b, err := ioutil.ReadFile("../testdata/video-005.gray.q50.jpeg")
+       if err != nil {
+               t.Fatal(err)
+       }
+       sosMarker := []byte{0xff, 0xda}
+       i := bytes.Index(b, sosMarker)
+       if i < 0 {
+               t.Fatal("SOS marker not found")
+       }
+       i += len(sosMarker)
+       j := i + 10
+       if j > len(b) {
+               j = len(b)
+       }
+       for ; i < j; i++ {
+               Decode(bytes.NewReader(b[:i]))
+       }
+}
+
 func TestExtraneousData(t *testing.T) {
        // Encode a 1x1 red image.
        src := image.NewRGBA(image.Rect(0, 0, 1, 1))