compress/flate: fix another deflate Reset inconsistency

While investigating #34121, fixed by CL 193605,
I discovered another case where Reset was not quite
resetting enough.

This specific case is not a problem in Reset itself but
rather that the Huffman bit writer in one code path
is using uninitialized memory left over from a previous
block, making the compression not choose the optimal
compression method.

Fixes #34121.

Change-Id: I29245b28214d924e382f91e2c56b4b8a9b7da13d
Reviewed-on: https://go-review.googlesource.com/c/go/+/243140
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Joe Tsai <thebrokentoaster@gmail.com>

diff --git a/src/compress/flate/deflate_test.go b/src/compress/flate/deflate_test.go
index 4b1ed549a46b32d8618358cae7a6e0e0b13874f5..49a0345fd1d4bc19d64f716e2fe1b34c10045725 100644 (file)
--- a/src/compress/flate/deflate_test.go
+++ b/src/compress/flate/deflate_test.go
@@ -512,33 +512,57 @@ func TestWriterReset(t *testing.T) {
                        t.Errorf("level %d Writer not reset after Reset", level)
                }
        }
-       testResetOutput(t, func(w io.Writer) (*Writer, error) { return NewWriter(w, NoCompression) })
-       testResetOutput(t, func(w io.Writer) (*Writer, error) { return NewWriter(w, DefaultCompression) })
-       testResetOutput(t, func(w io.Writer) (*Writer, error) { return NewWriter(w, BestCompression) })
-       dict := []byte("we are the world")
-       testResetOutput(t, func(w io.Writer) (*Writer, error) { return NewWriterDict(w, NoCompression, dict) })
-       testResetOutput(t, func(w io.Writer) (*Writer, error) { return NewWriterDict(w, DefaultCompression, dict) })
-       testResetOutput(t, func(w io.Writer) (*Writer, error) { return NewWriterDict(w, BestCompression, dict) })
+
+       levels := []int{0, 1, 2, 5, 9}
+       for _, level := range levels {
+               t.Run(fmt.Sprint(level), func(t *testing.T) {
+                       testResetOutput(t, level, nil)
+               })
+       }
+
+       t.Run("dict", func(t *testing.T) {
+               for _, level := range levels {
+                       t.Run(fmt.Sprint(level), func(t *testing.T) {
+                               testResetOutput(t, level, nil)
+                       })
+               }
+       })
 }
 
-func testResetOutput(t *testing.T, newWriter func(w io.Writer) (*Writer, error)) {
+func testResetOutput(t *testing.T, level int, dict []byte) {
+       writeData := func(w *Writer) {
+               msg := []byte("now is the time for all good gophers")
+               w.Write(msg)
+               w.Flush()
+
+               hello := []byte("hello world")
+               for i := 0; i < 1024; i++ {
+                       w.Write(hello)
+               }
+
+               fill := bytes.Repeat([]byte("x"), 65000)
+               w.Write(fill)
+       }
+
        buf := new(bytes.Buffer)
-       w, err := newWriter(buf)
+       var w *Writer
+       var err error
+       if dict == nil {
+               w, err = NewWriter(buf, level)
+       } else {
+               w, err = NewWriterDict(buf, level, dict)
+       }
        if err != nil {
                t.Fatalf("NewWriter: %v", err)
        }
-       b := []byte("hello world")
-       for i := 0; i < 1024; i++ {
-               w.Write(b)
-       }
+
+       writeData(w)
        w.Close()
        out1 := buf.Bytes()
 
        buf2 := new(bytes.Buffer)
        w.Reset(buf2)
-       for i := 0; i < 1024; i++ {
-               w.Write(b)
-       }
+       writeData(w)
        w.Close()
        out2 := buf2.Bytes()
 

diff --git a/src/compress/flate/huffman_bit_writer.go b/src/compress/flate/huffman_bit_writer.go
index 3e19061f8b57e5306612c01493cc1946eae7cf50..f111f9f592c59680aef8cf163c29f3c76321c932 100644 (file)
--- a/src/compress/flate/huffman_bit_writer.go
+++ b/src/compress/flate/huffman_bit_writer.go
@@ -634,6 +634,7 @@ func (w *huffmanBitWriter) writeBlockHuff(eof bool, input []byte) {
        w.literalFreq[endBlockMarker] = 1
 
        const numLiterals = endBlockMarker + 1
+       w.offsetFreq[0] = 1
        const numOffsets = 1
 
        w.literalEncoding.generate(w.literalFreq, 15)