Remove writer reference on close (#224)

Furthermore:

* Clean up dictionary handling & test.
* Fixes dictionary use in levels 1-6.

Fixes #219

flate/deflate.go

@@ -59,15 +59,13 @@ type compressionLevel struct {
 // See https://blog.klauspost.com/rebalancing-deflate-compression-levels/
 var levels = []compressionLevel{
 	{}, // 0
-	// Level 1-4 uses specialized algorithm - values not used
+	// Level 1-6 uses specialized algorithm - values not used
 	{0, 0, 0, 0, 0, 1},
 	{0, 0, 0, 0, 0, 2},
 	{0, 0, 0, 0, 0, 3},
 	{0, 0, 0, 0, 0, 4},
-	// For levels 5-6 we don't bother trying with lazy matches.
-	// Lazy matching is at least 30% slower, with 1.5% increase.
-	{6, 0, 12, 8, 12, 5},
-	{8, 0, 24, 16, 16, 6},
+	{0, 0, 0, 0, 0, 5},
+	{0, 0, 0, 0, 0, 6},
 	// Levels 7-9 use increasingly more lazy matching
 	// and increasingly stringent conditions for "good enough".
 	{8, 8, 24, 16, skipNever, 7},
@@ -203,9 +201,8 @@ func (d *compressor) writeBlockSkip(tok *tokens, index int, eof bool) error {
 // This is much faster than doing a full encode.
 // Should only be used after a start/reset.
 func (d *compressor) fillWindow(b []byte) {
-	// Do not fill window if we are in store-only mode,
-	// use constant or Snappy compression.
-	if d.level == 0 {
+	// Do not fill window if we are in store-only or huffman mode.
+	if d.level <= 0 {
 		return
 	}
 	if d.fast != nil {
@@ -667,6 +664,7 @@ func (d *compressor) init(w io.Writer, level int) (err error) {
 	default:
 		return fmt.Errorf("flate: invalid compression level %d: want value in range [-2, 9]", level)
 	}
+	d.level = level
 	return nil
 }
 
@@ -720,6 +718,7 @@ func (d *compressor) close() error {
 		return d.w.err
 	}
 	d.w.flush()
+	d.w.reset(nil)
 	return d.w.err
 }
 
@@ -750,8 +749,7 @@ func NewWriter(w io.Writer, level int) (*Writer, error) {
 // can only be decompressed by a Reader initialized with the
 // same dictionary.
 func NewWriterDict(w io.Writer, level int, dict []byte) (*Writer, error) {
-	dw := &dictWriter{w}
-	zw, err := NewWriter(dw, level)
+	zw, err := NewWriter(w, level)
 	if err != nil {
 		return nil, err
 	}
@@ -760,14 +758,6 @@ func NewWriterDict(w io.Writer, level int, dict []byte) (*Writer, error) {
 	return zw, err
 }
 
-type dictWriter struct {
-	w io.Writer
-}
-
-func (w *dictWriter) Write(b []byte) (n int, err error) {
-	return w.w.Write(b)
-}
-
 // A Writer takes data written to it and writes the compressed
 // form of that data to an underlying writer (see NewWriter).
 type Writer struct {
@@ -805,11 +795,12 @@ func (w *Writer) Close() error {
 // the result of NewWriter or NewWriterDict called with dst
 // and w's level and dictionary.
 func (w *Writer) Reset(dst io.Writer) {
-	if dw, ok := w.d.w.writer.(*dictWriter); ok {
+	if len(w.dict) > 0 {
 		// w was created with NewWriterDict
-		dw.w = dst
-		w.d.reset(dw)
-		w.d.fillWindow(w.dict)
+		w.d.reset(dst)
+		if dst != nil {
+			w.d.fillWindow(w.dict)
+		}
 	} else {
 		// w was created with NewWriter
 		w.d.reset(dst)

flate/deflate_test.go

@@ -516,54 +516,65 @@ 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) })
-	testResetOutput(t, func(w io.Writer) (*Writer, error) { return NewWriter(w, ConstantCompression) })
-	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) })
-	testResetOutput(t, func(w io.Writer) (*Writer, error) { return NewWriterDict(w, ConstantCompression, dict) })
-}
-
-func testResetOutput(t *testing.T, newWriter func(w io.Writer) (*Writer, error)) {
-	buf := new(bytes.Buffer)
-	w, err := newWriter(buf)
-	if err != nil {
-		t.Fatalf("NewWriter: %v", err)
-	}
-	b := []byte("hello world")
-	for i := 0; i < 1024; i++ {
-		w.Write(b)
-	}
-	w.Close()
-	out1 := buf.Bytes()
 
-	buf2 := new(bytes.Buffer)
-	w.Reset(buf2)
-	for i := 0; i < 1024; i++ {
-		w.Write(b)
+	for i := HuffmanOnly; i <= BestCompression; i++ {
+		testResetOutput(t, fmt.Sprint("level-", i), func(w io.Writer) (*Writer, error) { return NewWriter(w, i) })
 	}
-	w.Close()
-	out2 := buf2.Bytes()
-
-	if len(out1) != len(out2) {
-		t.Errorf("got %d, expected %d bytes", len(out2), len(out1))
+	dict := []byte(strings.Repeat("we are the world - how are you?", 3))
+	for i := HuffmanOnly; i <= BestCompression; i++ {
+		testResetOutput(t, fmt.Sprint("dict-level-", i), func(w io.Writer) (*Writer, error) { return NewWriterDict(w, i, dict) })
 	}
-	if bytes.Compare(out1, out2) != 0 {
-		mm := 0
-		for i, b := range out1[:len(out2)] {
-			if b != out2[i] {
-				t.Errorf("mismatch index %d: %02x, expected %02x", i, out2[i], b)
+	for i := HuffmanOnly; i <= BestCompression; i++ {
+		testResetOutput(t, fmt.Sprint("dict-reset-level-", i), func(w io.Writer) (*Writer, error) {
+			w2, err := NewWriter(nil, i)
+			if err != nil {
+				return w2, err
 			}
-			mm++
-			if mm == 10 {
-				t.Fatal("Stopping")
+			w2.ResetDict(w, dict)
+			return w2, nil
+		})
+	}
+}
+
+func testResetOutput(t *testing.T, name string, newWriter func(w io.Writer) (*Writer, error)) {
+	t.Run(name, func(t *testing.T) {
+		buf := new(bytes.Buffer)
+		w, err := newWriter(buf)
+		if err != nil {
+			t.Fatalf("NewWriter: %v", err)
+		}
+		b := []byte("hello world - how are you doing?")
+		for i := 0; i < 1024; i++ {
+			w.Write(b)
+		}
+		w.Close()
+		out1 := buf.Bytes()
+
+		buf2 := new(bytes.Buffer)
+		w.Reset(buf2)
+		for i := 0; i < 1024; i++ {
+			w.Write(b)
+		}
+		w.Close()
+		out2 := buf2.Bytes()
+
+		if len(out1) != len(out2) {
+			t.Errorf("got %d, expected %d bytes", len(out2), len(out1))
+		}
+		if bytes.Compare(out1, out2) != 0 {
+			mm := 0
+			for i, b := range out1[:len(out2)] {
+				if b != out2[i] {
+					t.Errorf("mismatch index %d: %02x, expected %02x", i, out2[i], b)
+				}
+				mm++
+				if mm == 10 {
+					t.Fatal("Stopping")
+				}
 			}
 		}
-	}
-	t.Logf("got %d bytes", len(out1))
+		t.Logf("got %d bytes", len(out1))
+	})
 }
 
 // TestBestSpeed tests that round-tripping through deflate and then inflate