ZLIB deflater.

R=rsc
APPROVED=rsc
DELTA=222  (219 added, 0 deleted, 3 changed)
OCL=35031
CL=35129

src/pkg/compress/zlib/Makefile

@@ -7,5 +7,6 @@ include $(GOROOT)/src/Make.$(GOARCH)
 TARG=compress/zlib
 GOFILES=\
 	reader.go\
+	writer.go\
 
 include $(GOROOT)/src/Make.pkg

src/pkg/compress/zlib/reader.go

@@ -2,8 +2,8 @@
 // Use of this source code is governed by a BSD-style
 // license that can be found in the LICENSE file.
 
-// The zlib package implements reading (and eventually writing) of
-// zlib format compressed files, as specified in RFC 1950.
+// The zlib package implements reading and writing of zlib
+// format compressed files, as specified in RFC 1950.
 package zlib
 
 import (
@@ -87,6 +87,10 @@ func (z *reader) Read(p []byte) (n int, err os.Error) {
 
 // Calling Close does not close the wrapped io.Reader originally passed to NewInflater.
 func (z *reader) Close() os.Error {
-	return z.inflater.Close();
+	if z.err != nil {
+		return z.err;
+	}
+	z.err = z.inflater.Close();
+	return z.err;
 }
 

src/pkg/compress/zlib/writer.go

@@ -0,0 +1,107 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package zlib
+
+import (
+	"compress/flate";
+	"hash";
+	"hash/adler32";
+	"io";
+	"os";
+)
+
+// These constants are copied from the flate package, so that code that imports
+// "compress/zlib" does not also have to import "compress/flate".
+const (
+	NoCompression = flate.NoCompression;
+	BestSpeed = flate.BestSpeed;
+	BestCompression = flate.BestCompression;
+	DefaultCompression = flate.DefaultCompression;
+)
+
+type writer struct {
+	w io.Writer;
+	deflater io.WriteCloser;
+	digest hash.Hash32;
+	err os.Error;
+	scratch [4]byte;
+}
+
+// NewDeflater calls NewDeflaterLevel with the default compression level.
+func NewDeflater(w io.Writer) (io.WriteCloser, os.Error) {
+	return NewDeflaterLevel(w, DefaultCompression);
+}
+
+// NewDeflater creates a new io.WriteCloser that satisfies writes by compressing data written to w.
+// It is the caller's responsibility to call Close on the WriteCloser when done.
+// level is the compression level, which can be DefaultCompression, NoCompression,
+// or any integer value between BestSpeed and BestCompression (inclusive).
+func NewDeflaterLevel(w io.Writer, level int) (io.WriteCloser, os.Error) {
+	z := new(writer);
+	// ZLIB has a two-byte header (as documented in RFC 1950).
+	// The first four bits is the CINFO (compression info), which is 7 for the default deflate window size.
+	// The next four bits is the CM (compression method), which is 8 for deflate.
+	z.scratch[0] = 0x78;
+	// The next two bits is the FLEVEL (compression level). The four values are:
+	// 0=fastest, 1=fast, 2=default, 3=best.
+	// The next bit, FDICT, is unused, in this implementation.
+	// The final five FCHECK bits form a mod-31 checksum.
+	switch level {
+	case 0, 1:
+		z.scratch[1] = 0x01;
+	case 2, 3, 4, 5:
+		z.scratch[1] = 0x5e;
+	case 6, -1:
+		z.scratch[1] = 0x9c;
+	case 7, 8, 9:
+		z.scratch[1] = 0xda;
+	default:
+		return nil, os.NewError("level out of range");
+	}
+	_, err := w.Write(z.scratch[0:2]);
+	if err != nil {
+		return nil, err;
+	}
+	z.w = w;
+	z.deflater = flate.NewDeflater(w, level);
+	z.digest = adler32.New();
+	return z, nil;
+}
+
+func (z *writer) Write(p []byte) (n int, err os.Error) {
+	if z.err != nil {
+		return 0, z.err;
+	}
+	if len(p) == 0 {
+		return 0, nil;
+	}
+	n, err = z.deflater.Write(p);
+	if err != nil {
+		z.err = err;
+		return;
+	}
+	z.digest.Write(p);
+	return;
+}
+
+// Calling Close does not close the wrapped io.Writer originally passed to NewDeflater.
+func (z *writer) Close() os.Error {
+	if z.err != nil {
+		return z.err;
+	}
+	z.err = z.deflater.Close();
+	if z.err != nil {
+		return z.err;
+	}
+	checksum := z.digest.Sum32();
+	// ZLIB (RFC 1950) is big-endian, unlike GZIP (RFC 1952).
+	z.scratch[0] = uint8(checksum>>24);
+	z.scratch[1] = uint8(checksum>>16);
+	z.scratch[2] = uint8(checksum>>8);
+	z.scratch[3] = uint8(checksum>>0);
+	_, z.err = z.w.Write(z.scratch[0:4]);
+	return z.err;
+}
+

src/pkg/compress/zlib/writer_test.go

@@ -0,0 +1,105 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package zlib
+
+import (
+	"io";
+	"os";
+	"testing";
+)
+
+var filenames = []string {
+	"testdata/e.txt",
+	"testdata/pi.txt",
+}
+
+// Tests that compressing and then decompressing the given file at the given compression level
+// yields equivalent bytes to the original file.
+func testFileLevel(t *testing.T, fn string, level int) {
+	// Read the file, as golden output.
+	golden, err := os.Open(fn, os.O_RDONLY, 0444);
+	if err != nil {
+		t.Errorf("%s (level=%d): %v", fn, level, err);
+		return;
+	}
+	defer golden.Close();
+
+	// Read the file again, and push it through a pipe that compresses at the write end, and decompresses at the read end.
+	raw, err := os.Open(fn, os.O_RDONLY, 0444);
+	if err != nil {
+		t.Errorf("%s (level=%d): %v", fn, level, err);
+		return;
+	}
+	piper, pipew := io.Pipe();
+	defer piper.Close();
+	go func() {
+		defer raw.Close();
+		defer pipew.Close();
+		zlibw, err := NewDeflaterLevel(pipew, level);
+		if err != nil {
+			t.Errorf("%s (level=%d): %v", fn, level, err);
+			return;
+		}
+		defer zlibw.Close();
+		var b [1024]byte;
+		for {
+			n, err0 := raw.Read(&b);
+			if err0 != nil && err0 != os.EOF {
+				t.Errorf("%s (level=%d): %v", fn, level, err0);
+				return;
+			}
+			_, err1 := zlibw.Write(b[0:n]);
+			if err1 == os.EPIPE {
+				// Fail, but do not report the error, as some other (presumably reportable) error broke the pipe.
+				return;
+			}
+			if err1 != nil {
+				t.Errorf("%s (level=%d): %v", fn, level, err1);
+				return;
+			}
+			if err0 == os.EOF {
+				break;
+			}
+		}
+	}();
+	zlibr, err := NewInflater(piper);
+	if err != nil {
+		t.Errorf("%s (level=%d): %v", fn, level, err);
+		return;
+	}
+	defer zlibr.Close();
+
+	// Compare the two.
+	b0, err0 := io.ReadAll(golden);
+	b1, err1 := io.ReadAll(zlibr);
+	if err0 != nil {
+		t.Errorf("%s (level=%d): %v", fn, level, err0);
+		return;
+	}
+	if err1 != nil {
+		t.Errorf("%s (level=%d): %v", fn, level, err1);
+		return;
+	}
+	if len(b0) != len(b1) {
+		t.Errorf("%s (level=%d): length mismatch %d versus %d", fn, level, len(b0), len(b1));
+		return;
+	}
+	for i := 0; i < len(b0); i++ {
+		if b0[i] != b1[i] {
+			t.Errorf("%s (level=%d): mismatch at %d, 0x%02x versus 0x%02x\n", fn, level, i, b0[i], b1[i]);
+			return;
+		}
+	}
+}
+
+func TestWriter(t *testing.T) {
+	for _, fn := range filenames {
+		testFileLevel(t, fn, DefaultCompression);
+		testFileLevel(t, fn, NoCompression);
+		for level := BestSpeed; level <= BestCompression; level++ {
+			testFileLevel(t, fn, level);
+		}
+	}
+}