1 files changed, 139 insertions, 0 deletions
diff --git a/src/pkg/compress/zlib/writer.go b/src/pkg/compress/zlib/writer.go
new file mode 100644
index 000000000..8f86e9c4c
--- /dev/null
+++ b/src/pkg/compress/zlib/writer.go
@@ -0,0 +1,139 @@
+// 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
+)
+
+// A Writer takes data written to it and writes the compressed
+// form of that data to an underlying writer (see NewWriter).
+type Writer struct {
+	w          io.Writer
+	compressor *flate.Writer
+	digest     hash.Hash32
+	err        os.Error
+	scratch    [4]byte
+}
+
+// NewWriter calls NewWriterLevel with the default compression level.
+func NewWriter(w io.Writer) (*Writer, os.Error) {
+	return NewWriterLevel(w, DefaultCompression)
+}
+
+// NewWriterLevel calls NewWriterDict with no dictionary.
+func NewWriterLevel(w io.Writer, level int) (*Writer, os.Error) {
+	return NewWriterDict(w, level, nil)
+}
+
+// NewWriterDict 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).
+// dict is the preset dictionary to compress with, or nil to use no dictionary.
+func NewWriterDict(w io.Writer, level int, dict []byte) (*Writer, 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 set if a dictionary is given.
+	// The final five FCHECK bits form a mod-31 checksum.
+	switch level {
+	case 0, 1:
+		z.scratch[1] = 0 << 6
+	case 2, 3, 4, 5:
+		z.scratch[1] = 1 << 6
+	case 6, -1:
+		z.scratch[1] = 2 << 6
+	case 7, 8, 9:
+		z.scratch[1] = 3 << 6
+	default:
+		return nil, os.NewError("level out of range")
+	}
+	if dict != nil {
+		z.scratch[1] |= 1 << 5
+	}
+	z.scratch[1] += uint8(31 - (uint16(z.scratch[0])<<8+uint16(z.scratch[1]))%31)
+	_, err := w.Write(z.scratch[0:2])
+	if err != nil {
+		return nil, err
+	}
+	if dict != nil {
+		// The next four bytes are the Adler-32 checksum of the dictionary.
+		checksum := adler32.Checksum(dict)
+		z.scratch[0] = uint8(checksum >> 24)
+		z.scratch[1] = uint8(checksum >> 16)
+		z.scratch[2] = uint8(checksum >> 8)
+		z.scratch[3] = uint8(checksum >> 0)
+		_, err = w.Write(z.scratch[0:4])
+		if err != nil {
+			return nil, err
+		}
+	}
+	z.w = w
+	z.compressor = flate.NewWriterDict(w, level, dict)
+	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.compressor.Write(p)
+	if err != nil {
+		z.err = err
+		return
+	}
+	z.digest.Write(p)
+	return
+}
+
+// Flush flushes the underlying compressor.
+func (z *Writer) Flush() os.Error {
+	if z.err != nil {
+		return z.err
+	}
+	z.err = z.compressor.Flush()
+	return z.err
+}
+
+// Calling Close does not close the wrapped io.Writer originally passed to NewWriter.
+func (z *Writer) Close() os.Error {
+	if z.err != nil {
+		return z.err
+	}
+	z.err = z.compressor.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
+}