1 files changed, 132 insertions, 0 deletions
diff --git a/src/compress/zlib/reader.go b/src/compress/zlib/reader.go
new file mode 100644
index 000000000..9e1aafda9
--- /dev/null
+++ b/src/compress/zlib/reader.go
@@ -0,0 +1,132 @@
+// 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 implements reading and writing of zlib format compressed data,
+as specified in RFC 1950.
+
+The implementation provides filters that uncompress during reading
+and compress during writing.  For example, to write compressed data
+to a buffer:
+
+	var b bytes.Buffer
+	w := zlib.NewWriter(&b)
+	w.Write([]byte("hello, world\n"))
+	w.Close()
+
+and to read that data back:
+
+	r, err := zlib.NewReader(&b)
+	io.Copy(os.Stdout, r)
+	r.Close()
+*/
+package zlib
+
+import (
+	"bufio"
+	"compress/flate"
+	"errors"
+	"hash"
+	"hash/adler32"
+	"io"
+)
+
+const zlibDeflate = 8
+
+var (
+	// ErrChecksum is returned when reading ZLIB data that has an invalid checksum.
+	ErrChecksum = errors.New("zlib: invalid checksum")
+	// ErrDictionary is returned when reading ZLIB data that has an invalid dictionary.
+	ErrDictionary = errors.New("zlib: invalid dictionary")
+	// ErrHeader is returned when reading ZLIB data that has an invalid header.
+	ErrHeader = errors.New("zlib: invalid header")
+)
+
+type reader struct {
+	r            flate.Reader
+	decompressor io.ReadCloser
+	digest       hash.Hash32
+	err          error
+	scratch      [4]byte
+}
+
+// NewReader creates a new io.ReadCloser.
+// Reads from the returned io.ReadCloser read and decompress data from r.
+// The implementation buffers input and may read more data than necessary from r.
+// It is the caller's responsibility to call Close on the ReadCloser when done.
+func NewReader(r io.Reader) (io.ReadCloser, error) {
+	return NewReaderDict(r, nil)
+}
+
+// NewReaderDict is like NewReader but uses a preset dictionary.
+// NewReaderDict ignores the dictionary if the compressed data does not refer to it.
+func NewReaderDict(r io.Reader, dict []byte) (io.ReadCloser, error) {
+	z := new(reader)
+	if fr, ok := r.(flate.Reader); ok {
+		z.r = fr
+	} else {
+		z.r = bufio.NewReader(r)
+	}
+	_, err := io.ReadFull(z.r, z.scratch[0:2])
+	if err != nil {
+		return nil, err
+	}
+	h := uint(z.scratch[0])<<8 | uint(z.scratch[1])
+	if (z.scratch[0]&0x0f != zlibDeflate) || (h%31 != 0) {
+		return nil, ErrHeader
+	}
+	if z.scratch[1]&0x20 != 0 {
+		_, err = io.ReadFull(z.r, z.scratch[0:4])
+		if err != nil {
+			return nil, err
+		}
+		checksum := uint32(z.scratch[0])<<24 | uint32(z.scratch[1])<<16 | uint32(z.scratch[2])<<8 | uint32(z.scratch[3])
+		if checksum != adler32.Checksum(dict) {
+			return nil, ErrDictionary
+		}
+		z.decompressor = flate.NewReaderDict(z.r, dict)
+	} else {
+		z.decompressor = flate.NewReader(z.r)
+	}
+	z.digest = adler32.New()
+	return z, nil
+}
+
+func (z *reader) Read(p []byte) (n int, err error) {
+	if z.err != nil {
+		return 0, z.err
+	}
+	if len(p) == 0 {
+		return 0, nil
+	}
+
+	n, err = z.decompressor.Read(p)
+	z.digest.Write(p[0:n])
+	if n != 0 || err != io.EOF {
+		z.err = err
+		return
+	}
+
+	// Finished file; check checksum.
+	if _, err := io.ReadFull(z.r, z.scratch[0:4]); err != nil {
+		z.err = err
+		return 0, err
+	}
+	// ZLIB (RFC 1950) is big-endian, unlike GZIP (RFC 1952).
+	checksum := uint32(z.scratch[0])<<24 | uint32(z.scratch[1])<<16 | uint32(z.scratch[2])<<8 | uint32(z.scratch[3])
+	if checksum != z.digest.Sum32() {
+		z.err = ErrChecksum
+		return 0, z.err
+	}
+	return
+}
+
+// Calling Close does not close the wrapped io.Reader originally passed to NewReader.
+func (z *reader) Close() error {
+	if z.err != nil {
+		return z.err
+	}
+	z.err = z.decompressor.Close()
+	return z.err
+}