6 files changed, 204 insertions, 0 deletions
diff --git a/src/pkg/Make.deps b/src/pkg/Make.deps
index 25dd17093..b600bcb46 100644
--- a/src/pkg/Make.deps
+++ b/src/pkg/Make.deps
@@ -6,6 +6,7 @@ bufio.install: io.install os.install strconv.install utf8.install
 bytes.install: os.install utf8.install
 compress/flate.install: bufio.install io.install os.install strconv.install
 compress/gzip.install: bufio.install compress/flate.install hash.install hash/crc32.install io.install os.install
+compress/zlib.install: bufio.install compress/flate.install hash.install hash/adler32.install io.install os.install
 container/list.install:
 container/ring.install:
 container/vector.install:
diff --git a/src/pkg/Makefile b/src/pkg/Makefile
index e6fdb06bd..6aecc9c52 100644
--- a/src/pkg/Makefile
+++ b/src/pkg/Makefile
@@ -20,6 +20,7 @@ DIRS=\
 	bytes\
 	compress/flate\
 	compress/gzip\
+	compress/zlib\
 	container/list\
 	container/ring\
 	container/vector\
@@ -81,6 +82,7 @@ TEST=\
 	bytes\
 	compress/flate\
 	compress/gzip\
+	compress/zlib\
 	container/list\
 	container/ring\
 	container/vector\
diff --git a/src/pkg/compress/gzip/gunzip.go b/src/pkg/compress/gzip/gunzip.go
index f4accf1a8..4455561fe 100644
--- a/src/pkg/compress/gzip/gunzip.go
+++ b/src/pkg/compress/gzip/gunzip.go
@@ -84,6 +84,7 @@ func NewGzipInflater(r io.Reader) (*GzipInflater, os.Error) {
 	return z, nil;
 }
 
+// GZIP (RFC 1952) is little-endian, unlike ZLIB (RFC 1950).
 func get4(p []byte) uint32 {
 	return uint32(p[0]) | uint32(p[1])<<8 | uint32(p[2])<<16 | uint32(p[3])<<24;
 }
diff --git a/src/pkg/compress/zlib/Makefile b/src/pkg/compress/zlib/Makefile
new file mode 100644
index 000000000..20f0e8aa1
--- /dev/null
+++ b/src/pkg/compress/zlib/Makefile
@@ -0,0 +1,11 @@
+# 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.
+
+include $(GOROOT)/src/Make.$(GOARCH)
+
+TARG=compress/zlib
+GOFILES=\
+	reader.go\
+
+include $(GOROOT)/src/Make.pkg
diff --git a/src/pkg/compress/zlib/reader.go b/src/pkg/compress/zlib/reader.go
new file mode 100644
index 000000000..a407aa891
--- /dev/null
+++ b/src/pkg/compress/zlib/reader.go
@@ -0,0 +1,87 @@
+// 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.
+
+// The zlib package implements reading (and eventually writing) of
+// zlib format compressed files, as specified in RFC 1950.
+package zlib
+
+import (
+	"bufio";
+	"compress/flate";
+	"hash";
+	"hash/adler32";
+	"io";
+	"os";
+)
+
+const zlibDeflate = 8
+
+var ChecksumError os.Error = os.ErrorString("zlib checksum error")
+var HeaderError os.Error = os.ErrorString("invalid zlib header")
+var UnsupportedError os.Error = os.ErrorString("unsupported zlib format")
+
+type reader struct {
+	r flate.Reader;
+	inflater io.Reader;
+	digest hash.Hash32;
+	err os.Error;
+}
+
+// NewZlibInflater creates a new io.Reader that satisfies reads by decompressing data read from r.
+// The implementation buffers input and may read more data than necessary from r.
+func NewZlibInflater(r io.Reader) (io.Reader, os.Error) {
+	z := new(reader);
+	if fr, ok := r.(flate.Reader); ok {
+		z.r = fr;
+	} else {
+		z.r = bufio.NewReader(r);
+	}
+	var buf [2]byte;
+	n, err := io.ReadFull(z.r, buf[0:2]);
+	if err != nil {
+		return nil, err;
+	}
+	h := uint(buf[0])<<8 | uint(buf[1]);
+	if (buf[0] & 0x0f != zlibDeflate) || (h % 31 != 0) {
+		return nil, HeaderError;
+	}
+	if buf[1] & 0x20 != 0 {
+		// BUG(nigeltao): The zlib package does not implement the FDICT flag.
+		return nil, UnsupportedError;
+	}
+	z.digest = adler32.New();
+	z.inflater = flate.NewInflater(z.r);
+	return z, nil;
+}
+
+func (z *reader) Read(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.inflater.Read(p);
+	z.digest.Write(p[0:n]);
+	if n != 0 || err != os.EOF {
+		z.err = err;
+		return;
+	}
+
+	// Finished file; check checksum.
+	var buf [4]byte;
+	if _, err := io.ReadFull(z.r, buf[0:4]); err != nil {
+		z.err = err;
+		return 0, err;
+	}
+	// ZLIB (RFC 1950) is big-endian, unlike GZIP (RFC 1952).
+	checksum := uint32(buf[0])<<24 | uint32(buf[1])<<16 | uint32(buf[2])<<8 | uint32(buf[3]);
+	if checksum != z.digest.Sum32() {
+		z.err = ChecksumError;
+		return 0, z.err;
+	}
+	return;
+}
+
diff --git a/src/pkg/compress/zlib/reader_test.go b/src/pkg/compress/zlib/reader_test.go
new file mode 100644
index 000000000..f178cb5f0
--- /dev/null
+++ b/src/pkg/compress/zlib/reader_test.go
@@ -0,0 +1,102 @@
+// 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 (
+	"bytes";
+	"io";
+	"os";
+	"testing";
+)
+
+type zlibTest struct {
+	desc string;
+	raw string;
+	compressed []byte;
+	err os.Error;
+}
+
+// Compare-to-golden test data was generated by the ZLIB example program at
+// http://www.zlib.net/zpipe.c
+
+var zlibTests = []zlibTest {
+	zlibTest {
+		"empty",
+		"",
+		[]byte {
+			0x78, 0x9c, 0x03, 0x00, 0x00, 0x00, 0x00, 0x01,
+		},
+		nil
+	},
+	zlibTest {
+		"goodbye",
+		"goodbye, world",
+		[]byte {
+			0x78, 0x9c, 0x4b, 0xcf, 0xcf, 0x4f, 0x49, 0xaa,
+			0x4c, 0xd5, 0x51, 0x28, 0xcf, 0x2f, 0xca, 0x49,
+			0x01, 0x00, 0x28, 0xa5, 0x05, 0x5e,
+		},
+		nil
+	},
+	zlibTest {
+		"bad header",
+		"",
+		[]byte {
+			0x78, 0x9f, 0x03, 0x00, 0x00, 0x00, 0x00, 0x01,
+		},
+		HeaderError
+	},
+	zlibTest {
+		"bad checksum",
+		"",
+		[]byte {
+			0x78, 0x9c, 0x03, 0x00, 0x00, 0x00, 0x00, 0xff,
+		},
+		ChecksumError,
+	},
+	zlibTest {
+		"not enough data",
+		"",
+		[]byte {
+			0x78, 0x9c, 0x03, 0x00, 0x00, 0x00,
+		},
+		io.ErrUnexpectedEOF,
+	},
+	zlibTest {
+		"excess data is silently ignored",
+		"",
+		[]byte {
+			0x78, 0x9c, 0x03, 0x00, 0x00, 0x00, 0x00, 0x01,
+			0x78, 0x9c, 0xff,
+		},
+		nil,
+	},
+}
+
+func TestZlibInflater(t *testing.T) {
+	b := new(bytes.Buffer);
+	for i, tt := range zlibTests {
+		in := io.NewByteReader(tt.compressed);
+		zlib, err := NewZlibInflater(in);
+		if err != nil {
+			if err != tt.err {
+				t.Errorf("%s: NewZlibInflater: %s", tt.desc, err);
+			}
+			continue;
+		}
+		b.Reset();
+		n, err := io.Copy(zlib, b);
+		if err != nil {
+			if err != tt.err {
+				t.Errorf("%s: io.Copy: %v want %v", tt.desc, err, tt.err);
+			}
+			continue;
+		}
+		s := string(b.Data());
+		if s != tt.raw {
+			t.Errorf("%s: got %d-byte %q want %d-byte %q", tt.desc, n, s, len(tt.raw), tt.raw);
+		}
+	}
+}