4 files changed, 55 insertions, 6 deletions
diff --git a/src/pkg/compress/gzip/gunzip.go b/src/pkg/compress/gzip/gunzip.go
index 1fb9b0964..4f398b194 100644
--- a/src/pkg/compress/gzip/gunzip.go
+++ b/src/pkg/compress/gzip/gunzip.go
@@ -89,6 +89,21 @@ func NewReader(r io.Reader) (*Reader, error) {
 	return z, nil
 }
 
+// Reset discards the Reader z's state and makes it equivalent to the
+// result of its original state from NewReader, but reading from r instead.
+// This permits reusing a Reader rather than allocating a new one.
+func (z *Reader) Reset(r io.Reader) error {
+	z.r = makeReader(r)
+	if z.digest == nil {
+		z.digest = crc32.NewIEEE()
+	} else {
+		z.digest.Reset()
+	}
+	z.size = 0
+	z.err = nil
+	return z.readHeader(true)
+}
+
 // 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/gzip/gunzip_test.go b/src/pkg/compress/gzip/gunzip_test.go
index 572fb5848..2471038f5 100644
--- a/src/pkg/compress/gzip/gunzip_test.go
+++ b/src/pkg/compress/gzip/gunzip_test.go
@@ -284,7 +284,7 @@ var gunzipTests = []gunzipTest{
 func TestDecompressor(t *testing.T) {
 	b := new(bytes.Buffer)
 	for _, tt := range gunzipTests {
-		in := bytes.NewBuffer(tt.gzip)
+		in := bytes.NewReader(tt.gzip)
 		gzip, err := NewReader(in)
 		if err != nil {
 			t.Errorf("%s: NewReader: %s", tt.name, err)
@@ -303,6 +303,26 @@ func TestDecompressor(t *testing.T) {
 		if s != tt.raw {
 			t.Errorf("%s: got %d-byte %q want %d-byte %q", tt.name, n, s, len(tt.raw), tt.raw)
 		}
+
+		// Test Reader Reset.
+		in = bytes.NewReader(tt.gzip)
+		err = gzip.Reset(in)
+		if err != nil {
+			t.Errorf("%s: Reset: %s", tt.name, err)
+			continue
+		}
+		if tt.name != gzip.Name {
+			t.Errorf("%s: got name %s", tt.name, gzip.Name)
+		}
+		b.Reset()
+		n, err = io.Copy(b, gzip)
+		if err != tt.err {
+			t.Errorf("%s: io.Copy: %v want %v", tt.name, err, tt.err)
+		}
+		s = b.String()
+		if s != tt.raw {
+			t.Errorf("%s: got %d-byte %q want %d-byte %q", tt.name, n, s, len(tt.raw), tt.raw)
+		}
 	}
 }
 
@@ -333,3 +353,17 @@ func TestIssue6550(t *testing.T) {
 		// ok
 	}
 }
+
+func TestInitialReset(t *testing.T) {
+	var r Reader
+	if err := r.Reset(bytes.NewReader(gunzipTests[1].gzip)); err != nil {
+		t.Error(err)
+	}
+	var buf bytes.Buffer
+	if _, err := io.Copy(&buf, &r); err != nil {
+		t.Error(err)
+	}
+	if s := buf.String(); s != gunzipTests[1].raw {
+		t.Errorf("got %q want %q", s, gunzipTests[1].raw)
+	}
+}
diff --git a/src/pkg/compress/gzip/gzip.go b/src/pkg/compress/gzip/gzip.go
index fe32d6871..3a0bf54e1 100644
--- a/src/pkg/compress/gzip/gzip.go
+++ b/src/pkg/compress/gzip/gzip.go
@@ -22,8 +22,8 @@ const (
 	DefaultCompression = flate.DefaultCompression
 )
 
-// A Writer is an io.WriteCloser that satisfies writes by compressing data written
-// to its wrapped io.Writer.
+// A Writer is an io.WriteCloser.
+// Writes to a Writer are compressed and written to w.
 type Writer struct {
 	Header
 	w           io.Writer
@@ -37,8 +37,8 @@ type Writer struct {
 	err         error
 }
 
-// NewWriter creates a new Writer that satisfies writes by compressing data
-// written to w.
+// NewWriter returns a new Writer.
+// Writes to the returned writer are compressed and written to w.
 //
 // It is the caller's responsibility to call Close on the WriteCloser when done.
 // Writes may be buffered and not flushed until Close.
diff --git a/src/pkg/compress/gzip/gzip_test.go b/src/pkg/compress/gzip/gzip_test.go
index 119be2e13..09271b24e 100644
--- a/src/pkg/compress/gzip/gzip_test.go
+++ b/src/pkg/compress/gzip/gzip_test.go
@@ -85,7 +85,7 @@ func TestRoundTrip(t *testing.T) {
 func TestLatin1(t *testing.T) {
 	latin1 := []byte{0xc4, 'u', 0xdf, 'e', 'r', 'u', 'n', 'g', 0}
 	utf8 := "Äußerung"
-	z := Reader{r: bufio.NewReader(bytes.NewBuffer(latin1))}
+	z := Reader{r: bufio.NewReader(bytes.NewReader(latin1))}
 	s, err := z.readString()
 	if err != nil {
 		t.Fatalf("readString: %v", err)