archive/zip: avoid data descriptor when writing directories

Java fails to unzip archives created by archive/zip because directories are
written with the "data descriptor" flag (bit 3) set, but emits no such
descriptor. To fix this, we explicitly clear the flag.

Fixes #25215

Change-Id: Id3af4c7f863758197063df879717c1710f86c0e5
Reviewed-on: https://go-review.googlesource.com/110795
Reviewed-by: Joe Tsai <thebrokentoaster@gmail.com>
Run-TryBot: Joe Tsai <thebrokentoaster@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

diff --git a/src/archive/zip/writer.go b/src/archive/zip/writer.go
index f3abe8770c44b6f0a86c7b734bd73665be64fdad..0f1a193345b463a9b36d55f9ede80e8ad43b2b49 100644 (file)
--- a/src/archive/zip/writer.go
+++ b/src/archive/zip/writer.go
@@ -263,8 +263,6 @@ func (w *Writer) CreateHeader(fh *FileHeader) (io.Writer, error) {
                return nil, errors.New("archive/zip: invalid duplicate FileHeader")
        }
 
-       fh.Flags |= 0x8 // we will write a data descriptor
-
        // The ZIP format has a sad state of affairs regarding character encoding.
        // Officially, the name and comment fields are supposed to be encoded
        // in CP-437 (which is mostly compatible with ASCII), unless the UTF-8
@@ -331,8 +329,17 @@ func (w *Writer) CreateHeader(fh *FileHeader) (io.Writer, error) {
        }
 
        if strings.HasSuffix(fh.Name, "/") {
+               // Set the compression method to Store to ensure data length is truly zero,
+               // which the writeHeader method always encodes for the size fields.
+               // This is necessary as most compression formats have non-zero lengths
+               // even when compressing an empty string.
+               fh.Method = Store
+               fh.Flags &^= 0x8 // we will not write a data descriptor
+
                ow = dirWriter{}
        } else {
+               fh.Flags |= 0x8 // we will write a data descriptor
+
                fw = &fileWriter{
                        zipw:      w.cw,
                        compCount: &countWriter{w: w.cw},

diff --git a/src/archive/zip/writer_test.go b/src/archive/zip/writer_test.go
index 271a36729cc0d03121c6857294dc531b13283aee..468424c72ae222b898f0d3c3dbbd41cbdf40b9c9 100644 (file)
--- a/src/archive/zip/writer_test.go
+++ b/src/archive/zip/writer_test.go
@@ -6,6 +6,7 @@ package zip
 
 import (
        "bytes"
+       "encoding/binary"
        "fmt"
        "io"
        "io/ioutil"
@@ -310,6 +311,41 @@ func TestWriterDir(t *testing.T) {
        }
 }
 
+func TestWriterDirAttributes(t *testing.T) {
+       var buf bytes.Buffer
+       w := NewWriter(&buf)
+       if _, err := w.Create("dir/"); err != nil {
+               t.Fatal(err)
+       }
+       if err := w.Close(); err != nil {
+               t.Fatal(err)
+       }
+
+       b := buf.Bytes()
+
+       var sig [4]byte
+       binary.LittleEndian.PutUint32(sig[:], uint32(fileHeaderSignature))
+
+       idx := bytes.Index(b, sig[:])
+       if idx == -1 {
+               t.Fatal("file header not found")
+       }
+       b = b[idx:]
+
+       if !bytes.Equal(b[6:10], []byte{0, 0, 0, 0}) { // FileHeader.Flags: 0, FileHeader.Method: 0
+               t.Errorf("unexpected method and flags: %v", b[6:10])
+       }
+
+       if !bytes.Equal(b[14:26], make([]byte, 12)) { // FileHeader.{CRC32,CompressSize,UncompressedSize} all zero.
+               t.Errorf("unexpected crc, compress and uncompressed size to be 0 was: %v", b[14:26])
+       }
+
+       binary.LittleEndian.PutUint32(sig[:], uint32(dataDescriptorSignature))
+       if bytes.Index(b, sig[:]) != -1 {
+               t.Error("there should be no data descriptor")
+       }
+}
+
 func testCreate(t *testing.T, w *Writer, wt *WriteTest) {
        header := &FileHeader{
                Name:   wt.Name,