archive/tar: roundtrip reading device numbers

Both GNU and BSD tar do not care if the devmajor and devminor values are
set on entries (like regular files) that aren't character or block devices.

While this is non-sensible, it is more consistent with the Writer to actually
read these fields always. In a vast majority of the cases these will still
be zero. In the rare situation where someone actually cares about these,
at least information was not silently lost.

Change-Id: I6e4ba01cd897a1b13c28b1837e102a4fdeb420ba
Reviewed-on: https://go-review.googlesource.com/55572Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/archive/tar/reader.go

@@ -468,10 +468,8 @@ func (tr *Reader) readHeader() (*Header, *block, error) {
 		ustar := tr.blk.USTAR()
 		hdr.Uname = p.parseString(ustar.UserName())
 		hdr.Gname = p.parseString(ustar.GroupName())
-		if hdr.Typeflag == TypeChar || hdr.Typeflag == TypeBlock {
 		hdr.Devmajor = p.parseNumeric(ustar.DevMajor())
 		hdr.Devminor = p.parseNumeric(ustar.DevMinor())
-		}
 
 		var prefix string
 		switch format {

src/archive/tar/reader_test.go

@@ -384,6 +384,17 @@ func TestReader(t *testing.T) {
 			Uid:     010000000,
 			ModTime: time.Unix(0, 0),
 		}},
+	}, {
+		// USTAR archive with a regular entry with non-zero device numbers.
+		file: "testdata/ustar-file-devs.tar",
+		headers: []*Header{{
+			Name:     "file",
+			Mode:     0644,
+			Typeflag: '0',
+			ModTime:  time.Unix(0, 0),
+			Devmajor: 1,
+			Devminor: 1,
+		}},
 	}}
 
 	for _, v := range vectors {