archive/tar: fix round-trip attributes

The issue was identified while
working with round trip FileInfo of the headers of hardlinks. Also,
additional test cases for hard link handling.
(review carried over from http://golang.org/cl/165860043)

Fixes #9027

Change-Id: I9e3a724c8de72eb1b0fbe0751a7b488894911b76
Reviewed-on: https://go-review.googlesource.com/6790
Reviewed-by: Russ Cox <rsc@golang.org>

5 files changed, 127 insertions, 24 deletions

diff --git a/src/archive/tar/common.go b/src/archive/tar/common.go
index e363aa793e..855e5fc4e6 100644
--- a/src/archive/tar/common.go
+++ b/src/archive/tar/common.go
@@ -139,8 +139,8 @@ func (fi headerFileInfo) Mode() (mode os.FileMode) {
 	}
 
 	switch fi.h.Typeflag {
-	case TypeLink, TypeSymlink:
-		// hard link, symbolic link
+	case TypeSymlink:
+		// symbolic link
 		mode |= os.ModeSymlink
 	case TypeChar:
 		// character device node
diff --git a/src/archive/tar/stat_unix.go b/src/archive/tar/stat_unix.go
index cb843db4cf..24b93111dc 100644
--- a/src/archive/tar/stat_unix.go
+++ b/src/archive/tar/stat_unix.go
@@ -16,17 +16,41 @@ func init() {
 }
 
 func statUnix(fi os.FileInfo, h *Header) error {
-	sys, ok := fi.Sys().(*syscall.Stat_t)
-	if !ok {
-		return nil
+	switch sys := fi.Sys().(type) {
+	case *syscall.Stat_t:
+		h.Uid = int(sys.Uid)
+		h.Gid = int(sys.Gid)
+		// TODO(bradfitz): populate username & group.  os/user
+		// doesn't cache LookupId lookups, and lacks group
+		// lookup functions.
+		h.AccessTime = statAtime(sys)
+		h.ChangeTime = statCtime(sys)
+		// TODO(bradfitz): major/minor device numbers?
+		if fi.Mode().IsRegular() && sys.Nlink > 1 {
+			h.Typeflag = TypeLink
+			h.Size = 0
+			// TODO(vbatts): Linkname?
+		}
+	case *Header:
+		// for the roundtrip logic
+		h.Uid = sys.Uid
+		h.Gid = sys.Gid
+		h.Uname = sys.Uname
+		h.Gname = sys.Gname
+		h.AccessTime = sys.AccessTime
+		h.ChangeTime = sys.ChangeTime
+		if sys.Xattrs != nil {
+			h.Xattrs = make(map[string]string)
+			for k, v := range sys.Xattrs {
+				h.Xattrs[k] = v
+			}
+		}
+		if sys.Typeflag == TypeLink {
+			// hard link
+			h.Typeflag = TypeLink
+			h.Size = 0
+			h.Linkname = sys.Linkname
+		}
 	}
-	h.Uid = int(sys.Uid)
-	h.Gid = int(sys.Gid)
-	// TODO(bradfitz): populate username & group.  os/user
-	// doesn't cache LookupId lookups, and lacks group
-	// lookup functions.
-	h.AccessTime = statAtime(sys)
-	h.ChangeTime = statCtime(sys)
-	// TODO(bradfitz): major/minor device numbers?
 	return nil
 }
diff --git a/src/archive/tar/tar_test.go b/src/archive/tar/tar_test.go
index ed333f3ea4..d63c072eb9 100644
--- a/src/archive/tar/tar_test.go
+++ b/src/archive/tar/tar_test.go
@@ -147,17 +147,6 @@ func TestHeaderRoundTrip(t *testing.T) {
 			},
 			fm: 0644,
 		},
-		// hard link.
-		{
-			h: &Header{
-				Name:     "hard.txt",
-				Mode:     0644 | c_ISLNK,
-				Size:     0,
-				ModTime:  time.Unix(1360600916, 0),
-				Typeflag: TypeLink,
-			},
-			fm: 0644 | os.ModeSymlink,
-		},
 		// symbolic link.
 		{
 			h: &Header{
@@ -246,6 +235,33 @@ func TestHeaderRoundTrip(t *testing.T) {
 			},
 			fm: 0600 | os.ModeSticky,
 		},
+		// hard link.
+		{
+			h: &Header{
+				Name:     "hard.txt",
+				Mode:     0644 | c_ISREG,
+				Size:     0,
+				Linkname: "file.txt",
+				ModTime:  time.Unix(1360600916, 0),
+				Typeflag: TypeLink,
+			},
+			fm: 0644,
+		},
+		// More information.
+		{
+			h: &Header{
+				Name:     "info.txt",
+				Mode:     0600 | c_ISREG,
+				Size:     0,
+				Uid:      1000,
+				Gid:      1000,
+				ModTime:  time.Unix(1360602540, 0),
+				Uname:    "slartibartfast",
+				Gname:    "users",
+				Typeflag: TypeReg,
+			},
+			fm: 0600,
+		},
 	}
 
 	for i, g := range golden {
@@ -268,12 +284,37 @@ func TestHeaderRoundTrip(t *testing.T) {
 		if got, want := h2.Size, g.h.Size; got != want {
 			t.Errorf("i=%d: Size: got %v, want %v", i, got, want)
 		}
+		if got, want := h2.Uid, g.h.Uid; got != want {
+			t.Errorf("i=%d: Uid: got %d, want %d", i, got, want)
+		}
+		if got, want := h2.Gid, g.h.Gid; got != want {
+			t.Errorf("i=%d: Gid: got %d, want %d", i, got, want)
+		}
+		if got, want := h2.Uname, g.h.Uname; got != want {
+			t.Errorf("i=%d: Uname: got %q, want %q", i, got, want)
+		}
+		if got, want := h2.Gname, g.h.Gname; got != want {
+			t.Errorf("i=%d: Gname: got %q, want %q", i, got, want)
+		}
+		if got, want := h2.Linkname, g.h.Linkname; got != want {
+			t.Errorf("i=%d: Linkname: got %v, want %v", i, got, want)
+		}
+		if got, want := h2.Typeflag, g.h.Typeflag; got != want {
+			t.Logf("%#v %#v", g.h, fi.Sys())
+			t.Errorf("i=%d: Typeflag: got %q, want %q", i, got, want)
+		}
 		if got, want := h2.Mode, g.h.Mode; got != want {
 			t.Errorf("i=%d: Mode: got %o, want %o", i, got, want)
 		}
 		if got, want := fi.Mode(), g.fm; got != want {
 			t.Errorf("i=%d: fi.Mode: got %o, want %o", i, got, want)
 		}
+		if got, want := h2.AccessTime, g.h.AccessTime; got != want {
+			t.Errorf("i=%d: AccessTime: got %v, want %v", i, got, want)
+		}
+		if got, want := h2.ChangeTime, g.h.ChangeTime; got != want {
+			t.Errorf("i=%d: ChangeTime: got %v, want %v", i, got, want)
+		}
 		if got, want := h2.ModTime, g.h.ModTime; got != want {
 			t.Errorf("i=%d: ModTime: got %v, want %v", i, got, want)
 		}
diff --git a/src/archive/tar/testdata/hardlink.tar b/src/archive/tar/testdata/hardlink.tar
new file mode 100644
index 0000000000..9cd1a26572
--- /dev/null
+++ b/src/archive/tar/testdata/hardlink.tar
diff --git a/src/archive/tar/writer_test.go b/src/archive/tar/writer_test.go
index 650899a10e..fe46a67ce3 100644
--- a/src/archive/tar/writer_test.go
+++ b/src/archive/tar/writer_test.go
@@ -147,6 +147,44 @@ var writerTests = []*writerTest{
 			},
 		},
 	},
+	// This file was produced using gnu tar 1.26
+	// echo "Slartibartfast" > file.txt
+	// ln file.txt hard.txt
+	// tar -b 1 --format=ustar -c -f hardlink.tar file.txt hard.txt
+	{
+		file: "testdata/hardlink.tar",
+		entries: []*writerTestEntry{
+			{
+				header: &Header{
+					Name:     "file.txt",
+					Mode:     0644,
+					Uid:      1000,
+					Gid:      100,
+					Size:     15,
+					ModTime:  time.Unix(1425484303, 0),
+					Typeflag: '0',
+					Uname:    "vbatts",
+					Gname:    "users",
+				},
+				contents: "Slartibartfast\n",
+			},
+			{
+				header: &Header{
+					Name:     "hard.txt",
+					Mode:     0644,
+					Uid:      1000,
+					Gid:      100,
+					Size:     0,
+					ModTime:  time.Unix(1425484303, 0),
+					Typeflag: '1',
+					Linkname: "file.txt",
+					Uname:    "vbatts",
+					Gname:    "users",
+				},
+				// no contents
+			},
+		},
+	},
 }
 
 // Render byte array in a two-character hexadecimal string, spaced for easy visual inspection.