os: add explicit tests for fchown(2) and lchown(2) on unix platforms

Fixes #11919

Issue #11918 suggested that os.File.Chown and os.Lchown were under tested.

Change-Id: Ib41f7cb2d2fe0066d2ccb4d1bdabe1795efe80fc
Reviewed-on: https://go-review.googlesource.com/12834Reviewed-by: Russ Cox <rsc@golang.org>
Run-TryBot: Russ Cox <rsc@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/os/os_unix_test.go

@@ -32,10 +32,10 @@ func checkUidGid(t *testing.T, path string, uid, gid int) {
 }
 
 func TestChown(t *testing.T) {
-	// Chown is not supported under windows os Plan 9.
+	// Chown is not supported under windows or Plan 9.
 	// Plan9 provides a native ChownPlan9 version instead.
 	if runtime.GOOS == "windows" || runtime.GOOS == "plan9" {
-		return
+		t.Skipf("%s does not support syscall.Chown", runtime.GOOS)
 	}
 	// Use TempDir() to make sure we're on a local file system,
 	// so that the group ids returned by Getgroups will be allowed
@@ -78,3 +78,109 @@ func TestChown(t *testing.T) {
 		checkUidGid(t, f.Name(), int(sys.Uid), gid)
 	}
 }
+
+func TestFileChown(t *testing.T) {
+	// Fchown is not supported under windows or Plan 9.
+	if runtime.GOOS == "windows" || runtime.GOOS == "plan9" {
+		t.Skipf("%s does not support syscall.Fchown", runtime.GOOS)
+	}
+	// Use TempDir() to make sure we're on a local file system,
+	// so that the group ids returned by Getgroups will be allowed
+	// on the file.  On NFS, the Getgroups groups are
+	// basically useless.
+	f := newFile("TestFileChown", t)
+	defer Remove(f.Name())
+	defer f.Close()
+	dir, err := f.Stat()
+	if err != nil {
+		t.Fatalf("stat %s: %s", f.Name(), err)
+	}
+
+	// Can't change uid unless root, but can try
+	// changing the group id.  First try our current group.
+	gid := Getgid()
+	t.Log("gid:", gid)
+	if err = f.Chown(-1, gid); err != nil {
+		t.Fatalf("fchown %s -1 %d: %s", f.Name(), gid, err)
+	}
+	sys := dir.Sys().(*syscall.Stat_t)
+	checkUidGid(t, f.Name(), int(sys.Uid), gid)
+
+	// Then try all the auxiliary groups.
+	groups, err := Getgroups()
+	if err != nil {
+		t.Fatalf("getgroups: %s", err)
+	}
+	t.Log("groups: ", groups)
+	for _, g := range groups {
+		if err = f.Chown(-1, g); err != nil {
+			t.Fatalf("fchown %s -1 %d: %s", f.Name(), g, err)
+		}
+		checkUidGid(t, f.Name(), int(sys.Uid), g)
+
+		// change back to gid to test fd.Chown
+		if err = f.Chown(-1, gid); err != nil {
+			t.Fatalf("fchown %s -1 %d: %s", f.Name(), gid, err)
+		}
+		checkUidGid(t, f.Name(), int(sys.Uid), gid)
+	}
+}
+
+func TestLchown(t *testing.T) {
+	// Lchown is not supported under windows or Plan 9.
+	if runtime.GOOS == "windows" || runtime.GOOS == "plan9" {
+		t.Skipf("%s does not support syscall.Lchown", runtime.GOOS)
+	}
+	// Use TempDir() to make sure we're on a local file system,
+	// so that the group ids returned by Getgroups will be allowed
+	// on the file.  On NFS, the Getgroups groups are
+	// basically useless.
+	f := newFile("TestLchown", t)
+	defer Remove(f.Name())
+	defer f.Close()
+	dir, err := f.Stat()
+	if err != nil {
+		t.Fatalf("stat %s: %s", f.Name(), err)
+	}
+
+	linkname := f.Name() + "2"
+	if err := Link(f.Name(), linkname); err != nil {
+		t.Fatalf("link %s -> %s: %v", f.Name(), linkname, err)
+	}
+	defer Remove(linkname)
+
+	f2, err := Open(linkname)
+	if err != nil {
+		t.Fatalf("open %s: %v", linkname, err)
+	}
+	defer f2.Close()
+
+	// Can't change uid unless root, but can try
+	// changing the group id.  First try our current group.
+	gid := Getgid()
+	t.Log("gid:", gid)
+	if err = Lchown(linkname, -1, gid); err != nil {
+		t.Fatalf("lchown %s -1 %d: %s", linkname, gid, err)
+	}
+	sys := dir.Sys().(*syscall.Stat_t)
+	checkUidGid(t, linkname, int(sys.Uid), gid)
+
+	// Then try all the auxiliary groups.
+	groups, err := Getgroups()
+	if err != nil {
+		t.Fatalf("getgroups: %s", err)
+	}
+	t.Log("groups: ", groups)
+	for _, g := range groups {
+		if err = Lchown(linkname, -1, g); err != nil {
+			t.Fatalf("lchown %s -1 %d: %s", linkname, g, err)
+		}
+		checkUidGid(t, linkname, int(sys.Uid), g)
+
+		// change back to gid to test fd.Chown
+		if err = f2.Chown(-1, gid); err != nil {
+			t.Fatalf("fchown %s -1 %d: %s", linkname, gid, err)
+		}
+		checkUidGid(t, linkname, int(sys.Uid), gid)
+	}
+}