gojs: adds support for uid and gid (#1245)

This adds `gojs.WithOSUser` which passes through current user IDs so
that GOOS=js compiled wasm can read them. This also adds support for
reading back the uid and gid on files. In summary, this passes
`os.TestChown` except on windows where it will not work due to lack of
support.

Signed-off-by: Adrian Cole <adrian@tetrate.io>

internal/platform/stat.go

@@ -19,6 +19,14 @@ type Stat_t struct {
 	// Ino is the file serial number.
 	Ino uint64
 
+	// Uid is the user ID that owns the file, or zero if unsupported.
+	// For example, this is unsupported on some virtual filesystems or windows.
+	Uid uint32
+
+	// Gid is the group ID that owns the file, or zero if unsupported.
+	// For example, this is unsupported on some virtual filesystems or windows.
+	Gid uint32
+
 	// Mode is the same as Mode on fs.FileInfo containing bits to identify the
 	// type of the file (fs.ModeType) and its permissions (fs.ModePerm).
 	Mode fs.FileMode

internal/platform/stat_bsd.go

@@ -37,8 +37,10 @@ func inoFromFileInfo(_ readdirFile, t fs.FileInfo) (ino uint64, err error) {
 
 func fillStatFromFileInfo(st *Stat_t, t fs.FileInfo) {
 	if d, ok := t.Sys().(*syscall.Stat_t); ok {
-		st.Ino = d.Ino
 		st.Dev = uint64(d.Dev)
+		st.Ino = d.Ino
+		st.Uid = d.Uid
+		st.Gid = d.Gid
 		st.Mode = t.Mode()
 		st.Nlink = uint64(d.Nlink)
 		st.Size = d.Size

internal/platform/stat_linux.go

@@ -40,8 +40,10 @@ func inoFromFileInfo(_ readdirFile, t fs.FileInfo) (ino uint64, err error) {
 
 func fillStatFromFileInfo(st *Stat_t, t fs.FileInfo) {
 	if d, ok := t.Sys().(*syscall.Stat_t); ok {
-		st.Ino = uint64(d.Ino)
 		st.Dev = uint64(d.Dev)
+		st.Ino = uint64(d.Ino)
+		st.Uid = d.Uid
+		st.Gid = d.Gid
 		st.Mode = t.Mode()
 		st.Nlink = uint64(d.Nlink)
 		st.Size = d.Size

internal/platform/stat_test.go

@@ -315,7 +315,8 @@ func TestStatFile_dev_inode(t *testing.T) {
 }
 
 func requireDirectoryDevIno(t *testing.T, st Stat_t) {
-	// windows before go 1.20 has trouble reading the inode information on directories.
+	// windows before go 1.20 has trouble reading the inode information on
+	// directories.
 	if runtime.GOOS != "windows" || IsGo120 {
 		require.NotEqual(t, uint64(0), st.Dev)
 		require.NotEqual(t, uint64(0), st.Ino)
@@ -324,3 +325,57 @@ func requireDirectoryDevIno(t *testing.T, st Stat_t) {
 		require.Zero(t, st.Ino)
 	}
 }
+
+// TestStat_uid_gid is similar to os.TestChown
+func TestStat_uid_gid(t *testing.T) {
+	if runtime.GOOS == "windows" {
+		t.Skip("windows")
+	}
+
+	// We don't attempt changing the uid of a file, as only root can do that.
+	// Also, this isn't a test of chown. The main goal here is to read-back
+	// the uid, gid, both of which are zero if run as root.
+	uid := uint32(os.Getuid())
+	gid := uint32(os.Getgid())
+
+	t.Run("Stat", func(t *testing.T) {
+		tmpDir := t.TempDir()
+		dir := path.Join(tmpDir, "dir")
+		require.NoError(t, os.Mkdir(dir, 0o0700))
+		require.NoError(t, chgid(dir, gid))
+
+		var st Stat_t
+		require.NoError(t, Stat(dir, &st))
+		require.Equal(t, uid, st.Uid)
+		require.Equal(t, gid, st.Gid)
+	})
+
+	t.Run("LStat", func(t *testing.T) {
+		tmpDir := t.TempDir()
+		link := path.Join(tmpDir, "link")
+		require.NoError(t, os.Symlink(tmpDir, link))
+		require.NoError(t, chgid(link, gid))
+
+		var st Stat_t
+		require.NoError(t, Lstat(link, &st))
+		require.Equal(t, uid, st.Uid)
+		require.Equal(t, gid, st.Gid)
+	})
+
+	t.Run("StatFile", func(t *testing.T) {
+		tmpDir := t.TempDir()
+		file := path.Join(tmpDir, "file")
+		require.NoError(t, os.WriteFile(file, nil, 0o0600))
+		require.NoError(t, chgid(file, gid))
+
+		var st Stat_t
+		require.NoError(t, Lstat(file, &st))
+		require.Equal(t, uid, st.Uid)
+		require.Equal(t, gid, st.Gid)
+	})
+}
+
+func chgid(path string, gid uint32) error {
+	// Note: In Chown, -1 is means leave the uid alone
+	return Chown(path, -1, int(gid))
+}