Add Stat function to filer.Filer interface (#421)

## Changes

TSIA

## Tests

New integration test passes.

internal/filer_test.go

@@ -68,11 +68,32 @@ func runFilerReadWriteTest(t *testing.T, ctx context.Context, f filer.Filer) {
 	assert.NoError(t, err)
 	filerTest{t, f}.assertContents(ctx, "/foo/bar", `hello universe`)
 
+	// Stat on a directory should succeed.
+	// Note: size and modification time behave differently between WSFS and DBFS.
+	info, err := f.Stat(ctx, "/foo")
+	require.NoError(t, err)
+	assert.Equal(t, "foo", info.Name())
+	assert.True(t, info.Mode().IsDir())
+	assert.Equal(t, true, info.IsDir())
+
+	// Stat on a file should succeed.
+	// Note: size and modification time behave differently between WSFS and DBFS.
+	info, err = f.Stat(ctx, "/foo/bar")
+	require.NoError(t, err)
+	assert.Equal(t, "bar", info.Name())
+	assert.True(t, info.Mode().IsRegular())
+	assert.Equal(t, false, info.IsDir())
+
 	// Delete should fail if the file doesn't exist.
 	err = f.Delete(ctx, "/doesnt_exist")
 	assert.True(t, errors.As(err, &filer.FileDoesNotExistError{}))
 	assert.True(t, errors.Is(err, fs.ErrNotExist))
 
+	// Stat should fail if the file doesn't exist.
+	_, err = f.Stat(ctx, "/doesnt_exist")
+	assert.True(t, errors.As(err, &filer.FileDoesNotExistError{}))
+	assert.True(t, errors.Is(err, fs.ErrNotExist))
+
 	// Delete should succeed for file that does exist.
 	err = f.Delete(ctx, "/foo/bar")
 	assert.NoError(t, err)

libs/filer/dbfs_client.go

@@ -22,11 +22,7 @@ type dbfsDirEntry struct {
 }
 
 func (entry dbfsDirEntry) Type() fs.FileMode {
-	typ := fs.ModePerm
-	if entry.fi.IsDir {
-		typ |= fs.ModeDir
-	}
-	return typ
+	return entry.Mode()
 }
 
 func (entry dbfsDirEntry) Info() (fs.FileInfo, error) {
@@ -47,7 +43,11 @@ func (info dbfsFileInfo) Size() int64 {
 }
 
 func (info dbfsFileInfo) Mode() fs.FileMode {
-	return fs.ModePerm
+	mode := fs.ModePerm
+	if info.fi.IsDir {
+		mode |= fs.ModeDir
+	}
+	return mode
 }
 
 func (info dbfsFileInfo) ModTime() time.Time {
@@ -240,3 +240,29 @@ func (w *DbfsClient) Mkdir(ctx context.Context, name string) error {
 
 	return w.workspaceClient.Dbfs.MkdirsByPath(ctx, dirPath)
 }
+
+func (w *DbfsClient) Stat(ctx context.Context, name string) (fs.FileInfo, error) {
+	absPath, err := w.root.Join(name)
+	if err != nil {
+		return nil, err
+	}
+
+	info, err := w.workspaceClient.Dbfs.GetStatusByPath(ctx, absPath)
+	if err != nil {
+		var aerr *apierr.APIError
+		if !errors.As(err, &aerr) {
+			return nil, err
+		}
+
+		// This API returns a 404 if the file doesn't exist.
+		if aerr.StatusCode == http.StatusNotFound {
+			if aerr.ErrorCode == "RESOURCE_DOES_NOT_EXIST" {
+				return nil, FileDoesNotExistError{absPath}
+			}
+		}
+
+		return nil, err
+	}
+
+	return dbfsFileInfo{*info}, nil
+}

libs/filer/filer.go

@@ -68,4 +68,7 @@ type Filer interface {
 
 	// Creates directory at `path`, creating any intermediate directories as required.
 	Mkdir(ctx context.Context, path string) error
+
+	// Stat returns information about the file at `path`.
+	Stat(ctx context.Context, name string) (fs.FileInfo, error)
 }

libs/filer/workspace_files_client.go

@@ -256,3 +256,26 @@ func (w *WorkspaceFilesClient) Mkdir(ctx context.Context, name string) error {
 		Path: dirPath,
 	})
 }
+
+func (w *WorkspaceFilesClient) Stat(ctx context.Context, name string) (fs.FileInfo, error) {
+	absPath, err := w.root.Join(name)
+	if err != nil {
+		return nil, err
+	}
+
+	info, err := w.workspaceClient.Workspace.GetStatusByPath(ctx, absPath)
+	if err != nil {
+		// If we got an API error we deal with it below.
+		var aerr *apierr.APIError
+		if !errors.As(err, &aerr) {
+			return nil, err
+		}
+
+		// This API returns a 404 if the specified path does not exist.
+		if aerr.StatusCode == http.StatusNotFound {
+			return nil, FileDoesNotExistError{absPath}
+		}
+	}
+
+	return wsfsFileInfo{*info}, nil
+}