Add implementation of filer.Filer for local filesystem (#460)

## Changes

Local file reads on Windows require the file handle to be closed after
using it. This commit includes an interface change to return an
`io.ReadCloser` from `Read` to accommodate this.

## Tests

The existing integration tests for the filer interface all pass.

internal/filer_test.go

@@ -31,6 +31,8 @@ func (f filerTest) assertContents(ctx context.Context, name string, contents str
 		return
 	}
 
+	defer reader.Close()
+
 	var body bytes.Buffer
 	_, err = io.Copy(&body, reader)
 	if !assert.NoError(f, err) {
@@ -309,3 +311,20 @@ func TestAccFilerDbfsReadDir(t *testing.T) {
 	ctx, f := setupFilerDbfsTest(t)
 	runFilerReadDirTest(t, ctx, f)
 }
+
+func setupFilerLocalTest(t *testing.T) (context.Context, filer.Filer) {
+	ctx := context.Background()
+	f, err := filer.NewLocalClient(t.TempDir())
+	require.NoError(t, err)
+	return ctx, f
+}
+
+func TestAccFilerLocalReadWrite(t *testing.T) {
+	ctx, f := setupFilerLocalTest(t)
+	runFilerReadWriteTest(t, ctx, f)
+}
+
+func TestAccFilerLocalReadDir(t *testing.T) {
+	ctx, f := setupFilerLocalTest(t)
+	runFilerReadDirTest(t, ctx, f)
+}

libs/filer/dbfs_client.go

@@ -139,7 +139,7 @@ func (w *DbfsClient) Write(ctx context.Context, name string, reader io.Reader, m
 	return err
 }
 
-func (w *DbfsClient) Read(ctx context.Context, name string) (io.Reader, error) {
+func (w *DbfsClient) Read(ctx context.Context, name string) (io.ReadCloser, error) {
 	absPath, err := w.root.Join(name)
 	if err != nil {
 		return nil, err
@@ -159,7 +159,13 @@ func (w *DbfsClient) Read(ctx context.Context, name string) (io.Reader, error) {
 		return nil, NotAFile{absPath}
 	}
 
-	return w.workspaceClient.Dbfs.Open(ctx, absPath, files.FileModeRead)
+	handle, err := w.workspaceClient.Dbfs.Open(ctx, absPath, files.FileModeRead)
+	if err != nil {
+		return nil, err
+	}
+
+	// A DBFS handle open for reading does not need to be closed.
+	return io.NopCloser(handle), nil
 }
 
 func (w *DbfsClient) Delete(ctx context.Context, name string, mode ...DeleteMode) error {

libs/filer/filer.go

@@ -111,7 +111,7 @@ type Filer interface {
 	Write(ctx context.Context, path string, reader io.Reader, mode ...WriteMode) error
 
 	// Read file at `path`.
-	Read(ctx context.Context, path string) (io.Reader, error)
+	Read(ctx context.Context, path string) (io.ReadCloser, error)
 
 	// Delete file or directory at `path`.
 	Delete(ctx context.Context, path string, mode ...DeleteMode) error

libs/filer/fs_test.go

@@ -70,13 +70,13 @@ func (f *fakeFiler) Write(ctx context.Context, p string, reader io.Reader, mode
 	return fmt.Errorf("not implemented")
 }
 
-func (f *fakeFiler) Read(ctx context.Context, p string) (io.Reader, error) {
+func (f *fakeFiler) Read(ctx context.Context, p string) (io.ReadCloser, error) {
 	_, ok := f.entries[p]
 	if !ok {
 		return nil, fs.ErrNotExist
 	}
 
-	return strings.NewReader("foo"), nil
+	return io.NopCloser(strings.NewReader("foo")), nil
 }
 
 func (f *fakeFiler) Delete(ctx context.Context, p string, mode ...DeleteMode) error {

libs/filer/local_client.go

@@ -0,0 +1,174 @@
+package filer
+
+import (
+	"context"
+	"io"
+	"io/fs"
+	"os"
+	"path/filepath"
+
+	"golang.org/x/exp/slices"
+)
+
+// LocalClient implements the [Filer] interface for the local filesystem.
+type LocalClient struct {
+	// File operations will be relative to this path.
+	root RootPath
+}
+
+func NewLocalClient(root string) (Filer, error) {
+	return &LocalClient{
+		root: NewRootPath(root),
+	}, nil
+}
+
+func (w *LocalClient) Write(ctx context.Context, name string, reader io.Reader, mode ...WriteMode) error {
+	absPath, err := w.root.Join(name)
+	if err != nil {
+		return err
+	}
+
+	flags := os.O_WRONLY | os.O_CREATE
+	if slices.Contains(mode, OverwriteIfExists) {
+		flags |= os.O_TRUNC
+	} else {
+		flags |= os.O_EXCL
+	}
+
+	absPath = filepath.FromSlash(absPath)
+	f, err := os.OpenFile(absPath, flags, 0644)
+	if os.IsNotExist(err) && slices.Contains(mode, CreateParentDirectories) {
+		// Create parent directories if they don't exist.
+		err = os.MkdirAll(filepath.Dir(absPath), 0755)
+		if err != nil {
+			return err
+		}
+		// Try again.
+		f, err = os.OpenFile(absPath, flags, 0644)
+	}
+
+	if err != nil {
+		switch {
+		case os.IsNotExist(err):
+			return NoSuchDirectoryError{path: absPath}
+		case os.IsExist(err):
+			return FileAlreadyExistsError{path: absPath}
+		default:
+			return err
+		}
+	}
+
+	_, err = io.Copy(f, reader)
+	cerr := f.Close()
+	if err == nil {
+		err = cerr
+	}
+
+	return err
+
+}
+
+func (w *LocalClient) Read(ctx context.Context, name string) (io.ReadCloser, error) {
+	absPath, err := w.root.Join(name)
+	if err != nil {
+		return nil, err
+	}
+
+	// This stat call serves two purposes:
+	// 1. Checks file at path exists, and throws an error if it does not
+	// 2. Allows us to error out if the path is a directory
+	absPath = filepath.FromSlash(absPath)
+	stat, err := os.Stat(absPath)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return nil, FileDoesNotExistError{path: absPath}
+		}
+		return nil, err
+	}
+
+	if stat.IsDir() {
+		return nil, NotAFile{path: absPath}
+	}
+
+	return os.Open(absPath)
+}
+
+func (w *LocalClient) Delete(ctx context.Context, name string, mode ...DeleteMode) error {
+	absPath, err := w.root.Join(name)
+	if err != nil {
+		return err
+	}
+
+	// Illegal to delete the root path.
+	if absPath == w.root.rootPath {
+		return CannotDeleteRootError{}
+	}
+
+	absPath = filepath.FromSlash(absPath)
+	err = os.Remove(absPath)
+
+	// Return early on success.
+	if err == nil {
+		return nil
+	}
+
+	if os.IsNotExist(err) {
+		return FileDoesNotExistError{path: absPath}
+	}
+
+	if os.IsExist(err) {
+		if slices.Contains(mode, DeleteRecursively) {
+			return os.RemoveAll(absPath)
+		}
+		return DirectoryNotEmptyError{path: absPath}
+	}
+
+	return err
+}
+
+func (w *LocalClient) ReadDir(ctx context.Context, name string) ([]fs.DirEntry, error) {
+	absPath, err := w.root.Join(name)
+	if err != nil {
+		return nil, err
+	}
+
+	absPath = filepath.FromSlash(absPath)
+	stat, err := os.Stat(absPath)
+	if err != nil {
+		if os.IsNotExist(err) {
+			return nil, NoSuchDirectoryError{path: absPath}
+		}
+		return nil, err
+	}
+
+	if !stat.IsDir() {
+		return nil, NotADirectory{path: absPath}
+	}
+
+	return os.ReadDir(absPath)
+}
+
+func (w *LocalClient) Mkdir(ctx context.Context, name string) error {
+	dirPath, err := w.root.Join(name)
+	if err != nil {
+		return err
+	}
+
+	dirPath = filepath.FromSlash(dirPath)
+	return os.MkdirAll(dirPath, 0755)
+}
+
+func (w *LocalClient) Stat(ctx context.Context, name string) (fs.FileInfo, error) {
+	absPath, err := w.root.Join(name)
+	if err != nil {
+		return nil, err
+	}
+
+	absPath = filepath.FromSlash(absPath)
+	stat, err := os.Stat(absPath)
+	if os.IsNotExist(err) {
+		return nil, FileDoesNotExistError{path: absPath}
+	}
+
+	return stat, err
+}

libs/filer/workspace_files_client.go

@@ -152,7 +152,7 @@ func (w *WorkspaceFilesClient) Write(ctx context.Context, name string, reader io
 	return err
 }
 
-func (w *WorkspaceFilesClient) Read(ctx context.Context, name string) (io.Reader, error) {
+func (w *WorkspaceFilesClient) Read(ctx context.Context, name string) (io.ReadCloser, error) {
 	absPath, err := w.root.Join(name)
 	if err != nil {
 		return nil, err
@@ -184,7 +184,7 @@ func (w *WorkspaceFilesClient) Read(ctx context.Context, name string) (io.Reader
 	if err != nil {
 		return nil, err
 	}
-	return bytes.NewReader(b), nil
+	return io.NopCloser(bytes.NewReader(b)), nil
 }
 
 func (w *WorkspaceFilesClient) Delete(ctx context.Context, name string, mode ...DeleteMode) error {