Add fs.FS adapter for the filer interface

libs/filer/fs.go

@@ -0,0 +1,151 @@
+package filer
+
+import (
+	"bytes"
+	"context"
+	"io"
+	"io/fs"
+)
+
+// filerFS implements the fs.FS interface for a filer.
+type filerFS struct {
+	ctx   context.Context
+	filer Filer
+}
+
+// NewFS returns an fs.FS backed by a filer.
+func NewFS(ctx context.Context, filer Filer) fs.FS {
+	return &filerFS{ctx: ctx, filer: filer}
+}
+
+func (fs *filerFS) Open(name string) (fs.File, error) {
+	stat, err := fs.filer.Stat(fs.ctx, name)
+	if err != nil {
+		return nil, err
+	}
+
+	if stat.IsDir() {
+		return &fsDir{fs: fs, name: name, stat: stat}, nil
+	}
+
+	return &fsFile{fs: fs, name: name, stat: stat}, nil
+}
+
+func (fs *filerFS) ReadDir(name string) ([]fs.DirEntry, error) {
+	return fs.filer.ReadDir(fs.ctx, name)
+}
+
+func (fs *filerFS) ReadFile(name string) ([]byte, error) {
+	reader, err := fs.filer.Read(fs.ctx, name)
+	if err != nil {
+		return nil, err
+	}
+
+	var buf bytes.Buffer
+	_, err = io.Copy(&buf, reader)
+	if err != nil {
+		return nil, err
+	}
+
+	return buf.Bytes(), nil
+}
+
+func (fs *filerFS) Stat(name string) (fs.FileInfo, error) {
+	return fs.filer.Stat(fs.ctx, name)
+}
+
+// Type that implements fs.File for a filer-backed fs.FS.
+type fsFile struct {
+	fs   *filerFS
+	name string
+	stat fs.FileInfo
+
+	reader io.Reader
+}
+
+func (f *fsFile) Stat() (fs.FileInfo, error) {
+	return f.stat, nil
+}
+
+func (f *fsFile) Read(buf []byte) (int, error) {
+	if f.reader == nil {
+		reader, err := f.fs.filer.Read(f.fs.ctx, f.name)
+		if err != nil {
+			return 0, err
+		}
+		f.reader = reader
+	}
+
+	return f.reader.Read(buf)
+}
+
+func (f *fsFile) Close() error {
+	if f.reader == nil {
+		return fs.ErrClosed
+	}
+	f.reader = nil
+	return nil
+}
+
+// Type that implements fs.ReadDirFile for a filer-backed fs.FS.
+type fsDir struct {
+	fs   *filerFS
+	name string
+	stat fs.FileInfo
+
+	open    bool
+	entries []fs.DirEntry
+}
+
+func (f *fsDir) Stat() (fs.FileInfo, error) {
+	return f.stat, nil
+}
+
+func (f *fsDir) Read(buf []byte) (int, error) {
+	return 0, fs.ErrInvalid
+}
+
+func (f *fsDir) ReadDir(n int) ([]fs.DirEntry, error) {
+	// Load all directory entries if not already loaded.
+	if !f.open {
+		entries, err := f.fs.ReadDir(f.name)
+		if err != nil {
+			return nil, err
+		}
+		f.open = true
+		f.entries = entries
+	}
+
+	// Return all entries if n <= 0.
+	if n <= 0 {
+		entries := f.entries
+		f.entries = nil
+		return entries, nil
+	}
+
+	// If there are no more entries, return io.EOF.
+	if len(f.entries) == 0 {
+		return nil, io.EOF
+	}
+
+	// If there are less than n entries, return all entries.
+	if len(f.entries) < n {
+		entries := f.entries
+		f.entries = nil
+		return entries, nil
+	}
+
+	// Return n entries.
+	entries := f.entries[:n]
+	f.entries = f.entries[n:]
+	return entries, nil
+}
+
+func (f *fsDir) Close() error {
+	if !f.open {
+		return fs.ErrClosed
+	}
+	f.open = false
+	f.entries = nil
+	return nil
+}