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// Copyright 2016 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// Package fs provides a backend-agnostic filesystem layer for storing
// performance results.
package fs
import (
// An FS stores uploaded benchmark data files.
type FS interface {
// NewWriter returns a Writer for a given file name.
// When the Writer is closed, the file will be stored with the
// given metadata and the data written to the writer.
NewWriter(ctx context.Context, name string, metadata map[string]string) (Writer, error)
// A Writer is an io.Writer that can also be closed with an error.
type Writer interface {
// CloseWithError cancels the writing of the file, removing
// any partially written data.
CloseWithError(error) error
// MemFS is an in-memory filesystem implementing the FS interface.
type MemFS struct {
mu sync.Mutex
content map[string]*memFile
// NewMemFS constructs a new, empty MemFS.
func NewMemFS() *MemFS {
return &MemFS{
content: make(map[string]*memFile),
// NewWriter returns a Writer for a given file name. As a side effect,
// it associates the given metadata with the file.
func (fs *MemFS) NewWriter(_ context.Context, name string, metadata map[string]string) (Writer, error) {
meta := make(map[string]string)
for k, v := range metadata {
meta[k] = v
return &memFile{fs: fs, name: name, metadata: meta}, nil
// Files returns the names of the files written to fs.
func (fs *MemFS) Files() []string {
var files []string
for f := range fs.content {
files = append(files, f)
return files
// memFile represents a file in a MemFS. While the file is being
// written, fs points to the filesystem. Close writes the file's
// content to fs and sets fs to nil.
type memFile struct {
fs *MemFS
name string
metadata map[string]string
content []byte
func (f *memFile) Write(p []byte) (int, error) {
f.content = append(f.content, p...)
return len(p), nil
func (f *memFile) Close() error {
if f.fs == nil {
return errors.New("already closed")
f.fs.content[] = f
f.fs = nil
return nil
func (f *memFile) CloseWithError(error) error {
f.fs = nil
return nil