blob: 909a8156326735dbfaca50dca573dcf38b8facfa [file] [log] [blame]
// Copyright 2009 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 ioutil implements some I/O utility functions.
package ioutil
import (
// readAll reads from r until an error or EOF and returns the data it read
// from the internal buffer allocated with a specified capacity.
func readAll(r io.Reader, capacity int64) (b []byte, err error) {
buf := bytes.NewBuffer(make([]byte, 0, capacity))
// If the buffer overflows, we will get bytes.ErrTooLarge.
// Return that as an error. Any other panic remains.
defer func() {
e := recover()
if e == nil {
if panicErr, ok := e.(error); ok && panicErr == bytes.ErrTooLarge {
err = panicErr
} else {
_, err = buf.ReadFrom(r)
return buf.Bytes(), err
// ReadAll reads from r until an error or EOF and returns the data it read.
// A successful call returns err == nil, not err == EOF. Because ReadAll is
// defined to read from src until EOF, it does not treat an EOF from Read
// as an error to be reported.
func ReadAll(r io.Reader) ([]byte, error) {
return readAll(r, bytes.MinRead)
// ReadFile reads the file named by filename and returns the contents.
// A successful call returns err == nil, not err == EOF. Because ReadFile
// reads the whole file, it does not treat an EOF from Read as an error
// to be reported.
func ReadFile(filename string) ([]byte, error) {
f, err := os.Open(filename)
if err != nil {
return nil, err
defer f.Close()
// It's a good but not certain bet that FileInfo will tell us exactly how much to
// read, so let's try it but be prepared for the answer to be wrong.
var n int64
if fi, err := f.Stat(); err == nil {
// Don't preallocate a huge buffer, just in case.
if size := fi.Size(); size < 1e9 {
n = size
// As initial capacity for readAll, use n + a little extra in case Size is zero,
// and to avoid another allocation after Read has filled the buffer. The readAll
// call will read into its allocated internal buffer cheaply. If the size was
// wrong, we'll either waste some space off the end or reallocate as needed, but
// in the overwhelmingly common case we'll get it just right.
return readAll(f, n+bytes.MinRead)
// WriteFile writes data to a file named by filename.
// If the file does not exist, WriteFile creates it with permissions perm;
// otherwise WriteFile truncates it before writing.
func WriteFile(filename string, data []byte, perm os.FileMode) error {
f, err := os.OpenFile(filename, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, perm)
if err != nil {
return err
n, err := f.Write(data)
if err == nil && n < len(data) {
err = io.ErrShortWrite
if err1 := f.Close(); err == nil {
err = err1
return err
// byName implements sort.Interface.
type byName []os.FileInfo
func (f byName) Len() int { return len(f) }
func (f byName) Less(i, j int) bool { return f[i].Name() < f[j].Name() }
func (f byName) Swap(i, j int) { f[i], f[j] = f[j], f[i] }
// ReadDir reads the directory named by dirname and returns
// a list of sorted directory entries.
func ReadDir(dirname string) ([]os.FileInfo, error) {
f, err := os.Open(dirname)
if err != nil {
return nil, err
list, err := f.Readdir(-1)
if err != nil {
return nil, err
return list, nil
type nopCloser struct {
func (nopCloser) Close() error { return nil }
// NopCloser returns a ReadCloser with a no-op Close method wrapping
// the provided Reader r.
func NopCloser(r io.Reader) io.ReadCloser {
return nopCloser{r}
type devNull int
// devNull implements ReaderFrom as an optimization so io.Copy to
// ioutil.Discard can avoid doing unnecessary work.
var _ io.ReaderFrom = devNull(0)
func (devNull) Write(p []byte) (int, error) {
return len(p), nil
func (devNull) WriteString(s string) (int, error) {
return len(s), nil
var blackHolePool = sync.Pool{
New: func() interface{} {
b := make([]byte, 8192)
return &b
func (devNull) ReadFrom(r io.Reader) (n int64, err error) {
bufp := blackHolePool.Get().(*[]byte)
readSize := 0
for {
readSize, err = r.Read(*bufp)
n += int64(readSize)
if err != nil {
if err == io.EOF {
return n, nil
// Discard is an io.Writer on which all Write calls succeed
// without doing anything.
var Discard io.Writer = devNull(0)