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// 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 (
"io"
"io/fs"
"os"
"sort"
)
// 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.
//
// As of Go 1.16, this function simply calls io.ReadAll.
func ReadAll(r io.Reader) ([]byte, error) {
return io.ReadAll(r)
}
// 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.
const minRead = 512
var n int64 = minRead
if fi, err := f.Stat(); err == nil {
// As initial capacity for readAll, use Size + 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.
if size := fi.Size() + minRead; size > n {
n = size
}
}
if int64(int(n)) != n {
n = minRead
}
b := make([]byte, 0, n)
for {
if len(b) == cap(b) {
// Add more capacity (let append pick how much).
b = append(b, 0)[:len(b)]
}
n, err := f.Read(b[len(b):cap(b)])
b = b[:len(b)+n]
if err != nil {
if err == io.EOF {
err = nil
}
return b, err
}
}
}
// WriteFile writes data to a file named by filename.
// If the file does not exist, WriteFile creates it with permissions perm
// (before umask); otherwise WriteFile truncates it before writing, without changing permissions.
func WriteFile(filename string, data []byte, perm fs.FileMode) error {
f, err := os.OpenFile(filename, os.O_WRONLY|os.O_CREATE|os.O_TRUNC, perm)
if err != nil {
return err
}
_, err = f.Write(data)
if err1 := f.Close(); err == nil {
err = err1
}
return err
}
// ReadDir reads the directory named by dirname and returns
// a list of directory entries sorted by filename.
func ReadDir(dirname string) ([]fs.FileInfo, error) {
f, err := os.Open(dirname)
if err != nil {
return nil, err
}
list, err := f.Readdir(-1)
f.Close()
if err != nil {
return nil, err
}
sort.Slice(list, func(i, j int) bool { return list[i].Name() < list[j].Name() })
return list, nil
}
// NopCloser returns a ReadCloser with a no-op Close method wrapping
// the provided Reader r.
//
// As of Go 1.16, this function simply calls io.NopCloser.
func NopCloser(r io.Reader) io.ReadCloser {
return io.NopCloser(r)
}
// Discard is an io.Writer on which all Write calls succeed
// without doing anything.
//
// As of Go 1.16, this value is simply io.Discard.
var Discard io.Writer = io.Discard
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