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从Golang项目中删除已弃用的ioutil包

Go 1.16之前

在Go 1.16以前的版本中，如果我们需要开发文件系统、IO等操作，通常会使用到一个名为io/ioutil的包。

目前很多网络上现存的教程文章，我们能够看到这个包的大量应用场景。

Go 1.16及之后版本

自从到了Go 1.16发布以后，io/ioutil就已经被正式弃用。当然，为了兼容性考虑，我们依旧可以正常调用这个包，只不过当我们调用ioutil里面的方法，最后都是跳转到了io以及os包。

你可以尝试将Go版本升级至1.17以上，然后进入io/ioutil包的源码，就可以看到里面只有两个go文件，ioutil.go和tempfile.go。

附：io/ioutil/ioutil.go源码（Go 1.17+）

// 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.
//
// Deprecated: As of Go 1.16, the same functionality is now provided
// by package io or package os, and those implementations
// should be preferred in new code.
// See the specific function documentation for details.
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.
//
// Deprecated: 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.
//
// Deprecated: As of Go 1.16, this function simply calls os.ReadFile.
func ReadFile(filename string) ([]byte, error) {
	return os.ReadFile(filename)
}

// 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.
//
// Deprecated: As of Go 1.16, this function simply calls os.WriteFile.
func WriteFile(filename string, data []byte, perm fs.FileMode) error {
	return os.WriteFile(filename, data, perm)
}

// ReadDir reads the directory named by dirname and returns
// a list of fs.FileInfo for the directory's contents,
// sorted by filename. If an error occurs reading the directory,
// ReadDir returns no directory entries along with the error.
//
// Deprecated: As of Go 1.16, os.ReadDir is a more efficient and correct choice:
// it returns a list of fs.DirEntry instead of fs.FileInfo,
// and it returns partial results in the case of an error
// midway through reading a directory.
//
// If you must continue obtaining a list of fs.FileInfo, you still can:
//
//	entries, err := os.ReadDir(dirname)
//	if err != nil { ... }
//	infos := make([]fs.FileInfo, 0, len(entries))
//	for _, entry := range entries {
//		info, err := entry.Info()
//		if err != nil { ... }
//		infos = append(infos, info)
//	}
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.
//
// Deprecated: 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.
//
// Deprecated: As of Go 1.16, this value is simply io.Discard.
var Discard io.Writer = io.Discard

Go 1.17之后（Go 1.17+）

从Go 1.17开始，io/ioutil/tempfile.go里面的两个函数TempFile和TempDir改为简单地调用os包

附：io/ioutil/tempfile.go源码

// Copyright 2010 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

import (
	"os"
)

// TempFile creates a new temporary file in the directory dir,
// opens the file for reading and writing, and returns the resulting *os.File.
// The filename is generated by taking pattern and adding a random
// string to the end. If pattern includes a "*", the random string
// replaces the last "*".
// If dir is the empty string, TempFile uses the default directory
// for temporary files (see os.TempDir).
// Multiple programs calling TempFile simultaneously
// will not choose the same file. The caller can use f.Name()
// to find the pathname of the file. It is the caller's responsibility
// to remove the file when no longer needed.
//
// Deprecated: As of Go 1.17, this function simply calls os.CreateTemp.
func TempFile(dir, pattern string) (f *os.File, err error) {
	return os.CreateTemp(dir, pattern)
}

// TempDir creates a new temporary directory in the directory dir.
// The directory name is generated by taking pattern and applying a
// random string to the end. If pattern includes a "*", the random string
// replaces the last "*". TempDir returns the name of the new directory.
// If dir is the empty string, TempDir uses the
// default directory for temporary files (see os.TempDir).
// Multiple programs calling TempDir simultaneously
// will not choose the same directory. It is the caller's responsibility
// to remove the directory when no longer needed.
//
// Deprecated: As of Go 1.17, this function simply calls os.MkdirTemp.
func TempDir(dir, pattern string) (name string, err error) {
	return os.MkdirTemp(dir, pattern)
}

总结

io/ioutil，就像名称中带有 util 的大多数东西一样，已被证明是一个定义不明确且难以理解的东西集合。通常我们不建议在Go项目中使用util作为包名称。

在Go1.16之后，官方已经将ioutil下面的所有函数迁移到io和os下面。我们可以在这两个包下面找到新的函数替代以前的ioutil。

如果我们曾经在项目中使用了io/ioutil包，那么接下来应该开始使用io和os包了。

相关提案：

https://github.com/golang/go/issues/40025

https://github.com/golang/go/issues/42026

参考：https://tehub.com/a/b28Y1oz6AC