Several common ways to copy files in Go language

This article will introduce the three most commonly used methods of copying files in the Go language. Each of these three methods has advantages and disadvantages. We only need to choose the most appropriate one in the application. , there is no need to blindly pursue performance.

Method 1

The first method will use the standard Go library’s <span style="box-sizing: border-box;background-image: initial;background-position: initial;background-size: initial;background-repeat: initial;background-attachment: initial;background-origin: initial;background-clip: initial;display: inline-block;padding-right: 2px;padding-left: 2px;font-size: 14px;">io</span><span style="box-sizing: border-box;background-image: initial;background-position: initial;background-size: initial;background-repeat: initial;background-attachment: initial;background-origin: initial;background-clip: initial;display: inline-block;padding-right: 2px;padding-left: 2px;font-size: 14px;">.</span><span style="box-sizing: border-box;background-image: initial;background-position: initial;background-size: initial;background-repeat: initial;background-attachment: initial;background-origin: initial;background-clip: initial;display: inline-block;padding-right: 2px;padding-left: 2px;font-size: 14px;"> Copy</span><span style="box-sizing: border-box;background-image: initial;background-position: initial;background-size: initial;background-repeat: initial;background-attachment: initial;background-origin: initial;background-clip: initial;display: inline-block;padding-right: 2px;padding-left: 2px;font-size: 14px;">()</span> function. The following is a code snippet for copying files implemented using io.Copy():

func copy(src, dst string) (int64, error) {
        sourceFileStat, err := os.Stat(src)
        if err != nil {
                return 0, err
        }

        if !sourceFileStat.Mode().IsRegular() {
                return 0, fmt.Errorf("%s is not a regular file", src)
        }

        source, err := os.Open(src)
        if err != nil {
                return 0, err
        }
        defer source.Close()

        destination, err := os.Create(dst)
        if err != nil {
                return 0, err
        }
        defer destination.Close()
        nBytes, err := io.Copy(destination, source)
        return nBytes, err
}

Method 2

The second method is to use <span style="box-sizing: border-box;background-image: initial;background-position: initial;background-size: initial;background-repeat: initial;background-attachment: initial;background-origin: initial;background-clip: initial;display: inline-block;padding-right: 2px;padding-left: 2px;font-size: 14px;">ioutil</span><span style="box-sizing: border-box;background-image: initial;background-position: initial;background-size: initial;background-repeat: initial;background-attachment: initial;background-origin: initial;background-clip: initial;display: inline-block;padding-right: 2px;padding-left: 2px;font-size: 14px;">.</span><span style="box-sizing: border-box;background-image: initial;background-position: initial;background-size: initial;background-repeat: initial;background-attachment: initial;background-origin: initial;background-clip: initial;display: inline-block;padding-right: 2px;padding-left: 2px;font-size: 14px;">WriteFile</span><span style="box-sizing: border-box;background-image: initial;background-position: initial;background-size: initial;background-repeat: initial;background-attachment: initial;background-origin: initial;background-clip: initial;display: inline-block;padding-right: 2px;padding-left: 2px;font-size: 14px;">( )</span> and <span style="box-sizing: border-box;background-image: initial;background-position: initial;background-size: initial;background-repeat: initial;background-attachment: initial;background-origin: initial;background-clip: initial;display: inline-block;padding-right: 2px;padding-left: 2px;font-size: 14px;">ioutil</span><span style="box-sizing: border-box;background-image: initial;background-position: initial;background-size: initial;background-repeat: initial;background-attachment: initial;background-origin: initial;background-clip: initial;display: inline-block;padding-right: 2px;padding-left: 2px;font-size: 14px;">.</span><span style="box-sizing: border-box;background-image: initial;background-position: initial;background-size: initial;background-repeat: initial;background-attachment: initial;background-origin: initial;background-clip: initial;display: inline-block;padding-right: 2px;padding-left: 2px;font-size: 14px;">ReadFile</span><span style="box-sizing: border-box;background-image: initial;background-position: initial;background-size: initial;background-repeat: initial;background-attachment: initial;background-origin: initial;background-clip: initial;display: inline-block;padding-right: 2px;padding-left: 2px;font-size: 14px;">()</span>, but due to the use of one-time read Fetch the file and then write it to the file all at once, so this method is not suitable for large files and is prone to memory overflow.

 input, err := ioutil.ReadFile(sourceFile)
        if err != nil {
                fmt.Println(err)
                return
        }

        err = ioutil.WriteFile(destinationFile, input, 0644)
        if err != nil {
                fmt.Println("Error creating", destinationFile)
                fmt.Println(err)
                return
        }

方法三

最后是使用os包中的 <span style="box-sizing: border-box;background-image: initial;background-position: initial;background-size: initial;background-repeat: initial;background-attachment: initial;background-origin: initial;background-clip: initial;display: inline-block;padding-right: 2px;padding-left: 2px;font-size: 14px;">os</span><span style="box-sizing: border-box;background-image: initial;background-position: initial;background-size: initial;background-repeat: initial;background-attachment: initial;background-origin: initial;background-clip: initial;display: inline-block;padding-right: 2px;padding-left: 2px;font-size: 14px;">.</span><span style="box-sizing: border-box;background-image: initial;background-position: initial;background-size: initial;background-repeat: initial;background-attachment: initial;background-origin: initial;background-clip: initial;display: inline-block;padding-right: 2px;padding-left: 2px;font-size: 14px;">Read</span><span style="box-sizing: border-box;background-image: initial;background-position: initial;background-size: initial;background-repeat: initial;background-attachment: initial;background-origin: initial;background-clip: initial;display: inline-block;padding-right: 2px;padding-left: 2px;font-size: 14px;">()</span> 和 <span style="box-sizing: border-box;background-image: initial;background-position: initial;background-size: initial;background-repeat: initial;background-attachment: initial;background-origin: initial;background-clip: initial;display: inline-block;padding-right: 2px;padding-left: 2px;font-size: 14px;">os</span><span style="box-sizing: border-box;background-image: initial;background-position: initial;background-size: initial;background-repeat: initial;background-attachment: initial;background-origin: initial;background-clip: initial;display: inline-block;padding-right: 2px;padding-left: 2px;font-size: 14px;">.</span><span style="box-sizing: border-box;background-image: initial;background-position: initial;background-size: initial;background-repeat: initial;background-attachment: initial;background-origin: initial;background-clip: initial;display: inline-block;padding-right: 2px;padding-left: 2px;font-size: 14px;">Write</span><span style="box-sizing: border-box;background-image: initial;background-position: initial;background-size: initial;background-repeat: initial;background-attachment: initial;background-origin: initial;background-clip: initial;display: inline-block;padding-right: 2px;padding-left: 2px;font-size: 14px;">()</span>，此方法是按块读取文件，块的大小也会影响到程序的性能。

  buf := make([]byte, BUFFERSIZE)
        for {
                n, err := source.Read(buf)
                if err != nil && err != io.EOF {
                        return err
                }
                if n == 0 {
                        break
                }

                if _, err := destination.Write(buf[:n]); err != nil {
                        return err
                }
        }

性能

这三种方式都能很方便的实现拷贝文件功能，那他们的性能如何呢，下面我们来尝试对比一下。三种方式都来拷贝同一个500M的文件，

以下是拷贝文件的时间明细（ <span style="box-sizing: border-box;background-image: initial;background-position: initial;background-size: initial;background-repeat: initial;background-attachment: initial;background-origin: initial;background-clip: initial;display: inline-block;padding-right: 2px;padding-left: 2px;font-size: 14px;">cp1</span><span style="box-sizing: border-box;background-image: initial;background-position: initial;background-size: initial;background-repeat: initial;background-attachment: initial;background-origin: initial;background-clip: initial;display: inline-block;padding-right: 2px;padding-left: 2px;font-size: 14px;">.</span><span style="box-sizing: border-box;background-image: initial;background-position: initial;background-size: initial;background-repeat: initial;background-attachment: initial;background-origin: initial;background-clip: initial;display: inline-block;padding-right: 2px;padding-left: 2px;font-size: 14px;">go</span>是第一种方式， <span style="box-sizing: border-box;background-image: initial;background-position: initial;background-size: initial;background-repeat: initial;background-attachment: initial;background-origin: initial;background-clip: initial;display: inline-block;padding-right: 2px;padding-left: 2px;font-size: 14px;">cp2</span><span style="box-sizing: border-box;background-image: initial;background-position: initial;background-size: initial;background-repeat: initial;background-attachment: initial;background-origin: initial;background-clip: initial;display: inline-block;padding-right: 2px;padding-left: 2px;font-size: 14px;">.</span><span style="box-sizing: border-box;background-image: initial;background-position: initial;background-size: initial;background-repeat: initial;background-attachment: initial;background-origin: initial;background-clip: initial;display: inline-block;padding-right: 2px;padding-left: 2px;font-size: 14px;">go</span>是第二种方式， <span style="box-sizing: border-box;background-image: initial;background-position: initial;background-size: initial;background-repeat: initial;background-attachment: initial;background-origin: initial;background-clip: initial;display: inline-block;padding-right: 2px;padding-left: 2px;font-size: 14px;">cp3</span><span style="box-sizing: border-box;background-image: initial;background-position: initial;background-size: initial;background-repeat: initial;background-attachment: initial;background-origin: initial;background-clip: initial;display: inline-block;padding-right: 2px;padding-left: 2px;font-size: 14px;">.</span><span style="box-sizing: border-box;background-image: initial;background-position: initial;background-size: initial;background-repeat: initial;background-attachment: initial;background-origin: initial;background-clip: initial;display: inline-block;padding-right: 2px;padding-left: 2px;font-size: 14px;">go</span>是第三种方式）

$ ls -l INPUT
-rw-r--r--  1 mtsouk  staff  512000000 Jun  5 09:39 INPUT
$ time go run cp1.go INPUT /tmp/cp1
Copied 512000000 bytes!

real    0m0.980s
user    0m0.219s
sys     0m0.719s
$ time go run cp2.go INPUT /tmp/cp2

real    0m1.139s
user    0m0.196s
sys     0m0.654s
$ time go run cp3.go INPUT /tmp/cp3 1000000
Copying INPUT to /tmp/cp3

real    0m1.025s
user    0m0.195s
sys     0m0.486s

从以上数据来看3种方式的性能非常接近，但依然可以看出Go的io标准包的性能更优。

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