需要使用io包的Copy方法

package main
import (
    "fmt"
    "io"
    "os"
)
//自己编写一个函数，接收两个文件路径 srcFileName dstFileName
func CopyFile(dstFileName string, srcFileName string) (written int64, err error) {
    srcFile, err := os.Open(srcFileName)
    if err != nil {
        fmt.Printf("open file err = %v\n", err)
        return
    }
    defer srcFile.Close()
    //打开dstFileName
    dstFile, err := os.OpenFile(dstFileName, os.O_WRONLY | os.O_CREATE, 0755)
    if err != nil {
        fmt.Printf("open file err = %v\n", err)
        return
    }
    defer dstFile.Close()
    return io.Copy(dstFile, srcFile)
}
func main() {
    result, err := CopyFile("./src/main/dst.png", "./src/main/file.png")
    if err == nil {
        fmt.Println("拷贝成功!,拷贝的字节数为: ", result)
    }
}

还可以使用下面的方法

package main
import (
    "bufio"
    "fmt"
    "io"
    "os"
)
//自己编写一个函数，接收两个文件路径 srcFileName dstFileName
func CopyFile(dstFileName string, srcFileName string) (written int64, err error) {
    srcFile, err := os.Open(srcFileName)
    if err != nil {
        fmt.Printf("open file err = %v\n", err)
        return
    }
    defer srcFile.Close()
    //通过srcFile，获取到Reader
    reader := bufio.NewReader(srcFile)
    //打开dstFileName
    dstFile, err := os.OpenFile(dstFileName, os.O_WRONLY | os.O_CREATE, 0666)
    if err != nil {
        fmt.Printf("open file err = %v\n", err)
        return
    }
    writer := bufio.NewWriter(dstFile)
    defer func() {
        writer.Flush() //把缓冲区的内容写入到文件
        dstFile.Close()
    }()
    return io.Copy(writer, reader)
}
func main() {
    result, err := CopyFile("./src/main/dst.png", "./src/main/file.png")
    if err == nil {
        fmt.Println("拷贝成功!拷贝的字节大写为: ", result)
    }
}