Golang implements file cutting

As the capacity of storage devices continues to increase, more and more data needs to be stored. When processing large files, we often encounter the problem of insufficient memory. At this time, file cutting becomes an effective solution. Today we will discuss how to use golang to implement file cutting.

File cutting refers to cutting a large file into several small files according to a certain size. These small files not only facilitate file transfer and storage, but also improve the efficiency of the program. In golang, file cutting can be easily achieved through the file package.

First of all, we need to understand some basic concepts in the file package:

• File pointer: The file pointer represents a position in the file and is an integer, indicating from the beginning of the file to The number of bytes at this position.
• File information: File information includes the basic attributes of the file, such as file name, file size, creation time, etc.
• File operations: File operations can be divided into read operations and write operations. A read operation refers to reading data from a file, and a write operation refers to writing data to a file.

After having these basic concepts, we can start to implement file cutting. We cut the large files into certain sizes and save the divided small files in the specified directory.

First, we need to introduce the three packages os, bufio and log, and define some constants and variables:

package main

import (
    "bufio"
    "log"
    "os"
)

const (
    bufferSize = 4096   // 缓冲区大小
    maxFileSize = 1024 * 1024 * 1024   // 最大文件大小（1GB）
)

var (
    srcFile string   // 原始文件路径
    dstDir string   // 目标目录路径
    fileNum int   // 文件编号
)

Next, we define a function to cut files, which receives two parameters : The file path and target directory path to be cut.

func splitFile(srcFile, dstDir string) {
    // 打开原始文件
    f, err := os.Open(srcFile)
    if err != nil {
        log.Fatal(err)
    }
    defer f.Close()

    // 获取原始文件信息
    fi, err := f.Stat()
    if err != nil {
        log.Fatal(err)
    }

    // 计算分割后的文件大小和个数
    fileSize := fi.Size()
    fileCount := int(fileSize/maxFileSize) + 1

    // 读取原始文件的缓冲区
    buffer := make([]byte, bufferSize)

    // 创建目标目录
    if _, err := os.Stat(dstDir); os.IsNotExist(err) {
        os.MkdirAll(dstDir, os.ModePerm)
    }

    // 将原始文件分割成多个小文件
    for i := 1; i <= fileCount; i++ {
        fileNum = i
        dstFile := dstDir + "/part_" + strconv.Itoa(i) + ".txt"
        f, err := os.Create(dstFile)
        if err != nil {
            log.Fatal(err)
        }
        writer := bufio.NewWriter(f)
        defer f.Close()

        // 将分割后的文件写入目标文件
        for j := 0; j < maxFileSize/bufferSize; j++ {
            n, err := f.Read(buffer)
            if err != nil {
                log.Fatal(err)
            }
            writer.Write(buffer[:n])
        }
        writer.Flush()
    }
}

In the above function, we first open the original file and obtain the file information. Then, we calculate the size and number of split files based on the set maximum file size. Next, we read the buffer of the original file, create the target directory, and split the original file into several small files.

In the process of dividing the file, we also need to write a function to obtain the file number, which will be used when cutting the file. This function is also very simple. It only needs to read the split files that already exist in the target directory, count the number of files and add 1.

func getFileNum(dstDir string) int {
    files, err := ioutil.ReadDir(dstDir)
    if err != nil {
        log.Fatal(err)
    }
    return len(files) + 1
}

Finally, we write another main function to call the above function to test the actual effect of the program.

func main() {
    srcFile := "bigfile.txt"
    dstDir := "./split"

    splitFile(srcFile, dstDir)

    log.Println("Done!")
}

Save and run the above code, we can see that the cut small files have been saved in the specified directory. In this way, we can easily cope with the processing needs of large files.

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