wget implemented by golang

1. Background

wget is a commonly used download tool in Linux systems, which can quickly download files, images and other resources. It has the characteristics of fast download speed, high reliability, and support for resumed downloads. Sometimes we need to use wget in other operating systems, but there is no similar tool.

In order to solve this problem, I tried to use golang to write a simple wget tool called golang-wget. It not only supports basic file downloads, but also supports breakpoint resume downloads, HTTP proxy and other functions.

This article will introduce the implementation principle, code structure and usage of golang-wget.

2. Implementation Principle

The implementation of golang-wget mainly relies on golang’s http package to implement HTTP protocol connection and file download.

The specific implementation principle is as follows:

1. Get command line parameters

Get the url passed in from the command line, save path, and whether through golang's flag package Parameters such as the need to resume the download from a breakpoint and whether to use a proxy.

2. Check whether breakpoint resumption is supported

If the user needs to perform breakpoint resumption, first check whether the target file exists, and if the file exists, obtain the file size. Use HTTP's Range request to get the starting position of the target file, which avoids downloading the entire file. If the file does not exist, the entire file is downloaded starting from 0.

3. Configuring HTTP Client

Use golang's http package to create HTTP Client, and configure HTTP Transport according to whether the user needs to use a proxy. For specific configuration methods, please refer to golang official documentation.

4. Download file

Use the Get, Head, Do and other methods of the http package to obtain the HTTP response, and use the Copy method in the io package to write the response body into the target file. . If you need to resume the transmission from a breakpoint, you need to locate the starting position before writing data.

3. Code Architecture

golang-wget is mainly divided into three parts: command line parameter analysis, HTTP client configuration, and file download.

Command line parameter parsing is implemented using the golang standard library flag, which can quickly parse command line parameters.

HTTP client configuration includes whether to use a proxy and HTTP Client configuration. Using a proxy requires more complex configuration.

File downloading includes checking whether breakpoint resumption is supported and using HTTP Client for file downloading.

The following is the framework of the main code:

func main() {
    // 解析命令行参数
    flag.Parse()

    // 配置HTTP客户端
    client := http.Client{
        Transport: &http.Transport{
            Proxy:      http.ProxyFromEnvironment,
            TLSClientConfig: &tls.Config{InsecureSkipVerify: true},
        },
    }

    // 下载文件
    download(&client, *url, *filePath, *isResume)
}

func download(client *http.Client, url, filePath string, isResume bool) error {
    // 检查是否支持断点续传
    var startPosition int64 = 0
    var err error
    if isResume {
        if isFileExists(filePath) {
            startPosition, err = getFileSize(filePath)
        }
    }

    // 创建HTTP请求
    req, err := http.NewRequest("GET", url, nil)
    if err != nil {
        return err
    }
    if isResume {
        req.Header.Set("Range", fmt.Sprintf("bytes=%d-", startPosition))
    }

    // 开始下载文件或续传文件
    res, err := client.Do(req)
    if err != nil {
        return err
    }
    defer res.Body.Close()

    f, err := os.OpenFile(filePath, os.O_CREATE|os.O_WRONLY, os.ModePerm)
    if err != nil {
        return err
    }
    defer f.Close()

    // 如果需要续传，则先将位置定位到起始位置
    if isResume {
        _, err = f.Seek(startPosition, io.SeekStart)
        if err != nil {
            return err
        }
    }
    _, err = io.Copy(f, res.Body)
    if err != nil {
        return err
    }

    return nil
}

4. Usage method

Using golang-wget is very simple, just enter the corresponding command on the command line.

The command format is as follows:

golang-wget -url=URL -out=FILE_PATH [-resume=true|false] [-proxy=true|false] [-proxyAddr=PROXY_ADDR] [-debug=true|false]

Among them:

-url: Download URL address;

-out: Saved file path;

-resume: Whether to support breakpoint resume (optional, default false);

-proxy: whether to use a proxy (optional, default false);

-proxyAddr: proxy Address (optional, only needs to be set when -proxy=true);

-debug: whether to enable debugging mode (optional, default false).

For example, to download https://golang.org/doc/gopher/pkg.png and save it in the local /tmp/pkg.png file, you can use the following command:

golang-wget -url=https://golang.org/doc/gopher/pkg.png -out=/tmp/pkg.png

If you need to support breakpoint resumption, you can add the -resume=true parameter:

golang-wget -url=https://golang.org/doc/gopher/pkg.png -out=/tmp/pkg.png -resume=true

If you need to download from a proxy server, you can add the -proxy=true and -proxyAddr parameters:

golang-wget -url=https://golang.org/doc/gopher/pkg.png -out=/tmp/pkg.png -proxy=true -proxyAddr=http://proxyserver:port

5. Summary

Through the implementation of golang-wget, we can see that golang’s http package is very powerful and can easily implement HTTP protocol connections and file downloads. Through this example, we can learn how to use golang to implement our own download tool and implement some advanced functions, such as resumable downloads and proxy.

Writing your own download tools can not only increase your own technical implementation capabilities, but also reduce your dependence on other tools and improve efficiency.

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