golang Websocket tutorial: How to develop online music playback function

In today's Internet era, Web applications increasingly require real-time interactive functions, and Websocket is one of this interactive methods. As an efficient programming language, Golang provides a native Websocket support library, making it easier and more efficient to develop real-time interactive applications. In this article, we will introduce how to use Golang to develop an online music playing application. This application makes full use of the real-time data transmission function of Websocket and can enable multiple users to play the same music at the same time. Let us learn together!

1. What is Websocket?

Websocket is part of HTML5 and is a protocol for real-time, two-way communication in web applications. Compared with the traditional HTTP request-response model, Websocket can establish a persistent connection between the client and the server. During the connection process, the client and the server can freely send messages to each other. Typical application scenarios of Websocket include online chat, real-time collaboration, multi-player games, online music playback and other application scenarios that require real-time interaction.

2. Golang’s Websocket library

In Golang, you can use the native Websocket library to develop Websocket applications. This library is located under the "net/http" package and provides a WebSocket structure type through which Websocket clients and servers can be operated. This library also provides three functions, which are used to upgrade the HTTP connection to a Websocket connection, read messages sent by the Websocket client, and send messages to the Websocket client.

3. Develop online music playback function

We are now starting to develop online music playback applications. In this application, we will use Websocket to enable multiple people to play the same music at the same time. The following are the specific implementation steps:

1. Prepare music files

We need to prepare a music file in MP3 format, which will be used as the music source file in our application . We can search online, download a piece of music we like, and then copy it locally. After this file is uploaded to the server, we also need to use the "gonum.org/v1/plot/vg/draw" library in Golang to process it so that it can be read and manipulated by Golang code.

2. Start the Websocket service on the server

First, we need to import the "net/http" package and the "golang.org/x/net/websocket" package. Then, you can use the http.ListenAndServe() function in the http package to start the Websocket service.

package main

import (
    "net/http"
    "golang.org/x/net/websocket"
)

func main() {
    // 在路径"/play"上开启Websocket服务
    http.Handle("/play", websocket.Handler(playHandler))
    http.ListenAndServe(":8080", nil)
}

3. Processing the connection request of the Websocket client

In step 2, we have opened the Websocket service with the path "/play". When the Websocket client requests this path, we need to process the request. We can set a processing function playHandler() for this request.

func playHandler(ws *websocket.Conn) {
    // 读取客户端发送的音乐播放请求
    playReq := make([]byte, 512)
    n, err := ws.Read(playReq)
    if err != nil {
        return
    }
    playReq = playReq[:n]
    playMusic(playReq, ws)
}

In this function, we will use the ws parameter of websocket.Conn type to perform read and write operations on the Websocket client. First, we need to read the music playback request sent by the client. This request will be a byte array. Then, we call the playMusic() function to handle this request and play the music.

4. Play music

In the playMusic() function, we will use the "gonum.org/v1/plot/vg/draw" library in Golang to read and processing music files. This library provides functions that encapsulate music files into Golang slices, allowing us to operate music more conveniently.

func playMusic(playReq []byte, ws *websocket.Conn) {
    // 解析请求，获取要播放的音乐文件名
    filename := string(playReq)
    filename = filename[:strings.Index(filename, "
")]

    // 使用Golang处理获取音乐文件
    musicFile, err := ioutil.ReadFile(filename)
    if err != nil {
        fmt.Fprintf(os.Stderr, "Error: %v
", err)
        return
    }
    musicData, err := mp3.Decode(audioContext, bytes.NewReader(musicFile), len(musicFile))
    if err != nil {
        fmt.Fprintf(os.Stderr, "Error: %v
", err)
        return
    }
    
    // 将播放任务交给一个协程处理
    go func() {
        for {
            // 读取客户端发送的播放位置控制数据
            pos := make([]byte, 8)
            n, err := ws.Read(pos)
            if err != nil {
                // 断开与客户端的连接
                ws.Close()
                break
            }
            pos = pos[:n]

            // 把客户端发送的控制数据转换成时间（秒）
            t := float64(binary.LittleEndian.Uint64(pos)) / float64(SampleRate) + 1.0

            // 每秒播放一次音乐
            time.Sleep(time.Second)

            // 从指定位置开始播放音乐
            musicData.Seek(time.Duration(t)*time.Second, 0)
            buf := make([]byte, 1024)
            // 把音乐数据分帧发送给客户端
            for musicData.Err() == nil {
                n, err := musicData.Read(buf)
                if err != nil {
                    break
                }
                ws.Write(buf[:n])
            }
            // 音乐播放完成后，关闭连接
            ws.Close()
            break
        }
    }()
}

In this function, we first parse the music file name sent by the Websocket client. Then, use the ioutil.ReadFile() function to read the file, and use the mp3.Decode() function to decode the file into music data. After the music data is decoded, we will hand over the music playback task to a coroutine. In this coroutine, we will continuously read the control data sent by the Websocket client and control the position of the music playback based on these data. After the music data is read, we will fragment it into 1024-byte frames and send it to the Websocket client. When the music playback is complete, we will close the connection to the Websocket client.

5. Use Websocket client to play music

Now that we have completed the server-side music playback function, next, we need to write Websocket code on the client to Use this feature. The Websocket client will send the music file name and playback position control data to the server to control the playback position of the music.

func main() {
    // 使用Golang内置的WebSocket库连接服务器
    ws, err := websocket.Dial("ws://127.0.0.1:8080/play", "", "http://127.0.0.1:8080")
    if err != nil {
        log.Fatal(err)
    }
    defer ws.Close()

    // 发送播放请求
    filename := "music.mp3
"
    pos := make([]byte, 8)

    for {
        // 持续发送控制数据
        binary.LittleEndian.PutUint64(pos, uint64(time.Now().UnixNano()))
        ws.Write(pos)

        // 一秒钟发送一次控制数据
        time.Sleep(time.Second)
    }
}

In this code, we first use the websocket.Dial() function to connect to the server. Then, we send the music file name and playback position control data to the server. In this code, we use an infinite loop to continuously send control data. Control data is sent every second to control where the music plays. This loop can continue until we manually stop it.

4. Summary

In this article, we introduce how to use Golang to develop an online music playing application. In this application, the real-time data transmission function of Websocket is fully utilized to support multiple people playing the same music at the same time. As a real-time, two-way communication protocol, Websocket plays an important role in real-time interactive applications. Not only that, as an efficient programming language, Golang also provides many conveniences for the development of Websocket applications. I believe that after reading this article, you have mastered the basic skills of how to use Golang to develop Websocket applications.

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