Explore how to implement SIP-based communication using Golang

SIP (Session Initiation Protocol) is a communication protocol used to establish, modify and terminate multimedia sessions on IP networks. The Go language (also known as Golang) is a programming language with strong concurrency and simplicity. This article will explore how to use Golang to implement SIP-based communication.

1. Introduction to SIP Protocol

SIP (Session Initiation Protocol) is a text-based protocol that is used to establish, modify and terminate sessions. Conversations can be audio, video, instant messaging, etc. SIP communication is based on the Request-Response Cycle, similar to HTTP. The request message in SIP contains method (such as INVITE, ACK, BYE) and header information, and the response message contains status code and header information.

Commonly used SIP status codes are 100~199 indicating information response, 200~299 indicating successful response, 300~399 indicating redirection response, 400~499 indicating client error response, and 500~599 indicating server error response. .

2. Combination of Golang and SIP

1. UDP/TCP communication

SIP can communicate using UDP or TCP protocol. Due to the high transmission efficiency of UDP, especially for application scenarios with high real-time requirements, SIP usually uses UDP as the transmission protocol. The TCP protocol is mainly used in scenarios where the SIP message transmission is large and cannot be lost.

In Golang, you can use the net package for UDP/TCP communication. The code example is as follows:

package main

import (
    "fmt"
    "net"
)

func main() {
    // UDP通信示例
    udpAddr, _ := net.ResolveUDPAddr("udp", "127.0.0.1:5000")
    conn, _ := net.DialUDP("udp", nil, udpAddr)
    defer conn.Close()
    conn.Write([]byte("hello, world!"))

    // TCP通信示例
    tcpAddr, _ := net.ResolveTCPAddr("tcp", "127.0.0.1:5001")
    conn, _ = net.DialTCP("tcp", nil, tcpAddr)
    defer conn.Close()
    conn.Write([]byte("hello, world!"))
}

2. SIP message parsing

SIP message request It is different from the response message format. Request messages typically contain request lines, headers, and entities, while response messages contain status lines, headers, and entities.

In Golang, you can use the bufio package to read and parse string literals and then convert them into structures. The following is a simple SIP request message parsing example:

package main

import (
    "bufio"
    "bytes"
    "fmt"
    "net"
    "strings"
)

type SIPRequest struct {
    Method  string
    Uri     string
    Version string
    Headers map[string]string
    Body    string
}

func ParseSIPRequest(msg string) *SIPRequest {
    request := &SIPRequest{Headers: make(map[string]string)}

    scanner := bufio.NewScanner(strings.NewReader(msg))
    scanner.Scan() // First line of Request

    // Parse Request line
    requestParts := strings.Split(scanner.Text(), " ")
    request.Method = requestParts[0]
    request.Uri = requestParts[1]
    request.Version = requestParts[2]

    // Parse Headers
    for scanner.Scan() {
        line := scanner.Text()
        if len(line) == 0 {
            break
        }
        headerParts := strings.SplitN(line, ":", 2)
        request.Headers[headerParts[0]] = strings.TrimSpace(headerParts[1])
    }

    // Parse Body (if any)
    if scanner.Scan() {
        request.Body = scanner.Text()
    }

    return request
}

func main() {
    udpAddr, _ := net.ResolveUDPAddr("udp", "127.0.0.1:5000")
    conn, _ := net.DialUDP("udp", nil, udpAddr)
    defer conn.Close()

    message := []byte("INVITE sip:alice@example.com SIP/2.0\r\n" +
        "To: Alice <alice>\r\n" +
        "From: Bob <bob>\r\n" +
        "Call-ID: 1234567890\r\n" +
        "CSeq: 1 INVITE\r\n" +
        "Content-Type: application/sdp\r\n" +
        "\r\n" +
        "v=0\r\n" +
        "o=- 0 0 IN IP4 127.0.0.1\r\n" +
        "s=-\r\n" +
        "c=IN IP4 127.0.0.1\r\n" +
        "t=0 0\r\n" +
        "m=audio 8000 RTP/AVP 0\r\n" +
        "a=rtpmap:0 PCMU/8000\r\n" +
        "\r\n")
    conn.Write(message)

    buffer := make([]byte, 4096)
    n, _ := conn.Read(buffer)

    request := ParseSIPRequest(string(bytes.Trim(buffer[:n], "\x00")))
    fmt.Println(request.Method)
    fmt.Println(request.Body)
}</bob></alice>

3. SIP message generation

Using Golang, SIP messages can be easily generated. The following is an example of a SIP response message:

package main

import (
    "fmt"
    "net"
)

func main() {
    response := []byte("SIP/2.0 200 OK\r\n" +
        "To: Alice <alice>;tag=1234\r\n" +
        "From: Bob <bob>;tag=5678\r\n" +
        "Call-ID: 1234567890\r\n" +
        "CSeq: 1 INVITE\r\n" +
        "Content-Type: application/sdp\r\n" +
        "\r\n" +
        "v=0\r\n" +
        "o=- 0 0 IN IP4 127.0.0.1\r\n" +
        "s=-\r\n" +
        "c=IN IP4 127.0.0.1\r\n" +
        "t=0 0\r\n" +
        "m=audio 8000 RTP/AVP 0\r\n" +
        "a=rtpmap:0 PCMU/8000\r\n" +
        "\r\n")

    udpAddr, _ := net.ResolveUDPAddr("udp", "127.0.0.1:5000")
    conn, _ := net.DialUDP("udp", nil, udpAddr)
    defer conn.Close()
    conn.Write(response)

    fmt.Println("SIP Response sent")
}</bob></alice>

3. Conclusion

The example in this article only shows how to use Golang to implement basic functions in SIP communication. More complex SIP implementations need to consider more details and features. However, using the Go language makes it easier for engineers to implement scalable and performant web applications.

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