golang tcp forwarding

Golang TCP Forwarding: Implementation Basics and Application Scenarios

TCP forwarding is a commonly used technology in data transmission. Its main function is to forward the TCP connection request received by the server to other servers for processing, so that Data traffic can be spread across multiple servers, thereby increasing the load capacity of the system. This article will introduce in detail the implementation basis and application scenarios of Golang TCP forwarding.

1. Implementation Basics

Before introducing the implementation basics of Golang TCP forwarding, let’s briefly introduce Golang’s TCP network programming. The Go language provides a set of standard libraries, which contain functions and interfaces related to TCP network programming. Through these functions and interfaces, the Golang TCP forwarding function can be implemented. The following is a simple sample code:

package main

import (
    "fmt"
    "net"
)

func main() {
    ln, err := net.Listen("tcp", ":8080")
    if err != nil {
        fmt.Println(err)
        return
    }
    defer ln.Close()

    for {
        conn, err := ln.Accept()
        if err != nil {
            fmt.Println(err)
            continue
        }
        go handleConnection(conn)
    }
}

func handleConnection(conn net.Conn) {
    defer conn.Close()

    buf := make([]byte, 4096)
    for {
        n, err := conn.Read(buf)
        if err != nil {
            fmt.Println(err)
            return
        }
        fmt.Println(string(buf[:n]))
    }
}

The above code creates a TCP server listening to port 8080 through the net.Listen function, receives the TCP connection request through the ln.Accept function, and then enables goroutine to process the connection. When there is data to read in the connection, the data is read through the conn.Read function and output to the console. Of course, this alone is far from enough to implement the TCP forwarding function. Below we will discuss in detail how to implement the TCP forwarding function.

Golang TCP forwarding can be implemented in the following two ways:

Method 1: Original TCP forwarding

The implementation of original TCP forwarding is very simple, mainly provided through the net package Function implementation, use the net.ListenTCP function with ip specified to create a TCP server that listens to the IP and port, and then receives requests from the client through the AcceptTCP method. Once a request is received, a new TCP connection will be established immediately, and then the data sent by the client will be transparently forwarded to the target server, thus realizing the forwarding of TCP data.

package main

import (
    "fmt"
    "io"
    "net"
)

func main() {
    listener, err := net.ListenTCP("tcp", &net.TCPAddr{
        IP:   net.ParseIP("0.0.0.0"),
        Port: 8888,
    })
    if err != nil {
        panic(err.Error())
    }
    defer listener.Close()

    targetTcpAddr, err := net.ResolveTCPAddr("tcp", "172.16.100.101:80")
    if err != nil {
        panic(err.Error())
    }

    for {
        clientConn, err := listener.AcceptTCP()
        if err != nil {
            fmt.Println(err)
            continue
        }
        go handleConnection(clientConn, targetTcpAddr)
    }
}

func handleConnection(clientConn *net.TCPConn, targetAddr *net.TCPAddr) {
    defer clientConn.Close()

    targetConn, err := net.DialTCP("tcp", nil, targetAddr)
    if err != nil {
        fmt.Println(err)
        return
    }
    defer targetConn.Close()

    io.Copy(targetConn, clientConn)
    io.Copy(clientConn, targetConn)
}

Method 2: TCP forwarding based on HTTP proxy

HTTP proxy is a common network transmission protocol, which can forward the client's request to the target server through the proxy server. Using the proxy idea to implement TCP forwarding is to encapsulate the TCP data packet into an HTTP request, use the HTTP proxy server to forward the request to the target server, and then encapsulate the data returned by the target server into an HTTP response and return it to the client.

package main

import (
    "fmt"
    "io"
    "net"
    "net/http"
)

func main() {
    http.HandleFunc("/", handleRequest)
    http.ListenAndServe(":8080", nil)
}

func handleRequest(w http.ResponseWriter, req *http.Request) {
    if req.Method != "CONNECT" {
        http.Error(w, "Method not allowed", http.StatusMethodNotAllowed)
        return
    }

    targetAddr := req.Host
    targetConn, err := net.Dial("tcp", targetAddr)
    if err != nil {
        fmt.Println(err)
        http.Error(w, "Internal server error", http.StatusInternalServerError)
        return
    }
    defer targetConn.Close()

    w.WriteHeader(http.StatusOK)
    hijacker, ok := w.(http.Hijacker)
    if !ok {
        http.Error(w, "Internal server error", http.StatusInternalServerError)
        return
    }

    clientConn, _, err := hijacker.Hijack()
    if err != nil {
        return
    }
    defer clientConn.Close()

    go func() {
        io.Copy(targetConn, clientConn)
    }()
    io.Copy(clientConn, targetConn)
}

The above code implements a simple HTTP proxy server. When the client connects to the proxy server, the proxy server will parse the address of the target server from the HTTP request header, establish a TCP connection with the target server, and then Establish a TCP connection with the client and forward the client's HTTP request to the target server. When the target server returns data, it also returns the data to the client through an HTTP response.

2. Application Scenarios

TCP forwarding is a very practical network technology and is often used in load balancing, high availability, data acceleration and other scenarios. The following will introduce several scenarios of TCP forwarding in practical applications.

Scenario 1: HTTP Load Balancing

In a website or application, when the number of user requests becomes large, a server often cannot withstand such a large pressure, and TCP is needed at this time. Forwarding technology is used to distribute requests to multiple servers for processing, thereby achieving load balancing. The HTTP protocol is based on the TCP protocol, so you can consider using TCP forwarding in conjunction with the HTTP protocol and implement it using HTTP load balancing.

Scenario 2: Highly available TCP service

In a distributed system, it is often necessary to start programs that provide the same service on multiple servers at the same time to achieve high availability. If the traditional TCP protocol is used, the IP addresses and port numbers of all servers need to be hard-coded in the client program. However, when a server goes down, a new machine needs to be brought online again and the software needs to be redeployed. For large-scale It is very troublesome to apply. Using TCP forwarding technology, you can achieve transparent and highly available TCP services. You only need to connect the client TCP to the forwarding server. The forwarding server forwards the connection request to an available server and returns the data returned by the server to the client. Achieve seamless high availability.

Scenario 3: Accelerated data transmission

TCP transmission is performed in segments. Sending data in segments can greatly increase the data transmission rate. However, the size of TCP data segments is automatically controlled by the underlying protocol stack, which often cannot meet user needs. Through TCP forwarding technology, you can customize the TCP segment size and transparently forward the data to the target server after segmentation, thereby increasing the data transmission rate.

3. Summary

This article introduces in detail the implementation basis and application scenarios of Golang TCP forwarding. Golang TCP forwarding is a very practical network technology that is often used in load balancing, high availability, data acceleration and other scenarios. By understanding TCP forwarding, we can better understand the data transmission mechanism in the network and provide more ideas and solutions for our application and system development.

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