How to change the message IP in golang

With the continuous development of the Internet and the continuous promotion of applications, network security problems have become more and more serious. In order to ensure the security of the network, data transmission during network communication must be effectively protected and encrypted. This process involves the transmission and modification of messages. This article will introduce how to change the message IP in golang.

Golang is a relatively new programming language that is widely welcomed by developers for its efficiency and ease of maintenance. It has a syntax similar to the C language and some modern programming features, such as garbage collection mechanism, concurrent programming and automatic type deduction. It has become more convenient and efficient to process network data and change messages through programs written in Golang. When making message changes, we can use Golang's net package and os package.

Below, we will introduce how to use Golang to change the message IP through a series of code demonstrations, which mainly include the following steps:

1. Create a listening socket and a connection socket
2. Receive and parse the original packet
3. Change the destination port and destination IP address
4. Re-encapsulate the packet and send to the original host

Create Listening socket and connecting socket

Before changing the message, we need to create a listening socket and connecting socket in order to receive and send data. Creating a listening socket is very simple. You only need to call the ListenPacket function in the net package. The code is as follows:

serverAddr, err := net.ResolveUDPAddr("udp", ":" + port)
if err != nil {
    fmt.Printf("ResolveUDPAddr 失败，%v\n", err)
    return
}

conn, err := net.ListenUDP("udp", serverAddr)
if err != nil {
    fmt.Printf("ListenUDP 失败，%v\n", err)
    return
}

defer conn.Close()

In the above code, we first use the ResolveUDPAddr function to encapsulate the port number and protocol type into a UDP address object. Then call the ListenUDP function to create a socket connection of the UDP protocol. Creating a connection socket is equally simple, just use the DialUDP function in the code.

Receive and parse the original data packet

The next step is to receive and parse the original data packet in order to change the destination port and destination IP address. To receive data packets, you can use the ReadFromUDP function, which blocks the program and waits for the arrival of data. When data arrives, the function returns a UDP address object and a byte slice representing the received data.

buffer := make([]byte, 1024)

n, addr, err := conn.ReadFromUDP(buffer)
if err != nil {
    fmt.Printf("ReadFromUDP 失败，%v\n", err)
    return
}

fmt.Printf("从 %s 接收到 %d 字节的数据\n", addr.String(), n)

The process of parsing data packets is relatively complicated. We need to first convert the received data packet into an IP data packet. This can be achieved by calling the ParseIPv4Header and ParseIPv6Header functions in the net package. Which one to choose depends on the protocol used by the data packet. Subsequently, we need to parse the destination port and IP address in the original packet and save them in a new structure. The code is as follows:

ipPacket := &net.IPv4{}
if err := ipPacket.Unmarshal(buffer[:n]); err != nil {
    return
}

// 解析出源IP地址和目标IP地址
srcIP := ipPacket.SrcIP
dstIP := ipPacket.DstIP

// 解析出源端口号和目标端口号
srcPort := binary.BigEndian.Uint16(buffer[n-4:n-2])
dstPort := binary.BigEndian.Uint16(buffer[n-2:n])
fmt.Printf("srcIP: %s, srcPort: %d, dstIP: %s, dstPort: %d\n", srcIP, srcPort, dstIP, dstPort)

Change the target port and target IP address

Next, we need to change the target port and target IP address to the values ​​we want. Here we only modify the target port and IP address. If other fields need to be changed, the code needs to be adjusted accordingly.

dstIP = net.ParseIP("127.0.0.1").To4() // 目标IP地址更改为127.0.0.1
dstPort = 8080 // 目标端口号更改为8080

Re-encapsulate the packet and send it to the original host

The last step, we need to re-encapsulate the changed packet and send it to the original host. What we need to note here is that when re-encapsulating the data packet, we need to pay special attention to the byte order of each field, otherwise it is easy to make errors.

// 构造一个新的IP数据包
newIPPacket := &net.IPv4{
    Version:  4,
    Protocol: ipPacket.Protocol,
    Src:      srcIP,
    Dst:      dstIP,
    TTL:      ipPacket.TTL,
}

// 构造一个新的UDP数据包
newUDPPacket := &net.UDP{
    Src: int(srcPort),
    Dst: int(dstPort),
}

// 将UDP数据包和IP数据包合并
payload := gopacket.Payload(buffer[ipPacket.HeaderLen:])
newPacket := gopacket.NewPacket(payload, layers.LayerTypeUDP, gopacket.Default)

newPacket.TransportLayer().SetNetworkLayerForChecksum(newIPPacket)
newPacket.TransportLayer().SetTransportLayerForChecksum(newUDPPacket)

// 构建新的字节切片
newBytes := make([]byte, 0)
buf := gopacket.NewSerializeBuffer()
err = gopacket.SerializeLayers(buf, gopacket.SerializeOptions{
    FixLengths:       true,
    ComputeChecksums: true,
}, newPacket.Layer(layers.LayerTypeUDP), gopacket.Payload(buf.Bytes()))

if err != nil {
    fmt.Println(err)
    return
}

newBytes = buf.Bytes()

// 发送新的数据包
if _, err := conn.WriteToUDP(newBytes, addr); err != nil {
    return
}

In this example, we use a third-party package gopacket to re-encapsulate the data packet, which can make the construction and parsing of the data packet more convenient and efficient. At the same time, since gopacket supports both IPv4 and IPv6 protocols, we don’t have to worry about the compatibility of protocol types.

Summary

In network communication, data transmission and processing are very important. Writing programs to process network data through Golang can make the program more convenient, reliable and efficient. In this article, we introduce how to use Golang to write a program to change the packet IP address. Through the above steps, we can easily parse, modify and encapsulate the data packet and send it to the target host. Of course, in actual application, we also need to consider many other factors, such as protocol type, network transmission level, etc. At the same time, the modification of data packets also needs to comply with certain laws and regulations and cannot be used for malicious attacks and other bad behaviors.

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