c language implementation of ip proxy: complete tutorial for building a local proxy server

Getting a proxy server is not as hard as you think

Recently, many brothers asked how to use C language to build their own proxy server, in fact, this thing it is similar to building blocks. Let's first understand the core principles:A proxy server is just a middleman.. Let's say you ask Zhang San to help you buy milk tea, Zhang San is your proxy. Specifically at the code level, it is to establish two connections - the client connects to our program, and the program goes to connect to the target server.

The core set of C jerk agents

Let's start with a few key points:

// Pseudo-code logic
Create a listening socket → wait for a client connection → parse client request →
connect to the target server → forward data in both directions → close the connection

Here is a pitfall to note, HTTP proxy needs to deal with the CONNECT method, while the SOCKS proxy protocol is a little more complex. Beginners are recommended to start with the HTTP proxy, the amount of code about 200 lines can run up.

Write a basic agent by hand

Here's a skeleton code for socket communication:

int main() {
    int server_fd = socket(AF_INET, SOCK_STREAM, 0);
    struct sockaddr_in address.
    // Bind ports and other general operations...

    while(1) {
        int client_sock = accept(server_fd, (struct sockaddr)&address, &addrlen); // Start a new thread here to handle the connection...
        // Start a new thread here to handle the connection
        pthread_create(&thread_id, NULL, handle_client, (void)&client_sock);
    }
}

void handle_client(void arg) {
    char buffer[1024];
    // Read the client request
    read(client_sock, buffer, sizeof(buffer));

    // Parse the target address and port
    char target_ip = parse_target(buffer);
    int target_port = parse_port(buffer); // Parse the target address and port.

    // Connect to the target server
    int target_sock = connect_target(target_ip, target_port); // Connect to the target server.

    // forward data in both directions
    while(1) {
        // Select is used here to handle duplex communication...
    }
}

Note that this is only the skeleton, the actual to deal with a variety of exceptions. For example, the target server timeout to add timeout, large file transfer to deal with buffers and so on.

How to choose a reliable proxy IP

Proxy programs written by yourself must be used with a quality proxy IP to work. Here are some recommendationsipipgoThe home service has a couple of advantages with their home IP resources:

In particular, their API docking thief convenient, C language integration is just a few lines of code. For example, the interface to get the IP is long like this:

curl -X GET "https://api.ipipgo.com/getip?key=你的密钥&type=http"

Common Rollover Scene QA

Q: The agent program runs unresponsive?
A: First check the firewall settings, then capture packets to see if there is any data flow. Recommended to use Wireshark to capture packets to analyze

Q: I always get connection timeout with dynamic IP?
A: may be the quality of the IP is not good, change ipipgo static residential IP to try, the stability of a number of grades higher!

Q: How can I increase my agent speed?
A: 1. enlarge the socket buffer 2. use non-blocking IO 3. choose the proxy IP of the nearest region

Speak from the heart.

The most troublesome thing about writing your own proxy server is not the code, but the later maintenance; IP is blocked, protocol upgrades, and a lot of other crap. How about using ready-made programs directly, like ipipgo such professional service providers, people have a specialized team to maintain the IP pool, than their own toss to save a lot of heartache. Especially their TK line, do cross-border business of the old iron people with said stable.

Lastly, remember to run the proxy program on the cloud server when testing, the local machine may be restricted by the operator's port. If you don't understand anything, you can go directly to the official website of ipipgo to find technical support, customer service response speed is faster than the delivery boy to deliver food.