This content originally appeared on DEV Community and was authored by Avinash Tare
You might be curious about how proxy servers work and how they serve data over the internet. In this blog, I am going to implement a proxy server using core NodeJs.I achieved this using a core NodeJs package called net which already comes with NodeJs.
How Proxy Works
a proxy server is an agent between the client and the server. When a
client sends a request to a server it is forwarded to a target proxy
server. The targeted proxy server processes the request and sends it
to the main server and the main server sends the back request to the
proxy server and the proxy server sends the request to the client.
Set up Proxy Server
Before, starting programming you know little about socket and NodeJs.You know what a is socket and how they work.
In NodeJs There are two methods to implement a proxy server. First I custom method and second in-build. Both are easy to understand.
To test your proxy server you can run your local HTTP serve on your local machine and then target the host machine.
- Now, I will define the
netpackage and then write the target server and port number.
const net = require('net');
// Define the target host and port
const targetHost = 'localhost'; // Specify the hostname of the target server. For Ex: (12.568.45.25)
const targetPort = 80; // Specify the port of the target server
- Creating and listening TCP server.
const server = net.createServer((clientSocket) => {
});
// Start listening for incoming connections on the specified port
const proxyPort = 3000; // Specify the port for the proxy server
server.listen(proxyPort, () => {
console.log(`Reverse proxy server is listening on port ${proxyPort}`);
});
- we have created a server using the net package. it's a TCP server which is running port number
3000as we define in using theproxyPortvariable. if the server starts it will show theReverse proxy server is listening on port 3000message on the console. - when the client tries to connect the proxy server it runs the callback function which is inside
createServer. In server function callback we have one parameter
clientSocketit's the user connection that we received for the connection.accept and receive data from the user
const targetHost = 'localhost'; // Specify the hostname of the target server. For Ex: (12.568.45.25)
const targetPort = 80; // Specify the port of the target server
// Create a TCP server
const server = net.createServer((clientSocket) => {
// Establish a connection to the target host
net.createConnection({host: targetHost, port: targetPort}, () => {
// When data is received from the client, write it to the target server
clientSocket.on("data", (data) => {
targetSocket.write(data);
});
// When data is received from the target server, write it back to the client
targetSocket.on("data", (data) => {
clientSocket.write(data);
});
});
});
- When a client tries to connect proxy server we will create a temporary connection to the server using create
createConnection -
createServerhave 2 arguments- 1st Host where we want to connect in this case we have to connect to our server host which is defined in
targetHostvariable. - 2nd Port where we want to connect in this case we have to connect to our server port which is defined in
targetPortvariable.
- 1st Host where we want to connect in this case we have to connect to our server host which is defined in
- Now, When user send data I will pass this data to server. using this code
clientSocket.on("data", (data) => {
targetSocket.write(data);
});
- Then, the Server sends data I will send this data to the user, using this code
targetSocket.on("data", (data) => {
clientSocket.write(data);
});
- Congratulations! you successfully created your proxy server.
Error Handling
While exploring the functionality of the proxy server is exciting, ensuring reliability requires robust error-handling methods to handle unexpected issues gracefully. To handle those types of errors we have an event called an error. It's very easy to implement.
const server = net.createServer((clientSocket) => {
// Establish a connection to the target host
const targetSocket = net.createConnection({host: targetHost,port: targetPort}, () => {
// Handle errors when connecting to the target server
targetSocket.on('error', (err) => {
console.error('Error connecting to target:', err);
clientSocket.end(); // close connection
});
// Handle errors related to the client socket
clientSocket.on('error', (err) => {
console.error('Client socket error:', err);
targetSocket.end(); // close connection
});
});
});
- when any error occurs we will console the error and then close the connection.
ALL Code
- replace host name and port number according to your preference.
const net = require('net');
// Define the target host and port
const targetHost = 'localhost'; // Specify the hostname of the target server
const targetPort = 80; // Specify the port of the target server
// Create a TCP server
const server = net.createServer((clientSocket) => {
// Establish a connection to the target host
const targetSocket = net.createConnection({
host: targetHost,
port: targetPort
}, () => {
// When data is received from the target server, write it back to the client
targetSocket.on("data", (data) => {
clientSocket.write(data);
});
// When data is received from the client, write it to the target server
clientSocket.on("data", (data) => {
targetSocket.write(data);
});
});
// Handle errors when connecting to the target server
targetSocket.on('error', (err) => {
console.error('Error connecting to target:', err);
clientSocket.end();
});
// Handle errors related to the client socket
clientSocket.on('error', (err) => {
console.error('Client socket error:', err);
targetSocket.end();
});
});
// Start listening for incoming connections on the specified port
const proxyPort = 3000; // Specify the port for the proxy server
server.listen(proxyPort, () => {
console.log(`Reverse proxy server is listening on port ${proxyPort}`);
});
Built Method
To reduce client and server connection complexity we have built-in method pipe.I will replace this syntax
// Handle errors when connecting to the target server
targetSocket.on("data", (data) => {
clientSocket.write(data);
});
// When data is received from the client, write it to the target server
clientSocket.on("data", (data) => {
targetSocket.write(data);
});
Into this syntax
// Pipe data from the client to the target
clientSocket.pipe(targetSocket);
// When data is received from the client, write it to the target server
targetSocket.pipe(clientSocket);
Here is all code
const net = require('net');
// Define the target host and port
const targetHost = 'localhost';
const targetPort = 80;
// Create a TCP server
const server = net.createServer((clientSocket) => {
// Establish a connection to the target host
const targetSocket = net.createConnection({
host: targetHost,
port: targetPort
}, () => {
// Pipe data from the client to the target
clientSocket.pipe(targetSocket);
// Pipe data from the target to the client
targetSocket.pipe(clientSocket);
});
// Handle errors
targetSocket.on('error', (err) => {
console.error('Error connecting to target:', err);
clientSocket.end();
});
clientSocket.on('error', (err) => {
console.error('Client socket error:', err);
targetSocket.end();
});
});
// Start listening for incoming connections
const proxyPort = 3000;
server.listen(proxyPort, () => {
console.log(`Reverse proxy server is listening on port ${proxyPort}`);
});
A Working Proxy Server!
Follow Me On GitHub avinashtare, Thanks.
This content originally appeared on DEV Community and was authored by Avinash Tare
Avinash Tare | Sciencx (2024-07-09T21:29:43+00:00) How I Build a Scratch Proxy Server Using Node.js. Retrieved from https://www.scien.cx/2024/07/09/how-i-build-a-scratch-proxy-server-using-node-js/
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