🕳️ Go TCP Tunneling (Like Ngrok)

A lightweight reverse TCP tunnel server + client in Go — like ngrok
Expose your local services running on localhost to the public internet via a single public server.

✨ Features

• Single binary client and server
• Reverse tunneling with no authentication
• Simple protocol using TCP

📦 Architecture

   ┌────────────┐                      ┌──────────────┐
   │  Client    │     control (7835)   │   Server     │
   │ (localhost)│◀────────────────────▶│ (public VPS) │
   └────┬───────┘                      └────┬─────────┘
        │                                   │
        │  data tunnel (7836)               │
        │◀──────────────────────────────────┤
        │                                   │
   ┌────▼───────┐                     ┌─────▼────────────┐
   │ Local App  │◀─── localhost:5000 ─│ External Request │
   │  (e.g. API)│                     │  (e.g. curl)     │
   └────────────┘                     └──────────────────┘

Key Elements

🔌 Control Connection (:7835)

This connection is used for the initial setup and communication of connection requests.

Client Initiates:

1. The client sends an EXPOSE command followed by the local port they want to expose.

   EXPOSE 5000
   

Server Responds:

1. Upon receiving the EXPOSE command, the server acknowledges with an OK message and provides a publicly accessible port (<publicPort>).

   OK 12345
   

Server Notifies of Incoming Connection:

1. When an external user connects to the <publicPort> on the server, the server sends a CONNECTION message to the client, including a unique connection identifier (<id>).

   CONNECTION abcdef123
   

🔄 Data Tunnel Connection (:7836)

This connection is established to create a tunnel for the actual data transfer.

Client Connects Back:

1. Upon receiving the CONNECTION message, the client establishes a new connection to the server on a different port (:7836).

2. Immediately after connecting, the client sends an ID message containing the <id> received in the CONNECTION message.

   ID abcdef123
   

Server Pipes Connections:

1. The server receives the ID and identifies the waiting user connection associated with that <id>.

2. The server then establishes a direct pipe between the client's Data Tunnel Connection and the waiting user's connection. Any data sent on one connection is directly forwarded to the other, creating a tunnel.

This two-step process allows the server to manage multiple exposed ports and efficiently connect incoming requests to the appropriate client.

📦 Getting Started

Follow these steps to set up and use the TCP tunnel.

---

1. Clone the Repository

git clone https://github.com/your-username/go-tcp-tunnel.git
cd go-tcp-tunnel

2. Run a Local Service (for Testing)

python3 -m http.server 5000

3. Start the Tunnel Server (for Testing)

go run server/main.go

4. Start the Tunnel Client (on Your Local Machine)

go run client/main.go

If successful, you’ll see responses like:

Server response: OK 9090

Server response: CONNECTION 12345

5. Test it

curl http://localhost:9090