How do I connect to a websocket manually, with netcat/ socat / telnet ?

To manually connect to WebSocket, a tool supporting the WebSocket protocol is typically required. Although netcat, socat, and telnet are primarily used for TCP/IP network communication, they can be employed to simulate communication with a WebSocket server through certain techniques and manual steps.

The following outlines the basic methods and steps for connecting to WebSocket using these tools:

Using socat

socat is a versatile networking tool capable of establishing almost any type of connection. To use socat for connecting to WebSocket, you can forward standard input and output to the WebSocket server. First, you need to know the WebSocket server address, for example, ws://example.com:80/path.

1. WebSocket Handshake Request: WebSocket protocol begins with an HTTP handshake, so first we need to send an appropriate HTTP request to initiate the handshake.

2. Convert WebSocket Address: Convert the ws:// URL to http:// format.

3. Initiate Connection with socat:

   bash
   socat - TCP:example.com:80

4. Send the HTTP WebSocket Handshake Request:

   shell
   GET /path HTTP/1.1
   Host: example.com
   Upgrade: websocket
   Connection: Upgrade
   Sec-WebSocket-Key: x3JJHMbDL1EzLkh9GBhXDw==
   Sec-WebSocket-Version: 13

   This handshake request includes necessary headers such as Upgrade: websocket and Connection: Upgrade.

5. Receive Server Response: If the server accepts the connection, it returns a response confirming the protocol upgrade.

6. Send and Receive Data: Once the handshake is successful, you can send and receive messages using socat. Note that WebSocket uses its own data frame format, so directly sending text messages may not be understood by the server.

Using netcat or telnet

Connecting to WebSocket using netcat or telnet is more challenging because they lack the capability to handle the data frame format within the WebSocket protocol. However, you can still use them to send and receive HTTP data.

1. Initiate TCP Connection:

   • For netcat:

     bash
     nc example.com 80

   • For telnet:

     bash
     telnet example.com 80

2. Manually Input the WebSocket HTTP Handshake Request, as shown above.

3. Observe and Parse the Server Response.

Note

• These methods require manual handling of WebSocket-specific data frames.
• In real-world scenarios, using dedicated WebSocket client libraries (such as the websocket-client library in Python) is more effective because they handle low-level details like the handshake and data frames.

Manual connection to WebSocket is primarily for educational and debugging purposes, to understand the underlying protocol operation. In production environments, it is recommended to use professional tools or libraries that support WebSocket.