Problems With Websocket Server in C

Question

I need to use NGINX as a WebSocket Proxy, and I've been able to run this tutorial without any problem. In this case, a simple WebSocket application is done using ws and Node.js. However, I need to substitute the code in javascript (server.js) with an application developed in C.

To do so, I've tried with the last example shown in this tutorial, which is very simple and easy to understand.

However, using the same port and configuration as in server.js, when running the compiled C code, it seems that the communication is not properly established. In this case, when I run wscat in the client's terminal, it seems it is waiting for something since the word 'connected' is never seen, but the communication is not finished either (this is why I say it seems it is waiting for something; in other cases, if I try with a different port, for instance, the communication is closed and it appears a sentence as 'error: unexpected server response').

On the other hand, on the server side, I can see there is a new connection. I suspect that the answer from the server is not arriving at the client, but I don't know why. Nginx is properly configured since the example done in javascript works properly, and I'm using the same ports in both javascript and C (in server.js I have: 'wss = new WebSocketServer({port: 8010});' and in server.c: 'server.sin_port = htons( 8010 );' from my point of view it should work...)

I've tried with other examples in C with a similar behavior. Does anyone know which may be the cause for this? Do you recommend other particular C codes for WebSocket servers?

Answer 1

The answer given by @MustacheMoses is very much to the point (I upvoted) - there's a huge difference between sockets and Websockets.

Websockets is a protocol that starts with an HTTP "upgrade" request and continues with a multiplexed message exchange protocol using a specific data packaging scheme.

Sockets refer to the lower level communication channels (i.e., Stream Sockets, such as TCP/IP sockets or Unix Sockets, or even Raw Sockets).

I would also point out that, much like node.js, websocket libraries / servers in C come in different flavors.

Some libraries provide an almost Web Framework approach (for example, kore.io or my own facil.io micro-framework) and others are more narrow in scope.

Much like node.js packages / servers (which are often written in C or C++), they all differ in performance and features (I would test this before I commit to a specific approach).

As @tadman rightfully pointed out, it might be better to stick with your existing code base and add any C libraries you need using FFI.

It's somewhat rare for high level services, such as web applications, to be authored using a lower level language.

The inverse is also true, it's often less desirable to author the lower level web server using a higher level language.

This is just my humble opinion, but consider that I'm writing this even though I'm the author of a websocket application framework written in C. When the time comes to write an actual production Websocket app, I often prefer to use facil.io as a Ruby C extension and write the app in Ruby (unless Ruby isn't available).

Answer 2

Your problem is that there's a very marked difference between websockets and sockets. Sockets are more low level network interfaces whereas websockets run on a web server of some kind.

I would recommend using a websocket library for C. :) Here's one I found after doing a quick google search. The documentation for said library can be found here as well.