libwebsocket server

libwebsocket-server.c

#include <stdio.h>
#include <stdlib.h>
#include <libwebsockets.h>
#include <string.h>


static int callback_http(struct libwebsocket_context * this,
                         struct libwebsocket *wsi,
                         enum libwebsocket_callback_reasons reason, void *user,
                         void *in, size_t len)
{
	return 0;
}



static int callback_dumb_increment(struct libwebsocket_context * this,
                                   struct libwebsocket *wsi,
                                   enum libwebsocket_callback_reasons reason,
                                   void *user, void *in, size_t len)
{
    switch (reason) {
        case LWS_CALLBACK_ESTABLISHED: // just log message that someone is connecting
            printf("connection established\n");
            break;
        case LWS_CALLBACK_RECEIVE: { // the funny part
            // create a buffer to hold our response
            // it has to have some pre and post padding. You don't need to care
            // what comes there, libwebsockets will do everything for you. For more info see
            // http://git.warmcat.com/cgi-bin/cgit/libwebsockets/tree/lib/libwebsockets.h#n597
            unsigned char *buf = (unsigned char*) malloc(LWS_SEND_BUFFER_PRE_PADDING + len +
                                                         LWS_SEND_BUFFER_POST_PADDING);
            
            int i;
            
            // pointer to `void *in` holds the incomming request
            // we're just going to put it in reverse order and put it in `buf` with
            // correct offset. `len` holds length of the request.
            for (i=0; i < len; i++) {
                buf[LWS_SEND_BUFFER_PRE_PADDING + (len - 1) - i ] = ((char *) in)[i];
            }
            
            // log what we recieved and what we're going to send as a response.
            // that disco syntax `%.*s` is used to print just a part of our buffer
            // http://stackoverflow.com/questions/5189071/print-part-of-char-array
            printf("received data: %s, replying: %.*s\n", (char *) in, (int) len,
                   buf + LWS_SEND_BUFFER_PRE_PADDING);
            
            // send response
            // just notice that we have to tell where exactly our response starts. That's
            // why there's `buf[LWS_SEND_BUFFER_PRE_PADDING]` and how long it is.
            // we know that our response has the same length as request because
            // it's the same message in reverse order.
            libwebsocket_write(wsi, &buf[LWS_SEND_BUFFER_PRE_PADDING], len, LWS_WRITE_TEXT);
            
            // release memory back into the wild
            free(buf);
            break;
        }
        default:
            break;
    }
    
    return 0;
}



static struct libwebsocket_protocols protocols[] = {
    /* first protocol must always be HTTP handler */
    {
        "http-only",   // name
        callback_http, // callback
        0              // per_session_data_size
    },
    {
        "dumb-increment-protocol", // protocol name - very important!
        callback_dumb_increment,   // callback
        0                          // we don't use any per session data
    },
    {
        NULL, NULL, 0   /* End of list */
    }
};

int main(void) {
    // server url will be http://localhost:9000
    int port = 9000;
    const char *interface = NULL;
    struct libwebsocket_context *context;
    // we're not using ssl
    const char *cert_path = NULL;
    const char *key_path = NULL;
    // no special options
    int opts = 0;

    struct lws_context_creation_info info;
    memset(&info, 0, sizeof(info));
    info.port = port;
    info.iface = interface;
    info.protocols = protocols;
    info.ssl_cert_filepath = cert_path;
    info.ssl_private_key_filepath = key_path;
    info.extensions = libwebsocket_get_internal_extensions();
    info.options = opts;

    context = libwebsocket_create_context(&info);
    // create libwebsocket context representing this server
    // context = libwebsocket_create_context(port, interface, protocols,
    //                                       libwebsocket_get_internal_extensions,
    //                                       cert_path, key_path, -1, -1, opts);
    
    if (context == NULL) {
        fprintf(stderr, "libwebsocket init failed\n");
        return -1;
    }
    
    printf("starting server...\n");
    
    // infinite loop, to end this server send SIGTERM. (CTRL+C)
    while (1) {
        libwebsocket_service(context, 50);
        // libwebsocket_service will process all waiting events with their
        // callback functions and then wait 50 ms.
        // (this is a single threaded webserver and this will keep our server
        // from generating load while there are not requests to process)
    }
    
    libwebsocket_context_destroy(context);
    
    return 0;
}

test-client.html

<!DOCTYPE html>
<html>
    <head>
        <meta charset="utf-8">
        <script src="http://ajax.googleapis.com/ajax/libs/jquery/1.7.2/jquery.min.js"></script>
        <script type="text/javascript">
            $(function() {
                window.WebSocket = window.WebSocket || window.MozWebSocket;
 
                var websocket = new WebSocket('ws://127.0.0.1:9000',
                                              'dumb-increment-protocol');
 
                websocket.onopen = function () {
                    $('h1').css('color', 'green');
                };
 
                websocket.onerror = function () {
                    $('h1').css('color', 'red');
                };
 
                websocket.onmessage = function (message) {
                    console.log(message.data);
                    $('div').append($('<p>', { text: message.data }));
                };
                
 
                $('button').click(function(e) {
                    e.preventDefault();
                    websocket.send($('input').val());
                    $('input').val('');
                });
            });
        </script>
        </head>
    <body>
        <h1>WebSockets test</h1>
        <form>
            <input type="text" />
            <button>Send</button>
        </form>
        <div></div>
    </body>
</html>