[Libwebsockets] Re-connection logic for libwebsockets

Hemant Kumar hkumar at arubanetworks.com
Tue Dec 8 20:06:07 CET 2015

Hi Andy

Basically, client thread calls the following function for websocket connection establishment.
For the very first time, or every time I kill the client process and start again , it is able to establish the connection with server.

But if I kill the server instead and make the client do connection retries, for which it calls the following function, it fails.
Stack trace on client end:

[441:1062] NOTICE: Initial logging level 15
[441:1062] NOTICE: Library version: 1.3 unknown-build-hash
[441:1062] NOTICE: IPV6 compiled in and enabled
[441:1062] NOTICE: libev support not compiled in
[441:1063] INFO:  LWS_MAX_HEADER_LEN: 1024
[441:1063] INFO:  LWS_MAX_PROTOCOLS: 5
[441:1063] INFO:  SYSTEM_RANDOM_FILEPATH: '/dev/urandom'
[441:1063] INFO:  LWS_MAX_ZLIB_CONN_BUFFER: 65536
[441:1064] NOTICE:  static allocation: 65912 + (12 x 1024 fds) = 78200 bytes
[441:1065] NOTICE:  canonical_hostname = XXX_Hemant
[441:1065] NOTICE:  per-conn mem: 128 + 1594 headers + protocol rx buf
[441:1137] NOTICE: context created
[441:1139] INFO: insert_wsi_socket_into_fds: wsi=0x51f234, sock=18, fds pos=1
[441:1140] NOTICE: libwebsocket_context_destroy

int amon_sender_websocket_proc(dest_ctxt_t *dcp)
    int n = 0;
    int ret = 0;
    int port = WS_PORT;
    int use_ssl = 0;
    __u32 server_address = 0;
    const char *address;
    struct in_addr serv_ip_addr;

    struct libwebsocket *client_socket;
    int ietf_version = -1; /* latest */
    struct lws_context_creation_info ctxt_info;

    fprintf(stderr, "amon_sender_websocket_proc()...\n");
    fprintf(stderr, "dcp = %p\n", dcp);
    thread_context_t *lws_queue_ctx;
    lws_queue_ctx = (thread_context_t*)malloc(sizeof(thread_context_t));
    memset((void*)lws_queue_ctx, 0, sizeof(thread_context_t));
    /*List of supported protocols*/
    struct libwebsocket_protocols protocols[] = { 
            sizeof(struct per_session_data__sprotocol),
        {   /* end of list */
    syslog(LOG_ERR," mgmt-server transport_type %d\n",dcp->mgmtsrv->transport_type);
    syslog(LOG_ERR," mgmt-server security_type %d\n",dcp->mgmtsrv->security_type);


    //Initialize the context info 
    memset((void *)&ctxt_info, 0, sizeof(ctxt_info)); <<<<<<<<<<,Doing memset of info struct for every time a connection attempt is made.

    //client side websocket do not listens on any port

 ctxt_info.port = CONTEXT_PORT_NO_LISTEN;
    ctxt_info.protocols = protocols;
    ctxt_info.gid = -1;
    ctxt_info.uid = -1;
    if ((dcp->mgmtsrv->transport_type == WEBSOCKET_MODE || dcp->mgmtsrv->transport_type == MIX_MODE)
            && dcp->mgmtsrv->security_type == SECURE_MODE )
        use_ssl = 2;
        syslog(LOG_ERR," use_ssl flag set\n");
    if(use_ssl == 2){
        syslog(LOG_ERR," starting WS-SSL \n");
        ctxt_info.ssl_cert_filepath = CERT_PATH;
        ctxt_info.ssl_private_key_filepath = KEY_PATH;
        ctxt_info.ssl_cert_filepath = NULL;
        ctxt_info.ssl_private_key_filepath = NULL;

    lws_set_log_level(LLL_ERR | LLL_WARN | LLL_NOTICE | LLL_INFO, NULL);

    server_address =  dcp->mgmtsrv->primary_server_ip;
    serv_ip_addr.s_addr = server_address;
    address = inet_ntoa(serv_ip_addr);
    dcp->context = libwebsocket_create_context(&ctxt_info);
    if (dcp->context == NULL) {
        fprintf(stderr, "Creating libwebsocket context failed\n");
        syslog(LOG_ERR," Creating libwebsocket context failed\n");
        return -1;

    lwsl_notice("context created\n");
    //register a signal handler for stopping the client
    signal(SIGINT, sighandler);

    lws_queue_ctx->dcp = dcp;

   //Get client web socket
    client_socket = libwebsocket_client_connect_extended(dcp->context, address, port, use_ssl,
                                                "/", address, address,
                                                protocols[0].name, ietf_version, (void*)(lws_queue_ctx));

    //Use it in sender thread for invoking the callback
    dcp->wsi = client_socket;

    if (client_socket == NULL) {
            fprintf(stderr, "libwebsocket connect failed: %s\n",address);
            syslog(LOG_ERR," libwebsocket connect failed: %s\n",address);
            ret = 1;
            goto bail;
        //lwsl_notice("connected to server..%s user data %d\n",address, *((int*)(client_socket->user_space)));
    syslog(LOG_ERR,"libwebsocket connected: %s",address);
    n = 0;
    while (n >= 0 && !dcp->was_closed && !dcp->force_exit) {
            n = libwebsocket_service(dcp->context, 100000);
            if (n < 0) {
                //continue;  TBD dharani


        fprintf(stderr, "Exiting\n");

        dcp->context = NULL;
        dcp->wsi = NULL;

        return ret;

Any help will be appreciated.


From: Andy Green [andy.green at linaro.org] on behalf of Andy Green [andy at warmcat.com]
Sent: Monday, December 7, 2015 7:52 PM
To: Hemant Kumar; libwebsockets at ml.libwebsockets.org
Subject: Re: [Libwebsockets] Re-connection logic for libwebsockets

On December 8, 2015 11:18:47 AM GMT+08:00, Hemant Kumar <hkumar at arubanetworks.com> wrote:
>I have a working libwebsocket client server and I am trying to
>implement reconnection logic between the two entities.
>Basically, when connectivity to server is down for some reason, client
>keeps on trying libwebsocket_connect with same
>parameters as used for the initial successful connection establishment.
>I do see , client making repeated tries but every time connection
>attempt fails , although server is UP on another end.
>For every failed try, I see libwebsocket_conext_destrory being also
>called, wondering if I am missing anything to clean
>the old context for the re-establishment of connection.

Need more info about where (and / or why) it fails.

However a common mistake is to not memset the info struct to zero before filling it in.

Another way to get 'memory' between sessions is via your protocols struct, try copying it each time into another protocols struct and give that one to lws_client_connect.


>Please advise.
>Libwebsockets mailing list
>Libwebsockets at ml.libwebsockets.org

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