[Libevent-users] Problems with outbound HTTP posts

[Ringel, Rick]

I've recently started a project that includes bi-directional HTTP messaging
to an embedded Ubuntu program (10.4).  Libevent has the perfect feature set
for this project, so I jumped on board, and started the implementation using
2.0.20.  I am a new libevent user.

 

The first phase was accepting inbound HTTP GET messages.  I had no issues
with that, and it seems to be rock solid. J  When I got to the second phase,
which is sending HTTP posts, I started running into all kinds of stability
issues.  When I watch the HTTP activity on Wireshark, I see many cases where
the TCP connection is set up perfectly, but the HTTP message is never sent.
I also see way too many retransmissions, considering this is a loopback IP
address.  I have run the program under Valgrind, and it doesn't report any
issues.   The response handler typically reports 'timeout'.

 

I may see three or four successful transmissions, then things fall apart.  I
occasionally get a callback to the fatal error handler, indicating something
is wrong.  The error is not the same every time, though.  Here is an
example: 

 

    event_del_internal: noting a del on a non-setup event

 

My code is pretty basic, but I am sure I am missing something.  It smells
like a multi-thread issue - the initialization code runs in a different
thread than the app generating the outbound HTTP messages, and in a
different thread than the event loop.

 

 

Initialization:

 

LibEventShell::LibEventShell()

{

    event_set_log_callback(eventLibLog);

    event_set_fatal_callback(eventFatal_cb);

    evthread_use_pthreads();

#pragma message("Debug mode enabled, should be turned off for production")

    event_enable_debug_mode();

}

 

 

    // The following is extracted from a constructor for my HTTP_Transport
class.

 

    LibEventShell();

    eventBase_ = event_base_new();

 

    event_base_priority_init(eventBase_, 1);

    eventHttp_ = evhttp_new(eventBase_);

    evhttp_set_gencb(eventHttp_,requestHandler,(void *)this);

    pDNSServer_ =  evdns_base_new   (eventBase_,1);

 

    serverThread_ = new cHTTPServer(eventBase_);

    serverThread_->detach();

    serverThread_->ThreadWait();

 

 

HTTP Event loop thread:

 

        while (1)

        {

            Thread::sleep(100);

            event_base_dispatch(eventBase_);

        }

 

 

Then, to send a request. I have trimmed it down to the bare minimum. no DNS,
no timeout.  I get the same results either way.

                     

                     //msg and URI are input parms.

 

                      struct evhttp_request *pReq =
evhttp_request_new(responseHandler, (void *)this);

 
evhttp_add_header(evhttp_request_get_output_headers(pReq),"Content-Type",
"text/xml; charset=utf-8");

 
evhttp_add_header(evhttp_request_get_output_headers(pReq),"User-Agent",
endpointIdentifier_.c_str());

             struct evbuffer * pOutBuf =
evhttp_request_get_output_buffer(pReq);

                    evbuffer_add(pOutBuf,msg.c_str(),msg.size());

 

                    pConn_ = evhttp_connection_base_new (eventBase_,
NULL/*pDNSServer_*/,  "127.0.0.1", 8083);

 
//evhttp_connection_set_local_address(pConn_,"127.0.0.1");

                    //evhttp_connection_set_timeout(pConn_,3);

                    http_result = evhttp_make_request(pConn_, pReq,
EVHTTP_REQ_POST, URI_.c_str());

 

 

 

Does anyone see something obvious here?  

 

 

 

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