Cesanta Mongoose - problems when connecting to localhost

Question

I'm having issues building an HTTP server using the Cesanta Mongoose web server library. The issue that I'm having occurs when I have an HTTP server built to listen on port 8080, and a client sending an HTTP request to localhost:8080. The problem is that the server processes the request fine and sends back a response, but the client only processes and prints the response after I kill the server process . Basically Mongoose works where you create connections which take an event handler function, ev_handler(). This event handler function is called whenever an "event" occurs, such as the receiving of a request or a reply. On the server side, the event handler function is called fine when it receives a request from the client on 8080. However, the client-side event handler function is not called when the response sends the reply, but is called only after the server process is killed. I suspected that this may have something to do with the fact that the connection is on localhost, and I was right - this issue does not occur when the client sends requests to addresses other than localhost. The event handler function is called fine. Here is the ev_handler function on the client-side for reference:

static void ev_handler(struct mg_connection *c, int ev, void *p) {
  if (ev == MG_EV_HTTP_REPLY) {
    struct http_message *hm = (struct http_message *)p;
    c->flags |= MG_F_CLOSE_IMMEDIATELY;
    fwrite(hm->message.p, 1, (int)hm->message.len, stdout);
    putchar('\n');
    exit_flag = 1;
  } else if (ev == MG_EV_CLOSE) {
    exit_flag = 1;
  };
  }

Is this a common issue when trying to establish a connection on localhost with a server on the same computer?

Answer 1

The cause of such behavior is the fact that client connection does not fire an event until all data is read. How client knows the all data is read? There are 3 possibilities:

1. Server has sent Content-Length: XXX header and client has read XXX bytes of the message body, so it knows it received everything.
2. Server has sent Transfer-Encoding: chunked header, and sent all data chunks followed by an empty chunk. When client receives an empty chunk, it knows it received everything.
3. Server set neither Content-Lenth , nor Transfer-Encoding . Client does not know in this case what is the size of the body, and it keeps reading until server closes the connection.

What you see is (3). Solution: set Content-Length in your server code.