Application-side message processing.

Usage on the router side:

    nxt_app_wmsg_t       wmsg;
    nxt_app_parse_ctx_t  parse_ctx;

    nxt_app_http_req_init(task, &parse_ctx);

    /* parse incoming request data */
    if (nxt_app_http_req_parse(task, &parse_ctx, buf) == NXT_DONE) {

        /* choose app */
        nxt_app = nxt_select_app(... &parse_ctx.r ...);

        /* find port */
        wmsg.port = nxt_get_app_port(... nxt_app ...);
        wmsg.buf = &wmsg.write;

        /* fill write message buffer in shared mem */
        nxt_app->prepare_msg(task, &parse_ctx.r, &wmsg);

        /* send message to app for processing */
        nxt_port_socket_write(task, wmsg.port, NXT_PORT_MSG_DATA,
                              -1, 0, 0, wmsg.write);
    }

src/nxt_runtime.h

@@ -135,6 +135,8 @@ void nxt_cdecl nxt_log_time_handler(nxt_uint_t level, nxt_log_t *log,
 void nxt_stream_connection_init(nxt_task_t *task, void *obj, void *data);
 nxt_int_t nxt_app_start(nxt_task_t *task, nxt_runtime_t *rt);
 
+void nxt_port_app_data_handler(nxt_task_t *task, nxt_port_recv_msg_t *msg);
+
 
 #define nxt_runtime_process_each(rt, process)                                 \
     do {                                                                      \