libzmq/src/proxy.cpp

/*
    Copyright (c) 2007-2014 Contributors as noted in the AUTHORS file

    This file is part of 0MQ.

    0MQ is free software; you can redistribute it and/or modify it under
    the terms of the GNU Lesser General Public License as published by
    the Free Software Foundation; either version 3 of the License, or
    (at your option) any later version.

    0MQ is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU Lesser General Public License for more details.

    You should have received a copy of the GNU Lesser General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.
*/

#include <stddef.h>
#include "poller.hpp"
#include "proxy.hpp"
#include "likely.hpp"

//  On AIX platform, poll.h has to be included first to get consistent
//  definition of pollfd structure (AIX uses 'reqevents' and 'retnevents'
//  instead of 'events' and 'revents' and defines macros to map from POSIX-y
//  names to AIX-specific names).
#if defined ZMQ_POLL_BASED_ON_POLL
#include <poll.h>
#endif

// These headers end up pulling in zmq.h somewhere in their include
// dependency chain
#include "socket_base.hpp"
#include "err.hpp"

// zmq.h must be included *after* poll.h for AIX to build properly
#include "../include/zmq.h"

int capture(
        class zmq::socket_base_t *capture_,
        zmq::msg_t& msg_,
        int more_ = 0)
{
    //  Copy message to capture socket if any
    if (capture_) {
        zmq::msg_t ctrl;
        int rc = ctrl.init ();
        if (unlikely (rc < 0))
            return -1;
        rc = ctrl.copy (msg_);
        if (unlikely (rc < 0))
            return -1;
        rc = capture_->send (&ctrl, more_? ZMQ_SNDMORE: 0);
        if (unlikely (rc < 0))
            return -1;
    }
    return 0;
}

int forward(
        class zmq::socket_base_t *from_,
        class zmq::socket_base_t *to_,
        class zmq::socket_base_t *capture_,
        zmq::msg_t& msg_)
{
    int more;
    size_t moresz;
    while (true) {
        int rc = from_->recv (&msg_, 0);
        if (unlikely (rc < 0))
            return -1;

        moresz = sizeof more;
        rc = from_->getsockopt (ZMQ_RCVMORE, &more, &moresz);
        if (unlikely (rc < 0))
            return -1;

        //  Copy message to capture socket if any
        rc = capture(capture_, msg_, more);
        if (unlikely (rc < 0))
            return -1;

        rc = to_->send (&msg_, more? ZMQ_SNDMORE: 0);
        if (unlikely (rc < 0))
            return -1;
        if (more == 0)
            break;
    }
    return 0;
}

int zmq::proxy (
    class socket_base_t *frontend_,
    class socket_base_t *backend_,
    class socket_base_t *capture_,
    class socket_base_t *control_)
{
    msg_t msg;
    int rc = msg.init ();
    if (rc != 0)
        return -1;

    //  The algorithm below assumes ratio of requests and replies processed
    //  under full load to be 1:1.

    int more;
    size_t moresz;
    zmq_pollitem_t items [] = {
        { frontend_, 0, ZMQ_POLLIN, 0 },
        { backend_, 0, ZMQ_POLLIN, 0 },
        { control_, 0, ZMQ_POLLIN, 0 }
    };
    int qt_poll_items = (control_ ? 3 : 2);

    //  Proxy can be in these three states
    enum {
        active,
        paused,
        terminated
    } state = active;

    while (state != terminated) {
        //  Wait while there are either requests or replies to process.
        rc = zmq_poll (&items [0], qt_poll_items, -1);
        if (unlikely (rc < 0))
            return -1;

        //  Process a control command if any
        if (control_ && items [2].revents & ZMQ_POLLIN) {
            rc = control_->recv (&msg, 0);
            if (unlikely (rc < 0))
                return -1;

            moresz = sizeof more;
            rc = control_->getsockopt (ZMQ_RCVMORE, &more, &moresz);
            if (unlikely (rc < 0) || more)
                return -1;

            //  Copy message to capture socket if any
            rc = capture(capture_, msg);
            if (unlikely (rc < 0))
                return -1;

            if (msg.size () == 5 && memcmp (msg.data (), "PAUSE", 5) == 0)
                state = paused;
            else
            if (msg.size () == 6 && memcmp (msg.data (), "RESUME", 6) == 0)
                state = active;
            else
            if (msg.size () == 9 && memcmp (msg.data (), "TERMINATE", 9) == 0)
                state = terminated;
            else {
                //  This is an API error, we should assert
                puts ("E: invalid command sent to proxy");
                zmq_assert (false);
            }
        }
        //  Process a request
        if (state == active
        &&  items [0].revents & ZMQ_POLLIN) {
            rc = forward(frontend_, backend_, capture_,msg);
            if (unlikely (rc < 0))
                return -1;
        }
        //  Process a reply
        if (state == active
        &&  items [1].revents & ZMQ_POLLIN) {
            rc = forward(backend_, frontend_, capture_,msg);
            if (unlikely (rc < 0))
                return -1;
        }
    }
    return 0;
}