Problem: assertion causes abort after ZAP stop.

[evoskuil]

The following code hits the zmq_assert (ok); line [with ok false] sometimes during shutdown. So zap_pipe can be non-null and yet the zap_pipe->write can fail. The presence of the assertion implies that the write should never fail - yet there are several conditions which can produce the failure, all of which appear to be normal behavior. Please let me know if I'm missing something here. I'll make a PR to fix it if someone can confirm my assumption about the intended use of assert.

int zmq::session_base_t::write_zap_msg (msg_t *msg_)
{
    if (zap_pipe == NULL) {
        errno = ENOTCONN;
        return -1;
    }

    const bool ok = zap_pipe->write (msg_);
    zmq_assert (ok);

    if ((msg_->flags () & msg_t::more) == 0)
        zap_pipe->flush ();

    const int rc = msg_->init ();
    errno_assert (rc == 0);
    return 0;
}

[evoskuil]

The problem propagates to all of the send_zap_request(...) methods:

void zmq::curve_server_t::send_zap_request (const uint8_t *key)
void zmq::gssapi_server_t::send_zap_request ()
void zmq::null_mechanism_t::send_zap_request ()
void zmq::plain_server_t::send_zap_request (const std::string &username, const std::string &password)

None of these perform error handling:

void zmq::curve_server_t::send_zap_request (const uint8_t *key)
{
    int rc;
    msg_t msg;

    //  Address delimiter frame
    rc = msg.init ();
    errno_assert (rc == 0);
    msg.set_flags (msg_t::more);
    rc = session->write_zap_msg (&msg);
    errno_assert (rc == 0);

    //  Version frame
    rc = msg.init_size (3);
    errno_assert (rc == 0);
    memcpy (msg.data (), "1.0", 3);
    msg.set_flags (msg_t::more);
    rc = session->write_zap_msg (&msg);
    errno_assert (rc == 0);

    //  Request ID frame
    rc = msg.init_size (1);
    errno_assert (rc == 0);
    memcpy (msg.data (), "1", 1);
    msg.set_flags (msg_t::more);
    rc = session->write_zap_msg (&msg);
    errno_assert (rc == 0);

    //  Domain frame
    rc = msg.init_size (options.zap_domain.length ());
    errno_assert (rc == 0);
    memcpy (msg.data (), options.zap_domain.c_str (), options.zap_domain.length ());
    msg.set_flags (msg_t::more);
    rc = session->write_zap_msg (&msg);
    errno_assert (rc == 0);

    //  Address frame
    rc = msg.init_size (peer_address.length ());
    errno_assert (rc == 0);
    memcpy (msg.data (), peer_address.c_str (), peer_address.length ());
    msg.set_flags (msg_t::more);
    rc = session->write_zap_msg (&msg);
    errno_assert (rc == 0);

    //  Identity frame
    rc = msg.init_size (options.identity_size);
    errno_assert (rc == 0);
    memcpy (msg.data (), options.identity, options.identity_size);
    msg.set_flags (msg_t::more);
    rc = session->write_zap_msg (&msg);
    errno_assert (rc == 0);

    //  Mechanism frame
    rc = msg.init_size (5);
    errno_assert (rc == 0);
    memcpy (msg.data (), "CURVE", 5);
    msg.set_flags (msg_t::more);
    rc = session->write_zap_msg (&msg);
    errno_assert (rc == 0);

    //  Credentials frame
    rc = msg.init_size (crypto_box_PUBLICKEYBYTES);
    errno_assert (rc == 0);
    memcpy (msg.data (), key, crypto_box_PUBLICKEYBYTES);
    rc = session->write_zap_msg (&msg);
    errno_assert (rc == 0);
}

And as a result the following method crashes on send_zap_request(...) instead of handling the send error as it handles the the receive error on the next line:

    //  Use ZAP protocol (RFC 27) to authenticate the user.
    rc = session->zap_connect ();
    if (rc == 0) {
        send_zap_request (client_key);
        rc = receive_and_process_zap_reply ();
        if (rc == 0)
            state = status_code == "200"
                ? send_ready
                : send_error;
        else
        if (errno == EAGAIN)
            state = expect_zap_reply;
        else
            return -1;
    }

[evoskuil]

Resolved in #2478