Problem: ZAP client code is duplicated in all mechanisms

Solution: created a zap_client_t class, extracted first function send_zap_request from curve_server_t

src/zap_client.cpp

@@ -0,0 +1,123 @@
+/*
+    Copyright (c) 2007-2016 Contributors as noted in the AUTHORS file
+
+    This file is part of libzmq, the ZeroMQ core engine in C++.
+
+    libzmq is free software; you can redistribute it and/or modify it under
+    the terms of the GNU Lesser General Public License (LGPL) as published
+    by the Free Software Foundation; either version 3 of the License, or
+    (at your option) any later version.
+
+    As a special exception, the Contributors give you permission to link
+    this library with independent modules to produce an executable,
+    regardless of the license terms of these independent modules, and to
+    copy and distribute the resulting executable under terms of your choice,
+    provided that you also meet, for each linked independent module, the
+    terms and conditions of the license of that module. An independent
+    module is a module which is not derived from or based on this library.
+    If you modify this library, you must extend this exception to your
+    version of the library.
+
+    libzmq 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 "precompiled.hpp"
+
+#include "zap_client.hpp"
+#include "msg.hpp"
+
+namespace zmq
+{
+int zap_client_t::send_zap_request (const char *mechanism,
+                                    size_t mechanism_length,
+                                    const uint8_t *credentials,
+                                    size_t credentials_size)
+{
+    // TODO  I don't think the rc can be -1 anywhere below.
+    // It might only be -1 if the HWM was exceeded, but on the ZAP socket,
+    // the HWM is disabled. They should be changed to zmq_assert (rc == 0);
+    // The method's return type can be changed to void then.
+
+    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);
+    if (rc != 0)
+        return close_and_return (&msg, -1);
+
+    //  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);
+    if (rc != 0)
+        return close_and_return (&msg, -1);
+
+    //  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);
+    if (rc != 0)
+        return close_and_return (&msg, -1);
+
+    //  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);
+    if (rc != 0)
+        return close_and_return (&msg, -1);
+
+    //  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);
+    if (rc != 0)
+        return close_and_return (&msg, -1);
+
+    //  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);
+    if (rc != 0)
+        return close_and_return (&msg, -1);
+
+    //  Mechanism frame
+    rc = msg.init_size (mechanism_length);
+    errno_assert (rc == 0);
+    memcpy (msg.data (), mechanism, mechanism_length);
+    msg.set_flags (msg_t::more);
+    rc = session->write_zap_msg (&msg);
+    if (rc != 0)
+        return close_and_return (&msg, -1);
+
+    //  Credentials frame
+    rc = msg.init_size (credentials_size);
+    errno_assert (rc == 0);
+    memcpy (msg.data (), credentials, credentials_size);
+    rc = session->write_zap_msg (&msg);
+    if (rc != 0)
+        return close_and_return (&msg, -1);
+
+    return 0;
+}
+}