MXS-1752: Add prototype concatenation router

The router concatenates multiple result sets.

server/modules/routing/cat/catsession.cc

@@ -0,0 +1,134 @@
+/*
+ * Copyright (c) 2016 MariaDB Corporation Ab
+ *
+ * Use of this software is governed by the Business Source License included
+ * in the LICENSE.TXT file and at www.mariadb.com/bsl11.
+ *
+ * Change Date: 2020-01-01
+ *
+ * On the date above, in accordance with the Business Source License, use
+ * of this software will be governed by version 2 or later of the General
+ * Public License.
+ */
+
+#include "cat.hh"
+#include "catsession.hh"
+#include "maxscale/protocol/mysql.h"
+#include "maxscale/modutil.h"
+
+using namespace maxscale;
+
+CatSession::CatSession(MXS_SESSION* session, Cat* router, SRWBackendList& backends):
+    RouterSession(session),
+    m_session(session),
+    m_backends(backends),
+    m_completed(0)
+{
+}
+
+CatSession::~CatSession()
+{
+}
+
+void CatSession::close()
+{
+}
+
+void CatSession::skip_unused()
+{
+    // Skip unused backends
+    while (m_current != m_backends.end() && !(*m_current)->in_use())
+    {
+        m_current++;
+    }
+}
+
+int32_t CatSession::routeQuery(GWBUF* pPacket)
+{
+    int32_t rval = 0;
+
+    m_completed = 0;
+    m_packet_num = 0;
+    m_query = pPacket;
+    m_current = m_backends.begin();
+
+    // If the first backend is not in use, find one that is
+    skip_unused();
+
+    if (m_current != m_backends.end())
+    {
+        // We have a backend, write the query only to this one. It will be
+        // propagated onwards in clientReply.
+        rval = (*m_current)->write(gwbuf_clone(pPacket));
+        (*m_current)->set_reply_state(REPLY_STATE_START);
+    }
+
+    return rval;
+}
+
+void CatSession::clientReply(GWBUF* pPacket, DCB* pDcb)
+{
+    auto backend = *m_current;
+    ss_dassert(backend->dcb() == pDcb);
+    bool send = false;
+    bool propagate = true;
+
+    if (m_completed == 0 && backend->get_reply_state() == REPLY_STATE_START &&
+        !mxs_mysql_is_result_set(pPacket))
+    {
+        propagate = false;
+    }
+
+    if (backend->reply_is_complete(pPacket))
+    {
+        backend->ack_write();
+        m_completed++;
+        m_current++;
+        skip_unused();
+
+        if (m_current == m_backends.end())
+        {
+            uint8_t eof_packet[] = {0x5, 0x0, 0x0, 0x0, 0xfe, 0x0, 0x0, 0x2, 0x0};
+            gwbuf_free(pPacket);
+            pPacket = gwbuf_alloc_and_load(sizeof(eof_packet), eof_packet);
+            send = true;
+            gwbuf_free(m_query);
+            m_query = NULL;
+        }
+        else if (propagate)
+        {
+            (*m_current)->write(gwbuf_clone(m_query));
+        }
+        else
+        {
+            send = true;
+            gwbuf_free(m_query);
+            m_query = NULL;
+        }
+    }
+
+    if (m_completed == 0)
+    {
+        send = backend->get_reply_state() != REPLY_STATE_DONE;
+    }
+    else if (backend->get_reply_state() == REPLY_STATE_RSET_ROWS &&
+             mxs_mysql_get_command(pPacket) != MYSQL_REPLY_EOF)
+    {
+        send = true;
+    }
+
+    if (send)
+    {
+        GWBUF_DATA(pPacket)[3] = m_packet_num++;
+        MXS_SESSION_ROUTE_REPLY(pDcb->session, pPacket);
+    }
+    else
+    {
+        gwbuf_free(pPacket);
+    }
+}
+
+void CatSession::handleError(GWBUF* pMessage, DCB* pProblem, mxs_error_action_t action, bool* pSuccess)
+{
+    *pSuccess = false;
+}