MXS-2068: Use RWBackend in schemarouter

The schemarouter now uses the RWBackend to track the response states. This
fixes the debug assertions that happened with the mxs1113_schemarouter_ps
test.

include/maxscale/protocol/rwbackend.hh

@@ -47,7 +47,7 @@ public:
     static SRWBackendList from_servers(SERVER_REF* servers);
 
     RWBackend(SERVER_REF* ref);
-    ~RWBackend();
+    virtual ~RWBackend();
 
     inline reply_state_t get_reply_state() const
     {

server/modules/routing/schemarouter/schemarouter.hh

@@ -30,6 +30,7 @@
 #include <maxscale/pcre2.h>
 #include <maxscale/service.h>
 #include <maxscale/backend.hh>
+#include <maxscale/protocol/rwbackend.hh>
 
 namespace schemarouter
 {
@@ -96,12 +97,12 @@ struct Stats
  *
  * Owned by router client session.
  */
-class SRBackend : public mxs::Backend
+class SRBackend : public mxs::RWBackend
 {
 public:
 
     SRBackend(SERVER_REF* ref)
-        : mxs::Backend(ref)
+        : mxs::RWBackend(ref)
         , m_mapped(false)
     {
     }

server/modules/routing/schemarouter/schemaroutersession.cc

@@ -440,7 +440,7 @@ int32_t SchemaRouterSession::routeQuery(GWBUF* pPacket)
             m_load_target = bref->backend()->server;
         }
 
-        MXS_INFO("Route query to \t%s:%d <", bref->backend()->server->address, bref->backend()->server->port);
+        MXS_INFO("Route query to \t%s %s <", bref->name(), bref->uri());
 
         if (bref->has_session_commands())
         {
@@ -459,7 +459,15 @@ int32_t SchemaRouterSession::routeQuery(GWBUF* pPacket)
                 ret = 1;
             }
         }
-        else if (bref->write(pPacket))
+        else
+        {
+            uint8_t cmd = mxs_mysql_get_command(pPacket);
+
+            auto responds = mxs_mysql_command_will_respond(cmd) ?
+                mxs::Backend::EXPECT_RESPONSE :
+                mxs::Backend::NO_RESPONSE;
+
+            if (bref->write(pPacket, responds))
             {
                 /** Add one query response waiter to backend reference */
                 mxb::atomic::add(&m_router->m_stats.n_queries, 1, mxb::atomic::RELAXED);
@@ -468,10 +476,10 @@ int32_t SchemaRouterSession::routeQuery(GWBUF* pPacket)
             }
             else
             {
-            MXS_ERROR("Routing query failed.");
                 gwbuf_free(pPacket);
             }
         }
+    }
 
     return ret;
 }
@@ -510,8 +518,6 @@ void SchemaRouterSession::handle_mapping_reply(SSRBackend& bref, GWBUF** pPacket
 }
 
 void SchemaRouterSession::process_sescmd_response(SSRBackend& bref, GWBUF** ppPacket)
-{
-    if (bref->has_session_commands())
 {
     mxb_assert(GWBUF_IS_COLLECTED_RESULT(*ppPacket));
     uint8_t command = bref->next_session_command()->get_command();
@@ -541,7 +547,6 @@ void SchemaRouterSession::process_sescmd_response(SSRBackend& bref, GWBUF** ppPa
         *ppPacket = NULL;
     }
 }
-}
 
 void SchemaRouterSession::clientReply(GWBUF* pPacket, DCB* pDcb)
 {
@@ -553,13 +558,7 @@ void SchemaRouterSession::clientReply(GWBUF* pPacket, DCB* pDcb)
         return;
     }
 
-    MXS_DEBUG("Reply from [%s] session [%p]"
+    bref->process_reply(pPacket);
-              " mapping [%s] queries queued [%s]",
-              bref->backend()->server->name,
-              m_client->session,
-              m_state & INIT_MAPPING ? "true" : "false",
-              m_queue.size() == 0 ? "none" :
-              m_queue.size() > 0 ? "multiple" : "one");
 
     if (m_state & INIT_MAPPING)
     {
@@ -574,6 +573,9 @@ void SchemaRouterSession::clientReply(GWBUF* pPacket, DCB* pDcb)
         m_current_db = m_connect_db;
         mxb_assert(m_state == INIT_READY);
 
+        gwbuf_free(pPacket);
+        pPacket = NULL;
+
         if (m_queue.size())
         {
             route_queued_query();
@@ -585,23 +587,14 @@ void SchemaRouterSession::clientReply(GWBUF* pPacket, DCB* pDcb)
         mxb_assert(m_state == INIT_READY);
         route_queued_query();
     }
-    else
+    else if (bref->reply_is_complete())
+    {
+        if (bref->has_session_commands())
         {
             process_sescmd_response(bref, &pPacket);
-
-        if (bref->is_waiting_result())
-        {
-            /** Set response status as replied */
-            bref->ack_write();
         }
 
-        if (pPacket)
+        if (bref->has_session_commands() && bref->execute_session_command())
-        {
-            MXS_SESSION_ROUTE_REPLY(pDcb->session, pPacket);
-            pPacket = NULL;
-        }
-
-        if (bref->execute_session_command())
         {
             MXS_INFO("Backend %s:%d processed reply and starts to execute active cursor.",
                      bref->backend()->server->address,
@@ -613,7 +606,10 @@ void SchemaRouterSession::clientReply(GWBUF* pPacket, DCB* pDcb)
         }
     }
 
-    gwbuf_free(pPacket);
+    if (pPacket)
+    {
+        MXS_SESSION_ROUTE_REPLY(pDcb->session, pPacket);
+    }
 }
 
 void SchemaRouterSession::handleError(GWBUF* pMessage,
@@ -1035,7 +1031,6 @@ int SchemaRouterSession::inspect_mapping_states(SSRBackend& bref,
             if (rc == SHOWDB_FULL_RESPONSE)
             {
                 (*it)->set_mapped(true);
-                (*it)->ack_write();
                 MXS_DEBUG("Received SHOW DATABASES reply from %s for session %p",
                           (*it)->backend()->server->name,
                           m_client->session);