Merge branch '2.3' into 2.4

server/modules/protocol/MySQL/mariadbbackend/mysql_backend.cc

@@ -918,6 +918,9 @@ static int gw_read_and_write(DCB* dcb)
              */
             GWBUF_DATA(read_buffer)[3] = 0x3;
             proto->changing_user = false;
+
+            auto s = (MYSQL_session*)session->client_dcb->data;
+            s->changing_user = false;
         }
     }
 

server/modules/protocol/MySQL/mariadbclient/mysql_client.cc

@@ -1718,7 +1718,15 @@ static int gw_client_hangup_event(DCB* dcb)
                 errmsg += ": " + extra;
             }
 
-            modutil_send_mysql_err_packet(dcb, 0, 0, 1927, "08S01", errmsg.c_str());
+            int seqno = 1;
+
+            if (dcb->data && ((MYSQL_session*)dcb->data)->changing_user)
+            {
+                // In case a COM_CHANGE_USER is in progress, we need to send the error with the seqno 3
+                seqno = 3;
+            }
+
+            modutil_send_mysql_err_packet(dcb, seqno, 0, 1927, "08S01", errmsg.c_str());
         }
         dcb_close(dcb);
     }
@@ -1921,6 +1929,10 @@ static int route_by_statement(MXS_SESSION* session, uint64_t capabilities, GWBUF
 
             if (!proto->changing_user && proto->current_command == MXS_COM_CHANGE_USER)
             {
+                // Track the COM_CHANGE_USER progress at the session level
+                auto s = (MYSQL_session*)session->client_dcb->data;
+                s->changing_user = true;
+
                 changed_user = true;
                 send_auth_switch_request_packet(session->client_dcb);
 

server/modules/protocol/MySQL/mysql_common.cc

@@ -38,7 +38,7 @@ uint8_t null_client_sha1[MYSQL_SCRAMBLE_LEN] = "";
 MYSQL_session* mysql_session_alloc()
 {
     MYSQL_session* ses = (MYSQL_session*)MXS_CALLOC(1, sizeof(MYSQL_session));
-
+    ses->changing_user = false;
     return ses;
 }
 

server/modules/protocol/MySQL/rwbackend.cc

@@ -96,6 +96,14 @@ bool RWBackend::write(GWBUF* buffer, response_type type)
 
     if (mxs_mysql_is_ps_command(cmd))
     {
+        // We need to completely separate the buffer this backend owns and the one that the caller owns to
+        // prevent any modifications from affecting the one that was written through this backend. If the
+        // buffer gets placed into the write queue of the DCB, subsequent modifications to the original buffer
+        // would be propagated to the one this backend owns.
+        GWBUF* tmp = gwbuf_deep_clone(buffer);
+        gwbuf_free(buffer);
+        buffer = tmp;
+
         uint32_t id = mxs_mysql_extract_ps_id(buffer);
         BackendHandleMap::iterator it = m_ps_handles.find(id);
 

server/modules/routing/readwritesplit/rwsplit_route_stmt.cc

@@ -235,12 +235,7 @@ bool RWSplitSession::route_single_stmt(GWBUF* querybuf)
 
     RWBackend* target = nullptr;
 
-    if (command == MXS_COM_STMT_EXECUTE && stmt_id == 0)
-    {
-        // Unknown prepared statement ID
-        succp = send_unknown_ps_error(extract_binary_ps_id(querybuf));
-    }
-    else if (TARGET_IS_ALL(route_target))
+    if (TARGET_IS_ALL(route_target))
     {
         succp = handle_target_is_all(route_target, querybuf, command, qtype);
     }
@@ -282,6 +277,11 @@ bool RWSplitSession::route_single_stmt(GWBUF* querybuf)
             target = m_prev_target;
             succp = true;
         }
+        else if (mxs_mysql_is_ps_command(command) && stmt_id == 0)
+        {
+            // Unknown prepared statement ID
+            succp = send_unknown_ps_error(extract_binary_ps_id(querybuf));
+        }
         else if (TARGET_IS_NAMED_SERVER(route_target) || TARGET_IS_RLAG_MAX(route_target))
         {
             if ((target = handle_hinted_target(querybuf, route_target)))

server/modules/routing/readwritesplit/rwsplitsession.cc

@@ -985,6 +985,18 @@ void RWSplitSession::handleError(GWBUF* errmsgbuf,
     RWBackend* backend = get_backend_from_dcb(problem_dcb);
     mxb_assert(backend->in_use());
 
+    if (backend->reply_has_started())
+    {
+        MXS_ERROR("Server '%s' was lost in the middle of a resultset, cannot continue the session: %s",
+                  backend->name(), extract_error(errmsgbuf).c_str());
+
+        // This effectively causes an instant termination of the client connection and prevents any errors
+        // from being sent to the client (MXS-2562).
+        dcb_close(m_client);
+        *succp = true;
+        return;
+    }
+
     switch (action)
     {
     case ERRACT_NEW_CONNECTION: