MXS-1861 Detect and handle multistatement responses

Multi-statement SELECTs were properly detected and handled,
but e.g. multi-statement UPDATESs were not, with the result
that erronous warnings were logged.

Now the responses are detected and handled properly.

server/modules/filter/masking/maskingfiltersession.cc

@@ -131,7 +131,21 @@ void MaskingFilterSession::handle_response(GWBUF* pPacket)
     switch (response.type())
     {
     case ComResponse::OK_PACKET:
-    // We'll end up here also in the case of a multi-result.
+        {
+            ComOK ok(response);
+
+            if (ok.status() & SERVER_MORE_RESULTS_EXIST)
+            {
+                m_res.reset_multi();
+                m_state = EXPECTING_RESPONSE;
+            }
+            else
+            {
+                m_state = EXPECTING_NOTHING;
+            }
+        }
+        break;
+
     case ComResponse::LOCAL_INFILE_PACKET: // GET_MORE_CLIENT_DATA/SEND_MORE_CLIENT_DATA
         m_state = EXPECTING_NOTHING;
         break;

server/modules/filter/masking/mysql.hh

@@ -658,6 +658,65 @@ private:
     uint16_t m_status;
 };
 
+class ComOK : public ComResponse
+{
+public:
+    ComOK(GWBUF* pPacket)
+        : ComResponse(pPacket)
+    {
+        ss_dassert(m_type == OK_PACKET);
+
+        extract_payload();
+    }
+
+    ComOK(const ComResponse& response)
+        : ComResponse(response)
+    {
+        ss_dassert(m_type == OK_PACKET);
+
+        extract_payload();
+    }
+
+    uint64_t affected_rows() const
+    {
+        return m_affected_rows;
+    }
+
+    uint64_t last_insert_id() const
+    {
+        return m_last_insert_id;
+    }
+
+    uint16_t warnings() const
+    {
+        return m_warnings;
+    }
+
+    uint16_t status() const
+    {
+        return m_status;
+    }
+
+private:
+    void extract_payload()
+    {
+        m_affected_rows = LEncInt(&m_pData).value();
+        m_last_insert_id = LEncInt(&m_pData).value();
+
+        m_status = *m_pData++;
+        m_status += (*m_pData++ << 8);
+
+        m_warnings = *m_pData++;
+        m_warnings += (*m_pData++ << 8);
+    }
+
+private:
+    uint64_t m_affected_rows;
+    uint64_t m_last_insert_id;
+    uint16_t m_status;
+    uint16_t m_warnings;
+};
+
 /**
  * @class ComRequest
  *