MXS-2435 Refactor error message extracting

Access to the error message is needed in different contexts.
Now the extraction code itself can be shared.

server/modules/routing/readwritesplit/readwritesplit.hh

@@ -423,6 +423,44 @@ std::pair<int, int> get_slave_counts(mxs::PRWBackends& backends, mxs::RWBackend*
  */
 void close_all_connections(mxs::PRWBackends& backends);
 
+/**
+ * Extract the SQL state from an error packet.
+ *
+ * @param pBuffer  Pointer to an error packet.
+ * @param ppState  On return will point to the state in @c pBuffer.
+ * @param pnState  On return the pointed to value will be 6.
+ */
+inline void extract_error_state(uint8_t* pBuffer, uint8_t** ppState, uint16_t* pnState)
+{
+    mxb_assert(MYSQL_IS_ERROR_PACKET(pBuffer));
+
+    // The payload starts with a one byte command followed by a two byte error code,
+    // followed by a 1 byte sql state marker and 5 bytes of sql state. In this context
+    // the marker and the state itself are combined.
+    *ppState = pBuffer + MYSQL_HEADER_LEN + 1 + 2;
+    *pnState = 6;
+}
+
+/**
+ * Extract the message from an error packet.
+ *
+ * @param pBuffer    Pointer to an error packet.
+ * @param ppMessage  On return will point to the start of the message in @c pBuffer.
+ * @param pnMessage  On return the pointed to value will be the length of the message.
+ */
+inline void extract_error_message(uint8_t* pBuffer, uint8_t** ppMessage, uint16_t* pnMessage)
+{
+    mxb_assert(MYSQL_IS_ERROR_PACKET(pBuffer));
+
+    int packet_len = MYSQL_HEADER_LEN + MYSQL_GET_PAYLOAD_LEN(pBuffer);
+
+    // The payload starts with a one byte command followed by a two byte error code,
+    // followed by a 1 byte sql state marker and 5 bytes of sql state, followed by
+    // a message until the end of the packet.
+    *ppMessage = pBuffer + MYSQL_HEADER_LEN + 1 + 2 + 1 + 5;
+    *pnMessage = packet_len - MYSQL_HEADER_LEN - 1 - 2 - 1 - 5;
+}
+
 /**
  * Utility function for extracting error messages from buffers
  *

server/modules/routing/readwritesplit/rwsplit_session_cmd.cc

@@ -28,7 +28,6 @@ using namespace maxscale;
  * Functions for session command handling
  */
 
-
 std::string extract_error(GWBUF* buffer)
 {
     std::string rval;
@@ -36,17 +35,20 @@ std::string extract_error(GWBUF* buffer)
     if (MYSQL_IS_ERROR_PACKET(((uint8_t*)GWBUF_DATA(buffer))))
     {
         size_t replylen = MYSQL_GET_PAYLOAD_LEN(GWBUF_DATA(buffer)) + MYSQL_HEADER_LEN;
-        char replybuf[replylen];
+        uint8_t replybuf[replylen];
-        gwbuf_copy_data(buffer, 0, sizeof(replybuf), (uint8_t*)replybuf);
+        gwbuf_copy_data(buffer, 0, sizeof(replybuf), replybuf);
-        std::string err;
+
-        std::string msg;
+        uint8_t* pState;
+        uint16_t nState;
+        extract_error_state(replybuf, &pState, &nState);
+
+        uint8_t* pMessage;
+        uint16_t nMessage;
+        extract_error_message(replybuf, &pMessage, &nMessage);
+
+        std::string err(reinterpret_cast<const char*>(pState), nState);
+        std::string msg(reinterpret_cast<const char*>(pMessage), nMessage);
 
-        /**
-         * The payload starts with a one byte command followed by a two byte error code, a six byte state and
-         * a human-readable string that spans the rest of the packet.
-         */
-        err.append(replybuf + MYSQL_HEADER_LEN + 3, 6);
-        msg.append(replybuf + MYSQL_HEADER_LEN + 3 + 6, replylen - MYSQL_HEADER_LEN - 3 - 6);
         rval = err + ": " + msg;
     }