MXS-1378 Provide access to current session

Provide access to current session and session id. This will
be used by the logging mechanism for logging the session id
together with messages.

include/maxscale/session.h

@@ -441,4 +441,21 @@ json_t* session_to_json(const MXS_SESSION *session, const char* host);
  */
 json_t* session_list_to_json(const char* host);
 
+/**
+ * @brief Return the session of the dcb currently being processed
+ *        by the calling thread.
+ *
+ * @return A session, or NULL if the calling thread is not currently handling
+ *         a dcb or if the calling thread is not a polling/worker thread.
+ **/
+MXS_SESSION* session_get_current();
+
+/**
+ * @brief Return the id of the session of the dcb currently being processed
+ *        by the calling thread.
+ *
+ * @return The id of the current session or 0 if there is no current session.
+ **/
+uint64_t session_get_current_id();
+
 MXS_END_DECLS

server/core/session.cc

@@ -1177,3 +1177,17 @@ json_t* session_list_to_json(const char* host)
     dcb_foreach(seslist_cb, &data);
     return mxs_json_resource(host, MXS_JSON_API_SESSIONS, data.json);
 }
+
+MXS_SESSION* session_get_current()
+{
+    DCB* dcb = dcb_get_current();
+
+    return dcb ? dcb->session : NULL;
+}
+
+uint64_t session_get_current_id()
+{
+    MXS_SESSION* session = session_get_current();
+
+    return session ? session->ses_id : 0;
+}