api server callback change tag to src; refactor.

lichao

2021-04-20 1f3729698a131b3f701f67adb6a1258aa1235dce

 utest/api_test.cpp

@@ -66,7 +66,7 @@
                const int proc_id_len,
                const void *data,
                const int data_len,
                const void *tag)
                void *src)
{
   // printf("ServerProc: ");
   // DEFER1(printf("\n"););
@@ -76,7 +76,7 @@
      reply.set_data(" reply: " + request.data());
      std::string s(reply.SerializeAsString());
      // printf("%s", reply.data().c_str());
      BHServerCallbackReply(tag, s.data(), s.size());
      BHSendReply(src, s.data(), s.size());
      ++Status().nserved_;
   }
}