Something wrong in either ruby server or cpp client with json processing

root@610510ab65c8:/thrift/src# test/test.py --server rb --client cpp 
Apache Thrift - Integration Test Suite
Thu Mar 22 00:40:46 2018
===============================================================================
server-client:          protocol:         transport:               result:
rb-cpp                  accel-binary      framed-ip                success
rb-cpp                  accel-binary      buffered-domain          success
rb-cpp                  accel-binary      buffered-ip              success
rb-cpp                  accel-binary      framed-domain            success
rb-cpp                  accel-binary      framed-ip-ssl            success
rb-cpp                  accel-binary      buffered-ip-ssl          success
rb-cpp                  compact           buffered-ip-ssl          success
rb-cpp                  compact           buffered-domain          success
rb-cpp                  compact           framed-ip-ssl            success
rb-cpp                  compact           buffered-ip              success
rb-cpp                  compact           framed-domain            success
rb-cpp                  compact           framed-ip                success
rb-cpp                  binary            buffered-ip              success
rb-cpp                  binary            buffered-domain          success
rb-cpp                  binary            framed-domain            success
rb-cpp                  binary            buffered-ip-ssl          success
rb-cpp                  binary            framed-ip-ssl            success
rb-cpp                  binary            framed-ip                success
rb-cpp                  json              buffered-ip-ssl          failure(timeout)
rb-cpp                  json              buffered-domain          success
rb-cpp                  json              buffered-ip              failure(timeout)
rb-cpp                  json              framed-domain            failure(timeout)
rb-cpp                  json              framed-ip-ssl            failure(timeout)
rb-cpp                  json              framed-ip                failure(timeout)
===============================================================================