code: function(params, cb) {
      var correlationId = _cbt.put(fetchResponse(cb));
      var msg = envelope(fech.encode()
                             .correlation(correlationId)
                             .client(_options.clientId)
                             .maxWait(params.maxWait)
                             .minBytes(params.minBytes)
                             .topic(params.topic)
                             .partition(params.partition)
                             .offset(params.offset)
                             .maxBytes(_options.maxBytes)
                             .end());
      sendMsg(msg, correlationId, cb);
    }
docs: write a fetch request to kafka
  
  params:
  topic: the topic to write to
  partition: the partition to write to
  offset: the offset to fetch from
  maxWait: the maximum wait time in ms
  minBytes: the minimum number of bytes that should be available before a response is sent