private String blockingRequest(String connectionId, String s) throws Exception {
    selector.poll(1000L, Collections.singletonList(SelectorTest.createSend(connectionId, s)));
    while (true) {
      selector.poll(1000L);
      for (NetworkReceive receive : selector.completedReceives()) {
        if (receive.getConnectionId().equals(connectionId)) {
          ByteBuf payload = receive.getReceivedBytes().content();
          try {
            return SelectorTest.asString(payload);
          } finally {
            payload.release();
          }
        }
      }
    }
  }
Make a request to the echo server and wait for the full response to come.
@param connectionId the ID of an established connection.
@param s the data to send.
@return the data received back from the echo server.
@throws Exception
ambry-network/src/test/java/com/github/ambry/network/SSLSelectorTest.java