This constant is used in the second parameter of method
swoole_client->recv. It means that the swoole client will not return untill received the data of specified length.
<?php $client->recv(8192, Swoole\Client::MSG_PEEK | Swoole\Client::MSG_WAITALL);
Receive the data in non-blocking mode.
If this constant has been added to the parameter, the recv of client will not change the pointer of recv data and read data from the same offset in next time.
Receive the out-of-band data.