Constant DATA_BUFFER 

const DATA_BUFFER: u32 = _; // 4_194_304u32

How many bytes of the client all streams of a connection hold together, before the connection is not read anymore. Without it, a client could make the server hold STREAM_QUEUE frames for each of MAX_STREAMS streams which do not take their data, like the data streams of port forward requests waiting for their error streams. The part which the reader waits to place comes on top.