how to read some in vibe.d tcpconnection?

[zhmt via Digitalmars-d-learn]

TCPConnecion has a read method, which will block untill the buf 
is fully filled.

This is not what I want.
I want a readSome method, which will return if some data comes 
from remote end, and notify the length of data to me. so I can 
process data in time.

what should I do ?