Returns nonzero if new request can be sent from local endpoint.
This function return 0 if request is not allowed for this session. There are several reasons why request is not allowed. Some of the reasons are: session is server; stream ID has been spent; GOAWAY has been sent or received.
The application can call
nghttp2_submit_request()without consulting this function. In that case,
nghttp2_submit_request()may return error. Or, request is failed to sent, and