Function nghttp2_session_want_write 

pub unsafe extern "C" fn nghttp2_session_want_write(
    session: *mut nghttp2_session,
) -> c_int

@function

Returns nonzero value if |session| wants to send data to the remote peer.

If both nghttp2_session_want_read() and nghttp2_session_want_write() return 0, the application should drop the connection.