To use: .setsockopt(SOL_SOCKET, 20, lambda sock: print(sock)). There's a
single underlying callback slot. For normal sockets, it serves as data
received callback, for listening sockets - connection arrived callback.
The idea is that if dupterm object can handle exceptions, it will handle
them itself. Otherwise, object state can be compromised and it's better
to terminate dupterm session. For example, disconnected socket will keep
throwing exceptions and dump messages about that.
When lwIP creates a incoming connection socket of a listen socket, it
sets its recv callback to one which discards incoming data. We set
proper callback only in accept() call, when we allocate Python-level
socket where we can queue incoming data. So, in lwIP accept callback
be sure to set recv callback to one which tells lwIP to not discard
incoming data.
This is strange asymmetry which is sometimes needed, e.g. for WebREPL: we
want to process only available input and no more; but for output, we want
to get rid of all of it, because there's no other place to buffer/store
it. This asymmetry is akin to CPython's asyncio asymmetry, where reads are
asynchronous, but writes are synchronous (asyncio doesn't expect them to
block, instead expects there to be (unlimited) buffering for any sync write
to completely immediately).
Paul Sokolovsky
Damien George
Tom Sparks