[Twisted-Python] Supporting a two-part client protocol.

[Colin Dunklau]

On Mon, Feb 3, 2020 at 8:06 PM Go Luhng <goluhng at gmail.com> wrote:
>
> Hi there,
>
> I'm planning to use Twisted to write a client for the following protocol:
>
> Each messages is composed of two separate messages:
>
> 1. A header, which is a serialized C struct, containing multiple
> fields, among them a `length` field.
> 2. A Protocol Buffer payload, which length is specified by the
> aforementioned `length` field on the header.
>
> While the initial implementation is focused on TCP, I do hope to
> support this same protocol over UDP eventually.
>
> What's the best way for me to implement such a client with Twisted?
> Specifically, to implement support for sending/receiving messages in
> the above format to/from a server?
>
> Thanks, Go

Assuming the header has a fixed length,
https://twistedmatrix.com/documents/current/api/twisted.protocols.basic.IntNStringReceiver.html
and its more-concrete subclasses are a decent source of inspiration.
OTOH, that's for stream protocols, so if you want to eventually handle
UDP, it's probably nicer to do the full sans-io thing
(https://sans-io.readthedocs.io/) and wire it up with a more-basic
Twisted protocol. Well, that's probably the better approach in any
case.