[Twisted-Python] COMMERCIAL:Re: Is there a nice way to writetransport-agnostic protocols and servers/clients?

[Barry Scott]

On Thursday, 17 August 2017 03:03:41 BST Kevin Conway wrote:
> > There is no datagram endpoints API as yet, though (see #4471), only
> 
> stream endpoints.
> 
> I'm not sure I understand the distinction. Endpoints supports UDP which is
> a datagram based transport. From a Protocol perspective, you only care
> about which bytes are received. If you have a framing concept I'm your data
> format then it should be handled there.

Oppss. last message escaped before being finished.

What I was trying to say is that trying to plug in UDP in place of TCP is not 
going to work. datagrams sent with UDP can be dropped and reorder, where
as TCP will always deliver in order and not drop data.

Protocols that use UDP understand these differences and exploit them.
For example DNS and media streaming.

Barry

> 
> What am I not understanding about this particular use case?
> 
> On Wed, Aug 16, 2017, 16:25 Jean-Paul Calderone <exarkun at twistedmatrix.com>
> 
> wrote:
> > On Wed, Aug 16, 2017 at 9:59 AM, Tristan Seligmann <
> > 
> > mithrandi at mithrandi.net> wrote:
> >> On Wed, 16 Aug 2017 at 15:28 Kevin Conway <kevinjacobconway at gmail.com>
> >> 
> >> wrote:
> >>> Maybe I misunderstand the issue, but I believe the Endpoints API solves
> >>> for this.
> >>> https://twistedmatrix.com/documents/16.4.1/core/howto/endpoints.html
> >>> 
> >>> This abstracts the transport and allows you to focus on only
> >>> interpreting the bytes transmitted over that transport by defining a
> >>> Protocol and a Factory that plug into strports. This should allow you to
> >>> have the business logic defined in only one location while
> >>> listening/requesting over different transports.
> >> 
> >> There is no datagram endpoints API as yet, though (see #4471), only
> >> stream endpoints.
> > 
> > Also, when there are datagram endpoints, they won't be compatible with
> > stream endpoints.  Endpoints don't abstract the transport, they abstract
> > *creating* the transport.
> > 
> > Twisted provides a uniform abstraction over stream-based transports like
> > TCP and gives you *ITransport* to implement an *IProtocol* against.  It
> > also provides a uniform abstraction over datagram-based transports like
> > UDP
> > and gives you *IUDPTransport* (oops; should have been *IDatagramTransport*
> > and some other things about it should probably be changed too) to
> > implement a *DatagramProtocol* (oops; no interface for this one, just
> > subclass: see, this should change) against.  But it doesn't provide a
> > uniform abstraction over both stream-based and datagram-based transports.
> > 
> > Implementing such a thing may be possible and even a good idea but no one
> > has yet done it for Twisted (as far as I know).
> > 
> > Jean-Paul
> > 
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