[Twisted-Python] stop/start client connections with loseConnection in ReconnectingClientFactory

[Tobias Oberstein]

>> The Autobahn guys still show ReconnectingClientFactory in their docs, 

Where did you find that? That would be a doc bug, but in the _docs_, 
there is no reference to ReconnectingClientFactory

(cpy372_3) oberstet at intel-nuci7:~$ find 
~/scm/crossbario/autobahn-python/docs/ -type f -exec grep -Hi 
"ReconnectingClientFactory" {} \;
(cpy372_3) oberstet at intel-nuci7:~$

We do have some example code using ReconnectingClientFactory though:

(cpy372_3) oberstet at intel-nuci7:~$ find 
~/scm/crossbario/autobahn-python/examples/ -type f -exec grep -Hi 
"ReconnectingClientFactory" {} \; | wc -l
8

>> and I remember looking at this before and ending up going with 
>> ReconnectingClientFactory because it works and didn't look like it'd 
>> need much effort to integrated into an existing code base.
> 
> Let me count the ways.
> 
>  1. ReconnectingClientFactory is destined for deprecation, eventually.
>       You should just adopt the "new" thing now so that if we get more
>     energy to cycle the APIs and delete the old stuff, you'll have less
>     hassle to deal with.  ("New" is in quotes here since it's been
>     around for well over 3 years at this point; Autobahn should update
>     too, not just you.)

Autobahn will automatically use

twisted.application.internet.ClientService

for auto-reconnect when on Twisted 16.1.0+

https://github.com/crossbario/autobahn-python/blob/master/autobahn/twisted/wamp.py#L349

>  2. ClientService works with endpoints, which means you can use it with
>     /any/ kind of transport, like SSH transports, subprocesses, etc.
>       Most practically, it works with HostnameEndpoint which is a much
>     better way to get TLS than connectSSL; ReconnectingClientFactory
>     works, kind of accidentally, with TLS since connectSSL is on the
>     reactor, but it won't use happy eyeballs and it won't connect over
>     IPv6, so connections will be slower and less reliable.
>  3. Conceptually, ClientService has a much clearer and more useful
>     responsibility: its job is to /maintain a state/ (i.e.: that there
>     is a single connection, that it is connected) rather than to /do a
>     thing/.  For example,
>      1. if you want to shut down a ReconnectingClientFactory:
>          1. you have to call stopTrying, then uh...
>          2. find the last protocol it built with buildProtocol, then
>          3. grab its transport (hope it's saving that transport as
>             '.transport', because it doesn't actually have to)
>          4. call loseConnection
>          5. remember to trap connectionLost so you can see when its done.
>      2. if you want to shut down a ClientService
>          1. call stopService
>          2. wait for the Deferred that it returned to fire
>  4. ClientService is (mostly) implemented using composition rather than
>     inheritance, so much less of the guts of the internal implementation
>     is hanging around where you might accidentally twiddle it and break
>     its assumptions, so you can trust its guarantees more.

++1

(note: Autobahn is a culprit to the overuse of inheritance vs 
composition too .. but the so-called "new API" (for WAMP) is following 
composition + observer pattern, while the "old API" (that is inheriting 
from ApplicationSession) is still pretty much around. we have some 
legacy already ..)

>      1. other benefits of composition: you don't have to override
>         attributes of your Protocol and thereby indulge in subclassing
>         yourself to get notifications; consider 'prepareConnection',
>         'whenConnected'.
>      2. the retry policy mechanics are better documented and much easier
>         to customize
>      3. it's backed by a formal state machine - not that I'm aware of
>         any specific bugs in ReconnectingClientFactory but do you think
>         it got /all/ of these state transitions correct:
>         https://gist.github.com/glyph/614be03151556333efe04b849fa05930
>  5. It's more testable because it just takes its clock and reactor as
>     constructor parameters, rather than requiring post-hoc
>     poorly-documented attribute patching to become testable.
> 
> 
> Hopefully at least some of this is convincing :)

all and each of them is convincing;)

> 
> -g
> 
> _______________________________________________
> Twisted-Python mailing list
> Twisted-Python at twistedmatrix.com
> https://twistedmatrix.com/cgi-bin/mailman/listinfo/twisted-python
> 


-- 

Tobias Oberstein - phone +49 176 2375 2055 - tobias.oberstein at crossbario.com
Crossbar.io GmbH - Waldstrasse 18 - 91054 Erlangen
HRB 15870 - Amtsgericht Fuerth - Geschäftsfuehrer/CEO - Tobias Oberstein

https://crossbar.io
https://crossbario.com