[Freeswitch-users] Subscribing to events in managed C# / .NET

[Michael Giagnocavo]

Great - hopefully we'll meet on IRC or the conference sometime on Friday. Email me when you're on.

A few questions I have:

Clarity - I agree with you there, and thanks!

Testability - is this even remotely practical? Looking at our FS code plugins, there's simply no way any amount of test environment code would get us to anything testable. We make tons of direct P/Invoke calls, and the whole model for what variables are set when, the state machine progression, etc. does not seem like something that we can hope to possibly model right. And it's subject to many external influences (all the modules you have loaded in FS). Logging is a pretty simple case, sure, we can make it not call FS for testing. But in a real app, it just seems that there are way too many dependencies, no? Maybe others who have apps written can chime in?

Modularity - I agree there are two parts. But, I think they are pretty tightly coupled. The FS interface into unmanaged code is done via unmanaged code and is really clear: App, Api, ApiBackground. The other ways I can think of are FS-specific, such as XML binding interface and so on. But those are things we should just add to the mod_managed core and be done with. I'm thinking maybe we are talking about different things? Can you provide some user stories that we want to cover with a pluggable loader/executor/etc.? Thanks for putting up with me!

-Michael

From: freeswitch-users-bounces at lists.freeswitch.org [mailto:freeswitch-users-bounces at lists.freeswitch.org] On Behalf Of Josh Rivers
Sent: Thursday, September 24, 2009 12:32 AM
To: freeswitch-users at lists.freeswitch.org
Subject: Re: [Freeswitch-users] Subscribing to events in managed C# / .NET


On Wed, Sep 23, 2009 at 7:31 PM, Michael Giagnocavo <mgg at giagnocavo.net<mailto:mgg at giagnocavo.net>> wrote:

Right off the bat: there can be tons of cleanup and refactoring, no doubt about that. Much of the current code is to satisfy my needs in production, which it does very well.
The current base doesn't have anything wrong with it for sure, in fact, I learned a good bit about PInvoke. AppDomains, and In-Process Remoting in the last week.

My refactoring had the following goals (in no particular order)
 - Testability - I'd really like to see a decent unit test suite on the more module so that we can change it with confidence. Also, it's been drilled into me that a testable design is a good design.
 - Clarity - Where possible, I extracted blocks of code that served a particular purpose so that purpose could be self-documenting in the method calls rather than mixed in.
 - Modularity - I wanted to make it easy to remove or add alternative behavior to the managed.dll.


I'm a bit hesitant to go too far from the FreeSWITCH core as far as architecture goes. For instance, I'm not quite sure why'd we have our own managed logging subsystem that allows them to plug in other things that aren't part of FS. Either they should use the FS logging system, or use their own such as log4net. Or perhaps I don't see why we'd want this behavior.
I completely agree, with the following caveats:
1) I'd like to see things testable. It's very hard to do isolation testing with classes making direct calls out to a static Log class that in turn pinvokes out to unmanaged code.
2) I'd like to allow folk to make changes to the default behavior (optimally) without recompiling managed.dll.

One thing at issue here is that there are two principal purposes for managed.dll. The first is to provide an interface into unmanaged code. The second is a module/plugin extensibility framework. The first purpose should absolutely provide the thinnest layer possible. The second purpose is very likely to need a lot of change and adaptation as people come up with development models that they would like to follow in using freeswitch. The extensibility framework should be mostly managed code, coded to interfaces for mock-ability and testabiliy. It should also be able to just push it out of the way and hook your own extensibilty framework in instead.

 Going away from the core as far as adding .NET specific features (like look at the static ManagedSession.Originate that takes hangup delegates, or the "nice" wrapper for Log (Write and WeiteLine, with an enum instead of a string) are keeping close to the core, just adding a tiny bit of API cleanup. FreeSWITCH exposes a lot of strings, and while maybe that's important for some languages, .NET users are going to expect stronger typing. But I don't think these types of things get people away from FreeSWITCH much.
No disagreement here. I would like to see these things made available by interface rather than concrete implementation. It's currently not possible to test a plugin without loading it into FS. That precludes automated testing, and leaves a pretty big round-trip to test a tweak. I'm a sloppy coder too, so I'm always introducing interesting regressions, and that's why I like doing my testing without having to bring up a full process :)

Things like making a published SOAP interface for FS seem not really related to mod_managed. They can easily be done as 3rd party plugins, or convince the core FS team that exposing via SOAP via mod_managed is the way to go. Also keep in mind that the majority of users are on Linux, so that rules out WCF and some other fun stuff that only works on the CLR - I'd say it all has to work on Mono.
This kind of stuff is definitely beyond the scope of mod_managed. Although there is a slippery slope since we're building in an extensibility model. I don't think a WCF host, or a winforms host, or any of that should be baked in. Rather, I think we should provide the hooks for adding such a thing. If somebody wants to build ESL via WCF, why should they need to leave managed code? If the module system is general enough, then such a thing should just be a module.
(BTW, I think WCF-Mono is getting there http://www.mono-project.com/WCF_Development)
Absolutely, everything in mod_managed and managed.dll should run on mono and the CLR. However, there shouldn't be any reason that a Win-only developer can't build a complete FS application framework that plugs in and only runs on Windows.

As for all the rest of it, can we talk interactively, perhaps with other users interested in mod_managed? Reading over your email, I think I'm not understanding many of the use cases that are being fixed.
I'd be very glad to get a discussion going. I definitely haven't covered all of the issues here.

-Josh

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