Replace TraceWriter with an Interface to improve code testability

[cmatskas]

At the moment Functions in C# take a TraceWriter as a method parameter. This means that testing locally becomes a challenge as it's very hard to mock this. Ideally the method parameter should be an interface like ILogger that allows to easily mock this during testing

[fabiocav]

Done :)

As of our last release, you can use an Microsoft.Extensions.Logging.ILogger instead of a TraceWriter and an ILogger instance will be provided.

@brettsam can share more details.

[cmatskas]

Booya! There's been no information around this so apologies for raising...I'm not part of the inner circle :(
Thanks for the quick response!

[DivineOps]

Hi @fabiocav,
If I switch to ILogger, I am having an issue with local logs displaying in AzureFunctions.CLI.
When I publish the function, the function logs are displayed, along with the function pulse. But when running locally only the function pulse is displayed (although no errors are thrown).
Is this a configuration issue?
Can you share a working code sample?

Also, it is worth noting that we are talking about Microsoft.Extensions.Logging.ILogger, because there is more than one library that defines ILogger

[brettsam]

The missing logs in the CLI is an issue being tracked here: Azure/azure-functions-core-tools#130 -- we're looking into it.

And yes, it's the Microsoft.Extensions.Logging.ILogger.

[DivineOps]

Thanks Brett!

[fabiocav]

Thanks for pointing out the ambiguity, @DivineOps. I've updated the original comment to make it clear I was referring to the Microsoft.Extensions.Logging.ILogger interface.

[DivineOps]

Ironically, I am finding it easier to mock TraceWriter than ILogger, since ILogger only exposes a single non-static Log method which requires a long list of parameters :)

[dersia]

Hi there I just realized, that there seems to be an issue with the new ILogger. If I select the ILogger, everything works as expected and there is no issue at all, but if I consume a nuget-package which has dependency on Microsoft.Extensions.Logging.Abstractions it stops working. I actually get a failure upon loading the function:

Microsoft.Azure.WebJobs.Host: Cannot bind parameter 'log' to type ILogger. Make sure the parameter Type is supported by the binding. If you're using binding extensions (e.g. ServiceBus, Timers, etc.) make sure you've called the registration method for the extension(s) in your startup code (e.g. config.UseServiceBus(), config.UseTimers(), etc.)

[brettsam]

@dersia -- I've opened a new issue for this: #334 -- can you hop over to that issue and let me know what package you added that broke this?

[tafs7]

@fabiocav Is this new ILogger interface documented anywhere on https://docs.microsoft.com ?

Is there any reference code or samples of how to leverage this both from a script function (e.g. csx) and from a pre-compiled function?

I assume we need to add a nuget package reference to the pre-compiled class library (Install-Package Microsoft.Extensions.Logging.Abstractions -Version 1.1.2), correct? I notice there's a pre-release pkg version 2.0, what is the difference? Which is supported by Azure Functions?

[cmatskas]

Seconded! A demo/sample code would awesome to help with adoption. Thanks

[brettsam]

I've just put together an ILogger wiki topic here: https://github.com/Azure/azure-webjobs-sdk-script/wiki/ILogger. I'll add more to it over time, but that should give some information on background and usage. Feel free to weigh in here with more questions and I'll fill them in on the wiki page.

[tafs7]

@brettsam quick questions - can the ILogger interface be used from local/debug (CLI)?