Implement Middleware for Handlers

[gkinsman]

This PR implements a middleware layer around handlers. Middlewares have a number of advantages over existing solutions:

• User provided middlewares can be provided via extension methods packages in nuget packages
• They are composable with other middlewares
• They don't require any custom code in or around IHandlerAsync<T>
• They are cancellable with CancellationToken, whereas IHandlerAsync<T> cannot change to add one (or at least we haven't decided to do that)
• They create a nice place for users to add in cross cutting code, like custom stats, retry strategies, locking, etc etc without needing to change JustSaying.

This work is largely based on the existing middleware code added by @maisiesadler that is used in the MessageReceiveBuffer's receive pipeline.

Some example code

Middlewares can be pulled from DI, or passed in explicitly:

var callRecord = new List<string>();

void Before(string id) => callRecord.Add($"Before_{id}");
void After(string id) => callRecord.Add($"After_{id}");

var outerMiddleware = new TrackingMiddleware("outer", Before, After);
var middleMiddleware = new TrackingMiddleware("middle", Before, After);
var innerMiddleware = new TrackingMiddleware("inner", Before, After);

var services = GivenJustSaying()
    .AddSingleton(outerMiddleware)
    .AddSingleton<IHandlerAsync<SimpleMessage>>(handler)
    .ConfigureJustSaying(builder => builder.WithLoopbackTopic<SimpleMessage>(UniqueName,
        topic => topic.WithMiddlewareConfiguration(app =>
        {
            app.Use<TrackingMiddleware>(); // from DI
            app.Use(() => middleMiddleware); // provide a Func<MiddlewareBase<HandleMessageContext, bool>
            app.Use(innerMiddleware); // Existing instance
        })));

Produces:

Before_outer
Before_middle
Before_inner
After_inner
After_middle
After_outer

Implementation of an extension method that makes a UseExactlyOnce method available to the pipeline, and resolves some services from DI

public static HandlerMiddlewareBuilder UseExactlyOnce<TMessage>(
    this HandlerMiddlewareBuilder builder,
    string lockKey,
    TimeSpan? lockDuration = null)
{
    HandleMessageMiddleware CreateMiddleware()
    {
        var messageLock = builder.ServicesBuilder?.MessageLock?.Invoke() ?? builder.ServiceResolver.ResolveService<IMessageLockAsync>();
        var logger = builder.ServiceResolver.ResolveService<ILogger<ExactlyOnceMiddleware<TMessage>>>();

        return new ExactlyOnceMiddleware<TMessage>(messageLock,
            lockDuration ?? TimeSpan.MaxValue,
            lockKey,
            logger);
    }

    builder.Use(CreateMiddleware);

    return builder;
}

Usage of UseExactlyOnce

.ConfigureJustSaying((builder) =>
    builder.WithLoopbackTopic<SimpleMessage>(UniqueName,
        c =>
            c.WithMiddlewareConfiguration(m =>
                m.UseExactlyOnce<SimpleMessage>("simple-message-lock"))))

They can be chained:

.Configure(pipe =>
                {
                    pipe.Use(m1);
                    pipe.Use(m2);
                    pipe.Use(m3);
                })

[codecov]

Codecov Report

Merging #809 (2ad8bb0) into master (a78936d) will decrease coverage by 0.05%.
The diff coverage is 87.64%.

@@            Coverage Diff             @@
##           master     #809      +/-   ##
==========================================
- Coverage   81.45%   81.39%   -0.06%     
==========================================
  Files         109      113       +4     
  Lines        2804     2838      +34     
==========================================
+ Hits         2284     2310      +26     
- Misses        520      528       +8     

Flag	Coverage Δ
linux	81.25% <87.64%> (-0.21%)	⬇️
macos	48.15% <67.05%> (-0.02%)	⬇️
windows	48.00% <67.05%> (-0.13%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/JustSaying/Fluent/ServicesBuilder.cs	60.86% <ø> (-4.52%)	⬇️
...criptionGroups/SubscriptionGroupSettingsBuilder.cs	86.20% <ø> (ø)
...aging/Middleware/Receive/ReceiveMessagesContext.cs	66.66% <ø> (ø)
...stSaying/Messaging/Monitoring/MonitorExtensions.cs	100.00% <ø> (ø)
...eware/Handle/HandlerMiddlewareBuilderExtensions.cs	33.33% <33.33%> (ø)
...iddleware/Handle/HandleMessageContextExtensions.cs	50.00% <50.00%> (ø)
...AwsTools/MessageHandling/Dispatch/MiddlewareMap.cs	62.96% <62.96%> (ø)
...trics/MetricsHandlerMiddlewareBuilderExtensions.cs	66.66% <66.66%> (ø)
...ng/Middleware/ExactlyOnce/ExactlyOnceMiddleware.cs	85.18% <71.42%> (ø)
...e/ExactlyOnceHandlerMiddlewareBuilderExtensions.cs	80.00% <80.00%> (ø)
... and 33 more

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[gkinsman]

@martincostello can we target this for post-beta? I'm really keen to get the beta process rolling so we can get some features using the new backend.

[martincostello]

@martincostello can we target this for post-beta? I'm really keen to get the beta process rolling so we can get some features using the new backend.

We can have as many alpha/beta/gamma/whatevers as we want before release internally, and we have the ProGet feed we can host packages in, so I don't think it really matters what label we give it or whatever the release cadence is (or the need to be super-strict on SemVer).

I'd only worry about these distinctions for putting something in NuGet.org, and I think we'd want to be fairly confidently "done" and happy it's working before publishing a beta there.

[gkinsman]

@martincostello can we target this for post-beta? I'm really keen to get the beta process rolling so we can get some features using the new backend.

We can have as many alpha/beta/gamma/whatevers as we want before release internally, and we have the ProGet feed we can host packages in, so I don't think it really matters what label we give it or whatever the release cadence is (or the need to be super-strict on SemVer).

I'd only worry about these distinctions for putting something in NuGet.org, and I think we'd want to be fairly confidently "done" and happy it's working before publishing a beta there.

That makes perfect sense, thanks 👍. The main reason for a beta was so that we can switch to a package feed instead of local packages, so as you say we can just use proget 🙂.

[gkinsman]

This is now ready for review! I've documented the public interfaces, added tests, and removed the old exactly-once and stopwatch handlers and reimplemented as middlewares.

[slang25]

Some minor comments, overall a really good addition 😃