Building a Custom Feature

Component: NServiceBus
NuGet Package NServiceBus (6.x)

Introduction

This sample illustrates how to build a custom Feature. In this Feature some diagnostics is performed:

Both of these are implemented as dependent Features that depend on the Diagnostics Feature.

Diagnostics Feature

public class DiagnosticsFeature :
    Feature
{
    internal DiagnosticsFeature()
    {
        EnableByDefault();
    }

    protected override void Setup(FeatureConfigurationContext context)
    {
        var container = context.Container;
        container.ConfigureComponent<CustomLogger>(DependencyLifecycle.SingleInstance);
    }
}

The Diagnostics Feature enables all dependent to be easily toggled enabling or disabling it through configuration. In this case it is enabled by default.

Custom Logger

This Feature injects a custom logger into the container that can then be used by below Features.

public class CustomLogger
{
    static ILog log = LogManager.GetLogger<CustomLogger>();

    public IDisposable StartTimer(string name)
    {
        return new Log(name);
    }

    public void WriteSaga(IContainSagaData sagaData)
    {
        var serialized = JsonConvert.SerializeObject(sagaData, Formatting.Indented);
        log.Warn($"Saga State: \r\n{serialized}");
    }

    class Log :
        IDisposable
    {
        string name;
        Stopwatch stopwatch;

        public Log(string name)
        {
            stopwatch = Stopwatch.StartNew();
            this.name = name;
        }

        public void Dispose()
        {
            log.Warn($"{name} took {stopwatch.ElapsedMilliseconds}ms to process");
        }
    }
}

Handler Timing Feature

This feature depends on both the Diagnostics Feature.

public class HandlerTimerFeature :
    Feature
{
    internal HandlerTimerFeature()
    {
        EnableByDefault();
        DependsOn<DiagnosticsFeature>();
    }

    protected override void Setup(FeatureConfigurationContext context)
    {
        var pipeline = context.Pipeline;
        pipeline.Register(
            stepId: "HandlerTimer",
            behavior: typeof(HandlerTimerBehavior),
            description: "Logs handler time");
    }
}

Behavior

The pipeline behavior that performs the handler timing.

class HandlerTimerBehavior :
    Behavior<IInvokeHandlerContext>
{
    CustomLogger logger;

    public HandlerTimerBehavior(CustomLogger logger)
    {
        this.logger = logger;
    }

    public override async Task Invoke(IInvokeHandlerContext context, Func<Task> next)
    {
        var handlerName = context.MessageHandler.Instance.GetType().Name;
        using (logger.StartTimer(handlerName))
        {
            await next()
                .ConfigureAwait(false);
        }
    }
}

Saga State Audit Feature

This feature depends on both the Diagnostics and Saga Features.

public class SagaStateAuditFeature :
    Feature
{
    internal SagaStateAuditFeature()
    {
        EnableByDefault();
        DependsOn<Sagas>();
        DependsOn<DiagnosticsFeature>();
    }

    protected override void Setup(FeatureConfigurationContext context)
    {
        var pipeline = context.Pipeline;
        pipeline.Register(
            stepId: "SagaStateAudit",
            behavior: typeof(SagaStateAuditBehavior),
            description: "Logs Saga State");
    }
}

Behavior

The pipeline behavior that captures the saga state.

class SagaStateAuditBehavior :
    Behavior<IInvokeHandlerContext>
{
    CustomLogger logger;

    public SagaStateAuditBehavior(CustomLogger logger)
    {
        this.logger = logger;
    }

    public override async Task Invoke(IInvokeHandlerContext context, Func<Task> next)
    {
        await next()
            .ConfigureAwait(false);
        ActiveSagaInstance activeSagaInstance;
        if (context.Extensions.TryGet(out activeSagaInstance))
        {
            var instance = activeSagaInstance.Instance.Entity;
            logger.WriteSaga(instance);
        }
    }
}

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