phillip-haydon / methoddecorator

Compile time decorator pattern via IL rewriting

MethodDecorator.Fody

Compile time decorator pattern via IL rewriting.

This is an add-in for Fody

It is expected that all developers using Fody either become a Patron on OpenCollective, or have a Tidelift Subscription. See Licensing/Patron FAQ for more information.

Usage

See also Fody usage.

NuGet installation

Install the MethodDecorator.Fody NuGet package and update the Fody NuGet package:

PM> Install-Package Fody
PM> Install-Package MethodDecorator.Fody

The Install-Package Fody is required since NuGet always defaults to the oldest, and most buggy, version of any dependency.

Your Code

// Attribute should be "registered" by adding as module or assembly custom attribute
[module: Interceptor]

// Any attribute which provides OnEntry/OnExit/OnException with proper args
[AttributeUsage(AttributeTargets.Method | AttributeTargets.Constructor | AttributeTargets.Assembly | AttributeTargets.Module)]
public class InterceptorAttribute : Attribute, IMethodDecorator	{
    // instance, method and args can be captured here and stored in attribute instance fields
    // for future usage in OnEntry/OnExit/OnException
    public void Init(object instance, MethodBase method, object[] args) {
        TestMessages.Record(string.Format("Init: {0} [{1}]", method.DeclaringType.FullName + "." + method.Name, args.Length));
    }

    public void OnEntry() {
        TestMessages.Record("OnEntry");
    }

    public void OnExit() {
        TestMessages.Record("OnExit");
    }

    public void OnException(Exception exception) {
        TestMessages.Record(string.Format("OnException: {0}: {1}", exception.GetType(), exception.Message));
    }
}

public class Sample	{
    [Interceptor]
    public void Method()
    {
        Debug.WriteLine("Your Code");
    }
}

What gets compiled

public class Sample {
    public void Method(int value) {
        InterceptorAttribute attribute =
            (InterceptorAttribute) Activator.CreateInstance(typeof(InterceptorAttribute));

        // in c# __methodref and __typeref don't exist, but you can create such IL
        MethodBase method = MethodBase.GetMethodFromHandle(__methodref (Sample.Method), __typeref (Sample));

        object[] args = new object[1] { (object) value };

        attribute.Init((object)this, method, args);

        attribute.OnEntry();
        try {
            Debug.WriteLine("Your Code");
            attribute.OnExit();
        }
        catch (Exception exception) {
            attribute.OnException(exception);
            throw;
        }
    }
}

NOTE: this is replaced by null when the decorated method is static or a constructor.

IntersectMethodsMarkedByAttribute

This is supposed to be used as

// all MSTest methods will be intersected by the code from IntersectMethodsMarkedBy
[module:IntersectMethodsMarkedBy(typeof(TestMethod))]

You can pass as many marker attributes to IntersectMethodsMarkedBy as you want

[module:IntersectMethodsMarkedBy(typeof(TestMethod), typeof(Fact), typeof(Obsolete))]

Example of IntersectMethodsMarkedByAttribute implementation

[AttributeUsage(AttributeTargets.Module | AttributeTargets.Assembly)]
public class IntersectMethodsMarkedByAttribute : Attribute {
    // Required
    public IntersectMethodsMarkedByAttribute() {}

    public IntersectMethodsMarkedByAttribute(params Type[] types) {
        if (types.All(x => typeof(Attribute).IsAssignableFrom(x))) {
            throw new Exception("Meaningfull configuration exception");
        }
    }
    public void Init(object instance, MethodBase method, object[] args) {}
    public void OnEntry() {}
    public void OnExit() {}
    public void OnException(Exception exception) {}
    // Optional
    //public void OnTaskContinuation(Task task) {}
}

Now all your code marked by [TestMethodAttribute] will be intersected by IntersectMethodsMarkedByAttribute methods. You can have multiple IntersectMethodsMarkedByAttributes applied if you want (don't have idea why). MethodDecorator searches IntersectMethodsMarkedByAttribute by predicate StartsWith("IntersectMethodsMarkedByAttribute")

In case of exception in async method you "OnException" will not be called, OnTaskContinuation will be called instead.

Icon

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