MethodBoundaryAspect.Fody 3.7.0

MethodBoundaryAspect.Fody

Run your own code when a method starts, ends or throws, by putting an attribute on it:

[Log]
public int Add(int a, int b) => a + b;

MethodBoundaryAspect.Fody is a Fody weaver: the calls to your aspect are woven into the IL of the method at build time. There is no runtime proxy, no dependency injection container and no interface or virtual method required. It works for static, private, generic and async methods of any class, on .NET Framework 4.6.2+ and .NET (Core) / .NET Standard 2.0+.

Typical aspects: logging, measuring execution time, transaction handling, exception wrapping, showing a wait cursor, argument validation, caching.

Quickstart

1. Add this package (it brings Fody along).

2. Add a FodyWeavers.xml file to the project root:

   <Weavers>
     <MethodBoundaryAspect />
   </Weavers>
   

3. Write an aspect by deriving from OnMethodBoundaryAspect and overriding any of OnEntry, OnExit and OnException:

   using System;
   using MethodBoundaryAspect.Fody.Attributes;
   
   public sealed class LogAttribute : OnMethodBoundaryAspect
   {
       public override void OnEntry(MethodExecutionArgs args) =>
           Console.WriteLine($"Entering {args.Method.Name}({string.Join(", ", args.Arguments)})");
   
       public override void OnExit(MethodExecutionArgs args) =>
           Console.WriteLine($"{args.Method.Name} returned {args.ReturnValue}");
   
       public override void OnException(MethodExecutionArgs args) =>
           Console.WriteLine($"{args.Method.Name} failed: {args.Exception.Message}");
   }
   

4. Apply it to a method, a class, a property or the whole assembly ([assembly: Log]) and build:

   public class Calculator
   {
       [Log]
       public int Add(int a, int b) => a + b;
   }
   
   new Calculator().Add(1, 2);
   // Entering Add(1, 2)
   // Add returned 3
   

What an aspect can do

All three aspect methods get a MethodExecutionArgs with the information of the call:

• Select the methods with [DisableWeaving], regular expression filters for namespace, type and method name, and the visibility of the methods (AttributeTargetMemberAttributes).
• Combine aspects on one method and order them with [AspectOrderIndex].
• Async methods are supported: OnEntry runs when the method is called, OnExit when it returns its Task (args.ReturnValue is that task, the work may not be finished), OnException when the asynchronous work fails.
• Low overhead: the weaver only provides the MethodExecutionArgs properties your aspects use, and creates aspects without state once instead of for every call.

Documentation

The complete documentation is the README on GitHub and the pages in its docs folder:

• How it works, Writing aspects and Applying aspects
• Changing the method behavior (return values, arguments, skipping the method, swallowing exceptions) and Async methods
• Limitations, Performance and the Configuration reference
• Troubleshooting (aspect not called, fields reset, null properties)
• Upgrading to version 3 and the Changelog
• Complete sample projects: .NET and .NET Framework

Questions and bug reports: GitHub issues. MIT license.