Ryder is a .NET Core library providing the ability to redirect method calls from one method to another. By extension, it can also redirect property accesses, and event subscriptions / raises.

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Redirect a method

public static int Incremented(int nbr) => nbr + 1;
public static int Decremented(int nbr) => nbr - 1;

Incremented(1); // => 2.

MethodRedirection r = Redirection.Redirect<Func<int, int>>(Incremented, Decremented);

Incremented(1); // => 0.

// You can also invoke the original method:
r.InvokeOriginal(null, 1); // => 2.

// You can also stop the redirection...
r.Stop(); // or r.IsRedirecting = false, or r.Dispose().
Incremented(1); // => 2.

// ... and restart it
r.Start(); // or r.IsRedirecting = true, unless you disposed it, in which case it's no longer usable
Incremented(1); // => 0.

Using Reactive Extensions

MethodInfo method = typeof(DateTime)
    .GetProperty(nameof(DateTime.Now), BindingFlags.Static | BindingFlags.Public)
    .GetGetMethod();

int count = 0;
DateTime bday = new DateTime(1955, 10, 28);

// Make "DateTime.get_Now()" return "bday" every two calls.
using (Redirection.Observe(method)
                  .Where(_ => count++ % 2 == 0)
                  .Subscribe(ctx => ctx.ReturnValue = bday))
{
    DateTime.Now.ShouldBe(bday);
    DateTime.Now.ShouldNotBe(bday);
    DateTime.Now.ShouldBe(bday);
    DateTime.Now.ShouldNotBe(bday);
}

DateTime.Now.ShouldNotBe(bday);
DateTime.Now.ShouldNotBe(bday);

Other features

Any Redirection also defines the following members:

• bool IsRedirecting { get; set; }
• void Start()
• void Stop()

Redirections can be created in multiple ways:

• MethodRedirection: Redirect(Delegate, Delegate), Redirect(MethodBase, MethodBase).
• PropertyRedirection: Redirect(PropertyInfo, PropertyInfo).
• EventRedirection: Redirect(EventInfo, EventInfo).

Tests:

All features are tested in Ryder.Tests. Please check it out, as it contains some real-world-usage code.

Gloriously unsafe:

By default, Ryder performs many safety checks when you create a new Redirection. However, should you decide to do some experimental things, disabling all those checks is as easy as setting the skipChecks parameter available on all Redirect methods to true.

Implicit JIT checks:

When creating a Redirection, Ryder will ensure that the methods you use have already been jitted. If they haven't, they will be compiled automatically.

Support for i386, x86_64, arm and arm64

Ryder is designed to work with i386, x86_64, arm and arm64 using purely runtime checks. This means that it works everywhere without additional configuration. Additionally, Windows, Linux and OSX are all supported.

Installation

You can install Ryder through the NuGet package manager:

Install-Package Ryder

Alternatively, if you don't want to add a dependency, you can copy-paste the Ryder.Lightweight.cs file in your project. Caution, however, since this version only provides the MethodRedirection class (simply called Redirection), and performs no safety checks.

Additional notes

• Make sure the method you want to redirect does not get inlined by the JIT; if it does get inlined, redirecting it will most likely break stuff in unexpected ways, or do nothing at all. Additionally, if the method you redirect hasn't been jitted yet, the same problems may arise.
• In order to keep the GC from collecting jitted methods, Ryder keeps static references to them. Those references are only deleted when Redirection.Dispose() is called, after which the Redirection is no longer guaranteed to work.

Inspiration

Ryder is highly inspired by Harmony, but tries to take a very minimal approach to redirection, instead of providing the ability to patch individual instructions. Moreover, it was made with .NET Core in mind.

Projects using Ryder

• The AnyConstraint analyzer uses Ryder.Lightweight to allow any constraint to be used, including Delegate and Enum.
• Cometary highly modifies the Roslyn compilation process in order to add custom features to C#.