Reflection-based Callee

July 30, 2017

Reflection-based Callee allows you to register classes instances with method decorated with a [WampProcedure] attribute as remote procedure operation to a WAMP realm.

Basic usage

public interface IArgumentsService
{
    [WampProcedure("com.arguments.ping")]
    void Ping();

    [WampProcedure("com.arguments.add2")]
    int Add2(int a, int b);

    [WampProcedure("com.arguments.stars")]
    string Stars(string nick = "somebody", int stars = 0);

    [WampProcedure("com.arguments.orders")]
    string[] Orders(string product, int limit = 5);
}

public class ArgumentsService : IArgumentsService
{
    public void Ping()
    {
    }

    public int Add2(int a, int b)
    {
        return a + b;
    }

    public string Stars(string nick = "somebody", int stars = 0)
    {
        return $"{nick} starred {stars}x";
    }

    public string[] Orders(string product, int limit = 5)
    {
        return Enumerable.Range(0, 50).Take(limit).Select(i => $"Product {i}").ToArray();
    }
}

public static async Task Main()
{
    const string location = "ws://127.0.0.1:8080/ws";

    DefaultWampChannelFactory channelFactory = new DefaultWampChannelFactory();

    IWampChannel channel = channelFactory.CreateJsonChannel(location, "realm1");

    await channel.Open().ConfigureAwait(false);

    IArgumentsService instance = new ArgumentsService();

    IWampRealmProxy realm = channel.RealmProxy;

    IAsyncDisposable disposable =
        await realm.Services.RegisterCallee(instance).ConfigureAwait(false);

    // This line is required in order to release the WebSocket thread, otherwise it will be blocked by the following Console.ReadLine() line.
    await Task.Yield();

    Console.WriteLine("Press enter to unregister");

    Console.ReadLine();

    await disposable.DisposeAsync().ConfigureAwait(false);

    Console.WriteLine("Unregistered!");
}

Supprted features

Both placing attributes on a class method and placing attributes on an interface implemented by the class are supported.

Instance providers

IWampRealmServiceProvider’s RegisterCallee method has some overloads which allow you to specify an instance provider for your callee service instance, that is a Func<> delegate that returns an instance of your callee service provider.

This allows you to control yourself the lifecycle of the callee service instance. You can of course use an dependency injection framework to help you manage that.

For instance, using Ninject:

public static async Task Main()
{
    IKernel kernel = new StandardKernel();

    kernel.Bind<IAddCalculator>().To<Calculator>();

    DefaultWampChannelFactory factory = new DefaultWampChannelFactory();

	IWampChannel channel =
		factory.CreateJsonChannel("ws://127.0.0.1:8080/ws", "realm1");

	await channel.Open().ConfigureAwait(false);

    await channel.RealmProxy.Services.RegisterCallee(() => kernel.Get<IAddCalculator>()).ConfigureAwait(false);

    // This line is required in order to release the WebSocket thread, otherwise it will be blocked by the following Console.ReadLine() line.
    await Task.Yield();

    Console.ReadLine();
}

public interface IAddCalculator
{
    [WampProcedure("com.arguments.add2")]
    int Add2(int x, int y);
}

public class Calculator : IAddCalculator
{
    public int Add2(int x, int y)
    {
        return (x + y);
    }
}

Note: if you’re using Ninject, you’re recomended to use Ninject.Extensions.Factory which allows you to get typed factories instances or Func<> instances without being aware about the dependency injection container.

Default parameter values

A method can have default value parameters. These will be used in case the user sends only part of the method’s parameters. Example:

public interface IArgumentsService
{
    [WampProcedure("com.arguments.stars")]
    string Stars(string nick = "somebody", int stars = 0);
}

Async method support

A method returning a Task<> will be awaited. Example:

public class SlowSquareService
{
    [WampProcedure("com.math.slowsquare")]
    public async Task<int> SlowSquare(int x)
    {
        await Task.Delay(1000).ConfigureAwait(false);
        return x * x;
    }

    [WampProcedure("com.math.square")]
    public int Square(int x)
    {
        return x * x;
    }
}

Note: The sample is based on this AutobahnJS sample

Tuples support

C# 7.0 tuples are supported as return values of reflection-based callee methods. The tuple will be serialized to either the arguments keywords or to the arguments array of the YIELD message, depending on whether the returned tuple has named elements or positional elements (tuples having elements which are partially named are not supported).

For example: A reflection-based callee that returns a tuple:

public interface IComplexResultService
{
    [WampProcedure("com.myapp.add_complex")]
    (int c, int ci) AddComplex(int a, int ai, int b, int bi);

    [WampProcedure("com.myapp.split_name")]
    (string, string) SplitName(string fullname);
}

public class ComplexResultService : IComplexResultService
{
    public (int c, int ci) AddComplex(int a, int ai, int b, int bi)
    {
       return (a + b, ai + bi);
    }

    public (string, string) SplitName(string fullname)
    {
        string[] splitted = fullname.Split(' ');

        string forename = splitted[0];
        string surname = splitted[1];

        return (forename, surname);
    }
}

Note: as usual, you can put the WampProcedureAttributes on the methods themselves instead of implementing an interface, i.e:

[WampProcedure("com.myapp.add_complex")]
public (int c, int ci) AddComplex(int a, int ai, int b, int bi)
{
   // ...
}

[WampProcedure("com.myapp.split_name")]
public (string, string) SplitName(string fullname)
{
   // ...
}

Which can be consumed from AutobahnJS:

session.call('com.myapp.add_complex', [2, 3, 4, 5]).then(
    function (res) {
        console.log("Result: " + res.kwargs.c + " + " + res.kwargs.ci + "i");
    }
);

session.call('com.myapp.split_name', ['Homer Simpson']).then(
    function (res) {
        console.log("Forename: " + res.args[0] + ", Surname: " + res.args[1]);
    }
;)

Note: The samples are based on this AutobahnJS/AutobahnPython sample

Note: this feature can be combined with other features, such as async method support or progressive call results.

Exception support

throw a WampException/WampRpcRuntimeException in order to send a ERROR message.

Example:

[WampProcedure("com.myapp.checkname")]
public void CheckName(string name)
{
    if (new[] {"foo", "bar"}.Contains(name))
    {
        throw new WampException("com.myapp.error.reserved");
    }

    if (name.ToLower() != name.ToUpper())
    {
        throw new WampException("com.myapp.error.mixed_case", name.ToLower(), name.ToUpper());
    }

    if ((name.Length < 3) || (name.Length > 10))
    {
        object[] arguments = new object[] {};

        IDictionary<string, object> argumentKeywords =
            new Dictionary<string, object>()
                {
                    {"min", 3},
                    {"max", 10}
                };

        throw new WampException("com.myapp.error.invalid_length", arguments, argumentKeywords);
    }
}

Note: The sample is based on this AutobahnJS sample

Progressive call results

In order to use progressive call result as a Callee, declare in your callee service a [WampProcedure] method having a [WampProgressiveResultProcedure] attribute and a IProgress<T> as the last parameter.

Note that the method return type should be Task<T> where this is the same T as in the IProgress<T> of the last parameter.

Example:

public interface ILongOpService
{
    [WampProcedure("com.myapp.longop")]
    [WampProgressiveResultProcedure]
    Task<int> LongOp(int n, IProgress<int> progress);
}

create a service with that implements that interface. In order to report progress, call the progress Report method. Example:

public class LongOpService : ILongOpService
{
    public async Task<int> LongOp(int n, IProgress<int> progress)
    {
        for (int i = 0; i < n; i++)
        {
            progress.Report(i);
            await Task.Delay(100).ConfigureAwait(false);
        }

        return n;
    }
}

Note: you can put the attributes on the method itself instead of implementing an interface, i.e:

public class LongOpService
{
    [WampProcedure("com.myapp.longop")]
    [WampProgressiveResultProcedure]
    public async Task<int> LongOp(int n, IProgress<int> progress)
    {
	    // ...
    }
 }

Then register it to the realm regularly:

public static async Task Main()
{
    DefaultWampChannelFactory factory = new DefaultWampChannelFactory();

    IWampChannel channel = factory.CreateJsonChannel("ws://localhost:8080/ws", "realm1");

    await channel.Open().ConfigureAwait(false);

    ILongOpService service = new LongOpService();

    IAsyncDisposable disposable =
        await channel.RealmProxy.Services.RegisterCallee(service).ConfigureAwait(false);

    Console.WriteLine("Registered LongOpService");

    // This line is required in order to release the WebSocket thread, otherwise it will be blocked by the following Console.ReadLine() line.
    await Task.Yield();

    Console.ReadLine();
}

Note: The sample is based on this AutobahnJS sample

Cancellation support

Cancellation is supported via the CancellationToken api. In order to declare a callee procedure which supports cancellation, declare an async method which receives as its last argument a CancellationToken:

public class CancellableOpService
{
    [WampProcedure("com.myapp.cancellableop")]
    public async Task<int> CancellableOp(int n, CancellationToken token)
    {
        for (int i = 0; i < n; i++)
        {
            if (token.IsCancellationRequested)
            {
                throw new WampRpcCanceledException($" {i * 100.0 / n}% of the work was done");
            }

            await Task.Delay(100, token).ConfigureAwait(false);
        }

        return n;
    }
}

Note: This works also with progressive call results:

public class LongCancellableOpService
{
    [WampProgressiveResultProcedure]
    [WampProcedure("com.myapp.longop")]
    public async Task<int> LongCancellableOp(int n, IProgress<int> progress, CancellationToken token)
    {
        for (int i = 0; i < n; i++)
        {
            if (token.IsCancellationRequested)
            {
                throw new WampRpcCanceledException($" {i * 100.0 / n}% of the work was done");
            }

            progress.Report(i);
            await Task.Delay(100, token).ConfigureAwait(false);
        }

        return n;
    }
}

out/ref parameters

For synchronous methods, out/ref parameters are supported.

Note: this is not supported for asynchronous methods.

Example:

public class ComplexResultService
{
    [WampProcedure("com.myapp.add_complex")]
    public void AddComplex(int a, int ai, int b, int bi, out int c, out int ci)
    {
        c = a + b;
        ci = ai + bi;
    }
}

Note: The sample is based on this AutobahnJS sample

Multivalued results

Multi-valued results: in order to return an multivalued array in the RESULT/YIELD WAMPv2 message, return an array from a rpc method and place above it a [return: WampResult(CollectionResultTreatment.Multivalued)] attribute. Example:

public class MultivaluedResultService
{
    [WampProcedure("com.myapp.split_name")]
    [return: WampResult(CollectionResultTreatment.Multivalued)]
    public string[] SplitName(string fullname)
    {
        string[] splitted = fullname.Split(' ');
        return splitted;
    }
}

Note: The sample is based on this AutobahnJS sample

WampInvocationContext

WampInvocationContext allows you to get the invocation details provided with the current invocation. It currently contains the caller identification (if present) and whether the caller requested a progressive call. Example:

public class LongOpService : ILongOpService
{
    public async Task<int> LongOp(int n, IProgress<int> progress)
    {
        InvocationDetails details =
            WampInvocationContext.Current.InvocationDetails;

        for (int i = 0; i < n; i++)
        {
            if (details.ReceiveProgress == true)
            {
                progress.Report(i);                    
            }

            await Task.Delay(100).ConfigureAwait(false);
        }

        return n;
    }
}

Registration customization

The RegisterCallee method of IWampRealmServiceProvider has an overload that receives an “interceptor” instance. The “interceptor” allows customizing the registration being performed.

This allows customizing the register options and the procedure uri sent upon REGISTER message.

The following sections discuss register options modifications that can be used in order to leverage WAMP advanced profile features.

Caller identification

It is possible to get caller identification details. According to WAMP2 specification, a Callee can request to get caller identification details (by specifying disclose_caller = true on registration).

Specifying this is possible on callee registration.

Callee registration example:

public static async Task Main()
{
    DefaultWampChannelFactory factory = new DefaultWampChannelFactory();

    IWampChannel channel =
        factory.CreateJsonChannel("ws://localhost:8080/ws", "realm1");

    await channel.Open().ConfigureAwait(false);

    SquareService service = new SquareService();

    var registerOptions =
        new RegisterOptions
        {
            DiscloseCaller = true
        };

    IAsyncDisposable disposable =
        await channel.RealmProxy.Services.RegisterCallee(service,
            new CalleeRegistrationInterceptor(registerOptions))
            .ConfigureAwait(false);

    // This line is required in order to release the WebSocket thread, otherwise it will be blocked by the following Console.ReadLine() line.
    await Task.Yield();

    Console.ReadLine();
}

In order to obtain these details as a Callee, access WampInvocationContext.Current.

Sample:

public class SquareService
{
    [WampProcedure("com.myapp.square")]
    public int Square(int n)
    {
        InvocationDetails details =
            WampInvocationContext.Current.InvocationDetails;

        Console.WriteLine("Someone is calling me: " + details.Caller);

        return n*n;
    }
}

Note: This sample is based on this AutobahnJS sample

Shared registrations

Shared registrations are supported.

In order to use shared registrations, pass to the Register methods, RegisterOptions with a desired Invoke (the policy to be used). The possible options are: single/first/last/random/roundrobin (there exists a static class named WampInvokePolicy with these values).

Example:

public static async Task Main()
{
    DefaultWampChannelFactory channelFactory = new DefaultWampChannelFactory();

    IWampChannel channel =
        channelFactory.CreateJsonChannel
            ("ws://127.0.0.1:8080/ws",
             "realm1");

    TaskCompletionSource<string> identTask = new TaskCompletionSource<string>();

    channel.RealmProxy.Monitor.ConnectionEstablished += (sender, args) =>
    {
        string ident =
            string.Format("MyComponent (PID {0}, Session {1})",
                          Process.GetCurrentProcess().Id,
                          args.SessionId);

        identTask.SetResult(ident);
    };

    await channel.Open().ConfigureAwait(false);

    string identValue = await identTask.Task;

    await channel.RealmProxy.Services.RegisterCallee(new MyComponent(identValue),
        new CalleeRegistrationInterceptor(new RegisterOptions()
        {
            Invoke = WampInvokePolicy.Roundrobin
        }))
        .ConfigureAwait(false);

    // This line is required in order to release the WebSocket thread, otherwise it will be blocked by the following Console.ReadLine() line.
    await Task.Yield();

    Console.ReadLine();
}

public class MyComponent
{
    private readonly string mIdent;

    public MyComponent(string ident)
    {
        mIdent = ident;
    }

    [WampProcedure("com.example.add2")]
    public object Add2(double x, double y)
    {
        Console.WriteLine("add2 called on {0}", mIdent);

        return new
        {
            result = x + y,
            ident = mIdent
        };
    }
}

Note: this sample is based on this Autobahn sample

Pattern-based registrations

Pattern-based registrations are supported.

In order to use pattern-based registrations, pass to the Register methods, RegisterOptions with a desired Match (the match pattern to be used). The possible options are: exact/prefix/wildcard. (these values are also available in a static class named WampMatchPattern)

Example:

public static async Task Main()
{
    DefaultWampChannelFactory channelFactory = new DefaultWampChannelFactory();

    IWampChannel channel =
        channelFactory.CreateJsonChannel("ws://127.0.0.1:8080/ws",
            "realm1");

    await channel.Open().ConfigureAwait(false);

    await channel.RealmProxy.Services.RegisterCallee(new Callee1())
        .ConfigureAwait(false);

    await channel.RealmProxy.Services.RegisterCallee
        (new Callee2(),
         new CalleeRegistrationInterceptor(new RegisterOptions
         {
             Match = WampMatchPattern.Prefix
         }))
         .ConfigureAwait(false);

    await channel.RealmProxy.Services.RegisterCallee
        (new Callee3(),
         new CalleeRegistrationInterceptor(new RegisterOptions
         {
             Match = WampMatchPattern.Wildcard
         }))
         .ConfigureAwait(false);

    // This line is required in order to release the WebSocket thread, otherwise it will be blocked by the following Console.ReadLine() line.
    await Task.Yield();

    Console.ReadLine();
}

public class Callee1
{
    [WampProcedure("com.example.procedure1")]
    public void Endpoint1(string message)
    {
        Console.WriteLine("endpoint1: msg = '{0}', procedure = '{1}'", message,
                          WampInvocationContext.Current.InvocationDetails.Procedure);
    }
}

public class Callee2
{
    [WampProcedure("com.example")]
    public void Endpoint2(string message)
    {
        Console.WriteLine("endpoint2: msg = '{0}', procedure = '{1}'", message,
                          WampInvocationContext.Current.InvocationDetails.Procedure);
    }             
}

public class Callee3
{
    [WampProcedure("com..procedure1")]
    public void Endpoint3(string message)
    {
        Console.WriteLine("endpoint3: msg = '{0}', procedure = '{1}'", message,
                          WampInvocationContext.Current.InvocationDetails.Procedure);
    }             
}

Note: this sample is based on this Autobahn sample

Reflection-based Callee

Basic usage

Supprted features

Instance providers

Default parameter values

Async method support

Tuples support

Exception support

Progressive call results

Cancellation support

out/ref parameters

Multivalued results

WampInvocationContext

Registration customization

Caller identification

Shared registrations

Pattern-based registrations

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