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Why F# interface differs greatly from C#
f#c#

Hi all~

I wanna test WCF by F#. When I try to define some interface (one for WebHttpBinding and the other for BasicHttpBinding). I got an error like this:

A first chance exception of type 'System.ArgumentNullException' occurred in System.ServiceModel.dll

I rewrite these code by C# again. Use the simple and normal method. It works.

the two program has the same config file and class name.

I try my best to find out the difference between them. When I use Reflector open two application. I see that:

C# implement interface, the method name is same as defined. (ViTarn.Wcf.Service.<WBR>GetDateTime())

But F# method name is surprising, like this: (ViTarn-Wcf-IDateTimeService-<WBR>GetDateTime())

I guest this is why my F# program jump that exception.

How to make it as a normal interface method name? Am I need some Attributes or the other implement way?

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using System;
using System.IO;
using System.ServiceModel;
using System.ServiceModel.Web;
using System.Text;
namespace ViTarn.Wcf
{
    public class Program
    {
        [STAThread]
        static void Main(string[] args)
        {
            var service = new ServiceHost(typeof(Service), new Uri[] { new Uri("http://localhost:82/") });
            service.Open();
            Console.Read();
        }
    }
    [ServiceContract]
    public interface IWebService
    {
        [OperationContract, WebGet(UriTemplate = "{file}")]
        Stream Get1(string file);
    }
    [ServiceContract]
    public interface IStringService
    {
        [OperationContract]
        string GetString();
    }
    [ServiceContract]
    public interface IDateTimeService
    {
        [OperationContract]
        DateTime GetDateTime();
    }
    public class Service : IWebService, IStringService, IDateTimeService
    {
         public Stream Get1(string file)
        {
            return new MemoryStream(Encoding.UTF8.GetBytes("<html><body>Return From C# WCF</body></html>")) as Stream;
        }
         public string GetString()
        {
            return "C# welcome";
        }
         public DateTime GetDateTime()
        {
            return DateTime.Now;
        }
    }
}
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#light
namespace ViTarn
module Wcf
open System
open System.IO
open System.ServiceModel
open System.ServiceModel.Web
[<ServiceContract>]
type IWebService =
    [<OperationContract; WebGet(UriTemplate = "{file}")>]
    abstract Get1 :string -> Stream
[<ServiceContract>]
type IStringService =
    [<OperationContract>]
    abstract GetString :unit -> string
[<ServiceContract>]
type IDateTimeService =
    [<OperationContract>]
    abstract GetDateTime :unit -> DateTime
type Service =
    interface IWebService with
        member public t.Get1(file :string) =
            new MemoryStream("<html><body>Return From F# WCF</body></html>" |> Text.Encoding.UTF8.GetBytes) :> Stream
    end
     interface IStringService with
        member public t.GetString() = "F# welcome"
    end
     interface IDateTimeService with
        member public t.GetDateTime() = DateTime.Now
    end
[<EntryPoint; STAThread>]
let main _ =
    let service = new ServiceHost(typeof<Service>, [| new Uri("http://localhost:83/") |])
    service.Open()
    Console.Read()
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<?xml version="1.0" encoding="utf-8"?>
<configuration>
    <system.serviceModel>
        <behaviors>
            <endpointBehaviors>
                <behavior name="webBehavior">
                    <webHttp />
                </behavior>
            </endpointBehaviors>
            <serviceBehaviors>
                <behavior name="serviceBehavior">
                    <serviceMetadata httpGetEnabled="true" />
                    <serviceDebug httpHelpPageEnabled="true" httpsHelpPageEnabled="true" />
                </behavior>
            </serviceBehaviors>
        </behaviors>
        <services>
            <service behaviorConfiguration="serviceBehavior" name="ViTarn.Wcf.Service">
                <endpoint address="" name="WebService" bindingName="WebService" binding="webHttpBinding" behaviorConfiguration="webBehavior"
                    contract="ViTarn.Wcf.IWebService" />
                <endpoint address="StringService" name="StringService" bindingName="StringService" binding="basicHttpBinding"
                    contract="ViTarn.Wcf.IStringService" />
                <endpoint address="DateTimeService" name="DateTimeService" bindingName="DateTimeService" binding="basicHttpBinding"
                    contract="ViTarn.Wcf.IDateTimeService" />
            </service>
        </services>
    </system.serviceModel>
</configuration>
.

F# always implicitly implements interfaces so you need to cast to the interface before you can use it. This is why you see string names. This is okay for WCF.

I think the problem is you need to give names to the arguments on your interface. WCF uses reflection to find the names of the parameters and put them in the message. You add names using the following syntax:

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[<ServiceContract>]

type IWebService =

    [<OperationContract; WebGet(UriTemplate = "{file}")>]

    abstract Get1: file:string -> Stream

Cheers,

Rob

By on 10/24/2008 6:59 AM ()

need to give names to the arguments on your interface. WCF uses reflection to find the names of the parameters and put them in the message. Cheers, Rob

Thanks for your answer first.

The Exception's message is my mother language and very short on my PC. The mean is:
Value can not be empty.
Parameter name: name

I am sorry for the word below. I'm not read your code clearly. Robert is right!

I think it's the reason that you say. But I try to add parameters to attribute of interface. Change parameter name and bindingname in config file. It's not work and jump the same exception many a time. 

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[<ServiceContract(Name = "IStringService")>]
type IStringService =
    [<OperationContract(Name = "GetString")>]
    abstract GetString :unit -> string

I cannot find any explain about Name property in MSDN.

By the way. If I donot define interface, add the attributes to class directly. Although it cannot listen multi endpoint. But it would work fine with one service and one endpoint.
So I think, the issue is INTERFACE

By on 10/24/2008 5:13 PM ()

The issue is the parameter name on methods in the interface.

In the example

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abstract Get1: file:string -> Stream

the key is "file:", it names the first string parameter. It's like "Get1(string file)" in C#. Without the "file:" bit, it's like "Get1(string _unnamed_)" in C#. WCF reflects on the name of the parameter in the interface, which means you need to give it a name in F#.

By on 10/24/2008 5:24 PM ()

F# always implicitly implements interfaces so you need to cast to the interface before you can use it. This is why you see string names. This is okay for WCF.

I think the problem is you need to give names to the arguments on your interface. WCF uses reflection to find the names of the parameters and put them in the message. You add names using the following syntax:

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[<ServiceContract>]

type IWebService =

    [<OperationContract; WebGet(UriTemplate = "{file}")>]

    abstract Get1: file:string -> Stream

Cheers,

Rob

The issue is the parameter name on methods in the interface.

In the example

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abstract Get1: file:string -> Stream

the key is "file:", it names the first string parameter.  It's like "Get1(string file)" in C#.  Without the "file:" bit, it's like "Get1(string _unnamed_)" in C#.  WCF reflects on the name of the parameter in the interface, which means you need to give it a name in F#.

You are Right answer. Thank you very much to my dear Rob and brianmcn. My service has running!

Now I understood: Wcf let us define interface / class / config file. And then he reflects us assembly, read config, open port, listen client.

Reflect the World!

By on 10/24/2008 6:29 PM ()

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