C# DLL 从 C++ 应用程序调用 SOAP Web 服务

Question

Following numerous articles online, I created a simple C# DLL Class Library that has just one method called Add. It accepts 2 integers and returns an integer like below. I also went to project properties > build > and selected "Register for COM interop" option:

namespace CSDLL
{
    [ComVisible(true)]
    public interface IMyClass
    {
        int Add(int x, int y);
    }

    [ComVisible(true)]
    [ClassInterface(ClassInterfaceType.None)]
    public class MyClass : IMyClass
    {
        public int Add(int x, int y)
        {
            return x + y;
        }
    }
}

I built it successfully (as admin) and it generated CSDLL.dll and CSDLL.tlb files.

Next I created a simple C++ console app like so:

#include "stdafx.h"
#include <Windows.h>
#import "C:\path\to\my\CSDLL.tlb" no_namespace

int main()
{
    CoInitialize(NULL);

    IMyClassPtr obj;
    obj.CreateInstance(__uuidof(MyClass));
    printf("Add result = %d\n", obj->Add(2, 5));
    CoUninitialize();
    getchar();

    return 0;
}

If I run this, I get expected result printed on console window. So, that is all fine.

Next I modified my Add method so that instead of adding 2 integers, it calls a SOAP endpoint. I wrapped the code in try...catch and I return 1 if SOAP executed as I would expect, 0 if it did not return what I expect, and I return 2 from within a catch block, meaning there was an exception like so:

public int Add()
{
    try
    {
        BasicHttpsBinding binding = new BasicHttpsBinding();
        binding.Security.Mode = BasicHttpsSecurityMode.Transport;
        binding.Security.Transport.ClientCredentialType = HttpClientCredentialType.Basic;
        binding.UseDefaultWebProxy = false;

        EndpointAddress address = new EndpointAddress(myEndPointString);

        // create service myService by passing it binding and endpoint address
        // pass necessary parameters to the service
        // set ClientCredentials for my service
        // get response from the service
        MyServiceResponse resp = myService.DoSomething();
        if (resp.acknowledged)
        {
            return 1;
        }
        else
        {
            return 0;
        }
    }
    catch (Exception ex)
    {
        // just return 2 in case of an exception
        return 2;
    }
}

If I call this modified DLL from a C++ console application, it always return 2 = meaning some exception was thrown and cought by my code above. I am on .NET Framework 4.8.

However, if I call it from a C# console application which I created by adding reference to my C# DLL above, the call to Add returns 1 = meaning it executed successfully with result I would expect to get from it.

So, the same C# DLL returns 2 different results depending whether it is called from C++ or C# Console application.

After setting some breakpoints and debugging my DLL, I found that the call to DoSomething response is throwing exception with following messages:

Exception Message: Message = "An error occurred while making the HTTP request to https://server-address:port/path . This could be due to the fact that the server certificate is not configured properly with HTTP.SYS in the HTTPS case. This could also be caused by a mismatch of the security binding between the client and the server. Inner Exception Message: Message = "Authentication failed because the remote party has closed the transport stream."

Why is it having this issue if the DLL is called from a C++ console app and not if the same DLL is called from a C# console app? It has to do something with security I guess as both will execute just fine if calling simple math Add method but if calling a method that does SOAP request, the C# console app will execute just fine whereas C++ console app will cause the DLL to throw exception?

Answer 1

After lots of reading, it turns out the reason for this was that SecurityProtocol gets set to different SecurityProtocolType if the C# DLL is called from a C# vs C++ application.

In order to resolve, I had to set SecurityProtocol like below before making any request:

if (ServicePointManager.SecurityProtocol == (SecurityProtocolType.Ssl3 | SecurityProtocolType.Tls))
{
    // This was crucial to do to make web service call work when C# DLL is called 
    // from a C++ app.  It turns out that if webservice call is made:
    //   1) from C# console app calling C# DLL that makes web service call, 
    //      the SecurityProtocol is set to TLS | TLS11 | TLS12 | TLS13
    //   2) from C++ console app calling C# DLL that makes web service call,
    //      the SecurityProtocol is set to SSL3 | TLS
    // In case of 2) above, the call would throw exception as explained above
    // whereas 1) would work just fine.
    ServicePointManager.SecurityProtocol = SecurityProtocolType.Tls 
       | SecurityProtocolType.Tls11 
       | SecurityProtocolType.Tls12; 
       // TLS13 was not available for some reason, so did not set it here
}