Internal access modifier is not working the way I thought it would.

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JT - 03 Nov 2006 13:30 GMT

Here is the overall structure I will be referring to:
End-program
    ProvideWorkFlow.dll
        Forms and methods that properly manipulate calls to methods in
AccessUtils
        AccessUtils (a web service)
            Hide.dll
                methods and data I want to remain hidden

I have a DLL, Hide.dll, that contains methods that I want to handle for
end-programmers. The methods in Hide.dll are declared as public. I
have a web service, AccessUtils, that provides access to these methods
by acting as a "go-between". It uses identical method signatures and
just returns the result of the method calls in the DLL. The WebMethods
are declared as public.

Example:
[WebMethod]
public string GetSensitiveInfo(string pKeyValue)
{
Hide.Utils HiddenUtils = new Hide.Utils();
return HiddenUtils.GetSensitiveInfo(pKeyValue);
} // end of GetSensitiveInfo()

Furthermore, there are programmers that need this functionality but
don't need, and shouldn't have, direct access to the methods in
Hide.dll, or even directly use the methods in the AccessUtils web
service. I have a DLL, ProvideWorkFlow.dll, that contains public
Windows Forms and methods that will make the appropriate calls to the
AccessUtils web service in the appropriate order and thereby enforce
the "work flow", although I'm not sure I would call it a true work flow
model. In ProvideWorkFlow.dll, I declare AccessUtils as an "internal"
to try to make its methods available only inside this
ProvideWorkFlow.dll assembly. However, if I act as a programmer that
would be using ProvideWorkFlow.dll, when I go to instantiate one of its
forms, I see that the forms are available, but also the namespace for
the AccessUtils web service is available to be instantiated. I tried
declaring AccessUtils as private in ProvideWorkFlow.dll but it was
still visible and available. I thought the whole purpose of declaring
something as internal was to prevent it from being visible outside the
containing DLL (assembly).

How do I need to set this up so that the end programmer only has access
to the forms and methods declared in ProvideWorkFlow.dll?

Reply to this Message

Dave Sexton - 03 Nov 2006 15:36 GMT

Hi,

You are correct that object definitions and members defined with the internal
modifier will only be visible to the assembly in which they are defined.

If you are able to construct internal classes or call internal methods then I
assume you are doing so from the same assembly. (BTW, namespaces cannot be
instantiated)

Your best option would probably be to build all of it into the
ProvideWorkFlow.dll, since that is the public interface, making objects and
methods private or internal as needed.

Signature

Dave Sexton

> Here is the overall structure I will be referring to:
> End-program
[quoted text clipped - 40 lines]
> How do I need to set this up so that the end programmer only has access
> to the forms and methods declared in ProvideWorkFlow.dll?

Reply to this Message

JT - 03 Nov 2006 17:51 GMT

Thanks Dave,

Actually, I mis-spoke. The classes within the web service's namespace
(AccessUtils) are able to be instantiated from within the end program.
Below I am going to indicate Intellisense options text between pound
signs, #. Also, AccessUtilities will represent the class defined
within the AccessUtils web service. So for instance, if I have a
reference to ProvideWorkFlow.dll and then, in the program, I begin to
instantiate methods and forms from ProvideWorkFlow, I will see
something like the following:

ProvideWorkFlow.InitialContactForm frmInitContact = new
ProvideWorkFlow.InitialContactForm();

ProvideWorkFlow.
#
InitialContactForm
CustomerFeedbackForm
CustomerProcessingMethods
{} AccessUtils <-- web service namespace
FollowUpForm
#

ProvideWorkFlow.AccessUtils.
#
AccessUtilities <-- class containing WebMethods
AssignCustomerToAgentEventArgs
AssignCustomerToAgentEventHandler
StartProcessingCustomerEventArgs
StartProcessingCustomerEventHandler
...
#

ProvideWorkFlow.AccessUtils.AccessUtilities auMethods = new
ProvideWorkFlow.AccessUtils.AccessUtilities();

auMethods.AssignCustomerToAgent(CustomerID, AgentID);

In the previous example, it would be completely inappropriate for the
programmer to have direct access to the AssignCustomerToAgent() method.

To address your other statement, the reason this needs to reside in a
web service is because the database is on a web server that is, well,
who really knows where? So that is why the ProvideWorkFlow.dll
references and instantiates the AccessUtils.AccessUtilities class. So
in ProvideWorkFlow.dll, I make the following declaration:

internal AccesUtils.AccessUtilities auMethods;
...
auMethods = new AccesUtils.AccessUtilities();

Then, the methods in ProvideWorkFlow.dll call the appropriate
AccessUtilities methods in a way that won't violate the business rules.

I reallly thought that would do what I needed. Any other suggestions?

Thanks,

JT

> Hi,
>
[quoted text clipped - 56 lines]
> > How do I need to set this up so that the end programmer only has access
> > to the forms and methods declared in ProvideWorkFlow.dll?

Reply to this Message

Dave Sexton - 04 Nov 2006 03:53 GMT

Hi,

Your example only shows me that you have marked a member variable as internal:

> internal AccesUtils.AccessUtilities auMethods;

However, the class definition is not marked internal and that's why it's
available to be instantiated externally:

namespace ProvideWorkFlow.AccessUtils
{
public class AccessUtilities
{
}
}

should be:

namespace ProvideWorkFlow.AccessUtils
{
internal class AccessUtilities
{
}
}

The problem is that once AccessUtilities is marked as internal it can't be
referenced by the ProvideWorkFlow.dll either. That's why I recommended that
you include the web service in your ProvideWorkFlow.dll instead of a separate
assembly. Then, you can make the web service internal to the ProvideWorkFlow
assembly.

If you require AccessUtilities to be located in a separate assembly then the
easiest solution is to just keep it public and tell your programmers to use
the interface supplied by ProvideWorkFlow.dll classes.

Although, you could use some design pattern to hide the implementation behind
an abstract factory and an interface so that programmers would be more
inclined to use the interface provided by ProvideWorkFlow.dll instead of
creating their own; however, they would be able to implement their own and
directly access the web service if they really wanted.

To be perfectly honest, I don't think it's a good idea to try and shield your
programmers from using the wrong tools, but instead educate them to use the
right ones. I highly recommend fostering open communication. Pair
programming, peer review and unit testing can help to shine a light on
"strays". So don't take the latter choice lightly - use at your own risk!

Signature

Dave Sexton

> Thanks Dave,
>
[quoted text clipped - 118 lines]
>> > How do I need to set this up so that the end programmer only has access
>> > to the forms and methods declared in ProvideWorkFlow.dll?

Reply to this Message

JT - 06 Nov 2006 20:10 GMT

Hey Dave,

Here's my problem. The programmers I'm referring to, I have never met,
may never meet, and may pass on the DLL to people I didn't expect. The
point is to provide this DLL to anyone and everyone who wants to use
it, as long as I can control how they use it. So while I would like to
think that it wouldn't end up in the hands of someone who wants to
cause harm or does so accidentally, I can't count on that.

I'm confused about what you're suggesting. Maybe there's an aspect I
haven't thought of. As far as I know (might not be as far as I think),
there is no way to include the web service in the DLL that I want to
distribute. It must refer to the web service on its web server and
therefore, can't be encapsulated as an additional class in the DLL's
namespace. If I'm wrong, then I'll need explicit instructions on how
to do that. Yes, I was hoping to make the instantiation of auMethods
an internal because I can do that with individual methods within
ProvideWorkFlow.dll, but it doesn't seem to honor that request for the
web service. For all I know, it may not be just web services, but also
instantiated DLLs as well. I haven't tried that yet.

Maybe I'll try marking my class as internal inside the web service, but
I am wondering if that will prevent the ProvideWorkFlow DLL from being
able to use it.

Tricky stuff. I'll let you know what I find.

JT

> Hi,
>
[quoted text clipped - 168 lines]
> >> > How do I need to set this up so that the end programmer only has access
> >> > to the forms and methods declared in ProvideWorkFlow.dll?

Reply to this Message

Bruce Wood - 06 Nov 2006 21:02 GMT

There is no such thing as an "internal assembly" in .NET. That is, once
you declare something public within a DLL then any program can include
that DLL as a reference and use that class / method / field / etc.

Stated another way, the highest level to which access modifiers apply
is the assembly. If something is publicly visible outside a DLL
assembly then it is publicly available to any code that references that
DLL.

> Hey Dave,
>
[quoted text clipped - 197 lines]
> > >> > How do I need to set this up so that the end programmer only has access
> > >> > to the forms and methods declared in ProvideWorkFlow.dll?

Reply to this Message

Dave Sexton - 06 Nov 2006 21:38 GMT

Hi,

You never mentioned that the web service in "Hide.dll" was the actual web
service implementation. I assumed that it was a client web-reference because
your question doesn't make sense otherwise.

In that case, the web service certainly must be in another assembly if
ProvideWorkFlow.dll will be distributed.

Web services provide public interfaces. Anyone can access them and there is
no way to force programmers to use your "ProvideWorkFlow.dll" components,
AFAIK, because there is no way to provide a secure authentication scheme
between your client components and service components that programmers
wouldn't be able to discover and circumvent if they desired.

You cannot mark web methods as internal because that breaks the public
contract to which web services must adhere.

Signature

Dave Sexton

> Hey Dave,
>
[quoted text clipped - 212 lines]
>> >> > access
>> >> > to the forms and methods declared in ProvideWorkFlow.dll?

Reply to this Message

JT - 07 Nov 2006 01:44 GMT

Bruce,

Yes, I see your point, but I have a public DLL, "primary", with a
public method, "primary.a", and its class is being instantiated in
another public method, "secondary", but it's being instantiated inside
an internal method, "secondary.MyInternal". An application that is
referencing the secondary.dll is not able to see primary.dll, which is
what I would want.

Dave,

Well, actually, Hide.dll is referenced by the web service. I know
we're going back quite a bit, so here's the code again:

> >> >> > Example:
> >> >> > [WebMethod]
[quoted text clipped - 3 lines]
> >> >> > return HiddenUtils.GetSensitiveInfo(pKeyValue);
> >> >> > } // end of GetSensitiveInfo()

I'm perfectly willing to let the DLL access the web service. I just
don't want anyone else to access the web service directly. I think
there's a way to hard-code the permissions so that only the DLL can use
the web methods. I just would prefer it if they would never see those
web methods. I guess that's what I'll have to do (if I can).

If any of you have any new insights, I'd be glad to hear them, but I
think the flies are already gathering around this horse.

Thanks to all for your very helpful knowledge.

JT

> Hi,
>
[quoted text clipped - 233 lines]
> >> >> > access
> >> >> > to the forms and methods declared in ProvideWorkFlow.dll?

Reply to this Message

Dave Sexton - 07 Nov 2006 02:43 GMT

Hi,

Web services provide public interfaces.

AFAIK, there is no way to use CAS permissions such as
StrongNameIdentityPermission over SOAP, so I don't think the CLR will be able
to enforce that your assembly can be the only client to access the service.
The reason for this is simple - SOAP is XML and can be spoofed very easily.

Any authentication / authorization scheme that you design will have to be
useable from the ProvideWorkFlow.dll in order for it to access the web
service, which means that all of the security information such as encryption
algorithms and credentials being used will be perfectly visible to any
programmer that has access to the ProvideWorkFlow.dll. No matter the security
mechanism that you choose, even with obfuscation, will just be security
through obscurity, which isn't really security at all.

You won't be able to prevent programmers from accessing your web service.

Instead of trying to prevent programmers from accessing the web service:

1. Provide programmers with all they need in the ProvideWorkFlow.dll so that
they don't go looking for workarounds

2. Carefully architect the web service so that it doesn't expose any
functionality that can be misused, just in case programmers become curious

For example, if you require certain methods to be called in a particular order
then enforce the order of execution within the web service itself, not
ProvideWorkFlow.dll. Web services can support Session information just like
an ASP.NET application, which will make things like that much easier since you
can store context information per connection.

"Using ASP.NET Session State in a Web Service"
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnservice/html/
service08062002.asp

3. Educate programmers about your architecture through documentation. Include
information about the ProvideWorkFlow.dll assembly and the web service that it
requires to run properly. Let programmers know that ProvideWorkFlow.dll
provides the only interface that will be useful to them since it acts as the
facade over a more complex system that requires a working knowledge of
internal implementation details in order to be used properly.

--
Authentication / authorization should be implemented anyway if the web service
will be accessible over a public IP address and contains sensitive
information, but this will only prevent unsolicited access from those clients
that don't have the ProvideWorkFlow.dll. You can't be sure that it will
prevent those that have the assembly from figuring out how to directly access
the web service from their own projects.

"Securing Xml Web Services created using ASP.NET"
http://msdn2.microsoft.com/en-us/library/w67h0dw7(VS.80).aspx

Hide.dll has nothing to do with this, apparently, because you're really just
trying to prevent access to your web service. Please correct me if I'm wrong.

HTH

Signature

Dave Sexton

> Bruce,
>
[quoted text clipped - 292 lines]
>> >> >> > access
>> >> >> > to the forms and methods declared in ProvideWorkFlow.dll?

Reply to this Message

JT - 09 Nov 2006 11:31 GMT

Hi Dave,

As soon as I get the chance, I'll go look through all that. I'm sure
there are some very good approaches in those articles. I appreciate
alll your help.

JT

> Hi,
>
[quoted text clipped - 354 lines]
> >> >> >> > access
> >> >> >> > to the forms and methods declared in ProvideWorkFlow.dll?

Reply to this Message

Internal access modifier is not working the way I thought it would.

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