In java you have package level protection that ensures classes are only usable within the package.
Namespaces in C# act more or less like packages. But C# does not have a protection level for protecting classes within a namespace.
Is there a specific reason for this?
There is no such access modifier: the closest modifier is internal, but the unit of protection is the assembly in which the class resides, not its namespace.
One could argue that it is possible to achieve similar level of control using internal, because both kinds of restriction keep outsiders from accessing the implementation details of your library. The only person to whom it makes a difference is you, the writer of the library, and you are in full control of what to expose and what to hide anyway. Essentially, it means that if you do not want to use a class outside its namespace, simply refrain from using it; if the class is internal, nobody else will be able to use that class either.
In .NET there are assemlies(dll or exe files), you can use internal modifier to limit access only within the same assembly
Is there a specific reason for this?
Mostly, it's because there are some key differences between packages and namespaces
To simplify what's already been said in the linked question and here: Namespaces in C# are mostly to help with organizing an assembly's contents, both internally and externally. Java packages have more in common with C# assemblies, and there is an access modifier in C# that restricts to the assembly level: internal.
Related
In C#, is it possible to restrict who can call a method at compile time?
I've looked into directives, but that didn't work since I can't assign values to symbols.
#define WHO VisualStudioUser.Current // does not work
I also looked into Code Access Security (CAS) but that's runtime enforcement, not compile time.
The requirement is to restrict access to a method at compile time for specific developers given the method exists in a pre-compiled assembly.
here's more details...
I'm building a framework or a series or assemblies for a team of developers. Because of our software license restrictions, I can only allow a few developers to write code to make a call to some restricted methods. The developers will not have access to the source code of the framework but they'll have access to the compiled framework assemblies.
The quick answer will be: No this isn't possible, and if you need to do it, you're Doing It Wrong.
How would this even work? Does it depend who who's running the code or who wrote it?
Edit There's kind of a way using InternalsVisibleTo and restricting accessing in source control to the assemblies that InternalsVisibleTo is specified for. See Jordão's answer
The requirement is to restrict access to a method at compile time for specific developers given the method exists in a pre-compiled assembly.
One way is to mark the method private or internal, it won't be callable by anyone outside the assembly. UPDATE: Also take a look at the InternalsVisibleTo attribute, which is used to define which assemblies can "see" internals of your assembly.
Another way is to divide the code you want to distribute from the code you don't want people to call into separate assemblies. Maybe you just share an assembly mostly of interfaces with your users, that they them compile against; and you have a separate assembly with implementations that they shouldn't reference directly. Your internal team would have access to the implementation assembly. This is just a common form of dependency management, the dependency inversion principle.
Draft:
Compile the restricted code into (obfuscated) DLLs: TypeA.dll, TypeB.dll etc.
Define an interface for each type, and compile them into separate DLLs: ITypeA.dll, ITypeB.dll etc.
Create a "guard assembly", and embed all restricted assemblies into it: Guard.dll. This has a ResolveEventHandler, and methods to instantiate different types defined in the embedded restricted DLLs. Instances are returned through their interface.
Developers get the interface DLLs and the Guard.dll. Each developer can get a Guard.dll with special authentication tokens in it. For example, a Guard.dll can be bound to PC, an IP address, a GUID issued to the developer, anything.
The developer can instantiate those types for which she has the proper authentication code, and uses the object instance through an interface.
Sorry this is a bit fuzzy, because it was more than a year ago when I used these techniques. I hope the main idea is clear.
Can you try using Extensible C# developed by ResolveCorp, some of the links for study and implementation are:
http://zef.me/782/extensible-c
http://www.codeproject.com/KB/architecture/DbCwithXCSharp.aspx
http://weblogs.asp.net/nunitaddin/archive/2003/02/14/2412.aspx
http://www.devx.com/dotnet/Article/11579/0/page/5
Okay, I have a solution I am working on that has 4 different projects in it. One of my projects (a console application) is trying to make reference to some of the classes defined in another project (a library); the only problem is, those called are defined as Internal in the library.
How can I use these Internal classes in other assemblies/projects in the same solution? I added references to the library, but that did not help. It is saying that the protection level is too high (because it is internal, it is only available in that assembly).
You generally shouldn't access something that's internal. That defeats the purpose of declaring it so in the first place. If, however, you do need to...
If you can change the assembly with internal things, either:
Make the classes public, or
Use the InternalsVisibleToAttribute to expose it to just the assemblies you want to.
If you cannot change it, or decide not to, then you can use reflection to access the internal classes. For some portions of what you then do with the class, you should be able to use the dynamic keyword to make access easier and faster than with reflection.
You must use reflection to access the internal classes in other assemblies, but it will be significantly slower and not generally optimizable by the compiler. It's also somewhat complicated.
It is recommended that you expose a public class that wraps your internal classes and methods from the other assembly, or simply switch the internal classes in the other assembly over to public.
I have two class libraries "MyLibrary.dll" and "MyLibraryEditor.dll" for a Unity runtime and editor extension. There are several class members inside "MyLibrary.dll" that are only intended for use by "MyLibraryEditor.dll".
My first thought was to use the internal keyword because I mistakenly thought that this constrained visibility to a namespace. Instead it is clear that this keyword limits visibility to the assembly.
What is the best way to constrain access to some class members to "MyLibrary.dll" and "MyLibraryEditor.dll" without hurting performance? Also, reflection is not an option.
I am happy to simply not document the functions, but unfortunately Intellisense (and MonoDevelop's equivalent) show these members.
If you want internals in one assembly to be visible from another assembly, you can use the InternalsVisibleTo attribute on the assembly containing the internals. See http://msdn.microsoft.com/en-us/library/system.runtime.compilerservices.internalsvisibletoattribute.aspx:
[assembly:InternalsVisibleTo("MyLibraryEditor")]
That answered, you might want to rethink your architectural design so that you don't need to use it, since it will open up all internals to the other assembly, not only the ones that you want.
You could make the members internal but use [InternalsVisibleTo] to give access to those members to the other assembly. They'd still be visible within the same assembly as well, of course... there's no way of getting round that.
I primarily use InternalsVisibleToAttribute for giving access to internal members to test classes, and would try to avoid doing this for non-test purposes - but sometimes it can be useful.
This is not possible using pure C# concepts. You are two seperate assemblies, that is as far seperate as you can get, and there is no relationship between the two as far as .Net is concerned.
you could do some things with signing or validation to make it so it would be difficult to use one assembly without the other, but not something you can do to prevent visibility of the classes/members.
I have an assembly which is being developed to create a facade around some potentially sensitive functionality and I want to allow a third party to call some of the methods contained within it but not others.
How can I prevent the third party calling unauthorised methods given they will have access to the entire DLL (I'm not concerned about them seeing the code, just executing it)?
This has to be compatible with the .net compact framework so unfortunately using the StrongNameIdentityPermission attribute is not possible.
I think you should ship two Facade implementations, one for 'internal' consumers which exposes all methods and another external that exposes only the sub-set. You can achieve this whilst maintaining only one code base by having two separate build processes. One technique that springs to mind is to use compiler directives to exclude a method from the external build, or mark it internal if it is required by other public methods. If you do ship sensitive methods with internal modifiers you may also want to implement obfuscation.
EDIT
Perhaps it would be cleaner, rather than having directives around each method to use partial classes, define a partial class for the sensitive methods and put the entire class implementation in a directive.
public partial class MyClass
{
public void NonSensitive(){}
}
#if INTERNAL_BUILD
public partial class MyClass
{
public void Sensitive(){}
}
#endif
You can have this partial class in the same or a separate file, which might be a nice level of separation as you could prepend the file name x_Sensitive.cs or similar.
Description
Assuming i understand your question.
You can mark your methods with the internal access modifier to make them not
accessable from other librarys.
But this does not help from security persepective, because it is always possible to run the method using reflection.
The internal keyword is an access modifier for types and type members. Internal types or members are accessible only within files in the same assembly
More Information
MSDN - internal (C# Reference)
If a third party can see the code, then they can run it - there is nothing you do to stop this.
Note however you have an application which is loading 3rd party plugins then you could load plugin assemblies with restrictions that prevent it from using reflection - this would mean that you can mark these methods / classes as internal to prevent plugins from being able to call these methods when loaded as a plugin in your application. Depending on the nature of the sensitive functionality this may or may not be useful to you from a security perspective.
For information on how to do this see How to: Run Partially Trusted Code in a Sandbox
Could you offer the functionality that you want the third party to consume as a Web API? They will not have any access to the source code OR the compiled binaries. They will only be able to see exactly what you want them to see. This would also offer additional security features such as Authentication and Authorization of callers.
I have the idea that it might be useful to enforce type visibility between namespaces rather than assemblies (internal) in C#.
It would seem that such a concept would assist developers working with a codebase, ensuring the correct types are used in places where another internal type supplying similar functionality is available, but would result in "architectural" disadvantages (unwanted dependencies etc).
Do others think this would be useful and is it currently possible? If not why not?
Also, would the concept of preclusions - the ability to specify negative constraints on references between namespaces and / or assemblies be a useful addition to C#?
A type is strongly bound to the assembly in which it is defined. A namespace is not, it can appear in multiple assemblies. System.Configuration for example.
Let's assume for a moment that the metadata format for an assembly would be changed (-1 billion points) to store attributes for a namespace. Those attributes would still have to be stored in an assembly because that's the storage unit for metadata. Now you have to deal with the possibility that the CLR loads another assembly and finds the same namespace but with conflicting attributes. How could it possibly resolve that?
More seriously, how would you prevent external code from simply using the same namespace and attributes to suddenly get access to implementation details that were meant to be private. This completely destroys the value of having the internal keyword.
You could make them public, tag them with a custom attribute, and then add a FxCop rule to check for accesses from the outside of the namespace.
This doesn't securely enforce the restriction and fails when the member is accessed with reflection, but if it's only about policy/codingstyle this should be enough.
I think there is also an existing attribute to hide members from Intellisense which you might use in conjunction with your custom attribute.