Interpreting and/or receiving dotNet code at run-time

Question

Html can contain little bits of Javascript embedded in it (e.g. defined in onclick event handlers).

1. If I were writing an Html browser using a dotNet language like C#, what technologies or APIs could I use to run such Javascript fragments, given that I don't receive it until run-time (and receive it as string data, not as executable code)?

2. Is it any easier or harder if the code to be run were C# snippets rather than Javascript?

3. Is there any technique which doesn't require my code to have unusual priviledges? For example, a method like CodeCompiler.FromSource requires SecurityPermissionFlag.UnmanagedCode (which seems to me excessive: I don't see why it's so risky to compile code).

4. If I controlled the server-side as well as the client-side code, I could also consider compiling such script fragments on the server instead of on the client, and then sending it as precompiled code to the client side to be executed. Is there a way to send such code (a dotNet assembly, presumably) over the network to the client, have client-side code receive it from the network into client-side RAM, and invoke it on the client side without storing it as a file on a client-side disk drive?

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Edit

I have answer to the first three questions: I've resigned myself to the fact that compiling takes high privileges. I don't see why; maybe (although I don't find this a very convincing reason) it's because the compiler is implemented using unmanaged code. Maybe this will change when they reimplement the compiler using managed code, in maybe the "C# version 5" timeframe. In any case, whatever the reason, that seems to be the way it is, and there are no work-arounds (other similar APIs but which require fewer privileges).

My remaining question then is how to get an Assembly instance from one machine to another. When I have time I'll find out whether untrusted code can run the Assembly.Load(byte[] rawAssembly) method.

Answer 1

1. Server side Javascript is one of the languages supported by the .NET platform. I used it many times in the scenrios when you need to insert small code snippets into existing code. Runtime it can be loaded from i.e. database and compiled, so there is no preformance penalty.

2. From the standpoint of making the plumbing work (retrieveing the source, compiling it, etc.) there is no difference. With strongly typed languages though it is much more difficult to assemble code snippets into a compilable compilation unit.

3. Permissions is certanly a challenge. I am not sure about the specific permission you mentioned, but security is a concern, after all the source you compile can be anything and if you are not careful about the source of your code it can become the backdoor into your system

4. The answer to this one is - yes of course. You can load an assembly from anywhere, not necessarily from a file, you can also compile in memory - that's what I do. There is no dll file in this case.

Answer 2

You're asking several questions, sort of, so I'll give you an idea on one of them. There's a very good article and some code samples from: http://www.west-wind.com/presentations/dynamicCode/DynamicCode.htm which talks about compiling and executing C# code at runtime. I found it very useful and I am using this in a standard c# application. Seems like it would be usable for your problem as well.