How to intercept the access to a file in a .NET Program

Question

I need to intercept when the system tries to access to a file, and do something before it happens.

Answer 1

You can use FileSystemWatcher - but this doesn't let you intercept the event and do things before hand - it only informs you after the fact that a particular file or directory has been affected in some way.

Intercepting file access is not something you can do easily.

You can write a file system filter driver, which is an unmanaged DLL which the O/S will load that can intercept operations on files or folders. However, this isn't a trivial task.

What are you trying to achieve, perhaps there's a simpler alternative?

Answer 2

There's a very similar thread here: How could I prevent a folder from being created using a windows service?. It may provide some more insight, but @LBushkin has already provided the same conclusion.

Answer 3

Interesting question. What kind of access? Read, write, delete, copy?

• If you need to prevent access to a file then the security would be the way. Then you can capture the access and do delegate the task to a higher privileged execution engine. Such as a service running as higher privileged user.

• If you want to stop system level access then you'll need an IFS filter.

• If all access is via your code, then I'd suggest a library that prevent's access.

• And as other people have mentioned, there is the FileSystemWatcher, but I think this post access not before.

Answer 4

Check http://easyhook.codeplex.com/, it provides you directly from c# c++ like dll method overwritting.

Answer 5

Using just .net it is impossible