Windows Explorer error messages?

Question

I'm wondering where Windows Explorer gets it's error messages from. My situation is quite specific, in that I'm using a custom WebDAV implementation, but the question I think could apply more broadly (any mapped drive).

So let's say I've got a mapped drive to my WebDAV share. I open the mapped drive window in Windows Explorer and from there I try and create a new folder. Now in my custom WebDAV implementation, I'm looking for the MKCOL WebDAV verb which creates folders, and in this case, I want to prevent the folder from being created. So I'm returning a 400 (Bad Request) back as the HTTP response.

The problem is, now matter how I handle this, Windows Explorer will pop up an error message that says:

File Too Large. The file '<%1 NULL:NameDest>' is too large for the destination file system.

What file is too large when the request is attempting to create a folder?

What I'm trying to figure out is where Windows Explorer got that? I can see all the details of how I'm handling the response using Fiddler (for example I can return custom exception details in the 400 response), so how does it connect my 400 to the message I'm getting above? Is there any way I can format the HTTP Response so that Windows Explorer will take the details I provide and use them in the error message?

Answer 1

Explorer treats ERROR_INVALID_PARAMETER as "file too large" since that's how some file systems report that error condition.