Tuesday, August 02, 2005

Operation Atomcity

This is the second blog post for today, but it really belongs as a separate topic.

This just hit me while I was mucking around finalizing the locking code. There might be an issue with concurrent requests, since the webDAV is running off the file system directly.

For example, if a file is constantly GETed, there will be no way to DELETE it since delete will fail because the file is always open for reading for the GET processes. Denial of Delete Service attack? There are potential clashes like this that could cause methods like MOVE or COPY to fail, even if the client does all the proper LOCKing beforehand.

The simple fix is to put a threading.RLock over all the operations, so that only one operation is being done, and done to completion before the next one comes in, but this really limits the server to a pseudo -single thread- operation, which is really means no concurrency support. The complex way would be to define locks such that operations can only be carried out concurrently if they do not conflict, defined loosely as if the two requests are not direct ancestor/descendants of each other in the file structure (since operations can have Depth == infinity).

I am just wondering if this level of robustness is required here......

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