Node-solid-server: Locking files when writing to avoid concurrency issues

[nicola]

The idea is to avoid two people writing at the same time

[nicola]

I have done some thinking and I think there is only a way to achieve this and still being working async. In other words, reads are fine to be async as they are, but for writes, the server has to have a global state of what file is being written at the moment which has some sort of queuing (or even simpler nextTick) until the resource is free.

By bringing back sync, a possible attack could be loading a 10 GB file while two people are chatting (hence breaking their conversation)

[RubenVerborgh]

Not a problem right now, can reconsider in the future.

[RubenVerborgh]

Reopening, as the future is now.

[RubenVerborgh]

Fixed in https://github.com/solid/node-solid-server/pull/1116