Prevent multiple nodes fopen-ing the same file

Should fix a server crash with the legacy downloader when multiple players try to receive the same file simultaneously.

Also displays the strerror output when this error occurs.

"Works" in the sense that the message appears when I force the file not to exist.

The current problem with this branch right now is that now if two players are downloading the same file, one is forced to wait, but once a player is done finishing downloading that file, the waiting player doesn't "resume" downloading, it just gets stuck, which should be fixed.

I think this branch could just be the error message to start with, because as far as I personally tested there's no problems when two players download the same file through the internal downloader. Once we see actual error messages pop out I believe a better solution can be found. Rescinding this part of the comment because opening the same file multiple times does lead into implementation-defined behaviour which is dangerous.

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• 533dc7d6 - Use strerror when file transfer can't be opened

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marked this merge request as draft

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• cc54d98a - New system to prevent multiple fopen

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• c332d48e - Only reseek if we have to

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marked this merge request as ready

merged

mentioned in commit e8dee823