Kyle Graehl home

Chrome fileSystem notes

(Update – I found out what the problem was. The app was being “suspended” and I was not listening for the event. When an app is suspended, nothing is guaranteed to work anymore). So make sure and listen for the chrome.runtime.onSuspend event!

I’ve been trying to fix a bug in JSTorrent for the past few days. The problem I’m seeing is that an HTML5 DirectoryEntry reference becomes “stuck” – doing any sort of request against it like .getFile() or .getMetadata() simply does not fire any callbacks. I’ve rewritten the whole Disk I/O subsystem of JSTorrent, hoping to get better insight into which conditions trigger this “broken” state.

One thing I’ve started doing is keeping a cache of FileEntry objects and re-using those. That seems to work pretty well. I haven’t run into any issues re-using a FileEntry reference, even when the underlying file changes due to other processes writing to or truncating the file.

However, if you do the same thing to the result of a FileEntry.file() (the actual File object on which you can do .slice() and use a FileReader to do reads), the reference becomes invalid once the underlying file is modified in any way (even “touch”ing the file will make the file reference invalid)

Originally I wanted to use the synchronous versions of all these APIs because that would have been much simpler. But unfortunately there is no way to pass a FileEntry to a web worker, (, and you need a FileEntry to be able to do file operations (currently you call FileEntry.createWriter and get a FileWriter object).

Experiment: what happens when you have a cached DirectoryEntry and somebody moves the file? It fires the error callback to whatever you try to do on it.

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