[web-devel] Generating, serving, and deleting temporary files
michael at snoyman.com
Sat Oct 23 19:54:39 CEST 2010
On Fri, Oct 22, 2010 at 8:21 PM, Matt Brown <matt at softmechanics.net> wrote:
> Hello all,
> I've been experimenting with generating graphs from log files using
> timeplot and serving them with yesod. Each generated graph is only
> served once, so I need a way to clean them up. A cron job would be
> ok, but it's one more thing I'd have to remember to do, and I'm lazy.
> Instead, I'd like to pass a "clean up action" to the enumerator
> sending the file, to be performed after EOF is reached. For most
> files, this would just close the handle. For temp files, it would
> also delete the file. Here's the gist of it:
> The first revision defines a monolithic fromTempFile :: FilePath ->
> Enumerator. The second imports a factored version from
> Network.Wai.Handler (see my wai commit:
> Not sure wai is the place for it. Perhaps wai-extra would be a better?
> Does this seem like a good approach?
This does seem like the right approach. Just as fair warning: using an
enumerator for serving files loses out on the possible optimization of
a sendfile system call. Another possibility may be to keep a pool of
file names to use as temporary files and keep rotating their usage.
But I *do* think your approach is the correct one.
Regarding the API changes to wai: they seem reasonable, and I'd
probably accept them. Some concerns about the implementation:
* Instead of fromHandle' and fromFile', perhaps fromHandleFinally and
* In fromFile', why are you calling hClose? withBinaryFile
automatically closes the file handle. Are you worried about the
temporary file getting deleted while the file handle is still open?
* In fromHandle', onEOF won't get called if the iteratee returns Left.
Is this intended behavior?
* Your code won't work in the presence of exceptions. Ideally the body
of fromHandle' would be wrapped with a call to finally. This point is
related to the previous one.
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