[web-devel] Generating, serving, and deleting temporary files with Wai/Yesod

[Michael Snoyman]

On Sat, Oct 23, 2010 at 11:04 PM, Gregory Collins
<greg at gregorycollins.net> wrote:
> Michael Snoyman <michael at snoyman.com> writes:
>
>> 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.
>
> On unixy systems the "correct" approach traditionally would be to open
> the file, then unlink it before you send the data out the socket. When
> the file descriptor is closed, the link count goes to zero and the file
> goes away. Obviously this isn't portable though.

Besides portability, it doesn't fit in with the WAI request/response
timeline. In WAI, the server won't start sending the response until
the application returns it. Matt got around this problem by using the
ResponseEnumerator constructor, which forces the server to run
arbitrary code, but there's no such mechanism for the ResponseFile
constructor.

So I suppose two other possible approaches might be:

* Extend the ResponseFile constructor to have a cleanup function. I
don't really like this, as I don't think it's generally necessary.
* Fork a thread just before returning the ResponseFile that sleeps for
some amount of time (5 seconds should be *more* than ample) and then
deletes the file.

However, over all, I think Matt has the correct approach given the
constraints involved.

Michael