sendFile and delete file afterwards?

[email protected]

unread,

Apr 2, 2021, 4:20:09 AM4/2/21

to Yesod Web Framework

Hi all,

In a GET handler, I need to

run an external command to generate a file
send the file with sendFile
delete the file afterwards

The problem is that sendFile is a short-circuit response, it skips the rest of the handler code.

How can I still delete the file afterwards? Or do I have to use an clean-up cronjob? I think the first option would be safer especially if the temporary files are stored on tmpfs.

Regards, Jakob

Michael Snoyman

unread,

Apr 2, 2021, 5:45:06 AM4/2/21

to [email protected]

You can leverage the MonadResource instance to schedule a cleanup when the request handling is finished. Using allocate[1], for instance, to create a new temporary file and schedule its deletion, would work.

[1] https://www.stackage.org/haddock/nightly-2021-04-02/resourcet-1.2.4.2/UnliftIO-Resource.html#v:allocate

--
You received this message because you are subscribed to the Google Groups "Yesod Web Framework" group.
To unsubscribe from this group and stop receiving emails from it, send an email to [email protected].
To view this discussion on the web visit https://groups.google.com/d/msgid/yesodweb/a1539366-e197-42a9-ac4b-6f64c582f321n%40googlegroups.com.

[email protected]

unread,

Apr 3, 2021, 11:55:43 AM4/3/21

to Yesod Web Framework

Thank you Michel! It works:

import Control.Monad.Trans.Resource (allocate)

createAndSendImage :: Handler TypedContent

createAndSendImage = do
(_, (imageFile, tempDir)) <- allocate allocateResource freeResource
putStrLn $ pack imageFile
sendFile typePng imageFile
where
    allocateResource :: IO (FilePath, FilePath)
    allocateResource = generateLilyPond >>= runLilyPond "/mnt/tmpfs" LyPng
    freeResource :: (FilePath, FilePath) -> IO ()
    freeResource (_, tempDir) = removeDirectoryRecursive tempDir

Reply all

Reply to author

Forward