How can I post FileInfo to a web service using Yesod and Http-Conduit? - web-services

Question

I am working with the default Yesod scaffolding project.
I have created a page that displays a simple form to upload files.
(The form will likely be created on the client using Javascript.)
For brevity, the form has a single file input:
<form method="post" action=#{UploadR}>
<input type="file" name="myfile">
<button type="submit">
My objective is to process the form data and then upload the file to a web service.
I have no trouble processing the form, my concern is interacting with the web service.
For example, given the following Yesod handler:
postUploadR :: Handler Html
postUploadR = do
mgr <- fmap httpManager getYesod
fi <- runInputPost $ ireq fileField "myfile"
let fSource = fileSource fi
fName = fileName fi
req <- parseUrl "http://webservice/upload"
let areq = req { method = methodPost
, requestBody = requestBodySourceChunked fSource
}
res <- httpLbs areq mgr
defaultLayout $ do
setTitle "file uploaded"
[whamlet|
<h3> Success
<p> You uploaded #{fName}.
|]
The webservice returns the error: fail post content-length, but everything else works as expected. Perhaps the server doesn't support a chunked request body?

Answer 1

I think your guess about chunked request body is correct. What you need to do is:
Stream the uploaded contents into a temporary file.
Get the size of that file.
Use requestBodySource and provide the file length and its contents.
Fortunately, steps (1) and (2) can be handled quite easily by the sinkCacheLength function. You'll end up with something like:
(fSize, fSource) <- fileSource fi $$ sinkCacheLength