[Haskell-cafe] CURL and upload a file

[Evgeny Dzhurinsky]

Hello!

I am trying to find out the way of uploading a file using HTTP
multipart/form-data.

I created simple application aimed to upload an image to imgpaste.com.
The source is below:

=========================================================
module ImgPaste.Upload where

import Control.Monad
import Network.Curl
import Data.ByteString
import Text.Regex.PCRE
import Text.Regex.PCRE.ByteString

type LocalCtx = ( ByteString, ByteString, ByteString, [ByteString] )
type UploadResult = Either UploadError ByteString
data UploadError = UploadError {
   message :: String,
   response :: ByteString
} deriving (Show)

extractResponse :: CurlResponse_ [(String,String)] ByteString -> ByteString
extractResponse = respBody

uploadFile :: String -> IO (ByteString)
uploadFile fileName = initialize >>= withCurlDo . (flip
uploadFileWithCurl fileName)

uploadFileWithCurl :: Curl -> String -> IO ( ByteString )
uploadFileWithCurl curl fileName = do
   liftM extractResponse $ do_curl_ curl "http://imgpaste.com/"
       [CurlPost True, CurlHttpPost postData, CurlVerbose True ]
   where
       postData = [
            HttpPost "upfile"
                Nothing
                ( ContentFile fileName )
                []
                Nothing,
           makeFormPost "submit" "Upload",
           makeFormPost "keep" "a"
           ]
       makeFormPost name value = HttpPost name Nothing
           (ContentString value)
           []
           Nothing

-- <input type="text" name="copyfield" size="31"
value="http://imgpaste.com/tmp/123456.png" />

extractUrl :: ByteString -> UploadResult
extractUrl src = match (src =~ "<input type=\"text\"
name=\"copyfield\" size=\"31\" value=\"([^\"]+?)\" />" :: LocalCtx)
   where
       match (_,_,_,[x]) = Right x
       match _ = Left $ UploadError "Can not parse content." src

pasteImage :: String -> IO ( UploadResult )
pasteImage = liftM extractUrl . uploadFile
=========================================================

however when invoking the function: pasteImage "image.png" no data is
posted to the server. The protocol dump looks like:

=========================================================
POST / HTTP/1.1
Host: imgpaste.com
Accept: */*
Content-Length: 241
Expect: 100-continue
Content-Type: multipart/form-data;
boundary=----------------------------630d154aaf3b
=========================================================

so the request data is not sent. Can somebody please advice, what am I
doing in a wrong way?

Thank you in advance!


--
regards
Eugene Dzhurinsky