ErrorClosed exception from Network.HTTP.simpleHTTP — trying to upload images via XML-RPC with haxr

I’m trying to use haxr 3000.8.5 to upload images to a WordPress blog using the metaWeblog API—specifically, the newMediaObject method.

I’ve gotten it to work for small images, having successfully uploaded 20×20 icons in both PNG and JPG formats. However, when I try medium-sized images (say, 300×300) I get an ErrorClosed exception, presumably from the HTTP package (I did a bit of source diving, and found that haxr ultimately calls Network.HTTP.simpleHTTP).

Can anyone shed light on the reasons why a call to simpleHTTP might fail with ErrorClosed? Suggestions of things to try and potential workarounds are also welcome.

Here are links to full tcpdump output from a successful upload and from an unsuccessful upload.

The (sanitized) code is also shown below, in case it’s of any use.

import           Network.XmlRpc.Client      (remote)
import           Network.XmlRpc.Internals   (Value(..), toValue)
import           Data.Char                  (toLower)
import           System.FilePath            (takeFileName, takeExtension)
import qualified Data.ByteString.Char8 as B
import           Data.Functor               ((<$>))

uploadMediaObject :: FilePath -> IO Value
uploadMediaObject file = do
  media <- mkMediaObject file
  remote "http://someblog.wordpress.com/xmlrpc.php" "metaWeblog.newMediaObject"
    "default" "username" "password" media

-- Create the required struct representing the image.
mkMediaObject :: FilePath -> IO Value
mkMediaObject filePath = do
  bits <- B.unpack <$> B.readFile filePath
  return $ ValueStruct
    [ ("name", toValue fileName)
    , ("type", toValue fileType)
    , ("bits", ValueBase64 bits)
    ]
  where
    fileName = takeFileName filePath
    fileType = case (map toLower . drop 1 . takeExtension) fileName of
                 "png"  -> "image/png"
                 "jpg"  -> "image/jpeg"
                 "jpeg" -> "image/jpeg"
                 "gif"  -> "image/gif"

main = do
  v <- uploadMediaObject "images/puppy.png"
  print v