dropPreamble :: ByteString -- ^ The boundary, without the initial dashes
             -> ByteString 
             -> ByteString
dropPreamble b s | BS.null s = BS.empty
                 | isBoundary b s = dropLine s
                 | otherwise = dropPreamble b (dropLine s)
dropPreamble :: ByteString -- ^ The boundary, without the initial dashes
             -> ByteString 
             -> ByteString
dropPreamble b s | BS.null s = BS.empty
                 | isBoundary b s = dropLine s
                 | otherwise = dropPreamble b (dropLine s)
dropPreamble b s | BS.null s = BS.empty
                 | isBoundary b s = dropLine s
                 | otherwise = dropPreamble b (dropLine s)