Network.HTTP.Req.Conduit

The module extends functionality available in Network.HTTP.Req with Conduit helpers for streaming big request bodies.

The package re-uses some pieces of code from the http-conduit package, but not to the extent that depending on that package is reasonable.

Streaming request bodies

data ReqBodySource

This body option streams contents of request body from the given Source. The Int64 value is size of the data in bytes.

Using of this body option does not set the Content-Type header.

Constructors

ReqBodySource Int64 (Source IO ByteString)

Instances

HttpBody ReqBodySource

Methods

getRequestBody :: ReqBodySource -> RequestBody

getRequestContentType :: ReqBodySource -> Maybe ByteString

Streaming response bodies

Streaming response is a bit tricky as acquiring and releasing a resource (initiating a connection and then closing it in our case) in the context of conduit streaming requires working with the ResourceT monad transformer. This does not play well with the framework req builds.

Essentially there are only two ways to make it work:

• Require that every MonadHttp must be an instance of MonadResource. This obviously makes the req package harder to work with and less user-friendly. Not to mention that most of the time the instance won't be necessary.
• Use the withReqManager in combination with ReturnRequest response interpretation to get both Manager and Request and then delegate the work to a custom callback.

We go with the second option. Here is an example of how to stream 100000 bytes and save them to a file:

{-# LANGUAGE FlexibleInstances #-}
{-# LANGUAGE OverloadedStrings #-}

module Main (main) where

import Control.Exception (throwIO)
import Control.Monad.IO.Class (MonadIO (..))
import Control.Monad.Trans.Resource (ResourceT)
import Data.Conduit ((=$=), runConduitRes, ConduitM)
import Network.HTTP.Req
import Network.HTTP.Req.Conduit
import qualified Data.Conduit.Binary as CB

instance MonadHttp (ConduitM i o (ResourceT IO)) where
  handleHttpException = liftIO . throwIO

main :: IO ()
main = runConduitRes $ do
  let size = 100000 :: Int
  req' GET (https "httpbin.org" /: "bytes" /~ size) NoReqBody mempty httpSource
    =$= CB.sinkFile "my-favorite-file.bin"

httpSource

Arguments

:: MonadResource m

=> Request

Pre-formed Request

-> Manager

Manger to use

-> Producer m ByteString

Response body as a Producer

Perform an HTTP request and get the response as a Producer.