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 becomes reasonable.

The easiest way to stream response of an HTTP request is to use the reqBr function in conjunction with responseBodySource:

{-# LANGUAGE OverloadedStrings #-}

module Main (main) where

import Data.Conduit ((.|), runConduitRes)
import Data.Default.Class
import Network.HTTP.Req
import Network.HTTP.Req.Conduit
import qualified Data.Conduit.Binary as CB

main :: IO ()
main = runReq def $ do
  let size = 100000 :: Int
  reqBr GET (https "httpbin.org" /: "bytes" /~ size) NoReqBody mempty $ \r ->
    runConduitRes $
      responseBodySource r .| CB.sinkFile "my-file.bin"

This solution benefits from the fact that Req still handles all the details like handling of exceptions and retrying for us. However this approach is only viable when the entire pipeline can be run in IO monad (in the function that is the last argument of reqBr).

If you need to use a more complex monad, use the lower-level function req':

{-# 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
import Network.HTTP.Req
import Network.HTTP.Req.Conduit
import qualified Data.Conduit.Binary as CB
import qualified Network.HTTP.Client as L

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
    (\request manager ->
      bracketP (L.responseOpen request manager) L.responseClose
        responseBodySource)
    .| CB.sinkFile "my-file.bin"

req' does not open/close connections, handle exceptions, and does not perform retrying though, so you're on your own.