Make Network.Wreq.Proxy from Network.HTTP.Proxy.Proxy - haskell

Question

Network.HTTP.Proxy has a nice function called fetchProxy:
fetchProxy :: Bool -> IO Proxy
fetchProxy flg gets the local proxy settings and parse the string into
a Proxy value. If you want to be informed of ill-formed proxy
configuration strings, supply True for flg. Proxy settings are sourced
from the HTTP_PROXY environment variable [...]
I want to use the Proxy obtained this way with Wreq library, which has it's own Proxy defined like this, by importing it from HTTP:
import Network.HTTP.Client.Internal (Proxy(..), Response)
There appears to be a type mismatch between Network.HTTP.Proxy.Proxy and Network.Wreq.Proxy, where I presume they must be identical.
I import both like this:
import Network.Wreq
import Network.HTTP.Proxy (fetchProxy)
How can I use HTTP.Proxy.Proxy with Wreq and why does GHC see them as different types?

Answer 1

It's likely that the Wreq authors were just unaware of the other Proxy as they seem to be storing equivalent information. It'll be tricky to get them to talk to each other, however, since fetchProxy stores the host:port as a string and Wreq's Proxy wants the individual host and port. You'll have to do some URI parsing:
import Control.Lens
import Data.Text.Strict.Lens
import Network.HTTP.Proxy
import Network.Wreq
import URI.ByteString
main :: IO ()
main = do
Network.HTTP.Proxy.Proxy host _ <- fetchProxy True
case parseURI strictURIParserOptions (host ^. packed . re utf8) of
Left e -> do
putStrLn "uh oh"
print e
Right uri ->
case ( uri ^? uriAuthorityL . _Just . authorityHostL . hostBSL
, uri ^? uriAuthorityL . _Just . authorityPortL . _Just . portNumberL) of
(Just host_, Just port_) -> do
let opts = defaults & proxy ?~ httpProxy host_ port_
response <- getWith opts "http://example.com"
print response
_ ->
putStrLn "uh oh"
I'm using lens here to do the boring bits and pieces of packing/unpacking strings, encoding UTF8, and talking to the uri-bytestring package to get URI parsing. But the general idea is that datatypes in Haskell can be sliced and diced simply by pattern matching on the constructor; once extracted, the host:string here is funneled down into the httpProxy call, which returns Wreq's Proxy type. By qualifying the name of the constructor (Newtork.HTTP.Proxy.Proxy) I've let the compiler know which module I want that name from.
It would also not be too difficult, and probably less code to boot, to manually parse proxy information from the environment variables yourself. You could even have a separate environment variable for host and port, which would obviate the need for URI parsing. URIs are have such massively low entropy that they're an awful format for storing configuration information.