urbit/pkg/king/lib/Vere/Http/Client.hs

{-
  - TODO When making a request, handle the case where the request id is
         already in use.
-}

module Vere.Http.Client where

import Arvo            (BlipEv(..), Ev(..), HttpClientEf(..), HttpClientEv(..),
                        HttpClientReq(..), HttpEvent(..), KingId,
                        ResponseHeader(..))
import UrbitPrelude    hiding (Builder)
import Vere.Pier.Types

import Vere.Http

import qualified Data.Map            as M
import qualified Network.HTTP.Client as H
import qualified Network.HTTP.Types  as HT

-- Types -----------------------------------------------------------------------

type ReqId = Word

data HttpClientDrv = HttpClientDrv
  { hcdManager :: H.Manager
  , hcdLive    :: TVar (Map ReqId (Async ()))
  }

--------------------------------------------------------------------------------

cvtReq :: HttpClientReq -> Maybe H.Request
cvtReq r =
  H.parseRequest (unpack (unCord $ url r)) <&> \init -> init
    { H.method = encodeUtf8 $ tshow (method r)
    , H.requestHeaders = unconvertHeaders (headerList r)
    , H.requestBody =
        H.RequestBodyBS $ case body r of
                            Nothing        -> ""
                            Just (Octs bs) -> bs
    }

cvtRespHeaders :: H.Response a -> ResponseHeader
cvtRespHeaders resp =
    ResponseHeader (fromIntegral $ HT.statusCode (H.responseStatus resp)) heads
  where
    heads = convertHeaders (H.responseHeaders resp)

--------------------------------------------------------------------------------

client :: forall e. HasLogFunc e
       => KingId -> QueueEv -> ([Ev], RAcquire e (EffCb e HttpClientEf))
client kingId enqueueEv = ([], runHttpClient)
  where
    runHttpClient :: RAcquire e (EffCb e HttpClientEf)
    runHttpClient = handleEffect <$> mkRAcquire start stop

    start :: RIO e (HttpClientDrv)
    start = HttpClientDrv <$>
      (io $ H.newManager H.defaultManagerSettings) <*>
      newTVarIO M.empty

    stop :: HttpClientDrv -> RIO e ()
    stop HttpClientDrv{..} = do
      -- Cancel all the outstanding asyncs, ignoring any exceptions.
      liveThreads <- atomically $ readTVar hcdLive
      mapM_ cancel liveThreads

    handleEffect :: HttpClientDrv -> HttpClientEf -> RIO e ()
    handleEffect drv = \case
      HCERequest _ id req -> newReq drv id req
      HCECancelRequest _ id -> cancelReq drv id

    newReq :: HttpClientDrv -> ReqId -> HttpClientReq -> RIO e ()
    newReq drv id req = do
      async <- runReq drv id req
      atomically $ modifyTVar (hcdLive drv) (insertMap id async)

    -- The problem with the original http client code was that it was written
    -- to the idea of what the events "should have" been instead of what they
    -- actually were. This means that this driver doesn't run like the vere
    -- http client driver. The vere driver was written assuming that parts of
    -- events could be compressed together: a Start might contain the only
    -- chunk of data and immediately complete, where here the Start event, the
    -- Continue (with File) event, and the Continue (completed) event are three
    -- separate things.
    runReq :: HttpClientDrv -> ReqId -> HttpClientReq -> RIO e (Async ())
    runReq HttpClientDrv{..} id req = async $
      case cvtReq req of
        Nothing -> do
          logDebug $ displayShow ("(malformed http client request)", id, req)
          planEvent id (Cancel ())
        Just r -> do
          logDebug $ displayShow ("(http client request)", id, req)
          withRunInIO $ \run ->
            H.withResponse r hcdManager $ \x -> run (exec x)
      where
        recv :: H.BodyReader -> RIO e (Maybe ByteString)
        recv read = io $ read <&> \case chunk | null chunk -> Nothing
                                              | otherwise  -> Just chunk

        exec :: H.Response H.BodyReader -> RIO e ()
        exec resp = do
          let headers  = cvtRespHeaders resp
              getChunk = recv (H.responseBody resp)
              loop     = getChunk >>= \case
                           Nothing -> planEvent id (Continue Nothing True)
                           Just bs -> do
                             planEvent id $
                               Continue (Just $ File $ Octs bs) False
                             loop
          planEvent id (Start headers Nothing False)
          loop

    planEvent :: ReqId -> HttpEvent -> RIO e ()
    planEvent id ev = do
      logDebug $ displayShow ("(http client response)", id, (describe ev))
      atomically $ enqueueEv $ EvBlip $ BlipEvHttpClient $
        HttpClientEvReceive (kingId, ()) (fromIntegral id) ev

    -- show an HttpEvent with byte count instead of raw data
    describe :: HttpEvent -> String
    describe (Start header Nothing final) =
      "(Start " ++ (show header) ++ " ~ " ++ (show final)
    describe (Start header (Just (File (Octs bs))) final) =
      "(Start " ++ (show header) ++ " (" ++ (show $ length bs) ++ " bytes) " ++
      (show final)
    describe (Continue Nothing final) =
      "(Continue ~ " ++ (show final)
    describe (Continue (Just (File (Octs bs))) final) =
      "(Continue (" ++ (show $ length bs) ++ " bytes) " ++ (show final)
    describe (Cancel ()) = "(Cancel ())"

    waitCancel :: Async a -> RIO e (Either SomeException a)
    waitCancel async = cancel async >> waitCatch async

    cancelThread :: ReqId -> Async a -> RIO e ()
    cancelThread id =
      waitCancel >=> \case Left _  -> planEvent id $ Cancel ()
                           Right _ -> pure ()

    cancelReq :: HttpClientDrv -> ReqId -> RIO e ()
    cancelReq drv id =
      join $ atomically $ do
        tbl <- readTVar (hcdLive drv)
        case lookup id tbl of
          Nothing    -> pure (pure ())
          Just async -> do writeTVar (hcdLive drv) (deleteMap id tbl)
                           pure (cancelThread id async)