From 2374ed3ce87ba6ef118aecb0219fd8278741e92a Mon Sep 17 00:00:00 2001
From: Benjamin Summers <benjamin@tlon.io>
Date: Thu, 16 May 2019 18:45:03 -0700
Subject: [PATCH] Don't send a Canceled event if the request already finished.

---
 pkg/hair/lib/Vere/Http/Client.hs | 65 ++++++++++++++++----------------
 1 file changed, 33 insertions(+), 32 deletions(-)

diff --git a/pkg/hair/lib/Vere/Http/Client.hs b/pkg/hair/lib/Vere/Http/Client.hs
index 589c4ad86..15218bca2 100644
--- a/pkg/hair/lib/Vere/Http/Client.hs
+++ b/pkg/hair/lib/Vere/Http/Client.hs
@@ -1,37 +1,31 @@
 {-
   - TODO When making a request, handle the case where the request id is
          already in use.
-  - TODO When canceling a request, don't send Http.Canceled if the
-         request already finished.
 -}
 
 module Vere.Http.Client where
 
 import ClassyPrelude
-import Data.Void
-import Vere.Http as Http
-import Control.Concurrent hiding (newEmptyMVar, putMVar)
+import Vere.Http
 
 import qualified Network.HTTP.Client as H
 
 --------------------------------------------------------------------------------
 
-
 type ReqId = Word
 
-data Ev = Receive ReqId Http.Event -- %receive
+data Ev = Receive ReqId Event -- [%receive @ todo]
 
 data Eff
-  = NewReq ReqId Request -- %request
-  | CancelReq ReqId      -- %cancel-request
+  = NewReq ReqId Request -- [%request @ todo]
+  | CancelReq ReqId      -- [%cancel-request @]
 
 data State = State
   { sManager :: H.Manager
-  , sLive    :: TVar (Map ReqId ThreadId)
+  , sLive    :: TVar (Map ReqId (Async ()))
   , sChan    :: MVar Ev
   }
 
-
 --------------------------------------------------------------------------------
 
 cvtReq :: Request -> H.Request
@@ -40,7 +34,6 @@ cvtReq = undefined
 cvtRespHeaders :: H.Response a -> ResponseHeader
 cvtRespHeaders resp = undefined
 
-
 --------------------------------------------------------------------------------
 
 initState :: IO State
@@ -49,38 +42,46 @@ initState = State <$> H.newManager H.defaultManagerSettings
                   <*> newEmptyMVar
 
 emit :: State -> Ev -> IO ()
-emit (State _ _ chan) event = putMVar chan event
+emit st event = putMVar (sChan st) event
 
 runEff :: State -> Eff -> IO ()
-runEff st@(State _ s _) = \case CancelReq id  -> cancelReq st id
-                                NewReq id req -> newReq st id req
+runEff st = \case CancelReq id  -> cancelReq st id
+                  NewReq id req -> newReq st id req
 
 newReq :: State -> ReqId -> Request -> IO ()
-newReq st id req = do tid <- runReq st id req
-                      atomically $ modifyTVar (sLive st) (insertMap id tid)
+newReq st id req = do async <- runReq st id req
+                      atomically $ modifyTVar (sLive st) (insertMap id async)
+
+waitCancel :: Async a -> IO (Either SomeException a)
+waitCancel async = cancel async >> waitCatch async
+
+cancelThread :: State -> ReqId -> Async a -> IO ()
+cancelThread st id =
+  waitCancel >=> \case Left _  -> emit st (Receive id Canceled)
+                       Right _ -> pure ()
 
 cancelReq :: State -> ReqId -> IO ()
 cancelReq st id =
   join $ atomically $ do
     tbl <- readTVar (sLive st)
     case lookup id tbl of
-      Nothing  -> pure (pure ())
-      Just tid -> do
-        writeTVar (sLive st) (deleteMap id tbl)
-        pure $ do killThread tid
-                  emit st (Receive id Canceled)
+      Nothing    -> pure (pure ())
+      Just async -> do writeTVar (sLive st) (deleteMap id tbl)
+                       pure (cancelThread st id async)
 
-runReq :: State -> ReqId -> Request -> IO ThreadId
-runReq st id request =
-    forkIO $ H.withResponse (cvtReq request) (sManager st) $ \resp -> do
-      let headers  = cvtRespHeaders resp
-      let getChunk = recv (H.responseBody resp)
-      let loop = getChunk >>= \case
-                   Just bs -> emit st (Receive id $ Received bs) >> loop
-                   Nothing -> emit st (Receive id Done)
-      emit st (Receive id $ Started headers)
-      loop
+runReq :: State -> ReqId -> Request -> IO (Async ())
+runReq st id req = async (H.withResponse (cvtReq req) (sManager st) exec)
   where
     recv :: H.BodyReader -> IO (Maybe ByteString)
     recv read = read <&> \case chunk | null chunk -> Nothing
                                      | otherwise  -> Just chunk
+
+    exec :: H.Response H.BodyReader -> IO ()
+    exec resp = do
+      let headers  = cvtRespHeaders resp
+          getChunk = recv (H.responseBody resp)
+          loop     = getChunk >>= \case
+                       Just bs -> emit st (Receive id $ Received bs) >> loop
+                       Nothing -> emit st (Receive id Done)
+      emit st (Receive id $ Started headers)
+      loop