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- Introduce SourceT, which is simple variant of "correct `ListT`". There are another variants possible (like in `streaming`), but I'm not sure there's much real difference. - Introduce `Codensity`. There's a flag if people don't want to depend on `kan-extensions`. - `StreamGenerator` and `ResultStream` are both `SourceT`. `Stream` combinator in `servant-client` uses `Codensity` for CPS. - Add servant-machines, servant-conduit, servant-pipes - Add streaming cookbook: just code, no explanations. - Add a script to run streaming 'benchmarks'
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| Original file line number | Diff line number | Diff line change |
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| # Streaming out-of-the-box | ||
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| In other words, without streaming libraries. | ||
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| ## Introduction | ||
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| - Servant supports streaming | ||
| - Some basic usage doesn't require usage of streaming libraries, | ||
| like `conduit`, `pipes`, `machines` or `streaming`. | ||
| We have bindings for them though. | ||
| - This is similar example file, which is bundled with each of the packages (TODO: links) | ||
| - `SourceT` doesn't have *Prelude* with handy combinators, so we have to write | ||
| things ourselves. (Note to self: `mapM` and `foldM` would be handy to have). | ||
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| ## Code | ||
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| ```haskell | ||
| {-# LANGUAGE BangPatterns #-} | ||
| {-# LANGUAGE DataKinds #-} | ||
| {-# LANGUAGE DeriveGeneric #-} | ||
| {-# LANGUAGE TypeOperators #-} | ||
| module Main (main) where | ||
| import Control.Concurrent | ||
| (threadDelay) | ||
| import Control.Monad.IO.Class | ||
| (MonadIO (..)) | ||
| import qualified Data.ByteString as BS | ||
| import Data.Maybe | ||
| (fromMaybe) | ||
| import Network.HTTP.Client | ||
| (defaultManagerSettings, newManager) | ||
| import Network.Wai | ||
| (Application) | ||
| import System.Environment | ||
| (getArgs, lookupEnv) | ||
| import Text.Read | ||
| (readMaybe) | ||
| import Servant | ||
| import Servant.Client | ||
| import qualified Servant.Types.SourceT as S | ||
| import qualified Network.Wai.Handler.Warp as Warp | ||
| type FastAPI = "get" :> Capture "num" Int :> StreamGet NewlineFraming JSON (SourceIO Int) | ||
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| type API = FastAPI | ||
| :<|> "slow" :> Capture "num" Int :> StreamGet NewlineFraming JSON (SourceIO Int) | ||
| -- monad can be ResourceT IO too. | ||
| :<|> "readme" :> StreamGet NoFraming OctetStream (SourceIO BS.ByteString) | ||
| -- we can have streaming request body | ||
| :<|> "proxy" | ||
| :> StreamBody NoFraming OctetStream (SourceIO BS.ByteString) | ||
| :> StreamPost NoFraming OctetStream (SourceIO BS.ByteString) | ||
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| api :: Proxy API | ||
| api = Proxy | ||
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| server :: Server API | ||
| server = fast :<|> slow :<|> readme :<|> proxy where | ||
| fast n = liftIO $ do | ||
| putStrLn $ "/get/" ++ show n | ||
| return $ fastSource n | ||
| slow n = liftIO $ do | ||
| putStrLn $ "/slow/" ++ show n | ||
| return $ slowSource n | ||
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| readme = liftIO $ do | ||
| putStrLn "/proxy" | ||
| return (S.readFile "README.md") | ||
| proxy c = liftIO $ do | ||
| putStrLn "/proxy" | ||
| return c | ||
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| -- for some reason unfold leaks? | ||
| fastSource = S.fromStepT . mk where | ||
| mk m | ||
| | m < 0 = S.Stop | ||
| | otherwise = S.Yield m (mk (m - 1)) | ||
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| slowSource m = S.mapStepT delay (fastSource m) where | ||
| delay S.Stop = S.Stop | ||
| delay (S.Error err) = S.Error err | ||
| delay (S.Skip s) = S.Skip (delay s) | ||
| delay (S.Effect ms) = S.Effect (fmap delay ms) | ||
| delay (S.Yield x s) = S.Effect $ | ||
| S.Yield x (delay s) <$ threadDelay 1000000 | ||
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| app :: Application | ||
| app = serve api server | ||
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| cli :: Client ClientM FastAPI | ||
| cli :<|> _ :<|> _ :<|> _ = client api | ||
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| main :: IO () | ||
| main = do | ||
| args <- getArgs | ||
| case args of | ||
| ("server":_) -> do | ||
| putStrLn "Starting cookbook-basic-streaming at http://localhost:8000" | ||
| port <- fromMaybe 8000 . (>>= readMaybe) <$> lookupEnv "PORT" | ||
| Warp.run port app | ||
| ("client":ns:_) -> do | ||
| n <- maybe (fail $ "not a number: " ++ ns) pure $ readMaybe ns | ||
| mgr <- newManager defaultManagerSettings | ||
| burl <- parseBaseUrl "http://localhost:8000/" | ||
| withClientM (cli n) (mkClientEnv mgr burl) $ \me -> case me of | ||
| Left err -> print err | ||
| Right src -> do | ||
| x <- S.unSourceT src (go (0 :: Int)) | ||
| print x | ||
| where | ||
| go !acc S.Stop = return acc | ||
| go !acc (S.Error err) = print err >> return acc | ||
| go !acc (S.Skip s) = go acc s | ||
| go !acc (S.Effect ms) = ms >>= go acc | ||
| go !acc (S.Yield _ s) = go (acc + 1) s | ||
| _ -> do | ||
| putStrLn "Try:" | ||
| putStrLn "cabal new-run cookbook-basic-streaming server" | ||
| putStrLn "cabal new-run cookbook-basic-streaming client 10" | ||
| putStrLn "time curl -H 'Accept: application/json' localhost:8000/slow/5" | ||
| ``` |
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| name: cookbook-basic-streaming | ||
| version: 2.1 | ||
| synopsis: Streaming in servant without streaming libs | ||
| homepage: http://haskell-servant.readthedocs.org/ | ||
| license: BSD3 | ||
| license-file: ../../../servant/LICENSE | ||
| author: Servant Contributors | ||
| maintainer: [email protected] | ||
| build-type: Simple | ||
| cabal-version: >=1.10 | ||
| tested-with: GHC==8.0.2, GHC==8.2.2, GHC==8.4.4, GHC==8.6.1 | ||
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| executable cookbook-basic-streaming | ||
| main-is: Streaming.lhs | ||
| build-tool-depends: markdown-unlit:markdown-unlit | ||
| default-language: Haskell2010 | ||
| ghc-options: -Wall -pgmL markdown-unlit -threaded -rtsopts | ||
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| hs-source-dirs: . | ||
| build-depends: base >= 4.8 && <4.13 | ||
| , aeson | ||
| , bytestring | ||
| , servant | ||
| , servant-server | ||
| , servant-client | ||
| , http-client | ||
| , wai | ||
| , warp |
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