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At this moment, such +-- annotations can be of any type. +type ServiceAnnotation = Type + +-- | A service is a set of methods. +data Service serviceName methodName + = Service serviceName [ServiceAnnotation] [Method methodName] + +-- | An annotation to define a package name. +-- This is used by some handlers, like gRPC. +data Package (s :: Symbol) + +-- | Find the 'Package' for a service, to be found +-- as part of the annotations. +type family FindPackageName (anns :: [ServiceAnnotation]) :: Symbol where + FindPackageName '[] = TypeError ('Text "Cannot find package name for the service") + FindPackageName (Package s ': rest) = s + FindPackageName (other ': rest) = FindPackageName rest + +-- | A method is defined by its name, arguments, and return type. +data Method methodName + = Method methodName [ServiceAnnotation] [Argument] Return + +-- | Look up a method in a service definition using its name. +-- Useful to declare handlers like @HandlerIO (MyService :-->: "MyMethod")@. +type family (:-->:) (s :: Service snm mnm) (m :: mnm) :: Method mnm where + 'Service sname anns methods :-->: m = LookupMethod methods m + +type family LookupMethod (s :: [Method mnm]) (m :: snm) :: Method snm where + LookupMethod '[] m = TypeError ('Text "could not find method " ':<>: 'ShowType m) + LookupMethod ('Method m anns args r ': ms) m = 'Method m anns args r + LookupMethod (other ': ms) m = LookupMethod ms m + +-- | Defines how to handle the type +data TypeRef where + ViaSchema :: Schema typeName fieldName -> typeName -> TypeRef + -- | Registry subject, type to convert to, and preferred serialization version + ViaRegistry :: Registry -> Type -> Nat -> TypeRef + -- | To be used only during TH generation! + ViaTH :: TH.Type -> TypeRef + +-- | Defines the way in which arguments are handled. +data Argument where + -- | Use a single value. + ArgSingle :: TypeRef -> Argument + -- | Consume a stream of values. + ArgStream :: TypeRef -> Argument + +-- | Defines the different possibilities for returning +-- information from a method. +data Return where + -- | Fire and forget. + RetNothing :: Return + -- | Return a single value. + RetSingle :: TypeRef -> Return + -- | Return a value or an error + -- (this can be found in Avro IDL). + RetThrows :: TypeRef -> TypeRef -> Return + -- | Return a stream of values + -- (this can be found in gRPC). + RetStream :: TypeRef -> Return diff --git a/src/Mu/Rpc/Examples.hs b/src/Mu/Rpc/Examples.hs new file mode 100644 --- /dev/null +++ b/src/Mu/Rpc/Examples.hs @@ -0,0 +1,89 @@ +{-# language DataKinds #-} +{-# language DeriveAnyClass #-} +{-# language DeriveGeneric #-} +{-# language FlexibleContexts #-} +{-# language FlexibleInstances #-} +{-# language GADTs #-} +{-# language MultiParamTypeClasses #-} +{-# language OverloadedStrings #-} +{-# language PartialTypeSignatures #-} +{-# language PolyKinds #-} +{-# language ScopedTypeVariables #-} +{-# language StandaloneDeriving #-} +{-# language TypeFamilies #-} +{-# language TypeOperators #-} +{-# language ViewPatterns #-} +{-# OPTIONS_GHC -fno-warn-partial-type-signatures #-} +{-| +Description : Examples for service and server definitions + +Look at the source code of this module. +-} +module Mu.Rpc.Examples where + +import Data.Conduit +import Data.Conduit.Combinators as C +import Data.Functor.MaybeLike +import qualified Data.Text as T +import GHC.Generics + +import Mu.Rpc +import Mu.Schema +import Mu.Server + +-- Defines the service from gRPC Quickstart +-- https://grpc.io/docs/quickstart/python/ + +type QuickstartSchema + = '[ 'DRecord "HelloRequest" + '[ 'FieldDef "name" ('TPrimitive T.Text) ] + , 'DRecord "HelloResponse" + '[ 'FieldDef "message" ('TPrimitive T.Text) ] + , 'DRecord "HiRequest" + '[ 'FieldDef "number" ('TPrimitive Int) ] + ] + +type QuickStartService + = 'Service "Greeter" '[Package "helloworld"] + '[ 'Method "SayHello" '[] + '[ 'ArgSingle ('ViaSchema QuickstartSchema "HelloRequest") ] + ('RetSingle ('ViaSchema QuickstartSchema "HelloResponse")) + , 'Method "SayHi" '[] + '[ 'ArgSingle ('ViaSchema QuickstartSchema "HiRequest")] + ('RetStream ('ViaSchema QuickstartSchema "HelloResponse")) + , 'Method "SayManyHellos" '[] + '[ 'ArgStream ('ViaSchema QuickstartSchema "HelloRequest")] + ('RetStream ('ViaSchema QuickstartSchema "HelloResponse")) ] + +newtype HelloRequest f = HelloRequest { name :: f T.Text } deriving (Generic) +deriving instance Functor f => ToSchema f QuickstartSchema "HelloRequest" (HelloRequest f) +deriving instance Functor f => FromSchema f QuickstartSchema "HelloRequest" (HelloRequest f) + +newtype HelloResponse f = HelloResponse { message :: f T.Text } deriving (Generic) +deriving instance Functor f => ToSchema f QuickstartSchema "HelloResponse" (HelloResponse f) +deriving instance Functor f => FromSchema f QuickstartSchema "HelloResponse" (HelloResponse f) + +newtype HiRequest f = HiRequest { number :: f Int } deriving (Generic) +deriving instance Functor f => ToSchema f QuickstartSchema "HiRequest" (HiRequest f) +deriving instance Functor f => FromSchema f QuickstartSchema "HiRequest" (HiRequest f) + +quickstartServer :: forall m f. + (MonadServer m, Applicative f, MaybeLike f) + => ServerT f QuickStartService m _ +quickstartServer + = Server (sayHello :<|>: sayHi :<|>: sayManyHellos :<|>: H0) + where sayHello :: HelloRequest f -> m (HelloResponse f) + sayHello (HelloRequest nm) + = return (HelloResponse (("hi, " <>) <$> nm)) + sayHi :: HiRequest f + -> ConduitT (HelloResponse f) Void m () + -> m () + sayHi (HiRequest (likeMaybe -> Just n)) sink + = runConduit $ C.replicate n (HelloResponse $ pure "hi!") .| sink + sayHi (HiRequest _) sink + = runConduit $ return () .| sink + sayManyHellos :: ConduitT () (HelloRequest f) m () + -> ConduitT (HelloResponse f) Void m () + -> m () + sayManyHellos source sink + = runConduit $ source .| C.mapM sayHello .| sink diff --git a/src/Mu/Server.hs b/src/Mu/Server.hs new file mode 100644 --- /dev/null +++ b/src/Mu/Server.hs @@ -0,0 +1,146 @@ +{-# language ConstraintKinds #-} +{-# language DataKinds #-} +{-# language ExistentialQuantification #-} +{-# language FlexibleContexts #-} +{-# language FlexibleInstances #-} +{-# language GADTs #-} +{-# language MultiParamTypeClasses #-} +{-# language PolyKinds #-} +{-# language RankNTypes #-} +{-# language TypeFamilies #-} +{-# language TypeOperators #-} +{-# language UndecidableInstances #-} +{-| +Description : Protocol-independent declaration of servers. + +A server (represented by 'ServerT') is a sequence +of handlers (represented by 'HandlersT'), one for each +operation in the corresponding Mu service declaration. + +In general, you should declare a server as: + +> server :: MonadServer m => ServerT w MyService m _ +> server = Server (h1 :<|>: h2 :<|>: ... :<|>: H0) + +where each of @h1@, @h2@, ... handles each method in +@MyService@ /in the order they were declared/. +The @_@ in the type allows GHC to fill in the boring +and long type you would need to write there otherwise. + +/Implementation note/: exceptions raised in handlers +produce an error to be sent as response to the client. +We recommend you to catch exceptions and return custom +'ServerError's instead. +-} +module Mu.Server ( + -- * Servers and handlers + MonadServer, ServerT(..), HandlersT(..) + -- ** Simple servers using only IO +, ServerErrorIO, ServerIO + -- * Errors which might be raised +, serverError, ServerError(..), ServerErrorCode(..) + -- ** Useful when you do not want to deal with errors +, alwaysOk +) where + +import Control.Monad.Except +import Data.Conduit +import Data.Kind + +import Mu.Rpc +import Mu.Schema + +-- | Constraint for monads that can be used as servers +type MonadServer m = (MonadError ServerError m, MonadIO m) +-- | Simplest monad which satisfies 'MonadServer'. +type ServerErrorIO = ExceptT ServerError IO +-- | Simple 'ServerT' which uses only 'IO' and errors. +type ServerIO w srv = ServerT w srv ServerErrorIO + +-- | Stop the current handler, +-- returning an error to the client. +serverError :: (MonadError ServerError m) + => ServerError -> m a +serverError = throwError + +-- | Wrapper for handlers which do not use errors. +-- Remember that any exception raised in 'IO' +-- is propagated to the client. +alwaysOk :: (MonadIO m) + => IO a -> m a +alwaysOk = liftIO + +-- | Errors raised in a handler. +data ServerError + = ServerError ServerErrorCode String + +-- | Possible types of errors. +-- Some of these are handled in a special way +-- by different transpoprt layers. +data ServerErrorCode + = Unknown + | Unavailable + | Unimplemented + | Unauthenticated + | Internal + | Invalid + | NotFound + deriving (Eq, Show) + +-- | Definition of a complete server for a service. +data ServerT (w :: Type -> Type) (s :: Service snm mnm) (m :: Type -> Type) (hs :: [Type]) where + Server :: HandlersT w methods m hs -> ServerT w ('Service sname anns methods) m hs + +infixr 5 :<|>: +-- | 'HandlersT' is a sequence of handlers. +-- Note that the handlers for your service +-- must appear __in the same order__ as they +-- are defined. +-- +-- In general you can choose any type you want +-- for your handlers, due to the following restrictions: +-- +-- * Haskell types must be convertible to the +-- corresponding schema type. In other words, +-- they must implement 'FromSchema' if they are +-- inputs, and 'ToSchema' if they are outputs. +-- * Normal returns are represented by returning +-- the corresponding Haskell type. +-- * Input streams turn into @Conduit () t m ()@, +-- where @t@ is the Haskell type for that schema type. +-- * Output streams turn into an __additional argument__ +-- of type @Conduit t Void m ()@. This stream should +-- be connected to a source to get the elements. +data HandlersT (w :: Type -> Type) (methods :: [Method mnm]) (m :: Type -> Type) (hs :: [Type]) where + H0 :: HandlersT w '[] m '[] + (:<|>:) :: Handles w args ret m h => h -> HandlersT w ms m hs + -> HandlersT w ('Method name anns args ret ': ms) m (h ': hs) + +-- Define a relation for handling +class Handles (w :: Type -> Type) (args :: [Argument]) (ret :: Return) + (m :: Type -> Type) (h :: Type) +class ToRef (w :: Type -> Type) (ref :: TypeRef) (t :: Type) +class FromRef (w :: Type -> Type) (ref :: TypeRef) (t :: Type) + +-- Type references +instance ToSchema w sch sty t => ToRef w ('ViaSchema sch sty) t +instance ToRef w ('ViaRegistry subject t last) t +instance FromSchema w sch sty t => FromRef w ('ViaSchema sch sty) t +instance FromRef w ('ViaRegistry subject t last) t + +-- Arguments +instance (FromRef w ref t, Handles w args ret m h, + handler ~ (t -> h)) + => Handles w ('ArgSingle ref ': args) ret m handler +instance (MonadError ServerError m, FromRef w ref t, Handles w args ret m h, + handler ~ (ConduitT () t m () -> h)) + => Handles w ('ArgStream ref ': args) ret m handler +-- Result with exception +instance (MonadError ServerError m, handler ~ m ()) + => Handles w '[] 'RetNothing m handler +instance (MonadError ServerError m, ToRef w eref e, ToRef w vref v, handler ~ m (Either e v)) + => Handles w '[] ('RetThrows eref vref) m handler +instance (MonadError ServerError m, ToRef w ref v, handler ~ m v) + => Handles w '[] ('RetSingle ref) m handler +instance (MonadError ServerError m, ToRef w ref v, handler ~ (ConduitT v Void m () -> m ())) + => Handles w '[] ('RetStream ref) m handler