Capnp.Rpc.Server

The term server in this context refers to a thread that handles method calls for a particular capability (The capnproto rpc protocol itself has no concept of clients and servers).

Documentation

data ServerOps m

The operations necessary to receive and handle method calls, i.e. to implement an object. It is parametrized over the monadic context in which methods are serviced.

Constructors

ServerOps

Fields

• handleCall :: Word64 -> Word16 -> MethodHandler m (Maybe (Ptr ConstMsg)) (Maybe (Ptr ConstMsg))

  Handle a method call; takes the interface and method id and returns a handler for the specific method.

• handleStop :: m ()

  Handle shutting-down the receiver; this is called when the last reference to the capability is dropped.

data CallInfo

A CallInfo contains information about a method call.

Constructors

CallInfo

Fields

• interfaceId :: !Word64

  The id of the interface whose method is being called.

• methodId :: !Word16

  The method id of the method being called.

• arguments :: Maybe (Ptr ConstMsg)

  The arguments to the method call.

• response :: Fulfiller (Maybe (Ptr ConstMsg))

  A Fulfiller which accepts the method's return value.

runServer :: Q CallInfo -> ServerOps IO -> IO ()

Handle incoming messages for a given object.

Accepts a queue of messages to handle, and ServerOps used to handle them. returns when it receives a Stop message.

Handling methods

data MethodHandler m p r

a MethodHandler m p r handles a method call with parameters p and return type r, in monad m.

The library represents method handlers via an abstract type MethodHandler, parametrized over parameter (p) and return (r) types, and the monadic context in which it runs (m). This allows us to provide different strategies for actually handling methods; there are various helper functions which construct these handlers.

At some point we will likely additionally provide handlers affording:

• Working directly with the low-level data types.
• Replying to the method call asynchronously, allowing later method calls to be serviced before the current one is finished.

Using high-level representations

pureHandler :: (MonadCatch m, MonadSTM m, PrimMonad m, s ~ PrimState m, Decerialize p, FromPtr ConstMsg (Cerial ConstMsg p), Cerialize r, ToStruct (MutMsg s) (Cerial (MutMsg s) r)) => (cap -> p -> m r) -> cap -> MethodHandler m p r

pureHandler f cap is a MethodHandler which calls a function f that accepts the receiver and the parameter type as exposed by the high-level API, and returns the high-level API representation of the return type.

Using low-level representations

rawHandler :: (MonadCatch m, MonadSTM m, PrimMonad m, s ~ PrimState m, Decerialize p, FromPtr ConstMsg (Cerial ConstMsg p), Decerialize r, ToStruct ConstMsg (Cerial ConstMsg r)) => (cap -> Cerial ConstMsg p -> m (Cerial ConstMsg r)) -> cap -> MethodHandler m p r

Like pureHandler, except that the parameter and return value use the low-level representation.

rawAsyncHandler :: (MonadCatch m, MonadSTM m, PrimMonad m, s ~ PrimState m, Decerialize p, FromPtr ConstMsg (Cerial ConstMsg p), Decerialize r, ToStruct ConstMsg (Cerial ConstMsg r)) => (cap -> Cerial ConstMsg p -> Fulfiller (Cerial ConstMsg r) -> m ()) -> cap -> MethodHandler m p r

Like rawHandler, except that it takes a fulfiller for the result, instead of returning it. This allows the result to be supplied some time after the method returns, making it possible to service other method calls before the result is available.

Always throwing exceptions

methodThrow :: MonadIO m => Exception -> MethodHandler m p r

methodThrow exn is a MethodHandler which always throws exn.

methodUnimplemented :: MonadIO m => MethodHandler m p r

A MethodHandler which always throws an unimplemented exception.

Working with untyped data

untypedHandler :: (Maybe (Ptr ConstMsg) -> Fulfiller (Maybe (Ptr ConstMsg)) -> m ()) -> MethodHandler m (Maybe (Ptr ConstMsg)) (Maybe (Ptr ConstMsg))

Construct a method handler from a function accepting an untyped pointer for the method's parameter, and a Fulfiller which accepts an untyped pointer for the method's return value.

toUntypedHandler :: MethodHandler m p r -> MethodHandler m (Maybe (Ptr ConstMsg)) (Maybe (Ptr ConstMsg))

Convert a MethodHandler for any parameter and return types into one that deals with untyped pointers.

fromUntypedHandler :: MethodHandler m (Maybe (Ptr ConstMsg)) (Maybe (Ptr ConstMsg)) -> MethodHandler m p r

Inverse of toUntypedHandler

Invoking methods

invoke :: MonadSTM m => MethodHandler m (Maybe (Ptr ConstMsg)) (Maybe (Ptr ConstMsg)) -> Maybe (Ptr ConstMsg) -> Fulfiller (Maybe (Ptr ConstMsg)) -> m ()