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

class Server a where

Base class for things that can act as capnproto servers.

Minimal complete definition

Nothing

Methods

shutdown :: a -> IO ()

Called when the last live reference to a server is dropped.

unwrap :: Typeable b => a -> Maybe b

Try to extract a value of a given type. The default implementation always fails (returns Nothing). If an instance chooses to implement this, it will be possible to use "reflection" on clients that point at local servers to dynamically unwrap the server value. A typical implementation will just call Typeable's cast method, but this needn't be the case -- a server may wish to allow local peers to unwrap some value that is not exactly the data the server has access to.

data ServerOps

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 (Maybe (Ptr 'Const)) (Maybe (Ptr 'Const))

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

• handleStop :: IO ()

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

• handleCast :: forall a. Typeable a => Maybe a

  used to unwrap the server when reflecting on a local client.

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 'Const)

  The arguments to the method call.

• response :: Fulfiller (Maybe (Ptr 'Const))

  A Fulfiller which accepts the method's return value.

runServer :: Q CallInfo -> ServerOps -> 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 p r

a MethodHandler p r handles a method call with parameters p and return type r.

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.

type UntypedMethodHandler = MethodHandler (Maybe (Ptr 'Const)) (Maybe (Ptr 'Const))

Alias for a MethodHandler whose parameter and return types are untyped pointers.

handleUntypedMethod :: UntypedMethodHandler -> Maybe (Ptr 'Const) -> Fulfiller (Maybe (Ptr 'Const)) -> IO ()

Working with untyped data

untypedHandler :: (Maybe (Ptr 'Const) -> Fulfiller (Maybe (Ptr 'Const)) -> IO ()) -> MethodHandler (Maybe (Ptr 'Const)) (Maybe (Ptr 'Const))

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 p r -> UntypedMethodHandler

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

fromUntypedHandler :: UntypedMethodHandler -> MethodHandler p r

Inverse of toUntypedHandler