Capnp.Rpc

This module exposes the most commonly used parts of the RPC subsystem.

Establishing connections

handleConn :: Transport -> ConnConfig -> IO ()

Handle a connection to another vat. Returns when the connection is closed.

data ConnConfig

Configuration information for a connection.

Constructors

ConnConfig

Fields

• maxQuestions :: !Word32

  The maximum number of simultanious outstanding requests to the peer vat. Once this limit is reached, further questsions will block until some of the existing questions have been answered.

  Defaults to 128.

• maxExports :: !Word32

  The maximum number of objects which may be exported on this connection.

  Defaults to 8192.

• debugMode :: !Bool

  In debug mode, errors reported by the RPC system to its peers will contain extra information. This should not be used in production, as it is possible for these messages to contain sensitive information, but it can be useful for debugging.

  Defaults to False.

• getBootstrap :: Supervisor -> STM (Maybe Client)

  Get the bootstrap interface we should serve for this connection. the argument is a supervisor whose lifetime is bound to the connection. If $sel:getBootstrap:ConnConfig returns Nothing, we will respond to bootstrap messages with an exception.

  The default always returns Nothing.

  $sel:getBootstrap:ConnConfig MUST NOT block; the connection will not be serviced and $sel:withBootstrap:ConnConfig will not be run until this returns. If you need to supply the bootstrap interface later, use newPromiseClient.

• withBootstrap :: Maybe (Supervisor -> Client -> IO ())

  An action to perform with access to the remote vat's bootstrap interface. The supervisor argument is bound to the lifetime of the connection. If this is Nothing (the default), the bootstrap interface will not be requested.

Instances

Default ConnConfig

Defined in Capnp.Rpc.Untyped

Methods

def :: ConnConfig

Calling methods

(?) :: InvokePureCtx m p r => MethodHandler m p r -> p -> m (Promise r)

Alias for invokePurePromise

Handling method calls

class Monad m => Server m a | a -> m where

Base class for things that can act as capnproto servers.

Minimal complete definition

Nothing

Methods

shutdown :: a -> m ()

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.

Instances

Server IO (Persistent sturdyRef owner)

Defined in Capnp.Gen.Capnp.Persistent.Pure

Methods

shutdown :: Persistent sturdyRef owner -> IO ()

unwrap :: Typeable b => Persistent sturdyRef owner -> Maybe b

Server IO (RealmGateway internalRef externalRef internalOwner externalOwner)

Defined in Capnp.Gen.Capnp.Persistent.Pure

Methods

shutdown :: RealmGateway internalRef externalRef internalOwner externalOwner -> IO ()

unwrap :: Typeable b => RealmGateway internalRef externalRef internalOwner externalOwner -> Maybe b

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.

pureHandler :: (MonadCatch m, MonadSTM m, PrimMonad m, s ~ PrimState m, Decerialize p, FromPtr ConstMsg (Cerial ConstMsg p), Cerialize s 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.

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.

methodUnimplemented :: MonadIO m => MethodHandler m p r

A MethodHandler which always throws an unimplemented exception.

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

methodThrow exn is a MethodHandler which always throws exn.

throwing errors

throwFailed :: MonadThrow m => Text -> m a

Throw an exception with a type field of Exception'Type'failed and the argument as a reason.

Transmitting messages

data Transport

A Transport handles transmitting RPC messages.

Constructors

Transport

Fields

• sendMsg :: ConstMsg -> IO ()

  Send a message

• recvMsg :: IO ConstMsg

  Receive a message

socketTransport :: Socket -> WordCount -> Transport

socketTransport socket limit is a transport which reads and writes messages to/from a socket. It uses limit as the traversal limit when reading messages and decoing.

handleTransport :: Handle -> WordCount -> Transport

handleTransport handle limit is a transport which reads and writes messages from/to handle. It uses limit as the traversal limit when reading messages and decoding.

tracingTransport :: (String -> IO ()) -> Transport -> Transport

tracingTransport log trans wraps another transport trans, loging messages when they are sent or received (using the log function). This can be useful for debugging.

Promises

module Capnp.Rpc.Promise

Clients

data Client

A reference to a capability, which may be live either in the current vat or elsewhere. Holding a client affords making method calls on a capability or modifying the local vat's reference count to it.

Instances

Eq Client

Defined in Capnp.Rpc.Untyped

Methods

(==) :: Client -> Client -> Bool

(/=) :: Client -> Client -> Bool

Show Client

Defined in Capnp.Rpc.Untyped

Methods

showsPrec :: Int -> Client -> ShowS

show :: Client -> String

showList :: [Client] -> ShowS

IsClient Client

Defined in Capnp.Rpc.Untyped

Methods

toClient :: Client -> Client

fromClient :: Client -> Client

class IsClient a where

Types which may be converted to and from Clients. Typically these will be simple type wrappers for capabilities.

Methods

toClient :: a -> Client

Convert a value to a client.

fromClient :: Client -> a

Convert a client to a value.

Instances

IsClient Client

Defined in Capnp.Rpc.Untyped

Methods

toClient :: Client -> Client

fromClient :: Client -> Client

IsClient (Persistent sturdyRef owner)

Defined in Capnp.Gen.Capnp.Persistent.Pure

Methods

toClient :: Persistent sturdyRef owner -> Client

fromClient :: Client -> Persistent sturdyRef owner

IsClient (RealmGateway internalRef externalRef internalOwner externalOwner)

Defined in Capnp.Gen.Capnp.Persistent.Pure

Methods

toClient :: RealmGateway internalRef externalRef internalOwner externalOwner -> Client

fromClient :: Client -> RealmGateway internalRef externalRef internalOwner externalOwner

newPromiseClient :: (MonadSTM m, IsClient c) => m (c, Fulfiller c)

Create a new client based on a promise. The fulfiller can be used to supply the final client.

waitClient :: (IsClient c, MonadSTM m) => c -> m c

Wait for the client to be fully resolved, and then return a client pointing directly to the destination.

If the argument is null, a local client, or a (permanent) remote client, this returns the argument immediately. If the argument is a promise client, then this waits for the promise to resolve and returns the result of the resolution. If the promise resolves to *another* promise, then this waits for that promise to also resolve.

If the promise is rejected, then this throws the corresponding exception.

Reflection

unwrapServer :: (IsClient c, Typeable a) => c -> Maybe a

Attempt to unwrap a client, to get at an underlying value from the server. Returns Nothing on failure.

This shells out to the underlying server's implementation of unwrap. It will fail with Nothing if any of these are true:

• The client is a promise.
• The client points to an object in a remote vat.
• The underlying Server's unwrap method returns Nothing for type a.

Supervisors

module Supervisors

Misc.