Capnp.TraversalLimit

This module is used to mitigate several pitfalls with the capnproto format, which could potentially lead to denial of service vulnerabilities.

In particular, while they are illegal according to the spec, it is possible to encode objects which have many pointers pointing the same place, or even cycles. A naive traversal therefore could involve quite a lot of computation for a message that is very small on the wire.

Accordingly, most implementations of the format keep track of how many bytes of a message have been accessed, and start signaling errors after a certain value (the "traversal limit") has been reached. The Haskell implementation is no exception; this module implements that logic. We provide a monad transformer and mtl-style type class to track the limit; reading from the message happens inside of this monad.

Documentation

class Monad m => MonadLimit m where

mtl-style type class to track the traversal limit. This is used by other parts of the library which actually do the reading.

Methods

invoice :: WordCount -> m ()

invoice n deducts n from the traversal limit, signaling an error if the limit is exhausted.

Instances

MonadThrow m => MonadLimit (LimitT m)

Defined in Capnp.TraversalLimit

Methods

invoice :: WordCount -> LimitT m ()

MonadLimit (PureBuilder s)

Defined in Internal.BuildPure

Methods

invoice :: WordCount -> PureBuilder s ()

MonadLimit m => MonadLimit (ReaderT r m)

Defined in Capnp.TraversalLimit

Methods

invoice :: WordCount -> ReaderT r m ()

(Monoid w, MonadLimit m) => MonadLimit (WriterT w m)

Defined in Capnp.TraversalLimit

Methods

invoice :: WordCount -> WriterT w m ()

MonadLimit m => MonadLimit (StateT s m)

Defined in Capnp.TraversalLimit

Methods

invoice :: WordCount -> StateT s m ()

MonadLimit m => MonadLimit (StateT s m)

Defined in Capnp.TraversalLimit

Methods

invoice :: WordCount -> StateT s m ()

(Monoid w, MonadLimit m) => MonadLimit (RWST r w s m)

Defined in Capnp.TraversalLimit

Methods

invoice :: WordCount -> RWST r w s m ()

data LimitT m a

Monad transformer implementing MonadLimit. The underlying monad must implement MonadThrow. invoice calls throwM TraversalLimitError when the limit is exhausted.

Instances

MonadTrans LimitT

Defined in Capnp.TraversalLimit

Methods

lift :: Monad m => m a -> LimitT m a

MonadState s m => MonadState s (LimitT m)

Defined in Capnp.TraversalLimit

Methods

get :: LimitT m s

put :: s -> LimitT m ()

state :: (s -> (a, s)) -> LimitT m a

Monad m => Monad (LimitT m)

Defined in Capnp.TraversalLimit

Methods

(>>=) :: LimitT m a -> (a -> LimitT m b) -> LimitT m b

(>>) :: LimitT m a -> LimitT m b -> LimitT m b

return :: a -> LimitT m a

Functor m => Functor (LimitT m)

Defined in Capnp.TraversalLimit

Methods

fmap :: (a -> b) -> LimitT m a -> LimitT m b

(<$) :: a -> LimitT m b -> LimitT m a

MonadFail m => MonadFail (LimitT m)

Defined in Capnp.TraversalLimit

Methods

fail :: String -> LimitT m a

Monad m => Applicative (LimitT m)

Defined in Capnp.TraversalLimit

Methods

pure :: a -> LimitT m a

(<*>) :: LimitT m (a -> b) -> LimitT m a -> LimitT m b

liftA2 :: (a -> b -> c) -> LimitT m a -> LimitT m b -> LimitT m c

(*>) :: LimitT m a -> LimitT m b -> LimitT m b

(<*) :: LimitT m a -> LimitT m b -> LimitT m a

MonadIO m => MonadIO (LimitT m)

Defined in Capnp.TraversalLimit

Methods

liftIO :: IO a -> LimitT m a

MonadThrow m => MonadThrow (LimitT m)

Defined in Capnp.TraversalLimit

Methods

throwM :: Exception e => e -> LimitT m a

MonadCatch m => MonadCatch (LimitT m)

Defined in Capnp.TraversalLimit

Methods

catch :: Exception e => LimitT m a -> (e -> LimitT m a) -> LimitT m a

(PrimMonad m, s ~ PrimState m) => PrimMonad (LimitT m)

Defined in Capnp.TraversalLimit

Associated Types

type PrimState (LimitT m)

Methods

primitive :: (State# (PrimState (LimitT m)) -> (# State# (PrimState (LimitT m)), a #)) -> LimitT m a

MonadThrow m => MonadLimit (LimitT m)

Defined in Capnp.TraversalLimit

Methods

invoice :: WordCount -> LimitT m ()

type PrimState (LimitT m)

Defined in Capnp.TraversalLimit

type PrimState (LimitT m) = PrimState m

runLimitT :: MonadThrow m => WordCount -> LimitT m a -> m (a, WordCount)

Run a LimitT, returning the value from the computation and the remaining traversal limit.

evalLimitT :: MonadThrow m => WordCount -> LimitT m a -> m a

Run a LimitT, returning the value from the computation.

execLimitT :: MonadThrow m => WordCount -> LimitT m a -> m WordCount

Run a LimitT, returning the remaining traversal limit.

defaultLimit :: WordCount

A sensible default traversal limit. Currently 64 MiB.