Audit `http2` for uses of `catch` from `unliftio`

[edsko]

In kazu-yamamoto/http2#92 we changed things so that the KilledByHttp2ThreadManager exception would not be remain uncaught, but a later change to unliftio meant that the behaviour of catch changed: only synchronous exceptions are caught! We should check all uses of catch and friends in http2.

[edsko]

Chances are good that this will fix #156.

[FinleyMcIlwaine]

Searching for SyncOrAsync in unliftio, only try, catch, and handle have this weird behavior, so they might be the only functions we need to audit usages of.

[edsko]

Below is an exhaustive (I think) list of all functions in unliftio that require scrutiny; all of these functions intentionally do not deal with asynchronous exceptions. Auditing would take one of two forms:

1. Functions that are polymorphic in the exception type, such as

   catch         :: (..) => m a -> (e -> m a) -> m a
   catchJust     :: (..) => (e -> Maybe b) -> m a -> (b -> m a) -> m a

   would depend on how e is instantiated; if instantiated to SomeException, and the intention is to catch also asynchronous exception, this function cannot be used (unliftio offers catchSyncOrAsync).

2. Functions using SomeException, such as

   catchAny      :: (..) => m a -> (SomeException -> m a) -> m a

   need to be audited to see if the intention really is to catch only synchronous exceptions.

The full list:

catch         :: (..) => m a -> (e -> m a) -> m a
catchAny      :: (..) => m a -> (SomeException -> m a) -> m a
catchDeep     :: (..) => m a -> (e -> m a) -> m a
catchAnyDeep  :: (..) => m a -> (SomeException -> m a) -> m a
catchJust     :: (..) => (e -> Maybe b) -> m a -> (b -> m a) -> m a

handle        :: (..) => (e -> m a) -> m a -> m a
handleAny     :: (..) => (SomeException -> m a) -> m a -> m a
handleDeep    :: (..) => (e -> m a) -> m a -> m a
handleAnyDeep :: (..) => (SomeException -> m a) -> m a -> m a
handleJust    :: (..) => (e -> Maybe b) -> (b -> m a) -> m a -> m a

try           :: (..) => m a -> m (Either e a)
tryAny        :: (..) => m a -> m (Either SomeException a)
tryDeep       :: (..) => m a -> m (Either e a)
tryAnyDeep    :: (..) => m a -> m (Either SomeException a)
tryJust       :: (..) => (e -> Maybe b) -> m a -> m (Either b a)

pureTry       ::         a -> Either SomeException a
pureTryDeep   :: (..) => a -> Either SomeException a

catches       :: (..) => m a -> [Handler m a] -> m a
catchesDeep   :: (..) => m a -> [Handler m a] -> m a

mapExceptionM :: (..) => (e1 -> e2) -> m a -> m a

catching      :: (..) => Getting (First a) SomeException a -> m r -> (a -> m r) -> m r
catching_     :: (..) => Getting (First a) SomeException a -> m r -> m r -> m r
handling      :: (..) => Getting (First a) SomeException a -> (a -> m r) -> m r -> m r
handling_     :: (..) => Getting (First a) SomeException a -> m r -> m r -> m r
trying        :: (..) => Getting (First a) SomeException a -> m r -> m (Either a r)
trying_       :: (..) => Getting (First a) SomeException a -> m r -> m (Maybe r)

[edsko]

Report and PR at kazu-yamamoto/http2#138 .