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{-# LANGUAGE TupleSections #-}
{-# LANGUAGE DeriveFunctor #-}
module Data.PacketBuffer
( PacketBuffer
, newPacketBuffer
, PacketOutboundEvent(..)
, PacketInboundEvent(..)
, grokOutboundPacket
, grokInboundPacket
, awaitReadyPacket
, packetNumbersToRequest
, expectingSequenceNumber
, nextToSendSequenceNumber
, retrieveForResend
, decompressSequenceNumbers
) where
import Data.PacketQueue as Q
import Control.Concurrent.STM
import Control.Monad
import Data.Maybe
import Data.Word
data PacketBuffer a b = PacketBuffer
{ inQueue :: PacketQueue a
, outBuffer :: PacketQueue b
}
-- | Initialize the packet buffers. Note, the capacity of the inbound packet
-- queue is currently hardcoded to 200 packets and the capacity of the outbound
-- buffer is hardcoded to 400 packets.
newPacketBuffer :: STM (PacketBuffer a b)
newPacketBuffer = PacketBuffer <$> Q.new 200 0
<*> Q.new 400 0
-- | Input for 'grokPacket'.
data PacketOutboundEvent b
= PacketSent { poSeqNum :: Word32 -- ^ Sequence number for payload.
, poSentPayload :: b -- ^ Payload packet we sent to them.
}
deriving Functor
data PacketInboundEvent a
= PacketReceived { peSeqNum :: Word32 -- ^ Sequence number for payload.
, peReceivedPayload :: a -- ^ Payload packet they sent to us.
, peAcknowledgedNum :: Word32 -- ^ Earliest sequence number they've seen from us.
}
| PacketReceivedLossy { peSeqNum :: Word32 -- ^ Sequence number for lossy packet.
, peAcknowledgedNum :: Word32 -- ^ Earliest sequence number they've seen from us.
}
deriving Functor
-- | Whenever a packet is received or sent (but not resent) from the network,
-- this function should be called to update the relevant buffers.
--
-- On outgoing packets, if the outbound buffer is full, this will block
-- indefinitely until it is called in another thread with an inbound
-- acknowledgement.
grokOutboundPacket :: PacketBuffer a b -> PacketOutboundEvent b -> STM ()
grokOutboundPacket (PacketBuffer _ outb) (PacketSent seqno a)
= do (n,_) <- Q.enqueue outb seqno a
when (n/=0) retry
grokInboundPacket :: PacketBuffer a b -> PacketInboundEvent a -> STM ()
grokInboundPacket (PacketBuffer inb outb) (PacketReceived seqno a ack)
= do Q.enqueue inb seqno a
Q.dropPacketsBefore outb ack
grokInboundPacket (PacketBuffer inb outb) (PacketReceivedLossy seqno ack)
= do Q.observeOutOfBand inb seqno
Q.dropPacketsBefore outb ack
-- | Wait until an inbound packet is ready to process. Any necessary
-- re-ordering will have been done.
awaitReadyPacket :: PacketBuffer a b -> STM a
awaitReadyPacket (PacketBuffer inb _) = Q.dequeue inb
-- | Obtain a list of sequence numbers that may have been dropped. This would
-- be any number not yet received that is prior to the maxium sequence number
-- we have received. For convenience, a lowerbound for the missing squence numbers
-- is also returned as the second item of the pair.
packetNumbersToRequest :: PacketBuffer a b -> STM ([Word32],Word32)
packetNumbersToRequest (PacketBuffer inb _) = do
ns <- Q.getMissing inb
lb <- Q.getLastDequeuedPlus1 inb
return (ns,lb)
expectingSequenceNumber :: PacketBuffer a b -> STM Word32
expectingSequenceNumber (PacketBuffer inb _ ) = Q.getLastDequeuedPlus1 inb
nextToSendSequenceNumber :: PacketBuffer a b -> STM Word32
nextToSendSequenceNumber (PacketBuffer _ outb) = Q.getLastEnqueuedPlus1 outb
-- | Retrieve already-sent packets by their sequence numbers. See
-- 'decompressSequenceNumbers' to obtain the sequence number list from a
-- compressed encoding. There is no need to call 'grokPacket' when sending the
-- packets returned from this call.
retrieveForResend :: PacketBuffer a b -> [Word32] -> STM [(Word32,b)]
retrieveForResend (PacketBuffer _ outb) seqnos =
catMaybes <$> forM seqnos (\no -> fmap (no,) <$> Q.lookup outb no)
-- | Expand a compressed set of sequence numbers. The first squence number is
-- given directly and the rest are computed using 8-bit offsets. This is
-- normally used to obtain input for 'retrieveForResend'.
decompressSequenceNumbers :: Word32 -> [Word8] -> [Word32]
decompressSequenceNumbers baseno ns = foldr doOne (const []) ns (baseno-1)
where
doOne :: Word8 -> (Word32 -> [Word32]) -> Word32 -> [Word32]
doOne 0 f addend = f (addend+255)
doOne x f addend = let y = fromIntegral x + addend
in y : f y
|
