1 files changed, 49 insertions, 0 deletions
diff --git a/src/Network/WireGuard/Internal/PacketQueue.hs b/src/Network/WireGuard/Internal/PacketQueue.hs
new file mode 100644
index 0000000..bc390f8
--- /dev/null
+++ b/src/Network/WireGuard/Internal/PacketQueue.hs
@@ -0,0 +1,49 @@
+{-# LANGUAGE RecordWildCards #-}
+
+module Network.WireGuard.Internal.PacketQueue
+  ( PacketQueue
+  , newPacketQueue
+  , popPacketQueue
+  , pushPacketQueue
+  , tryPushPacketQueue
+  ) where
+
+import           Control.Concurrent.STM
+
+data PacketQueue packet = PacketQueue
+                        { tqueue    :: TQueue packet
+                        , allowance :: TVar Int
+                        }
+
+-- | Create a new PacketQueue with size limit of |maxQueuedPackets|.
+newPacketQueue :: Int -> STM (PacketQueue packet)
+newPacketQueue maxQueuedPackets = PacketQueue <$> newTQueue <*> newTVar maxQueuedPackets
+
+-- | Pop a packet out from the queue, blocks if no packet is available.
+popPacketQueue :: PacketQueue packet -> STM packet
+popPacketQueue PacketQueue{..} = do
+    packet <- readTQueue tqueue
+    modifyTVar' allowance (+1)
+    return packet
+
+-- | Push a packet into the queue. Blocks if it's full.
+pushPacketQueue :: PacketQueue packet -> packet -> STM ()
+pushPacketQueue PacketQueue{..} packet = do
+    allowance' <- readTVar allowance
+    if allowance' <= 0
+      then retry
+      else do
+          writeTQueue tqueue packet
+          writeTVar allowance (allowance' - 1)
+
+-- | Try to push a packet into the queue. Returns True if it's pushed.
+tryPushPacketQueue :: PacketQueue packet -> packet -> STM Bool
+tryPushPacketQueue PacketQueue{..} packet = do
+    allowance' <- readTVar allowance
+    if allowance' <= 0
+      then return False
+      else do
+          writeTQueue tqueue packet
+          writeTVar allowance (allowance' - 1)
+          return True
+