Add config for max snd buffer size (#440)

* Add config for max snd buffer size

eth/utp/send_buffer_tracker.nim

@@ -20,13 +20,27 @@ type SendBufferTracker* = ref object
 
   # remote receive window updated based on packed wndSize field
   maxRemoteWindow*: uint32
+
+  # configuration option for maxium number of bytes in snd buffer
+  maxSndBufferSize*: uint32
   waiters: seq[(uint32, Future[void])]
 
-proc new*(T: type SendBufferTracker, currentWindow: uint32,  maxRemoteWindow: uint32): T =
-  return SendBufferTracker(currentWindow: currentWindow, maxRemoteWindow: maxRemoteWindow, waiters: @[])
+proc new*(
+  T: type SendBufferTracker,
+  currentWindow: uint32,
+  maxRemoteWindow: uint32, 
+  maxSndBufferSize: uint32): T =
+  return (
+    SendBufferTracker(
+      currentWindow: currentWindow,
+      maxRemoteWindow: maxRemoteWindow,
+      maxSndBufferSize: maxSndBufferSize,
+      waiters: @[]
+    )
+  )
 
 proc currentFreeBytes*(t: SendBufferTracker): uint32 =
-  let maxSend = t.maxRemoteWindow
+  let maxSend = min(t.maxRemoteWindow, t.maxSndBufferSize)
   if (maxSend <= t.currentWindow):
     return 0
   else:

eth/utp/utp_socket.nim

@@ -57,6 +57,9 @@ type
     # Maximnal size of receive buffer in bytes
     optRcvBuffer*: uint32
 
+    # Maximnal size of send buffer in bytes
+    optSndBuffer*: uint32
+
     # If set to some(`Duration`), the incoming socket will be initialized in
     # `SynRecv` state and the remote peer will have `Duration` to transfer data
     # to move the socket in `Connected` state.
@@ -278,12 +281,14 @@ proc init*(
   dataResendsBeforeFailure: uint16 = defaultDataResendsBeforeFailure,
   optRcvBuffer: uint32 = defaultOptRcvBuffer,
   incomingSocketReceiveTimeout: Option[Duration] = some(defaultRcvRetransmitTimeout),
-  remoteWindowResetTimeout: Duration = defaultResetWindowTimeout
+  remoteWindowResetTimeout: Duration = defaultResetWindowTimeout,
+  optSndBuffer: uint32 = defaultOptRcvBuffer
   ): T =
   SocketConfig(
     initialSynTimeout: initialSynTimeout,
     dataResendsBeforeFailure: dataResendsBeforeFailure,
     optRcvBuffer: optRcvBuffer,
+    optSndBuffer: optSndBuffer,
     incomingSocketReceiveTimeout: incomingSocketReceiveTimeout,
     remoteWindowResetTimeout: remoteWindowResetTimeout
   )
@@ -560,7 +565,7 @@ proc new[A](
     closeEvent: newAsyncEvent(),
     closeCallbacks: newSeq[Future[void]](),
     # start with 1mb assumption, field will be updated with first received packet
-    sendBufferTracker: SendBufferTracker.new(0, 1024 * 1024),
+    sendBufferTracker: SendBufferTracker.new(0, 1024 * 1024, cfg.optSndBuffer),
     # queue with infinite size
     writeQueue: newAsyncQueue[WriteRequest](),
     zeroWindowTimer: Moment.now() + cfg.remoteWindowResetTimeout,

tests/utp/test_utp_socket.nim

@@ -956,3 +956,51 @@ procSuite "Utp socket unit test":
       p.payload == someData
 
     await outgoingSocket.destroyWait()
+
+  asyncTest "Writing data should respect max snd buffer option":
+    let q = newAsyncQueue[Packet]()
+    let initialRemoteSeq = 10'u16
+    let someData1 = @[1'u8]
+    let somedata2 = @[2'u8]
+    let (outgoingSocket, initialPacket) = 
+      connectOutGoingSocket(
+        initialRemoteSeq,
+        q,
+        cfg = SocketConfig.init(
+          optSndBuffer = 1
+        )
+      )
+
+    check:
+      outgoingSocket.isConnected()
+
+    # snd buffer got 1 byte of space so this future shold finish
+    let write1 = await outgoingSocket.write(someData1)
+
+    let writeFut2 = outgoingSocket.write(someData2)
+
+    # wait until 2 re-sends to check we do not accidently free buffer during re-sends
+    discard await q.get()
+    discard await q.get()
+    let firstPacket = await q.get()
+
+    check:
+      # this write still cannot progress as 1st write is not acked
+      not writeFut2.finished()
+
+    let someAckFromRemote = ackPacket(initialRemoteSeq, initialPacket.header.connectionId, initialPacket.header.seqNr + 1, 10)
+
+    # acks first write, so there is space in buffer for new data and second
+    # write should progress
+    await outgoingSocket.processPacket(someAckFromRemote)
+
+    yield writeFut2
+
+    let secondPacket =  await q.get()
+
+    check:
+      writeFut2.finished()
+      firstPacket.payload == someData1
+      secondPacket.payload == somedata2
+
+    await outgoingSocket.destroyWait()