UDP improvements for the sockets module. Renamed ftpclient.fileExists to

existsFile for consistency. Added tasyncudp test.

tests/run/tasyncudp.nim

@@ -0,0 +1,77 @@
+discard """
+  file: "tasyncudp.nim"
+  output: "2000"
+"""
+import asyncio, sockets, strutils, times
+
+const
+  swarmSize = 5
+  messagesToSend = 200
+
+var
+  disp = newDispatcher()
+  msgCount = 0
+  currentClient = 0
+
+proc serverRead(s: PAsyncSocket) =
+  var data = ""
+  var address = ""
+  if s.recvFromAsync(data, 9, address):
+    assert address == "127.0.0.1"
+    msgCount.inc()
+  
+  discard """
+  
+  var line = ""
+  assert s.recvLine(line)
+  
+  if line == "":
+    assert(false)
+  else:
+    if line.startsWith("Message "):
+      msgCount.inc()
+    else:
+      assert(false)
+  """
+
+proc swarmConnect(s: PAsyncSocket) =
+  for i in 1..messagesToSend:
+    s.send("Message\c\L")
+
+proc createClient(disp: var PDispatcher, port: TPort,
+                  buffered = true) =
+  currentClient.inc()
+  var client = AsyncSocket(typ = SOCK_DGRAM, protocol = IPPROTO_UDP,
+                           buffered = buffered)
+  client.handleConnect = swarmConnect
+  disp.register(client)
+  client.connect("localhost", port)
+
+proc createServer(port: TPort, buffered = true) =
+  var server = AsyncSocket(typ = SOCK_DGRAM, protocol = IPPROTO_UDP,
+                           buffered = buffered)
+  server.handleRead = serverRead
+  disp.register(server)
+  server.bindAddr(port)
+
+let serverCount = 2
+
+createServer(TPort(10335), false)
+createServer(TPort(10336), true)
+var startTime = epochTime()
+while true:
+  if epochTime() - startTime >= 300.0:
+    break
+
+  if not disp.poll():
+    break
+  
+  if (msgCount div messagesToSend) * serverCount == currentClient:
+    createClient(disp, TPort(10335), false)
+    createClient(disp, TPort(10336), true)
+  
+  if msgCount == messagesToSend * serverCount * swarmSize:
+    break
+
+assert msgCount == messagesToSend * serverCount * swarmSize
+echo(msgCount)