#1115 find available ports to use in acceptance tests

test/Ocelot.AcceptanceTests/RandomPortFinder.cs

@@ -0,0 +1,55 @@
+using System;
+using System.Collections.Concurrent;
+using System.Collections.Generic;
+using System.Linq;
+using System.Net;
+using System.Net.Http;
+using System.Net.Sockets;
+using System.Text;
+
+namespace Ocelot.AcceptanceTests
+{
+    public static class RandomPortFinder
+    {
+        private static readonly int TrialNumber = 100;
+        private static readonly int BeginPortRange = 20000;
+        private static readonly int EndPortRange = 45000;
+
+        private static Random random = new Random();
+        private static ConcurrentBag<int> usedPorts = new ConcurrentBag<int>();
+
+        public static int GetRandomPort()
+        {
+            int randomPort = 0;
+            for (int i = 0; i < TrialNumber; i++)
+            {
+                randomPort = random.Next(BeginPortRange, EndPortRange);
+                if (usedPorts.Any(p => p == randomPort))
+                {
+                    continue;
+                }
+                else
+                {
+                    usedPorts.Add(randomPort);
+                }
+
+                try
+                {
+                    IPEndPoint ipe = new IPEndPoint(IPAddress.Loopback, randomPort);
+                    using (var socket = new Socket(ipe.AddressFamily, SocketType.Stream, ProtocolType.Tcp))
+                    {
+                        socket.Bind(ipe);
+                        socket.Close();
+                        return randomPort;
+                    }
+                }
+                catch (Exception)
+                {
+                    continue;
+                }                
+            }
+
+            throw new Exception("Cannot find available port to bind to.");
+        }
+    }
+}