Updating Darwin OS detection

src/Microsoft.AspNet.Server.Kestrel/KestrelEngine.cs

@@ -44,11 +44,7 @@ namespace Microsoft.AspNet.Server.Kestrel
                         architecture, 
                         "libuv.dll");
                 }
-                else if ((int)Environment.OSVersion.Platform == 4)
+                else if (Libuv.IsDarwin)
-                {
-                    libraryPath = "libuv.so.1";
-                }
-                else
                 {
                     libraryPath = Path.Combine(
                         libraryPath,
@@ -57,6 +53,10 @@ namespace Microsoft.AspNet.Server.Kestrel
                         "universal",
                         "libuv.dylib");
                 }
+                else
+                {
+                    libraryPath = "libuv.so.1";
+                }
             }
             Libuv.Load(libraryPath);
         }

src/Microsoft.AspNet.Server.Kestrel/Networking/Libuv.cs

@@ -13,9 +13,15 @@ namespace Microsoft.AspNet.Server.Kestrel.Networking
         public Libuv()
         {
             IsWindows = PlatformApis.IsWindows();
+            if (!IsWindows)
+            {
+                IsDarwin = PlatformApis.IsDarwin();
+            }
         }
 
         public bool IsWindows;
+        public bool IsDarwin;
+
         public Func<string, IntPtr> LoadLibrary;
         public Func<IntPtr, bool> FreeLibrary;
         public Func<IntPtr, string, IntPtr> GetProcAddress;

src/Microsoft.AspNet.Server.Kestrel/Networking/PlatformApis.cs

@@ -20,6 +20,34 @@ namespace Microsoft.AspNet.Server.Kestrel.Networking
 #endif
         }
 
+        [DllImport("libc")]
+        static extern int uname(IntPtr buf);
+
+        static unsafe string GetUname()
+        {
+            var buffer = new byte[8192];
+            try
+            {
+                fixed (byte* buf = buffer)
+                {
+                    if (uname((IntPtr)buf) == 0)
+                    {
+                        return Marshal.PtrToStringAnsi((IntPtr)buf);
+                    }
+                }
+                return string.Empty;
+            }
+            catch
+            {
+                return string.Empty;
+            }
+        }
+
+        public static bool IsDarwin()
+        {
+            return string.Equals(GetUname(), "Darwin", StringComparison.Ordinal);
+        }
+
         public static void Apply(Libuv libuv)
         {
             if (libuv.IsWindows)