Properly detect Mac OS X in DepotDownloader.

OSVersion.Platform just returns Unix on Mono.

DepotDownloader/CDRManager.cs

@@ -159,7 +159,7 @@ namespace DepotDownloader
                 if ( ver.VersionID == version )
                 {
                     if ( ver.IsEncryptionKeyAvailable )
-                        return DecodeHexString( ver.DepotEncryptionKey );
+                        return Util.DecodeHexString( ver.DepotEncryptionKey );
                     break;
                 }
             }
@@ -183,7 +183,7 @@ namespace DepotDownloader
 
             if ( platform == PlatformID.Win32NT )
                 platformStr = "windows";
-            else if ( platform == PlatformID.MacOSX )
+            else if ( Util.IsMacOSX() )
                 platformStr = "macos";
             
             foreach ( var blobField in appInfoBlob.FileSystems )
@@ -212,7 +212,7 @@ namespace DepotDownloader
 
             if ( platform == PlatformID.Win32NT )
                 platformSuffix = "-win32";
-            else if ( platform == PlatformID.Unix )
+            else if ( platform == PlatformID.Unix && !Util.IsMacOSX() )
                 platformSuffix = "-linux";
 
             int gameLen = gameName.Length;
@@ -280,18 +280,5 @@ namespace DepotDownloader
                 return null;
             }
         }
-        static byte[] DecodeHexString( string hex )
-        {
-            if ( hex == null )
-                return null;
-
-            int chars = hex.Length;
-            byte[] bytes = new byte [ chars / 2 ];
-
-            for ( int i = 0 ; i < chars ; i += 2 )
-                bytes[ i / 2 ] = Convert.ToByte( hex.Substring( i, 2 ), 16 );
-
-            return bytes;
-        }
     }
 }

DepotDownloader/DepotDownloader.csproj

@@ -72,6 +72,7 @@
     <Compile Include="Properties\AssemblyInfo.cs" />
     <Compile Include="ServerCache.cs" />
     <Compile Include="Steam3Session.cs" />
+    <Compile Include="Util.cs" />
   </ItemGroup>
   <ItemGroup>
     <ProjectReference Include="..\..\..\SteamKit2\SteamKit2\SteamKit2.csproj">

DepotDownloader/Util.cs

@@ -0,0 +1,68 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Runtime.InteropServices;
+
+namespace DepotDownloader
+{
+    static class Util
+    {
+        [DllImport( "libc" )]
+        static extern int uname( IntPtr buf );
+
+        static int _isMacOSX = -1;
+
+        // Environment.OSVersion.Platform returns PlatformID.Unix under Mono on OS X
+        // Code adapted from Mono: mcs/class/Managed.Windows.Forms/System.Windows.Forms/XplatUI.cs
+        public static bool IsMacOSX()
+        {
+            if ( _isMacOSX != -1 )
+                return _isMacOSX == 1;
+
+            IntPtr buf = IntPtr.Zero;
+
+            try
+            {
+                // The size of the utsname struct varies from system to system, but this _seems_ more than enough
+                buf = Marshal.AllocHGlobal( 4096 );
+
+                if ( uname( buf ) == 0 )
+                {
+                    string sys = Marshal.PtrToStringAnsi( buf );
+                    if ( sys == "Darwin" )
+                    {
+                        _isMacOSX = 1;
+                        return true;
+                    }
+                }
+            }
+            catch
+            {
+                // Do nothing?
+            }
+            finally
+            {
+                if ( buf != IntPtr.Zero )
+                    Marshal.FreeHGlobal( buf );
+            }
+
+            _isMacOSX = 0;
+            return false;
+        }
+
+        public static byte[] DecodeHexString( string hex )
+        {
+            if ( hex == null )
+                return null;
+
+            int chars = hex.Length;
+            byte[] bytes = new byte[ chars / 2 ];
+
+            for ( int i = 0 ; i < chars ; i += 2 )
+                bytes[ i / 2 ] = Convert.ToByte( hex.Substring(i, 2), 16 );
+
+            return bytes;
+        }
+    }
+}