Add a class to find Squirrel-aware PE images

src/Squirrel/NativeMethods.cs

@@ -0,0 +1,27 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Runtime.InteropServices;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Squirrel
+{
+    static class NativeMethods
+    {
+        [DllImport("version.dll", SetLastError = true)]
+        public static extern bool GetFileVersionInfo(
+            string lpszFileName, 
+            IntPtr dwHandleIgnored,
+            int dwLen, 
+            [MarshalAs(UnmanagedType.LPArray)] byte[] lpData);
+
+        [DllImport("version.dll", SetLastError = true)]
+        public static extern int GetFileVersionInfoSize(
+            string lpszFileName,
+            IntPtr dwHandleIgnored);
+
+        [DllImport("version.dll")]
+        public static extern bool VerQueryValue(byte[] pBlock, string pSubBlock, out IntPtr pValue, out int len);
+    }
+}

src/Squirrel/Squirrel.csproj

@@ -71,12 +71,14 @@
     <Compile Include="FileDownloader.cs" />
     <Compile Include="IUpdateManager.cs" />
     <Compile Include="MarkdownSharp.cs" />
+    <Compile Include="NativeMethods.cs" />
     <Compile Include="PackageExtensions.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />
     <Compile Include="ReleaseEntry.cs" />
     <Compile Include="ReleaseExtensions.cs" />
     <Compile Include="ReleasePackage.cs" />
     <Compile Include="ShellFile.cs" />
+    <Compile Include="SquirrelAwareExecutableDetector.cs" />
     <Compile Include="TaskbarHelper.cs" />
     <Compile Include="UpdateInfo.cs" />
     <Compile Include="UpdateManager.cs" />

src/Squirrel/SquirrelAwareExecutableDetector.cs

@@ -0,0 +1,73 @@
+using System;
+using System.Collections.Generic;
+using System.Globalization;
+using System.IO;
+using System.Linq;
+using System.Reflection;
+using System.Runtime.InteropServices;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace Squirrel
+{
+    static class SquirrelAwareExecutableDetector
+    {
+        public static int? GetPESquirrelAwareVersion(string executable)
+        {
+            if (!File.Exists(executable)) return null;
+            var fullname = Path.GetFullPath(executable);
+
+            return GetAssemblySquirrelAwareVersion(fullname) ?? GetVersionBlockSquirrelAwareValue(fullname);
+        }
+
+        static int? GetAssemblySquirrelAwareVersion(string executable)
+        {
+            try 
+            {
+                var assembly = Assembly.ReflectionOnlyLoadFrom(executable);
+                var attrs = assembly.GetCustomAttributesData();
+                var attribute = attrs.FirstOrDefault(x => 
+                {
+                    if (x.AttributeType != typeof(AssemblyMetadataAttribute)) return false;
+                    if (x.ConstructorArguments.Count != 2) return false;
+                    return x.ConstructorArguments[0].Value.ToString() == "SquirrelAwareVersion";
+                });
+
+                if (attribute == null) return null;
+
+                int result;
+                if (!Int32.TryParse(attribute.ConstructorArguments[1].Value.ToString(), NumberStyles.Integer, CultureInfo.CurrentCulture, out result)) 
+                {
+                    return null;
+                }
+
+                return result;
+            } 
+            catch (FileLoadException) { return null; }
+            catch (BadImageFormatException) { return null; }
+        }
+
+        static int? GetVersionBlockSquirrelAwareValue(string executable)
+        {
+            int size = NativeMethods.GetFileVersionInfoSize(executable, IntPtr.Zero);
+
+            // Nice try, buffer overflow
+            if (size <= 0 || size > 4096) return null;
+
+            var buf = new byte[size];
+            if (!NativeMethods.GetFileVersionInfo(executable, IntPtr.Zero, size, buf)) return null;
+
+            IntPtr result; int resultSize;
+            if (!NativeMethods.VerQueryValue(buf, "\\StringFileInfo\\040904B0\\SquirrelAwareVersion", out result, out resultSize)) 
+            {
+                return null;
+            }
+
+            int ret;
+            string resultData = Marshal.PtrToStringAnsi(result, resultSize-1 /* Subtract one for null terminator */);
+            if (!Int32.TryParse(resultData, NumberStyles.Integer, CultureInfo.CurrentCulture, out ret)) return null;
+
+            return ret;
+        }
+    }
+}