Add an IsManagedAssembly() implementation that doesn't throw on native assemblies.

The downside of the previous method is that it was throwing a first-chance exception on native binaries. This makes it harder to debug.

Also the new implementation is 4 times faster for success cases and 5-6 times faster for failure cases (native binary).

1 files changed, 66 insertions, 5 deletions

diff --git a/Mono.Addins/Mono.Addins.Database/Util.cs b/Mono.Addins/Mono.Addins.Database/Util.cs
index 72e48c1..5a80a35 100644
--- a/Mono.Addins/Mono.Addins.Database/Util.cs
+++ b/Mono.Addins/Mono.Addins.Database/Util.cs
@@ -248,12 +248,73 @@ namespace Mono.Addins.Database
 				yield return gacDir + "_MSIL";
 		}
 
-		internal static bool IsManagedAssembly (string file)
+		internal static bool IsManagedAssembly (string filePath)
 		{
-			try {
-				AssemblyName.GetAssemblyName (file);
-				return true;
-			} catch (BadImageFormatException) {
+			try
+			{
+				using (Stream fileStream = new FileStream(filePath, FileMode.Open, FileAccess.Read, FileShare.ReadWrite | FileShare.Delete))
+				using (BinaryReader binaryReader = new BinaryReader(fileStream))
+				{
+					if (fileStream.Length < 64)
+					{
+						return false;
+					}
+
+					// PE Header starts @ 0x3C (60). Its a 4 byte header.
+					fileStream.Position = 0x3C;
+					uint peHeaderPointer = binaryReader.ReadUInt32();
+					if (peHeaderPointer == 0)
+					{
+						peHeaderPointer = 0x80;
+					}
+
+					// Ensure there is at least enough room for the following structures:
+					//     24 byte PE Signature & Header
+					//     28 byte Standard Fields         (24 bytes for PE32+)
+					//     68 byte NT Fields               (88 bytes for PE32+)
+					// >= 128 byte Data Dictionary Table
+					if (peHeaderPointer > fileStream.Length - 256)
+					{
+						return false;
+					}
+
+					// Check the PE signature.  Should equal 'PE\0\0'.
+					fileStream.Position = peHeaderPointer;
+					uint peHeaderSignature = binaryReader.ReadUInt32();
+					if (peHeaderSignature != 0x00004550)
+					{
+						return false;
+					}
+
+					// skip over the PEHeader fields
+					fileStream.Position += 20;
+
+					const ushort PE32 = 0x10b;
+					const ushort PE32Plus = 0x20b;
+
+					// Read PE magic number from Standard Fields to determine format.
+					var peFormat = binaryReader.ReadUInt16();
+					if (peFormat != PE32 && peFormat != PE32Plus)
+					{
+						return false;
+					}
+
+					// Read the 15th Data Dictionary RVA field which contains the CLI header RVA.
+					// When this is non-zero then the file contains CLI data otherwise not.
+					ushort dataDictionaryStart = (ushort)(peHeaderPointer + (peFormat == PE32 ? 232 : 248));
+					fileStream.Position = dataDictionaryStart;
+
+					uint cliHeaderRva = binaryReader.ReadUInt32();
+					if (cliHeaderRva == 0)
+					{
+						return false;
+					}
+
+					return true;
+				}
+			}
+			catch (Exception)
+			{
 				return false;
 			}
 		}