Check whether a Dll is Managed Assembly(C#)

.NET environment may contain a mixed DLLs (.net assembly DLLs & native DLLs) on Windows OS. If we have to know programmatically(C#) whether a file (with .dll extension) is a native DLL (or) .NET Assembly DLL, we can use the following function.


public static bool IsManagedAssembly(string fileName)
try {
uint peHeader;
uint peHeaderSignature;
ushort machine;
ushort sections;
uint timestamp;
uint pSymbolTable;
uint noOfSymbol;
ushort optionalHeaderSize;
ushort characteristics;
ushort dataDictionaryStart;

uint[] dataDictionaryRVA = new uint[16];
uint[] dataDictionarySize = new uint[16];

Stream fs = new FileStream(fileName, FileMode.Open, FileAccess.Read);
BinaryReader reader = new BinaryReader(fs);

//PE Header starts @ 0x3C (60). Its a 4 byte header.
fs.Position = 0x3C;
peHeader = reader.ReadUInt32();

//Moving to PE Header start location...
fs.Position = peHeader;
peHeaderSignature = reader.ReadUInt32();

//We can also show all these value, but we will be
//limiting to the CLI header test.
machine = reader.ReadUInt16();
sections = reader.ReadUInt16();
timestamp = reader.ReadUInt32();
pSymbolTable = reader.ReadUInt32();
noOfSymbol = reader.ReadUInt32();
optionalHeaderSize = reader.ReadUInt16();
characteristics = reader.ReadUInt16();

// Now we are at the end of the PE Header and from here, the PE Optional Headers starts... To go directly to the datadictionary, we'll increase the stream’s current position to with 96 (0x60). 96 because, 28 for Standard fields 68 for NT-specific fields From here DataDictionary starts...and its of total 128 bytes. DataDictionay has 16 directories in total, doing simple maths 128/16 = 8. So each directory is of 8 bytes. In this 8 bytes, 4 bytes is of RVA and 4 bytes of Size. btw, the 15th directory consist of CLR header! if its 0, its not a CLR file :)

dataDictionaryStart = Convert.ToUInt16(Convert.ToUInt16(fs.Position) + 0x60);
fs.Position = dataDictionaryStart;
for (int i = 0; i < 15; i++)
dataDictionaryRVA[i] = reader.ReadUInt32();
dataDictionarySize[i] = reader.ReadUInt32();

if (dataDictionaryRVA[14] == 0) return false;
else return true;
catch(Exception e)
// ToDo