Reading some assemblies take a lot of memory (> 100x more than System.Reflection.Metadata)

[joelverhagen]

I was doing some analysis of all assemblies on NuGet.org using Azure Functions and I found some packages failed with OutOfMemoryException. Many assemblies load without a problem, but I found several that take more than 1 GB of memory to load. The assembly itself is not even 5 MB so I'm not sure what's going on. Perhaps the DLL is obfuscated? No clue.

Anyway, I am trying to get the assembly public key token. Here's some example code, showing both memory consumption and durations.

var path = "Oracle.ManagedDataAccess.dll";
var sw = Stopwatch.StartNew();
double mb = Math.Pow(1024, 2);
Console.WriteLine(Process.GetCurrentProcess().PrivateMemorySize64 / mb + " MB");

Console.WriteLine("== System.Reflection.Metadata ==");
using (var fileStream = File.OpenRead(path))
using (var peReader = new PEReader(fileStream))
{
    Console.WriteLine(peReader.GetMetadataReader().GetAssemblyDefinition().GetAssemblyName());
    Console.WriteLine(Process.GetCurrentProcess().PrivateMemorySize64 / mb + " MB");
    Console.WriteLine(sw.Elapsed);
}

Console.WriteLine("== Mono.Cecil ==");
using (var cecilModule = Mono.Cecil.ModuleDefinition.ReadModule(path))
{
    Console.WriteLine(cecilModule.Assembly.FullName);
    Console.WriteLine(Process.GetCurrentProcess().PrivateMemorySize64 / mb + " MB");
    Console.WriteLine(sw.Elapsed);
}

The output is:

7.6640625 MB
== System.Reflection.Metadata ==
Oracle.ManagedDataAccess, Version=4.122.1.0, PublicKeyToken=89b483f429c47342
8.43359375 MB
00:00:00.0405080
== Mono.Cecil ==
Oracle.ManagedDataAccess, Version=4.122.1.0, Culture=neutral, PublicKeyToken=89b483f429c47342
1601.359375 MB
00:00:01.5745009

Nearly 1.6 GB of memory to load this DLL. The DLL was found in this package: https://www.nuget.org/packages/Flexygo/1.0.13.36-rc

A minimal repro is here: ConsoleApp2.zip

[jbevain]

Yeah this DLL is obfuscated and designed to break tools like Cecil. Would be interesting to see if there are low hanging fruits to mitigate the issue.