How to debug (step into) BinaryFormatter.Deserialize()?

Question

My app tries to deserialize data sent by client and it fails with the following error:

Exception thrown: 'System.Runtime.Serialization.SerializationException' in mscorlib.dll

Additional information: Cannot get the member '<.ctor>b__0'.

googling gives no results. Okay, I decided I would step into deserialization logic and try to figure out what exactly is causing this. Well, a day has passed and I'm nowhere close.

I used instructions from Microsoft Reference Source website to configure Visual Studio. It does download something

MicrosoftPublicSymbols\mscorlib.pdb\
   DCF1E4D31F6944AC87E7A634262BEE881\mscorlib.pdb (780kb)
   E47257B512BA49BC9FC367C532FC5F1E2\mscorlib.pdb (953kb)

but debugger does not step in.

I googled more and found another way to do it - installed dotTrace app and used it as source server. And that does not help either. I still see the following:

Symbol Load Information popup for mscorlib.pdb says

C:\Users\me\AppData\Local\Temp\SymbolCache\MicrosoftPublicSymbols\mscorlib.pdb\e47257b512ba49bc9fc367c532fc5f1e2\mscorlib.pdb: Symbols loaded.

I can step in into System.Windows.Forms, System.Linq, etc - so generally speaking, it works - it just this particular call to BinaryFormatter.Deserialize() does not work. What could be the reasons for that and how can I get it to step into?

Could it be because of SecuritySafeCritical attribute?

[System.Security.SecuritySafeCritical] 
public Object Deserialize(Stream serializationStream)

I'm using VS 2015 .Net 4.5.2 (though I tried 4.5 with the same results).

Answer 1

Without any details i can assume this is compatibility issue with versions of objects you trying to serialize & deserialize. Looks like client sends you some old object bits(without lambda in constructor). And your server running newer version of software searching for some lambda method.

<.ctor>b__0 - is method name for first lambda method in .ctor (object constructor).

So for example if you had on client's machine object A:

class A {
  public A() {
   int a = 5;
   int b = 7;
   // Plain code, no lambdas
  }
}

Then you updated your class on server introducing lambda in constructor:

class A {
  public A() {
   int a = 5;
   int b = 7;
   Func<int,int> some = x => x * 2 + a; 
  }
}

After that their binary representation is not the same, server version of A has private invisible method <.ctor>b__0 in it.

Answer 2

Microsoft doesn't upload the source of every mscorlib.dll update, this is why you only get public PDBs without any source data. But there is a Visual Studio Addon from Redgate's Reflector where you can decompile 3rd party DLLs and step through them in the VS debugger.

DotPeek from Jetbrains also supports PDB generation and hosting of a Symbol server to allow debugging.

Maybe this helps you to debug your issue.