.net - 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

MicrosoftPublicSymbolsmscorlib.pdb
   DCF1E4D31F6944AC87E7A634262BEE881mscorlib.pdb (780kb)
   E47257B512BA49BC9FC367C532FC5F1E2mscorlib.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:UsersmeAppDataLocalTempSymbolCacheMicrosoftPublicSymbolsmscorlib.pdbe47257b512ba49bc9fc367c532fc5f1e2mscorlib.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.