What assembly is this RuntimeAssembly?

Say that you are debugging a .NET application in windbg and happen to have a System.Reflection.RuntimeAssembly (the actual implementation of System.Reflection.Assembly) and you want to find out which assembly it actually references. You could try dumping the object (i'm using the sosex extension here):

0:004> !mdt -r 05f7868c
05f7868c (System.Reflection.RuntimeAssembly)
_ModuleResolve:NULL (System.Reflection.ModuleResolveEventHandler)
m_fullname:NULL (System.String)
m_syncRoot:NULL (System.Object)
m_assembly:0eaa4ba8 (System.IntPtr)
m_flags:0x0 (ASSEMBLY_FLAGS_UNKNOWN) (System.Reflection.RuntimeAssembly+ASSEMBLY_FLAGS)

That wasn't very helpful. The object is just a thin wrapper around the native object pointed to by m_assembly. So what is this object? This is what it looks like:

0:004> dd 0eaa4ba8 L30
0eaa4ba8 692addec 014ad1b8 0f7307d8 00000000
0eaa4bb8 0fd49ca4 0000000c 0987de05 00000000
0eaa4bc8 00000007 00000001 00000000 00000000
0eaa4bd8 00000000 00000000 6d079b44 0987de01
0eaa4be8 0f842758 00000000 005508d0 00000002
0eaa4bf8 00000000 00000000 00000000 00000001
0eaa4c08 00000000 00000005 0eaa4ba8 f149a627
0eaa4c18 191e1826 33a15c96 1fa78d20 00000000
0eaa4c28 00000000 00000000 00000101 00000000
0eaa4c38 36664efa 8c001f00 692addec ...

A good trick is to check whether the first value is a vtable pointer:

0:004> ln 692addec
(692addec) clr!DomainAssembly::`vftable' ...

So apparently the object is a DomainAssembly object, whatever that is (you can find some of these classes in the Rotor source, but the structure of them are vastly different). Using this trick combined with the !mln sosex command we find:

692addec: clr!DomainAssembly::`vftable'
014ad1b8: -> to clr!AppDomain
0f7307d8: -> to clr!PEAssembly
0fd49ca4: -> to clr!EditAndContinueModule
0987de05: Heap Object: 09877108[System.Object[]]
offset 00006cfd
0987de04 -> RuntimeModule (05f78868) : m_runtimeAssemblt = 05f7868c
6d079b44: not a pointer
0987de01: Heap Object: 09877108[System.Object[]]
offset 00006cf9
0987de01 -> RuntimeAssembly (05f7868c)
0f842758: -> to clr!AssemblySecurityDescriptor
0eaa4ba8: -> this
f149a627: not a pointer
191e1826: not a pointer
33a15c96: not a pointer
1fa78d20: not a pointer
36664efa: not a pointer
8c001f00: not a pointer

692addec: start of next clr!DomainAssembly object...

The PEAssembly object:

0:004> dd 0f7307d8 L100
0f7307d8 692e2a64 0f5cb928 0f5cc828 00000000
692e2a64: vtable (clr!PEAssembly::`vftable')
0f5cb928: ???
0f5cc828: ??
0f7307e8 00000001 00000001 0149fc38 00000000
0149fc38: -> to clr!MDInternalRO
0f7307f8 00000000 00000000 00000000 00000000
0f730808 0f5b1340 00000006 00000000 00002002
0f5b1340: ??
0f730818 00000000 00000000 00000000 00000000
0f730828 ffffffff ffffffff 00000000 00000000
0f730838 00000000 020007d0 c0000000 00000000
020007d0: not a pointer
0f730848 00000000 00000000 0ea0b930 0f722e80
0ea0b930: -> to clr!CAssemblyName
0f722e80: -> to clr!CAssembly
0f730858 00000000 00000001 00000000 00000000
0f730868 00000000 00000002 00000000 00000001
0f730878 35f26672 88001820 692e2a64 00000000
35f26672: not a pointer
88001820: not a pointer
692e2a64: vtable pointer for next PEAssembly

CAssemblyName? That sounds promising, right?

0:004> dd 0ea0b930
0ea0b930 692b3210 692de934 454d414e 00000005
0ea0b940 504f5250 00000000 00000000 00000000
0ea0b950 00000000 00000000 00000000 0f722a58


0:004> du 0f722a58
0f722a58 "AxInterop.AcroPDFLib"

There was the name. And we had a pointer to the AppDomain earlier, so that should be sufficient to uniquely identify the assembly. I haven't figured out where the actual assembly or module objects as used by !DumpAssembly and !DumpModule resides, but they are probably somewhere in there (the modules are CModule objects, the assembly objects starts with a null pointer, so I couldn't tell the C++ class from that).

Reading raw attribute constructor data

Disassembling a custom attribute gives you a blob of raw bytes – what do they mean? Here is an example from the output from ildasm:
[code lang="cil"]
.custom instance void [mscorlib]System.Reflection.DefaultMemberAttribute::.ctor(string) = (
01 00 04 49 74 65 6d 00 00
) // …Item..
This represents a DefaultMemberAttribute("Item") which is autgenerated by C# when your class has an indexer. The word "Item" is definitely in there – but what does the rest of the data mean? A google search doesn't give any useful answer from what I could find. I ended up looking in the Ecma Standard (page 267). This diagram gives an overview of the structure:

The prolog is always 0x0010 and little-endian encoded. The FixedArgs are the arguments to the constructor and the NamedArgs are properties. A string is encoded as a SerString, which is a single byte length called a PackedLen followed by a UTF8 string. NumNamed is also a little-endian encoded integer containing the number of properties being set (named arguments).

So in this case the data can be broken down as:

01 00: The Prolog (0x0010 in little-endian)
04: The string is 4 characters long
49 74 65 6d: "Item"
00 00: We have 0 properties

Stupid Hack: Add / Remove only property in C#

UPDATE: The screenshot below was lost to the big /dev/null in a server move, so you have to use your imagination.

Can you make a property in C# that you can only add to and remove from? That is what an event does, but that only works with delegates. You can (ab)use an implicit conversion to get something like this:
[code lang="csharp"]

class Foo
public delegate void FooDelegate();
public string Message { get; set; }

public Foo(string message)
Message = message;

public static implicit operator FooDelegate(Foo foo)
return foo.Dummy;

private void Dummy() { }

class Bar
public List FooList { get; private set; }

public event Foo.FooDelegate Foos

public Bar()
FooList = new List();
Using it:
[code lang="csharp"]
static void Main(string[] args)
Bar bar = new Bar();
bar.Foos += new Foo("Hello, World!");
bar.Foos += new Foo("LOL!");
foreach (Foo foo in bar.FooList)
It works – I wouldn't recommend using it in production code though… Maybe more interresting is what would happen if we modified the CIL for an event to accept a non delegate type. Well let's try it and see what happens!

The original C# code:
[code lang="csharp"]
public class EventTester
private List testList = new List();
public List TestList { get { return testList; } }
public event Action TestEvent
Relevant parts of the generated CIL code:
[code lang="cil"]
.method public hidebysig specialname
instance void add_TestEvent (
class [mscorlib]System.Action 'value'
) cil managed
// Method begins at RVA 0x2068
// Code size 15 (0xf)
.maxstack 8

IL_0000: nop
IL_0001: ldarg.0
IL_0002: ldfld class [mscorlib]System.Collections.Generic.List`1 EventTest.EventTester::testList
IL_0007: ldarg.1
IL_0008: callvirt instance void class [mscorlib]System.Collections.Generic.List`1::Add(!0)
IL_000d: nop
IL_000e: ret
} // end of method EventTester::add_TestEvent

.method public hidebysig specialname
instance void remove_TestEvent (
class [mscorlib]System.Action 'value'
) cil managed
// Method begins at RVA 0x2078
// Code size 15 (0xf)
.maxstack 8

IL_0000: nop
IL_0001: ldarg.0
IL_0002: ldfld class [mscorlib]System.Collections.Generic.List`1 EventTest.EventTester::testList
IL_0007: ldarg.1
IL_0008: callvirt instance bool class [mscorlib]System.Collections.Generic.List`1::Remove(!0)
IL_000d: pop
IL_000e: ret
} // end of method EventTester::remove_TestEvent

// Events
.event [mscorlib]System.Action TestEvent
.addon instance void EventTest.EventTester::add_TestEvent(class [mscorlib]System.Action)
.removeon instance void EventTest.EventTester::remove_TestEvent(class [mscorlib]System.Action)
Let us replace "System.Action" with "System.Object" and see what happens. Running ilasm:

C:\Users\poizan\Documents\Visual Studio 2010\Projects\Test>ilasm /DLL EventTest.il

Microsoft (R) .NET Framework IL Assembler.  Version 4.0.30319.1
Copyright (c) Microsoft Corporation.  All rights reserved.
Assembling 'EventTest.il'  to DLL --> 'EventTest.dll'
Source file is ANSI

Assembled method EventTest.EventTester::get_TestList
Assembled method EventTest.EventTester::add_TestEvent
Assembled method EventTest.EventTester::remove_TestEvent
Assembled method EventTest.EventTester::.ctor
Creating PE file

Emitting classes:
Class 1:        EventTest.EventTester

Emitting fields and methods:
Class 1 Fields: 1;      Methods: 4;
Resolving local member refs: 7 -> 7 defs, 0 refs, 0 unresolved

Emitting events and properties:
Class 1 Events: 1;      Props: 1;
Resolving local member refs: 0 -> 0 defs, 0 refs, 0 unresolved
Writing PE file
Operation completed successfully

So far so good. Let us try to use it:
[code lang="csharp"]
class Program
static void Main(string[] args)
EventTester et = new EventTester();
et.TestEvent += "Hello, World!";
et.TestEvent += "Magic!";
foreach (string s in et.TestList.OfType())
It builds successfully. And running it:

 And that is one more thing the C# compiler supports just fine but refuses to create.

Has the webservice client lost the connection?

How do you tell if an exception from a call to a webservice is caused by an IO error?

        public static bool IsIoException(Exception e)
            return (e is TimeoutException || e is CommunicationException || e is EndpointNotFoundException) && !(e is FaultException);

Easy, right?

FaultException is derived from CommunicationException, but it occours when the server sends a SOAP fault back, so definitely not a communication problem (at least between client and webservice). I'm not sure why an EndpointNotFoundException would be thrown because of not being able to talk with the host, but I've seen it happen after unplugging my ethernet cable…

So why exactly can't I just have one sort of exception to catch? Am I not supposed to handle a lost connection in a graceful way?

Oww Microsoft thou art a heartless bitch…


In .NET windows forms you can't not have a default button on a dialog

I haven't tested if this only applies to forms shown with ShowDialog or to every form, but the form will always have a default (accept) button – the one receiving enter presses.

Setting the AcceptButton property to null will nevertheless select a button as the default button. Actually the AcceptButton property is complety ignored. Don't believe anything on the MSDN page. The only thing that decides which button receives an enter press is which control has focus.

So what can you do if you don't want a button to has focus when first showing the form? A control must have focus, and it must be visible. But nothing stops you from placing it in an invisible position such as setting Left to -1000. Set it as the form's ActiveControl and set TabStop to false, meaning that the user won't get back to the dummy button when tabbing around.