C# – How does reflector show types when Assembly.GetTypes() fails due to a missing referenced assembly

creflection

I have a broken Assembly that I want to reflect over, its not broken badly, it just cannot find a referenced assembly, so it does fail a PEVerify. But….Assembly.LoadFrom() will still load it and GetTypes() will throw a ReflectionTypeLoadException, the .LoaderExceptions array shows me what referenced assembly cannot be found. At this point I am roadblocked.

However, the great little tool Reflector is able to go further and actually display the contained types, and handles gracefully the missing reference issue by giving me a pop-up dialog to browse for it. My question is, How after the GetTypes() fails does reflector manage to get the types anyway?

Best Answer

Reflector doesn't use System.Reflection to analyse an assembly.

I don't know which library Reflector uses, but you might want to have a look at Cecil.

Signing Third-Party Assemblies

The basic principle to sign a thirp-party is to

Disassemble the assembly using ildasm.exe and save the intermediate language (IL):
```
ildasm /all /out=thirdPartyLib.il thirdPartyLib.dll 
```

Rebuild and sign the assembly:

ilasm /dll /key=myKey.snk thirdPartyLib.il

Fixing Additional References

The above steps work fine unless your third-party assembly (A.dll) references another library (B.dll) which also has to be signed. You can disassemble, rebuild and sign both A.dll and B.dll using the commands above, but at runtime, loading of B.dll will fail because A.dll was originally built with a reference to the unsigned version of B.dll.

The fix to this issue is to patch the IL file generated in step 1 above. You will need to add the public key token of B.dll to the reference. You get this token by calling

sn -Tp B.dll

which will give you the following output:

Microsoft (R) .NET Framework Strong Name Utility  Version 4.0.30319.33440
Copyright (c) Microsoft Corporation.  All rights reserved.

Public key (hash algorithm: sha1):
002400000480000094000000060200000024000052534131000400000100010093d86f6656eed3
b62780466e6ba30fd15d69a3918e4bbd75d3e9ca8baa5641955c86251ce1e5a83857c7f49288eb
4a0093b20aa9c7faae5184770108d9515905ddd82222514921fa81fff2ea565ae0e98cf66d3758
cb8b22c8efd729821518a76427b7ca1c979caa2d78404da3d44592badc194d05bfdd29b9b8120c
78effe92

Public key token is a8a7ed7203d87bc9

The last line contains the public key token. You then have to search the IL of A.dll for the reference to B.dll and add the token as follows:

.assembly extern /*23000003*/ MyAssemblyName
{
  .publickeytoken = (A8 A7 ED 72 03 D8 7B C9 )                         
  .ver 10:0:0:0
}

C# – How to get custom attributes from an assembly that is not (really) loaded

It is possible to load (reflection only) assemblies with dependencies.

AppDomain.CurrentDomain.ReflectionOnlyAssemblyResolve += (s, e) => Assembly.ReflectionOnlyLoad(e.Name);

would fix failures when loading, assuming they are all in the same folder.

Best Answer

Related Solutions

C# – How to fix “Referenced assembly does not have a strong name” error

Signing Third-Party Assemblies

Fixing Additional References

C# – How to get custom attributes from an assembly that is not (really) loaded

Related Topic