wyDay blog

In todays article Im going to talk about an interesting problem: detecting .NET assemblies. More than that, Ill be talking about detecting some features of .NET assemblies and how you can expand and mold our code for your own uses. The codes at the bottom of the article, its written in C# and licensed under the BSD license. Go get it.

Ive seen this question pop up in a few different forms:

• How do I detect .NET assemblies?
• How can I detect the difference between .NET 2.0 and .NET 4.0 assemblies?
• How can I detect the difference between x86, x64, and AnyCPU .NET assemblies?

And the list goes on and on. But this raises the question

Why detect .NET assemblies?

We detect .NET assemblies because we respect humans time. Let me explain.

When wyUpdate (our open source updater) installs updates it can do a few things beyond simple patching, registry changing, and file copying. Namely it can:

• NGEN assemblies
• Install & update COM assemblies using RegAsm
• Install & update assemblies in the GAC (Global Assembly Cache).

Which means wyUpdate needs to know whether the executable (or dll) is a .NET assembly, whether its strong signed, and what platform target it is (i.e. x86, x64, or Any CPU).

We could ask the user for every file, but thats such a hassle. Who wants to waste time checking boxes for every exe and dll in their project? Rather than wasting the users time we quickly scan the .dll and .exe files for their details when the update is built inside wyBuild.

How not to do .NET detection

Do not use LoadLibrary(), or Assembly.Load() functions to load an assembly in memory to then parse it. This breaks when you have an x86 process trying to a load an x64 assembly (or vice versa).

How to detect .NET

Instead of using LoadLibrary (or one of its brethren) well just treat the executables as dumb files. That is, just run a simple loop over the file and skip over the unneeded parts. You can check out the C# code posted at the bottom of this article, but you should be aware of 2 resources we used when designing the .NET detection algorithm:

• CLI Partition II: Metadata Definition and Semantics (get the PDF) from the ECMA C# and Common Language Infrastructure Standards
• Portable Executable and Common Object File Format Specification (i.e. the PECOFF Spec)

The PECOFF spec gives you the general layout of .exe and .dll files, and the CLI Partition II gives .NET specific features that we detect. Namely, is the assembly strong signed, is it built for Any CPU or x86 alone, and what base version of the .NET framework is it built for (2.0 or 4.0).

Also, when you check out the code, notice how the code handles PE32 files versus how it handles PE32+ files. That is to say, 32-bit assemblies have a subtly different layout than 64-bit assemblies.

Tell me if you find this useful how are you using it?

If you find this code useful, tell me how youre using it in the comments.

Get the C# source

Download the AssemblyDetails C# source. It works with .NET 2.0, 3.0, 3.5, 4.0.

Example usage:

AssemblyDetails ad = AssemblyDetails.FromFile(filename);


// ad == null for non .NET assemblies
if (ad != null)
    Console.WriteLine(Path.GetFileName(filename) + ": " + ad.CPUVersion + ", " + ad.FrameworkVersion);
else
    Console.WriteLine(Path.GetFileName(filename) + ": Not a .NET 2.0+ executable.");

Update 7/3/2010: There was a slight bug in the first version. Re-download the code.

2 months ago we released wyBuild & wyUpdate v2.5. This release adds a free automatic updater control for C# & VB.NET apps. And because we wanted to keep things simple we left the wyUpdate.exe to do all the hard work (checking, download, installing) in the background while the AutomaticUpdater control is visible on your apps main form.

We wanted the AutomaticUpdater to be able to control the update steps, view progress, and cancel the updating. But we also wanted to keep all the updating logic in the wyUpdate.exe. For this to be successful we needed a way for the AutomaticUpdater control to talk to wyUpdate.exe while its running.

The Answer: Inter-process communication (IPC)

Inter-Process communication is a fancy computer science way of saying processes that can talk to each other. Google Chrome uses IPC to communicate between tabs of the browser & plugins. Its a simple way to keep parts of your program isolated from crashes.

For instance, if a tab of Google Chrome crashes only that single tab is killed. The rest of your tabs will continue to function normally.

Lots of bad ways to do IPC

Now that you know what inter-process communication is, let me tell you the worst ways to do it.

• Shared memory: Difficult to set up & difficult to manage.
• Shared files / registry: Very slow due to the writing & reading to/from disk. Difficult to manage.
• SendMessage / PostMessage: Locks up the UI thread while the message is processed. Messages are limited to integer values. Cant communicate from a non-admin process to an admin process. Assumes that your processes have a window.

Named Pipes

Inter process communication using named pipes is what Google Chrome uses and what we use for wyUpdate and the AutomaticUpdater control. Let me teach you about named pipes.

Like Marios pipes?

Exactly like Marios pipes. Except, instead of jumping Mario through the pipe, you push data through the pipe:

What do you put in the pipe?

You can transfer any data between your processes. So what data should your transfer? The answer is it depends. The rule of thumb is to keep it short, and keep it simple. Heres what we do with the named pipe between wyUpdate and the AutomaticUpdater control sitting on your application:

• Command codes: The AutomaticUpdater can command wyUpdate to check for updates, download the updates, extract the update, and install the update, or cancel any current progress.
• Responses: wyUpdate can tell the AutomaticUpdater if theres an update available, what changes there are in the update, and the progress of the current step (e.g. downloading).

With this simple setup the AutomaticUpdater control thats on your application is completely isolated from wyUpdate.

Get the C# source

Download the named pipes C# source. It works with .NET 2.0, 3.0, 3.5 on Windows 2000 Windows 7.

There are two files that do all the work: PipeServer.cs and PipeClient.cs. We use the PipeServer.cs file inside wyUpdate, and we use the PipeClient.cs file inside the AutomaticUpdater control.

Also included in the zip file is a simple messaging program to demonstrate communication between two separate processes:

Tell me what you think in the comments. I want to hear from you.

This week I was doing work on LimeLM that involved virtual machines. In particular preventing piracy in an environment where the whole PC can be duplicated bit-for-bit. As you can imagine this meant installing and using many virtual machines; VMware, Virtual PC, Virtual Box, Hyper-V, Parallels, and every other obscure VM.

When I ran Parallels the first time it reminded me of a split test I ran on wyBuild a couple of years ago. Heres the first run of Parallels:

Youre seeing this right 4 windows stacked on top of one another. Theyre even polite enough to welcome me twice.

No one reads dialogs.

The worst part is that I still havent read what the dialogs say and this is even after I cropped & arranged the dialogs in Photoshop, proof-read this article 3 times, and written this very sentence. They could say some pretty vulgar things and I wouldnt even know.

If a dialog has more than 3 words I just look at the buttons and guess what the dialog says. Heres what I read:

I clicked OK on the last dialog, and a new dialog popped up:

Oh God, theyre breeding. Im sure Copyright Notice is real page-turner, but I have better things to do.

What can you learn from Parallels Mistakes?

By this point Ive forgotten what Parallels Workstation is. I think its a dialog generating machine.

What can we learn from Parallels horrific design?

• Their developers havent read The Elements of Style. Rule 17: Omit needless words.
• The Parallels developers dont do clean installs of their programs.
• They havent sat a user down and had them use Parallels from start to finish (from setup to the first virtual machine).

Ok, but what can I apply to my own work?

Parallels first-run faults seem easy to apply for web & desktop developers alike. But if you clear the front door let users actually use your program will you convert more trial users to paying users? What if you clutter the first run do users care?

Yes, they do.

In wyBuilds early betas (back when it was still called InstantUpdate Designer) I ran a split test comparing how long a person used wyBuild. Group A had a version of wyBuild with crap similar to Parallels Workstation; the user had to dismiss a couple of useful dialogs before they could use wyBuild. Group B had an experience similar to what we use today; a dead-simple first screen:

I foolishly thought the first-run dialog boxes would give users a better understanding of our product.

In retrospect the results arent surprising. Group B, the group that wasnt interrupted, used wyBuild more than twice as long as Group A. More than that, the people in Group B were around 2 times as likely to save their project and build their first update.

So, the group that was bothered by a bunch of pointless dialogs often quit before theyd created their first update. (And this was back when wyBuild was free. The only measure of success was if the user actually used the product).

Because this data was collected remotely (it was opt-in, of course; Im not a sleaze), we couldnt ask the people in Group A why they gave up. If I were to guess Id say their thoughts ranged from Its too confusing to Ill do it later, when I have some free time (i.e. never).

Anticlimactic lesson: Dont waste your users time.

You almost certainly have a competitor that is faster, cheaper, better, or all of the above. So, the next time you add just one more dialog or just one more field to your order webpage, think about how many potential customers youre losing.

Scratch that. Test to see how many users youre losing.