Mocking HtmlHelper in ASP.NET MVC 2 and 3 using Moq

Still having trouble mocking HtmlHelper? This is an update to my previous post on mocking HtmlHelper way back when ASP.NET MVC RC1 was released. Eric notified me through a comment on the post and a question on StackOverflow that the code for ASP.NET MVC RC1 did not work with ASP.NET MVC 2. The code in this post should work with ASP.NET MVC 2 and ASP.NET MVC 3 Preview 1.

Minimalistic MapReduce in .NET 4.0 with the new Task Parallel Library(TPL)

Among the news in .NET 4.0 are several additions by the [Parallel Computing Platform Team](http://blogs.msdn.com/pfxteam/). As I wandered through the documentation of the Task library with cloud computing and parallelism buzz in the back of my head, I got the idea of using tasks to create a minimalistic MapReduce. Here's the result, a rather crude and simple, but efficient MapReduce for you to play with and utilize!

What is MapReduce? 

For those of you who don't know what MapReduce is: MapReduce is a simplified interface for parallel data processing. MapReduce was initially described by the Google engineers Jeffrey Dean and Sanjay Ghemawat in the 2004 paper titled [MapReduce: Simplified data processing on large clusters](http://labs.google.com/papers/mapreduce.html).

MapReduce processes data by splitting the processing in to a set of transformations (in functional programming, this is called the "map" function (it maps or transforms an input to an output)). The results of the transformations are then combined into a single result (in functional programming, this is called the "reduce" function (it reduces a set of values to a single value)). On a sidenote, Linq has equivalent functions, but the names are different, presumably to make them more familiar to people with SQL knowledge. In Linq, map is called `Select`, and reduce is called `Aggregate`.

Shortly put, to process a huge set of data, you split the data into chunks and process each chunk in parallel. This eventually creates a new set of intermediary results, which is reduced to a single result.

Implementing a minimalistic MapReduce in .NET 4.0

The signature of my MapReduce function is static Task Start(Func map, Func reduce, params TInput[] inputs);

In other words, to start a MapReduce run, you supply a map function, a reduce function, and a set of inputs. Each input will be turned into an intermediate result (of type TPartial). Inputs are transformed concurrently. When all inputs are transformed, the reduce function is called to transform the partial results into a final result (of type TResult). Cool!

The map part is implemented by starting a task for each supplied input using Task.Factory.StartNew(() => map(input)).

The reduce part is implemented as a continuation of all the map tasks, meaning that the reduce task waits for all the map tasks to complete, and then executes. This is achieved using Task.Factory.ContinueWhenAll(mapTasks, tasks => PerformReduce(reduce, tasks)).
As you can see, the implementation is minimalistic and simple, and usage is likewise.

Here's a simple example using MapReduce to calculate the root mean square (MSE) of a set of values:

Actual applications of MapReduce are of course far more interesting than this simple example.

Applications of MapReduce

MapReduce can essentially be applied to any problem where you need a number of things to be done in parallel. It can even be applied in cases where you don't need a final result. Just return an arbitrary value as the result (or even better, implement a variant of my MapReduce which uses Action).

A few obvious use cases:

• Distributed search
• Distributed sort
• Tokenization
• Indexing
• Log processing
• Machine learning
• General artificial intelligence
• General data mining
• Large scale image processing
• ...

The list goes on and on, these are just a few things off the top of my head.

You can grab the source code for MapReduce here (requires .NET 4.0 or later):


As usual, play around with it, have fun, and let me know if you find it useful!

RSA using BouncyCastle

Trying to do RSA using BouncyCastle, but struggling to find your way around the API? In a previous post (see [here](/posts/why-cripple-the-net-rsa-implementation)) I pondered why the RSA implementation in `System.Security.Cryptography` is restricted to only the most common usage scenarios. I mentioned [BouncyCastle](http://bouncycastle.org) as an alternative for those who wanted a more flexible API, but never got around to providing examples where BouncyCastle was used. By request, this post provides usage examples by building a crude and simple, but efficient set of methods for RSA key generation, encryption, and decryption, all built on top of BouncyCastle.

NOTE: The general cryptographical security of the presented method is beyond the scope of the article. The code presented is not cryptographically secure for large data sets. If you're here looking for a way to do cryptographically secure RSA in the general case, you should look into more complicated approaches including padding, blinding, and more sophisticated block cipher modes. Cryptography is a topic undergoing constant research, so stay up to date and be sure to evaluate the strength of your solution for the scenarios in which you apply it.

BouncyCastle provides flexibility and control over your encryption approach, which comes at a cost. The BouncyCastle API might be a bit hard to cope with at first, but if you know encryption in general you should be able to find your way around the API without too much effort. This post will be focusing on RSA, since that was my original need, but it should be mentioned that BouncyCastle provides many other asymmetric (and symmetric) algorithms for which the usage is similar to what you find below.

Creating RSA keys

Creating RSA keys is a simple task. The method below lets you specify the key size in bits, and creates a key pair for you.

That's all there is to it.

Encryption

Now that we have a key pair, we are ready to encrypt and decrypt using RSA. In the example below, we use a key (public or private) to encrypt a byte sequence. To encrypt a string, simply convert the string to a byte array using Encoding.GetBytes.

The approach above uses a list to gather output for the sake of simplicity. Note that the RSA engine can only process a limited block size at a time (block size depends on the key size). The approach above processes a data set of an arbitrary size.

The above method does not impose constraints on which key you use for encryption. Use the public key or the private key as you see fit for your solution.

Decryption

The Decrypt method is very similar to the Encrypt method:

Again, it's up to you which key you choose to use. If you want to use the common approach, encrypt using a symmetric cipher, hash the data, and sign the hash with your private key using the above Encrypt method. If you want to use another approach like encrypting the actual data using your private key, you are of course free to do so.

I hope this post helps those of you who want to apply RSA (or any other asymmetric cipher) to more subtle cases than those supported by the .NET framework.

Mocking HtmlHelper in ASP.NET MVC RC1 using Moq

For those of you trying to mock HtmlHelper, but finding it difficult, here's a mock that works in ASP.NET MVC RC1.

The ViewDataDictionary that is passed to the HtmlHelper can be empty, or made to contain the data you want for your test.

Why cripple the .NET RSA implementation?

I just found out that `RSACryptoServiceProvider`, the RSA implementation in .NET, does not allow you to use a private key to encrypt data. I'm no cryptographic expert, but I do know how asymmetric key algorithms like RSA work, and that you can use a private key for encryption. That's how signing works. But why cripple the implementation and limit it to just signing?

Strongly typed data binding in Windows Forms

Windows Forms data binding is a great tool for model-view-style applications, where the connection between the model and its view is easily declared. However, data binding is also an error-prone and tedious process with no IntelliSense support where properties are specified as strings.

Tired of the need of looking up property names when you declare data bindings? Sick of mistyping a property name when you bind and not discovering the mistake until you run your application? Have a look at Strongbind.

Strongbind vs traditional data binding

Traditional data binding is typically declared like this:
Obviously, several errors can arise from this declaration: Your control may not have a Text property, or you might have spelled it wrong. The same goes the Description property of your source.

The same declaration in Strongbind is written as follows:

As you probably understand, the risk of mistyping is removed, and we get IntelliSense support out of the box.

Behind the scenes of Strongbind

To achieve this strongly typed data binding, Strongbind uses a technique known as proxying. Strongbind dynamically generates a proxy for your business object and your control, and uses the proxies to intercept the calls to the property getters during runtime to declare the data binding. Hence, you need to declare a bindable source and bindable target first to create the proxies, and then use these proxies during the binding declaration. You will get a runtime error if you try to use your real objects when declaring data bindings.

Limitations of Strongbind

Although Strongbind makes data binding a far more declarative process, the library does have its limitations.

Controls containing ActiveX components are not supported. If the control containing an ActiveX component is a custom control created by you, you can get around it by declaring an interface for
the control and specifying that as the type to use when declaring your binding source:

Also, binding to concrete binding sources with non-virtual properties is not supported. Again, the recommended workaround is to create an interface for your binding source and use that when declaring the data bindings. (You always want to create these interfaces, since decoupling your objects' interfaces from their implementation is recommended for testability, maintainability, and is generally A Good Thing(tm).)

Apart from these two issues, which can be worked around in most cases, Strongbind should work flawlessly. If it does not, please let me know.

Where do I get it?

Strongbind is an open source project hosted at Github. To get the latest version, check out the code from its repository.

Strongbind is still in an early development stage, so no releases have been created yet. I still encourage you to check out and start using the library as soon as possible, though. A beta will be released as soon as I feel comfortable doing it.

If you want to contribute to Strongbind, I happily welcome you to do so.

Bind away!

Extension methods for copying or cloning objects

C# 3.0 includes a new feature known as extension methods, and fiddling with it triggered the idea of creating a mechanism for copying or cloning (virtually) any .NET object or graph of objects. The manifestation of that idea has become a rather decent little framework for copying objects. It performs a deep copy as automatically as it possibly can, and provides mechanisms to easily solve many of the cases which cannot be covered automatically. It is great for copying your custom object hierarchies, and saves you the pain of a solution like implementing ICloneable for an entire hierarchy of objects.

Let's start off with a few words on extension methods. They are best explained through an example. Let's say we want to be able to calculate area given size. Wouldn't it be nice to be able to add GetArea to the already existing Size class? Well, let's do so!

As you can see, the new syntax simply allows you to tell the compiler that the this of this method is a Size. This means that the method is an extension of the Size class.

As mentioned, I had the idea of extending the very base of the C# class hierarchy (System.Object) with a method for copying or cloning "any" object. Obviously, the method cannot automatically copy _any_ object, since it cannot possibly know how to construct an object from an arbitrary class. Hence, a small framework needed to be created. The goals were to:

• Enable copying of many objects automatically.
• Enable copying of virtually any object with very little effort.
• Automate and hide away as much as possible (The KISS Principle).

The result is Copyable (pun intended).

The Copyable framework

Copyable is a small framework for copying (or cloning, if you will) objects. The straightforward way of using it is to just reference the assembly it's in from your project, and start copying!

The instance copy is now a deep copy of instance, no matter how complex the object graph for instance is. The relations in the copy graph is the same as in instance, but all objects in the copy object graph are copies of those in instance.

For the automated copy to work, though, one of the following statements must hold for instance:

• Its type must have a parameterless constructor, or
• It must be a Copyable, or
• It must have an IInstanceProvider registered for its type.

Besides the Copy method, The Copyable class and IInstanceProvider interface are the two major building blocks of the Copyable framework. Each of these blocks enable copying of objects that cannot automatically be copied.

The Copyable base class

Copyable is an abstract base class for objects that can be copied. To create a copyable class, you simply subclass Copyable and call its constructor with the arguments of your constructor.

This code above makes MyClass a copyable class. Note that if MyClass had had a parameterless constructor, subclassing Copyable would not be necessary.

MyClass can now be copied just like the previous example, e.g. MyClass b = new MyClass(1, 2.0, "3").Copy().

The introduction of the Copyable base class solves many problems, but not all. Let's say you wanted to copy a System.Drawing.SolidBrush. This class does not have a parameterless constructor, which means it cannot be copied "automatically" by the framework. Also, you cannot alter it so that it subclasses Copyable. So, what do you do? You create an instance provider.

The IInstanceProvider interface

An instance provider is defined by the interface IInstanceProvider. As the name clearly states, the implementation is a provider of instances. One instance provider can provide instances of one given type. The Copyable framework automatically detects IInstanceProvider implementations in all assembies in its application domain, so all you need to do to create a working instance provider is to define it. No registration or other additional operations are required. To simplify the implementation of instance providers and the IInstanceProvider interface, an abstract class InstanceProvider is included in the framework.

This implementation will be used automatically by the Copyable framework. NOTE: To be usable, the instance provider MUST have a parameterless constructor.

The instance provider pattern does not solve the case where you want different initial states for your SolidBrush instances depending on which context you use them for copying. For those cases, an overload of Copy() exists which takes an already created instance as an argument. This argument will become the copy.

Limitations and pitfalls

Although this solution works in most cases, it's not a silver bullet. Be aware when you copy classes that hold unmanaged resources such as handles. If these classes are designed on the premise that their resources are exclusive to them, they will manage them as they see fit. Imagine if you copied a class which holds a handle, disposed one of the instances, and continued using the copy. The handle will (probably) be freed by the original instance, and the copy will generate an access violation by attempting reading or writing freed memory.

That's it! The Copyable framework can be downloaded from Github. For those interested in reading more on extension methods, MSDN provides an excellent explanation in the C# Programming Guide, and Scott Guthrie has an introduction article here.

Enjoy Copyable, and please let me know if you find it useful or come across any problems with it.

UPDATE 2009-12-11: Due to popular demand, I have made the source code for Copyable available under the MIT license.

UPDATE 2010-01-31: The requirement of parameterless constructors has been removed in the latest version of Copyable available on Github. A new release will follow soon.