This post originated from an RSS feed registered with .NET Buzz by Peter G Provost. Original Post: OpenPGP.NET - Part 1 - Getting Back Into TDD Feed Title: Peter Provost's Geek Noise Feed URL: /error.aspx?aspxerrorpath=/Rss.aspx Feed Description: Technology news, development articles, Microsoft .NET, and other stuff... Latest .NET Buzz Posts Latest .NET Buzz Posts by Peter G Provost Latest Posts From Peter Provost's Geek Noise

I've decided to keep a running log of my progress on this project... at least until I get sick and tired of it or until I bring on any other developers. I've also added a category called OpenPGP.NET to group all of these messages. Here goes...

Last night I started the project. As I stated earlier I want to follow a few important guidelines while developing this this:

1. Test-driven Development (aka Example Driven Development)
2. Since it is primarily a class library it should pass FxCop's rules
3. It should reuse as much of System.Security.Cryptography as possible
4. It must comply with OpenPGP RFC 2440

Having read all of the code for SharpPrivacy, some of the code for the Cryptix OpenPGP Library for Java,  and most of the RFC, I decided to get started by implementing the packet types.

I started with a blank VS.NET solution and added a Class Library Project called Core. I then added another project called Unit Tests. Setup my references and started thinking about which tests to start with.

To gain familiarity with the OpenPGP packet structure, I decided to start with the simplest packet: the User ID Packet. This packet has an OpenPGP packet header (packet tag and length) followed by a packet body, which for this packet is defined as follows:

A User ID packet consists of data that is intended to represent the name and email address of the key holder. By convention, it includes an RFC 822 mail name, but there are no restrictions on its content. The packet length in the header specifies the length of the user id. If it is text, it is encoded in UTF-8.

So the packet structure is a byte for the packet tag (in this case 13), a byte for the length (not really true, but also not really important for this packet type) followed by atrbitrary UTF-8 string.

I decided (for no good reason) to use Streams, so I wrote the following test. Note that I am using NUnit 2.1 so this syntax may look a little different from what I've written before.

[Test]



public void TestParsePacket() 


{ 


MemoryStream s1 = new MemoryStream( 


Encoding.UTF8.GetBytes("\u000d\u0011Peter Provost \ 


<peter@provost.org>") ); 


UserIdPacket packet1 = UserIdPacket.ReadPacket( s1 ); 


Assert.IsNotNull(packet1); 


}

Compiled and of course it failed because UserIdPacket didn't exist. Added the UserIdPacket class and added a static ReadPacket method that returned null. Compiled and ran the tests and of course it failed on the IsNotNull assertion. Excellent.

Now, as Kent Beck points out in his book Test-Driven Development, you can take teeny-tiny little steps like this, or once you get comfortable you can take bigger steps. Not feeling comfortable about the code you have to write? Go back to teeny-tiny steps again.

So I updated the code in ReadPacket to have it return a new UserIdPacket. Voila! The test runs. Time to move on. I know the code isn't implemented right, but that is a failure in my tests, not a failure in my code.

So let's fix that by adding more tests. Here is the new TestParsePacket:

[Test]



public void TestParsePacket() 


{ 


MemoryStream s1 = new MemoryStream( 


Encoding.UTF8.GetBytes("\u000d\u0011Peter Provost \ 


<peter@provost.org>") ); 


UserIdPacket packet1 = UserIdPacket.ReadPacket( s1 ); 


Assert.IsNotNull(packet1); 


Assert.AreEqual( "Peter Provost <peter@provost.org>", 


packet1.UserId ); 


} 

Now the test fails as it should. Back to the ParsePacket code...

Some people would go ahead and do the correct implementation at this point, but for demonstration I'm going to continue taking teeny-tiny steps.

I added a UserId property and initialized it to "Peter Provost <peter@provost.org>". Bam! Test passes. I win. :)

Once again, the problem is in the tests and not the code. My tests are exhaustive enough so I will write more tests. I decided to copy the test body and repeat it passing a different stream and testing for a different value. This test will probably get me what I want.

Here is the final TestParsePacket:

[Test]



public void TestParsePacket() 


{ 


MemoryStream s1 = new MemoryStream( 


Encoding.UTF8.GetBytes("\u000d\u0011Peter Provost \ 


<peter@provost.org>") ); 


UserIdPacket packet1 = UserIdPacket.ReadPacket( s1 ); 


Assert.IsNotNull(packet1); 


Assert.AreEqual( "Peter Provost <peter@provost.org>", 


packet1.UserId ); 




MemoryStream s2 = new MemoryStream( 


Encoding.UTF8.GetBytes("\u000d\u0011Jimmy Provost \ 


<emily@provost.org>") ); 


UserIdPacket packet2 = UserIdPacket.ReadPacket( s2 ); 


Assert.IsNotNull( packet2 ); 


Assert.AreEqual( "Jimmy Provost <jimmy@provost.org>", 


packet2.UserId ); 


}

Now I actually have to implement the code. Here is what I came up with at this point:

public class UserIdPacket 


{ 


private string _userId; 




public string UserId 


{ 


get { return this._userId;
} 


set { this._userId
= value; } 


} 




public static UserIdPacket
ReadPacket( Stream s ) 


{ 


StreamReader reader = new StreamReader(s, Encoding.UTF8); 


UserIdPacket packet = new UserIdPacket(); 


int packetType = s.ReadByte(); 


int length = s.ReadByte(); 


packet.UserId = reader.ReadToEnd(); 


return packet; 


} 


}

All done! One simple little method done to parse the User Id Packet. More coming soon...