A really quick note, MobileTFL, the London Tube status application for Windows Mobile 6+, has just been updated to version 1.1.0.0.

Changes: Supported new TFL data feed format, fixed breaking bug.

Get it here: http://www.davidwhitney.co.uk/content/blog/index.php/software/

I’m currently an Android user while awaiting Windows Phone 7, so I’ve only been able to test this against unit tests and the device emulator, but it looks fine. That said, feedback would be appreciated.

Thanks to all the people that emailed me to let me know the app had broken.

What are APIs anyway?

Everyone’s heard of APIs these days.  Facebook has them, Twitter has them, Hotmail has them, Microsoft Office has them, Windows has them, Mac OS has them, pretty much everything has them.  I’m going to try and explain in simple terms, but also, almost by contradiction, in detail, what an API really is.  I’ll try and explain why SOAP isn’t how you clean yourself, and how being restful isn’t the same as being lazy.

APIs aren’t new, in fact, APIs are really really old.

Let’s start with a really simple definition.  API is an acronym and it stands for “Application Programming Interface”

To steal the current definition from Wikipedia “An application programming interface (API) is an interface implemented by a software program to enable interaction with other software, much in the same way that a user interface facilitates interaction between humans and computers. APIs are implemented by applications, libraries and operating systems to determine the vocabulary and calling conventions the programmer should employ to use their services. It may include specifications for routines, data structures, object classes and protocols used to communicate between the consumer and implementer of the API.”

That’s a mouthful.  So to translate that into English, an API is a pre-defined set of “stuff” that allows one program to “talk” to another program.  This “stuff” is normally a set of “functions” that another program can call which makes the program being called do something.  Sometimes that other program is really just another part of the same program, and sometimes it’s a different system on a different machine in a different country.  That something is normally described in some kind of documentation, written somewhere, by someone.

If this sounds really vague it’s because in the real world, it really is.  Some of the first “APIs” involved dropped text files into directories on a computer that another program would watch for a read from, and subsequently do “something”.  Arguably the most widely used API is the one that we use to write software for Windows (the Win32 API) and by contrast, that’s a C++ library of code that you can only call if you’re a programmer.  In the real world, we’ve tried to solve some of this ambiguity by standardizing the way APIs work around a few common bits of technology; both for our own sanity and to hopefully help software all just kind of work together.

A lot of APIs are code libraries called by other code libraries to do a specific task.  Microsoft released DirectX to deal with 3d graphics, OpenGL offered an open alternative.  Microsoft released the Windows API for Windows development; Apple released Carbon and Cocoa to program Mac OS.  That said when you hear about or discuss APIs casually, what you’re probably thinking about are actually “Web APIs”.

Web APIs

A Web API is an API like anything else, except it’s designed to work over the web.  As a result of this, since about 1994, there have been a number of efforts by a number of people (yes, that vague again!) to standardize the way systems communicate over the internet.

At first, everyone kind of invented their own way of communicating over the internet, people would connect to a server on some port (a port is just a pre-defined “way in”) and send some random pre-defined data in there, and that would make the computer at the other end do something.  Every API was different, and every time that you needed to talk to a different system, you had a really steep learning curve to work out how to talk to every application you wanted to integrate with.  It was a bit rubbish really.

So in 1998 a bunch of really smart people (Dave Winer, Don Box, Bob Atkinson, and Mohsen Al-Ghosein) got together and came up with SOAP (“Simple Object Access Protocol”).  SOAP is a big bunch of XML that was designed (and ratified) as a standard language that every different system could understand. SOAP is often also referred to as “web services”.

Basically it was designed to reduce the learning curve of learning the details of each system.  So now, if Timmy wanted to talk to Peters shiny new web application, he could point his developer tools at a standard location (something called a WSDL (web service description) document) and he could just ask Peters web application what it did, and how he could use it.

SOAP was actually pretty good and solved a lot of problems and is still widely used today.  It really made waves by helping Microsoft software work pretty well with Java software and everyone was happy.

Almost.

See, because SOAP was solving a lot of big problems in freaking huge enterprise systems, it had a lot to be concerned about; lots of security, lots of encryption, lots of authentication.   That meant that the SOAP “language” was pretty big.  As an example, here (stolen from Wikipedia again!) is the SOAP message that would be sent across the internet to get the current stock price of IBM, from some cool stock price giving web service.

POST /InStock HTTP/1.1

Host: www.example.org

Content-Type: application/soap+xml; charset=utf-8

<?xml version=”1.0″?>

<soap:Envelope

xmlns:soap=”http://www.w3.org/2001/12/soap-envelope”

soap:encodingStyle=”http://www.w3.org/2001/12/soap-encoding”>

<soap:Body xmlns:m=”http://www.example.org/stock”>

<m:GetStockPrice>

<m:StockName>IBM</m:StockName>

</m:GetStockPrice>

</soap:Body>

</soap:Envelope>

People soon started thinking “Look at all that crap! What’s it all for! Why do I need it?! There’s lots of overhead here!  It slows me down!” and everyone thought “oh actually, well said” and RESTful web services were born.

REST is yet another stupid acronym that actually doesn’t count as an acronym because it uses random letters but developers think is either cool clever or funny.  What it claims to mean is “REpresentational State Transfer” and was largely both a reaction to the complexity and overheads of SOAP, but also being designed by Roy Fielding (one of the authors of the “Hypertext transfer protocol”, the silly http:// bit you type in a browser) it was conceived as an API model that was “closer to the nature of the web”.

What this means to us lay folk, is that while SOAP can technically be used over other protocols (it’s not bound to http), and as such has to bake in security and authentication models into its protocol, REST is designed specifically for the web, it doesn’t work without the web, and it wouldn’t make any sense without the web.  Fielding basically decided that “the web does all of that stuff anyway”, we have security via https / SSL certificates, we have semantics that describe getting and pushing data in the HTTP headers (HTTP headers explain what you’re trying to do to the server you’re connecting to, for example, you use GET for getting stuff, POST and PUT for doing stuff), so let’s just use that and be done with it.

As a result of this way of thinking, REST is a simplified and less general Web API pattern, not concerned with infrastructure like SOAP is.  I’ll convert the above stock price example into a REST example below.

GET /Stocks/Price/IBM HTTP/1.1

Host: www.example.org

Content-Type: application/xml; charset=utf-8

Done.

Basically, REST takes out all the fluff, an decides that if you want to get a stock price for IBM, just make a GET request to the URL http://www.example.org/Stocks/Price/IBM and let the web server at the other end work out what to do from the URL.

The above example would probably return an XML document that looks like this.

<stocks><stock name=”IBM” price=”3.45”/></stocks>

People have started to gravitate towards REST due to its simplicity.  There’s lots of other stuff a RESTful web service should do, it should provided you with all the information that a computer would need to go through a process, just like a user interface gives the user all the information they need to click through a process, but fundamentally it’s simple and leverages the existing semantics of the web to its advantage.

Ok, Give Me One Of Those!

So now we know what an API is there to do (let two systems talk to each other) and how they do it (as a general rule, either via SOAP or RESTful services) and we know that everyone else has one, let’s get one of our own.

There are plenty of tools available in pretty much any programming language to make making creating APIs pretty easy.  There are plenty of design concerns to take into account when building an API but in my opinion, the way to approach the problem is to work out what your users really want to do with your application, website or platform, and let them do it.

A good API lets another programmer talk to your system using terms that he understands, so take the time building up a glossary of your business terms vs. what the public understands those concepts to be.  Don’t build API methods that look like:

/PaymentResolutionProcess/PaymentResolveTable3/Resolve/EntityId/123

because it means nothing to anyone, instead, build a bunch of methods that make sense for people to use, the above example could look like this instead:

/Payment/MakePayment/123

Watch your language, and build sensible interactions with your system.  Don’t make APIs for stuff that isn’t going to be used, and where possible, just have the APIs call the same code that your website does.

Get this right, and you’re on a gradual but successful road to calling your “website” a “platform”.

Here’s an interesting example from a brief discussion I was having on twitter yesterday with @DotNetWill.

Did you realize that access modifiers in .NET are type specific rather than instance specific. It’s not a weird edge case, it is exactly how the language spec lays it out, but it’s not how most people think access modifiers work. This is because it’s not very often that any given type will have a reference to ANOTHER instance of that type, it just tends to not come up.

Either way, could make for some hilariously difficult debugging if you weren’t aware of it and something was “playing with your privates” by reference.

You might have seen this kind of usage in a singlet*on, constructor or builder class (or as @jagregory pointed out, cloning methods), but generally it’s just not a very common usage example. However, it WILL both compile and execute.

// Example of access modifiers being specific to a type not an instance
public class MyType
{
     private MyType _innerMyType;

     public MyType()
     {
     }

     public void MakeInnerMyType()
     {
          _innerMyType = new MyType();
          _innerMyType._innerMyType = new MyType();
     }
}

Nothing ground breaking, but a fun and interesting little example illustrating a common misconception.

At work we’re currently discussing coding standards, specifically to synchronise development in two countries and keep the style consistent across the teams.  You know, the usual stuff. 

When people start discussing coding standards, it quickly devolves into a religious debate and honestly, I think a lot of it comes down to personal preference.  Because of that, I’m going to spend a post or two telling your why you’re wrong and why I wouldn’t take your code to dinner however much it offered to put out.  Because clearly my way is the only right way!

Joking aside, I want to go into some detail on how I present and write my code, and hopefully explain why.  It’s all going to be slanted towards (who do I think I’m kidding, it’s going to be in) C# so as ever, your mileage may vary with any advice you extrapolate.  I’m going to start out by showing you some bad examples, attempt to explain why I think they’re bad, and offer my alternative.

Properties and Variables

The way you declare your properties and variables is seemingly insignificant, but if you get it wrong it trashes the readability of your code.  Take this code sample for example:

All I’ve done in the above screenshot is declare a few properties, a few instance variables and a constructor.  And it looks awful and un-maintainable despite the lack of any significant code smell, all due to the manner in which I’ve declared the variables.  It’s a laundry list of mistakes.

1. Using field backed properties when an auto-property will suffice.
2. Defining auto-properties split across multiple lines for no explicable reason.
3. Adding utterly redundant code comments (the code-criticism comments aside).
4. Terrible and ambiguous variable naming.
5. Variable names that contain hints at data types.

The above code sample is practically unreadable, even without the comments, it’s long winded and obtuse:

Now, I come from the school of thinking that is pretty much convinced that typing things is bad, repeating yourself is bad, hell, writing code is bad.  So don’t.  Less really is more, pick your favourite buzz phrase.  Cleaning up your code should involve making it as simple and as clear as is humanly possible.

Thankfully, if you take advantage of the language features of C#3, you can quickly make something like that look like this:

Just by tidying up the way you declare and use your variables, you can make your code eminently more readable.  If you compare the two examples, you’ll see that all I’ve done is

Use single line declarations for auto-properties.

• Why waste 3-5 lines on an auto-property that can easily fit one one without any loss in readability.

Removed data backed properties in exchange for auto-properties with access modifiers on the setter.

• Functionally equivalent and far neater

Renamed badly named properties (in the first example “FLineOfAddress”) to be more meaningful.

• Remove abbreviations where possible, they damage readability
• Assume the maintainer of your code has no business knowledge, make things easy
• Meaning is always better in variable names than in comments / meta-data
• Don’t fear long variable names, modern IDEs have auto-complete, you don’t have to type that stuff by hand.  Embrace your tooling!
• If you can’t tell what’s in your property or variable from it’s name, you’ve failed, go back and try again.
  • This honestly includes stuff like foreach(var item in MyCollection) and StringBuilder sb = new StringBuilder();  Both bad and wrong, don’t do it.

Only retained comments where the comment data is truly meaningful. 

• The above example isn’t particularly good (everyone knows what a URL is), but only keep comments in your code where they add something that you couldn’t attain with careful renaming and code restructuring / refactoring.  The meaning of your code should be obvious to the reader without metadata.

Stick to a solid naming convention for public / private / protected variables and properties.

• The well trodden convention I’m following above is lowerCamelCase plus…
  • A leading underscore for private instance variables (determining scope)
  • Regular lowerCamelCase for local variables
  • UpperCamelCase for property names, constants and statics.
  • No data types in your variable names.  This is not 1980. The IDE gives you all that lovely meta-data, don’t give yourself RSI duplicating it in your variable names.

Cleaning up usage

• Removing this., you get the same scoping from using _ by convention in your variable names, save those fingers from RSI…
• Using instance and local variables instantly becomes clearer by sticking to convention.

Using var to reduce duplication in code.

This is often controversial but I feel that using var, for the most part, reduces the amount of typing required without any loss of clarity.  Take the following examples:

It’s clear to me that no clarity is lost by not typing "StringBuilder” twice.  It’s still right there in front of you and allows you to keep your variable declarations more uniform.  Despite popular misconception this doesn’t affect the type safety of C#, the language and your variable are still strongly typed, the compiler just infers that when you said var you meant StringBuilder at compile time.   If it isn’t really obvious what an object is when you instantiate it, you’re probably doing something really wrong elsewhere.

People occasionally like to argue that while for declarations var is all well and good, when you’re using it for return values it causes a loss of clarity.  It’s an interesting point but always feels slightly off the mark to me.  Whenever people attempt to give me an example of this lack of clarity, it’s always that their variables or properties are ambiguously or inappropriately named, and the code clarity can be regained and even improved by naming the variables involved in a more descriptive way.  Take the following snippet for example:

In the first case, I’d agree that using a var called “l” to store the return value of that method would lead to a loss in clarity.  But if you had string l = RetrieveTextLabel(); and then, say, 20 lines down attempted to use a variable called “l” you’d probably deserve a swift kicking for naming something so poorly.  By contrast, var textLabel is exceptionally descriptive.  People also occasionally say that using var in foreach loops causes this ambiguity, but again, if you name your collection appropriately and your yeilded value correctly, it really is never an issue.

Even more importantly, if you get your naming right, var actually helps you quickly refactor your code.  As long as you understand the “meaning” of your variables, the IDE can fill in the blanks with regard to data types, because for the most part, it really doesn’t matter what type of data is actually in that variable when you’re reading the code as long as it’s meaning is a known quantity.  I actually feel that the dynamic language crowd learnt this lesson long ago, and people that work predominantly in strongly typed languages actually tend to rely on the type system like a crutch to excuse terrible naming conventions.  Time to learn from PHP…

In conclusion…

To make your code readable you should stick to conventions for naming, always strive to add meaning in variable names and be as brief as possible.  Don’t litter your code with crap and you’ll be thankful for it later.

Obviously, this is all my opinion, but I swear by it.

I’ll be following up this post in the next few days with some continued patterns for readable code.

With the popularity of service oriented architectures and other buzz phrases related to software as service, good API design has become a significant selling point for any software platform in the past 5-10 years.  People make purchasing decisions based on how easy it is to interoperate with your applications and code and as such the number of client / public facing APIs attached to software has skyrocketed.  I’d like to believe the days of dropping strategic text files in directories to trigger some action or another in an application are behind us.

In this article I’m going to talk about the following things

• Why you should choose your method names carefully, and what to call
• Why pretending to be a data access layer is a terrible thing for an API to do
• Talk about the dangers of leaky abstractions in an API
• Explain the benefits of creating a data contract between you and the calling code
• Explain why it’s vital to support standards
• Make sure that your users can retrieve values they’re going to want to modify
• Suggest supplying compiled libraries alongside your API documentation
• Explain why it’s important to keep your API implementation clean
• Talk about the benefits of dogfooding your API
• Consider supporting atomic operations including rollbacks on failure
• Discuss bulk operations
• Try and convince you that both logging and security should be first class citizens
• Beg you to maintain integration tests and most of all to keep it simple!

Your API Sucks

You’ve probably used an API and there’s a good chance you’ve had to write one.  This probably won’t surprise you; most APIs suck.  They’re horrible to use and built around illogical leaky abstractions that leave you flicking through huge wads of documentation just to make the most rudimentary feature work.

About 18 months ago, after a year of struggling with a broken third party API that almost brought a business to it’s knees by placing significant roadblocks in front of in house development, I was part of a team tasked with designing our own client facing API.  With no desire to expose other developers to the cruel and unusual punishments of software design we’d had to endure, we came to the conclusion that it was really important that we god this piece of the system right.  People say first impressions are everything, and your API design can make or break the faith other developers have in your ability to produce software.  Show somebody a shitty API and they’ll perhaps correctly assume the rest of your code sucks too.

The Best Man For The Job

There’s a bit of a trend that I’ve noticed with some of the worst APIs I’ve worked with: they seem to be designed by the wrong people.  The wrong people to design an API are 1) the guy that wrote the internal code to do the job the API is providing access to and 2) the consumer of the API. 

The guy that wrote the code that the API is calling under the hood will be inherently slanted to implement an API which exposes this functionality and will have a predisposition to creating a leaky abstraction.  This is especially bad for the consumer APIs designed by the internal implementer tend to assume the consumer knows far more than he really does, or has access to internal data that in reality, he doesn’t.

Conversely, an API designed by the consumer of the API will have a tendency towards solving problems that are not the concern of the API itself.  The consumer will, either accidently or by intention, attempt to offload some of the work that should be the responsibility of the calling code into the API.

Ideally, the person that’s writing the API will have knowledge of the system internals, but not be the guy that wrote them. A fellow team member with passive experience to the code would be a good person, or ideally, a pair design exercise between the person that originally wrote the code and an API designer, with the consumer as a consultant.

Speaking The Same Language

Like a lot of software development, you make good progress when you get your terminology right and understand exactly what you’re trying to produce.  I’ve consistently found that the best way to think of a client facing API is as a orchestrating thin wrapper that summarises, in code, a set of business processes that you wish to expose to the public.

In order to get your API design right, you need to clearly define and agree on the boundaries of the system with both your internal team, and your consumers.  It’s important that you have a clear understanding of the following:

• The responsibility of the calling code
• The responsibility of the API layer
• The responsibility of the internal code the API makes calls to

This might sound like a really simple suggestion but I’ve taken part in countless discussions where people on both sides of the API just “presumed” that either the calling code or the API would perform specific functions (data cleansing, logging etc) when in fact, this confusion had lead to none of the implementers bothering to write the required functionality.  Make sure you know for certain what your API is responsible for doing.

Defining Your API – Tips and Tricks

Defining your API methods (or the “contract” of the API) is the most important thing to get right and there are several vital things to remember.

• Choose Your Names Wisely Using the language of the business
  
  It’s vital that your API methods speak in terms that the caller is going to understand.  Your API should be readable.  If your users go hunting for the documentation every time they want to use a method, then you’re probably doing it wrong.

  Clarity in naming is exceptionally important.  The names of your API methods should succinctly state what action that method call is going to perform.  Don’t fear using long method names, embrace them for clarity.  As a general rule, your pmethods should probably always be in the form DoSomething(object withThis);

  Ensure that when naming methods you reflect business operations in the method names, not the underlying implementation.

  Bad example:     void InsertToTblCustomer(string[] custDataValues);
  Good example:   void AddCustomer(Customer customer);
  Good example:   void DisableAccount(string accountId); 

• Don’t pretend to be a data access layer

  APIs should summarise business operations in a logical and meaningful fashion.  You are not a public facing data access layer and you should never pretend to be.  If your users want raw database access give them read only permissions on some tables and a copy of SQL Management Studio.  So don’t write methods for CRUD operations in your API (unless you’re writing some kind of online file management utility).

  Bad example:     void InsertToTblCustomer(string[] custDataValues);
  Bad example:     void UpdateTblCustomer(string[] custDataValues);
  There are no good examples!

• Avoid leaky abstractions

  This is a fundamental and simple rule – don’t expose your callers to anything that they’re not interested in or won’t understand.  If it’s not important, don’t show it.  Don’t code for things nobody will ever need and don’t require your callers to have intimate knowledge of data types or internal categories in your system.

• Create a data contract between you and the calling code
  
  I’m going to borrow some of the terminology from WCF here because I’ve found it an appropriate label.  Create a Data Contract library for use in your API.  This library should summarise the business process and the outward facing view of your software.  It might contain terminology that doesn’t actually exist in the software itself, but in the business processes that the software models.  Either way, this, and only this, should be the language that the API talks to your callers.

  Where possible, create this data contract in a separate assembly that’s entirely decoupled from your core system and distribute it to people that want to use your API.  This is especially beneficial when using WCF as your clients can generate a service proxy and deal in the same data types that you are in your API code.

  It should be the responsibility of the API layer to marshal the data from your data contract into the domain model of your internal components.

  You data contract should contain every type used to communicate with your API and the object model should be named in a way which is meaningful for the consumers.

  Because your data contract is NOT the object model of your internal components, you’re able to add properties and objects that don’t logically exist in your internal components.  This means that you can perform an operation using some internal component, gather the output in your API layer and then compose the output data in a meaningful way using classes written specifically for the data contract.  This way, by the time the user has access to the output data, it’s in a format and language which they understand.

• Support standards!  Don’t reinvent the wheel!
  
  Here’s a true story; while working with an API, my team was faced with the following API method:
  object Run(string request);

  It was the only method on the API, and “covered up” for around 30 methods all made available through one giant black hole in the side of the system.  Underneath that there was an XML format that the request had to be in in order to call the appropriate method.

  If you’re writing an API, stick to some kind of standards.  Ideally, expose a web service endpoint with an accurate WSDL that people can call or use a simple and obvious REST endpoint.  

  Please, please, please, do not make other developer suffer by rolling your own delivery mechanism.  We have enough of them, don’t confuse people by adding some more.  If you’re going to use a raw sockets connection, supply a calling library and stick to some standard middleware like WCF rather than rolling your own. 

  Thousands of people have spent thousands of man years writing code based on existing techniques, you’re not better than all of them combined.

  Reinventing the wheel is never good for anyone.

• Ensure that the user can retrieve values they’re going to want to modify

  The number of times I’ve used APIs that let me set or update objects without returning the current state of the object is mind blowing.  So always remember: If you’re going to let them set it, let them get it.  Providing an update or “upsert” method without allowing your consumers to query the current state of data in the system is a complete waste of time.

• Supply compiled libraries to work with your API documentation

  This may not always be possible, but it’s a really good idea to supply a sample implementation and compiled binaries with your API that covers the most common scenarios of usage.  Not only does this prevent the consumer from struggling to get to grips with you API, but it allows you to outline and illustrate a set of best practices for usage.  In an ideal world, the user could just use your sample code in their application, so ensure you license the code appropriately.

  This is an exceptionally good way to deal with any authentication your API may require as you have the ability to provide additional helper classes to perform some common tasks (authenticate –> perform action –> logout, for example).

• Keep your implementation clean

  Delegate the API logic to your middleware components / reusable libraries.  Do your best to ensure the API layer doesn’t actually contain the logic required to perform operations, just the logic required to marshal the data from the API format into your internal data structures.  The API should simply orchestrate calls to one or more internal methods because your API should simply be exposing existing functionality.

  If the API is exposing some new, API specific functionality, consider splitting this behaviour into a separate assembly or binary to aid testability.

• Consider dogfooding

  Dogfooding is the act of using the software you’re creating.  I worked on a project where we were developing an order placement system in ASP.net MVC, and as part of the design process we decided that we wanted to have an API that was a first class citizen.  It then dawned on us that in order to produce the API in a way that accurately mirrored the functionality of the website, we should have the website consume the API like any other client would.  The website had it’s own concept of user authentication, and when a user logged in, the web application logged in to the API as the current user.

  Doing this not only ensured that our security model was watertight, but that any additional web functionality would immediately be available to API users because they were actually the same thing.  On top of that, you gain confidence in your own API because you know that it’s called often by your own code, reducing the likelihood of users discovering bugs in your API because it’s not a product you actually use.

• Support atomic operations including rollbacks on failure

  When implementing your API methods, ensure that if an exception occurs or an operation doesn’t complete, the all the changes made by your API call are reversed.  Consider explicitly supporting transaction scopes in your API to let your consumers compose their own “set” of operations.

• Support bulk operations where appropriate

  Building support for bulk operations into your API can often prevent performance issues occurring later when a user tries to, for example, insert 10,000 customers sequentially.  Consider pluralising your methods, so instead of providing an AddCustomer(Customer customer) method, provide only a AddCustomers(List<Customer> customers); method.  Doing this prevents callers from overloading your system by bulking data through your API in unintended ways, allowing you to properly cache required data and cater for these bulk operations.

  This isn’t always appropriate, however I’d always strongly suggest offering pluralised versions of methods that you suspect may be used in bulk, in order to help optimise your API calls and reduce the amount of data being transferred over the wire.

• Logging as a first class citizen

  Don’t wait until somebody asks about API usage to decide to log it.  Build logging into your API wrapper, from the start, at the point of every method call.  It doesn’t need to be fancy, and you can use a number of freely available components to handle these logs and log rotation (consider using log4net or log4j for simple log rotation).

  Log each method call and some summary or identifiable element of the data passed to it.  This’ll help you profile API usage, and identify how data changed in your previously closed system.

• Security as a first class citizen

  Consider the security of your API from the start of the project.  Understand who will have access to your API, which organisations and which individuals.  Do you require roll based security?  Do you need a way to disable API support for specific customers?  Are you transferring data that needs to be encrypted over the wire?

  Beware of over baking your security.  WS-* offers some very robust packet level security features, but if your API doesn’t need them, or is restricted to an internal network, then don’t bog down your implementation in unneeded security.  Beware of making security choices that tie you down to a specific protocol or technology stack – you want to keep your API usable for the consumers.  Do the simplest thing that works.

• Have integration tests!

  Make sure you have integration tests with mocking at the business logic layer. These tests are for your API wrappers, NOT your logic. The logic should be tested independently, you’re just ensuring your API layer, marshalling and method calls operate correctly at this level.

  With any luck, your business logic should already be tested as part of your existing test suite (which you have right?) but if not, ensure the business logic is tested separate from the API code.

  Consider using a TDD or BDD approach to designing your API calls, designing the specification first in the form of some calling code, then write the code required to make your usage examples compile.  This will help you understand exactly what calls the client will have to make for to your API to achieve specific functionality.  These tests can happily double up as regression tests when you make changes to the API.

• Keep it simple!  If all else fails, do what the big boys do.

  Always strive to keep your API simple.  Pretend your the consumer at all times.  If you’re unsure of how to proceed, I’ve always found inspiration, both for what to do and what not to do, from reading the API documentation of some large companies that have widely used APIs.  It’s safe to say that the likes of Amazon, Google and Microsoft have had to put some thought into their API designs.  Beware of trusting their decisions blindly, but liberally borrow anything you, as a consumer, would find pleasing in your API.

I’m not going to try and convince you that by following my advice that your API design will be flawless.  I’m really hoping for a little discussion on this topic as it seems like something that is rarely covered and often “felt out” by the people left to implement APIs for the public.  These are just some lessons I’ve learnt on the way while implementing several public facing APIs.

Want to talk about APIs?  Send me an email!

A common complaint when faced with localizing ASP.net MVC pages is that littering your code with tonnes of runat=”server” tags breaks the “purity” of the MVC model.  Regardless of how meaningful that debate is, there is a way to achieve globalisation without server controls.

I’m going to walk you through a sample implementation which should hopefully make this clearer.  As a standard disclaimer, none of this code has been tested in a production environment and I wouldn’t advise implementing it blindly.

I’m going to attempt to play this out mostly in screenshots…

The Idea

• The required language is stored in a database / session / extrapolated from the Url route information
• Your view pages derive from the type TranslatableViewPage

• This page adds support for a LanguageCode property that you can make use of inside the view along with adding a class implementing ITranslator, a class that provides hooks into a translation database.

• This controller add a method called ViewInLanguage(string languageCode) that you use instead of View() or View(model) to return your Asp.net MVC view.

Class Layout

The following is built upon the standard Asp.net MVC starter project for the sake of illustration.

Implementation

First, configure the translation settings and register your translator…

You need to configure a fail-safe default language code and a type that implements ITranslator.  This translator will be responsible for doing the heavy lifting.  Ideally we’d add some inversion of control here to allow you to define the translator implementation at configuration time, but that’s outside of the scope of this example.  I’ve implemented a very crude resource .resx translator for the example.

Next, make your controllers inherit from TranslatableController

Once inherited, switch from using the View(); method to ViewInLanguage() passing in your desired language code (gathered from the user session / database / Url route).

Then set your view type (or derive your view from) TranslatableViewPage…

Once your view is inheriting from TranslatableViewPage, you’ll have access to an instance of your specified Translator and the LanguageCode inside the view which you can use in a manner similar to the built in HtmlHelper class to access your translated strings.

How It Works

The TranslatableController provides you with ViewInLanguage and when called generates the standard MVC ActionResult.  This ActionResult will be a ViewResult, which is then wrapped in a LocalizedViewResult wrapper class adding a LanguageCode.

When ExecuteResult is called on the LocalizedViewResult to render the view, the LanguageCode is placed in the TempData array in the TranslatableViewPage.  Then, when the OnInit(EventArgs e) method is called on the TranslatableViewPage, this LanguageCode is extracted and placed in the LanguageCode property on the page.  In addition to this the page provides a constructed instance of ITranslator which you can use in your views to source translated data as the page is rendered.

Source Code

Download Here

One of the most valued practices in software development is brevity.  Writing code is bad.  When you write code you create bugs, and creating bugs is bad.  The solution?  Don’t write much code.  Commenting your code however, has traditionally been seen as a “good thing”.  So much so that most modern programming environments make some provision for document generation and offer style-guidelines for commenting your code.

I believe, however, that excessive commenting is actually an anti-pattern and should treated with caution, and as far as possible, avoided.  I’m going to illustrate my point with a (somewhat contrived, but in no way unusual or outlandish) example.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace XmlDocumentationAntiPattern
{
    /// <summary>
    /// XmlCommentHell
    /// </summary>
    /// <example>var xmlCommentHell = new XmlCommentHell</example>
    public class XmlCommentHell
    {
        /// <summary>
        /// Description
        /// </summary>
        /// <remarks>String description of XmlCommentHell.</remarks>
        /// <example>instance.Description = "some description";</example>
        public string Description { get; set; }

        /// <summary>
        /// XmlCommentHell ctor
        /// </summary>
        /// <param name="description">Description string</param>
        public XmlCommentHell(string description)
        {
            // Assign description
            Description = description;
        }

        /// <summary>
        /// Gets the description property, but in reverse!
        /// </summary>
        /// <returns>Reversed description</returns>
        public string GetReversedDescription()
        {
            return Description.Reverse().ToString();
        }
    }
}

The context of this example is C# but similarly applies in other programming languages.

If you find yourself engaging in XML comments like the above example, I really believe “you’re doing it wrong”.  Why?

• Reduced code readability

  The Xml comment clutter in the code above actually reduces it’s usefulness.  The code now takes three times as much screen real estate to maintain and understand.

• Low signal to noise ratio - too many characters that add no value

  When you’re maintaining systems however large, the act of actually writing code takes time and adds maintenance overhead.  Past the visual unpleasantness the amount of mark up required to document relatively simple methods actually reduces the codes utility.  Only ever type ANYTHING in your IDE if it adds value.

• Incredibly obvious comments

  There’s a wonderful quote to the tune of “always pretend that the person that’s going to maintain your code is an axe wielding manic who knows where you live”.  I’d like to extend that by adding “so don’t insult their intelligence”.  There are few things I find as frustrating as reading comments that not only add no value but also make me feel like I’ve wasted a tiny piece of my life reading them.  Don’t waste your time or mine.

• Violating the DRY principle

  The DRY principle is very well agreed upon in software development.  Don’t repeat yourself.  If your XML comments just repeat your method signatures, you’re not only repeating yourself (and thus wasting time) but you’re leaving yourself open to a maintained nightmare as the code changes and the comments are left unchanged leading to confusion and misinformation.

• Possible misuse – the generation of utterly useless documentation

  When I see projects documented in this way I often joke that someone should run Sandcastle or javaDoc over the code to gain some tangible value in the form of MSDN-esq documentation.  I’m actually wrong.  This is a terrible idea.  Pop quiz time!  What’s worse than tedious documentation that adds no value?  Tonnes of hyperlinked documentation that adds no value!  Think of the poor developer wasting minutes to hours searching for the value in generated documentation before painfully realising that there’s none to be had.

I occasionally get met with some resistance when I state my opinion on this for a couple of reasons.  People often argue that they do it for the sake of intellisense and IDE tooling, that they do it for generated documentation or just out of habit.  I feel like these are all dangerous reasons.

Firstly, if you’re generating documentation for documentations sake, you’re either trying to please some form of middle management that doesn’t understand what documentation really exists for (hint: to help developers develop), or you’re wasting time.

Secondly, if you’re documenting methods for intellisense you’re probably missing the point.  See, intellisense and other IDE self-help mechanisms are very good; they’ll display method signatures and method names with minimal fuss, any extra comments you glue on top of every method will either clutter your GUI, or become ignored white noise, potentially leading to that one important comment going ignored as your developers slowly desensitise themselves to reading the human generated “auto-doc” garbage.

Finally, if you find that you need to cover your methods in comments because they legitimately don’t make too much sense at a glance then you’re falling foul of a different problem: you have code that’s not legible maintainable and clear.  In this case you’d be far better served by ensuring your methods are named well, take logical parameters and have single clearly defined purposes.  In my experience, whenever somebody says that they need to comment their methods because the method is unclear, they really should be refactoring, not documenting.

Please DON’T bury your code in comments, just keep it all readable ok?

A quick code snippet.  These two extension methods (C# 3.0+) enables you to return custom attributes from types, both on a specific type and any data type.  They both return null if the attribute is not present.  

The first extension is useful for extending a type of your choice.  It’s especially useful when considering Enums and the DescriptionAttribute, or other enumeration attributes (especially custom attributes).  The usage examples below should make the use more obvious.

The second extension allows you to return an Attribute from ANY type.  Use with caution, but I find it interesting that it’s actually possible to write an extension method that works that way.

    public static class ElementExtensions
    {    

        public static T GetAttributeValue<T>(this SomeConcreteType val)
        {
            var attributes = val.GetType().GetField(val.ToString()).GetCustomAttributes(typeof(T), false);

            T response = default(T);
            if(attributes.Length > 0)
            {
                response = (T)attributes[0];
            }

            return response;
        }

        public static TReturnType GetAttributeValueFromType<TInstanceType, TReturnType>(this TInstanceType val)
        {
            var attributes = val.GetType().GetField(val.ToString()).GetCustomAttributes(typeof(TReturnType), false);

            TReturnType response = default(TReturnType);
            if(attributes.Length > 0)
            {
                response = (TReturnType)attributes[0];
            }

            return response;
        }       
    }   

Some usage examples….

    public enum RegexEnum
    {
        [RandomAttribute("^(([a-zA-Z]{1}[0-9]{3,4})|([a-zA-Z]{2}[0-9]{2,3})|[0-9]{4})$")]
        SomeEnumValue,
    }   

    public class RandomAttribute: Attribute
    {
        public string Expression { get; set; }

        public RandomAttribute(string expression)
        {
            Expression = expression;
        }
    }

    private static void Example()
    {
        // Both of these are equivalent
        foreach(var enumMember in Enum.GetValues(typeof(RegexEnum)))
        {
            var value = enumMember.GetAttributeValue();   
            var valueFromAnyType = enumMember.GetAttributeValueFromType<RegexEnum, RandomAttribute>();
        }       
    }

Some nice syntactic sugar for use with enumerations.

Fear Of Deployment

When you start working on a new project there are four really important pieces of information you should be aware of regarding the deployment of your software

1. Are you unafraid of deploying your code to production?
2. Do you know how your code will react in your production environment with production configuration?
3. Does your code react in the same way in your production environment as it does in development?
4. Are you confident in the repeatability of your installation procedure?

Fear and uncertainty in the deployment of software projects is a common theme I’ve seen across all the companies where I’ve worked and it’s never good for your project.  The fear of deployment is always a good indicator of the confidence your staff have in the project they are working on.

A project with unknown qualities and suspicious (or known but unreported) bugs often causes an serious fear of deployment.  There’s nothing like the fear of deploying an application and reducing a business critical system to it’s knees.

I’ve worked on a handful of projects where I’ve taken it upon myself to reign in this deployment fear and chaos, and more often than not, the fear has it’s roots in an uncontrolled development environment.

Configuring A Development Environment

I have very few suggestions regarding which tools you should use to develop your software.  I think that you gain the maximum benefit by allowing developers to pick and choose the absolute best tools for the job, be that technically or by preference.  Allowing developers to use their tools of choice makes happy developers.

By contrast however, the one thing I’m really certain about is that every development environment should start with an absolute base configuration that should not be changed.  This is the first way to solve the eternal “works on my machine” developer problem.  In essence, if all the development environments start off the same, there’s no excuse for a “works on my machine” error.  Not only will this reduce friction between team members, but it’ll speed up the development process because you’re all working to one known configuration.

Furthermore, the development environments alone shouldn’t share this configuration, they should share the base configuration with your production servers.  A huge percentage of software release issues are relating to the differences between production and test and development and the only way to solve what amounts to human error is to make this discrepancy go away.

In the current IT landscape where virtualisation is painfully simple (and often free) there are no excuses not to have a development environment (or at the very least development staging virtual machine) that accurately and completely mirrors your production server.  If you’re struggling with licenses of third party software, produce mocks / proxies / approximations.  I can assure you that the time you spend building these glorified testing rigs will work healthily towards eradicating development-to-production errors.

If It’s Worth Doing Once, It’s Worth Doing Three Times

Another nasty pattern I see frequently is the development-to-production pattern.  If you’re compiling software on your development machines and releasing it to production, “you’re doing it wrong”.  What’s worse than a “works-on-my-machine” conversation with a colleague?  You got it, a “works-on-my-machine” conversation with a system administrator.  It’s not an excuse.  Stop it.

You need to start dog-fooding your deployments, and this means environment cloning and real test servers.  I always follow a simple pattern; developer machine -> developer test box -> system-test box -> user acceptance test box -> production.

In order to do this you’ll need a series of environments (physical or virtual)

• Developer machine
• Developer environment
• Test environment
• UAT environment
• Production environment

That might sound like a lot of hardware but it really isn’t.  Use virtualisation and use it well.  Clone your virtual environments if need be.  Use snapshots and rollbacks to test deployments.  It shouldn’t take any time to administer (and I’ll explain why in the next section) and by the time your code is running on production you’ll have moved it through three different environments.  This is absolutely key to having faith in your deployment procedures.  When you’ve deployed your code so many times that you’re sure it works, in an environment that’s a mirror image of production, production is a far less scary place to be deploying to.

The key to this technique is that the environments all have very clearly defined purposes.  The developer produces his code changes to a system on his development box.  The code seems to work so it’s deployed to the developer environment and checked into your source control repository.  The development environment should be treated as a place where things could potentially get messed up, but it’s also a good place to host joint resources (a database, some middleware) that all the developers make use of.  If the code works in the developer environment it can be promoted to the test environment for the system tester (or a developer wearing a system testers hat) to test.  Once passed on the test box, the code changes can be promoted to the UAT environment for users to preview coming code releases.  Once these changes have been accepted, the code is released into production.

Beware of release insanity.  It makes perfect sense to frequently deploy to the developer environment but only occasionally promote code up to test and UAT.  This should fit around your way of working, just be sure to keep the conceptual integrity of the environments.  If you find a bug in test, don’t fix it in the test environment, fix it in development. It’s up to you to ensure you know what code is running across your environments to avoid any nasty surprises.

One Install To Rule Them All

At this point you’re probably thinking that this all sounds like a huge amount of effort but it isn’t.  The reason it isn’t is that you should, for the most part, be able to deploy your entire system in about 5 clicks / commands.  Don’t let your deployment mechanism be the week link in your application.  There are tonnes of install technologies on the market, both free and costly, to match whichever platform and tool chain you’re working in.

I wish I could remember where I read it, but one of the pieces of setup advice I read long ago that always stuck with me is that you should aim for a one-click install.  You might not achieve it, but you should aim to get very very close.

You need to invest time in configuration management for your application.  Build tools to auto-generate configurations for your deployment environments, build tools to automate setup and deployment.  These tools are worthwhile, because from the moment they’re built, you never need to worry about deploying your software.  They remove risk, and anything that removes risk from software development should be embraced.

Once you’ve build these tools and installers you’ll find your able to do things that you only thought were possible in large companies with seemingly limitless resources.  You’ll be able to configure nightly builds using a continuous integration package of your choice and have the nightly builds install themselves in your developer environment,  You’ll be confident that at any point you can provide a working copy of your software on request.

No Fear Of The Unexpected

The wonderful benefit you get at the end of this process is confidence in your software.

So you’ve released your system to production, do you then feel the need to slavishly test the system in the live environment? 

Imagine that urge going away, knowing that by the time the code hits production that any environmental glitches that could manifest have had the ability to fail three times already.  Any amount of cursory testing you could perform at this point should pale in comparison to the testing you did in the test environment and the user testing environment.  If your “at a glance” testing somehow discovers a bug, you’ve done something very very wrong in the lead up to release.  You should be confident in the fact that your code has been run exhaustively and often by the time it’s reached production.

The world isn’t perfect however, and it’s obviously advisable to a quick audit of the software once installed, just don’t force yourself to repeat your system tests in production (an obvious anti-pattern) and you’ll gain no benefits from doing so.

If you can devise an automated tool to verify your deployments after install, you’ll be able to round off your sense of deployment-security.

A Zen-like State Of Satisfaction

I opened this piece with a few simple questions.

• Are you unafraid of deploying your code to production?
• Do you know how your code will react in your production environment with production configuration?
• Does your code react in the same way in your production environment as it does in development?
• Are you confident in the repeatability of your installation procedure?

I can answer yes to all three questions because I understand my environments and I hope you can too.

[NOTE: This post relates to an old version of MobileTFL - Please see http://www.davidwhitney.co.uk/software for the latest version]

I’ve just compiled what I hope is the final version of this application barring London growing extra underground lines.

I’ve written a small Windows Mobile application for phones running WinMo 5.0+ with Compact Framework 2.0+.  It syndicates the Transport for London live data in similar way to the pre-existing iPhone and Android applications allowing you to view the current tube network status, planned engineering outages and local station notifications at the push of a finger on your Windows Mobile.

It’s currently living at a holding page at http://www.davidwhitney.co.uk/software (soon to become a larger site) and it’s a free download for anyone that uses Windows Mobile.

The 1.0.0.4 update is a reaction to some feedback I’ve received over at http://www.xda-developers.com and comes complete with coloured glyphs representing each tube line and enhanced resolution support for devices with “unusual” resolutions such as the Sony X1.  I’ve also had a stab at some font and UI element scaling so hopefully the interface will look quite natural on all your devices.

I’ve only managed to test it in the wild on a Touch Diamond, Touch Cruise and the Windows Mobile 5.0 Virtual Machine (along with in Windows).  It seems to run admirably in those conditions.

Obviously it requires a data plan so beware of any provider costs.

You can download the .cab directly at this link: http://www.davidwhitney.co.uk/software/repository/MobileTFL/1.0.0.4/MobileTFL.Setup.CAB