I'll write a application but I've never experienced to allow people to use my application programming interface before.I mean how kinda design I should make to let people use my methods from outside world like API.
Please some one show me a way.I am kinda new to this.
Expose as little as you can. Every bit you publish, will return to you x100 in next version. Keeping compatibility is very hard.
Create abstractions for everything you publish. You will definitely change your internals, but your existing users should stay compatible.
Mark everything as internal. Even the main method of your application. Every single method that could be used, will be used.
Test your public API the same way you would for interfaces. Integration tests and so on. Note that your API will be used in unpredictable ways.
Maximize convention over configuration. This is required. Even if your API is a single method you will still need to support this. Just makes your life easier.
Sign, and strong name your assemblies, this is good practice.
Resolve as many FxCop and StyleCop errors as possible.
Check your API is compatible with the Naming Guidelines of your platform.
Provide as many examples as you can, and remember that most of the usage of your API will be Ctrl+C and Ctrl+V from these examples.
Try to provide documentation. Check that you do not have GhostDoc-style auto-generated documentation. Everybody hates this.
Include information on how to find you.
Do not bother with obfuscation. This will help you and your users.
ADDED
API should have as less dependencies as you can. For example, dependecies on the IoC containers should be prohibited. If your code uses it internally. Just ilmerge them into your assemblies.
It may not be the funniest reading, and certainly not the only reading to do on the subject, but while designing your class library (your API), do check in with the Design Guidelines for Developing Class Libraries every now and then, it's a good idea to have a design that corresponds a bit with the .NET Framework iteself.
Make your methods you want to expose to the outside world public.
I found this presentation to be particularly insightful:
How to Design a Good API and Why it Matters
http://lcsd05.cs.tamu.edu/slides/keynote.pdf
One way to do it is to create a DLL for your main functionality that others will use and an EXE that calls the methods in the DLL. If you want your application to support plug-ins, have a look at the System.AddIn namespace.
If you want to see what's new in this area, check out the Managed Extensibility Framework. It's a new/"unified (see the comments...)" method for exposing features for add-ins and other extensibility/modularity.
Related
I have an application that I have designed and this app has a pretty decent core dll that contains an API that my main view's exe uses. I would like to allow other developers to access this core dll as well but I don't want them to have as much access as me since it would be a security risk. What is the standard way of exposing my core dll? Are there any particular design patterns I should be looking at?
I'm using C#
Edit: my question was a little vague so here is some clarification
My program is deployed as a windows exe which references the core.dll. I want other people to create extensions which dynamically get loaded into my program at start up by loading dlls in the /extensions directory. The 3rd party dlls will inherit/implement certain classes/interfaces in my core.dll. I only want to give 3rd parties limited access to my core but I want to give my exe additional access to the core.
I should mention that this is the first time I have written a program that imports DLLs. Perhaps this whole method of allowing users to add extensions is wrong.
How do I modify/expose my API for
other developers?
To deliberately allow other developers to work with an API you've built touches on many things, which can be broken into two areas:
Resources (documentation, samples, etc) that makes it easier for them to understand (yes - basically an SDK).
Architecting, constructing and deploying your solution so that it's easy to actually work with.
Examples include:
By packing it in a way that suits re-use.
By using naming conventions and member names that others can easily follow.
Documentation, samples.
Providing the source code (as open source) if you're happy for them to modify it.
I would like to allow other developers
to access this core dll as well but I
don't want them to have as much access
as me since it would be a security
risk.
Ok, so this gets us right into the second area - the actual solution.
The problem you have is not a trivial one - but it's also quite do-able; I'd suggest:
Looking into existing material on plugins (https://stackoverflow.com/questions/tagged/plugins+.net)
Personally, I've found using attributes and Dependency Inversion to be a great approach.
There's also stuff like the Managed Extensibility Framework which you should consider.
The big issue you face is that you're into serious architecture territory - the decisions you make now will have a profound impact on all aspects of the solution over time. So you might not be able to make an informed decision quickly. Still - you have to start somewhere :)
The "design patterns" in terms of an API are more related to things like REST.
I don't want them to have as much
access as me since it would be a
security risk
Then i would (for the sake of maintenance), layer on top of the core DLL extra logic to prevent this.
The thing is, the "clients" call the API, not the Core DLL.
"How" the API accesses the Core DLL is under your full control. Just only expose operation contracts that you wish.
Since you're using C#, I would look at Microsoft's Framework Design Guidelines: Conventions, Idioms, and Patterns for Reusable .NET Libraries and use FxCop to in-force many of them (latest version here). This won't be all you'll likely need, but it would help put you in the right direction.
Also, take a look at the freely available distillation of Framework Design Guidelines by the same author.
I have a small Utility library containing some useful utility methods which have been fully unit-tested. At the moment, my library has no external dependencies. I am toying with the idea of adding logging to my classes which might be useful for debugging purposes. But this would mean bundling logging libraries along with my project.
My question is: should I keep my library dependency free? Are there any advantages of doing so?
I would add a logging interface that the can be used to abstract the logging. Then the allow users to add logging via this interface. You too should use this interface, and you should supply a 'NullLogger' built into your library that would be used if no other logging is needed.
You can make it easy to not use the NullLogger by asking users to configure a new one, simply by config file or by run time discovery.
Use Java Logging. It's part of JRE/JDK so no external libs are needed.
Check out examples.
There are many advantages of doing so, not the least the ability to run on most any operating system.
One way of keeping your library pretty dependency free, is to require it to initialized prior to use. Then you would in your_lib_init(); function take a function pointer to logging backend. This means, the backend can be rewritten for any platform it might run on.
Also figure out, if you want a library totally free of all library dependencies, or one that depends on the standard class path. If it is pure Java, it will run on J2ME, Android, native compiled Java with GCJ and what not. If it uses class path, it will be portable across all class path implementations, in practice wherever OpenJDK runs.
Pro:
Your library will be much smaller (chances are that you're only using a small part of the full functionality of any dependency)
No update hell (like your code needs library C, version 2, product X needs your code and library C, version 1).
You won't need to bend your spoon to the whims of someone else (say the library you goes from 1.x to 2.x -> you need to update your code)
Con:
Wasted code if product X also needs the library
How smart are you? Chances are that you can't match the thought, wisdom and time that already went into the library.
PS: If you want to support logging, add slf4j to your code; this is a 30KiB API which allows users of your code to use any logging framework out there. Do not use commons-logging.
I've inherited an enormous .NET solution of about 200 projects. There are now some developers who wish to start adding their own components into our application, which will require that we begin exposing functionality via an API.
The major problem with that, of course, is that the solution we've got on our hands contains such a spider web of dependencies that we have to be careful to avoid sabotaging the API every time there's a minor change somewhere in the app. We'd also like to be able to incrementally expose new functionality without destroying any previous third party apps.
I have a way to solve this problem, but i'm not sure it's the ideal way - i was looking for other ideas.
My plan would be to essentially have three dlls.
APIServer_1_0.dll - this would be the dll with all of the dependencies.
APIClient_1_0.dll - this would be the dll our developers would actual refer to. No references to any of the mess in our solution.
APISupport_1_0.dll - this would contain the interfaces which would allow the client piece to dynamically load the "server" component and perform whatever functions are required. Both of the above dlls would depend upon this. It would be the only dll that the "client" piece refers to.
I initially arrived at this design, because the way in which we do inter process communication between windows services is sort of similar (except that the client talks to the server via named pipes, rather than dynamically loading dlls).
While i'm fairly certain i can make this work, i'm curious to know if there are better ways to accomplish the same task.
You may wish to take a look at Microsoft Managed Add-in Framework [MAF] and Managed Extensibiility Framework [MEF] (links courtesy of Kent Boogaart). As Kent states, the former is concerned with isolation of components, and the latter is primarily concerned with extensibility.
In the end, even if you do not leverage either, some of the concepts regarding API versioning are very useful - ie versioning interfaces, and then providing inter-version support through adapters.
Perhaps a little overkill, but definitely worth a look!
Hope this helps! :)
Why not just use the Assembly versioning built into .NET?
When you add a reference to an assembly, just be sure to check the 'Require specific version' checkbox on the reference. That way you know exactly which version of the Assembly you are using at any given time.
Sure, there's a type of project in Visual Studio that outputs a DLL that people can use. I know that. I'm just wondering what are some of the standards that devs will expect when using my DLL file.
I'll be providing a class that searches for movies in IMDB and returns results for a dev to consume.
Not a webservice, but a local DLL file. (I'm aware that IMDB frowns upon web scraping, but I'm also aware that they give permission to people if asked. My permission is already sent.)
How should I approach this?
Check out Microsoft's Design Guidelines for Class Library Developers.
Or the newer version of same (thanks to paper1337).
You're then interested in best practices when designing a class library. There is much to say to this thema.
One of the first and foremost things you need to do is to publish all your dependencies. Avoid any hidden dependencies in your code.
For example, don't rely on some key to be set in a shared key-value collection, such as Session. There is no way a user of your library can find it out.
If some method requires some service to be preinitialized, require a valid reference to be passed as an argument.
You need to provide a simple to use API, full documentation and worked examples as a minimum. If you can provide unit tests that would be a bonus.
Internally, you need to verify all inputs into your routines, as well as clearly document what configuration the user is expected to do. Solid exception handling is a given, and you should possibly consider some localisation support in there as well.
If you, or anybody, is serious about creating a good framework for others to use, check out http://www.amazon.com/Framework-Design-Guidelines-Conventions-Libraries/dp/0321246756
What ever you make public, should remain public and their signatures cannot be changed in your next version and you must support it forever.
So, take care in establishing your contracts and document them with examples. Make public members only if it needs to be.
Easy-to-use API with appropriate class, method and property names.
API has been tested (e.g. unit tests)
Supporting documentation.
My company is currently in the process of creating a large multi-tier software package in C#. We have taken a SOA approach to the structure and I was wondering whether anyone has any advice as to how to make it extensible by users with programming knowledge.
This would involve a two-fold process: approval by the administrator of a production system to allow a specific plugin to be used, and also the actual plugin architecture itself.
We want to allow the users to write scripts to perform common tasks, modify the layout of the user interface (written in WPF) and add new functionality (ie. allowing charting of tabulated data). Does anyone have any suggestions of how to implement this, or know where one might obtain the knowledge to do this kind of thing?
I was thinking this would be the perfect corner-case for releasing the software open-source with a restrictive license on distribution, however, I'm not keen on allowing the competition access to our source code.
Thanks.
EDIT: Thought I'd just clarify to explain why I chose the answer I did. I was referring to production administrators external to my company (ie. the client), and giving them someway to automate/script things in an easier manner without requiring them to have a full knowledge of c# (they are mostly end-users with limited programming experience) - I was thinking more of a DSL. This may be an out of reach goal and the Managed Extensibility Framework seems to offer the best compromise so far.
Just use interfaces. Define an IPlugin that every plugin must implement, and use a well defined messaging layer to allow the plugin to make changes in the main program. You may want to look at a program like Mediaportal or Meedios which heavily depend on user plugins.
As mentioned by Steve, using interfaces is probably the way to go. You would need to design the set of interfaces that you would want your clients to use, design entry points for the plugins as well as a plugin communication model. Along with the suggestions by Steve, you might also want to take a look at the Eclipse project. They have a very well defined plugin architecture and even though its written in java, it may be worth taking a look at.
Another approach might be to design an API available to a scripting language. Both
IronPythonand Boo are dynamic scripting languages that work well with C#. With this approach, your clients could write scripts to interact with and extend your application. This approach is a bit more of a lightweight solution compared to a full plugin system.
I would take a look at the MEF initiative from Microsoft. It's a framework that lets you add extensibility to your applications. It's in beta now, but should be part of .Net 4.0.
Microsoft shares the source, so you can look how it's implemented and interface with it. So basically your extensibility framework will be open for everyone to look at but it won't force you to publish your application code or the plug-ins code.
Open source is not necessary in any way shape or form to make a product extensible.
I agree that open source is a scary idea in this situation. When you say approval by a production administrator - is that administrator within your company, or external?
Personally, I would look at allowing extensibility through inheritance (allowing third parties to subclass your code without giving them the source) and very carefully specified access modifiers.
Microsoft already did exactly this, resulting in Reporting Services, which has every attribute you mention: user defined layout, scriptability, charting, customisable UI. This includes a downloadable IDE. No access to source code is provided or required, yet it's absolutely littered with extensibility hooks. The absence of source code inhibits close-coupling and promotes SOA thinking.
We are currently in a similar situation. We identified different scenarios where people may want to create a live connection on a data level. In that case they can have access to a sinle webservice to request and import data.
At some point they may want to have a custom user interface (in our case Silverlight 2). For this scenario we can provide a base class and have them register the module in a central repository. It then integrates into our application in a uniform way, including security, form and behaviour and interaction with services.