CodeIgniter Internals Overview

This guide should help contributors understand how the core of the framework works, and what needs to be done when creating new functionality. Specifically, it details the information needed to create new packages for the core.

Dependencies

All packages should be designed to be completely isolated from the rest of the packages, if possible. This will allow them to be used in projects outside of CodeIgniter. Basically, this means that any dependencies should be kept to a minimum. Any dependencies must be able to be passed into the constructor. If you do need to use one of the other core packages, you can create that in the constructor using the service() function, as long as you provide a way for dependencies to override that:

    public function __construct(?Foo $foo = null)
    {
        $this->foo = $foo ?? service('foo');
    }

Type Declarations

PHP7 provides Type declarations for method parameters and return types. Use it where possible. Return type declaration is not always practical, but do try to make it work.

At this time, shipped CI4 production code does use Strict typing as much as possible.

Abstractions

The amount of abstraction required to implement a solution should be the minimal amount required. Every layer of abstraction brings additional levels of technical debt and unnecessary complexity. That said, don't be afraid to use it when it's needed and can help things.

Don't create a new container class when an array will do just fine.
Start simple, refactor as necessary to achieve clean separation of code, but don't overdo it.

Testing

Any new packages submitted to the framework must be accompanied by unit tests. The target is 80%+ code coverage of all classes within the package.

Test only public methods, not protected and private unless the method really needs it due to complexity.
Don't just test that the method works, but test for all fail states, thrown exceptions, and other pathways through your code.

You should be aware of the extra assertions that we have made, provisions for accessing private properties for testing, and mock services. We have also made a CITestStreamFilter to capture test output. Do check out similar tests in tests/system/, and read the "Testing" section in the user guide, before you dig in to your own.

Some testing needs to be done in a separate process, in order to setup the PHP globals to mimic test situations properly. See tests/system/HTTP/ResponseSendTest for an example of this.

Namespaces and Files

All new packages should live under the CodeIgniter namespace. The package itself will need its own sub-namespace that collects all related files into one grouping, like CodeIgniter\HTTP.

Files MUST be named the same as the class they hold, and they must match the Style Guide, meaning CamelCase class and file names. They should be in their own directory that matches the sub-namespace under the system directory.

Take the Router class as an example. The Router lives in the CodeIgniter\Router namespace. Its two main classes, RouteCollection and Router, are in the files system/Router/RouteCollection.php and system/Router/Router.php respectively.

Interfaces

Most base classes should have an interface defined for them. At the very least this allows them to be easily mocked and passed to other classes as a dependency, without breaking the type-hinting. The interface names should match the name of the class with "Interface" appended to it, like RouteCollectionInterface.

The Router package mentioned above includes the CodeIgniter\Router\RouteCollectionInterface and CodeIgniter\Router\RouterInterface interfaces to provide the abstractions for the two classes in the package.

Handlers

When a package supports multiple "drivers", the convention is to place them in a Handlers directory, and name the child classes as Handlers. You will often find that creating a BaseHandler, that the child classes can extend, to be beneficial in keeping the code DRY.

See the Log and Session packages for examples.

Configuration

Should the package require user-configurable settings, you should create a new file just for that package under app/Config. The file name should generally match the package name.

Autoloader

All source files within the system/ThirdParty should be added to system/Config/AutoloadConfig.php, in the $coreClassmap property. This is only used for loading the third party packages without Composer.

Command-Line Support

CodeIgniter has never been known for its strong CLI support. However, if your package could benefit from it, create a new file under system/Commands.

Documentation

All packages must contain appropriate documentation that matches the tone and style of the rest of the user guide. In most cases, the top portion of the package's page should be treated in tutorial fashion, while the second half would be a class reference.

Modification of the `env` file

CodeIgniter is shipped with a template env file to support adding secrets too sensitive to be stored in a version control system. Contributors adding new entries to the env file should always ensure that these entries are commented, i.e., starting with a hash (#). This is because we have spark commands that actually copy the template file to a .env file (which is actually the live version actually read by CodeIgniter for secrets) if the latter is missing. As much as possible, we do not want settings to go live unexpectedly without the user's knowledge.

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