New Developers' Guide

CKAN - New contributor guidelines

About this document

This document aims to explain the inner workings of CKAN as well as describe the currently agreed upon workflow. Hopefully, this will reduce friction for new contributors entering CKAN development.

As with anything CKAN, this document is always open to corrections and improvements. Please note that any contribution must follow the Contribution guidelines and the Code of Conduct.

Due to CKAN being actively developed this document may be incomplete or incorrect, some details may change or may have already changed. Hopefully the program structure remains relatively the same (or it'd be reasonable to update this).

All code examples are in pseudo- C#. All typenames look like SomeClassType. This is some code:

void foo() { return 1; }

foo(1);

The CKAN project

In its essence, CKAN consists of a core library module ("core"), a command-line client ("the command-line") and a GUI client ("the GUI") - collectively referred to as "CKAN" and a large number of supporting tools such as parsers, validators and bots ("CKAN Tools", "the tools" or "the toolset").

While CKAN itself is written exclusively in C# .NET, the toolset sports a variety of programming languages such as Perl, bash and others. Contributions to CKAN are expected to be in C#, use .NET 4.5 and be compatible with both Mono (Win32, Linux, MacOSX) and Visual Studio (Win32) environments. There is no such limitation present when contributing to the tools, they can be in any language and use any platform as long as it is FOSS and is available on all of our development targets - modern Linux-based and Windows operating systems.

Glossary

Client - an end-user software package that enables the user to manage his or her installed mods by using metadata provided by a CKAN repository
Repository - an online service which enables clients to fetch the latest available mod metadata and mod authors to upload new metadata
Module - A modification or enhancement to Kerbal Space Program, provided by mod authors to users under a certain license. A module is a collection of files, their licensing and the metadata related to those files. Uniquely identified by a string called identifier
Metadata - a JSON- encoded string that represents all the metadata related to a particular module without the contents of the module itself. It describes the mod itself (e.g. version, author, download url, homepage etc.) as well as the steps necessary to perform a complete installation. The metadata also contains information about the relationships between mods such as dependencies and recommendations. Note that the metadata does not usually fall under the same license as the mod contents.
Schema - the JSON schema (Draft v4) against which all metadata strings are validated before being accepted into a repository, the latest version of the schema is available here
Mono - the FOSS Mono project is a complete .NET- compatible platform available for all modern desktop operating systems. Used in lieu of Microsoft's .NET where the latter is not available (more or less everything but Windows).

CKAN Core

The core of CKAN contains all the code necessary to facilitate basic package management operations such as communicating with a CKAN repository and installing modules.

You can find all relevant code for this section in master/CKAN/Core.

Here is a graph that contains all of the core classes and their relationships. Don't be intimidated by the amount of classes, CKAN's core is very understandable when you are aware of the important stuff. So, here's the important stuff (in no particular order):

Module (Module.cs)

A base class for modules.
Strongly- typed representation of CKAN metadata.
Modules are uniquely identified by their string identifier field, two different mods cannot have the same identifier (this is enforced at repository level)
Contains accessors for all schema fields, for example:
```
CkanModule mod = ...;
Console.WriteLine(mod.download);
```
will print the download URL for a mod. Note that optional fields in the schema can result in null values, so remember to check!

CkanModule (CkanModule.cs)

A concrete instance of a CKAN module.
Inherits from Module and allows converting JSON to a CkanModule and vice versa.
Available CkanModules are generated at run-time by JSON- parsing repository- obtained .ckan metadata files and are located in the Registry.
This class will probably get merged with Module as we phase out bundles

Registry (Registry.cs)

Represents a database of modules
The two important fields are two dictionaries - available_modules and installed_modules. Both are indexed by a module identifier.
available_modules is a dictionary mapping a string module identifier to an AvailableModule (AvailableModule.cs) instance. This is the list of all modules currently available in the repository. AvailableModule is a helper class that tracks module versions. This allows multiple versions of a single mod to co-exist in the repository. A call to AvailableModule.Latest(KSPVersion kspVersion) will produce a CkanModule compatible with the given KSP version (or throw if no such version exists)
installed_modules tracks all CKAN installed modules. It uses the InstalledModule(InstalledModule.cs) class which contains a list of installed files and a Module instance.

RegistryManager (RegistryManager.cs)

Singleton, use RegistryManager.Instance()
Holds the current registry and provides methods for serialization
In most cases you will need the registry field which is the current Registry

ModuleInstaller (ModuleInstaller.cs)

Singleton, use ModuleInstaller.Instance
Contains all the logic for installing, updating and uninstalling modules
Important public functions are IsCached, InstallList, Uninstall
InstallList is what the clients call to install mods. It resolves dependencies according to RelationshipResolverOptions, downloads the data and performs the necessary file operations.
Uninstall will automatically uninstall mods that depend on whatever you're uninstalling unless you explicitly tell it not to.

KSP

Net

RelationshipResolver

RelationshipResolverOptions

Repo

FilesystemTransaction (TransactionalFilesystem.cs)

Enables filesystem operations in an atomic fashion
Allows us to manipulate files without worrying about incomplete changes due to run- time errors.
You can use it by instantiating a new FilesystemTransaction object, then using its methods OpenFileWrite, RemoveFile, CreateDirectory, DeleteDirectory. To actually apply all the operations, call Commit(). It's useful to Rollback() if you're sure to roll back a transaction, but it's not necessary, not calling Commit() is enough to be sure you haven't done any damage to the user's files
OpenFileWrite returns a TransactionalFileWriter object, you can use its Stream property to get a FileStream instance which you can write to.
Isn't actually atomic, most filesystems and/or hardware don't support it. It just queues all operations and then executes them at once on Commit()

User (User.cs)

The User class allows interaction with the User from core code
Works in both the command-line and GUI clients
WriteLine displays a message to the user
YesNo displays a message and a Yes/No prompt
Error displays an error
Use sparingly, popping up 20 dialogs at once in the GUI is not fun for the user :(

Logging

We use log4net for logging.

Command-line client

The command-line client resides in CmdLine/Main.cs. This is the place to look if you wish to know how a particular feature works or if you're just starting to read the code.

GUI client

The GUI client is sadly much more complicated than the command-line one, mostly because 90% of it is interface code with WindowsForms and the window designs themselves. The GUI is done in Visual Studio and although there are other WindowsForms editors, they have not been tested with CKAN (tell us if they work :P).

CKAN Tools

Setting up your development environment

Linux-based operating systems

You will need at least MonoDevelop and Mono to be able to open and build the CKAN.sln file. MonoDevelop aims to be a full C#- capable IDE similarly to Visual Studio and comes with an editor, compiler and debugger.

Run the included build script to download all the dependencies via the NuGet packaging system and build CKAN and NetKAN with the Cake build system.

Windows

You most likely want to use Visual Studio. Although proprietary, the Express version is fully capable (same compiler as the other versions) and comes at zero cost. As an alternative, you can also use MonoDevelop on Windows.

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