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Repositories

This chapter will explain the concept of packages and repositories, what kinds of repositories are available, and how they work.

Concepts

Before we look at the different types of repositories that exist, we need to understand some of the basic concepts that composer is built on.

Package

Composer is a dependency manager. It installs packages locally. A package is essentially just a directory containing something. In this case it is PHP code, but in theory it could be anything. And it contains a package description which has a name and a version. The name and the version are used to identify the package.

In fact, internally composer sees every version as a separate package. While this distinction does not matter when you are using composer, it's quite important when you want to change it.

In addition to the name and the version, there is useful data. The information most relevant for installation is the source definition, which describes where to get the package contents. The package data points to the contents of the package. And there are two options here: dist and source.

Dist: The dist is a packaged version of the package data. Usually a released version, usually a stable release.

Source: The source is used for development. This will usually originate from a source code repository, such as git. You can fetch this when you want to modify the downloaded package.

Packages can supply either of these, or even both. Depending on certain factors, such as user-supplied options and stability of the package, one will be preferred.

Repository

A repository is a package source. It's a list of packages, of which you can pick some to install.

You can also add more repositories to your project by declaring them in composer.json.

Types

Composer

The main repository type is the composer repository. It uses a single packages.json file that contains all of the package metadata. The JSON format is as follows:

{
    "vendor/packageName": {
        "name": "vendor/packageName",
        "description": "Package description",
        "versions": {
            "master-dev": { @composer.json },
            "1.0.0": { @composer.json }
        }
    }
}

The @composer.json marker would be the contents of the composer.json from that package version including as a minimum:

  • name
  • version
  • dist or source

Here is a minimal package definition:

{
    "name": "smarty/smarty",
    "version": "3.1.7",
    "dist": {
        "url": "http://www.smarty.net/files/Smarty-3.1.7.zip",
        "type": "zip"
    }
}

It may include any of the other fields specified in the [schema].

The composer repository is also what packagist uses. To reference a composer repository, just supply the path before the packages.json file. In case of packagist, that file is located at /packages.json, so the URL of the repository would be http://packagist.org. For http://example.org/packages.org the repository URL would be http://example.org.

VCS

VCS stands for version control system. This includes versioning systems like git, svn or hg. Composer has a repository type for installing packages from these systems.

There are a few use cases for this. The most common one is maintaining your own fork of a third party library. If you are using a certain library for your project and you decide to change something in the library, you will want your project to use the patched version. If the library is on GitHub (this is the case most of the time), you can simply fork it there and push your changes to your fork. After that you update the project's composer.json. All you have to do is add your fork as a repository and update the version constraint to point to your custom branch.

Example assuming you patched monolog to fix a bug in the bugfix branch:

{
    "repositories": [
        {
            "type": "vcs",
            "url": "http://github.com/igorw/monolog"
        }
    ],
    "require": {
        "monolog/monolog": "dev-bugfix"
    }
}

When you run php composer.phar update, you should get your modified version of monolog/monolog instead of the one from packagist.

Git is not the only version control system supported by the VCS repository. The following are supported:

To get packages from these systems you need to have their respective clients installed. That can be inconvenient. And for this reason there is special support for GitHub and BitBucket that use the APIs provided by these sites, to fetch the packages without having to install the version control system. The VCS repository provides dists for them that fetch the packages as zips.

The VCS driver to be used is detected automatically based on the URL.

PEAR

It is possible to install packages from any PEAR channel by using the pear repository. Composer will prefix all package names with pear-{channelName}/ to avoid conflicts.

Example using pear2.php.net:

{
    "repositories": [
        {
            "type": "pear",
            "url": "http://pear2.php.net"
        }
    ],
    "require": {
        "pear-pear2/PEAR2_HTTP_Request": "*"
    }
}

In this case the short name of the channel is pear2, so the PEAR2_HTTP_Request package name becomes pear-pear2/PEAR2_HTTP_Request.

Note: The pear repository requires doing quite a few requests per package, so this may considerably slow down the installation process.

Package

If you want to use a project that does not support composer through any of the means above, you still can define the package yourself by using a package repository.

Basically, you define the same information that is included in the composer repository's packages.json, but only for a single package. Again, the minimum required fields are name, version, and either of dist or source.

Here is an example for the smarty template engine:

{
    "repositories": [
        {
            "type": "package",
            "package": {
                "name": "smarty/smarty",
                "version": "3.1.7",
                "dist": {
                    "url": "http://www.smarty.net/files/Smarty-3.1.7.zip",
                    "type": "zip"
                },
                "source": {
                    "url": "http://smarty-php.googlecode.com/svn/",
                    "type": "svn",
                    "reference": "tags/Smarty_3_1_7/distribution/"
                }
            }
        }
    ],
    "require": {
        "smarty/smarty": "3.1.*"
    }
}

Typically you would leave the source part off, as you don't really need it.

Hosting your own

While you will probably want to put your packages on packagist most of the time, there are some use cases for hosting your own repository.

  • Private company packages: If you are part of a company that uses composer for their packages internally, you might want to keep those packages private.

  • Separate ecosystem: If you have a project which has its own ecosystem, and the packages aren't really reusable by the greater PHP community, you might want to keep them separate to packagist. An example of this would be wordpress plugins.

When hosting your own package repository it is recommended to use a composer one. This is type that is native to composer and yields the best performance.

There are a few tools that can help you create a composer repository.

Packagist

The underlying application used by packagist is open source. This means that you can just install your own copy of packagist, re-brand, and use it. It's really quite straight-forward to do.

Packagist is a Symfony2 application, and it is available on GitHub. It uses composer internally and acts as a proxy between VCS repositories and the composer users. It holds a list of all VCS packages, periodically re-crawls them, and exposes them as a composer repository.

To set your own copy, simply follow the instructions from the packagist github repository.

Satis

Satis is a static composer repository generator. It is a bit like an ultra- lightweight, static file-based version of packagist.

You give it a composer.json containing repositories, typically VCS and package repository definitions. It will fetch all the packages that are required and dump a packages.json that is your composer repository.

Check the satis GitHub repository for more information.

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