Create a Composer command line installer with the Symfony2 CLI

    This post is part of the ”Symfony2 components in your own userland” series; here is a list of all the articles contained this series:

  1. Using the Symfony2 Dependency Injection Container as a standalone component
  2. Launching PHPUnit tests from a browser with Symfony2
  3. Using the Console component to write an interactive installer for Composer

Today we are going to see the power of Symfony2’s Console component, which lets us build powerful interactive command line applications in pure PHP.

In this episode we are going to create an interactive shell able to generate new composer-based projects: we will have a command to define which dependencies we need and another one to:

The approach we’re going to use will be very rough and incomplete: no error handling, no decent abstraction, but is intended to give you a clue about the potentiality of the CLI tool and to show you how you can easily create PHP command line applications without the need to write too much good code.

Approach and installation

The Symfony2 Console lets use extend the Console\Command\Command class to implement your own commands, so we will add a couple custom commands, one to register dependencies and one to execute the installation.

First of all, let create our own composer.json, to download the Console and Process1 components:

composer.json
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{
    "require": {
        "php": ">=5.3.2",
        "symfony/console": "2.0.10",
        "symfony/process": "2.0.10"
    }
}

then install everything and create your installer.php script which serves as the entry point for the console:

installing the dependencies
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wget http://getcomposer.org/composer.phar

php composer.phar install
installer.php
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<?php

require 'vendor/.composer/autoload.php';
require 'Command/DependencyContainer.php';
require 'Command/Install.php';

use Symfony\Component\Console\Shell;
use Symfony\Component\Console\Application;

$application            = new Application('Installer', '1.0.0-alpha');
$dependencyContainer    = new DependencyContainer();
$application->add($dependencyContainer);
$application->add(new Install($dependencyContainer));
$shell = new Shell($application);

$shell->run();

In the installer.php we are instantiating a new interactive shell application, adding to it 2 new commands and then we run it: don’t try it now, as the added command classes don’t exist yet.

A container for the dependencies

The first custom command we are going to add is a dependency container, which is a convenient class storing the dependencies, like symfony/yaml, in an attribute, and exposes a getDependencies() method that will be used by the installer command to retrieve the dependencies to install.

Command/DependencyContainer.php
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<?php

use Symfony\Component\Console\Command\Command;
use Symfony\Component\Console\Input\InputInterface;
use Symfony\Component\Console\Output\OutputInterface;

class DependencyContainer extends Command
{
    protected $dependencies = array();

    public function getDependencies()
    {
        return $this->dependencies;
    }

    protected function execute(InputInterface $input, OutputInterface $output)
    {
        $dialog  = $this->getHelperSet()->get('dialog');
        $package = $dialog->ask($output, '<question>Please enter the name of the package you want to install</question>');

        if ($package) {
            $this->dependencies[] = '"' . $package . '": "master"';
            $output->writeln(sprintf('<info>Package %s was succesfully registered</info>', $package));
        } else {
            $output->writeln('<error>You must insert a package name</error>');
        }
    }

    protected function configure()
    {
        $this
            ->setName('add-dependency');
        ;
    }
}

As you see, the command will be called when doing a add-dependency from the console and will ask the user to prompt the dependency we wants to add; a basic check is done:

Checking for non-empty input
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<?php
...

if ($package) {
    $this->dependencies[] = '"' . $package . '": "master"';
    $output->writeln(sprintf('<info>Package %s was succesfully registered</info>', $package));
} else {
    $output->writeln('<error>You must insert a package name</error>');
}

Note that, for being quick’n’dirty, we store the dependencies in the composer way:

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"dependencyvendor/dependencyname": "dependencyversion"

and we use master as the only version available2.

This is it: now we only need to create the command to install everything.

The installation command

The Install command will be called with install from the command line, and executes 4 sub-tasks to finish the installation process:

This command takes a DependencyContainer argument in the constructor to extract the dependencies needed to be installed:

Command/Install.php
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<?php

use Symfony\Component\Console\Command\Command;
use Symfony\Component\Console\Output\OutputInterface;
use Symfony\Component\Console\Input\InputInterface;
use Symfony\Component\Process\Process;

class Install extends Command
{
    protected $installDir;
    protected $failingProcess;
    protected $dependenciesContainer;

    public function __construct(DependencyContainer $dependenciesContainer)
    {
        parent::__construct();

        $this->dependenciesContainer = $dependenciesContainer;
    }

    protected function execute(InputInterface $input, OutputInterface $output)
    {
        if ($this->createInstallationDirectory($output)
         && $this->downloadComposer($output)
         && $this->generateJson($output)
         && $this->install($output)) {
            $output->writeln('<info>MISSION ACCOMPLISHED</info>');
        } else {
            $output->writeln('<error>Nasty error happened :\'-(</error>');

            if ($this->failingProcess instanceOf Process) {
                $output->writeln('<error>%s</error>', $this->failingProcess->getErrorOutput());
            }
        }
    }

    protected function configure()
    {
        $this
            ->setName('install')
        ;
    }
}

as you see we execute this 4 tasks and, if an error happens, we output an error, otherwise a confirmation message tells the user that everything went fine.

If a failure happens, we get the error message thanks to the Process method getErrorOutput().

Let’s see how the tasks are implemented in this class: first of all, we need a createInstallationDirectory() method that launches a new mkdir process and returns a boolean value, indicating the successfulness of the process; before returning false, the class’ internal attribute $failingProcess is updated:

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<?php
...

protected function createInstallationDirectory(OutputInterface $output)
{
    $dialog             = $this->getHelperSet()->get('dialog');
    $this->installDir   = $dialog->ask($output, '<question>Please specify a non-existing directory to start the installation</question>');

    if (!is_dir($this->installDir)) {
        $mkdir = new Process(sprintf('mkdir -p %s', $this->installDir));
        $mkdir->run();

        if ($mkdir->isSuccessful()) {
            $output->writeln(sprintf('<info>Directory %s succesfully  created</info>', $this->installDir));

            return true;
        }
    }

    $this->failingProcess = $mkdir;
    return false;
}

As you see, the user will be asked to provide an $installDir in which we are going to execute the whole process.

Now we need to create the downloadComposer() method, which uses wget to put composer.phar in the installation directory:

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<?php
...

protected function downloadComposer(OutputInterface $output)
{
    $wget = new Process(sprintf('wget getcomposer.org/composer.phar -O %s/composer.phar', $this->installDir, $this->installDir));
    $wget->run();

    if ($wget->isSuccessful()) {
        $output->writeln('<info>Downloaded composer in the installation directory</info>');

        return true;
    }

    $this->failingProcess = $wget;
    return false;
}

Then we generate a composer.json in the installation directory:

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<?php
...

protected function generateJson(OutputInterface $output)
{
    $skeleton       = file_get_contents(__DIR__ . "/../composer.s");
    $dependencies   = implode(',', $this->dependenciesContainer->getDependencies());
    $skeleton       = str_replace('PLACEHOLDER', $dependencies, $skeleton);

    if (file_put_contents($this->installDir . "/composer.json", $skeleton)) {
        $output->writeln('<info>composer.json has been generated</info>');

        return true;
    }

    return false;
}

Note that you will need a template file to do so:

composer.s
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{
    "require": {
        PLACEHOLDER
    }
}

The last step consists in launching a new process which runs the usual composer’s installation process on the installation directory:

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<?php
...

protected function install(OutputInterface $output)
{
    $install = new Process(sprintf('cd %s && php composer.phar install', $this->installDir));
    $install->run();

    if ($install->isSuccessful()) {
        $output->writeln('<info>Packages succesfully installed</info>');

        return true;
    }

    $this->failingProcess = $install;
    return false;
}

This is the console output for generating a new project which depends on symfony/yaml and symfony/dom-crawler:

The auto-generated composer.json will look like:

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{
    "require": {
        "symfony/yaml": "master","symfony/dom-crawler": "master"
    }
}

Conclusion

As said, this implementation is pretty naive and can definitely be improved: but with a couple classes and basic logic you are able to write a powerful tool that doesn’t require a web frontend and runs directly from the command line with a pure implementation in PHP, thanks to the Symfony2 components.

Notes
  1. The Process component will be used to execute shell commands directly from PHP ↩
  2. Tip: if you want, you can add the code to show the user another dialog to indicate the dependency version, and use master as a fallback ↩

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