# composer/xdebug-handler

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Restart a CLI process without loading the Xdebug extension.

Originally written as part of [composer/composer](https://github.com/composer/composer),
now extracted and made available as a stand-alone library.

## Installation

Install the latest version with:

```bash
$ composer require composer/xdebug-handler
```

## Requirements

* PHP 5.3.2 minimum, although functionality is disabled below PHP 5.4.0. Using the latest PHP version is highly recommended.

## Basic Usage
```php
use Composer\XdebugHandler\XdebugHandler;

$xdebug = new XdebugHandler('myapp');
$xdebug->check();
unset($xdebug);
```

The constructor takes two parameters:

#### _$envPrefix_
This is used to create distinct environment variables and is upper-cased and prepended to default base values. The above example enables the use of:

- `MYAPP_ALLOW_XDEBUG=1` to override automatic restart and allow Xdebug
- `MYAPP_ORIGINAL_INIS` to obtain ini file locations in a restarted process

#### _$colorOption_
This optional value is added to the restart command-line and is needed to force color output in a piped child process. Only long-options are supported, for example `--ansi` or `--colors=always` etc.

If the original command-line contains an argument that pattern matches this value (for example `--no-ansi`, `--colors=never`) then _$colorOption_ is ignored.

If the pattern match ends with `=auto` (for example `--colors=auto`), the argument is replaced by _$colorOption_. Otherwise it is added at either the end of the command-line, or preceding the first double-dash `--` delimiter.

## Advanced Usage

* [How it works](#how-it-works)
* [Limitations](#limitations)
* [Helper methods](#helper-methods)
* [Setter methods](#setter-methods)
* [Process configuration](#process-configuration)
* [Troubleshooting](#troubleshooting)
* [Extending the library](#extending-the-library)

### How it works

A temporary ini file is created from the loaded (and scanned) ini files, with any references to the Xdebug extension commented out. Current ini settings are merged, so that most ini settings made on the command-line or by the application are included (see [Limitations](#limitations))

* `MYAPP_ALLOW_XDEBUG` is set with internal data to flag and use in the restart.
* The command-line and environment are [configured](#process-configuration) for the restart.
* The application is restarted in a new process.
    * The restart settings are stored in the environment.
    * `MYAPP_ALLOW_XDEBUG` is unset.
    * The application runs and exits.
* The main process exits with the exit code from the restarted process.

#### Signal handling
From PHP 7.1 with the pcntl extension loaded, asynchronous signal handling is automatically enabled. `SIGINT` is set to `SIG_IGN` in the parent
process and restored to `SIG_DFL` in the restarted process (if no other handler has been set).

From PHP 7.4 on Windows, `CTRL+C` and `CTRL+BREAK` handling is ignored in the parent process and automatically enabled in the restarted process.

### Limitations
There are a few things to be aware of when running inside a restarted process.

* Extensions set on the command-line will not be loaded.
* Ini file locations will be reported as per the restart - see [getAllIniFiles()](#getallinifiles).
* Php sub-processes may be loaded with Xdebug enabled - see [Process configuration](#process-configuration).

### Helper methods
These static methods provide information from the current process, regardless of whether it has been restarted or not.

#### _getAllIniFiles()_
Returns an array of the original ini file locations. Use this instead of calling `php_ini_loaded_file` and `php_ini_scanned_files`, which will report the wrong values in a restarted process.

```php
use Composer\XdebugHandler\XdebugHandler;

$files = XdebugHandler::getAllIniFiles();

# $files[0] always exists, it could be an empty string
$loadedIni = array_shift($files);
$scannedInis = $files;
```

These locations are also available in the `MYAPP_ORIGINAL_INIS` environment variable. This is a path-separated string comprising the location returned from `php_ini_loaded_file`, which could be empty, followed by locations parsed from calling `php_ini_scanned_files`.

#### _getRestartSettings()_
Returns an array of settings that can be used with PHP [sub-processes](#sub-processes), or null if the process was not restarted.

```php
use Composer\XdebugHandler\XdebugHandler;

$settings = XdebugHandler::getRestartSettings();
/**
 * $settings: array (if the current process was restarted,
 * or called with the settings from a previous restart), or null
 *
 *    'tmpIni'      => the temporary ini file used in the restart (string)
 *    'scannedInis' => if there were any scanned inis (bool)
 *    'scanDir'     => the original PHP_INI_SCAN_DIR value (false|string)
 *    'phprc'       => the original PHPRC value (false|string)
 *    'inis'        => the original inis from getAllIniFiles (array)
 *    'skipped'     => the skipped version from getSkippedVersion (string)
 */
```

#### _getSkippedVersion()_
Returns the Xdebug version string that was skipped by the restart, or an empty value if there was no restart (or Xdebug is still loaded, perhaps by an extending class restarting for a reason other than removing Xdebug).

```php
use Composer\XdebugHandler\XdebugHandler;

$version = XdebugHandler::getSkippedVersion();
# $version: '2.6.0' (for example), or an empty string
```

### Setter methods
These methods implement a fluent interface and must be called before the main `check()` method.

#### _setLogger($logger)_
Enables the output of status messages to an external PSR3 logger. All messages are reported with either `DEBUG` or `WARNING` log levels. For example (showing the level and message):

```
// Restart overridden
DEBUG    Checking MYAPP_ALLOW_XDEBUG
DEBUG    The Xdebug extension is loaded (2.5.0)
DEBUG    No restart (MYAPP_ALLOW_XDEBUG=1)

// Failed restart
DEBUG    Checking MYAPP_ALLOW_XDEBUG
DEBUG    The Xdebug extension is loaded (2.5.0)
WARNING  No restart (Unable to create temp ini file at: ...)
```

Status messages can also be output with `XDEBUG_HANDLER_DEBUG`. See [Troubleshooting](#troubleshooting).

#### _setMainScript($script)_
Sets the location of the main script to run in the restart. This is only needed in more esoteric use-cases, or if the `argv[0]` location is inaccessible. The script name `--` is supported for standard input.

#### _setPersistent()_
Configures the restart using [persistent settings](#persistent-settings), so that Xdebug is not loaded in any sub-process.

Use this method if your application invokes one or more PHP sub-process and the Xdebug extension is not needed. This avoids the overhead of implementing specific [sub-process](#sub-processes) strategies.

Alternatively, this method can be used to set up a default _Xdebug-free_ environment which can be changed if a sub-process requires Xdebug, then restored afterwards:

```php
function SubProcessWithXdebug()
{
    $phpConfig = new Composer\XdebugHandler\PhpConfig();

    # Set the environment to the original configuration
    $phpConfig->useOriginal();

    # run the process with Xdebug loaded
    ...

    # Restore Xdebug-free environment
    $phpConfig->usePersistent();
}
```

### Process configuration
The library offers two strategies to invoke a new PHP process without loading Xdebug, using either _standard_ or _persistent_ settings. Note that this is only important if the application calls a PHP sub-process.

#### Standard settings
Uses command-line options to remove Xdebug from the new process only.

* The -n option is added to the command-line. This tells PHP not to scan for additional inis.
* The temporary ini is added to the command-line with the -c option.

>_If the new process calls a PHP sub-process, Xdebug will be loaded in that sub-process (unless it implements xdebug-handler, in which case there will be another restart)._

This is the default strategy used in the restart.

#### Persistent settings
Uses environment variables to remove Xdebug from the new process and persist these settings to any sub-process.

* `PHP_INI_SCAN_DIR` is set to an empty string. This tells PHP not to scan for additional inis.
* `PHPRC` is set to the temporary ini.

>_If the new process calls a PHP sub-process, Xdebug will not be loaded in that sub-process._

This strategy can be used in the restart by calling [setPersistent()](#setpersistent).

#### Sub-processes
The `PhpConfig` helper class makes it easy to invoke a PHP sub-process (with or without Xdebug loaded), regardless of whether there has been a restart.

Each of its methods returns an array of PHP options (to add to the command-line) and sets up the environment for the required strategy. The [getRestartSettings()](#getrestartsettings) method is used internally.

* `useOriginal()` - Xdebug will be loaded in the new process.
* `useStandard()` - Xdebug will **not** be loaded in the new process - see [standard settings](#standard-settings).
* `userPersistent()` - Xdebug will **not** be loaded in the new process - see [persistent settings](#persistent-settings)

If there was no restart, an empty options array is returned and the environment is not changed.

```php
use Composer\XdebugHandler\PhpConfig;

$config = new PhpConfig;

$options = $config->useOriginal();
# $options:     empty array
# environment:  PHPRC and PHP_INI_SCAN_DIR set to original values

$options = $config->useStandard();
# $options:     [-n, -c, tmpIni]
# environment:  PHPRC and PHP_INI_SCAN_DIR set to original values

$options = $config->usePersistent();
# $options:     empty array
# environment:  PHPRC=tmpIni, PHP_INI_SCAN_DIR=''
```

### Troubleshooting
The following environment settings can be used to troubleshoot unexpected behavior:

* `XDEBUG_HANDLER_DEBUG=1` Outputs status messages to `STDERR`, if it is defined, irrespective of any PSR3 logger. Each message is prefixed `xdebug-handler[pid]`, where pid is the process identifier.

* `XDEBUG_HANDLER_DEBUG=2` As above, but additionally saves the temporary ini file and reports its location in a status message.

### Extending the library
The API is defined by classes and their accessible elements that are not annotated as @internal. The main class has two protected methods that can be overridden to provide additional functionality:

#### _requiresRestart($isLoaded)_
By default the process will restart if Xdebug is loaded. Extending this method allows an application to decide, by returning a boolean (or equivalent) value. It is only called if `MYAPP_ALLOW_XDEBUG` is empty, so it will not be called in the restarted process (where this variable contains internal data), or if the restart has been overridden.

Note that the [setMainScript()](#setmainscriptscript) and [setPersistent()](#setpersistent) setters can be used here, if required.

#### _restart($command)_
An application can extend this to modify the temporary ini file, its location given in the `tmpIni` property. New settings can be safely appended to the end of the data, which is `PHP_EOL` terminated.

Note that the `$command` parameter is the escaped command-line string that will be used for the new process and must be treated accordingly.

Remember to finish with `parent::restart($command)`.

#### Example
This example demonstrates two ways to extend basic functionality:

* To avoid the overhead of spinning up a new process, the restart is skipped if a simple help command is requested.

* The application needs write-access to phar files, so it will force a restart if `phar.readonly` is set (regardless of whether Xdebug is loaded) and change this value in the temporary ini file.

```php
use Composer\XdebugHandler\XdebugHandler;
use MyApp\Command;

class MyRestarter extends XdebugHandler
{
    private $required;

    protected function requiresRestart($isLoaded)
    {
        if (Command::isHelp()) {
            # No need to disable Xdebug for this
            return false;
        }

        $this->required = (bool) ini_get('phar.readonly');
        return $isLoaded || $this->required;
    }

    protected function restart($command)
    {
        if ($this->required) {
            # Add required ini setting to tmpIni
            $content = file_get_contents($this->tmpIni);
            $content .= 'phar.readonly=0'.PHP_EOL;
            file_put_contents($this->tmpIni, $content);
        }

        parent::restart($command);
    }
}
```

## License
composer/xdebug-handler is licensed under the MIT License, see the LICENSE file for details.
