轻量级解析.env文件的类库，轻量到只需要一个类文件，可用于生产环境

浏览次数:264 日期:2021-02-22 22:27:00

### 背景
Laravel读取.env文件配置时，业务层里面访问一个配置项则Laravel底层会解析一次.env问题，那么Codeigniter4是这样的吗?最近有在读CodeIgniter4的源码,虽然现在还不是特别稳定，但是里面一些优秀的思想以及优秀的库还是值得学习的，比如其中的限流、异常界面实现、Kint调试利器等。今天再Codeigniter贴吧看到一个问答，是关于读取.env文件配置的问题，大致问题是:
> Laravel读取.env文件配置时，业务层里面访问一个配置项则Laravel底层会解析一次.env问题，那么Codeigniter4是这样的吗?

处于好奇，并且最近在看CodeIgniter，于是就研究了下CodeIngiter解析.env文件的方式，自己又稍作改动，自动解析bool、null变量。

### 代码
整个DotEnv.php文件内容如下
```php
<?php

/**
 * Environment-specific configuration
 */
class DotEnv
{
	/**
	 * The directory where the .env file can be located.
	 *
	 * @var string
	 */
	protected $path;

//--------------------------------------------------------------------

/**
	 * Builds the path to our file.
	 *
	 * @param string $path
	 * @param string $file
	 */
	public function __construct(string $path, string $file = '.env')
	{
		$this->path = rtrim($path, DIRECTORY_SEPARATOR) . DIRECTORY_SEPARATOR . $file;
	}

//--------------------------------------------------------------------

/**
	 * The main entry point, will load the .env file and process it
	 * so that we end up with all settings in the PHP environment vars
	 * (i.e. getenv(), $_ENV, and $_SERVER)
	 *
	 * @return boolean
	 */
	public function load(): bool
	{
		$vars = $this->parse();

return ($vars === null ? false : true);
	}
    
    //--------------------------------------------------------------------

/**
	 * get .env value by key name
	 *
	 * @return boolean|string|null
	 */
     
    public function getenv($name) {
        $value = $this->getVariable($name);
        switch (strtolower($value)) {
            case 'true':
            case '(true)':
                return true;
            case 'false':
            case '(false)':
                return false;
            case 'empty':
            case '(empty)':
                return '';
            case 'null':
            case '(null)':
                return;
        }
        return $value;
    }

//--------------------------------------------------------------------

/**
	 * Parse the .env file into an array of key => value
	 *
	 * @return array|null
	 */
	protected function parse(): ?array
	{
		// We don't want to enforce the presence of a .env file, they should be optional.
		if (! is_file($this->path))
		{
			return null;
		}

// Ensure the file is readable
		if (! is_readable($this->path))
		{
			throw new InvalidArgumentException("The .env file is not readable: {$this->path}");
		}

$vars = [];

$lines = file($this->path, FILE_IGNORE_NEW_LINES | FILE_SKIP_EMPTY_LINES);

foreach ($lines as $line)
		{
			// Is it a comment?
			if (strpos(trim($line), '#') === 0)
			{
				continue;
			}

// If there is an equal sign, then we know we are assigning a variable.
			if (strpos($line, '=') !== false)
			{
				list($name, $value) = $this->normaliseVariable($line);
				$vars[$name]        = $value;
				$this->setVariable($name, $value);
			}
		}

return $vars;
	}

//--------------------------------------------------------------------

/**
	 * Sets the variable into the environment. Will parse the string
	 * first to look for {name}={value} pattern, ensure that nested
	 * variables are handled, and strip it of single and double quotes.
	 *
	 * @param string $name
	 * @param string $value
	 */
	protected function setVariable(string $name, string $value = '')
	{
		if (! getenv($name, true))
		{
			putenv("$name=$value");
		}

if (empty($_ENV[$name]))
		{
			$_ENV[$name] = $value;
		}

if (empty($_SERVER[$name]))
		{
			$_SERVER[$name] = $value;
		}
	}

//--------------------------------------------------------------------

/**
	 * Parses for assignment, cleans the $name and $value, and ensures
	 * that nested variables are handled.
	 *
	 * @param string $name
	 * @param string $value
	 *
	 * @return array
	 */
	protected function normaliseVariable(string $name, string $value = ''): array
	{
		// Split our compound string into its parts.
		if (strpos($name, '=') !== false)
		{
			list($name, $value) = explode('=', $name, 2);
		}

$name  = trim($name);
		$value = trim($value);

// Sanitize the name
		$name = str_replace(['export', '\'', '"'], '', $name);

// Sanitize the value
		$value = $this->sanitizeValue($value);

$value = $this->resolveNestedVariables($value);

return [
			$name,
			$value,
		];
	}

//--------------------------------------------------------------------

/**
	 * Strips quotes from the environment variable value.
	 *
	 * This was borrowed from the excellent phpdotenv with very few changes.
	 * https://github.com/vlucas/phpdotenv
	 *
	 * @param string $value
	 *
	 * @return string
	 * @throws InvalidArgumentException
	 */
	protected function sanitizeValue(string $value): string
	{
		if (! $value)
		{
			return $value;
		}

// Does it begin with a quote?
		if (strpbrk($value[0], '"\'') !== false)
		{
			// value starts with a quote
			$quote        = $value[0];
			$regexPattern = sprintf(
					'/^
					%1$s          # match a quote at the start of the value
					(             # capturing sub-pattern used
								  (?:          # we do not need to capture this
								   [^%1$s\\\\] # any character other than a quote or backslash
								   |\\\\\\\\   # or two backslashes together
								   |\\\\%1$s   # or an escaped quote e.g \"
								  )*           # as many characters that match the previous rules
					)             # end of the capturing sub-pattern
					%1$s          # and the closing quote
					.*$           # and discard any string after the closing quote
					/mx', $quote
			);

$value = preg_replace($regexPattern, '$1', $value);
			$value = str_replace("\\$quote", $quote, $value);
			$value = str_replace('\\\\', '\\', $value);
		}
		else
		{
			$parts = explode(' #', $value, 2);

$value = trim($parts[0]);

// Unquoted values cannot contain whitespace
			if (preg_match('/\s+/', $value) > 0)
			{
				throw new InvalidArgumentException('.env values containing spaces must be surrounded by quotes.');
			}
		}

return $value;
	}

//--------------------------------------------------------------------

/**
	 *  Resolve the nested variables.
	 *
	 * Look for ${varname} patterns in the variable value and replace with an existing
	 * environment variable.
	 *
	 * This was borrowed from the excellent phpdotenv with very few changes.
	 * https://github.com/vlucas/phpdotenv
	 *
	 * @param string $value
	 *
	 * @return string
	 */
	protected function resolveNestedVariables(string $value): string
	{
		if (strpos($value, '$') !== false)
		{
			$value = preg_replace_callback(
				'/\${([a-zA-Z0-9_]+)}/',
				function ($matchedPatterns) {
					$nestedVariable = $this->getVariable($matchedPatterns[1]);

if (is_null($nestedVariable))
					{
						return $matchedPatterns[0];
					}

return $nestedVariable;
				},
				$value
			);
		}

return $value;
	}

//--------------------------------------------------------------------

/**
	 * Search the different places for environment variables and return first value found.
	 *
	 * This was borrowed from the excellent phpdotenv with very few changes.
	 * https://github.com/vlucas/phpdotenv
	 *
	 * @param string $name
	 *
	 * @return string|null
	 */
	protected function getVariable(string $name)
	{
		switch (true)
		{
			case array_key_exists($name, $_ENV):
				return $_ENV[$name];
			case array_key_exists($name, $_SERVER):
				return $_SERVER[$name];
			default:
				$value = getenv($name);

// switch getenv default to null
				return $value === false ? null : $value;
		}
	}

//--------------------------------------------------------------------
}

```
.env文件内容如下

```shell

# app配置
APP_DEBUG = False
APP_URL=http://localhost
APP_NAME = "json 博客" #值有空格等特殊字符，用引号括起来

#数据库配置
DB_HOST=localhost  #数据库名,这是注释
DB_PORT=3306
DB_DATABASE=demo
DB_USERNAME=root
DB_PASSWORD=root
DB_DSN = "mysql://${DB_USERNAME}:${DB_PASSWORD}@${DB_HOST}/${DB_DATABASE}"

#redis配置
REDIS_HOST=127.0.0.1
REDIS_PASSWORD=null
REDIS_PORT=6379
REDIS_PREFIX=

#这是注释

```

### 使用方式

```php
require_once './DotEnv.php';

$env = new DotEnv('./');//参数是.env文件所在目录
$env->load();

var_dump($env->getenv("APP_NAME"));
var_dump($env->getenv("APP_DEBUG"));//自动解析bool结果true
var_dump($env->getenv("DB_DSN"));//支持嵌套变量
var_dump($env->getenv("REDIS_PASSWORD"));//自动解析null字符串为null值
```

### 输出结果
```shell
string(11) "json 博客"
bool(false)
string(32) "mysql://root:root@localhost/demo"
NULL
```

### 注意
- 如果值里面有空格需要用单引号、双引号引用起来
- 支持值嵌套，用${xx}表示变量
- 以#开头的行是注释，不会解析
- 行内支持注释，#后面的不会解析为value
- False、false、FALSE解析成false布尔值
- True、true、TRUE解析成true布尔值
- null字符串解析成null类型值

最后更新时间为: 4个月前 (2021-02-22 22:27:00)