/**
	 * Determine HTTP proxy from environment settings respecting
	 * 'http_proxy' and 'no_proxy' environment variables
	 */
	public static function envProxy( $url )
	{
		if ( $proxy = getenv( "http_proxy" ) )
		{
			$useproxy = true;
			if ( $url && ( $noproxy = preg_split( "#\s*,\s*#is", getenv( "no_proxy" ) ) ) )
			{
				foreach ( $noproxy as $n )
				{
					if ( preg_match('#(\d+)\.(\d+)\.(\d+)\.(\d+)/(\d+)#s', $n, $m) &&
						preg_match('#^[a-z0-9_]+://(?:[^/]*:[^/]*@)?([^/@]+)(?:/|$|\?)#is', $url, $ip) )
					{
						$mask = array(
							max( 0x100 - ( 1 << max(  8-$m[5], 0 ) ), 0 ),
							max( 0x100 - ( 1 << max( 16-$m[5], 0 ) ), 0 ),
							max( 0x100 - ( 1 << max( 24-$m[5], 0 ) ), 0 ),
							max( 0x100 - ( 1 << max( 32-$m[5], 0 ) ), 0 ),
						);
						$ip = @gethostbyname( $ip[1] );
						if ( preg_match( '#(\d+)\.(\d+)\.(\d+)\.(\d+)#s', $ip, $ipm ) &&
							( intval( $ipm[1] ) & $mask[0] ) == intval( $m[1] ) &&
							( intval( $ipm[2] ) & $mask[1] ) == intval( $m[2] ) &&
							( intval( $ipm[3] ) & $mask[2] ) == intval( $m[3] ) &&
							( intval( $ipm[4] ) & $mask[3] ) == intval( $m[4] ) )
						{
							$useproxy = false;
							break;
						}
					}
					else
					{
						$n = preg_replace( '/#.*$/is', '', $n );
						$n = preg_quote( $n );
						$n = str_replace( '\\*', '.*', $n );
						if ( preg_match( '#'.$n.'#is', $url ) )
						{
							$useproxy = false;
							break;
						}
					}
				}
			}
			if ( $useproxy )
			{
				$proxy = preg_replace( '#^http://#is', '', $proxy );
				$proxy = preg_replace( '#/*$#is', '', $proxy );
			}
			else
				$proxy = '';
			return $proxy;
		}
		return NULL;
	}