src/Debug/FileStreamWrapper.php
public function stream_open($path, $mode, $options, &$openedPath)
    {
        if ($this->handle) {
            return false;
        }
        $useIncludePath = (bool) $options & STREAM_USE_PATH;
        $context = $this->context;
        if ($context === null) {
            $context = \stream_context_get_default();
        }
        self::restorePrev();
        if (\strpos($mode, 'r') !== false && !\file_exists($path)) {
            return false;
        } elseif (\strpos($mode, 'x') !== false && \file_exists($path)) {
            return false;
        }
        $handle = \fopen($path, $mode, $useIncludePath, $context);
        self::register();
        if ($handle === false) {
            return false;
        }
        /*
            Determine opened path
        */
        $meta = \stream_get_meta_data($handle);
        if (!isset($meta['uri'])) {
            throw new \UnexpectedValueException('Uri not in meta data');
        }
        $this->filepath = $openedPath = $meta['uri'];
        $this->handle = $handle;
        return true;
    }
public function stream_open($path, $mode, $options, &$openedPath)
    {
        if ($this->handle) {
            return false;
        }
        $useIncludePath = (bool) $options & STREAM_USE_PATH;
        $context = $this->context;
        if ($context === null) {
            $context = \stream_context_get_default();
        }
        self::restorePrev();
        if (\strpos($mode, 'r') !== false && !\file_exists($path)) {
            return false;
        } elseif (\strpos($mode, 'x') !== false && \file_exists($path)) {
            return false;
        }
        $handle = \fopen($path, $mode, $useIncludePath, $context);
        self::register();
        if ($handle === false) {
            return false;
        }
        /*
            Determine opened path
        */
        $meta = \stream_get_meta_data($handle);
        if (!isset($meta['uri'])) {
            throw new \UnexpectedValueException('Uri not in meta data');
        }
        $this->filepath = $openedPath = $meta['uri'];
        $this->handle = $handle;
        return true;
    }
Opens file or URL

@param string   $path       Specifies the file/URL that was passed to the original function.
@param string   $mode       The mode used to open the file, as detailed for fopen().
@param integers $options    Holds additional flags set by the streams API. I
@param string   $openedPath the full path of the file/resource that was actually opened

@return boolean

@see    http://php.net/manual/en/streamwrapper.stream-open.php
@throws \UnexpectedValueException