How to stream a big file through Slim


#1

Hi,

I have some big files I want to stream to the user without exceeding the memory limit. Is this possible with Slim 3 out of the box?

I found some topics like this one : http://help.slimframework.com/discussions/questions/1579-is-there-a-way-to-stream-the-response-with-slim , but is there a cleaner way, now that Slim 3 is released?

Similar question : Is there a way to use a generator function as a response body? This way, we could yield some values without reaching the memory limit? I ask this question because I also want a truncated version of the file (a log), with a header indicating that only the last lines are shown.

I thought of something like this:

function writer() {
    $file = fopen("/path/to/file", 'rb');
    yield "------\n";
    yield "This is a ";
    yield "sample header.";
    yield "------\n";
    while($chunk = fread($file, 1024)) {
        yield $chunk;
    }
    fclose($file);
}

Large output with Slim 3
#2

The App::respond() method in Slim 3 reads the data in chunks of 4096 bytes by default (set in the responseChunkSize setting). In the route you can disable output buffering (or do this for the full application). A file could be streamed as follows:

$app->get('/bigfile', function($request, $response) {
    $fh = fopen('path/to/bigfile', 'rb');
    $stream = new Slim\Http\Stream($fh);
    return $response
            ->withBody($stream)
            ->withHeader('Content-Type', 'audio/flac');
})->setOutputBuffering(false);

Note that the full file may still get buffered in memory by PHP if output buffering is set to On. I don’t think there is way yet in Slim 3 to periodically flush the output buffer to overcome this.

For your second question, you could look into implementing StreamInterface to encapsulate only reading the first part of the log file. Slim provides an implementation in Slim\Http\Stream, that you can probably extend for this end.


#3

Thanks for your reply, the Stream works well for this task.

I did my own implementation for a data Stream using a string Generator

<?php
use Psr\Http\Message\StreamInterface;

class TextGeneratorStream implements StreamInterface
{
    /** @var \Generator $generator */
    private $generator;

    /** @var string $buffer */
    private $buffer = '';

    /** @var bool $isClosed */
    private $isClosed = false;

    /** @var int $bytesRead */
    private $bytesRead = 0;

    public function __construct(\Generator $generator)
    {
        $this->generator = $generator;
    }

    /**
     * Reads all data from the stream into a string, from the beginning to end.
     *
     * This method MUST attempt to seek to the beginning of the stream before
     * reading data and read the stream until the end is reached.
     *
     * Warning: This could attempt to load a large amount of data into memory.
     *
     * This method MUST NOT raise an exception in order to conform with PHP's
     * string casting operations.
     *
     * @see http://php.net/manual/en/language.oop5.magic.php#object.tostring
     * @return string
     */
    public function __toString()
    {
        if($this->isClosed) {
            return '';
        }

        try {
            $this->generator->rewind(); // Will throw if not at the beginning
            return $this->getContents();
        } catch (\Throwable $e) {
            return '';
        }
    }

    /**
     * Closes the stream and any underlying resources.
     *
     * @return void
     */
    public function close()
    {
        $this->buffer = '';
        $this->isClosed = true;
    }

    /**
     * Separates any underlying resources from the stream.
     *
     * After the stream has been detached, the stream is in an unusable state.
     *
     * @return resource|null Underlying PHP stream, if any
     */
    public function detach()
    {
        return null;
    }

    /**
     * Get the size of the stream if known.
     *
     * @return int|null Returns the size in bytes if known, or null if unknown.
     */
    public function getSize()
    {
        return null;
    }

    /**
     * Returns the current position of the file read/write pointer
     *
     * @return int Position of the file pointer
     * @throws \RuntimeException on error.
     */
    public function tell()
    {
        return $this->bytesRead;
    }

    /**
     * Returns true if the stream is at the end of the stream.
     *
     * @return bool
     */
    public function eof()
    {
        return $this->buffer === '' && !$this->generator->valid();
    }

    /**
     * Returns whether or not the stream is seekable.
     *
     * @return bool
     */
    public function isSeekable()
    {
        return false;
    }

    /**
     * Seek to a position in the stream.
     *
     * @link http://www.php.net/manual/en/function.fseek.php
     * @param int $offset Stream offset
     * @param int $whence Specifies how the cursor position will be calculated
     *     based on the seek offset. Valid values are identical to the built-in
     *     PHP $whence values for `fseek()`.  SEEK_SET: Set position equal to
     *     offset bytes SEEK_CUR: Set position to current location plus offset
     *     SEEK_END: Set position to end-of-stream plus offset.
     * @throws \RuntimeException on failure.
     */
    public function seek($offset, $whence = SEEK_SET)
    {
        throw new \RuntimeException('Unable to seek');
    }

    /**
     * Seek to the beginning of the stream.
     *
     * If the stream is not seekable, this method will raise an exception;
     * otherwise, it will perform a seek(0).
     *
     * @see seek()
     * @link http://www.php.net/manual/en/function.fseek.php
     * @throws \RuntimeException on failure.
     */
    public function rewind()
    {
        $this->seek(0);
    }

    /**
     * Returns whether or not the stream is writable.
     *
     * @return bool
     */
    public function isWritable()
    {
        return false;
    }

    /**
     * Write data to the stream.
     *
     * @param string $string The string that is to be written.
     * @return int Returns the number of bytes written to the stream.
     * @throws \RuntimeException on failure.
     */
    public function write($string)
    {
        throw new \RuntimeException('Unable to write');
    }

    /**
     * Returns whether or not the stream is readable.
     *
     * @return bool
     */
    public function isReadable()
    {
        return true;
    }

    /**
     * Read data from the stream.
     *
     * @param int $length Read up to $length bytes from the object and return
     *     them. Fewer than $length bytes may be returned if underlying stream
     *     call returns fewer bytes.
     * @return string Returns the data read from the stream, or an empty string
     *     if no bytes are available.
     * @throws \RuntimeException if an error occurs.
     */
    public function read($length)
    {
        if($this->isClosed) {
           throw new \RuntimeException('Stream is closed');
        }

        // If there is not enough bytes in the string
        if(strlen($this->buffer) < $length) {
            // Get the next value and store it into the buffer
            $this->generator->next();
            if($this->generator->valid()) {
                $this->buffer = $this->buffer . $this->generator->current();
            }
        }

        $result = mb_strcut($this->buffer, 0, $length);
        $this->bytesRead = $this->bytesRead + strlen($result);
        $this->buffer = mb_substr($this->buffer, mb_strlen($result));

        return $result;
    }

    /**
     * Returns the remaining contents in a string
     *
     * @return string
     * @throws \RuntimeException if unable to read or an error occurs while
     *     reading.
     */
    public function getContents()
    {
        $content = '';
        while(!$this->eof()) {
            $content = $content . $this->read(1024);
        }

        return $content;
    }

    /**
     * Get stream metadata as an associative array or retrieve a specific key.
     *
     * The keys returned are identical to the keys returned from PHP's
     * stream_get_meta_data() function.
     *
     * @link http://php.net/manual/en/function.stream-get-meta-data.php
     * @param string $key Specific metadata to retrieve.
     * @return array|mixed|null Returns an associative array if no key is
     *     provided. Returns a specific key value if a key is provided and the
     *     value is found, or null if the key is not found.
     */
    public function getMetadata($key = null)
    {
        return null;
    }
}

#4

Looks good to me. Glad to know it works.