Example of PHP streaming pngquant

phpquant.php

<?php
  $new_path = '/path/to/input.png';

  $cmd = 'pngquant -';
  $descriptorspec = array(
    0 => array("pipe", "r"),  // stdin is a pipe that the child will read from
    1 => array("pipe", "w"),  // stdout is a pipe that the child will write to
    2 => array("file", "/tmp/error-output.txt", "a") // stderr is a file to write to
  );
  $process = proc_open($cmd, $descriptorspec, $pipes);

  if (is_resource($process)) {

    fwrite($pipes[0], file_get_contents($new_path)); // file_get_contents('php://stdin')
    fclose($pipes[0]);

    $content = stream_get_contents($pipes[1]);
    fclose($pipes[1]);

    file_put_contents($new_path . '-min.png', $content);

    $return_value = proc_close($process);

    header('Content-type: image/png');
    echo $content;
  }