Real simple Webp on demand based on cwebp

webp-on-demand.php

<?php

/******************
 * .htaccess exemple
 ******************

<IfModule mod_rewrite.c>
  RewriteEngine On

  # Redirect to existing converted image in cache-dir (if browser supports webp)
  RewriteCond %{HTTP_ACCEPT} image/webp
  RewriteCond %{REQUEST_FILENAME} -f
  RewriteCond %{REQUEST_FILENAME}.webp -f
  RewriteRule ^/?(.+)\.(jpe?g|png)$ /$1.$2.webp [NC,T=image/webp,E=EXISTING:1,E=ADDVARY:1,L]

  # Redirect images to webp-on-demand.php (if browser supports webp)
  RewriteCond %{HTTP_ACCEPT} image/webp
  RewriteCond %{REQUEST_FILENAME} -f
  RewriteRule ^/?(.+)\.(jpe?g|png)$ /images/webp-on-demand.php?path=/$1.$2 [NC,L,E=REQFN:%{REQUEST_FILENAME}]

  # Make sure that browsers which does not support webp also gets the Vary:Accept header
  # when requesting images that would be redirected to webp on browsers that does.
  <IfModule mod_headers.c>
    <FilesMatch "(?i)\.(jpe?g|png)$">
      Header append "Vary" "Accept"
    </FilesMatch>
  </IfModule>

</IfModule>

*/

ignore_user_abort(true);
set_time_limit(90);

$vroot = realpath(dirname(__FILE__));

function command_exist($cmd) {
  $return = shell_exec(sprintf("which %s", escapeshellarg($cmd)));

  if (empty($return)) {
    $return = false;
  }

  return trim($return);
}

$nice = command_exist('nice');
$imgopt = command_exist('imgopt');
$cwebp = command_exist('cwebp');

if ($nice === false) {
  $nice = '';
} else {
  // using full path to nice bugs cwebp
  $nice = $nice . ' ';
}

if ($cwebp === false) {
  http_response_code(500);
  die("Command cwebp could not be found in PATH: ".getenv('PATH'));
} else {
  $cwebp = $nice . $cwebp;
}

if ($imgopt !== false) {
  $imgopt = $nice . $imgopt;
}

if ($_GET['path']) {
  $path =  realpath(dirname(__FILE__).$_GET["path"]);
} else {
  $path =  realpath(dirname(__FILE__).$_SERVER["PATH_INFO"]);
}

if (
  substr($path, 0, strlen($vroot)) !== $vroot // path outside of vroot
  ) {
  http_response_code(404);
  die('Error 404');
}

$ext = strtolower(pathinfo($path, PATHINFO_EXTENSION));

if (
  !in_array($ext, Array('jpg', 'jpeg', 'png'))
) {
  http_response_code(400);
  die('Can only be used with jpg/jpeg or png!');
}

if( strpos( $_SERVER['HTTP_ACCEPT'], 'image/webp' ) === false ) {
  // webp not supported, lets send original

  header('Last-Modified: '.gmdate('D, d M Y H:i:s', filemtime($path)).' GMT', true, 200);

  if($ext === 'png') {
    header('Content-Type: image/png');
  } else {
    header('Content-Type: image/jpeg');
  }

  header('Content-Length: ' . filesize($path));

  print file_get_contents($path);
} else {
  $webp_path = $path . '.webp';
  $lock = $webp_path . '.lock';

  // credit https://stackoverflow.com/questions/5449395/file-locking-in-php
  // atomic, simpler and faster than flock!
  // https://docstore.mik.ua/orelly/webprog/pcook/ch18_25.htm

  // loop until we can successfully make the lock directory

  $locked = 0;

  while (! $locked) {
    if (
      @mkdir($lock, 0777)
      || time() - filemtime($lock.'/.') > 30 // if lock is older than 30s bypass it
    ) {
      $locked = 1;
    } else {
      sleep(1);
    }
  }

  // if during lock other process yet had converted the file
  if(
    file_exists($webp_path)
    && filesize($webp_path) > 0
  ) {
    header('Last-Modified: '.gmdate('D, d M Y H:i:s', filemtime($webp_path)).' GMT', true, 200);
    header('Content-Type: image/webp');
    header('Content-Length: ' . filesize($webp_path));

    print file_get_contents($webp_path);
  } else {
    touch($lock); // in case of dead lock, try limit other waiting running in here

    if ($imgopt !== false) {
      // run imgopt on original file - strip out exif and aggressively recompress png
      $cmd = $imgopt . ' ' . $path;
      $output = null;
      $retval = null;
      exec($cmd, $output, $retval);
    }

    if($ext == 'jpg' || $ext === 'jpeg') {
      $cmd = $cwebp . ' -quiet -z 6 -q 80 -o "'. $webp_path .'" -- "'. $path .'"';
    } else {
      // png
      $cmd = $cwebp . ' -quiet -z 6 -alpha_q 80 -near_lossless 60 -lossless -o "' . $webp_path .'" -- "'. $path .'"';
    }

    $output = null;
    $retval = null;
    exec($cmd, $output, $retval);

    if(
      $retval === 0
      && file_exists($webp_path)
      && filesize($webp_path) > 0
    ) {
      header('Last-Modified: '.gmdate('D, d M Y H:i:s', filemtime($webp_path)).' GMT', true, 200);
      header('Content-Type: image/webp');
      header('Content-Length: ' . filesize($webp_path));

      print file_get_contents($webp_path);
    } else {
      http_response_code(500);
      print $cmd;
      print '<pre>';
      print_r($output);
      print '</pre>';
    }
  }

  // release lock
  @rmdir($lock);
}