How to download large files with PHP?

Question

I spent a week to find right answer on this question. 'Right' I mean absolutely conform to existing web-standards, reliable and performance effective. Finally, I've found the solution.

All what I've found on StackOverflow (Downloading large files reliably in PHP, How to download large files through PHP script) is not works for me:

1. Both solutions are not support of range requests. It makes them not working for video and audio streaming and download resuming;

2. All examples have nothing about caching and performance;

PHP 7.0 code tested with desktop versions of Chrome, Safari, Opera and Firefox. Vivaldi test was not successful.

Answer 1

const STDOUT_CHUNK_SIZE = 128 * 1024; // Buffer size to send data to browser. MUST be less then 1/3 of PHP memory size
const CACHE_EXP_SEC = 1800;  // Cache expire time is 30 min.

$fileName = "large_video.mp4";
$contentSize = filesize($fileName);
$isAttachment = false;  // false allows to use a file as inline element of web page 

// Parse range request. Browser asks for part of file
if (isset($_SERVER["HTTP_RANGE"])) {
  list($units, $range) = explode("=", $_SERVER["HTTP_RANGE"], 2);
  if ($units !== "bytes") {
    http_response_code(416); // Requested Range Not Satisfiable
    exit;
  }
  $range = explode(",", $range, 2)[0]; // Get only first range. You can improve this ;)
  list($from, $to) = explode("-", $range, 2);
  $to = empty($to) ? ($contentSize - 1) : min(abs((int)$to), ($contentSize - 1));
  $from = (empty($from) || $to < abs((int)$from)) ? 0 : max(abs((int)$from), 0);
}
else {
  // Request for whole content
  $from = 0;
  $to = $contentSize - 1;
}

// Set response headers
if ($from > 0 || $to < ($contentSize - 1))
{
  http_response_code(206); // Partial Content
  header("Content-Type: video/mp4"));
  header("Content-Range: bytes $from-$to/$contentSize");
  header("Content-Length: " . ($from - $to + 1));
}
else {
  $etag = md5($file);  // Content is immutable but file name can be changed
  if (isset($_SERVER["HTTP_IF_NONE_MATCH"]) && trim($_SERVER["HTTP_IF_NONE_MATCH"]) === $etag) {
    http_response_code(304); // Not Modified
    setCacheHeaders($etag);
    exit;
  }

  http_response_code(200);  // Ok
  header("Content-Type: video/mp4"));
  header("Content-Length: $contentSize");
  if ($isAttachment) header("Content-Disposition: attachment; filename=\"$fileName\"");
  else header("Content-Disposition: inline");

  header("Accept-Ranges: bytes");
  setCacheHeaders($etag);
}

// Send response to client
if ($file = fopen($fileName, "rb")) {
  fseek($file, $from);
  $counter = $from;
  set_time_limit(0);
  while (!feof($file) && $counter <= $to) {
    $bytesToRead = STDOUT_CHUNK_SIZE;
    if ($counter + $bytesToRead > $to) $bytesToRead = $to - $counter + 1;
    $data = fread($file, $bytesToRead);
    $counter += $bytesToRead;
    echo $data;
    flush();
  }
fclose($file);

function setCacheHeaders(string $etag, bool $cacheEnabled = true, bool $public = true)
{
  if ($cacheEnabled) {
    header("ETag: $etag");
    $scope = $public ? "public" : "private";
    $sec = CACHE_EXP_SEC;
    $age = ($sec >= 0) ? ", max-age=$sec, s-maxage=$sec" : "";
    header("Cache-Control: $scope$age, no-transform");
  }
  else header("Cache-Control: no-cache, no-store, must-revalidate");
}