HTTP 范围请求标头可用于请求资源的特定部分。

服务器可以通过将接受范围添加到响应头来向客户端指定支持范围头，这是这样做的：

HTTP/1.1 200 Ok
accept-ranges: bytes

在流式传输音频和视频文件时使用范围标头，以便通过控件启用“跳过”。
但是，它也用于允许客户端暂停和恢复下载。

下面是从范围标题中提取单个范围的简单方法：

//Define start and end of stream
$start = 0;
$end = $file_size - 1; //Minus 1 (Byte ranges are zero-indexed)
if (preg_match('|=([0-9]+)-([0-9]+)$|', $_SERVER['HTTP_RANGE'], $matches)) {
  $start = $matches["1"];
  $end = $matches["2"] - 1;
} elseif (preg_match('|=([0-9]+)-?$|', $_SERVER['HTTP_RANGE'], $matches)) {
  //If no end-range was provided
  $start = $matches["1"];
}

//Make sure we are not out of range
if (($start > $end) || ($start > $file_size) || ($end > $file_size) || ($end <= $start)) {
  http_response_code(416);
  exit();
}

这不足以支持范围标头，但它向我们展示了如何使用正则表达式处理它。

支持范围标头

Web 服务器可能已经支持静态文件的范围标头，但是如果我们想从 PHP 提供文件，则需要实现我们自己的范围标头支持。

下面的函数将允许我们从 PHP 中“流式传输”静态文件：

function http_stream_file($file_path) {
    if (!file_exists($file_path)) {
      throw new Exception('The file did not exist');
    }
    if (($file_size = filesize($file_path)) === false) {
      throw new Exception('Unable to get filesize.');
    }

  //Define start and end of stream
  $start = 0;
  $end = $file_size - 1; //Minus 1 (Byte ranges are zero-indexed)

  //Attempt to Open file for (r) reading (b=binary safe)
  if (($fp = @fopen($file_path, 'rb')) == false) {
    throw new Exception('Unable to open file.');
  }

  //----------------------
  //Handle "range" requests
  //----------------------
  //A Range request is sent when a client requests a specific part of a file
  //such as when using the video controls or when a download is resumed.
  //We need to handle range requests in order to send back the requested part of a file.

  //Determine if the "range" Request Header was set
  if (isset($_SERVER['HTTP_RANGE'])) {

    //Parse the range header
    if (preg_match('|=([0-9]+)-([0-9]+)$|', $_SERVER['HTTP_RANGE'], $matches)) {
      $start = $matches["1"];
      $end = $matches["2"] - 1;
    } elseif (preg_match('|=([0-9]+)-?$|', $_SERVER['HTTP_RANGE'], $matches)) {
      $start = $matches["1"];
    }

    //Make sure we are not out of range
    if (($start > $end) || ($start > $file_size) || ($end > $file_size) || ($end <= $start)) {
      http_response_code(416);
      exit();
    }

    //Position the file pointer at the requested range
    fseek($fp, $start);

    //Respond with 206 Partial Content
    http_response_code(206);

    //A "content-range" response header should only be sent if the "range" header was used in the request
      $response_headers['content-range'] = 'bytes ' . $start . '-' . $end . '/' . $file_size;
  } else {
    //If the range header is not used, respond with a 200 code and start sending some content
    http_response_code(200);
  }

  //Tell the client we support range-requests
  $response_headers['accept-ranges'] = 'bytes';
  //Set the content length to whatever remains
  $response_headers['content-length'] = ($file_size - $start);

  //--------------------
  //Send the file headers
  //--------------------
  //Send the "last-modified" response header
  //and compare with the "if-modified-since" request header (if present)

  if (($timestamp = filemtime($file_path)) !== false) {
    $response_headers['last-modified'] = gmdate("D, d M Y H:i:s", $timestamp) . ' GMT';
    if ((isset($_SERVER['HTTP_IF_MODIFIED_SINCE'])) && ($_SERVER['HTTP_IF_MODIFIED_SINCE'] == $response_headers['last-modified'])) {
      http_response_code(304); //Not Modified
      exit();
    }
  }

  //Set HTTP response headers
  $response_headers['content-type'] = 'video/mp4';
  foreach ($response_headers as $header => $value) {
    header($header . ': ' . $value);
  }

  //--------------------
  //Start the file output
  //--------------------
  $buffer = 8192;
  while (!feof($fp) && ($pointer = ftell($fp)) <= $end) {

    //If next $buffer will pass $end,
    //calculate remaining size
    if ($pointer + $buffer > $end) {
      $buffer = $end - $pointer + 1;
    }
    echo @fread($fp, $buffer);
      flush();
    }
    fclose($fp);
    exit();
  }

要对驻留在同一目录中的文件调用此函数，我们可以这样做：

http_stream_file('some-video-file.mp4');