下面整理了幾個作法，可參考自行試做看看，整合成自己需要的。
在 PHP 的官網上，提供一個最簡單的作法，
<?php
$file = 'monkey.gif';
if (file_exists($file)) {
header('Content-Description: File Transfer');
header('Content-Type: application/octet-stream');
header('Content-Disposition: attachment; filename="'.basename($file).'"');
header('Expires: 0');
header('Cache-Control: must-revalidate');
header('Pragma: public');
header('Content-Length: ' . filesize($file));
readfile($file);
exit;
}
注意，filename 的 「"」不能少掉，因為檔名可能包含空白。
另外，參考下述網頁的討論，
Fastest Way to Serve a File Using PHP
可用 X-SendFile header，交由 Apache 下載，對於大檔案，會比較有效率。
header("X-Sendfile: $file_name");
header("Content-type: application/octet-stream");
header('Content-Disposition: attachment; filename="' . basename($file_name) . '"');$file_name is the full path on the file system.再來，可以控制下載速率，支援續傳功能
function Download($path, $speed = null, $multipart = true)
{
while (ob_get_level() > 0)
{
ob_end_clean();
}
if (is_file($path = realpath($path)) === true)
{
$file = @fopen($path, 'rb');
$size = sprintf('%u', filesize($path));
$speed = (empty($speed) === true) ? 1024 : floatval($speed);
if (is_resource($file) === true)
{
set_time_limit(0);
if (strlen(session_id()) > 0)
{
session_write_close();
}
if ($multipart === true)
{
$range = array(0, $size - 1);
if (array_key_exists('HTTP_RANGE', $_SERVER) === true)
{
$range = array_map('intval', explode('-', preg_replace('~.*=([^,]*).*~', '$1', $_SERVER['HTTP_RANGE'])));
if (empty($range[1]) === true)
{
$range[1] = $size - 1;
}
foreach ($range as $key => $value)
{
$range[$key] = max(0, min($value, $size - 1));
}
if (($range[0] > 0) || ($range[1] < ($size - 1)))
{
header(sprintf('%s %03u %s', 'HTTP/1.1', 206, 'Partial Content'), true, 206);
}
}
header('Accept-Ranges: bytes');
header('Content-Range: bytes ' . sprintf('%u-%u/%u', $range[0], $range[1], $size));
}
else
{
$range = array(0, $size - 1);
}
header('Pragma: public');
header('Cache-Control: public, no-cache');
header('Content-Type: application/octet-stream');
header('Content-Length: ' . sprintf('%u', $range[1] - $range[0] + 1));
header('Content-Disposition: attachment; filename="' . basename($path) . '"');
header('Content-Transfer-Encoding: binary');
if ($range[0] > 0)
{
fseek($file, $range[0]);
}
while ((feof($file) !== true) && (connection_status() === CONNECTION_NORMAL))
{
echo fread($file, round($speed * 1024)); flush(); sleep(1);
}
fclose($file);
}
exit();
}
else
{
header(sprintf('%s %03u %s', 'HTTP/1.1', 404, 'Not Found'), true, 404);
}
return false;
}
The code is as efficient as it can be, it closes the session handler so that other PHP scripts can run concurrently for the same user / session. It also supports serving downloads in ranges (which is also what Apache does by default I suspect), so that people can pause/resume downloads and also benefit from higher download speeds with download accelerators. It also allows you to specify the maximum speed (in Kbps) at which the download (part) should be served via the
$speedargument.再一個，
A better implementation, with cache support, customized http headers.
serveStaticFile($fn, array(
'headers'=>array(
'Content-Type' => 'image/x-icon',
'Cache-Control' => 'public, max-age=604800',
'Expires' => gmdate("D, d M Y H:i:s", time() + 30 * 86400) . " GMT",
)
));
function serveStaticFile($path, $options = array()) {
$path = realpath($path);
if (is_file($path)) {
if(session_id())
session_write_close();
header_remove();
set_time_limit(0);
$size = filesize($path);
$lastModifiedTime = filemtime($path);
$fp = @fopen($path, 'rb');
$range = array(0, $size - 1);
header('Last-Modified: ' . gmdate("D, d M Y H:i:s", $lastModifiedTime)." GMT");
if (( ! empty($_SERVER['HTTP_IF_MODIFIED_SINCE']) && strtotime($_SERVER['HTTP_IF_MODIFIED_SINCE']) == $lastModifiedTime ) ) {
header("HTTP/1.1 304 Not Modified", true, 304);
return true;
}
if (isset($_SERVER['HTTP_RANGE'])) {
//$valid = preg_match('^bytes=\d*-\d*(,\d*-\d*)*$', $_SERVER['HTTP_RANGE']);
if(substr($_SERVER['HTTP_RANGE'], 0, 6) != 'bytes=') {
header('HTTP/1.1 416 Requested Range Not Satisfiable', true, 416);
header('Content-Range: bytes */' . $size); // Required in 416.
return false;
}
$ranges = explode(',', substr($_SERVER['HTTP_RANGE'], 6));
$range = explode('-', $ranges[0]); // to do: only support the first range now.
if ($range[0] === '') $range[0] = 0;
if ($range[1] === '') $range[1] = $size - 1;
if (($range[0] >= 0) && ($range[1] <= $size - 1) && ($range[0] <= $range[1])) {
header('HTTP/1.1 206 Partial Content', true, 206);
header('Content-Range: bytes ' . sprintf('%u-%u/%u', $range[0], $range[1], $size));
}
else {
header('HTTP/1.1 416 Requested Range Not Satisfiable', true, 416);
header('Content-Range: bytes */' . $size);
return false;
}
}
$contentLength = $range[1] - $range[0] + 1;
//header('Content-Disposition: attachment; filename="xxxxx"');
$headers = array(
'Accept-Ranges' => 'bytes',
'Content-Length' => $contentLength,
'Content-Type' => 'application/octet-stream',
);
if(!empty($options['headers'])) {
$headers = array_merge($headers, $options['headers']);
}
foreach($headers as $k=>$v) {
header("$k: $v", true);
}
if ($range[0] > 0) {
fseek($fp, $range[0]);
}
$sentSize = 0;
while (!feof($fp) && (connection_status() === CONNECTION_NORMAL)) {
$readingSize = $contentLength - $sentSize;
$readingSize = min($readingSize, 512 * 1024);
if($readingSize <= 0) break;
$data = fread($fp, $readingSize);
if(!$data) break;
$sentSize += strlen($data);
echo $data;
flush();
}
fclose($fp);
return true;
}
else {
header('HTTP/1.1 404 Not Found', true, 404);
return false;
}
}
結論
If you wish to hide where the file is located and people with specific privilege may download the file then it is a good idea to use PHP as relay, and you have to sacrifice some CPU time to gain more security and control.
續傳 (Resume download) 在 Apache 的 X-SendFile 與 FireFox 的問題
在續傳 (Resume download) 時，瀏覽器除了會送出 HTTP_RANGE 的 header 外，還會送出其他的 header。如 Firefox 會額外送出 HTTP_IF_MATCH 和 HTTP_IF_UNMODIFIED_SINCE，使得 Apache 傳回 404 的錯誤。而 Chrome 會多送出 HTTP_IF_RANGE，但這不影響正常運作。不論如何，把這些多的 header 都拿掉，在 Apache 的設定檔，或 .htaccess 中，加入下面的設定。
# 將會造成 resume download 的 header 拿掉
SetEnvIf Range .+ HAS_RANGE_HEADER
RequestHeader unset If-Range env=HAS_RANGE_HEADER
RequestHeader unset If-Match env=HAS_RANGE_HEADER
RequestHeader unset If-Unmodified-Since env=HAS_RANGE_HEADER
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