透過 fread 分塊讀取 + sleep + flush 實現應用層流控。適用於大檔案下載限速、進度條演示、防止單用戶佔滿頻寬。
<?php
$localFile = 'large.zip'; // 伺服器實際檔案
$downloadName = 'download.zip'; // 用戶看到的檔名
$rateKB = 512; // 限速 512 KB/s
if (!file_exists($localFile)) {
http_response_code(404);
exit('檔案不存在');
}
$fileSize = filesize($localFile);
// 快取控制：允許瀏覽器快取、支援斷點續傳
header('Cache-Control: public, must-revalidate');
header('Content-Type: application/octet-stream');
header('Content-Length: ' . $fileSize);
header('Content-Disposition: attachment; filename="' . $downloadName . '"');
header('Accept-Ranges: bytes'); // 聲明支援範圍請求
// 斷點續傳支援（簡易版）
if (isset($_SERVER['HTTP_RANGE'])) {
list($unit, $range) = explode('=', $_SERVER['HTTP_RANGE'], 2);
if ($unit === 'bytes') {
list($start, $end) = explode('-', $range);
$start = intval($start);
$end = $end ? intval($end) : $fileSize - 1;
header('HTTP/1.1 206 Partial Content');
header("Content-Range: bytes $start-$end/$fileSize");
header('Content-Length: ' . ($end - $start + 1));
}
}
$fp = fopen($localFile, 'rb');
if (isset($start)) fseek($fp, $start);
$bufferSize = $rateKB * 1024; // 每秒讀取位元組數
$remaining = isset($end) ? $end - $start + 1 : $fileSize;
while (!feof($fp) && $remaining > 0) {
$readSize = min($bufferSize, $remaining, 8192); // 8KB 塊
$data = fread($fp, $readSize);
echo $data;
@flush(); // 刷新 PHP 輸出緩衝
@ob_flush(); // 刷新 Web Server 緩衝
$remaining -= $readSize;
if ($remaining > 0) sleep(1); // 限速關鍵：每秒發送一次
}
fclose($fp);
| 技術 | 作用 |
|---|---|
fread($fp, $size) | 二進位讀取，避免記憶體一次載入整檔 |
flush() + ob_flush() | 雙重刷新，確保數據實時送達瀏覽器 |
sleep(1) | 應用層限速，每秒發送一個 buffer |
Accept-Ranges + HTTP_RANGE | 支援斷點續傳、多執行緒下載 |
Content-Length | 瀏覽器顯示進度條、預估剩餘時間的依據 |
$rateBps = 512 * 1024; // 位元組/秒
$bucket = $rateBps; // 初始令牌桶滿
$last = microtime(true);
while (!feof($fp) && $remaining > 0) {
$now = microtime(true);
$elapsed = $now - $last;
$bucket += $elapsed * $rateBps; // 產生令牌
if ($bucket > $rateBps) $bucket = $rateBps; // 桶上限
$readSize = min(8192, $remaining);
if ($bucket >= $readSize) {
$bucket -= $readSize;
echo fread($fp, $readSize);
@flush(); @ob_flush();
$remaining -= $readSize;
} else {
usleep(10000); // 10ms 等待令牌
}
$last = $now;
}
優點：平滑限速、不依賴 sleep(1) 秒級粒度、CPU 佔用低。
// 前端：定時請求進度 API
setInterval(() => {
fetch('/download_progress.php?file=large.zip')
.then(r => r.json())
.then(d => {
document.getElementById('bar').style.width = d.percent + '%';
document.getElementById('speed').textContent = d.speed + ' KB/s';
});
}, 1000);
// download_progress.php：透過 tmp 檔或 Redis 記錄已傳送位元組
$sent = (int)file_get_contents("/tmp/dl_progress_{$file}");
$total = filesize($file);
echo json_encode(['percent' => round($sent/$total*100,1), 'speed' => round(($sent-$lastSent)/1024)]);
limit_rate、sendfile），PHP 僅做權限驗證後 X-Accel-Redirect 或 X-Sendfile
