PHP 檔案下載與線上預覽 PDF 實作範例

標準檔案下載（含快取控制）

<?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('Content-Transfer-Encoding: binary');
    header('Expires: 0');
    header('Cache-Control: must-revalidate, post-check=0, pre-check=0');
    header('Pragma: public');
    header('Content-Length: ' . filesize($file));

    // 清除輸出緩衝，避免前有空白導致檔案損毀
    ob_clean();
    flush();

    readfile($file); // 直接輸出檔案內容，效率優於 fread 迴圈
    exit;
}
?>

線上預覽 PDF（inline 而非 attachment）

<?php
function previewPdf(string $pdfPath) {
    if (!is_file($pdfPath) || !is_readable($pdfPath)) {
        http_response_code(404);
        exit('檔案不存在');
    }

    // IE 相容需加 public
    header('Cache-Control: public');
    header('Content-Type: application/pdf');
    // inline 讓瀏覽器嘗試內嵌顯示（需瀏覽器支援 PDF Viewer）
    header('Content-Disposition: inline; filename="' . basename($pdfPath) . '"');
    header('Content-Length: ' . filesize($pdfPath));

    readfile($pdfPath);
    exit;
}

// 使用
// previewPdf($_SERVER['DOCUMENT_ROOT'] . '/pdf/fdd/sample.pdf');
?>

關鍵差異對照

進階：支援 Range 斷點續傳的統一函數

<?php
function sendFile(string $path, string $disposition = 'attachment', ?string $mime = null) {
    if (!is_file($path) || !is_readable($path)) { http_response_code(404); exit; }

    $size = filesize($path);
    $mime = $mime ?: mime_content_type($path);
    $name = basename($path);

    // Range 處理
    $start = 0; $end = $size - 1; $code = 200;
    if (isset($_SERVER['HTTP_RANGE'])) {
        if (preg_match('/bytes=(\d+)-(\d*)/', $_SERVER['HTTP_RANGE'], $m)) {
            $start = (int)$m[1];
            $end = $m[2] !== '' ? (int)$m[2] : $size - 1;
            $code = 206;
        }
    }
    $length = $end - $start + 1;

    header('Content-Type: ' . $mime);
    header('Content-Disposition: ' . $disposition . '; filename="' . rawurlencode($name) . '"');
    header('Accept-Ranges: bytes');
    header('Content-Length: ' . $length);
    if ($code === 206) {
        http_response_code(206);
        header('Content-Range: bytes ' . $start . '-' . $end . '/' . $size);
    }

    $fp = fopen($path, 'rb');
    fseek($fp, $start);
    while (!feof($fp) && $length > 0) {
        $chunk = min(1024 * 1024, $length);
        echo fread($fp, $chunk);
        $length -= $chunk;
    }
    fclose($fp);
    exit;
}

// 下載
// sendFile('/data/report.pdf', 'attachment');
// 線上預覽
// sendFile('/data/report.pdf', 'inline', 'application/pdf');
?>