php代码实现文件下载

PHP 文件下载的实现方法

使用 header 函数强制下载

通过设置 HTTP 头部信息强制浏览器下载文件而非直接打开。

$file = 'path/to/file.pdf';
if (file_exists($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;
}

大文件分块下载

对于大文件，使用分块读取避免内存问题。

$file = 'large_file.zip';
$chunk_size = 1024 * 1024; // 1MB per chunk

if (file_exists($file)) {
    header('Content-Type: application/octet-stream');
    header('Content-Disposition: attachment; filename="'.basename($file).'"');

    $handle = fopen($file, 'rb');
    while (!feof($handle)) {
        echo fread($handle, $chunk_size);
        ob_flush();
        flush();
    }
    fclose($handle);
    exit;
}

动态生成文件并下载

创建临时文件或动态生成内容供下载。

header('Content-Type: text/csv');
header('Content-Disposition: attachment; filename="data.csv"');

$output = fopen('php://output', 'w');
fputcsv($output, ['Name', 'Email', 'Phone']);
fputcsv($output, ['John Doe', 'john@example.com', '123456789']);
fclose($output);

安全下载注意事项

验证文件路径防止目录遍历攻击。

$base_dir = '/safe/download/directory/';
$requested_file = $_GET['file'];
$real_path = realpath($base_dir . $requested_file);

if ($real_path && strpos($real_path, $base_dir) === 0 && is_file($real_path)) {
    // 安全下载逻辑
} else {
    die('Invalid file');
}

断点续传支持

实现支持 Range 头的断点续传功能。

$file = 'large_video.mp4';
$fp = fopen($file, 'rb');

$size = filesize($file);
$length = $size;
$start = 0;
$end = $size - 1;

header("Accept-Ranges: bytes");
if (isset($_SERVER['HTTP_RANGE'])) {
    $c_start = $start;
    $c_end = $end;
    list(, $range) = explode('=', $_SERVER['HTTP_RANGE'], 2);
    if (strpos($range, ',') !== false) {
        header('HTTP/1.1 416 Requested Range Not Satisfiable');
        exit;
    }
    if ($range == '-') {
        $c_start = $size - substr($range, 1);
    } else {
        $range = explode('-', $range);
        $c_start = $range[0];
        $c_end = (isset($range[1]) && is_numeric($range[1])) ? $range[1] : $size;
    }
    $c_end = ($c_end > $end) ? $end : $c_end;
    if ($c_start > $c_end || $c_start > $size - 1 || $c_end >= $size) {
        header('HTTP/1.1 416 Requested Range Not Satisfiable');
        exit;
    }
    $start = $c_start;
    $end = $c_end;
    $length = $end - $start + 1;
    fseek($fp, $start);
    header('HTTP/1.1 206 Partial Content');
}

header("Content-Range: bytes $start-$end/$size");
header("Content-Length: $length");

$buffer = 1024 * 8;
while (!feof($fp) && ($p = ftell($fp)) <= $end) {
    if ($p + $buffer > $end) {
        $buffer = $end - $p + 1;
    }
    echo fread($fp, $buffer);
    flush();
}
fclose($fp);
exit;