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php如何实现下载功能

2026-02-13 19:42:58PHP

使用 `header()` 函数强制下载

通过设置 HTTP 头信息，强制浏览器触发文件下载而非直接打开文件。核心代码如下：

$file_path = '/path/to/file.pdf';
$file_name = 'document.pdf';

header('Content-Description: File Transfer');
header('Content-Type: application/octet-stream');
header('Content-Disposition: attachment; filename="'.basename($file_name).'"');
header('Expires: 0');
header('Cache-Control: must-revalidate');
header('Pragma: public');
header('Content-Length: ' . filesize($file_path));
readfile($file_path);
exit;

分块下载大文件

对于大文件下载，建议使用分块读取方式避免内存溢出：

$chunk_size = 1024 * 1024; // 1MB chunks
$handle = fopen($file_path, 'rb');
while (!feof($handle)) {
    echo fread($handle, $chunk_size);
    ob_flush();
    flush();
}
fclose($handle);

安全验证处理

在提供下载前应进行权限验证：

session_start();
if (!isset($_SESSION['user_auth'])) {
    die('Access denied');
}

if (!file_exists($file_path)) {
    http_response_code(404);
    die('File not found');
}

动态生成文件下载

对于需要实时生成的内容（如 CSV 导出）：

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

$output = fopen('php://output', 'w');
fputcsv($output, ['ID', 'Name', 'Email']);
// 添加数据行...
fclose($output);

断点续传支持

实现支持断点续传的下载功能：

$fp = fopen($file_path, 'rb');
$size = filesize($file_path);
$length = $size;
$start = 0;
$end = $size - 1;

header("Accept-Ranges: 0-$length");
if (isset($_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);