Download remote file straight to client

download_file.php

function downloadFile($fileUrl)
{
	$isRemoteFile = null === parse_url($fileUrl, PHP_URL_HOST) ? false : true;

	$fileName = $isRemoteFile ? ltrim(parse_url($fileUrl, PHP_URL_PATH), '/') : pathinfo($fileUrl, PATHINFO_BASENAME);

	// 获取文件大小
	if ($isRemoteFile) {
		$ch = curl_init($fileUrl);
		$options = [
			CURLOPT_URL            => $fileUrl,
			CURLOPT_RETURNTRANSFER => true,
			CURLOPT_HEADER         => true,
			CURLOPT_NOBODY         => true,
		];
		curl_setopt_array($ch, $options);

		curl_exec($ch);
		$fileSize = curl_getinfo($ch, CURLINFO_CONTENT_LENGTH_DOWNLOAD);
		curl_close($ch);
	} else {
		$fileSize = filesize($fileUrl);
	}

	// 输出响应
	ob_start();
	header('Content-Description: File Transfer');
	header('Content-Type: application/octet-stream');
	header("Accept-Ranges:bytes");
	header('Content-Disposition: attachment; filename="'.$fileName.'"');
	header('Expires: 0');
	header('Cache-Control: must-revalidate');
	header('Pragma: public');
	header('Content-Length: ' . $fileSize);
	//readfile($fileUrl);

	$file = @fopen($fileUrl,"rb");
	while(!feof($file))
	{
		// 利用输出缓冲增量输出，适合大文件下载
		print(@fread($file, 1024*8));
		ob_flush();
		flush();
	}

	exit;
}