php中使用head进行二进制流输出，让用户下载PDF等附件的方法

function downloadFile( $fullPath ){

// Must be fresh start
if( headers_sent() )
die('Headers Sent');

// Required for some browsers
if(ini_get('zlib.output_compression'))
ini_set('zlib.output_compression', 'Off');

// File Exists?
if( file_exists($fullPath) ){

// Parse Info / Get Extension
$fsize = filesize($fullPath);
$path_parts = pathinfo($fullPath);
$ext = strtolower($path_parts["extension"]);

// Determine Content Type
switch ($ext) {
case "pdf": $ctype="application/pdf"; break;
case "exe": $ctype="application/octet-stream"; break;
case "zip": $ctype="application/zip"; break;
case "doc": $ctype="application/msword"; break;
case "xls": $ctype="application/vnd.ms-excel"; break;
case "ppt": $ctype="application/vnd.ms-powerpoint"; break;
case "gif": $ctype="image/gif"; break;
case "png": $ctype="image/png"; break;
case "jpeg":
case "jpg": $ctype="image/jpg"; break;
default: $ctype="application/force-download";
}

header("Pragma: public"); // required
header("Expires: 0");
header("Cache-Control: must-revalidate, post-check=0, pre-check=0");
header("Cache-Control: private",false); // required for certain browsers
header("Content-Type: $ctype");
header("Content-Disposition: attachment; filename=\"".basename($fullPath)."\";" );
header("Content-Transfer-Encoding: binary");
header("Content-Length: ".$fsize);
ob_clean();
flush();
readfile( $fullPath );

} else
die('File Not Found');

}