如何覆盖curl_exec设置标头

Question

I'm building a combine/minify php script for js, using a number of online minify scripts, and I'm stuck at Google's Closure minify script. This particular script requires that you do a POST with the content that needs to be minified, and you get the minified code in the response. My script needs to work like this:
1. user adds the file or files to be minified and/or combined
2. the user clicks 'Start'
3. the script runs in the background, and a download is started; the file downloaded is either:
3a. one big js file containing the combined minified content of the files provided OR
3b. one archive containing the minified versions of the provided files.

The point of 3a is that no file is created on the server, but instead I change the header and simply output the minified content. And here's where I have problems. The code in my minify method looks like this:

$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, 'http://closure-compiler.appspot.com/compile');
curl_setopt($ch, CURLOPT_POST, 1);
curl_setopt($ch, CURLOPT_POSTFIELDS, 'output_info=compiled_code&output_format=text&compilation_level=SIMPLE_OPTIMIZATIONS&js_code=' . urlencode($str));
$result = curl_exec($ch);

return $result;

and later in the code, I have

$js = mini($js);
header('Content-Description: File Transfer');
header('Content-Type: application/javascript');
header('Content-Disposition: attachment; filename='.$ourFileName);
header('Content-Transfer-Encoding: text');
echo $js;

if it's not clear, the $str variable from the first code segment is the actual combined content of all the files, and mini is the minify method. The problem is that, if I run this, I see the content in the browser window (truncated), and if I inspect the page, I see an error:

Cannot modify header information - headers already sent by (output started at E:\work\AdoTube\workspace\php\script.php:47)

(line 47 is the curl_exec call). If I bypass the minify method, I get a nice 'download file', and the file looks ok. So, my guess is the curl_exec call sets some headers on my script which prevent me from changing the headers later in the code.
How do I fix it? I know one idea would be to write the result to a temp file, and just download that, but i don't want to do that, unless it's the only option.. Thank you.

Answer 1

curl_setopt($ch, CURLOPT_RETURNTRANSFER, 1);