Lost session data when setting http headers (in CodeIgniter) - php

Question

EDIT #2
Ok, the problem is different to what I originally thought, so I'm putting this 'edit' up the top. I've also updated the question title (the old one was 'Streaming wav audio from a mysql blob').
The problem now seems to be related to CodeIgniter sessions. The above script will only run if the user is logged in. For some reason, when I manually set the response headers (either
with php's header() or codeigniters output class) I can see from my logs that everything gets reloaded and reinitilised -- and that the session data is lost, so the user is no longer logged in, so the script is actually outputting an error.
Once I removed any requirement or reference to session data the audio plays fine... but this isn't really an option unless I can manage to authenticate the user some other way. Very frustrating.
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** Original Text **
I have a mysql blob which contains audio data in wav format. I'm trying to output that to the browser to stream in whatever audio player plugin the browser wants to use.
The audio player works fine if I point it at a physical .wav file, so that doesn't seem to be a problem. However, if I point it at my PHP script I get a 'Search for suitable plugin?' popup in Firefox (which fails to find anything), and just an empty inactive player in Chrome.
Here's the PHP, the $aud object contains information retrieved from the database:
header("Content-length: $aud->size");
header("Content-type: audio/x-wav");
echo $aud->recording;
exit();
If I add header("Content-Disposition: attachment; filename=$name"); to the above I get to download the file, which then plays fine in an external audio player, but that's not what I want.
This snippit is part of a CodeIgniter application, if that would make a difference. I have routing set up so that /audio/$id.wav will grab the appropriate data and output it with the code above.
Can anyone see or think of any reason the above might not be working?
EDIT
These are the headers returned by the php script:
Date: Tue, 22 Mar 2011 22:12:06 GMT
Server: Apache/2.2.16 (Ubuntu)
X-Powered-By: PHP/5.3.3-1ubuntu9.3
Set-Cookie: ci_session=<long encrypted session string>; expires=Wed, 23-Mar-2011 00:12:06 GMT; path=/
Content-Length: 12345
Keep-Alive: timeout=15, max=98
Connection: Keep-Alive
Content-Type: audio/x-wav
200 OK
And for comparison, these headers are returned when I force a download of the above audio and open that wav file directly in the browser:
Date: Tue, 22 Mar 2011 22:10:53 GMT
Server: Apache/2.2.16 (Ubuntu)
Last-Modified: Tue, 22 Mar 2011 22:08:30 GMT
Etag: "200a83-3039-49f197bfcb380"
Accept-Ranges: bytes
Content-Length: 12345
Content-Type: audio/x-wav
200 OK
Saving and then opening the file directly does work. Having the PHP script output to the browser does not.

Answer 1

I would start investigating this problem by comparing the HTTP content-length, content-type, and all the other headers sent by the web server when pointing to the physical .wav file, with the headers sent when trying to open the PHP script. I think the actual content body is correct, according to your post stating that if you download the file as an attachment, it can be played with an audio player application.

Answer 2

Try adding this header in there:
header('Content-Transfer-Encoding: binary');
See if that helps it out.