Timeout serving large requests

[BrindleFly]

I'm struggling to find the source of a timeout. I am running Nginx (1.2.6),
Passenger 3.0.18, and Rails 3.2.11. On serving one long running request, I
find the results (CSV file) truncated after being returned from the client.
The Rails application however continues to serve up the data until complete,
at which time it reports:

    Couldn't forward the HTTP response back to the HTTP client: It seems the
user clicked on the 'Stop' button in his browser.

Nginx access.log however reports a 200 for the request.

Some things I have tried:
1) I modified the Nginx read/send timeouts in the Passenger gem
(ext/nginx/Configuration.c) and recompiled, with no impact.
2) I ran a test of bypassing Nginx/Passenger by going direct to my app
running in Unicorn, and it serves up the result fine. I then took Passenger
out of the equation by configuring Nginx to pass the requests to Unicorn,
and the truncated result is back again.
3) I've played with the Nginx keepalive_timeout, proxy_read_timeout,
proxy_send_timeout and send_timeout - all with no impact.

Any thoughts/advice would be much appreciated.

Joe

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,236201,236201#msg-236201