pre-existing data on a connection

[Maxim Dounin]

Hello!

On Mon, Jan 06, 2020 at 04:32:24PM -0800, Frank Liu wrote:

> When using nginx as a reverse proxy, how does it handle the
> pre-existing data on a keepalive connection to the backend?
> 
> eg: for a request, the backend has a bug that sends 2 identical
> responses. I assume nginx will take the first response and send it to
> client. What will happen to the extra data (duplicate response)? Now
> when nginx gets a second request and re-uses the same keepalive
> connection to backend, will nginx take the pre-existing data (the
> duplicate response for the first request) on that connection and send
> it to second client or will it drop those and read the new response
> from backend to send to client?
> If nginx uses the pre-existing data, all the subsequent requests will
> get the response shifted.

The behaviour heavily depends on the timing.  As long as nginx 
will be able to detect there are additional data after the 
response is already sent, nginx will close the connection (and 
will use another one for the next request to the same upstream 
server).  It might not be able to detect there are additional 
data though, and will only read the duplicate response after it 
will sent the next request to the connection, so the duplicate 
response will be sent to the second client.

-- 
Maxim Dounin
http://mdounin.ru/