Backend responding with 100 Continue results in the actual response being lost

[Maxim Dounin]

Hello!

On Mon, Jul 22, 2013 at 08:20:04PM -0400, rstarkov wrote:

> I'm using nginx as a reverse proxy, configured to use HTTP 1.1 so as to
> support range requests. The server responds to some of the requests with a
> "100 Continue", even if there was no "Expect: 100-continue" in the request.
> The server then proceeds to read the rest of the request and, eventually,
> sends the "200 OK" reponse.
> 
> In my testing, in this scenario Nginx will forward the 100 Continue to the
> requesting browser, but the 200 OK response never makes it. It seems to be
> silently dropped. The result is that the browser is stuck waiting for a
> response until the request times out.
> 
> Is this expected behaviour? From my reading of the HTTP 1/1 spec, this
> server is not in violation of the spec. I'm using v1.4.2 on Windows.

As of now nginx doesn't know how to handle 1xx informational 
responses, and it always removes Expect from a requests sent to 
backends due to this.  RFC 2616 say:

        An origin server SHOULD NOT send a 100 (Continue) response if
        the request message does not include an Expect request-header
        field with the "100-continue" expectation, and MUST NOT send a
        100 (Continue) response if such a request comes from an HTTP/1.0
        (or earlier) client.

That is, it's 100 Continue isn't expected to be returned to nginx 
from a complaint HTTP/1.1 server even if a request is via 
HTTP/1.1.

If your backend server returns 100 Continue for some reason, you 
may try switching proxy_http_version back to 1.0 as by default.  
Most of HTTP servers are capable of handling Range requests via 
HTTP/1.0 as well, you shouldn't need HTTP/1.1 for Range requests 
to work.

-- 
Maxim Dounin
http://nginx.org/en/donation.html