Incomplete HTTP request body sent to upstream
roman.borschel at googlemail.com
Wed Nov 19 13:13:41 UTC 2014
I'm experiencing an issue whereby nginx and the upstream server get into
disagreement about the state of the HTTP interaction, apparently caused by
nginx not transmitting the complete request body. The scenario is as
follows, using nginx as a reverse proxy with upstream keepalive:
1. Client sends a POST request to nginx with a Content-Length header and a
relatively large body, i.e. spanning many TCP segments.
2. Nginx forwards the request line and headers and starts forwarding the
body to the upstream server.
3. While nginx is still sending, the upstream server responds early with a
409 based on information in the request headers, without consuming the body.
4. Nginx eventually stops sending the body, i.e. it does not transmit the
full number of bytes as specified in the Content-Length, presumably because
of the server response.
5. Nginx reuses the same upstream connection for a different request, in
this case a GET request.
6. The upstream server does not see this as a new HTTP request, as it is
still awaiting more data according to the Content-Length.
At this point the client who sent the GET request and nginx wait for a
response while the upstream server is waiting for more data until one of
them hits a timeout (whichever has the lowest timeout) which eventually
results in the connection being closed.
According to RFC2616, 8.2.2  if the request contained a Content-Length
and the client (nginx in this case) ceases to transmit the body (due to an
error response) the client (nginx) would have to close the connection,
which does not happen.
I am reasonably certain that the client is always transmitting the full
body as the problem does not occur when the client talks directly to the
upstream server and an otherwise identical request/response pattern (i.e.
an early error response).
Can someone clarify on whether this is expected behaviour / as designed on
behalf of nginx?
Nginx versions used: 1.6.0, 1.6.2, 1.7.7
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