Hi,

If you read the same RFC, section 6.5, right before the section you
mentioned, you can see:

A client sending a message body SHOULD monitor the network connection
for an error response while it is transmitting the request. If the
client sees a response that indicates the server does not wish to
receive the message body and is closing the connection, the client
SHOULD immediately cease transmitting the body and close its side of
the connection.


In this case, server sent HTTP/413 (along with Connection: close) to
indicate it did not wish to receive the message body. Does nginx
immediately cease transmitting the body and close its side of the
connection?

Thanks!
Frank


On Wed, Dec 18, 2019 at 11:37 AM Maxim Dounin <mdounin@mdounin.ru> wrote:

> Hello!
>
> On Wed, Dec 18, 2019 at 10:09:56AM -0800, Frank Liu wrote:
>
> > Our upstream returns HTTP/413 along with "Connection: close" in the
> header,
> > then closes the socket. It seems nginx catches the socket close in the
> > middle of sending the large payload. This triggers additional 502 and
> > client gets both 413 and 502 from nginx.
>
> Your upstream server's behaviour is incorrect: it have to continue
> reading data in the socket buffers and in transit (usually this is
> called "lingering close", see http://nginx.org/r/lingering_close),
> or nginx simply won't get the response. The client will get
> simple and quite reasonable 502 in such a situation (not "413 and
> 502").
>
> This problem is explicitly documented in RFC 7230, "6.6.
> Tear-down" (https://tools.ietf.org/html/rfc7230#section-6.6):
>
> If a server performs an immediate close of a TCP connection, there is
> a significant risk that the client will not be able to read the last
> HTTP response. If the server receives additional data from the
> client on a fully closed connection, such as another request that was
> sent by the client before receiving the server's response, the
> server's TCP stack will send a reset packet to the client;
> unfortunately, the reset packet might erase the client's
> unacknowledged input buffers before they can be read and interpreted
> by the client's HTTP parser.
>
> To avoid the TCP reset problem, servers typically close a connection
> in stages. First, the server performs a half-close by closing only
> the write side of the read/write connection. The server then
> continues to read from the connection until it receives a
> corresponding close by the client, or until the server is reasonably
> certain that its own TCP stack has received the client's
> acknowledgement of the packet(s) containing the server's last
> response. Finally, the server fully closes the connection.
>
> If the upstream server fails to do connection teardown properly,
> the only option is to fix the upstream server: it should either
> implemenent proper connection teardown, or avoid returning
> responses without reading the request body first.
>
> --
> Maxim Dounin
> http://mdounin.ru/
> _______________________________________________
> nginx mailing list
> nginx@nginx.org
> http://mailman.nginx.org/mailman/listinfo/nginx
>
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