Pound forwards requests containing both Transfer-Encoding and Content-Length headers

[kenballus]

When Pound receives a request containing both an unrecognized Transfer-Encoding value and a Content-Length value, both are forwarded to the backend. This violates RFC 9112, section 6.2:

A sender MUST NOT send a Content-Length header field in any message that contains a Transfer-Encoding header field.

To see this for yourself, start up Pound and send it the following request:

POST / HTTP/1.1\r\n
Host: a\r\n
Content-Length: 5\r\n
Transfer-Encoding: invalid!!\r\n
\r\n
0\r\n\r\n

You should see the following forwarded to the backend:

POST / HTTP/1.1\r\n
Host: a\r\n
Content-Length: 5\r\n
Transfer-Encoding: invalid!!\r\n
X-Forwarded-For: 172.19.0.1\r\n
X-Forwarded-Proto: http\r\n
X-Forwarded-Port: 80\r\n
\r\n
0\r\n\r\n

Note that both headers remain.