dnsdist: webserver should set Connection: close in standard headers

[DrewBloechl]

• Program: dnsdist
• Issue type: Bug report

Short description

The dnsdist webserver seems to close connections after each request without signaling to the client that it's going to do so with a Connection: close header. This introduces a race condition where an HTTP/1.1 client that implements connection reuse may try to send a second request over the connection if it doesn't receive the TCP FIN in time, and this second request will get hung up on.

Specifying {["Connection"]="close"} in webserver()'s custom headers seems to work around the problem.

Environment

• Operating system: Debian buster (aka "testing" as of right now)
• Software version: 1.3.0
• Software source: Debian repo