Version of OpenTTD

Since masterserver protocol v2.

Expected result

When I start a server with dualstack (IPv4 + IPv6), I expect a single masterserver registration with both IPs.

Actual result

The first time, I register two servers: one for IPv4, and one for IPv6. Only when the second announcement happens, they are collapsed into a single entry.

Steps to reproduce

Start a cleanly installed OpenTTD server. Your server will briefly (well, for the next 15 minutes) show up as 2 servers on the serverlist.

What is going wrong?

When a server registers to the master server, initial he does this without a session_key (well, it is set to zero). In response, the masterserver will send back a unique session_key to track this server. The idea behind it is that the server can announce on multiple IPs; as long as the session_key is unique the masterserver knows that this is the same server with multiple IPs.

The server runs registration async; and you can guess now what happens. On the first run, both the IPv4 and IPv6 announce with a session_key of zero, indicating the masterserver should allocate one. He does so, two unique session_keys, because the masterserver has no clue this is in fact the same server. In result, two servers show up instead of one.

When the re-announcement happens, 15 minutes later, the game did settle on either one of the session_key. From this point on, the masterserver collapses the two entries into one, and all is well again.

Suggested fix

When the session_key is zero, don't register all IPs at once. Do one first, and when a session_key is received, register the others.