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Code Issues 151 Wiki Activity

multiplayer stage 8: state correction and surviving a dropped connection

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Two things were still missing once a session ran for a while: a peer that had
drifted apart from the authority had no way back short of restarting, and a
connection that blinked cost the player their seat and handed their vehicle to
the AI while the other driver was still sitting in it.

- a client that disagrees with the authoritative digest for 120 steps in a row
  asks to be put back in line, and the server answers with a fresh snapshot.
  There is a cooldown between requests, so a correction that needs a moment to
  take hold does not turn into a stream of them
- the server hands out a session token with its hello and remembers it. Present
  it again on the next connection and you come back as the same peer, with the
  same id
- a lost connection no longer removes the peer from its crews: the seat is held
  for a minute. Come back in time and nothing changed; stay away and the seat
  is given up properly, handing the vehicle back to the AI only when that
  leaves the crew empty and the AI was driving it in the first place
- after applying a snapshot a peer that finds itself on a crew walks into that
  cab, which is what makes a reconnect land the player back where they were
- the vehicle roster is sent to a joining peer right before its snapshot, so
  the crew section resolves to names instead of waiting for the next broadcast
This commit is contained in:
Hirek
2026-09-06 19:48:06 +00:00
parent 54d8b112b8
commit 30fa68cfd8
11 changed files with 209 additions and 5 deletions
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52
network/network.cpp
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@@ -53,6 +53,7 @@ void network::connection::connected()
msg.version = EU07_NETWORK_VERSION;
msg.start_packet = packet_counter;
msg.app_version = Global.asVersion;
msg.session_token = Global.network_session_token;
send_message(msg);
}
}
@@ -93,9 +94,10 @@ void network::server::prune_clients()
if ((*it)->state == connection::DEAD) {
if ((*it)->peer_id != PEER_NONE) {
WriteLog("net: peer " + std::to_string((*it)->peer_id) + " disconnected", logtype::net);
// a vehicle keeps running for whoever is left on board; it only falls back
// to the AI when the crew becomes empty, which Crews decides on its own
Crews.drop_peer((*it)->peer_id);
// the seat is held for a while in case the peer comes straight back. a
// vehicle keeps running for whoever is left on board either way; it only
// falls back to the AI once the crew really is empty
Crews.suspend_peer((*it)->peer_id);
}
it = clients.erase(it);
continue;
@@ -169,7 +171,8 @@ void network::server::handle_message(std::shared_ptr<connection> conn, const mes
reply.config = 0; // TODO: pass bitfield with state of relevant setting switches
reply.scenario = Global.SceneryFile;
reply.app_version = Global.asVersion;
reply.peer_id = allocate_peer_id();
reply.session_token = cmd.session_token;
reply.peer_id = resolve_peer_identity(reply.session_token);
conn->peer_id = reply.peer_id;
// the peer now goes and loads the scenario. it gets the state of the world as a
// snapshot when it reports back, instead of replaying the session frame by frame
@@ -195,6 +198,11 @@ void network::server::handle_message(std::shared_ptr<connection> conn, const mes
return;
}
// the roster first, so that the crew section of the snapshot resolves to names
vehicle_list roster;
roster.vehicles = Entities.entries();
conn->send_message(roster);
snapshot reply;
reply.tick = Global.simulation_tick;
reply.blob = take_snapshot();
@@ -209,6 +217,17 @@ void network::server::handle_message(std::shared_ptr<connection> conn, const mes
// and it still has to learn who is where
Crews.mark_all_pending();
}
else if (msg.type == message::REQUEST_RESYNC) {
const auto& cmd = dynamic_cast<const request_resync&>(msg);
WriteLog("net: resync requested by peer " + std::to_string(conn->peer_id) + " at tick "
+ std::to_string(cmd.tick) + " (its digest " + std::to_string(cmd.state_hash) + ")", logtype::net);
snapshot reply;
reply.tick = Global.simulation_tick;
reply.blob = take_snapshot();
conn->send_message(reply);
}
else if (msg.type == message::CLAIM_VEHICLE) {
const auto& cmd = dynamic_cast<const claim_vehicle&>(msg);
@@ -355,6 +374,17 @@ void network::client::send_ready()
WriteLog("net: scenario loaded, asking the server for a snapshot", logtype::net);
}
void network::client::send_resync_request(uint64_t tick, uint64_t state_hash)
{
if (!conn || conn->state != connection::ACTIVE)
return;
request_resync msg;
msg.tick = tick;
msg.state_hash = state_hash;
conn->send_message(msg);
}
void network::client::send_claim(NetworkEntityId entity_id)
{
if (!conn || conn->state != connection::ACTIVE)
@@ -419,6 +449,11 @@ void network::client::handle_message(std::shared_ptr<connection> conn, const mes
WriteLog("net: assigned peer id " + std::to_string(cmd.peer_id), logtype::net);
}
if (cmd.session_token != 0) {
// kept for the next connection, so that a dropout does not cost us our seat
Global.network_session_token = cmd.session_token;
}
Global.network_status.clear();
WriteLog("net: accept received", logtype::net);
@@ -438,6 +473,15 @@ void network::client::handle_message(std::shared_ptr<connection> conn, const mes
if (apply_snapshot(cmd.blob)) {
Global.network_snapshot_applied = true;
// the roster may say we are on a crew already - after a reconnect, or because
// the claim was granted while we were still loading. walk into that cab
auto const own = Crews.vehicle_of(Global.network_peer_id);
if (own != ENTITY_NONE) {
auto const name = Entities.name_of(own);
if (!name.empty())
Global.network_pending_vehicle = name;
}
}
else {
ErrorLog("net: could not apply the snapshot handed to us", logtype::net);