CNA-BUG-172: A joined SystemLink session reports MaxGamers 31 and PrivateGamerSlots 4 instead of the host's values

CNA snapshot 009d40f5  ·  Known Issues › Current bugs  ·  source links pinned to 009d40f5

EndJoin constructs the client's NetworkSession with the placeholders MaxSupportedGamers and 4 that FNA marks FIXME, and nothing in the handshake updates them, so a client's MaxGamers, PrivateGamerSlots and session-full check disagree with the host.

Identifier

CNA-BUG-172

Category

Bug

Subsystem

Networking & gamer services

Status

Open

Verified against

CNA 009d40f5 (009d40f5dd085c4e674d3479675fac84b12b3e0a)

Severity

Low (a triage suggestion, not a project priority)

Evidence basis

Source-verified: read at TARGET, not executed

Tests touching this area

Yes: see Current tests

Affected contract

Microsoft::Xna::Framework::Net::NetworkSession::getMaxGamersProperty() and getPrivateGamerSlotsProperty() on a session obtained from Join, and the client-side session-full check in AddRemoteGamer

Expected behaviour

In XNA 4.0 every member of a session sees the session's slot configuration: ProcessUpdateSessionInfo overwrites maxGamers and privateGamerSlots from the session information the host publishes (decompiled NetworkSession), so a client's MaxGamers equals the host's and follows later changes.

Actual behaviour at TARGET

EndJoin in NetworkSession.cpp constructs the joining session with MaxSupportedGamers (31) and 4 private slots, both commented // FIXME upstream. The ServerWelcome carries a roster, wire ids and the session properties but no slot counts, and neither ENetBackend.cpp nor the packet codec updates maxGamers_ or privateGamerSlots_ on a client. A client therefore reports MaxGamers 31 and PrivateGamerSlots 4 whatever the host chose, its AddRemoteGamer full-session check compares against 31, and a later change on the host is never seen. The values are known at join time: the discovery announcement the client joined from carries the host's maximum and open private slots.

Source locations

• modules/net/src/Xna/NetworkSession.cpp — EndJoin passes MaxSupportedGamers and 4 (both marked FIXME upstream) to the NetworkSession constructor
• modules/net/src/Internal/ENetBackend.cpp — HandleServerWelcome and the broadcasts update roster, host and properties, not slot counts
• modules/net/src/Internal/NetPacketCodec.cpp — ServerWelcome encoding carries no MaxGamers or PrivateGamerSlots
• modules/net/tests/Microsoft/Xna/Framework/Net/NetworkSessionTests.cpp — slot-count assertions exist only for sessions created locally

Evidence

Checked by reading NetworkSession.cpp, ENetBackend.cpp and the codec at 009d40f5; not executed. XNA's behaviour is from the decompiled NetworkSession (ProcessUpdateSessionInfo and SetGamerSlots). A chapter review of this area flagged the same placeholders.

Independently observed as a separate finding (merged): EndJoin constructs the client's session with MaxSupportedGamers and four private slots (FNA's FIXME placeholders), and nothing later copies the host's values.

Focused reproduction

// Illustrative; not compiled or run for this entry.
// Host: NetworkSession::Create(NetworkSessionType::SystemLink, 1, 8, 2, NetworkSessionProperties{});
// Client, after finding that session:
NetworkSession* joined = NetworkSession::Join(&found[0]);
int maxGamers   = joined->getMaxGamersProperty();          // 31, host has 8
int privateSlot = joined->getPrivateGamerSlotsProperty();  // 4, host has 2

Current tests

NetworkSessionTests.cpp asserts MaxGamers and PrivateGamerSlots only for sessions created on the same machine; ENetBackendTests.cpp and the two-process test check rosters and data, not a client's slot counts.

Regression test

A backend test in which a client joins a host created with 8 gamers and 2 private slots and expects the client to report 8 and 2, and to follow a host-side change; fixed by carrying the slot counts in ServerWelcome (and a broadcast for later changes), or at least by seeding them from the AvailableNetworkSession used to join.

Blast radius

Client-side lobby UI that shows free slots or capacity, client code that checks MaxGamers before inviting or adding players, and the discovery announcements a client sends (see CNA-BUG-170), which advertise 31 and 4. The host's own view and its admission control are unaffected.

Workaround

Read capacity on the host and send it to clients in game data, or use the values of the AvailableNetworkSession the client joined from.