bugfix(crc): Fix spurious mismatches for disconnected players at low CRC intervals

[Caball009]

• Related to PR bugfix(network): Improve compare method of command id's to keep network commands in chronological order when overflowing #2736

This PR introduces a small to fix to avoid spurious mismatches that can occur if the following conditions are met simultaneously:

1. Low CRC intervals; e.g. once per frame instead of once per 100 frames (default value).
2. Runahead decreases, so that multiple frames are executed in one go.
3. Player disconnects during one of these frames.

As players disconnect they stop sending data to other players to speed up the disconnect process. If that coincides with a decrease in runahead, it's possible that a single execution frame contains e.g. 5 CRC messages per player, but fewer for the disconnecting player. The game only checks a player's most recent CRC value. This would lead to a mismatch because the most recent CRC value for the disconnecting player is not up-to-date with the other (connected) players.

You can see it mismatch here as the player disconnects (this was with a special test build):
https://www.youtube.com/live/RM27jEkTGfw?t=2099s
https://www.youtube.com/live/V_l-q9Y-DmA?t=7576s

Here's a replay for the second match. The mismatch happens at frame 3836 because of player index 6 disconnecting from the game: MM NED.zip

I have no idea how to reproduce this in a test environment, unfortunately.

TODO:

• Replicate in Generals.

[greptile-apps]

Greptile Summary

This PR fixes a false CRC mismatch triggered when a player disconnects during a frame that processes multiple CRC messages (runahead decrease with low CRC intervals). The disconnecting player's stale CRC was being compared against fresh CRCs from connected players, producing a spurious desync report.

• Introduces a CachedCRCMap typedef to clean up verbose iterator declarations across both Generals and GeneralsMD code paths.
• Replaces the old "unconditionally take the first map entry as the reference" pattern with a hasReferenceCRC flag that only ever selects the reference CRC from a confirmed-connected player, and skips all disconnected players during comparison — fixing the stale-validator case where the disconnecting player held the lowest slot index.

Confidence Score: 5/5

Safe to merge; the fix correctly handles all edge cases including disconnecting players in any slot position.

The previous concern about a disconnecting player in the lowest slot contaminating the reference CRC is fully resolved: the new hasReferenceCRC flag defers reference selection until the first connected player is found, so stale CRCs from disconnected players are skipped both when setting the reference and during comparison. The numPlayers guard and the inner loop both call isPlayerConnected in close succession in a single-threaded logic frame and will return consistent results.

No files require special attention.

Important Files Changed

Filename	Overview
Generals/Code/GameEngine/Source/GameLogic/System/GameLogic.cpp	Core fix: replaces unconditional begin()-as-validator with hasReferenceCRC pattern that only compares connected players, correctly skipping stale CRCs from disconnecting players regardless of slot index.
GeneralsMD/Code/GameEngine/Source/GameLogic/System/GameLogic.cpp	Identical fix applied to the Zero Hour counterpart; logic is consistent with the Generals version.
Generals/Code/GameEngine/Include/GameLogic/GameLogic.h	Adds CachedCRCMap typedef inside the private section, consistent with the existing ControlBarOverrideMap typedef pattern in the same class.
GeneralsMD/Code/GameEngine/Include/GameLogic/GameLogic.h	Same typedef addition as the Generals header; no issues.

Flowchart

%%{init: {'theme': 'neutral'}}%%
flowchart TD
    A[processCommandList called] --> B[Clear m_cachedCRCs
m_shouldValidateCRCs = FALSE]
    B --> C[Dispatch all messages
via logicMessageDispatcher]
    C --> D{m_shouldValidateCRCs
AND no prior mismatch?}
    D -- No --> Z[Return]
    D -- Yes --> E[Count connected players
via isPlayerConnected loop]
    E --> F{m_cachedCRCs.size
< numPlayers?}
    F -- Yes --> G[sawCRCMismatch = TRUE
Not enough CRCs]
    F -- No --> H[hasReferenceCRC = FALSE
referenceCRC = 0]
    H --> I[Iterate m_cachedCRCs]
    I --> J{isPlayerConnected
for this entry?}
    J -- No --> I
    J -- Yes --> K{hasReferenceCRC?}
    K -- No --> L[Set referenceCRC
hasReferenceCRC = TRUE]
    L --> I
    K -- Yes --> M{referenceCRC
== current CRC?}
    M -- Yes --> I
    M -- No --> N[sawCRCMismatch = TRUE]
    N --> I
    G --> O{sawCRCMismatch?}
    I -- done --> O
    O -- Yes --> P[Log mismatch details
TheNetwork setSawCRCMismatch]
    O -- No --> Z
    P --> Z

Loading

%%{init: {'theme': 'base', 'themeVariables': {"darkMode": true, "background": "#0d1117", "primaryColor": "#21262d", "primaryTextColor": "#e6edf3", "primaryBorderColor": "#8b949e", "lineColor": "#8b949e", "textColor": "#e6edf3", "edgeLabelBackground": "#161b22", "actorBkg": "#21262d", "actorBorder": "#8b949e", "actorTextColor": "#e6edf3", "actorLineColor": "#8b949e", "signalColor": "#8b949e", "signalTextColor": "#e6edf3", "noteBkgColor": "#373320", "noteBorderColor": "#d4a72c", "noteTextColor": "#f0e6c0", "labelBoxBkgColor": "#21262d", "labelBoxBorderColor": "#8b949e", "labelTextColor": "#e6edf3", "loopTextColor": "#e6edf3", "activationBkgColor": "#30363d", "activationBorderColor": "#8b949e"}}}%%
flowchart TD
    A[processCommandList called] --> B[Clear m_cachedCRCs
m_shouldValidateCRCs = FALSE]
    B --> C[Dispatch all messages
via logicMessageDispatcher]
    C --> D{m_shouldValidateCRCs
AND no prior mismatch?}
    D -- No --> Z[Return]
    D -- Yes --> E[Count connected players
via isPlayerConnected loop]
    E --> F{m_cachedCRCs.size
< numPlayers?}
    F -- Yes --> G[sawCRCMismatch = TRUE
Not enough CRCs]
    F -- No --> H[hasReferenceCRC = FALSE
referenceCRC = 0]
    H --> I[Iterate m_cachedCRCs]
    I --> J{isPlayerConnected
for this entry?}
    J -- No --> I
    J -- Yes --> K{hasReferenceCRC?}
    K -- No --> L[Set referenceCRC
hasReferenceCRC = TRUE]
    L --> I
    K -- Yes --> M{referenceCRC
== current CRC?}
    M -- Yes --> I
    M -- No --> N[sawCRCMismatch = TRUE]
    N --> I
    G --> O{sawCRCMismatch?}
    I -- done --> O
    O -- Yes --> P[Log mismatch details
TheNetwork setSawCRCMismatch]
    O -- No --> Z
    P --> Z

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_{Reviews (6): Last reviewed commit: "Replicated in Generals." | Re-trigger Greptile}

[Mauller]

Looks okay to me, i don't think it can be much simpler since zero can be a valid CRC funnily enough for crc32.

[xezon]

This change assumes that all player disconnects are perfectly in sync. Is this guaranteed?

[xezon]

For a follow up, consider moving the Network test before the above TheNetwork->sawCRCMismatch()

[xezon]

Needs replicate in Generals

[Caball009]

Replicated in Generals.