Repository navigation
fix ordered Lua packet timestamp comparison - #7877
Open
Goober5000 wants to merge 1 commit into
Open
Goober5000 wants to merge 1 commit into
Goober5000 wants to merge 1 commit into
Conversation
Goober5000
added
fix
Goober5000
force-pushed
the
fix/multi_lua_packet_order
branch
2 times, most recently
from
October 16, 2026 08:09
2108567 to
c7f22eb
Compare
Ordered Lua packets carry a 16-bit millisecond timestamp, and the receiver tossed packets it judged older than the last one accepted on the same channel. That check was broken in several ways: the ushort subtraction was promoted to int, so a delayed packet produced a negative difference and was always accepted; the 10% margin check had its multiplier on the wrong side, tossing genuinely newer packets sent more than a second apart; and even when corrected, the margin compared the sender's gap against the receive gap, so ordinary network jitter tossed newer packets. Replace the heuristic with serial number arithmetic: a packet is stale when the wrapped 16-bit difference falls in the upper half of the range. Once more than ~16 seconds of local time have passed since the last accepted packet the remote difference is ambiguous, so the packet is accepted as new. The comparison is exposed as multi_lua_packet_is_stale() and covered by unit tests. The per-channel state was also never cleared, and player ids restart at 0 each game, so a previous game's timestamps could in principle cause packets to be tossed if the next game started within the window. Reset it in multi_level_init() and drop a player's channels in delete_player(), which also keeps the map bounded. Fixes scp-fs2open#7872. Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Goober5000
force-pushed
the
fix/multi_lua_packet_order
branch
from
October 16, 2026 08:24
c7f22eb to
ad2b69d
Compare
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
1 participant
Add this suggestion to a batch that can be applied as a single commit.This suggestion is invalid because no changes were made to the code.Suggestions cannot be applied while the pull request is closed.Suggestions cannot be applied while viewing a subset of changes.Only one suggestion per line can be applied in a batch.Add this suggestion to a batch that can be applied as a single commit.Applying suggestions on deleted lines is not supported.You must change the existing code in this line in order to create a valid suggestion.Outdated suggestions cannot be applied.This suggestion has been applied or marked resolved.Suggestions cannot be applied from pending reviews.Suggestions cannot be applied on multi-line comments.Suggestions cannot be applied while the pull request is queued to merge.Suggestion cannot be applied right now. Please check back later.
Ordered Lua packets carry a 16-bit millisecond timestamp, and the receiver tossed packets it judged older than the last one accepted on the same channel. That check was broken in several ways: the ushort subtraction was promoted to int, so a delayed packet produced a negative difference and was always accepted; the 10% margin check had its multiplier on the wrong side, tossing genuinely newer packets sent more than a second apart; and even when corrected, the margin compared the sender's gap against the receive gap, so ordinary network jitter tossed newer packets.
Replace the heuristic with serial number arithmetic: a packet is stale when the wrapped 16-bit difference falls in the upper half of the range. Once more than ~16 seconds of local time have passed since the last accepted packet the remote difference is ambiguous, so the packet is accepted as new. The comparison is exposed as multi_lua_packet_is_stale() and covered by unit tests.
The per-channel state was also never cleared, and player ids restart at 0 each game, so a previous game's timestamps could cause packets in the next game to be tossed. Reset it in multi_level_init() and drop a player's channels in delete_player().
Fixes #7872.