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P_AttackActor.md

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P_AttackActor

Direction: Both (C→S "I'm attacking this target"; S→C "the attack resolved") Numeric ID: 18 Server handler: ServerNet.bb:1548 Server attack engine: GameServer.bb:300 (ActorAttack) Client handler: ClientNet.bb:1109

Purpose

The combat packet. Carries melee + ranged-projectile attack initiation from client to server, and the resolved attack (hit / miss / observer-visible swing) from server to client. The server runs the entire damage formula, faction check, weapon-range check, and HP mutation; the client only animates and updates its HUD.

Field layout

C → S — "I'm attacking RuntimeID X"

A fixed 2-byte payload, no sub-code. The client tags the target by RuntimeID; the server resolves to ActorInstance via RuntimeIDList.

Offset Width Type Field Notes
1 2 Int Target RuntimeID The actor the client wants to hit. Resolved server-side via RuntimeIDList.

Total: 2 bytes. Validated by Len(M\MessageData$) = 2 (ServerNet.bb:1550) — packets of any other length are silently dropped.

S → C — three sub-codes covering attacker, victim, and observers

Sub-code Recipient Layout Purpose
"H" Attacker (A1\RNID) 1B sub + 2B Victim\RuntimeID + 2B Damage+1 + 1B DamageType "I hit them" — for the attacker's HUD (damage numbers, attack animation).
"Y" Victim (A2\RNID) 1B sub + 2B Attacker\RuntimeID + 2B Damage+1 + 1B DamageType "They hit me" — for the victim's HUD (incoming damage, parry/hit animation).
"O" All other players in the same area 1B sub + 2B Attacker\RuntimeID + 2B Victim\RuntimeID (no damage payload) Observer swing animation. Observers re-sync HP via the next P_StatUpdate, so the damage isn't replicated on this channel. Subtle: the ClientNet "Else" branch doesn't decode a fresh Damage from the wire — in non-Strict UpdateNetwork(), Damage is an implicit function-scope variable that persists across Select Case iterations within one call, so it reads whatever the prior H/Y packet (or zero, on the first call) left there. Current behaviour is benign because P_StatUpdate re-syncs HP authoritatively.

Damage+1 encoding: The 2-byte Damage field carries Damage + 1 so a value of 0 on the wire means "miss" (rendered as a parry animation). The wire field can be negative (signed 2-byte = -32768..32767), which lets the server signal a miss explicitly. Client subtracts 1 to recover the actual damage at ClientNet.bb:1117 / :1145.

Damage type bounds: The 1-byte DamageType is clamped client-side to [0, 19] before indexing into DamageTypes$ (ClientNet.bb:1121-1123). A malformed packet with a wild value falls back to type 0 instead of crashing the client.

Validation requirements

C → S handler (ServerNet.bb:1548-1571)

Six gates, all required to fire:

  1. Sender validity: AI <> Null (FindActorInstanceFromRNID resolves the sender).
  2. Packet shape: Len(M\MessageData$) = 2.
  3. Combat delay: MilliSecs() - AI\LastAttack >= CombatDelay. Prevents attack-spam cheating; AI\LastAttack is set on every successful attack in ActorAttack.
  4. Not riding a mount: AI\Mount = Null. Mounted players can't attack (intentional gameplay constraint).
  5. Same-area gate (added PR #276): both attacker and victim must be in the same AreaInstance. Resolved via Object.AreaInstance(AI\ServerArea) and Object.AreaInstance(A2\ServerArea); the dual lookup guards both sides against stale ServerArea mid-portal.
  6. PvP / NPC permission: A2\RNID < 0 Or AInstance\Area\PvP = True. NPCs (RNID -1) are always attackable; players are only attackable in PvP-enabled areas.

ActorAttack damage engine (GameServer.bb:300-600+)

The damage engine itself runs additional checks:

  • Already-dead target: If A2\Attributes\Value[HealthStat] <= 0 Then Return False. Without this, two attackers landing in the same tick both saw HP > 0, both subtracted, both called KillActor against freed memory (double-XP + use-after-free).
  • Both Aggressiveness ≠ 3: NPCs with Aggressiveness = 3 are non-combatant (typed mobs / vendors).
  • Faction rating: A1\FactionRatings[A2\HomeFaction] > 150 blocks the attack (friendly faction).
  • Range check: melee uses 7.0 + A1\Actor\Radius + A2\Actor\Radius squared. Ranged projectile uses weapon.Range + A1.Radius + A2.Radius squared.

Hit chance + damage formula (4 variants, selected by CombatFormula global)

CombatFormula Hit chance Damage formula
1 (Normal) 90% weapon.Damage ± strength-rolled bonus, critical 1/10 (×2). Armour subtracts GetArmourLevel + Resistances[DamageType] - 100 + ToughnessStat / 8.
2 (No strength bonus) 90% weapon.Damage flat. Critical 1/10 (×2). Same armour formula.
3 (Multiplied) 90% weapon.Damage × Strength. Critical 1/10.
4 (Attack script) N/A Delegates to a ThreadScript("Attack", "Main", attacker, victim) — content authors implement the formula in .rsl. No range/damage check server-side.

CombatFormula is a global set at server boot from project config. The attack-script variant (4) is the modder hook for completely custom combat.

Broadcast pattern

After damage is applied, the server emits three packets:

  1. To attacker (if A1\RNID > 0): "H" + victim_rid + damage + dtype
  2. To victim (if A2\RNID > 0): "Y" + attacker_rid + damage + dtype
  3. To all others in the same AInstance\FirstInZone chain: "O" + attacker_rid + victim_rid (no damage)

The "O" loop (GameServer.bb:575-584) skips A1 and A2 (they already got their personalised packet) and skips Null-AreaInstance (stale-area mid-portal).

Anti-cheat surface

P_AttackActor is one of the most security-sensitive packets — a single attack hit/miss decision drives PvP outcomes. The validation requirements above cover the known attack surface; the recent same-area gate (#276) was the most-recently-added defence (specifically against cross-area packet injection that would have bypassed PvP rules).

The handler is NOT privilege-gated like the BVM clicker handlers — combat is the player's privilege; the gate is "are you allowed to fight this target?" not "are you allowed to call this function?".

Historical bugs / PR references

PR Fixed
#276 Same-area gate (cross-area injection prevention)
Two-attackers-same-tick fix (pre-PR) The already-dead target guard at GameServer.bb:308 — prevents double KillActor + use-after-free
Defensive AInstance Null check The broadcast loop at GameServer.bb:575 skips when AInstance is Null (mid-warp race)
#282 FindActorInstanceFromRNID(M\FromID) -- O(1) sender resolution
#283 Per-area FirstInZone chain walk in the observer broadcast loop
#287 Pet-aggro broadcast (ActorAttack's pet recruitment) now walks the per-leader FirstSlave chain

Related packets

  • P_StandardUpdate — movement, including the speed-hack clamp that prevents teleport-into-range attacks
  • P_StatUpdate — broadcasts HP changes; observers see victim's HP drop via this rather than the "O" P_AttackActor
  • P_ActorDead — broadcast when victim's HP drops ≤ 0
  • P_Projectile — projectile-launch broadcast (separate from this packet; ranged attacks emit both)
  • P_ActorEffect — debuff / status effects that combat triggers

See also