Core/Spells: implement SpellInfo helper to filter for relevant mechanic immunities in spell_start packet (#26183)

* Core/Spells: implement SpellInfo helper to filter for relevant mechanic immunities when sending SMSG_SPELL_START packets.

According to sniff analysis Blizzard does not send all mechanic immunities of creatures but instead only the ones that are responsible for actual interrupts which are MECHANIC_INTERRUPT  and MECHANIC_SILENCE. Additionally we no longer send immunities for instant cast spells as sniffs confirm that they are not sent for spells without a cast time.

3 files changed, 22 insertions, 2 deletions

diff --git a/src/server/game/Spells/Spell.cpp b/src/server/game/Spells/Spell.cpp
index 1ff4cffe812..cd78f49cd84 100644
--- a/src/server/game/Spells/Spell.cpp
+++ b/src/server/game/Spells/Spell.cpp
@@ -4176,8 +4176,8 @@ void Spell::SendSpellStart()
     uint32 mechanicImmunityMask = 0;
     if (Unit* unitCaster = m_caster->ToUnit())
     {
-        schoolImmunityMask = unitCaster->GetSchoolImmunityMask();
-        mechanicImmunityMask = unitCaster->GetMechanicImmunityMask();
+        schoolImmunityMask = m_timer!= 0 ? unitCaster->GetSchoolImmunityMask() : 0;
+        mechanicImmunityMask = m_timer != 0 ? m_spellInfo->GetMechanicImmunityMask(unitCaster) : 0;
     }
 
     if (schoolImmunityMask || mechanicImmunityMask)
diff --git a/src/server/game/Spells/SpellInfo.cpp b/src/server/game/Spells/SpellInfo.cpp
index f0d42133088..492ced10a64 100644
--- a/src/server/game/Spells/SpellInfo.cpp
+++ b/src/server/game/Spells/SpellInfo.cpp
@@ -3038,6 +3038,24 @@ uint32 SpellInfo::GetAllowedMechanicMask() const
     return _allowedMechanicMask;
 }
 
+uint32 SpellInfo::GetMechanicImmunityMask(Unit* caster) const
+{
+    uint32 casterMechanicImmunityMask = caster->GetMechanicImmunityMask();
+    uint32 mechanicImmunityMask = 0;
+
+    // @todo: research other interrupt flags
+    if (InterruptFlags & SPELL_INTERRUPT_FLAG_INTERRUPT)
+    {
+        if (casterMechanicImmunityMask & (1 << MECHANIC_SILENCE))
+            mechanicImmunityMask |= (1 << MECHANIC_SILENCE);
+
+        if (casterMechanicImmunityMask & (1 << MECHANIC_INTERRUPT))
+            mechanicImmunityMask |= (1 << MECHANIC_INTERRUPT);
+    }
+
+    return mechanicImmunityMask;
+}
+
 float SpellInfo::GetMinRange(bool positive /*= false*/) const
 {
     if (!RangeEntry)
diff --git a/src/server/game/Spells/SpellInfo.h b/src/server/game/Spells/SpellInfo.h
index 6f2e8588009..f1a501b0286 100644
--- a/src/server/game/Spells/SpellInfo.h
+++ b/src/server/game/Spells/SpellInfo.h
@@ -533,6 +533,8 @@ class TC_GAME_API SpellInfo
 
         uint32 GetAllowedMechanicMask() const;
 
+        uint32 GetMechanicImmunityMask(Unit* caster) const;
+
     private:
         // loading helpers
         void _InitializeExplicitTargetMask();