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fix(gacha): prevent panics from misconfigured gacha entries (#175)

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getRandomEntries panics with rand.Intn(0) when box gacha has more rolls
than available entries. Fix by clamping rolls, guarding empty entries
and zero-weight pools, and fixing an out-of-bounds slice in the receive
handler overflow path.
This commit is contained in:
Houmgaor
2026-03-10 11:19:22 +01:00
parent eaac12fac5
commit 915e9bc0b0
3 changed files with 61 additions and 5 deletions
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26
server/channelserver/svc_gacha.go
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@@ -103,11 +103,17 @@ func (svc *GachaService) spendGachaCoin(userID uint32, quantity uint16) {
// resolveRewards selects random entries and resolves them into rewards.
func (svc *GachaService) resolveRewards(entries []GachaEntry, rolls int, isBox bool) []GachaReward {
rewardEntries, _ := getRandomEntries(entries, rolls, isBox)
rewardEntries, err := getRandomEntries(entries, rolls, isBox)
if err != nil {
svc.logger.Warn("Failed to select gacha entries", zap.Error(err))
return nil
}
var rewards []GachaReward
for i := range rewardEntries {
entryItems, err := svc.gachaRepo.GetItemsForEntry(rewardEntries[i].ID)
if err != nil {
svc.logger.Warn("Gacha entry has no items",
zap.Uint32("entryID", rewardEntries[i].ID), zap.Error(err))
continue
}
for _, item := range entryItems {
@@ -228,11 +234,17 @@ func (svc *GachaService) PlayBoxGacha(userID, charID, gachaID uint32, rollType u
if err != nil {
return nil, err
}
rewardEntries, _ := getRandomEntries(entries, rolls, true)
rewardEntries, err := getRandomEntries(entries, rolls, true)
if err != nil {
svc.logger.Warn("Failed to select box gacha entries", zap.Error(err))
return &GachaPlayResult{}, nil
}
var rewards []GachaReward
for i := range rewardEntries {
entryItems, err := svc.gachaRepo.GetItemsForEntry(rewardEntries[i].ID)
if err != nil {
svc.logger.Warn("Box gacha entry has no items",
zap.Uint32("entryID", rewardEntries[i].ID), zap.Error(err))
continue
}
if err := svc.gachaRepo.InsertBoxEntry(gachaID, rewardEntries[i].ID, charID); err != nil {
@@ -299,11 +311,21 @@ func (svc *GachaService) ResetBox(gachaID, charID uint32) error {
// chosen with weighted probability (with replacement). In box mode, entries are
// chosen uniformly without replacement.
func getRandomEntries(entries []GachaEntry, rolls int, isBox bool) ([]GachaEntry, error) {
if len(entries) == 0 {
return nil, errors.New("no gacha entries available")
}
// Box mode draws without replacement, so clamp rolls to available entries.
if isBox && rolls > len(entries) {
rolls = len(entries)
}
var chosen []GachaEntry
var totalWeight float64
for i := range entries {
totalWeight += entries[i].Weight
}
if !isBox && totalWeight <= 0 {
return nil, errors.New("gacha entries have zero total weight")
}
for rolls != len(chosen) {
if !isBox {
result := rand.Float64() * totalWeight