Ensure Apple receipts with duplicate transaction identifiers are proc…

…essed cleanly.

CHANGELOG.md

@@ -4,6 +4,8 @@ All notable changes to this project are documented below.
 The format is based on [keep a changelog](http://keepachangelog.com) and this project uses [semantic versioning](http://semver.org).
 
 ## [Unreleased]
+### Fixed
+- Ensure Apple receipts with duplicate transaction identifiers are processed cleanly.
 
 ## [3.21.1] - 2024-03-22
 ### Added

server/core_purchase.go

@@ -67,17 +67,22 @@ func ValidatePurchasesApple(ctx context.Context, logger *zap.Logger, db *sql.DB,
 		env = api.StoreEnvironment_SANDBOX
 	}
 
+	seenTransactionIDs := make(map[string]struct{}, len(validation.Receipt.InApp)+len(validation.LatestReceiptInfo))
 	storagePurchases := make([]*storagePurchase, 0, len(validation.Receipt.InApp)+len(validation.LatestReceiptInfo))
 	for _, purchase := range validation.Receipt.InApp {
 		if purchase.ExpiresDateMs != "" {
 			continue
 		}
+		if _, seen := seenTransactionIDs[purchase.TransactionId]; seen {
+			continue
+		}
 
 		purchaseTime, err := strconv.ParseInt(purchase.PurchaseDateMs, 10, 64)
 		if err != nil {
 			return nil, err
 		}
 
+		seenTransactionIDs[purchase.TransactionId] = struct{}{}
 		storagePurchases = append(storagePurchases, &storagePurchase{
 			userID:        userID,
 			store:         api.StoreProvider_APPLE_APP_STORE,
@@ -94,12 +99,16 @@ func ValidatePurchasesApple(ctx context.Context, logger *zap.Logger, db *sql.DB,
 		if purchase.ExpiresDateMs != "" {
 			continue
 		}
+		if _, seen := seenTransactionIDs[purchase.TransactionId]; seen {
+			continue
+		}
 
 		purchaseTime, err := strconv.ParseInt(purchase.PurchaseDateMs, 10, 64)
 		if err != nil {
 			return nil, err
 		}
 
+		seenTransactionIDs[purchase.TransactionId] = struct{}{}
 		storagePurchases = append(storagePurchases, &storagePurchase{
 			userID:        userID,
 			store:         api.StoreProvider_APPLE_APP_STORE,