Add Stripe webhook idempotency persistence guard

backend/models/subscription_models.py

@@ -408,3 +408,17 @@ class FraudWarning(Base):
     reason_notes = Column(Text, nullable=True)
     meta_info = Column(JSON, nullable=True)
     created_at = Column(DateTime, default=datetime.utcnow)
+
+
+class StripeWebhookEvent(Base):
+    """Processed Stripe webhook events for idempotency and replay protection."""
+
+    __tablename__ = "stripe_webhook_events"
+
+    event_id = Column(String(100), primary_key=True)
+    event_type = Column(String(100), nullable=False)
+    status = Column(String(20), nullable=False, default="processing")  # processing, processed, failed
+    error_message = Column(Text, nullable=True)
+    processed_at = Column(DateTime, nullable=True)
+    created_at = Column(DateTime, default=datetime.utcnow, nullable=False)
+

backend/services/subscription/stripe_service.py

@@ -4,7 +4,8 @@ from typing import Optional, Dict, Any
 from loguru import logger
 from fastapi import HTTPException
 from sqlalchemy.orm import Session
-from models.subscription_models import UserSubscription, SubscriptionPlan, SubscriptionTier, BillingCycle, UsageStatus, FraudWarning
+from sqlalchemy.exc import IntegrityError
+from models.subscription_models import UserSubscription, SubscriptionPlan, SubscriptionTier, BillingCycle, UsageStatus, FraudWarning, StripeWebhookEvent
 from services.subscription.pricing_service import PricingService
 from datetime import datetime
 
@@ -216,6 +217,35 @@ class StripeService:
             logger.error(f"Error creating portal session: {e}")
             raise HTTPException(status_code=500, detail=str(e))
 
+    def _ensure_webhook_event_table(self) -> None:
+        """Ensure webhook idempotency table exists before processing events."""
+        try:
+            bind = self.db.get_bind()
+            if bind is not None:
+                StripeWebhookEvent.__table__.create(bind=bind, checkfirst=True)
+        except Exception as e:
+            logger.warning(f"Failed to ensure stripe_webhook_events table exists: {e}")
+
+    def _mark_webhook_event_status(
+        self,
+        event_id: str,
+        status: str,
+        error_message: Optional[str] = None,
+    ) -> None:
+        """Update persisted webhook event processing status."""
+        event_row = self.db.query(StripeWebhookEvent).filter(
+            StripeWebhookEvent.event_id == event_id
+        ).first()
+        if not event_row:
+            return
+
+        event_row.status = status
+        event_row.error_message = (error_message or "")[:1000] if error_message else None
+        if status == "processed":
+            event_row.processed_at = datetime.utcnow()
+
+        self.db.commit()
+
     async def handle_webhook(self, payload: bytes, sig_header: str):
         """
         Handle Stripe webhooks.
@@ -235,25 +265,64 @@ class StripeService:
             logger.error(f"Invalid signature: {e}")
             raise HTTPException(status_code=400, detail="Invalid signature")
 
-        event_type = event["type"]
-        data = event["data"]["object"]
+        event_id = event.get("id")
+        event_type = event.get("type")
+        data = event.get("data", {}).get("object", {})
 
-        logger.info(f"Received Stripe webhook: {event_type}")
-        
-        if event_type == "checkout.session.completed":
-            await self._handle_checkout_completed(data)
-        elif event_type == "invoice.payment_succeeded":
-            await self._handle_invoice_payment_succeeded(data)
-        elif event_type == "invoice.payment_failed":
-            await self._handle_invoice_payment_failed(data)
-        elif event_type == "customer.subscription.updated":
-            await self._handle_subscription_updated(data)
-        elif event_type == "customer.subscription.deleted":
-            await self._handle_subscription_deleted(data)
-        elif event_type.startswith("radar.early_fraud_warning."):
-            await self._handle_early_fraud_warning(data)
+        if not event_id or not event_type:
+            logger.error("Stripe webhook missing event id/type")
+            raise HTTPException(status_code=400, detail="Invalid Stripe event payload")
 
-        return {"status": "success"}
+        # Idempotency guard: persist event id before mutating subscription state.
+        self._ensure_webhook_event_table()
+        existing_event = self.db.query(StripeWebhookEvent).filter(
+            StripeWebhookEvent.event_id == event_id
+        ).first()
+        if existing_event:
+            logger.info(f"Skipping already processed Stripe event: {event_id} ({existing_event.status})")
+            return {"status": "success", "idempotent": True}
+
+        try:
+            event_row = StripeWebhookEvent(
+                event_id=event_id,
+                event_type=event_type,
+                status="processing",
+            )
+            self.db.add(event_row)
+            self.db.commit()
+        except IntegrityError:
+            self.db.rollback()
+            logger.info(f"Skipping duplicate Stripe event insert: {event_id}")
+            return {"status": "success", "idempotent": True}
+
+        logger.info(f"Received Stripe webhook: {event_type} ({event_id})")
+
+        try:
+            if event_type == "checkout.session.completed":
+                await self._handle_checkout_completed(data)
+            elif event_type == "invoice.payment_succeeded":
+                await self._handle_invoice_payment_succeeded(data)
+            elif event_type == "invoice.payment_failed":
+                await self._handle_invoice_payment_failed(data)
+            elif event_type == "customer.subscription.updated":
+                await self._handle_subscription_updated(data)
+            elif event_type == "customer.subscription.deleted":
+                await self._handle_subscription_deleted(data)
+            elif event_type.startswith("radar.early_fraud_warning."):
+                await self._handle_early_fraud_warning(data)
+
+            self._mark_webhook_event_status(event_id=event_id, status="processed")
+            return {"status": "success"}
+
+        except Exception as e:
+            self.db.rollback()
+            self._mark_webhook_event_status(
+                event_id=event_id,
+                status="failed",
+                error_message=str(e),
+            )
+            logger.error(f"Failed Stripe webhook handling for {event_id}: {e}")
+            raise
 
     async def _handle_checkout_completed(self, session: Dict[str, Any]):
         """