validate position exists at createPaidRebalancer time

Author: holyfuchs

cadence/contracts/FlowALPModels.cdc

@@ -2123,6 +2123,9 @@ access(all) contract FlowALPModels {
             pullFromTopUpSource: Bool
         ): @{FungibleToken.Vault}
 
+        /// Returns true if a position with the given ID exists in the pool.
+        access(all) view fun positionExists(pid: UInt64): Bool
+
         /// Rebalances the specified position.
         access(EPosition | ERebalance) fun rebalancePosition(pid: UInt64, force: Bool)
 

cadence/contracts/FlowALPRebalancerPaidv1.cdc

@@ -239,9 +239,9 @@ access(all) contract FlowALPRebalancerPaidv1 {
     /// Returns a RebalancerPaid resource; the underlying PositionRebalancer is stored in this contract
     /// and the first run is scheduled.
     access(all) fun createPaidRebalancer(positionID: UInt64) {
-        let rebalancer <- create PositionRebalancer(
-            positionID: positionID
-        )
+        let pool = self.poolCap!.borrow()!
+        assert(pool.positionExists(pid: positionID), message: "Invalid position ID \(positionID) - position does not exist")
+        let rebalancer <- create PositionRebalancer(positionID: positionID)
         // will panic if the rebalancer already exists
         self.storeRebalancer(rebalancer: <-rebalancer, positionID: positionID)
         self.setSelfCapability(positionID: positionID).fixReschedule()

cadence/contracts/FlowALPv0.cdc

@@ -1694,6 +1694,10 @@ access(all) contract FlowALPv0 {
         /// Rebalancing is done on a best effort basis (even when force=true). If the position has no sink/source,
         /// of either cannot accept/provide sufficient funds for rebalancing, the rebalance will still occur but will
         /// not cause the position to reach its target health.
+        access(all) view fun positionExists(pid: UInt64): Bool {
+            return self.positions[pid] != nil
+        }
+
         access(FlowALPModels.EPosition | FlowALPModels.ERebalance) fun rebalancePosition(pid: UInt64, force: Bool) {
             pre {
                 !self.isPaused(): "Withdrawal, deposits, and liquidations are paused by governance"

cadence/tests/paid_auto_balance_test.cdc

@@ -320,6 +320,19 @@ access(all) fun test_supervisor_stale_uuid_does_not_panic() {
     Test.assertEqual(1, removedEvts2.length)
 }
 
+access(all) fun test_invalid_position_id() {
+    let invalidPositionID: UInt64 = 9999
+
+    let createRes = Test.executeTransaction(Test.Transaction(
+        code: Test.readFile("./transactions/rebalancer/add_paid_rebalancer_with_id.cdc"),
+        authorizers: [protocolAccount.address],
+        signers: [protocolAccount],
+        arguments: [invalidPositionID]
+    ))
+    Test.expect(createRes, Test.beFailed())
+    Test.assertError(createRes, errorMessage: "position does not exist")
+}
+
 access(all) fun test_supervisor() {
     Test.moveTime(by: 100.0)
     Test.commitBlock()

cadence/tests/transactions/rebalancer/add_paid_rebalancer_with_id.cdc

@@ -0,0 +1,7 @@
+import "FlowALPRebalancerPaidv1"
+
+transaction(positionID: UInt64) {
+    prepare(signer: auth(Storage) &Account) {
+        FlowALPRebalancerPaidv1.createPaidRebalancer(positionID: positionID)
+    }
+}