Merge pull request #129 from onflow/gio/fix-storage-underflow

Fix cases of underflow in event of storage decrease
onflow · Oct 17, 2024 · d0c8e29 · d0c8e29
2 parents a3e9cb8 + ebdcec4
commit d0c8e29
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Showing 2 changed files with 16 additions and 2 deletions.
diff --git a/cadence/contracts/bridge/FlowEVMBridgeNFTEscrow.cdc b/cadence/contracts/bridge/FlowEVMBridgeNFTEscrow.cdc
@@ -104,7 +104,14 @@ access(all) contract FlowEVMBridgeNFTEscrow {
         locker.deposit(token: <-nft)
         let postStorageSnapshot = self.account.storage.used
 
-        return postStorageSnapshot - preStorageSnapshot
+        // Return the amount of storage used by the locker after storing the NFT
+        if postStorageSnapshot < preStorageSnapshot {
+            // Due to atree inlining, account storage usage may counterintuitively decrease at times - return 0
+            return 0
+        } else {
+            // Otherwise, return the storage usage delta
+            return postStorageSnapshot - preStorageSnapshot
+        }
     }
 
     /// Unlocks the NFT of the given type and ID, reverting if it isn't in escrow

diff --git a/cadence/contracts/bridge/FlowEVMBridgeTokenEscrow.cdc b/cadence/contracts/bridge/FlowEVMBridgeTokenEscrow.cdc
@@ -97,7 +97,14 @@ access(all) contract FlowEVMBridgeTokenEscrow {
         locker.deposit(from: <-vault)
         let postStorageSnapshot = self.account.storage.used
 
-        return postStorageSnapshot - preStorageSnapshot
+        // Return the amount of storage used by the locker after storing the NFT
+        if postStorageSnapshot < preStorageSnapshot {
+            // Due to atree inlining, account storage usage may counterintuitively decrease at times - return 0
+            return 0
+        } else {
+            // Otherwise, return the storage usage delta
+            return postStorageSnapshot - preStorageSnapshot
+        }
     }
 
     /// Unlocks the tokens of the given type and amount, reverting if it isn't in escrow