feat: allow scaling of trusting period for client upgrades

modules/light-clients/07-tendermint/upgrade.go

@@ -2,8 +2,10 @@ package tendermint
 
 import (
 	"fmt"
+	"time"
 
 	errorsmod "cosmossdk.io/errors"
+	sdkmath "cosmossdk.io/math"
 	storetypes "cosmossdk.io/store/types"
 	upgradetypes "cosmossdk.io/x/upgrade/types"
 
@@ -17,8 +19,10 @@ import (
 )
 
 // VerifyUpgradeAndUpdateState checks if the upgraded client has been committed by the current client
-// It will zero out all client-specific fields (e.g. TrustingPeriod) and verify all data
-// in client state that must be the same across all valid Tendermint clients for the new chain.
+// It will zero out all client-specific fields and verify all data in client state that must
+// be the same across all valid Tendermint clients for the new chain.
+// Note, if there is a decrease in the UnbondingPeriod, then the TrustingPeriod, despite being a client-specific field
+// is scaled down by the same ratio.
 // VerifyUpgrade will return an error if:
 // - the upgradedClient is not a Tendermint ClientState
 // - the latest height of the client state does not have the same revision number or has a greater
@@ -93,12 +97,17 @@ func (cs ClientState) VerifyUpgradeAndUpdateState(
 		return errorsmod.Wrapf(err, "consensus state proof failed. Path: %s", upgradeConsStatePath.GetKeyPath())
 	}
 
+	trustingPeriod := cs.TrustingPeriod
+	if tmUpgradeClient.UnbondingPeriod < cs.UnbondingPeriod {
+		trustingPeriod = calculateNewTrustingPeriod(trustingPeriod, cs.UnbondingPeriod, tmUpgradeClient.UnbondingPeriod)
+	}
+
 	// Construct new client state and consensus state
 	// Relayer chosen client parameters are ignored.
 	// All chain-chosen parameters come from committed client, all client-chosen parameters
 	// come from current client.
 	newClientState := NewClientState(
-		tmUpgradeClient.ChainId, cs.TrustLevel, cs.TrustingPeriod, tmUpgradeClient.UnbondingPeriod,
+		tmUpgradeClient.ChainId, cs.TrustLevel, trustingPeriod, tmUpgradeClient.UnbondingPeriod,
 		cs.MaxClockDrift, tmUpgradeClient.LatestHeight, tmUpgradeClient.ProofSpecs, tmUpgradeClient.UpgradePath,
 	)
 
@@ -165,3 +174,19 @@ func constructUpgradeConsStateMerklePath(upgradePath []string, lastHeight export
 
 	return commitmenttypes.NewMerklePath(consStateKey...)
 }
+
+// calculateNewTrustingPeriod converts the provided durations to decimal representation to avoid floating-point precision issues
+// and calculates the new trusting period, decreasing it by the ratio between the original and new unbonding period.
+func calculateNewTrustingPeriod(trustingPeriod, originalUnbonding, newUnbonding time.Duration) time.Duration {
+	origUnbondingDec := sdkmath.LegacyNewDec(originalUnbonding.Nanoseconds())
+	newUnbondingDec := sdkmath.LegacyNewDec(newUnbonding.Nanoseconds())
+	trustingPeriodDec := sdkmath.LegacyNewDec(trustingPeriod.Nanoseconds())
+
+	// compute decrease ratio: (originalUnbonding - newUnbonding) / originalUnbonding
+	decreaseRatio := origUnbondingDec.Sub(newUnbondingDec).Quo(origUnbondingDec)
+
+	// compute new trusting period: trustingPeriod * (1 - decreaseRatio)
+	newTrustingPeriodDec := trustingPeriodDec.Mul(sdkmath.LegacyOneDec().Sub(decreaseRatio))
+
+	return time.Duration(newTrustingPeriodDec.TruncateInt64()) * time.Nanosecond
+}

modules/light-clients/07-tendermint/upgrade_test.go

@@ -2,6 +2,7 @@ package tendermint_test
 
 import (
 	"errors"
+	"time"
 
 	upgradetypes "cosmossdk.io/x/upgrade/types"
 
@@ -86,6 +87,38 @@ func (suite *TendermintTestSuite) TestVerifyUpgrade() {
 			},
 			expErr: nil,
 		},
+		{
+			name: "successful upgrade scales trusting period with unbonding period decrease",
+			setup: func() {
+				newUnbondingPeriod := time.Hour * 24 * 7 * 2
+				upgradedClient = ibctm.NewClientState(suite.chainB.ChainID, ibctm.DefaultTrustLevel, trustingPeriod, newUnbondingPeriod, maxClockDrift, clienttypes.NewHeight(clienttypes.ParseChainID(suite.chainB.ChainID), upgradedClient.(*ibctm.ClientState).LatestHeight.GetRevisionHeight()+10), commitmenttypes.GetSDKSpecs(), upgradePath)
+				upgradedClient = upgradedClient.(*ibctm.ClientState).ZeroCustomFields()
+				upgradedClientBz, err = clienttypes.MarshalClientState(suite.chainA.App.AppCodec(), upgradedClient)
+				suite.Require().NoError(err)
+
+				// upgrade Height is at next block
+				lastHeight = clienttypes.NewHeight(0, uint64(suite.chainB.GetContext().BlockHeight()+1))
+
+				// zero custom fields and store in upgrade store
+				suite.chainB.GetSimApp().UpgradeKeeper.SetUpgradedClient(suite.chainB.GetContext(), int64(lastHeight.GetRevisionHeight()), upgradedClientBz)            //nolint:errcheck // ignore error for test
+				suite.chainB.GetSimApp().UpgradeKeeper.SetUpgradedConsensusState(suite.chainB.GetContext(), int64(lastHeight.GetRevisionHeight()), upgradedConsStateBz) //nolint:errcheck // ignore error for test
+
+				// commit upgrade store changes and update clients
+
+				suite.coordinator.CommitBlock(suite.chainB)
+				err := path.EndpointA.UpdateClient()
+				suite.Require().NoError(err)
+
+				cs, found := suite.chainA.App.GetIBCKeeper().ClientKeeper.GetClientState(suite.chainA.GetContext(), path.EndpointA.ClientID)
+				suite.Require().True(found)
+				tmCs, ok := cs.(*ibctm.ClientState)
+				suite.Require().True(ok)
+
+				upgradedClientProof, _ = suite.chainB.QueryUpgradeProof(upgradetypes.UpgradedClientKey(int64(lastHeight.GetRevisionHeight())), tmCs.LatestHeight.GetRevisionHeight())
+				upgradedConsensusStateProof, _ = suite.chainB.QueryUpgradeProof(upgradetypes.UpgradedConsStateKey(int64(lastHeight.GetRevisionHeight())), tmCs.LatestHeight.GetRevisionHeight())
+			},
+			expErr: nil,
+		},
 		{
 			name: "unsuccessful upgrade: upgrade path not set",
 			setup: func() {