Increase redemption fee by a step from the two latest events

pkg/extensions/tbtc/tbtc.go

@@ -472,14 +472,29 @@ func (t *tbtc) monitorProvideRedemptionProof(
 		latestRedemptionRequestedEvent :=
 			redemptionRequestedEvents[len(redemptionRequestedEvents)-1]
 
+		// Deposit expects that the fee is always increased by a constant value
+		// equal to the fee of the initial redemption request.
+		feeBumpStep := big.NewInt(0)
+		if len(redemptionRequestedEvents) == 1 {
+			feeBumpStep = latestRedemptionRequestedEvent.RequestedFee // initial fee
+		} else {
+			// When there are many events on-chain we don't need to get the very
+			// first one, it is enough to calculate a difference between the
+			// latest fee and the one before the latest fee.
+			feeBumpStep = new(big.Int).Sub(
+				latestRedemptionRequestedEvent.RequestedFee,
+				redemptionRequestedEvents[len(redemptionRequestedEvents)-2].RequestedFee,
+			)
+		}
+
 		previousOutputValue := new(big.Int).Sub(
 			latestRedemptionRequestedEvent.UtxoValue,
 			latestRedemptionRequestedEvent.RequestedFee,
 		)
 
 		newOutputValue := new(big.Int).Sub(
 			previousOutputValue,
-			redemptionRequestedEvents[0].RequestedFee, // initial fee
+			feeBumpStep,
 		)
 
 		err = t.chain.IncreaseRedemptionFee(

pkg/extensions/tbtc/tbtc_test.go

@@ -1189,58 +1189,64 @@ func TestProvideRedemptionProof_TimeoutElapsed(t *testing.T) {
 		t.Fatal(err)
 	}
 
-	keepSignature, err := submitKeepSignature(depositAddress, tbtcChain)
-	if err != nil {
-		t.Fatal(err)
-	}
-
-	err = tbtcChain.ProvideRedemptionSignature(
-		depositAddress,
-		keepSignature.V,
-		keepSignature.R,
-		keepSignature.S,
-	)
-	if err != nil {
-		t.Fatal(err)
-	}
-
-	// wait a bit longer than the monitoring timeout
-	// to make sure the potential transaction completes
-	time.Sleep(2 * timeout)
+	// Increase the fee at least 3 times to test fee increase step determination
+	// from the two latests events.
+	for i := 1; i <= 3; i++ {
+		keepSignature, err := submitKeepSignature(depositAddress, tbtcChain)
+		if err != nil {
+			t.Fatal(err)
+		}
 
-	expectedIncreaseRedemptionFeeCalls := 1
-	actualIncreaseRedemptionFeeCalls := tbtcChain.Logger().
-		IncreaseRedemptionFeeCalls()
-	if expectedIncreaseRedemptionFeeCalls != actualIncreaseRedemptionFeeCalls {
-		t.Errorf(
-			"unexpected number of IncreaseRedemptionFee calls\n"+
-				"expected: [%v]\n"+
-				"actual:   [%v]",
-			expectedIncreaseRedemptionFeeCalls,
-			actualIncreaseRedemptionFeeCalls,
+		err = tbtcChain.ProvideRedemptionSignature(
+			depositAddress,
+			keepSignature.V,
+			keepSignature.R,
+			keepSignature.S,
 		)
-	}
+		if err != nil {
+			t.Fatal(err)
+		}
 
-	expectedDepositRedemptionFee := new(big.Int).Mul(
-		big.NewInt(2),
-		initialDepositRedemptionFee,
-	)
+		// wait a bit longer than the monitoring timeout
+		// to make sure the potential transaction completes
+		time.Sleep(2 * timeout)
+
+		expectedIncreaseRedemptionFeeCalls := i
+		actualIncreaseRedemptionFeeCalls := tbtcChain.Logger().
+			IncreaseRedemptionFeeCalls()
+		if expectedIncreaseRedemptionFeeCalls != actualIncreaseRedemptionFeeCalls {
+			t.Errorf(
+				"unexpected number of IncreaseRedemptionFee calls after [%d] increase\n"+
+					"expected: [%v]\n"+
+					"actual:   [%v]",
+				i,
+				expectedIncreaseRedemptionFeeCalls,
+				actualIncreaseRedemptionFeeCalls,
+			)
+		}
 
-	actualDepositRedemptionFee, err := tbtcChain.DepositRedemptionFee(
-		depositAddress,
-	)
-	if err != nil {
-		t.Fatal(err)
-	}
+		expectedDepositRedemptionFee := new(big.Int).Mul(
+			new(big.Int).Add(big.NewInt(1), big.NewInt(int64(i))),
+			initialDepositRedemptionFee,
+		)
 
-	if expectedDepositRedemptionFee.Cmp(actualDepositRedemptionFee) != 0 {
-		t.Errorf(
-			"unexpected redemption fee value\n"+
-				"expected: [%v]\n"+
-				"actual:   [%v]",
-			expectedDepositRedemptionFee.Text(10),
-			actualDepositRedemptionFee.Text(10),
+		actualDepositRedemptionFee, err := tbtcChain.DepositRedemptionFee(
+			depositAddress,
 		)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		if expectedDepositRedemptionFee.Cmp(actualDepositRedemptionFee) != 0 {
+			t.Errorf(
+				"unexpected redemption fee value after [%d] increase\n"+
+					"expected: [%v]\n"+
+					"actual:   [%v]",
+				i,
+				expectedDepositRedemptionFee.Text(10),
+				actualDepositRedemptionFee.Text(10),
+			)
+		}
 	}
 }