feat: update totalFee calculation

src/order-book/transformOrder.test.ts

@@ -0,0 +1,59 @@
+import { Order, OrderClass, OrderKind, OrderStatus, SigningScheme } from './generated'
+import { transformOrder } from './transformOrder'
+
+const ORDER: Order = {
+  sellToken: '0x6810e776880c02933d47db1b9fc05908e5386b96',
+  buyToken: '0x6810e776880c02933d47db1b9fc05908e5386b96',
+  sellAmount: '1234567890',
+  buyAmount: '1234567890',
+  validTo: 0,
+  appData: '0x0000000000000000000000000000000000000000000000000000000000000000',
+  partiallyFillable: true,
+  kind: OrderKind.BUY,
+  class: OrderClass.MARKET,
+  feeAmount: '1234567890',
+  signature:
+    '0x4d306ce7c770d22005bcfc00223f8d9aaa04e8a20099cc986cb9ccf60c7e876b777ceafb1e03f359ebc6d3dc84245d111a3df584212b5679cb5f9e6717b69b031b',
+  signingScheme: SigningScheme.EIP1271,
+  creationDate: '2020-12-03T18:35:18.814523Z',
+  owner: '0x6810e776880c02933d47db1b9fc05908e5386b96',
+  uid: '0x59920c85de0162e9e55df8d396e75f3b6b7c2dfdb535f03e5c807731c31585eaff714b8b0e2700303ec912bd40496c3997ceea2b616d6710',
+  executedSellAmount: '1234567890',
+  executedSellAmountBeforeFees: '1234567890',
+  executedBuyAmount: '1234567890',
+  executedFeeAmount: '1234567890',
+  invalidated: true,
+  status: OrderStatus.FULFILLED,
+}
+
+describe('transformOrder', () => {
+  describe('addTotalFeeToOrder', () => {
+    test('should use executedFeeAmount when executedSurplusFee is 0', () => {
+      const rawOrder = { ...ORDER, executedFeeAmount: '1', executedSurplusFee: '0' }
+      const transformedOrder = transformOrder(rawOrder)
+
+      expect(transformedOrder.totalFee).toEqual(rawOrder.executedFeeAmount)
+    })
+
+    test('should use executedSurplusFee when executedFeeAmount is 0', () => {
+      const rawOrder = { ...ORDER, executedFeeAmount: '0', executedSurplusFee: '1' }
+      const transformedOrder = transformOrder(rawOrder)
+
+      expect(transformedOrder.totalFee).toEqual(rawOrder.executedSurplusFee)
+    })
+
+    test('should use sum of executedFeeAmount and executedSurplusFee', () => {
+      const rawOrder = { ...ORDER, executedFeeAmount: '1', executedSurplusFee: '1' }
+      const transformedOrder = transformOrder(rawOrder)
+
+      expect(transformedOrder.totalFee).toEqual('2')
+    })
+
+    test('should not fail when executedSurplusFee is falsy', () => {
+      const rawOrder = { ...ORDER, executedSurplusFee: null }
+      const transformedOrder = transformOrder(rawOrder)
+
+      expect(transformedOrder.totalFee).toEqual(rawOrder.executedFeeAmount)
+    })
+  })
+})

src/order-book/transformOrder.ts

@@ -16,16 +16,23 @@ export function transformOrder(order: Order): EnrichedOrder {
 /**
  * Add the total fee to the order.
  *
- * The `executedSurplusFee` represents exactly the fee that was charged (regardless of the fee
- * signed with the order). So, while the protocol currently does not allow placing a limit order
- * with any other fee than 0 - the backend is designed to support these kinds of orders for the
- * future.
+ * The total fee of the order will be represented by the `totalFee` field, which is the sum of `executedSurplusFee`
+ * and `executedFeeAmount`.
+ *
+ * Note that either `executedSurplusFee` or `executedFeeAmount` may be `0`, or both might have a non `0` value.
+ *
+ * See https://cowservices.slack.com/archives/C036G0J90BU/p1705322037866779?thread_ts=1705083817.684659&cid=C036G0J90BU
+ *
  * @param dto The order to add the total fee to.
  * @returns The order with the total fee added.
  */
 function addTotalFeeToOrder(dto: Order): EnrichedOrder {
   const { executedFeeAmount, executedSurplusFee } = dto
-  const totalFee = executedSurplusFee ?? executedFeeAmount
+
+  const _executedFeeAmount = BigInt(executedFeeAmount || '0')
+  const _executedSurplusFee = BigInt(executedSurplusFee || '0')
+
+  const totalFee = String(_executedFeeAmount + _executedSurplusFee)
 
   return {
     ...dto,