From 5c1c9c8f161a1d8ed96d88b8f5b586f125d9a588 Mon Sep 17 00:00:00 2001
From: David Walsh <davidwalsh83@gmail.com>
Date: Wed, 21 Oct 2020 15:05:48 -0500
Subject: [PATCH] Fix 9632 - Prevent old fetches from polluting the swap state

---
 app/scripts/controllers/swaps.js  | 14 ++++++++++++++
 ui/app/ducks/swaps/swaps.js       |  5 +++++
 ui/app/helpers/constants/swaps.js |  1 +
 3 files changed, 20 insertions(+)

diff --git a/app/scripts/controllers/swaps.js b/app/scripts/controllers/swaps.js
index ced804a35..a464729c1 100644
--- a/app/scripts/controllers/swaps.js
+++ b/app/scripts/controllers/swaps.js
@@ -12,6 +12,7 @@ import {
   DEFAULT_ERC20_APPROVE_GAS,
   QUOTES_EXPIRED_ERROR,
   QUOTES_NOT_AVAILABLE_ERROR,
+  SWAPS_FETCH_ORDER_CONFLICT,
 } from '../../../ui/app/helpers/constants/swaps'
 import {
   fetchTradesInfo as defaultFetchTradesInfo,
@@ -88,6 +89,8 @@ export default class SwapsController {
     this.pollCount = 0
     this.getProviderConfig = getProviderConfig
 
+    this.indexOfNewestCallInFlight = 0
+
     this.ethersProvider = new ethers.providers.Web3Provider(provider)
 
     this._setupSwapsLivenessFetching()
@@ -124,6 +127,10 @@ export default class SwapsController {
     if (!isPolledRequest) {
       this.setSwapsErrorKey('')
     }
+
+    const indexOfCurrentCall = this.indexOfNewestCallInFlight + 1
+    this.indexOfNewestCallInFlight = indexOfCurrentCall
+
     let newQuotes = await this._fetchTradesInfo(fetchParams)
 
     newQuotes = mapValues(newQuotes, (quote) => ({
@@ -184,11 +191,18 @@ export default class SwapsController {
       }
     }
 
+    // If a newer call has been made, don't update state with old information
+    // Prevents timing conflicts between fetches
+    if (this.indexOfNewestCallInFlight !== indexOfCurrentCall) {
+      throw new Error(SWAPS_FETCH_ORDER_CONFLICT)
+    }
+
     const { swapsState } = this.store.getState()
     let { selectedAggId } = swapsState
     if (!newQuotes[selectedAggId]) {
       selectedAggId = null
     }
+
     this.store.updateState({
       swapsState: {
         ...swapsState,
diff --git a/ui/app/ducks/swaps/swaps.js b/ui/app/ducks/swaps/swaps.js
index e6fbb71e7..ad45036d4 100644
--- a/ui/app/ducks/swaps/swaps.js
+++ b/ui/app/ducks/swaps/swaps.js
@@ -36,6 +36,7 @@ import {
   QUOTES_NOT_AVAILABLE_ERROR,
   ETH_SWAPS_TOKEN_OBJECT,
   SWAP_FAILED_ERROR,
+  SWAPS_FETCH_ORDER_CONFLICT,
 } from '../../helpers/constants/swaps'
 import { SWAP, SWAP_APPROVAL } from '../../helpers/constants/transactions'
 import { fetchBasicGasAndTimeEstimates, fetchGasEstimates, resetCustomGasState } from '../gas/gas.duck'
@@ -399,6 +400,10 @@ export const fetchQuotesAndSetQuoteState = (history, inputValue, maxSlippage, me
         dispatch(setInitialGasEstimate(selectedAggId))
       }
     } catch (e) {
+      // A newer swap request is running, so simply bail and let the newer request respond
+      if (e.message === SWAPS_FETCH_ORDER_CONFLICT) {
+        return
+      }
       dispatch(setSwapsErrorKey(ERROR_FETCHING_QUOTES))
     }
 
diff --git a/ui/app/helpers/constants/swaps.js b/ui/app/helpers/constants/swaps.js
index f9ccc5a78..a20000a0c 100644
--- a/ui/app/helpers/constants/swaps.js
+++ b/ui/app/helpers/constants/swaps.js
@@ -14,6 +14,7 @@ export const SWAP_FAILED_ERROR = 'swap-failed-error'
 export const ERROR_FETCHING_QUOTES = 'error-fetching-quotes'
 export const QUOTES_NOT_AVAILABLE_ERROR = 'quotes-not-avilable'
 export const OFFLINE_FOR_MAINTENANCE = 'offline-for-maintenance'
+export const SWAPS_FETCH_ORDER_CONFLICT = 'swaps-fetch-order-conflict'
 
 // A gas value for ERC20 approve calls that should be sufficient for all ERC20 approve implementations
 export const DEFAULT_ERC20_APPROVE_GAS = '0x1d4c0'