improve network connectivity (#441)

package.json

@@ -10,7 +10,7 @@
     "@uniswap/sdk": "^1.0.0-beta.4",
     "copy-to-clipboard": "^3.2.0",
     "escape-string-regexp": "^2.0.0",
-    "ethers": "^4.0.33",
+    "ethers": "^4.0.36",
     "i18next": "^15.0.9",
     "i18next-browser-languagedetector": "^3.0.1",
     "i18next-xhr-backend": "^2.0.1",
@@ -27,7 +27,7 @@
     "react-spring": "^8.0.20",
     "react-switch": "^5.0.1",
     "styled-components": "^4.2.0",
-    "web3-react": "^5.0.4"
+    "web3-react": "5.0.5"
   },
   "scripts": {
     "start": "react-scripts start",

src/NetworkOnlyConnector.js

+import { ethers } from 'ethers'
+import { Connectors } from 'web3-react'
+
+const { Connector } = Connectors
+
+function getFallbackProvider(providerURL) {
+  const etherscan = new ethers.providers.EtherscanProvider()
+  const infura = new ethers.providers.JsonRpcProvider(providerURL)
+
+  const providers = [infura, etherscan]
+
+  return new ethers.providers.FallbackProvider(providers)
+}
+
+export default class NetworkOnlyConnector extends Connector {
+  constructor(kwargs) {
+    const { providerURL, ...rest } = kwargs || {}
+    super(rest)
+    this.providerURL = providerURL
+  }
+
+  async onActivation() {
+    if (!this.engine) {
+      const provider = getFallbackProvider(this.providerURL)
+      provider.polling = false
+      provider.pollingInterval = 300000 // 5 minutes
+      this.engine = provider
+    }
+  }
+
+  async getNetworkId(provider) {
+    const networkId = await provider.getNetwork().then(network => network.chainId)
+    return super._validateNetworkId(networkId)
+  }
+
+  async getProvider() {
+    return this.engine
+  }
+
+  async getAccount() {
+    return null
+  }
+}

src/index.js

 import React from 'react'
 import ReactDOM from 'react-dom'
 import ReactGA from 'react-ga'
-import Web3Provider, { Connectors } from 'web3-react'
+import Web3Provider from 'web3-react'
 
 import ThemeProvider, { GlobalStyle } from './theme'
 import LocalStorageContextProvider, { Updater as LocalStorageContextUpdater } from './contexts/LocalStorage'
@@ -13,6 +13,7 @@ import AllowancesContextProvider from './contexts/Allowances'
 import AllBalancesContextProvider from './contexts/AllBalances'
 
 import App from './pages/App'
+import NetworkOnlyConnector from './NetworkOnlyConnector'
 import InjectedConnector from './InjectedConnector'
 
 import './i18n'
@@ -24,9 +25,8 @@ if (process.env.NODE_ENV === 'production') {
 }
 ReactGA.pageview(window.location.pathname + window.location.search)
 
-const { NetworkOnlyConnector } = Connectors
-const Injected = new InjectedConnector({ supportedNetworks: [Number(process.env.REACT_APP_NETWORK_ID || '1')] })
 const Network = new NetworkOnlyConnector({ providerURL: process.env.REACT_APP_NETWORK_URL || '' })
+const Injected = new InjectedConnector({ supportedNetworks: [Number(process.env.REACT_APP_NETWORK_ID || '1')] })
 const connectors = { Injected, Network }
 
 function ContextProviders({ children }) {