Handle JSONRPC error codes in web3 providers (#491)

oracle/src/services/HttpListProvider.js

@@ -1,6 +1,9 @@
 const fetch = require('node-fetch')
 const promiseRetry = require('promise-retry')
 
+// From EIP-1474 and Infura documentation
+const JSONRPC_ERROR_CODES = [-32603, -32002, -32005]
+
 const defaultOptions = {
   requestTimeout: 0,
   retry: {
@@ -61,6 +64,12 @@ function send(url, payload, options) {
       }
     })
     .then(response => response.json())
+    .then(response => {
+      if (response.error && JSONRPC_ERROR_CODES.includes(response.error.code)) {
+        throw new Error(response.error.message)
+      }
+      return response
+    })
 }
 
 async function trySend(payload, urls, initialIndex, options) {

oracle/src/services/RedundantHttpListProvider.js

@@ -13,7 +13,6 @@ function RedundantHttpListProvider(urls, options = {}) {
 
   this.urls = urls
   this.options = { ...defaultOptions, ...options }
-  this.currentIndex = 0
 }
 
 RedundantHttpListProvider.prototype.send = async function send(payload, callback) {