Handle 429 error (#102)

* [handle-429-error] improve createProvider method

* [handle-429-error] improves

src/index.ts

@@ -3,5 +3,5 @@ import './types/global'
 
 export * from './utils/enums'
 export { createContract } from './contracts'
-export { BigDecimal, configs, getGas } from './utils'
 export { default as StakeWiseSDK } from './StakeWiseSDK'
+export { BigDecimal, configs, getGas, createProvider } from './utils'

src/utils/apiUrls.ts

@@ -1,11 +1,13 @@
 import configs from './configs'
 
 
+const getWeb3Url = (options: StakeWise.Options) => options.endpoints?.web3 || configs[options.network].network.url
 const getBackendUrl = (options: StakeWise.Options) => options.endpoints?.api || configs[options.network].api.backend
 const getSubgraphqlUrl = (options: StakeWise.Options) => options.endpoints?.subgraph || configs[options.network].api.subgraph
 
 
 export default {
+  getWeb3Url,
   getBackendUrl,
   getSubgraphqlUrl,
 }

src/utils/createProvider.ts

@@ -1,26 +1,60 @@
-import { JsonRpcProvider, FallbackProvider } from 'ethers'
+import { JsonRpcProvider, FallbackProvider, FetchRequest, FetchResponse } from 'ethers'
 
-import configs from './configs'
+import apiUrls from './apiUrls'
 
 
 const createProvider = (options: StakeWise.Options) => {
-  const urls = options.endpoints?.web3
+  const { network } = options
 
-  if (!urls) {
-    return new JsonRpcProvider(configs[options.network].network.url)
-  }
+  const urls = apiUrls.getWeb3Url(options)
 
   if (Array.isArray(urls)) {
     if (urls.length === 1) {
       return new JsonRpcProvider(urls[0])
     }
     else {
-      const providers: ConstructorParameters<typeof FallbackProvider>[0] = urls.map((url, index) => ({
-        provider: new JsonRpcProvider(url),
-        priority: index + 1,
-      }))
+      const providers: ConstructorParameters<typeof FallbackProvider>[0] = urls.map((url, index) => {
+        // Why do we use FetchRequest and change the behavior of the 429 error?
+        // Because inside ethers error 429 is handled only by resending the request
+        // and in this case no additional node is started. This is a problem for public nodes,
+        // so we think it is better to use an additional node in case of 429 error
+        const fetchRequest = new FetchRequest(url)
+
+        fetchRequest.setThrottleParams({
+          slotInterval: 2 * 1000,
+          maxAttempts: 2,
+        })
+
+        fetchRequest.processFunc = async (_, resp) => {
+          if (resp.statusCode === 429) {
+            // mutate the response to 500 to start an additional node
+            // https://github.com/ethers-io/ethers.js/blob/main/src.ts/utils/fetch.ts#L519
+            const newResponse = new FetchResponse(500, '', resp.headers, null)
+
+            return newResponse
+          }
+
+          return resp
+        }
+
+        fetchRequest.retryFunc = async (_, response) => {
+          if (response.statusCode === 429) {
+            // stop retry attempts
+            // https://github.com/ethers-io/ethers.js/blob/main/src.ts/utils/fetch.ts#L556
+            return false
+          }
+
+          return true
+        }
+
+        return {
+          provider: new JsonRpcProvider(fetchRequest, network),
+          priority: index + 1,
+          weight: 1,
+        }
+      })
 
-      const provider = new FallbackProvider(providers) as StakeWise.CustomFallbackProvider
+      const provider = new FallbackProvider(providers, network) as StakeWise.CustomFallbackProvider
 
       provider.getSigner = () => {
         throw new Error('Pass your provider to the SDK class instance to get a signer')