client - Add functionality to specify cors for rpc server (#1762)

* Add functionality to specify cors for rpc server

Author: g11tech

package-lock.json

@@ -159,6 +159,11 @@ const args = yargs(hideBin(process.argv))
     describe: 'Additionally log complete RPC calls on log level debug (i.e. --loglevel=debug)',
     boolean: true,
   })
+  .option('rpcCors', {
+    describe: 'Configure the Access-Control-Allow-Origin CORS header for RPC server',
+    string: true,
+    default: '*',
+  })
   .option('maxPerRequest', {
     describe: 'Max items per block or header request',
     number: true,

packages/client/bin/cli.ts

@@ -20,6 +20,7 @@ type RPCArgs = {
   helprpc: boolean
   'jwt-secret'?: string
   rpcEngineAuth: boolean
+  rpcCors: string
 }
 
 /**
@@ -104,6 +105,7 @@ export function startRPCServers(client: EthereumClient, args: RPCArgs) {
     rpcEnginePort,
     'jwt-secret': jwtSecretPath,
     rpcEngineAuth,
+    rpcCors,
   } = args
   const manager = new RPCManager(client, config)
   const jwtSecret = parseJwtSecret(config, jwtSecretPath)
@@ -121,6 +123,7 @@ export function startRPCServers(client: EthereumClient, args: RPCArgs) {
 
     if (rpc) {
       rpcHttpServer = createRPCServerListener({
+        rpcCors,
         server,
         withEngineMiddleware:
           withEngineMethods && rpcEngineAuth
@@ -140,6 +143,7 @@ export function startRPCServers(client: EthereumClient, args: RPCArgs) {
     }
     if (ws) {
       const opts: any = {
+        rpcCors,
         server,
         withEngineMiddleware: withEngineMethods && rpcEngineAuth ? { jwtSecret } : undefined,
       }
@@ -166,6 +170,7 @@ export function startRPCServers(client: EthereumClient, args: RPCArgs) {
     server.on('response', onBatchResponse)
 
     createRPCServerListener({
+      rpcCors,
       server,
       withEngineMiddleware: rpcEngineAuth
         ? {

packages/client/bin/startRpc.ts

@@ -3,10 +3,12 @@ import { Server as RPCServer, HttpServer } from 'jayson/promise'
 import { json as jsonParser } from 'body-parser'
 import { decode, TAlgorithm } from 'jwt-simple'
 import Connect, { IncomingMessage } from 'connect'
+import cors from 'cors'
 
 const algorithm: TAlgorithm = 'HS256'
 
 type CreateRPCServerListenerOpts = {
+  rpcCors?: string
   server: RPCServer
   withEngineMiddleware?: WithEngineMiddleware
 }
@@ -24,8 +26,10 @@ function checkHeaderAuth(req: any, jwtSecret: Buffer): void {
 }
 
 export function createRPCServerListener(opts: CreateRPCServerListenerOpts): HttpServer {
-  const { server, withEngineMiddleware } = opts
+  const { server, withEngineMiddleware, rpcCors } = opts
+
   const app = Connect()
+  if (rpcCors) app.use(cors({ origin: rpcCors }))
   app.use(jsonParser())
 
   if (withEngineMiddleware) {
@@ -54,9 +58,18 @@ export function createRPCServerListener(opts: CreateRPCServerListenerOpts): Http
 export function createWsRPCServerListener(
   opts: CreateRPCServerListenerOpts & { httpServer?: HttpServer }
 ): HttpServer | undefined {
-  const { server, withEngineMiddleware } = opts
+  const { server, withEngineMiddleware, rpcCors } = opts
+
   // Get the server to hookup upgrade request on
-  const httpServer = opts.httpServer ?? createServer()
+  let httpServer = opts.httpServer
+  if (!httpServer) {
+    const app = Connect()
+    // In case browser pre-flights the upgrade request with an options request
+    // more likely in case of wss connection
+    if (rpcCors) app.use(cors({ origin: rpcCors }))
+    httpServer = createServer(app)
+  }
+
   const wss = server.websocket({ noServer: true })
 
   httpServer.on('upgrade', (req, socket, head) => {

packages/client/lib/util/rpc.ts

@@ -60,6 +60,7 @@
     "body-parser": "^1.19.2",
     "chalk": "^4.1.2",
     "connect": "^3.7.0",
+    "cors": "^2.8.5",
     "debug": "^4.3.3",
     "ethereumjs-util": "^7.1.4",
     "fs-extra": "^10.0.0",