add webSocket example (nodejs#2626)

* add webSocket example

* lint

* refactor: Organize proxy-related code into separate files

* refactor: Organize proxy-related code into separate files

* feat: move websocket instance to separate file

---------

Co-authored-by: Mert Can Altin <mert.altin@trendyol.com>

examples/proxy/index.js

@@ -45,5 +45,3 @@ async function run () {
 }
 
 run()
-
-// TODO: Add websocket example.

examples/proxy/websocket.js

@@ -0,0 +1,89 @@
+const { Pool, Client } = require('../../')
+const http = require('http')
+const proxy = require('./proxy')
+const WebSocket = require('ws')
+
+const pool = new Pool('http://localhost:4001', {
+  connections: 256,
+  pipelining: 1
+})
+
+function createWebSocketServer () {
+  const wss = new WebSocket.Server({ noServer: true })
+
+  wss.on('connection', ws => {
+    ws.on('message', message => {
+      console.log(`Received message: ${message}`)
+      ws.send('Received your message!')
+    })
+  })
+
+  return wss
+}
+
+async function run () {
+  await Promise.all([
+    new Promise(resolve => {
+      // Proxy
+      http.createServer((req, res) => {
+        proxy({ req, res, proxyName: 'example' }, pool).catch(err => {
+          if (res.headersSent) {
+            res.destroy(err)
+          } else {
+            for (const name of res.getHeaderNames()) {
+              res.removeHeader(name)
+            }
+            res.statusCode = err.statusCode || 500
+            res.end()
+          }
+        })
+      }).listen(4000, resolve)
+    }),
+    new Promise(resolve => {
+      // Upstream
+      http.createServer((req, res) => {
+        res.end('hello world')
+      }).listen(4001, resolve)
+    }),
+    new Promise(resolve => {
+      // WebSocket server
+      const server = http.createServer((req, res) => {
+        res.writeHead(200, { 'Content-Type': 'text/plain' })
+        res.end('WebSocket server is running!')
+      })
+
+      const wss = createWebSocketServer()
+
+      server.on('upgrade', (request, socket, head) => {
+        wss.handleUpgrade(request, socket, head, ws => {
+          wss.emit('connection', ws, request)
+        })
+      })
+
+      server.listen(4002, resolve)
+    })
+  ])
+
+  const client = new Client('http://localhost:4000')
+  const { body } = await client.request({
+    method: 'GET',
+    path: '/'
+  })
+
+  for await (const chunk of body) {
+    console.log(String(chunk))
+  }
+
+  // WebSocket client
+  const ws = new WebSocket('ws://localhost:4002')
+  ws.on('open', () => {
+    ws.send('Hello, WebSocket Server!')
+  })
+
+  ws.on('message', message => {
+    console.log(`WebSocket Server says: ${message}`)
+    ws.close()
+  })
+}
+
+run()