add reconnection example

Author: simone-sanfratello

README.md

@@ -245,15 +245,18 @@ To enable the feature, set the `wsReconnect` option to an object with the follow
 - `reconnectOnClose`: Whether to reconnect on close, as long as the connection from the related client to the proxy is active (default: `false`).
 - `logs`: Whether to log the reconnection process (default: `false`).
 
+See the example in [examples/reconnection](examples/reconnection).
+
 ## wsHooks
 
 On websocket events, the following hooks are available, note **the hooks are all synchronous**.
 
-- `onConnect`: A hook function that is called when the connection is established `onConnect(source, target)` (default: `undefined`).
-- `onDisconnect`: A hook function that is called when the connection is closed `onDisconnect(source)` (default: `undefined`).
-- `onReconnect`: A hook function that is called when the connection is reconnected `onReconnect(source, target)` (default: `undefined`).
 - `onIncomingMessage`: A hook function that is called when the request is received from the client `onIncomingMessage({ data, binary })` (default: `undefined`).
 - `onOutgoingMessage`: A hook function that is called when the response is received from the target `onOutgoingMessage({ data, binary })` (default: `undefined`).
+- `onConnect`: A hook function that is called when the connection is established `onConnect(source, target)` (default: `undefined`).
+- `onDisconnect`: A hook function that is called when the connection is closed `onDisconnect(source)` (default: `undefined`).
+- `onReconnect`: A hook function that is called when the connection is reconnected `onReconnect(source, target)` (default: `undefined`). The function is called if reconnection feature is enabled.
+- `onPong`: A hook function that is called when the target responds to the ping `onPong(source, target)` (default: `undefined`). The function is called if reconnection feature is enabled.
 
 ## Benchmarks
 

examples/reconnection/ReconnectionExample.md

@@ -0,0 +1,60 @@
+# Reconnection Example
+
+This example demonstrates how to use the reconnection feature of the proxy.
+
+It simulates an unstable target service: slow to start, unresponsive due to block of the event loop, crash and restart.
+
+The goal is to ensures a more resilient and customizable integration, minimizing disruptions caused by connection instability.
+
+
+## How to run
+
+Run the unstable target
+
+```
+cd examples/reconnection/unstable-target
+npm run unstable
+```
+
+Run the proxy
+
+```
+cd examples/reconnection/proxy
+npm run start
+```
+
+Then run the client
+
+```
+cd examples/reconnection/client
+npm run start
+```
+
+---
+
+## How it works
+
+### Proxy Connection Monitoring and Recovery
+
+The proxy monitors the target connection using a ping/pong mechanism. If a pong response does not arrive on time, the connection is closed, and the proxy attempts to reconnect.
+
+If the target service crashes, the connection may close either gracefully or abruptly. Regardless of how the disconnection occurs, the proxy detects the connection loss and initiates a reconnection attempt.
+
+### Connection Stability
+
+- The connection between the client and the proxy remains unaffected by an unstable target.
+- The connection between the proxy and the target may be closed due to:
+- The target failing to respond to ping messages, even if the connection is still technically open (e.g., due to a freeze or blockage).
+- The target crashing and restarting.
+
+### Handling Data Loss During Reconnection
+
+The proxy supports hooks to manage potential data loss during reconnection. These hooks allow for custom logic to ensure message integrity when resending data from the client to the target.
+
+Examples of how hooks can be used based on the target service type:
+
+- GraphQL subscriptions: Resend the subscription from the last received message.
+- Message brokers: Resend messages starting from the last successfully processed message.
+
+In this example, the proxy re-sends the messages from the last ping to ensure all the messages are sent to the target, without any additional logic. 
+Resending messages from the last pong ensures that the target does not miss any messages, but it may send messages more than once.

examples/reconnection/client/index.js

@@ -0,0 +1,75 @@
+'use strict'
+
+const WebSocket = require('ws')
+
+const port = process.env.PORT || 3001
+
+// connect to proxy
+
+const url = `ws://localhost:${port}/`
+const ws = new WebSocket(url)
+const client = WebSocket.createWebSocketStream(ws, { encoding: 'utf8', objectMode: true })
+
+client.setEncoding('utf8')
+
+let i = 1
+setInterval(() => {
+  client.write(JSON.stringify({
+    message: i
+  }))
+  i++
+}, 1000).unref()
+const responses = {}
+
+client.on('data', message => {
+  const data = JSON.parse(message)
+  console.log('Received', data)
+  responses[data.response] = responses[data.response] ? responses[data.response] + 1 : 1
+})
+
+client.on('error', error => {
+  console.log('Error')
+  console.error(error)
+})
+
+client.on('close', () => {
+  console.log('\n\n\nConnection closed')
+
+  console.log('\n\n\nResponses')
+  for (const key in responses) {
+    if (!responses[key]) {
+      console.log('missing', key)
+    } else if (responses[key] !== 1) {
+      console.log('extra messages', key, responses[key])
+    }
+  }
+})
+
+client.on('unexpected-response', (error) => {
+  console.log('Unexpected response')
+  console.error(error)
+})
+
+client.on('redirect', (error) => {
+  console.log('Redirect')
+  console.error(error)
+})
+
+client.on('upgrade', (error) => {
+  console.log('Upgrade')
+  console.error(error)
+})
+
+client.on('ping', (error) => {
+  console.log('Ping')
+  console.error(error)
+})
+
+client.on('pong', (error) => {
+  console.log('Pong')
+  console.error(error)
+})
+
+process.on('SIGINT', () => {
+  client.end()
+})

examples/reconnection/client/package.json

@@ -0,0 +1,12 @@
+{
+  "name": "client",
+  "version": "1.0.0",
+  "main": "index.js",
+  "scripts": {
+    "start": "node index.js",
+    "dev": "node --watch index.js"
+  },
+  "dependencies": {
+    "ws": "^8.18.0"
+  }
+}

examples/reconnection/proxy/index.js

@@ -0,0 +1,73 @@
+'use strict'
+
+const { setTimeout: wait } = require('node:timers/promises')
+const fastify = require('fastify')
+const fastifyHttpProxy = require('../../../')
+
+async function main () {
+  const port = process.env.PORT || 3001
+
+  const wsReconnect = {
+    logs: true,
+    pingInterval: 3_000,
+    reconnectOnClose: true,
+  }
+
+  let backup = []
+  let lastPong = Date.now()
+
+  // resend messages from last ping
+  // it may send messages more than once
+  // in case the target already received messages between last ping and the reconnection
+  async function resendMessages (target) {
+    const now = Date.now()
+
+    for (const m of backup) {
+      if (m.timestamp < lastPong || m.timestamp > now) {
+        continue
+      }
+      console.log(' >>> resending message #', m)
+      target.send(m.message)
+      // introduce a small delay to avoid to flood the target
+      await wait(250)
+    }
+  };
+
+  const wsHooks = {
+    onPong: () => {
+      console.log('onPong')
+      lastPong = Date.now()
+      // clean backup from the last ping
+      backup = backup.filter(message => message.timestamp > lastPong)
+    },
+    onIncomingMessage: (message) => {
+      const m = message.data.toString()
+      console.log('onIncomingMessage backup', m)
+      backup.push({ message: m, timestamp: Date.now() })
+    },
+    // onOutgoingMessage: (message) => {
+    //   console.log('onOutgoingMessage', message.data.toString())
+    // },
+    onDisconnect: () => {
+      console.log('onDisconnect')
+      backup.length = 0
+    },
+    onReconnect: (source, target) => {
+      console.log('onReconnect')
+      resendMessages(target)
+    },
+  }
+
+  const proxy = fastify({ logger: true })
+  proxy.register(fastifyHttpProxy, {
+    upstream: 'http://localhost:3000/',
+    websocket: true,
+    wsUpstream: 'ws://localhost:3000/',
+    wsReconnect,
+    wsHooks,
+  })
+
+  await proxy.listen({ port })
+}
+
+main()

examples/reconnection/proxy/package.json

@@ -0,0 +1,12 @@
+{
+  "name": "proxy",
+  "version": "1.0.0",
+  "main": "index.js",
+  "scripts": {
+    "start": "node index.js",
+    "dev": "node --watch index.js"
+  },
+  "dependencies": {
+    "fastify": "^5.2.1"
+  }
+}

examples/reconnection/unstable-target/index.js

@@ -0,0 +1,75 @@
+'use strict'
+
+const { setTimeout: wait } = require('node:timers/promises')
+const fastify = require('fastify')
+
+// unstable service
+
+async function main () {
+  const SLOW_START = process.env.SLOW_START || 2_000
+  const UNSTABLE_MIN = process.env.UNSTABLE_MIN || 1_000
+  const UNSTABLE_MAX = process.env.UNSTABLE_MAX || 10_000
+  const BLOCK_TIME = process.env.BLOCK_TIME || 5_000
+
+  const app = fastify({ logger: true })
+
+  // slow start
+
+  await wait(SLOW_START)
+
+  app.register(require('@fastify/websocket'))
+  app.register(async function (app) {
+    app.get('/', { websocket: true }, (socket) => {
+      socket.on('message', message => {
+        let m = message.toString()
+        console.log('incoming message', m)
+        m = JSON.parse(m)
+
+        socket.send(JSON.stringify({
+          response: m.message
+        }))
+      })
+    })
+  })
+
+  try {
+    const port = process.env.PORT || 3000
+    await app.listen({ port })
+  } catch (err) {
+    app.log.error(err)
+    process.exit(1)
+  }
+
+  if (process.env.STABLE) {
+    return
+  }
+
+  function runProblem () {
+    const problem = process.env.PROBLEM || (Math.random() < 0.5 ? 'crash' : 'block')
+    const unstabilityTimeout = process.env.UNSTABLE_TIMEOUT || Math.round(UNSTABLE_MIN + Math.random() * (UNSTABLE_MAX - UNSTABLE_MIN))
+
+    if (problem === 'crash') {
+      console.log(`Restarting (crash and restart) in ${unstabilityTimeout}ms`)
+      setTimeout(() => {
+        console.log('UNHANDLED EXCEPTION')
+        throw new Error('UNHANDLED EXCEPTION')
+      }, unstabilityTimeout).unref()
+    } else {
+      console.log(`Blocking EL in ${unstabilityTimeout}ms for ${BLOCK_TIME}ms`)
+
+      setTimeout(() => {
+        console.log('Block EL ...')
+        const start = performance.now()
+        while (performance.now() - start < BLOCK_TIME) {
+          // just block
+        }
+        console.log('Block ends')
+        runProblem()
+      }, unstabilityTimeout).unref()
+    }
+  }
+
+  runProblem()
+}
+
+main()

examples/reconnection/unstable-target/package.json

@@ -0,0 +1,14 @@
+{
+  "name": "unstable-target",
+  "version": "1.0.0",
+  "main": "index.js",
+  "scripts": {
+    "stable": "STABLE=1 node index.js",
+    "unstable": "forever index.js",
+    "dev": "node --watch index.js"
+  },
+  "dependencies": {
+    "fastify": "^5.2.1",
+    "forever": "^4.0.3"
+  }
+}