fix(websocket): bound automatic PONG writes under backpressure

Signed-off-by: Matteo Collina <hello@matteocollina.com>
(cherry picked from commit b217373)
(cherry picked from commit 5394462)

Author: UlisesGascon

lib/web/websocket/receiver.js

@@ -249,6 +249,20 @@ class ByteParser extends Writable {
         if (isControlFrame(this.#info.opcode)) {
           this.#loop = this.parseControlFrame(body)
           this.#state = parserStates.INFO
+
+          // If the automatic PONG/CLOSE reply filled the socket's write buffer,
+          // stop parsing and resume on drain so a PING flood cannot grow the
+          // outbound queue without bound.
+          const socket = this.ws[kResponse].socket
+          if (this.#loop && socket.writableNeedDrain) {
+            this.#loop = false
+            socket.once('drain', () => {
+              if (this.destroyed) return
+              this.#loop = true
+              this.run(callback)
+            })
+            return
+          }
         } else {
           if (!this.#info.compressed) {
             if (!this.writeFragments(body)) {

test/websocket/pong-backpressure.js

@@ -0,0 +1,101 @@
+'use strict'
+
+const assert = require('node:assert')
+const { test } = require('node:test')
+const { EventEmitter } = require('node:events')
+const { ByteParser } = require('../../lib/web/websocket/receiver')
+const { kReceivedClose, kResponse } = require('../../lib/web/websocket/symbols')
+
+// An unmasked, empty PING frame as sent by a server (FIN + opcode 0x9).
+const serverPingFrame = Buffer.from([0x89, 0x00])
+
+// A socket stub whose writes report backpressure (write() returns false and
+// writableNeedDrain stays set) until drain() is called.
+function createBackpressuredSocket () {
+  const socket = new EventEmitter()
+  socket.pongWrites = 0
+  socket.blocked = true
+  socket.writableNeedDrain = false
+  socket.write = () => {
+    socket.pongWrites += 1
+    if (socket.blocked) {
+      socket.writableNeedDrain = true
+      return false
+    }
+    return true
+  }
+  socket.drain = () => {
+    socket.writableNeedDrain = false
+    socket.emit('drain')
+  }
+  return socket
+}
+
+function createPingHandler (socket) {
+  return {
+    [kReceivedClose]: false,
+    [kResponse]: { socket }
+  }
+}
+
+test('ByteParser stops auto-writing PONGs once the socket applies backpressure', () => {
+  const socket = createBackpressuredSocket()
+  const parser = new ByteParser(createPingHandler(socket))
+  const pingFlood = Buffer.concat(Array.from({ length: 50 }, () => serverPingFrame))
+
+  parser.write(pingFlood)
+
+  return new Promise((resolve) => {
+    setImmediate(() => {
+      assert.strictEqual(socket.pongWrites, 1)
+      parser.destroy()
+      resolve()
+    })
+  })
+})
+
+test('ByteParser resumes auto-writing PONGs after the socket drains', () => {
+  const socket = createBackpressuredSocket()
+  const parser = new ByteParser(createPingHandler(socket))
+  const pingFlood = Buffer.concat(Array.from({ length: 50 }, () => serverPingFrame))
+
+  parser.write(pingFlood)
+
+  return new Promise((resolve) => {
+    setImmediate(() => {
+      assert.strictEqual(socket.pongWrites, 1)
+
+      socket.blocked = false
+      socket.drain()
+
+      setImmediate(() => {
+        assert.strictEqual(socket.pongWrites, 50)
+        parser.destroy()
+        resolve()
+      })
+    })
+  })
+})
+
+test('ByteParser does not resume PONG writes if destroyed while paused', () => {
+  const socket = createBackpressuredSocket()
+  const parser = new ByteParser(createPingHandler(socket))
+  const pingFlood = Buffer.concat(Array.from({ length: 50 }, () => serverPingFrame))
+
+  parser.write(pingFlood)
+
+  return new Promise((resolve) => {
+    setImmediate(() => {
+      assert.strictEqual(socket.pongWrites, 1)
+
+      parser.destroy()
+      socket.blocked = false
+      socket.drain()
+
+      setImmediate(() => {
+        assert.strictEqual(socket.pongWrites, 1)
+        resolve()
+      })
+    })
+  })
+})