fix: avoid premature cleanup of dispatcher in Agent

lib/dispatcher/agent.js

@@ -1,7 +1,7 @@
 'use strict'
 
 const { InvalidArgumentError, MaxOriginsReachedError } = require('../core/errors')
-const { kClients, kRunning, kClose, kDestroy, kDispatch, kUrl } = require('../core/symbols')
+const { kBusy, kClients, kConnected, kRunning, kClose, kDestroy, kDispatch, kUrl } = require('../core/symbols')
 const DispatcherBase = require('./dispatcher-base')
 const Pool = require('./pool')
 const Client = require('./client')
@@ -65,7 +65,7 @@ class Agent extends DispatcherBase {
 
   get [kRunning] () {
     let ret = 0
-    for (const { dispatcher } of this[kClients].values()) {
+    for (const dispatcher of this[kClients].values()) {
       ret += dispatcher[kRunning]
     }
     return ret
@@ -86,54 +86,52 @@ class Agent extends DispatcherBase {
       throw new MaxOriginsReachedError()
     }
 
-    const result = this[kClients].get(key)
-    let dispatcher = result && result.dispatcher
+    let dispatcher = this[kClients].get(key)
     if (!dispatcher) {
-      const closeClientIfUnused = (connected) => {
-        const result = this[kClients].get(key)
-        if (result) {
-          if (connected) result.count -= 1
-          if (result.count <= 0) {
-            this[kClients].delete(key)
-            if (!result.dispatcher.destroyed) {
-              result.dispatcher.close()
-            }
-          }
+      dispatcher = this[kFactory](opts.origin, allowH2 === false
+        ? { ...this[kOptions], allowH2: false }
+        : this[kOptions])
 
-          let hasOrigin = false
-          for (const entry of this[kClients].values()) {
-            if (entry.origin === origin) {
-              hasOrigin = true
-              break
-            }
-          }
+      const closeClientIfUnused = () => {
+        if (this[kClients].get(key) !== dispatcher) {
+          return
+        }
+
+        if (dispatcher[kConnected] > 0 || dispatcher[kBusy]) {
+          return
+        }
+
+        this[kClients].delete(key)
+        if (!dispatcher.destroyed) {
+          dispatcher.close()
+        }
 
-          if (!hasOrigin) {
-            this[kOrigins].delete(origin)
+        let hasOrigin = false
+        for (const client of this[kClients].values()) {
+          if (client[kUrl].origin === dispatcher[kUrl].origin) {
+            hasOrigin = true
+            break
           }
         }
+
+        if (!hasOrigin) {
+          this[kOrigins].delete(dispatcher[kUrl].origin)
+        }
       }
-      dispatcher = this[kFactory](opts.origin, allowH2 === false
-        ? { ...this[kOptions], allowH2: false }
-        : this[kOptions])
+
+      dispatcher
         .on('drain', this[kOnDrain])
-        .on('connect', (origin, targets) => {
-          const result = this[kClients].get(key)
-          if (result) {
-            result.count += 1
-          }
-          this[kOnConnect](origin, targets)
-        })
+        .on('connect', this[kOnConnect])
         .on('disconnect', (origin, targets, err) => {
-          closeClientIfUnused(true)
+          closeClientIfUnused()
           this[kOnDisconnect](origin, targets, err)
         })
         .on('connectionError', (origin, targets, err) => {
-          closeClientIfUnused(false)
+          closeClientIfUnused()
           this[kOnConnectionError](origin, targets, err)
         })
 
-      this[kClients].set(key, { count: 0, dispatcher, origin })
+      this[kClients].set(key, dispatcher)
       this[kOrigins].add(origin)
     }
 
@@ -142,7 +140,7 @@ class Agent extends DispatcherBase {
 
   [kClose] () {
     const closePromises = []
-    for (const { dispatcher } of this[kClients].values()) {
+    for (const dispatcher of this[kClients].values()) {
       closePromises.push(dispatcher.close())
     }
     this[kClients].clear()
@@ -152,7 +150,7 @@ class Agent extends DispatcherBase {
 
   [kDestroy] (err) {
     const destroyPromises = []
-    for (const { dispatcher } of this[kClients].values()) {
+    for (const dispatcher of this[kClients].values()) {
       destroyPromises.push(dispatcher.destroy(err))
     }
     this[kClients].clear()
@@ -162,7 +160,7 @@ class Agent extends DispatcherBase {
 
   get stats () {
     const allClientStats = {}
-    for (const { dispatcher } of this[kClients].values()) {
+    for (const dispatcher of this[kClients].values()) {
       if (dispatcher.stats) {
         allClientStats[dispatcher[kUrl].origin] = dispatcher.stats
       }

lib/dispatcher/client-h1.js

@@ -1106,7 +1106,7 @@ function writeH1 (client, request) {
     socket[kReset] = reset
   }
 
-  if (client[kMaxRequests] && socket[kCounter]++ >= client[kMaxRequests]) {
+  if (client[kMaxRequests] && ++socket[kCounter] >= client[kMaxRequests]) {
     socket[kReset] = true
   }
 

lib/mock/mock-agent.js

@@ -167,7 +167,7 @@ class MockAgent extends Dispatcher {
   }
 
   [kMockAgentSet] (origin, dispatcher) {
-    this[kClients].set(origin, { count: 0, dispatcher })
+    this[kClients].set(origin, dispatcher)
   }
 
   [kFactory] (origin) {
@@ -179,9 +179,9 @@ class MockAgent extends Dispatcher {
 
   [kMockAgentGet] (origin) {
     // First check if we can immediately find it
-    const result = this[kClients].get(origin)
-    if (result?.dispatcher) {
-      return result.dispatcher
+    const dispatcher = this[kClients].get(origin)
+    if (dispatcher) {
+      return dispatcher
     }
 
     // If the origin is not a string create a dummy parent pool and return to user
@@ -192,11 +192,11 @@ class MockAgent extends Dispatcher {
     }
 
     // If we match, create a pool and assign the same dispatches
-    for (const [keyMatcher, result] of Array.from(this[kClients])) {
-      if (result && typeof keyMatcher !== 'string' && matchValue(keyMatcher, origin)) {
+    for (const [keyMatcher, nonExplicitDispatcher] of Array.from(this[kClients])) {
+      if (nonExplicitDispatcher && typeof keyMatcher !== 'string' && matchValue(keyMatcher, origin)) {
         const dispatcher = this[kFactory](origin)
         this[kMockAgentSet](origin, dispatcher)
-        dispatcher[kDispatches] = result.dispatcher[kDispatches]
+        dispatcher[kDispatches] = nonExplicitDispatcher[kDispatches]
         return dispatcher
       }
     }
@@ -210,7 +210,7 @@ class MockAgent extends Dispatcher {
     const mockAgentClients = this[kClients]
 
     return Array.from(mockAgentClients.entries())
-      .flatMap(([origin, result]) => result.dispatcher[kDispatches].map(dispatch => ({ ...dispatch, origin })))
+      .flatMap(([origin, dispatcher]) => dispatcher[kDispatches].map(dispatch => ({ ...dispatch, origin })))
       .filter(({ pending }) => pending)
   }
 

test/issue-4244.js

@@ -62,4 +62,96 @@ describe('Agent should close inactive clients', () => {
 
     await p
   })
+
+  test('should reuse replacement keep-alive connection after server closes the previous one', async (t) => {
+    let nextSocketId = 0
+    const socketIds = new Map()
+    const requestsPerSocket = new Map()
+
+    const server = createServer((req, res) => {
+      const socket = req.socket
+      if (!socketIds.has(socket)) {
+        socketIds.set(socket, ++nextSocketId)
+      }
+
+      const count = (requestsPerSocket.get(socket) || 0) + 1
+      requestsPerSocket.set(socket, count)
+
+      const remaining = 3 - count
+      res.setHeader('x-socket-id', String(socketIds.get(socket)))
+
+      if (remaining > 0) {
+        res.setHeader('connection', 'Keep-Alive')
+        res.setHeader('keep-alive', `timeout=30, max=${remaining}`)
+      } else {
+        res.setHeader('connection', 'close')
+      }
+
+      res.writeHead(200)
+      res.end('ok')
+    }).listen(0)
+
+    t.after(() => {
+      server.closeAllConnections?.()
+      server.close()
+    })
+
+    const agent = new Agent({ connections: 1 })
+    t.after(() => agent.close())
+
+    const socketSequence = []
+    for (let i = 0; i < 5; i++) {
+      const { statusCode, headers, body } = await request(`http://localhost:${server.address().port}`, {
+        dispatcher: agent
+      })
+
+      assert.equal(statusCode, 200)
+      await body.dump()
+      socketSequence.push(headers['x-socket-id'])
+    }
+
+    assert.deepEqual(socketSequence.slice(0, 3), ['1', '1', '1'])
+    assert.deepEqual(socketSequence.slice(3), ['2', '2'])
+  })
+
+  test('should reuse replacement connection after keep-alive max closes the previous one', async (t) => {
+    let nextSocketId = 0
+    const socketIds = new Map()
+
+    const server = createServer((req, res) => {
+      const socket = req.socket
+      if (!socketIds.has(socket)) {
+        socketIds.set(socket, ++nextSocketId)
+      }
+
+      res.setHeader('x-socket-id', String(socketIds.get(socket)))
+      res.setHeader('connection', 'Keep-Alive')
+      res.setHeader('keep-alive', 'timeout=30')
+
+      res.writeHead(200)
+      res.end('ok')
+    }).listen(0)
+
+    t.after(() => {
+      server.closeAllConnections?.()
+      server.close()
+    })
+
+    const agent = new Agent({ connections: 1, maxRequestsPerClient: 3 })
+    t.after(() => agent.close())
+
+    const socketSequence = []
+    for (let i = 0; i < 5; i++) {
+      const { statusCode, headers, body } = await request(`http://localhost:${server.address().port}`, {
+        dispatcher: agent
+      })
+
+      assert.equal(statusCode, 200)
+      await body.dump()
+      socketSequence.push(headers['x-socket-id'])
+    }
+
+    assert.deepEqual(socketSequence.slice(0, 3), ['1', '1', '1'])
+    assert.deepEqual(socketSequence.slice(3), ['2', '2'])
+  })
 })