Enforce maxFree

Author: JoshMock

lib/core/symbols.js

@@ -70,5 +70,6 @@ module.exports = {
   kPingInterval: Symbol('ping interval'),
   kNoProxyAgent: Symbol('no proxy agent'),
   kHttpProxyAgent: Symbol('http proxy agent'),
-  kHttpsProxyAgent: Symbol('https proxy agent')
+  kHttpsProxyAgent: Symbol('https proxy agent'),
+  kMaxFree: Symbol('max free')
 }

lib/dispatcher/pool-base.js

@@ -3,7 +3,7 @@
 const { PoolStats } = require('../util/stats.js')
 const DispatcherBase = require('./dispatcher-base')
 const FixedQueue = require('./fixed-queue')
-const { kConnected, kSize, kRunning, kPending, kQueued, kBusy, kFree, kUrl, kClose, kDestroy, kDispatch } = require('../core/symbols')
+const { kConnected, kSize, kRunning, kPending, kQueued, kBusy, kFree, kUrl, kClose, kDestroy, kDispatch, kMaxFree } = require('../core/symbols')
 
 const kClients = Symbol('clients')
 const kNeedDrain = Symbol('needDrain')
@@ -40,6 +40,14 @@ class PoolBase extends DispatcherBase {
       needDrain = !client.dispatch(item.opts, item.handler)
     }
 
+    if (this[kMaxFree] < Infinity && this[kFree] > this[kMaxFree]) {
+      for (let i = 0; i < this[kClients].length; i++) {
+        const client = this[kClients][i]
+        if (!client[kNeedDrain]) this[kRemoveClient](client)
+        if (this[kFree] <= this[kMaxFree]) break
+      }
+    }
+
     client[kNeedDrain] = needDrain
 
     if (!needDrain && this[kNeedDrain]) {

lib/dispatcher/pool.js

@@ -13,7 +13,7 @@ const {
   InvalidArgumentError
 } = require('../core/errors')
 const util = require('../core/util')
-const { kUrl } = require('../core/symbols')
+const { kUrl, kMaxFree } = require('../core/symbols')
 const buildConnector = require('../core/connect')
 
 const kOptions = Symbol('options')
@@ -37,6 +37,7 @@ class Pool extends PoolBase {
     autoSelectFamilyAttemptTimeout,
     allowH2,
     clientTtl,
+    maxFree = Infinity,
     ...options
   } = {}) {
     if (connections != null && (!Number.isFinite(connections) || connections < 0)) {
@@ -51,6 +52,10 @@ class Pool extends PoolBase {
       throw new InvalidArgumentError('connect must be a function or an object')
     }
 
+    if (typeof maxFree !== 'number' || Number.isNaN(maxFree) || maxFree <= 0) {
+      throw new InvalidArgumentError('maxFree must be a number greater than 0')
+    }
+
     if (typeof connect !== 'function') {
       connect = buildConnector({
         ...tls,
@@ -67,11 +72,12 @@ class Pool extends PoolBase {
 
     this[kConnections] = connections || null
     this[kUrl] = util.parseOrigin(origin)
-    this[kOptions] = { ...util.deepClone(options), connect, allowH2, clientTtl }
+    this[kOptions] = { ...util.deepClone(options), connect, allowH2, clientTtl, maxFree }
     this[kOptions].interceptors = options.interceptors
       ? { ...options.interceptors }
       : undefined
     this[kFactory] = factory
+    this[kMaxFree] = maxFree
 
     this.on('connect', (origin, targets) => {
       if (clientTtl != null && clientTtl > 0) {

types/agent.d.ts

@@ -25,6 +25,8 @@ declare namespace Agent {
 
     interceptors?: { Agent?: readonly Dispatcher.DispatchInterceptor[] } & Pool.Options['interceptors']
     maxOrigins?: number
+    /** The max number of free (idle) connections to keep open per origin. Passed to each Pool. Default `Infinity`. */
+    maxFree?: number
   }
 
   export interface DispatchOptions extends Dispatcher.DispatchOptions {

types/pool.d.ts

@@ -35,6 +35,8 @@ declare namespace Pool {
     connections?: number | null;
     /** The amount of time before a client is removed from the pool and closed. `null` if no time limit. Default `null` */
     clientTtl?: number | null;
+    /** The max number of free (idle) connections to keep open per origin. Default `Infinity`. */
+    maxFree?: number;
 
     interceptors?: { Pool?: readonly Dispatcher.DispatchInterceptor[] } & Client.Options['interceptors']
   }