fix(types): add missing pool stats (nodejs#1573)

* fix(types): add missing pool stats

* fix(test): expect type fix

test/types/pool.test-d.ts

@@ -1,5 +1,5 @@
 import { Duplex, Readable, Writable } from 'stream'
-import { expectAssignable } from 'tsd'
+import { expectAssignable, expectType } from 'tsd'
 import { Dispatcher, Pool, Client } from '../..'
 import { URL } from 'url'
 
@@ -16,6 +16,7 @@ expectAssignable<Pool>(new Pool('', { connections: 1 }))
   // properties
   expectAssignable<boolean>(pool.closed)
   expectAssignable<boolean>(pool.destroyed)
+  expectAssignable<Pool.PoolStats>(pool.stats)
 
   // request
   expectAssignable<Promise<Dispatcher.ResponseData>>(pool.request({ origin: '', path: '', method: 'GET' }))
@@ -100,4 +101,12 @@ expectAssignable<Pool>(new Pool('', { connections: 1 }))
   expectAssignable<void>(pool.destroy(() => {}))
   expectAssignable<void>(pool.destroy(new Error(), () => {}))
   expectAssignable<void>(pool.destroy(null, () => {}))
+
+  // stats
+  expectType<number>(pool.stats.connected)
+  expectType<number>(pool.stats.free)
+  expectType<number>(pool.stats.pending)
+  expectType<number>(pool.stats.queued)
+  expectType<number>(pool.stats.running)
+  expectType<number>(pool.stats.size)
 }

types/pool-stats.d.ts

@@ -0,0 +1,19 @@
+import Pool = require("./pool")
+
+export = PoolStats
+
+declare class PoolStats {
+  constructor(pool: Pool);
+  /** Number of open socket connections in this pool. */
+  connected: number;
+  /** Number of open socket connections in this pool that do not have an active request. */
+  free: number;
+  /** Number of pending requests across all clients in this pool. */
+  pending: number;
+  /** Number of queued requests across all clients in this pool. */
+  queued: number;
+  /** Number of currently active requests across all clients in this pool. */
+  running: number;
+  /** Number of active, pending, or queued requests across all clients in this pool. */
+  size: number;
+}

types/pool.d.ts

@@ -1,5 +1,6 @@
 import Client = require('./client')
 import Dispatcher = require('./dispatcher')
+import TPoolStats = require('./pool-stats')
 import { URL } from 'url'
 
 export = Pool
@@ -10,9 +11,12 @@ declare class Pool extends Dispatcher {
   closed: boolean;
   /** `true` after `pool.destroyed()` has been called or `pool.close()` has been called and the pool shutdown has completed. */
   destroyed: boolean;
+  /** Aggregate stats for a Pool. */
+  readonly stats: TPoolStats;
 }
 
 declare namespace Pool {
+  export type PoolStats = TPoolStats;
   export interface Options extends Client.Options {
     /** Default: `(origin, opts) => new Client(origin, opts)`. */
     factory?(origin: URL, opts: object): Dispatcher;