Wait out the messages the application holds before shutting a session down

src/send-window.ts

@@ -1,8 +1,10 @@
+import { IdleWaiters } from './idle-waiters.ts';
+
 /** Caps how many requests are on the wire at once; anything past the limit waits its turn. */
 export class SendWindow {
+	private readonly idleWaiters = new IdleWaiters();
 	private readonly limit: number;
 	private readonly waiting: (() => void)[] = [];
-	private readonly waitingForIdle: (() => void)[] = [];
 	private inFlight = 0;
 
 	constructor(limit: number) {
@@ -32,9 +34,7 @@ export class SendWindow {
 
 		if (this.inFlight > 0) return;
 
-		for (const resolve of this.waitingForIdle.splice(0)) {
-			resolve();
-		}
+		this.idleWaiters.settle();
 	}
 
 	/** Everything the caller is still owed: on the wire, plus queued behind a full window. */
@@ -42,34 +42,8 @@ export class SendWindow {
 		return this.inFlight + this.waiting.length;
 	}
 
-	/**
-	 * Resolves 0 once nothing is left, or with what still is when the timeout or the signal cuts the
-	 * wait short. A timeout of 0 waits forever.
-	 */
+	/** Resolves 0 once nothing is left on the wire, or with what still is. */
 	idle(timeout: number, signal?: AbortSignal): Promise<number> {
-		if (this.inFlight === 0) return Promise.resolve(0);
-
-		if (signal?.aborted === true) return Promise.resolve(this.unfinished());
-
-		return new Promise<number>(resolve => {
-			let timer: NodeJS.Timeout | undefined = undefined;
-			const done = (): void => {
-				const index = this.waitingForIdle.indexOf(done);
-
-				if (timer) clearTimeout(timer);
-				if (index !== -1) this.waitingForIdle.splice(index, 1);
-
-				signal?.removeEventListener('abort', done);
-				resolve(this.unfinished());
-			};
-
-			if (timeout > 0) {
-				timer = setTimeout(done, timeout);
-				timer.unref();
-			}
-
-			signal?.addEventListener('abort', done, { once: true });
-			this.waitingForIdle.push(done);
-		});
+		return this.idleWaiters.wait(() => this.unfinished(), timeout, signal);
 	}
 }