Give the gate, the window and the pending map one owner

AGENTS.md

@@ -66,7 +66,7 @@ src/
 	index.ts             Public surface. Named exports only, no default export.
 	client.ts            client() -> { err, session }
 	server.ts            server() -> { err, server }, server owns the listener + close()
-	session.ts           Session: dispatch, events, and the collaborators below
+	session.ts           Session: the socket's life, dispatch, events, and the collaborators below
 	sms.ts               The live handle emitted as the 'sms' event (sendResp/sendDlr)
 	dlr.ts               Delivery receipts: text and TLV parsing, receipt status codes
 	dlr-merger.ts        DlrMerger: per-segment receipts counted into one MessageDlr
@@ -79,6 +79,7 @@ src/
 	link-timers.ts       LinkTimers: the enquire_link heartbeat and the idle timeout
 	log.ts               SmppLog, the logger contract, and silentLog — the default
 	message.ts           Encoding detection, splitting, bit counting, SMPP date formatting
+	outgoing-requests.ts OutgoingRequests: the gate, the window, the pending map and the retry
 	pdu.ts               pduToObj / objToPdu / pduReturn — synchronous, result-returning
 	pdu-framer.ts        PduFramer: a byte stream cut into complete PDUs
 	pdu-transport.ts     PduTransport: the socket a session reads complete PDUs off
@@ -91,6 +92,7 @@ src/
 	session-options.ts   SessionOptions, ReconnectOptions, bind direction and the session defaults
 	sms-id.ts            The notation a peer writes message ids in, normalised for comparison
 	udh.ts               User data header: the concatenation fields of a long SMS, and their reference
+	unanswered-error.ts  UnansweredError: it went out and no answer came back
 	uuid.ts              uuidv7() — the ids the library generates for messages
 	defs/
 		commands.ts      The 33 commands, their ids and ordered parameter lists
@@ -252,7 +254,10 @@ Grouped by what each one constrains.
   `super.on()` call needs one. The cost is that a subclass can no longer reach those seven through
   `super` — re-declaring them the same way is its way out. `unknown` rather than
   `void | Promise<void>` because a listener may return anything: `session.on('close', () =>
-  set.delete(session))` returns a boolean.
+  set.delete(session))` returns a boolean. This also settles what the drain can wait on: a listener's
+  own promise would be the better completion signal, and reaching it needs `listeners()`, which
+  cannot be re-declared the same way — Node types it invariantly enough that widening `void` to
+  `unknown` is `TS2416`. Re-probed 2026-09-01; `sendResp()` stays the signal.
 
 ### The wire
 
@@ -344,7 +349,12 @@ Grouped by what each one constrains.
   `teardown()` drops what is still held for the same reason it drops inbound segments. The release
   is one turn late, so a listener that sends its receipt straight after the response is still
   holding when the drain looks; `sendDlr()` is the one send that goes out past the drain's refusal,
-  being part of answering a message the drain is itself waiting for.
+  and only while the message is still held — past that it is an ordinary send, because the drain it
+  would slip past is no longer waiting for it. `shutdownTimeout: 0` does not carry over to this
+  half: waiting forever is safe for the peer, whose every request is bounded by `responseTimeout`,
+  and unsafe for the application, which nothing bounds — `close()` is what you reach for when the
+  application is stuck, so it may not block on the application coming unstuck. That half falls back
+  to `responseTimeout`, the same answer the link gate's hold already takes.
 
 - **A reconnect keeps the delivery-receipt merges; everything else the link held is dropped.**
   `onDeliverSm()` answers each receipt before the group it belongs to is complete, and `teardown()`

README.md

@@ -101,7 +101,7 @@ Every one is optional.
 | `enquireLinkInterval` | `20000` | How often to send `enquire_link` on a quiet link. |
 | `idleTimeout` | `2 × enquireLinkInterval` | Give up on a link the peer has stopped answering, and re-bind unless `reconnect` is `false`. |
 | `responseTimeout` | `30000` | How long to wait for a response before giving up on it, and how long a send with no link waits for the next one; `0` waits forever. |
-| `shutdownTimeout` | `5000` | How long `close()` and `unbind()` wait for the requests this end already sent and the messages the application has not answered; `0` waits forever. |
+| `shutdownTimeout` | `5000` | How long `close()` and `unbind()` wait for the requests this end already sent and the messages the application has not answered. `0` waits forever for the requests, which the peer answers or times out; the messages fall back to `responseTimeout`, since nothing but the application ends that wait. |
 | `maxOutstanding` | `10` | Requests allowed on the wire at once; further sends queue. |
 | `smsIdFormat` | — | The notation the SMSC writes message ids in, per place it writes them: `{ receipt: 'decimal', submitResp: 'hex' }`. Only needed where the two disagree. |
 | `reconnect` | on | Re-binds after a drop, an idle timeout, or a stream the library cannot read, backing off from `minDelay` 1 s to `maxDelay` 30 s and starting over at `minDelay` once a link has lasted `maxDelay`. `{ minDelay, maxDelay }` retunes it; `false` turns it off, so a drop ends the session. |
@@ -331,10 +331,12 @@ TypeScript users can import `SmppLog` to have the compiler check one.
 
 `sendSms()`, `send()`, `sendReturn()`, `unbind()` and `close()`. Both `close()` and `unbind()`
 refuse further sends, wait out the requests this end already sent for up to `shutdownTimeout`, and
-then tear down whatever is left, resolving to an `err` that says what was lost. They wait on the
+then tear down whatever is left, resolving to an `err` that says what was lost. They also wait for
-`sms` events the application has not answered yet too, so a peer whose `submit_sm` is still being
+every `sms` the application has not called `sendResp()` on, so a peer whose `submit_sm` is still
-handled is answered rather than left to re-send it; `sendDlr()` goes out during that wait, and every
+being handled is answered rather than left to re-send it — answering its PDUs through `sendReturn()`
-other send is refused. `close({ signal })` takes an
+instead leaves that wait running until it gives up. `sendDlr()` is the one send the refusal lets
+past, and it catches the wait when issued straight after `sendResp()`; await anything in between and
+it races the shutdown like any other send. `close({ signal })` takes an
 `AbortSignal` that cuts the wait short; `unbind()` takes none, and waits a further
 `responseTimeout` for its own response. `send()` reaches any of the 33 SMPP commands the codec
 knows, not just the four the session handles natively:

src/held-messages.ts

@@ -10,6 +10,11 @@ export class HeldMessages {
 		this.held.add(pduObjs);
 	}
 
+	/** Whether a drain is still waiting for this message to be answered. */
+	has(pduObjs: PduObject[]): boolean {
+		return this.held.has(pduObjs);
+	}
+
 	release(pduObjs: PduObject[]): void {
 		if (!this.held.delete(pduObjs)) return;
 

src/incoming-requests.ts

@@ -21,8 +21,8 @@ export type IncomingRequestsOptions = {
 	maxReassembly?: number | undefined;
 	onRequest?: OnRequest | undefined;
 	reassemblyTimeout?: number | undefined;
-	/** Past the drain gate: a receipt answering a message the shutdown is still waiting for. */
+	/** Past a drain's refusal, for a receipt the drain is itself waiting for. */
-	sendHeld: (input: PduObjectInput) => Promise<Result<{ pduObj: PduObject }>>;
+	sendPastDrain: (input: PduObjectInput) => Promise<Result<{ pduObj: PduObject }>>;
 	session: Session;
 	smsIdFormat?: SmsIdFormat | undefined;
 	systemId?: string | undefined;
@@ -35,7 +35,7 @@ export class IncomingRequests {
 	private readonly log: SmppLog;
 	private readonly onRequest: OnRequest | undefined;
 	private readonly reassembler: Reassembler;
-	private readonly sendHeld: IncomingRequestsOptions['sendHeld'];
+	private readonly sendPastDrain: IncomingRequestsOptions['sendPastDrain'];
 	private readonly session: Session;
 	private readonly smsIdFormat: SmsIdFormat;
 	private readonly systemId: string;
@@ -50,7 +50,7 @@ export class IncomingRequests {
 			maxOctets: options.maxOctets,
 			timeout: options.reassemblyTimeout ?? defaults.reassemblyTimeout,
 		});
-		this.sendHeld = options.sendHeld;
+		this.sendPastDrain = options.sendPastDrain;
 		this.session = options.session;
 		this.smsIdFormat = options.smsIdFormat ?? {};
 		this.systemId = options.systemId ?? defaults.systemId;
@@ -167,7 +167,8 @@ export class IncomingRequests {
 		}, {
 			// A turn later, so a listener sending its receipt straight after the response still holds.
 			onAnswered: () => { setImmediate(() => { this.held.release(pduObjs); }); },
-			send: this.sendHeld,
+			// Past the refusal only while a drain is still waiting for this message; an ordinary send after.
+			send: input => (this.held.has(pduObjs) ? this.sendPastDrain(input) : this.session.send(input)),
 		});
 
 		this.held.hold(pduObjs);

src/link-gate.ts

@@ -47,9 +47,11 @@ export class LinkGate {
 		return this.up || this.returning ? undefined : over();
 	}
 
-	/** When a hold starting now has to give up. 0 never does. */
+	/** One budget for a request, however many links it waits through. 0 never gives up. */
-	deadline(): number {
+	hold(signal: AbortSignal | undefined): () => Promise<VoidResult> {
-		return this.timeout > 0 ? this.now() + this.timeout : 0;
+		const deadline = this.timeout > 0 ? this.now() + this.timeout : 0;
+
+		return () => this.wait(deadline, signal);
 	}
 
 	/** A link is up and bound: everything held goes out on it. */
@@ -73,7 +75,7 @@ export class LinkGate {
 	}
 
 	/** Resolves once a link can carry the request, or with the reason none ever will. */
-	wait(deadline: number, signal: AbortSignal | undefined): Promise<VoidResult> {
+	private wait(deadline: number, signal: AbortSignal | undefined): Promise<VoidResult> {
 		if (this.up) return Promise.resolve({});
 
 		const refused = this.refusal();
@@ -86,10 +88,10 @@ export class LinkGate {
 
 		if (deadline !== 0 && left <= 0) return Promise.resolve({ err: expired() });
 
-		return this.hold(left, signal);
+		return this.waitForLink(left, signal);
 	}
 
-	private hold(left: number, signal: AbortSignal | undefined): Promise<VoidResult> {
+	private waitForLink(left: number, signal: AbortSignal | undefined): Promise<VoidResult> {
 		this.log.verbose('linkGate - holding a request until a link is back', { timeout: left });
 
 		return new Promise<VoidResult>(resolve => {

src/outgoing-requests.ts

@@ -0,0 +1,168 @@
+import type { PduObject, PduObjectInput } from './pdu.ts';
+import type { PduTransport } from './pdu-transport.ts';
+import type { Result, VoidResult } from './result.ts';
+import type { SendOptions } from './session-options.ts';
+import type { SmppLog } from './log.ts';
+import { LinkGate } from './link-gate.ts';
+import { PendingRequests } from './pending-requests.ts';
+import { SendWindow } from './send-window.ts';
+import { UnansweredError } from './unanswered-error.ts';
+import { bindCommands } from './session-options.ts';
+import { objToPdu } from './pdu.ts';
+
+export type OutgoingRequestsOptions = {
+	log: SmppLog;
+	maxOutstanding: number;
+	responseTimeout: number;
+	transport: PduTransport;
+};
+
+/** `retryOnNextLink`: the write failed, so nothing reached the socket and another link may carry it. */
+type Attempt = { result: Result<{ pduObj: PduObject }>; retryOnNextLink: boolean };
+
+function abortedBeforeSend(): Error {
+	return new Error('Aborted before the request was sent');
+}
+
+/** Everything this end asks of the peer: which link carries it, how many at once, and the answer. */
+export class OutgoingRequests {
+	private readonly gate: LinkGate;
+	private readonly log: SmppLog;
+	private readonly pending: PendingRequests;
+	private readonly responseTimeout: number;
+	private readonly transport: PduTransport;
+	private readonly window: SendWindow;
+
+	private draining = false;
+
+	constructor(options: OutgoingRequestsOptions) {
+		this.gate = new LinkGate({ log: options.log, timeout: options.responseTimeout });
+		this.log = options.log;
+		this.pending = new PendingRequests(options.log);
+		this.responseTimeout = options.responseTimeout;
+		this.transport = options.transport;
+		this.window = new SendWindow(options.maxOutstanding);
+	}
+
+	/** Read through a method: a drop can land while a request is awaiting. */
+	linkDown(): boolean {
+		return !this.gate.isUp() || this.transport.sock.destroyed;
+	}
+
+	/** A link is up and bound, so everything held for one goes out on it. */
+	linkUp(): void {
+		this.gate.open();
+	}
+
+	/** The link is gone; `returning` says whether another one is on its way. */
+	linkLost(returning: boolean): void {
+		this.gate.shut(returning);
+		this.pending.settleAll(new Error('Session closed before a response arrived'));
+	}
+
+	/** Hands a response to the request waiting for it. False means nothing was. */
+	deliver(pduObj: PduObject): boolean {
+		return this.pending.deliver(pduObj);
+	}
+
+	/** Sends a request and resolves with the peer's response. */
+	request(input: PduObjectInput, options: SendOptions): Promise<Result<{ pduObj: PduObject }>> {
+		// A drain on a live link. A link that is down is the gate's answer, which says closed instead.
+		if (this.draining && !this.linkDown()) {
+			return Promise.resolve({ err: new Error('Session is shutting down') });
+		}
+
+		return this.pastDrain(input, options);
+	}
+
+	/** The same path without that refusal, which a receipt for a held message has to take. */
+	async pastDrain(
+		input: PduObjectInput,
+		options: SendOptions,
+	): Promise<Result<{ pduObj: PduObject }>> {
+		const refused = this.refuse(input, options);
+
+		if (refused) return { err: refused };
+
+		// A bind is what makes a link usable, so it cannot wait for one.
+		if (bindCommands.includes(input.cmdName)) return this.now(input, options);
+
+		const waitForLink = this.gate.hold(options.signal);
+
+		for (;;) {
+			const held = await waitForLink();
+
+			if (held.err) return { err: held.err };
+
+			await this.window.acquire();
+
+			const attempt = await this.attempt(input, options).finally(() => { this.window.release(); });
+
+			// Nothing reached the socket, so the next link carries it instead of the caller resending.
+			if (!attempt.retryOnNextLink || this.gate.isUp() || this.gate.refusal()) return attempt.result;
+		}
+	}
+
+	/** Past the gate, the window and a drain, for what has to go out either way. */
+	async now(input: PduObjectInput, options: SendOptions = {}): Promise<Result<{ pduObj: PduObject }>> {
+		return (await this.attempt(input, options)).result;
+	}
+
+	/** Refuses every request from here on, on a link that is already down as much as a live one. */
+	stopAccepting(): void {
+		this.draining = true;
+	}
+
+	/** Waits out the requests already on the wire, and says how many never finished. */
+	async drain(timeout: number, signal: AbortSignal | undefined): Promise<VoidResult> {
+		const unfinished = await this.window.idle(timeout, signal);
+
+		if (unfinished === 0) return {};
+
+		this.log.warn('session - shutting down with requests unfinished', { timeout, unfinished });
+
+		return { err: new Error(`Shut down with ${String(unfinished)} request(s) unfinished`) };
+	}
+
+	/** Why a request cannot go out at all, as opposed to not yet. */
+	private refuse(input: PduObjectInput, options: SendOptions): Error | undefined {
+		if (input.cmdName.endsWith('_resp')) {
+			return new Error(`Use sendReturn() for responses, not send(): ${input.cmdName}`);
+		}
+
+		// Before the gate and the window, or an aborted call waits for what it will never use.
+		if (options.signal?.aborted === true) return abortedBeforeSend();
+
+		// A bind skips the gate below, so the answer it would have given is given here instead.
+		return bindCommands.includes(input.cmdName) ? this.gate.refusal() : undefined;
+	}
+
+	private async attempt(input: PduObjectInput, options: SendOptions): Promise<Attempt> {
+		// pending.wait() alone settles the caller while the request still goes out to the peer.
+		if (options.signal?.aborted === true) {
+			return { result: { err: abortedBeforeSend() }, retryOnNextLink: false };
+		}
+
+		const seqNr = this.pending.nextSeqNr();
+		const built = objToPdu({ ...input, seqNr });
+
+		if (built.err) return { result: { err: built.err }, retryOnNextLink: false };
+
+		const response = this.pending.wait(seqNr, {
+			signal: options.signal,
+			timeout: this.responseTimeout,
+		});
+		const written = this.transport.write(built.buffer);
+
+		if (written.err) {
+			this.pending.settle(seqNr, { err: written.err });
+
+			return { result: { err: written.err }, retryOnNextLink: true };
+		}
+
+		const answered = await response;
+
+		// It went out, so a failure now means the peer may have taken it and the answer was the loss.
+		return { result: answered.err ? { err: new UnansweredError(answered.err) } : answered, retryOnNextLink: false };
+	}
+}

src/pending-requests.ts

@@ -12,14 +12,6 @@ type Pending = {
 	settle: (result: Result<{ pduObj: PduObject }>) => void;
 };
 
-/** The request went out and no answer came back: the peer may have accepted it. */
-export class UnansweredError extends Error {
-	constructor(cause: Error) {
-		super(`No answer came back, so the peer may have accepted it: ${cause.message}`, { cause });
-		this.name = 'UnansweredError';
-	}
-}
-
 /** Hands out sequence numbers and matches responses to the requests waiting for them. */
 export class PendingRequests {
 	private readonly log: SmppLog;

src/send-sms.ts

@@ -4,7 +4,7 @@ import type { PduObject, PduObjectInput } from './pdu.ts';
 import type { Result } from './result.ts';
 import type { SmppLog } from './log.ts';
 import type { SmsIdNotation } from './sms-id.ts';
-import { UnansweredError } from './pending-requests.ts';
+import { UnansweredError } from './unanswered-error.ts';
 import { consts } from './defs/constants.ts';
 import { detect } from './defs/encodings.ts';
 import { normaliseSmsId } from './sms-id.ts';

src/session.ts

@@ -10,17 +10,15 @@ import type { Socket } from 'node:net';
 import { DlrMerger } from './dlr-merger.ts';
 import { EventEmitter } from 'node:events';
 import { IncomingRequests } from './incoming-requests.ts';
-import { LinkGate } from './link-gate.ts';
 import { LinkTimers } from './link-timers.ts';
+import { OutgoingRequests } from './outgoing-requests.ts';
 import { PduTransport } from './pdu-transport.ts';
-import { PendingRequests, UnansweredError } from './pending-requests.ts';
 import { ReconnectLoop } from './reconnect-loop.ts';
-import { SendWindow } from './send-window.ts';
 import { leftOf } from './idle-waiters.ts';
 import { errorFrom } from './error-from.ts';
 import { optionalParamsMinVersion } from './defs/constants.ts';
 import { bindCarries, bindCommands, defaultSystemId, defaults } from './session-options.ts';
-import { isResp, objToPdu, pduReturn } from './pdu.ts';
+import { isResp, pduReturn } from './pdu.ts';
 import { silentLog } from './log.ts';
 import { submitSms, unsent } from './send-sms.ts';
 import { ConcatReference } from './udh.ts';
@@ -41,13 +39,6 @@ export { bindCommands, defaultSystemId };
 /** A listener may return a promise: an `async` one that rejects is routed like one that throws. */
 type SessionListener<K extends keyof SessionEvents> = (...args: SessionEvents[K]) => unknown;
 
-function abortedBeforeSend(): Error {
-	return new Error('Aborted before the request was sent');
-}
-
-/** `retryOnNextLink`: the write failed, so nothing reached the socket and another link may carry it. */
-type Attempt = { result: Result<{ pduObj: PduObject }>; retryOnNextLink: boolean };
-
 export class Session extends EventEmitter<SessionEvents> {
 	declare addListener: <K extends keyof SessionEvents>(event: K, listener: SessionListener<K>) => this;
 	declare off: <K extends keyof SessionEvents>(event: K, listener: SessionListener<K>) => this;
@@ -68,17 +59,14 @@ export class Session extends EventEmitter<SessionEvents> {
 
 	private readonly concatReference = new ConcatReference();
 	private readonly dlrMerger: DlrMerger;
-	private readonly gate: LinkGate;
 	private readonly incoming: IncomingRequests;
 	private readonly options: SessionOptions;
-	private readonly pending: PendingRequests;
+	private readonly outgoing: OutgoingRequests;
 	private readonly reconnectLoop: ReconnectLoop | undefined;
 	private readonly timers: LinkTimers;
 	private readonly transport: PduTransport;
-	private readonly window: SendWindow;
 
 	private closed = false;
-	private draining = false;
 	private ended = false;
 
 	/** A listener that throws is the application's bug; it must not become ours. Hard rule 1. */
@@ -123,7 +111,6 @@ export class Session extends EventEmitter<SessionEvents> {
 			max: defaults.maxDlrMerges,
 			timeout: defaults.dlrMergeTimeout,
 		});
-		this.gate = new LinkGate({ log: this.log, timeout: options.responseTimeout ?? defaults.responseTimeout });
 		this.incoming = new IncomingRequests({
 			dlrMerger: this.dlrMerger,
 			log: this.log,
@@ -131,12 +118,11 @@ export class Session extends EventEmitter<SessionEvents> {
 			maxReassembly: options.maxReassembly,
 			onRequest: options.onRequest,
 			reassemblyTimeout: options.reassemblyTimeout,
-			sendHeld: input => this.sendThrough(input, {}),
+			sendPastDrain: input => this.outgoing.pastDrain(input, {}),
 			session: this,
 			smsIdFormat: options.smsIdFormat,
 			systemId: options.systemId,
 		});
-		this.pending = new PendingRequests(this.log);
 		this.reconnectLoop = this.loopFor(options.reconnect);
 		this.timers = new LinkTimers({
 			enquireLinkInterval: options.enquireLinkInterval,
@@ -147,7 +133,12 @@ export class Session extends EventEmitter<SessionEvents> {
 			onIdle: () => { this.teardown(); },
 		});
 		this.transport = this.transportFor(options.sock);
-		this.window = new SendWindow(options.maxOutstanding ?? defaults.maxOutstanding);
+		this.outgoing = new OutgoingRequests({
+			log: this.log,
+			maxOutstanding: options.maxOutstanding ?? defaults.maxOutstanding,
+			responseTimeout: options.responseTimeout ?? defaults.responseTimeout,
+			transport: this.transport,
+		});
 
 		this.resetTimers();
 	}
@@ -170,56 +161,7 @@ export class Session extends EventEmitter<SessionEvents> {
 
 	/** Sends a request and resolves with the peer's response. */
 	send(input: PduObjectInput, options: SendOptions = {}): Promise<Result<{ pduObj: PduObject }>> {
-		// A drain on a live link. A link that is down is the gate's answer, which says closed instead.
+		return this.outgoing.request(input, options);
-		if (this.draining && !this.linkDown()) return Promise.resolve({ err: new Error('Session is shutting down') });
-
-		return this.sendThrough(input, options);
-	}
-
-	/** The same path without that refusal, which a receipt for a held message has to take. */
-	private async sendThrough(
-		input: PduObjectInput,
-		options: SendOptions = {},
-	): Promise<Result<{ pduObj: PduObject }>> {
-		const refused = this.refuseSend(input, options);
-
-		if (refused) return { err: refused };
-
-		// A bind is what makes a link usable, so it cannot wait for one.
-		if (bindCommands.includes(input.cmdName)) return (await this.attempt(input, options)).result;
-
-		const deadline = this.gate.deadline();
-
-		for (;;) {
-			const held = await this.gate.wait(deadline, options.signal);
-
-			if (held.err) return { err: held.err };
-
-			await this.window.acquire();
-
-			const attempt = await this.attempt(input, options).finally(() => { this.window.release(); });
-
-			// Nothing reached the socket, so the next link carries it instead of the caller resending.
-			if (!attempt.retryOnNextLink || this.gate.isUp() || !this.retrying()) return attempt.result;
-		}
-	}
-
-	/** Why a request cannot go out at all, as opposed to not yet. */
-	private refuseSend(input: PduObjectInput, options: SendOptions): Error | undefined {
-		if (input.cmdName.endsWith('_resp')) {
-			return new Error(`Use sendReturn() for responses, not send(): ${input.cmdName}`);
-		}
-
-		// Before the gate and the window, or an aborted call waits for what it will never use.
-		if (options.signal?.aborted === true) return abortedBeforeSend();
-
-		// A bind skips the gate below, so the answer it would have given is given here instead.
-		return bindCommands.includes(input.cmdName) ? this.gate.refusal() : undefined;
-	}
-
-	/** Read through a method: a drop can land while a send is awaiting. */
-	private linkDown(): boolean {
-		return !this.gate.isUp() || this.sock.destroyed;
 	}
 
 	/** Answers a request the peer sent us. Responses are never waited on. */
@@ -269,9 +211,9 @@ export class Session extends EventEmitter<SessionEvents> {
 	async unbind(): Promise<VoidResult> {
 		const drained = await this.drain(undefined);
 		const wasOpen = !this.closed;
-		// attempt(), not send(): the drain gate refuses a send, and the unbind goes out either way.
+		// now(), not send(): a drain refuses a send, and the unbind goes out either way.
 		const sent = wasOpen
-			? (await this.attempt({ cmdName: 'unbind' }, {})).result
+			? await this.outgoing.now({ cmdName: 'unbind' })
 			: { err: new Error('Session is closed') };
 		const closedOnUnbind = wasOpen && this.closed;
 
@@ -341,7 +283,7 @@ export class Session extends EventEmitter<SessionEvents> {
 		}
 
 		this.resetTimers();
-		this.gate.open();
+		this.outgoing.linkUp();
 		this.log.info('session - reconnected');
 		this.emit('reconnected');
 
@@ -353,58 +295,27 @@ export class Session extends EventEmitter<SessionEvents> {
 		this.closed = false;
 	}
 
-	private async attempt(input: PduObjectInput, options: SendOptions): Promise<Attempt> {
-		// pending.wait() alone settles the caller while the request still goes out to the peer.
-		if (options.signal?.aborted === true) {
-			return { result: { err: abortedBeforeSend() }, retryOnNextLink: false };
-		}
-
-		const seqNr = this.pending.nextSeqNr();
-		const built = objToPdu({ ...input, seqNr });
-
-		if (built.err) return { result: { err: built.err }, retryOnNextLink: false };
-
-		const response = this.pending.wait(seqNr, {
-			signal: options.signal,
-			timeout: this.options.responseTimeout ?? defaults.responseTimeout,
-		});
-		const written = this.transport.write(built.buffer);
-
-		if (written.err) {
-			this.pending.settle(seqNr, { err: written.err });
-
-			return { result: { err: written.err }, retryOnNextLink: true };
-		}
-
-		const answered = await response;
-
-		// It went out, so a failure now means the peer may have taken it and the answer was the loss.
-		return { result: answered.err ? { err: new UnansweredError(answered.err) } : answered, retryOnNextLink: false };
-	}
-
 	/** Stops new sends and waits out the messages we hold and the requests already issued. */
 	private async drain(signal: AbortSignal | undefined): Promise<VoidResult> {
 		this.reconnectLoop?.stop();
-		this.draining = true;
+		this.outgoing.stopAccepting();
 
-		if (this.linkDown()) return {};
+		if (this.outgoing.linkDown()) return {};
 
 		const timeout = this.options.shutdownTimeout ?? defaults.shutdownTimeout;
 		const deadline = timeout > 0 ? Date.now() + timeout : 0;
+		// Only the application answers a held message, so that half falls back rather than wait forever.
+		const answering = timeout > 0 ? timeout : (this.options.responseTimeout ?? defaults.responseTimeout);
 		// Answering a message can put a receipt on the wire; nothing on the wire produces a message.
-		const messages = await this.incoming.drain(timeout, signal);
+		const messages = await this.incoming.drain(answering, signal);
-		const unfinished = await this.window.idle(leftOf(deadline), signal);
+		const requests = await this.outgoing.drain(leftOf(deadline), signal);
 
 		// The window empties on a teardown too, which settles everything the link was carrying.
-		if (this.linkDown()) return { err: new Error('The session closed before the drain finished') };
+		if (this.outgoing.linkDown()) {
+			return { err: new Error('The session closed before the drain finished') };
+		}
 
-		if (messages.err) return messages;
+		return messages.err ? messages : requests;
-
-		if (unfinished === 0) return {};
-
-		this.log.warn('session - shutting down with requests unfinished', { timeout, unfinished });
-
-		return { err: new Error(`Shut down with ${String(unfinished)} request(s) unfinished`) };
 	}
 
 	/** The session is over now, drained or not. Nothing brings it back. */
@@ -419,7 +330,7 @@ export class Session extends EventEmitter<SessionEvents> {
 		if (this.ended) return;
 
 		this.ended = true;
-		this.gate.shut(false);
+		this.outgoing.linkLost(false);
 		this.emit('close');
 	}
 
@@ -427,9 +338,8 @@ export class Session extends EventEmitter<SessionEvents> {
 		if (this.closed) return;
 
 		this.closed = true;
-		this.gate.shut(this.retrying());
+		this.outgoing.linkLost(this.retrying());
 		this.timers.clear();
-		this.pending.settleAll(new Error('Session closed before a response arrived'));
 		this.incoming.clear();
 		this.sock.destroy();
 
@@ -448,7 +358,7 @@ export class Session extends EventEmitter<SessionEvents> {
 
 	private dispatch(pduObj: PduObject): void {
 		if (isResp(pduObj)) {
-			if (!this.pending.deliver(pduObj)) {
+			if (!this.outgoing.deliver(pduObj)) {
 				this.log.debug('session - response with no matching request', { seqNr: pduObj.seqNr });
 			}
 

src/unanswered-error.ts

@@ -0,0 +1,7 @@
+/** The request went out and no answer came back: the peer may have accepted it. */
+export class UnansweredError extends Error {
+	constructor(cause: Error) {
+		super(`No answer came back, so the peer may have accepted it: ${cause.message}`, { cause });
+		this.name = 'UnansweredError';
+	}
+}

test/session-extras.test.ts

@@ -819,12 +819,12 @@ describe('LinkGate', () => {
 	test('refuses a hold whose deadline has already passed', async () => {
 		let now = 0;
 		const gate = new LinkGate({ log: silentLog, now: () => now, timeout: 100 });
-		const deadline = gate.deadline();
+		const waitForLink = gate.hold(undefined);
 
 		gate.shut(true);
 		now = 101;
 
-		const held = await gate.wait(deadline, undefined);
+		const held = await waitForLink();
 
 		assert.match(held.err?.message ?? '', /did not come back in time/);
 	});
@@ -836,7 +836,7 @@ describe('LinkGate', () => {
 		gate.shut(true);
 
 		const before = timers();
-		const held = gate.wait(gate.deadline(), undefined);
+		const held = gate.hold(undefined)();
 
 		assert.equal(timers(), before + 1, 'an unref\'d timer is not counted here, which is the point');
 
@@ -851,7 +851,7 @@ describe('LinkGate', () => {
 
 		gate.shut(true);
 
-		const held = await gate.wait(gate.deadline(), AbortSignal.abort());
+		const held = await gate.hold(AbortSignal.abort())();
 
 		assert.match(held.err?.message ?? '', /Aborted while waiting for a link/);
 	});
@@ -1102,6 +1102,17 @@ describe('graceful shutdown', () => {
 		assert.match(closed.err.message, /1 message\(s\) unanswered/);
 	});
 
+	// Waiting forever is safe for the peer, which every request times out on. The application is not.
+	test('falls back to responseTimeout for a held message when the shutdown waits forever', async t => {
+		const { smpp } = await submitInFlight(t, {}, { responseTimeout: 200, shutdownTimeout: 0 });
+		const started = Date.now();
+		const closed = await peerOf(smpp).close();
+
+		assert.ok(closed.err instanceof Error);
+		assert.match(closed.err.message, /1 message\(s\) unanswered/);
+		assert.ok(Date.now() - started < 2000);
+	});
+
 	// The README's own listener answers and then sends its receipt, one turn later.
 	test('a receipt sent right after the response still goes out mid-drain', async t => {
 		const { sent, session, smpp, sms } = await submitInFlight(t);

todo.md

@@ -57,6 +57,7 @@ Rules the API follows:
 | `smsIdFormat`: a peer's `submit_sm_resp` and receipt ids read into one notation before they are compared | `test/dlr.test.ts`, `test/session-extras.test.ts` |
 | A draining `close()` and `unbind()`, bounded by `shutdownTimeout` or an abort | `test/session-extras.test.ts` |
 | A drain that also waits out the messages the application has not answered, with `sendDlr()` the one send that passes it | `test/session-extras.test.ts` |
+| `OutgoingRequests`: the gate, the window, the pending map and the retry under one owner, told when a link comes up or goes down | `test/session-extras.test.ts`, `test/session.test.ts` |
 | A send with no link held for the next one, and one the link dropped under counted as `unanswered` | `test/session-extras.test.ts` |
 | Every runnable README example | `test/readme.test.ts` |
 | Receipt-versus-message classification by `esm_class` | `test/dlr.test.ts`, `test/session.test.ts` |
@@ -118,26 +119,25 @@ session message is a change to every call site.
       loses every incomplete group, and a peer has no reason to resend a receipt it already had
       answered. Surviving one means exposing the merge state for the application to persist and hand
       back, which is a public-surface decision.
-- [ ] **Group the session's collaborators under `src/session/`.** Only `session.ts` imports
+- [ ] **Group the session's collaborators under `src/session/`.** `session.ts` imports
-      `reassembly`, `dlr-merger`, `send-window`, `link-timers`, `link-gate`, `reconnect-loop`,
+      `dlr-merger`, `incoming-requests`, `link-timers`, `outgoing-requests`, `pdu-transport`,
-      `pending-requests` and `send-sms`, so the directory would make that boundary visible.
+      `reconnect-loop` and `send-sms`, and nothing else does, so the directory would make that
-      `pdu-transport` joined them on 2026-08-31, `link-gate` and `idle-waiters` on 2026-09-01, all
+      boundary visible. The `OutgoingRequests` extraction this was to be done with landed on
-      without the move being made, so it is a move of its own now. Do it together with the extraction below rather
+      2026-09-01, so it is the remaining half. Raised by review, 2026-09-01.
-      than before it — three reactive splits at whatever boundary fitted under the line cap is what
+
-      produced the current shape. Raised by review, 2026-09-01.
+- [ ] **`leftOf()` and the link gate's own budget are one concept counted twice.**
-- [ ] **An `OutgoingRequests` collaborator, owning `LinkGate`, `SendWindow` and `PendingRequests`.**
+      `idle-waiters.ts` reads what is left of a budget as `Math.max(1, deadline - now)`, because 0
-      `session.ts` sits three lines under its 350-line cap and every split so far has been made to
+      means "forever" there; `link-gate.ts` runs the same subtraction and calls `<= 0` expired.
-      get back under it — the inbound drain on 2026-09-01 only fitted once `ConcatReference` and the
+      Neither is reachable from the other, so nothing can disagree today, but a reader who learns one
-      unsent-result shape moved out to `udh.ts` and `send-sms.ts`. The seam that holds: one object owning the gate, the window, the pending
+      and applies it to the other is wrong. A budget type both take would close it. Raised by review,
-      map and the retry loop, exposing a gated `request()` and the ungated door `unbind()` and the
-      bind already need, with `Session` calling it when a link comes up or goes down instead of
-      spreading `linkDown()` and `retrying()` across both sides. It would also close two smaller
-      things — `LinkGate.deadline()` and `wait(deadline)` are a two-call protocol whose only failure
-      mode is calling `deadline()` inside the loop, which nothing catches; `Session.linkDown()` is
-      read from both sides of the seam; and `UnansweredError` sits in `pending-requests.ts`, which
-      never uses it, for the sole edge that makes `send-sms` import that module at all. Every one of
-      these is unpublished, so it is a two-way door and belongs after 1.0.0. Raised by review,
       2026-09-01.
+
+- [ ] **A message the reconnect dropped is answered into the void, and reported as delivered.**
+      `teardown()` clears the held messages along with the inbound segments, which is right — but the
+      application still holds the `Sms`, so `sendResp()` writes the old link's sequence numbers to the
+      new socket, succeeds, and returns `{}` for a response that correlates with nothing at the peer.
+      `HeldMessages` now knows exactly which messages went that way, so saying so is a small
+      addition. Goal 2, low frequency. Raised by review, 2026-09-01.
 - [ ] **Does an intermediate delivery notification deserve to be a `dlr`?** `esm_class` message type
       `INTERMEDIATE_DELIVERY` (0x20) is classified as a message today, so a peer that reports
       non-final states with it hands the application a raw `id:… stat:ENROUTE` text as an inbound