Let the session own its bind state, written by bound() alone

AGENTS.md

@@ -309,6 +309,7 @@ the file.
 - A store at its bound answers `ESME_RTHROTTLED` to a submission and `ESME_RX_T_APPN` to a delivery,
   a `data_sm` by whichever it stands in for.
 - A reconnect keeps the delivery-receipt merges; everything else the link held is dropped.
+- The bind state is the session's, `bound()` alone writes it, and it holds through a reconnect's gap.
 - A message id base is merged at most once.
 - A send that never reached the socket waits for the next link; one that did is counted, not resent.
 - A send queued for a send-window slot is bounded by the caller's `signal`, and by nothing else.

CHANGELOG.md

@@ -74,6 +74,10 @@
   `alert_on_message_delivery` and `broadcast_area_identifier`, the names they read back under. The
   two alternate names are gone from `tlvs` too, which is now typed by `TlvName`: narrow a `string` with `isTlvName()` before indexing it.
 - `cmds.broadcast_sm_resp.tlvMap` is removed; nothing read it.
+- `session.boundAs` and `session.peerInterfaceVersion` are read-only, and `session.loggedIn` is
+  removed: read `session.boundAs !== undefined`. A session you wire yourself records the bind it
+  accepted or had accepted with `session.bound(bindType, declaredVersion)`; an assignment to either
+  field now throws a `TypeError`.
 
 ## 0.5.0
 

README.md

@@ -421,8 +421,12 @@ const { err, pduObj } = await session.send({
 - `acceptsOptionalParams()`: whether the peer declared SMPP 3.4 or later, the version from which
   optional parameters may be sent to it. The library's own senders check it before attaching a TLV;
   a `send()` you build is passed through as written, so check it yourself.
-- `peerInterfaceVersion`: the version the peer declared, `0x00` if none.
+- `peerInterfaceVersion`: the version the peer declared, `0x00` if none, `undefined` before any bind.
 - `bindAllows(cmdName)` and `boundAs`: what the bind direction carries: [Bind direction](#bind-direction).
+- Both hold through a reconnect's gap: the loop binds again as before.
+- `bound(bindType, declaredVersion)`: how a session you construct yourself records a bind, whichever
+  end accepted it. A `declaredVersion` that is not a number is none declared. Both fields are
+  read-only.
 
 ## Receiving in depth
 
@@ -539,7 +543,8 @@ if (err) throw err;
 - `enquire_link` and `unbind` reach the hook too, and an unanswered `enquire_link` has the peer drop
   the link. Guard on the command name, as above, and a failing hook costs only its own request.
 - A `Session` you construct yourself takes the same hook as a session option, and that is where a
-  peer's bind gets accepted, since a hand-wired session has no bind handling of its own.
+  peer's bind gets accepted, since a hand-wired session has no bind handling of its own: call
+  `session.bound(bindType, pduObj.params.interface_version)` before answering it.
 
 **`sendDlr()`** takes `SCHEDULED`, `ENROUTE`, `DELIVERED`, `EXPIRED`, `DELETED`, `UNDELIVERABLE`,
 `ACCEPTED`, `UNKNOWN`, `REJECTED` or `SKIPPED`. The first two go out as intermediate delivery

docs/decisions.md

@@ -715,6 +715,15 @@ rule and an index of the titles below.
   assembled that way. What goes there is traffic already answered, which is why each group reaches
   `sessionError` like every other one given up on.
 
+- **The bind state is the session's, `bound()` alone writes it, and it holds through a reconnect's
+  gap.** Maintainer's call, 2026-09-28. `client()` and `server()` call `bound()` as a hand-wired
+  session does, so one method is the one spelling, and `loggedIn` went as a second spelling of
+  `boundAs !== undefined`. Clearing the state at `teardown()` was rejected: `bindAllows()` and
+  `acceptsOptionalParams()` then answer yes to everything while the link is down, so a
+  receiver-bound client queues a `submit_sm` the peer refuses and a receipt built then carries TLVs a
+  pre-3.4 peer must not get — goal 4. Valid while the reconnect loop binds again with the same bind
+  type to the same peer.
+
 - **A message id base is merged at most once.** A receipt carries nothing but `<base>-<n>`, so a
   straggler for a message whose group is gone cannot be told from a receipt for a later message the
   peer handed the same ids — an SMSC whose id counter restarts with its process is the realistic

interop-tests/smppload.test.ts

@@ -62,6 +62,6 @@ describe('smppload (blocked)', () => {
 		await waitFor(() => (closed ? true : undefined), 5000);
 		assert.equal(closed, true);
 		assert.ok(bound);
-		assert.equal(bound.loggedIn, false);
+		assert.equal(bound.boundAs, undefined);
 	});
 });

src/client.ts

@@ -8,7 +8,7 @@ export type { BindType };
 
 import { ReconnectLoop } from './reconnect-loop.ts';
 import { Session } from './session.ts';
-import { checkSessionOptions, undeclaredInterfaceVersion } from './session-options.ts';
+import { checkSessionOptions } from './session-options.ts';
 import { connect as netConnect } from 'node:net';
 import { connect as tlsConnect } from 'node:tls';
 import { defaultInterfaceVersion } from './defs/constants.ts';
@@ -174,13 +174,7 @@ async function bind(session: Session, options: ClientOptions): Promise<VoidResul
 		return { err: new Error(`Remote host refused login: ${sent.pduObj.cmdStatus ?? 'unknown'}`) };
 	}
 
-	const declared = sent.pduObj.tlvs.sc_interface_version?.tagValue;
-
-	session.boundAs = bindType;
-	session.loggedIn = true;
-	session.peerInterfaceVersion = typeof declared === 'number'
-		? declared
-		: undeclaredInterfaceVersion;
+	session.bound(bindType, sent.pduObj.tlvs.sc_interface_version?.tagValue);
 	session.log.info('client - bound', { bindType, systemId });
 
 	return {};

src/server.ts

@@ -1,12 +1,12 @@
-import type { CloseOptions, OnRequest } from './session-options.ts';
+import type { BindType, CloseOptions, OnRequest } from './session-options.ts';
 import type { PduObject, TlvInputs } from './pdu.ts';
 import type { Result, VoidResult } from './result.ts';
 import type { Server as NetServer, Socket } from 'node:net';
 import type { Server as TlsServer, TlsOptions } from 'node:tls';
 import type { SmppLog } from './log.ts';
 import { EventEmitter } from 'node:events';
-import { Session, bindCommands, defaultSystemId } from './session.ts';
-import { bindTypeFromCommand, checkSessionOptions, undeclaredInterfaceVersion } from './session-options.ts';
+import { Session, defaultSystemId } from './session.ts';
+import { bindTypeFromCommand, checkSessionOptions } from './session-options.ts';
 import { createServer as createNetServer } from 'node:net';
 import { createServer as createTlsServer } from 'node:tls';
 import { defaultInterfaceVersion } from './defs/constants.ts';
@@ -173,21 +173,21 @@ function bindRespTlvs(session: Session, options: ServerOptions): TlvInputs | und
 async function acceptBind(
 	session: Session,
 	pduObj: PduObject,
+	bindType: BindType,
 	options: ServerOptions,
 	identity: Record<string, string>,
 ): Promise<void> {
-	const declared = pduObj.params.interface_version;
-
-	session.boundAs = bindTypeFromCommand(pduObj.cmdName);
-	session.loggedIn = true;
-	session.peerInterfaceVersion = typeof declared === 'number'
-		? declared
-		: undeclaredInterfaceVersion;
+	session.bound(bindType, pduObj.params.interface_version);
 
 	await session.sendReturn(pduObj, 'ESME_ROK', identity, bindRespTlvs(session, options));
 }
 
-async function onBind(session: Session, pduObj: PduObject, options: ServerOptions): Promise<void> {
+async function onBind(
+	session: Session,
+	pduObj: PduObject,
+	bindType: BindType,
+	options: ServerOptions,
+): Promise<void> {
 	const identity = { system_id: options.systemId ?? defaults.systemId };
 	const systemId = paramText(pduObj.params.system_id);
 
@@ -198,7 +198,7 @@ async function onBind(session: Session, pduObj: PduObject, options: ServerOption
 		return;
 	}
 
-	await acceptBind(session, pduObj, options, identity);
+	await acceptBind(session, pduObj, bindType, options, identity);
 	session.log.verbose('server - bound', { systemId });
 }
 
@@ -211,16 +211,16 @@ async function handleRequest(
 	pduObj: PduObject,
 	options: ServerOptions,
 ): Promise<boolean> {
-	const isBind = bindCommands.includes(pduObj.cmdName);
+	const bindType = bindTypeFromCommand(pduObj.cmdName);
 
-	if (session.loggedIn) {
-		if (isBind || !options.onRequest) return false;
+	if (session.boundAs !== undefined) {
+		if (bindType || !options.onRequest) return false;
 
 		return options.onRequest(session, pduObj);
 	}
 
-	if (isBind) {
-		await onBind(session, pduObj, options);
+	if (bindType) {
+		await onBind(session, pduObj, bindType, options);
 
 		return true;
 	}

src/session.ts

@@ -19,7 +19,7 @@ import { ReconnectLoop } from './reconnect-loop.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 { bindCarries, bindCommands, defaultSystemId, defaults, undeclaredInterfaceVersion } from './session-options.ts';
 import { isResp, objToPdu, pduReturn } from './pdu.ts';
 import { refusalAnswer } from './pdu-refusal.ts';
 import { guardedLog } from './log.ts';
@@ -54,15 +54,12 @@ export class Session extends EventEmitter<SessionEvents> {
 
 	readonly log: SmppLog;
 
-	/** The role the ESME bound with, whichever end of the link this is. Undefined before any bind. */
-	boundAs: BindType | undefined = undefined;
 	/** Which end of the link this is. `server()` sets it; a hand-wired SMSC must set it too. */
 	linkEnd: LinkEnd = 'esme';
-	loggedIn = false;
-	/** What the peer declared when binding: 0x00 if it declared none, undefined before any bind. */
-	peerInterfaceVersion: number | undefined = undefined;
 	userData: unknown = undefined;
 
+	private bind: { as: BindType; peerVersion: number } | undefined = undefined;
+
 	private readonly concatReference = new ConcatReference();
 	private readonly dlrMerger: DlrMerger;
 	private readonly incoming: IncomingRequests;
@@ -154,6 +151,23 @@ export class Session extends EventEmitter<SessionEvents> {
 		return this.transport.sock;
 	}
 
+	/** The role the ESME bound with, whichever end of the link this is. Undefined before any bind. */
+	get boundAs(): BindType | undefined {
+		return this.bind?.as;
+	}
+
+	/** What the peer declared when binding: 0x00 if it declared none, undefined before any bind. */
+	get peerInterfaceVersion(): number | undefined {
+		return this.bind?.peerVersion;
+	}
+
+	/** Records a bind this link accepted or had accepted, until the next one. A version that is not a number is none. */
+	bound(bindType: BindType, declaredVersion: unknown): void {
+		const peerVersion = typeof declaredVersion === 'number' ? declaredVersion : undeclaredInterfaceVersion;
+
+		this.bind = { as: bindType, peerVersion };
+	}
+
 	/** Whether this session's bind direction carries a command. Consulted by the library's senders. */
 	bindAllows(cmdName: string): boolean {
 		return bindCarries(this.boundAs, cmdName, this.linkEnd);
@@ -171,15 +185,13 @@ export class Session extends EventEmitter<SessionEvents> {
 	}
 
 	/** Answers a request the peer sent us. Responses are never waited on. */
-	async sendReturn(
+	sendReturn(
 		pdu: PduObject,
 		status: ErrorName = 'ESME_ROK',
 		params: Record<string, ParamValue> = {},
 		tlvs?: TlvInputs,
 	): Promise<VoidResult> {
-		return Promise.resolve(
-			this.answer(pduReturn(pdu, status, params, tlvs), pdu.cmdName, pdu.seqNr),
-		);
+		return Promise.resolve(this.answer(pduReturn(pdu, status, params, tlvs), pdu.cmdName, pdu.seqNr));
 	}
 
 	private answer(built: Result<{ buffer: Buffer }>, cmdName: string, seqNr: number): VoidResult {

test/session-extras.test.ts

@@ -628,6 +628,10 @@ describe('reconnect', () => {
 
 		const reconnected = once<true>(resolve => { session.on('reconnected', () => { resolve(true); }); });
 		const halfPdu = once<true>(resolve => { session.on('data', () => { resolve(true); }); });
+		const boundBefore = [session.boundAs, session.peerInterfaceVersion];
+		const whileDown = once<unknown[]>(resolve => {
+			session.on('disconnected', () => { resolve([session.boundAs, session.peerInterfaceVersion]); });
+		});
 
 		// A PDU header promising 32 octets and sending 8: the next link must not continue it.
 		peerOf(smpp).sock.write(Buffer.from([0, 0, 0, 32, 0, 0, 0, 4]));
@@ -640,7 +644,9 @@ describe('reconnect', () => {
 
 		await reconnected;
 
-		assert.ok(session.loggedIn);
+		// The loop rebinds as before, so the gap keeps answering bindAllows() for the bind to come.
+		assert.deepEqual(await whileDown, boundBefore);
+		assert.equal(session.boundAs, 'transceiver');
 
 		// The session object survives the drop, so listeners stay attached and it is usable again.
 		const sent = await session.sendSms({
@@ -867,7 +873,7 @@ describe('reconnect from the first bind', () => {
 
 		assert.equal(err, undefined);
 		assert.ok(session);
-		assert.equal(session.loggedIn, true);
+		assert.equal(session.boundAs, 'transceiver');
 		assert.ok(spy.delays.length >= 3, 'the SMSC was down for several attempts');
 		assert.deepEqual(spy.delays.slice(0, 3), [10, 20, 40], 'each wait doubles, up to maxDelay');
 		assert.ok(

test/session.test.ts

@@ -229,7 +229,7 @@ describe('bind', () => {
 
 		assert.equal(err, undefined);
 		assert.ok(session);
-		assert.ok(session.loggedIn);
+		assert.equal(session.boundAs, 'transceiver');
 
 		assert.deepEqual(await session.unbind(), {});
 	});
@@ -448,6 +448,28 @@ describe('bind', () => {
 		assert.ok(session.acceptsOptionalParams());
 	});
 
+	test('records a hand-wired bind through bound(), and nothing else writes it', t => {
+		const session = new Session({ sock: new net.Socket() });
+
+		closeAfter(t, session);
+		assert.equal(session.boundAs, undefined);
+		assert.equal(session.peerInterfaceVersion, undefined);
+
+		session.bound('receiver', 0x34);
+
+		assert.equal(session.boundAs, 'receiver');
+		assert.equal(session.peerInterfaceVersion, 0x34);
+		assert.equal(session.bindAllows('submit_sm'), false);
+
+		session.bound('transmitter', undefined);
+
+		assert.equal(session.peerInterfaceVersion, 0x00, 'no declared version is pre-3.4');
+		assert.equal(Reflect.set(session, 'boundAs', 'transceiver'), false);
+		assert.equal(Reflect.set(session, 'peerInterfaceVersion', 0x50), false);
+		assert.equal(session.boundAs, 'transmitter');
+		assert.equal('loggedIn' in session, false);
+	});
+
 	// The spec: an absent sc_interface_version means the SMSC supports no optional parameters.
 	test('takes an SMSC that declares no version as older than 3.4', async t => {
 		const peer = await smscPeer(t);

test/tls.test.ts

@@ -135,7 +135,7 @@ describe('tls', () => {
 
 		assert.equal(err, undefined);
 		assert.ok(session);
-		assert.ok(session.loggedIn);
+		assert.equal(session.boundAs, 'transceiver');
 		closeAfter(t, session);
 
 		const sock = session.sock;

todo.md

@@ -204,11 +204,6 @@ and 5. Every seat ranked the session's lifecycle hardest and least wanted to mod
 
 - [ ] **Lift Locality to 7, and confirm it with a scoring run.** A run reading 7.0 or above also
       retires the #30 decision. The sub-items are what the 2026-09-28 run named, most seats first.
-- [ ] **Let `Session` own its bind state.** `client.ts` and `server.ts` write `boundAs`, `loggedIn`
-      and `peerInterfaceVersion` onto the session from outside, and `loggedIn` duplicates
-      `boundAs !== undefined`. A method such as `session.bound(bindType, declaredVersion)` with the
-      three fields read-only changes the public surface a hand-wired SMSC uses, so it needs the
-      maintainer's call first. All four seats.
 - [ ] **Name what `request()`, `carry()` and `now()` each skip.** Three ways onto the wire differ
       only in which of the drain, the gate and the window they bypass, and none of the names says
       which. Three seats.