diff --git a/AGENTS.md b/AGENTS.md
index d791e9d..8e083bc 100644
--- a/AGENTS.md
+++ b/AGENTS.md
@@ -307,6 +307,11 @@ Grouped by what each one constrains.
shutdown emits `close`. A retry that opens a socket and then loses it clears `closed` through
`attach()`, which is why a second drop emits again.
+- **An answer belongs to the link the message arrived on; a receipt does not.** Maintainer's call,
+ 2026-09-01. Rejected: answering on the new link, which succeeds and reports `{}` for a response
+ that correlates with nothing — goal 2's wrong answer. Accepted: a receipt sent after a refused
+ response names an id the peer has no record of.
+
- **`reconnect` takes `{ minDelay, maxDelay }` to retune and `false` to turn off**, so absent means
on and there is one spelling for each. Only `client()` reconnects — a `server()` session is a
connection the peer opened, and nothing at this end can reopen it. The retry timer is `unref()`'d,
diff --git a/README.md b/README.md
index 51acdc6..48108aa 100644
--- a/README.md
+++ b/README.md
@@ -316,7 +316,7 @@ TypeScript users can import `SmppLog` to have the compiler check one.
| Event | Fires when |
| --- | --- |
-| `sms` | An SMS arrives, reassembled if it was multipart. Carries `sendResp()`, `sendDlr()` and the `smsId` it was answered with. |
+| `sms` | An SMS arrives, reassembled if it was multipart. Carries `sendResp()`, `sendDlr()` and its `smsId`. |
| `dlr` | A delivery report arrives, one per segment. `smsId` is undefined when the peer marked a receipt whose body carries no readable id. `statusMsg` names `statusId` unless the peer sent a `message_state` this library cannot name — then `statusId` is that raw value and `statusMsg` is whatever the body said, or `UNKNOWN`. |
| `messageDlr` | Every segment of a multipart message sent with `dlr: true` has been reported on, carrying the worst status of the segments. Merging needs the SMSC to number its segment ids `-`, which is this library's own server's convention — an SMSC that hands out unrelated ids per segment never fires it. A base is merged once: a later message the SMSC gives the same ids is reported on through `dlr` alone, and an earlier one still collecting loses its merged report as well. |
| `close` | The session is over, because nothing will bring the link back. Fires once, whether you closed it or the link failed for good. |
@@ -355,6 +355,11 @@ so it fails, and `sendSms()` and `sms.sendDlr()` count it in `unanswered`, wheth
under it, the peer never answered in time, or you aborted it after it went out. Neither applies with `reconnect: false`,
where a drop ends the session and every send after it is refused.
+An answer cannot wait for a link that way, because it carries the sequence number the message arrived
+on: `sms.sendResp()` on a message whose link dropped writes nothing and returns an `err`. Where a
+reconnect follows, its `sms.sendDlr()` still goes out on the new link, since a receipt is a request
+of its own, correlated by the id it names.
+
`responseTimeout` bounds the wait for a link and the wait for an answer separately, and a send also
queues for a `maxOutstanding` slot, which nothing bounds — so it is not a deadline for the call.
Pass `{ signal: AbortSignal.timeout(ms) }` when you need one.
@@ -394,7 +399,8 @@ The spec tables are exported both individually (`cmds`, `consts`, `encodings`, `
- **`server()` resolves once, when it is listening**, and gives you a handle with `close()`, `port`
and a `session` event. It no longer calls your callback once per incoming connection.
- **The id a message is answered with goes to `sendResp({ smsId })`**, and `sms.smsId` is read-only:
- it reports what the response actually carried. Delete any `sms.smsId = …` line — assigning to it
+ it reports the id `sendResp()` was given, or the UUID v7 generated instead. Delete any
+ `sms.smsId = …` line — assigning to it
throws a `TypeError`, since modules are always strict mode — and pass the id to `sendResp()`.
- **`checkuserpass` is now `authenticate`**, takes `{ password, session, systemId, systemType }` and
returns `false` or `{ userData }`.
diff --git a/src/incoming-requests.ts b/src/incoming-requests.ts
index 202f3af..547015a 100644
--- a/src/incoming-requests.ts
+++ b/src/incoming-requests.ts
@@ -39,6 +39,7 @@ export class IncomingRequests {
private readonly session: Session;
private readonly smsIdFormat: SmsIdFormat;
private readonly systemId: string;
+ private linkGeneration = 0;
constructor(options: IncomingRequestsOptions) {
this.dlrMerger = options.dlrMerger;
@@ -62,8 +63,17 @@ export class IncomingRequests {
}
async handle(pduObj: PduObject): Promise {
+ const generation = this.linkGeneration;
+
if (this.onRequest && await this.onRequest(this.session, pduObj)) return;
+ // The link it arrived on went while the hook ran, so nothing we answer now correlates.
+ if (this.linkGeneration !== generation) {
+ this.log.info('session - dropping a request whose link went', { cmdName: pduObj.cmdName });
+
+ return;
+ }
+
if (!this.session.bindAllows(pduObj.cmdName)) {
this.log.info('session - command the peer\'s bind direction does not carry', {
bindType: this.session.boundAs ?? '',
@@ -96,6 +106,7 @@ export class IncomingRequests {
/** Drops the segments of every message that never became whole, and of every one still held. */
clear(): void {
+ this.linkGeneration++;
this.held.clear();
this.reassembler.clear();
}
@@ -163,6 +174,8 @@ export class IncomingRequests {
if (!first) return;
+ const generation = this.linkGeneration;
+
const sms = createSms({
from: paramText(first.params.source_addr),
message: decodeSegments(pduObjs),
@@ -170,6 +183,7 @@ export class IncomingRequests {
session: this.session,
to: paramText(first.params.destination_addr),
}, {
+ lostLink: () => this.linkGeneration !== generation,
// A turn later, so a listener sending its receipt straight after the response still holds.
onAnswered: () => { setImmediate(() => { this.held.release(pduObjs); }); },
// Past the refusal only while a drain is still waiting for this message; an ordinary send after.
diff --git a/src/sms.ts b/src/sms.ts
index a93cf6f..8b74b1d 100644
--- a/src/sms.ts
+++ b/src/sms.ts
@@ -38,7 +38,7 @@ export type Sms = {
/** Answers every segment. Part of the protocol, not optional. Defaults to ESME_ROK. */
sendResp: (options?: SendRespOptions) => Promise;
session: Session;
- /** The id answered to the peer: what sendResp() was given, or a generated UUID v7. */
+ /** The id `sendResp()` was given, or a generated UUID v7. */
readonly smsId: string;
submitTime: Date;
to: string;
@@ -54,6 +54,7 @@ export type SmsInput = {
/** What the session's incoming side gives a message so it can be answered and accounted for. */
export type SmsHandlers = {
+ lostLink: () => boolean;
onAnswered: () => void;
send: (input: PduObjectInput) => Promise>;
};
@@ -76,7 +77,8 @@ export function createSms(input: SmsInput, handlers: SmsHandlers): Sms {
message: input.message,
pduObjs: input.pduObjs,
sendDlr: status => sendDlr(sms, handlers.send, status),
- sendResp: options => sendResp(sms, answered, options ?? {}).finally(handlers.onAnswered),
+ sendResp: options => sendResp(sms, answered, options ?? {}, handlers.lostLink)
+ .finally(handlers.onAnswered),
session: input.session,
get smsId(): string {
return answered.smsId;
@@ -92,6 +94,7 @@ async function sendResp(
sms: Sms,
answered: { smsId: string },
options: SendRespOptions,
+ lostLink: () => boolean,
): Promise {
const total = sms.pduObjs.length;
@@ -105,6 +108,11 @@ async function sendResp(
if (options.smsId !== undefined) answered.smsId = options.smsId;
+ // A response carries the sequence number it was asked on, which the next link knows nothing about.
+ if (lostLink()) {
+ return { err: new Error('The link this message arrived on is gone, so nothing would correlate the response') };
+ }
+
const results = await Promise.all(sms.pduObjs.map((pduObj, index) => sms.session.sendReturn(
pduObj,
options.status ?? 'ESME_ROK',
diff --git a/test/session-extras.test.ts b/test/session-extras.test.ts
index 91c41be..1608de2 100644
--- a/test/session-extras.test.ts
+++ b/test/session-extras.test.ts
@@ -13,6 +13,7 @@ import type { Sms } from '../src/sms.ts';
import type { SmppServer } from '../src/server.ts';
import type { TestContext } from 'node:test';
import { HeldMessages } from '../src/held-messages.ts';
+import { IncomingRequests } from '../src/incoming-requests.ts';
import { UnansweredError } from '../src/unanswered-error.ts';
import { createSms } from '../src/sms.ts';
import { LinkGate } from '../src/link-gate.ts';
@@ -557,6 +558,88 @@ describe('reconnect', () => {
assert.equal(report.segments.length, 3);
});
+ test('refuses to answer a message whose link went, held or already answered', async t => {
+ const smpp = await startServer(t);
+ const { session } = await connect(t, smpp, { reconnect: { maxDelay: 100, minDelay: 20 } });
+
+ assert.ok(session);
+
+ const arrived: Sms[] = [];
+ const both = once(resolve => {
+ session.on('sms', sms => {
+ arrived.push(sms);
+
+ if (arrived.length === 2) resolve(true);
+ });
+ });
+
+ for (const text of ['answered before the drop', 'never answered']) {
+ void peerOf(smpp).send({
+ cmdName: 'deliver_sm',
+ params: {
+ destination_addr: '46701113311',
+ short_message: text,
+ source_addr: '46709771337',
+ },
+ });
+ }
+
+ await both;
+
+ const [answered, held] = arrived;
+
+ assert.ok(answered);
+ assert.ok(held);
+ assert.equal(answered.message, 'answered before the drop');
+ assert.equal((await answered.sendResp()).err, undefined);
+
+ const reconnected = once(resolve => { session.on('reconnected', () => { resolve(true); }); });
+
+ await peerOf(smpp).close({ signal: AbortSignal.abort() });
+ await reconnected;
+
+ let taken = 0;
+
+ // A response is dispatched before `incomingPduObj`, so only the raw event sees one arrive.
+ peerOf(smpp).on('incomingPdu', () => { taken++; });
+
+ assert.match((await answered.sendResp()).err?.message ?? '', /link this message arrived on is gone/);
+ assert.match((await held.sendResp()).err?.message ?? '', /link this message arrived on is gone/);
+
+ assert.equal((await held.sendDlr('DELIVERED')).err, undefined);
+ assert.equal(taken, 1, 'a refused response reached the new link');
+ });
+
+ test('drops a message whose link went while onRequest was still running', async t => {
+ const session = new Session({ sock: new net.Socket() });
+
+ closeAfter(t, session);
+ session.boundAs = 'transceiver';
+
+ const incoming = new IncomingRequests({
+ dlrMerger: new DlrMerger({ log: silentLog, max: 10, timeout: 10_000 }),
+ log: silentLog,
+ onRequest: async () => { await delay(10); return false; },
+ sendPastDrain: () => Promise.resolve({ err: new Error('never sent') }),
+ session,
+ });
+ let messages = 0;
+
+ session.on('sms', () => { messages++; });
+
+ const handled = incoming.handle(submitPdu(1));
+
+ incoming.clear();
+
+ await handled;
+
+ assert.equal(messages, 0);
+
+ await incoming.handle(submitPdu(2));
+
+ assert.equal(messages, 1, 'the harness delivers a message whose link stayed');
+ });
+
test('does not reconnect after an explicit close', async t => {
const smpp = await startServer(t);
const { session } = await connect(t, smpp, { reconnect: { maxDelay: 50, minDelay: 10 } });
@@ -944,6 +1027,7 @@ describe('sendDlr()', () => {
session,
to: '46709771337',
}, {
+ lostLink: () => false,
onAnswered: () => undefined,
send: () => {
call++;
diff --git a/todo.md b/todo.md
index 1f1cacb..e965f55 100644
--- a/todo.md
+++ b/todo.md
@@ -60,6 +60,7 @@ Rules the API follows:
| `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` |
| Held messages capped and expiring, so an application that answers nothing cannot grow them | `test/session-extras.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` |
+| A message whose link dropped refused an answer, with its receipt still allowed out | `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` |
| A listener that throws, or rejects, reaching `sessionError`/`serverError` rather than the process | `test/session.test.ts`, `test/error-from.test.ts` |
@@ -140,12 +141,11 @@ session message is a change to every call site.
until the message expires. Same cost as the `onRequest`-answers-nothing case that was declined,
but reached by a bug rather than a policy. 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.
+- [ ] **A refused `sendResp()` releases the hold anyway.** Every early return runs
+ `.finally(onAnswered)`, so `sendResp({ smsId: '' })` refuses and stops the drain waiting for a
+ message the peer was never answered, which `close()` then reports as answered. 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