Read an intermediate delivery notification as a report, and keep it out of the merge

AGENTS.md

@@ -18,16 +18,19 @@ one wins. They do not override the hard rules below.
 1. **Correct on the wire.** SMPP 3.4 as SMSCs actually run it. Every other goal yields to this one;
    the defect table below is what the alternative costs.
 2. **Never give the application a wrong answer about what happened.** An outcome we cannot determine
-   is reported as undetermined rather than guessed; a request the peer may already have taken is
-   never re-sent on the library's own initiative; work the peer has no reason to send again is not
-   dropped.
+   is reported as undetermined rather than guessed; a report the peer marked as not final settles
+   nothing, so nothing the library concludes may rest on one; a request the peer may already have
+   taken is never re-sent on the library's own initiative; work the peer has no reason to send again
+   is not dropped.
 3. **Strict in what we send, generous in what we read.** The library's own senders follow 3.4, and
    the codec parses whatever arrives. Where the letter of the spec would discard traffic a real SMSC
    sends, keep the traffic.
 4. **A peer an operator never has to complain about.** No bind flooding, nothing a bind direction
    forbids, no optional parameters to a peer that declared none, nothing held without a bound.
 5. **The session layer is in here, and its defaults are what most applications should run.**
-   Keepalive, reconnect, the send window, reassembly and receipt correlation. An option retunes a
+   Keepalive, reconnect, the send window, reassembly and receipt correlation. What the network says
+   about a message the application sent reaches it as a report rather than as an inbound message, and
+   says whether it is final, so nothing has to read the PDU to tell those apart. An option retunes a
    default or opts out of it; an option does not switch on the thing the caller obviously wanted.
 6. **A small, stable public surface over reshapeable internals.** Only what `src/index.ts` exports is
    published. A new option has to beat "the application can do this itself", and has to keep a
@@ -273,12 +276,15 @@ Grouped by what each one constrains.
   and sent no optional parameters, which is how the spec reads an absent `sc_interface_version`.
 
 - **`esm_class` decides what a `deliver_sm` is, and the body is read only when it names nothing.**
-  `MC_DELIVERY_RECEIPT` (0x04) makes it a receipt whatever the body parses to, so a receipt in a
-  format `dlrFromPdu()` cannot read reaches `dlr` with `smsId` undefined instead of arriving as an
-  inbound SMS. Any other named type is not a receipt and its body is not scraped; a message type of 0
-  or one of the ten reserved keeps the scrape, and a non-empty `receipted_message_id` TLV marks a
-  receipt on the same footing. A receipt this library recognises never reaches the reassembler, so an
-  SMSC that splits one across segments gets a `dlr` per segment rather than one merged report. The
+  The two types the MC writes about a message we submitted — `MC_DELIVERY_RECEIPT` (0x04) and
+  `INTERMEDIATE_DELIVERY` (0x20) — are reports whatever the body parses to, so one in a format
+  `dlrFromPdu()` cannot read reaches `dlr` with `smsId` undefined instead of arriving as an inbound
+  SMS. The three the far-end SME writes (0x08, 0x10, 0x18) are messages and their bodies are not
+  scraped: Kannel reads 0x08 as report-bearing and this does not, because a delivery acknowledgement
+  is the handset's word about a message, not the network's. A message type of 0 or one of the ten
+  reserved keeps the scrape, and a non-empty `receipted_message_id` TLV marks a report on the same
+  footing. A report this library recognises never reaches the reassembler, so an SMSC that splits one
+  across segments gets a `dlr` per segment rather than one merged report. The
   `message_state` TLV is authoritative only where it names a state in the table — SMPP reserves
   0x80-0xFF for MC-vendor-specific values, so an unnameable one keeps its raw `statusId` and leaves
   `statusMsg` to the body.

README.md

@@ -163,7 +163,9 @@ session.on('sms', async sms => {
 Delivery receipts travel on the same SMPP command but reach you as `dlr`, so nothing you write has
 to tell the two apart. `esm_class` is what tells them apart; where it names no message type a
 `receipted_message_id` TLV does, and failing both the message body is read for the standard
-`id:` and `stat:` receipt fields.
+`id:` and `stat:` receipt fields. An intermediate delivery notification is the SMSC reporting too,
+and arrives with `dlr.intermediate` true: nothing about the message is settled, and a later receipt
+says how it ended.
 
 Matching a receipt to a send means comparing `dlr.smsId` against the `smsIds` that `sendSms()`
 returned. Some SMSCs write the two in different notations — a hex `message_id` on the
@@ -317,8 +319,8 @@ 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 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 `<base>-<n>`, 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. |
+| `dlr` | A delivery report arrives, one per segment. `intermediate` is true where the SMSC marked it a report it will follow with a final receipt. `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. An intermediate report never counts towards it. Merging needs the SMSC to number its segment ids `<base>-<n>`, 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. |
 | `disconnected` | The link dropped and the reconnect loop will retry it. Do not open a replacement client here — the session you hold comes back on its own, and `reconnected` says when. Fires again for each attempt that reconnects and then fails, so it is not one-to-one with `reconnected`. |
 | `reconnected` | The client re-bound after a drop. |

src/dlr-merger.ts

@@ -41,7 +41,8 @@ const severity: Record<MessageState, number> = {
  * Merges the per-segment receipts of a multipart message into one report, but only when the peer
  * numbered its ids `<base>-<n>` off one base — the convention this library's own server follows. An
  * SMSC that hands out unrelated ids per segment cannot be merged, so nothing is reported for it.
- * A base is merged at most once: a reused id cannot be told apart from a straggler.
+ * A base is merged at most once: a reused id cannot be told apart from a straggler, and a report the
+ * peer marked intermediate is never counted — it would fill a slot before the real receipt arrives.
  */
 export class DlrMerger {
 	private readonly groups: ExpiringGroups<Group>;
@@ -95,7 +96,7 @@ export class DlrMerger {
 	collect(dlr: Dlr): MessageDlr | undefined {
 		this.sweep();
 
-		if (dlr.smsId === undefined) return undefined;
+		if (dlr.intermediate || dlr.smsId === undefined) return undefined;
 
 		const match = numbered.exec(dlr.smsId);
 		const base = match?.[1];

src/dlr.ts

@@ -50,6 +50,7 @@ export type Receipt = {
 export type Dlr = {
 	doneDate: Date | undefined;
 	errorCode: string | undefined;
+	intermediate: boolean;
 	receipt: Receipt | undefined;
 	smsId: string | undefined;
 	statusId: number;
@@ -127,13 +128,12 @@ export function parseReceipt(message: string): Receipt {
 	};
 }
 
-type MessageType = 'other' | 'receipt' | 'unmarked';
+type MessageType = 'intermediate' | 'other' | 'receipt' | 'unmarked';
 
-/** The message types the spec names that are not receipts. It reserves the remaining ten. */
-const notReceiptTypes: number[] = [
+/** The types the far-end SME writes, rather than the MC reporting. The spec reserves the remaining ten. */
+const smeMessageTypes: number[] = [
 	consts.ESM_CLASS.CONVERSATION_ABORT,
 	consts.ESM_CLASS.DELIVERY_ACKNOWLEDGEMENT,
-	consts.ESM_CLASS.INTERMEDIATE_DELIVERY,
 	consts.ESM_CLASS.USER_ACKNOWLEDGEMENT,
 ];
 
@@ -145,7 +145,8 @@ function messageType(pduObj: PduObject): MessageType {
 	const type = messageTypeOf(paramNumber(pduObj.params.esm_class, 0));
 
 	if (type === consts.ESM_CLASS.MC_DELIVERY_RECEIPT) return 'receipt';
-	if (notReceiptTypes.includes(type)) return 'other';
+	if (type === consts.ESM_CLASS.INTERMEDIATE_DELIVERY) return 'intermediate';
+	if (smeMessageTypes.includes(type)) return 'other';
 
 	return nonEmptyText(pduObj.tlvs.receipted_message_id?.tagValue) === undefined ? 'unmarked' : 'receipt';
 }
@@ -214,6 +215,7 @@ export function dlrFromPdu(pduObj: PduObject, format: SmsIdFormat = {}): Dlr | u
 	return {
 		doneDate: receiptDate(receipt?.doneDate),
 		errorCode: receipt?.err,
+		intermediate: type === 'intermediate',
 		receipt,
 		smsId,
 		statusId,

test/dlr.test.ts

@@ -145,6 +145,7 @@ describe('dlrFromPdu()', () => {
 		assert.equal(dlr.smsId, undefined);
 		assert.equal(dlr.statusMsg, 'UNKNOWN');
 		assert.equal(dlr.statusId, 7);
+		assert.equal(dlr.intermediate, false);
 	});
 
 	// pduToObj leaves a UDH-carrying short_message a buffer, so the body needs decoding before it
@@ -196,17 +197,31 @@ describe('dlrFromPdu()', () => {
 		assert.equal(dlr.statusMsg, 'DELIVERED');
 	});
 
-	test('leaves a message the peer marked as another type to arrive as an SMS', () => {
+	test('leaves a message the far-end SME marked as another type to arrive as an SMS', () => {
 		for (const esmClass of [
 			consts.ESM_CLASS.CONVERSATION_ABORT,
 			consts.ESM_CLASS.DELIVERY_ACKNOWLEDGEMENT,
-			consts.ESM_CLASS.INTERMEDIATE_DELIVERY,
 			consts.ESM_CLASS.USER_ACKNOWLEDGEMENT,
 		]) {
 			assert.equal(dlrFromPdu(deliverSm(receiptText, undefined, esmClass)), undefined);
 		}
 	});
 
+	test('reads an intermediate delivery notification as a report, marked as one', () => {
+		const enroute = 'id:0195f0c7 sub:001 dlvrd:000 submit date:2508251430 done date:2508251431 stat:ENROUTE err:000 text:';
+		const dlr = dlrFromPdu(deliverSm(enroute, undefined, consts.ESM_CLASS.INTERMEDIATE_DELIVERY));
+
+		assert.ok(dlr);
+		assert.equal(dlr.smsId, '0195f0c7');
+		assert.equal(dlr.statusMsg, 'ENROUTE');
+		assert.equal(dlr.intermediate, true);
+
+		const unreadable = dlrFromPdu(deliverSm('no fields here', undefined, consts.ESM_CLASS.INTERMEDIATE_DELIVERY));
+
+		assert.ok(unreadable, 'the marker makes it a report whatever the body parses to');
+		assert.equal(unreadable.intermediate, true);
+	});
+
 	test('exposes the raw receipt alongside the resolved fields', () => {
 		const dlr = dlrFromPdu(deliverSm(receiptText));
 

test/session-extras.test.ts

@@ -203,10 +203,11 @@ describe('merged delivery reports', () => {
 });
 
 describe('merging segment statuses', () => {
-	function receipt(smsId: string, statusMsg: MessageState): Dlr {
+	function receipt(smsId: string, statusMsg: MessageState, intermediate = false): Dlr {
 		return {
 			doneDate: undefined,
 			errorCode: undefined,
+			intermediate,
 			receipt: undefined,
 			smsId,
 			statusId: consts.MESSAGE_STATE[statusMsg],
@@ -214,6 +215,24 @@ describe('merging segment statuses', () => {
 		};
 	}
 
+	// Filling every slot with a non-final report merges early and spends the base, so the receipts
+	// that say what actually happened would report nothing.
+	test('never counts an intermediate report toward a merge', () => {
+		const merger = new DlrMerger({ log: silentLog, max: 10, now: () => 0, timeout: 60_000 });
+
+		merger.expect(['msg-1', 'msg-2']);
+
+		assert.equal(merger.collect(receipt('msg-1', 'ENROUTE', true)), undefined);
+		assert.equal(merger.collect(receipt('msg-2', 'ENROUTE', true)), undefined);
+		assert.equal(merger.collect(receipt('msg-1', 'DELIVERED')), undefined);
+
+		const merged = merger.collect(receipt('msg-2', 'DELIVERED'));
+
+		assert.ok(merged);
+		assert.equal(merged.statusMsg, 'DELIVERED');
+		assert.equal(merged.segments.length, 2);
+	});
+
 	// MESSAGE_STATE is a flat enum: ACCEPTED is 6 where UNDELIVERABLE is 5, so reducing on the
 	// wire value called a part-failed message delivered.
 	test('reports the worse of two states the wire numbers the other way round', () => {

test/session.test.ts

@@ -685,7 +685,7 @@ describe('receiving', () => {
 		assert.equal(answered.pduObj.params.message_id, 'inbound-id');
 	});
 
-	test('hands a client a receipt it cannot read as a dlr rather than as an sms', async t => {
+	test('hands a client a report as a dlr rather than as an sms', async t => {
 		const { peer, session } = await inbound(t);
 		const reported = once<Dlr>(resolve => { session.on('dlr', resolve); });
 		let messages = 0;
@@ -711,6 +711,28 @@ describe('receiving', () => {
 
 		assert.ok(answered.pduObj);
 		assert.equal(answered.pduObj.cmdName, 'deliver_sm_resp');
+
+		const notified = once<Dlr>(resolve => { session.on('dlr', resolve); });
+		const notification = peer.send({
+			cmdName: 'deliver_sm',
+			params: {
+				destination_addr: '46709771337',
+				esm_class: consts.ESM_CLASS.INTERMEDIATE_DELIVERY,
+				short_message: 'id:0195f0c7 stat:ENROUTE err:000 text:',
+				source_addr: '46701113311',
+			},
+		});
+		const report = await raceWithin(2000, notified);
+
+		assert.ok(report, 'an intermediate notification is the MC reporting on our send, not an inbound SMS');
+		assert.equal(report.intermediate, true);
+		assert.equal(report.statusMsg, 'ENROUTE');
+		assert.equal(messages, 0);
+
+		const answeredNotification = await notification;
+
+		assert.ok(answeredNotification.pduObj);
+		assert.equal(answeredNotification.pduObj.cmdName, 'deliver_sm_resp');
 	});
 
 	test('reassembles a multipart inbound SMS before the sms event', async t => {
@@ -1494,6 +1516,7 @@ describe('merged delivery report bounds', () => {
 		return {
 			doneDate: undefined,
 			errorCode: undefined,
+			intermediate: false,
 			receipt: undefined,
 			smsId,
 			statusId: 2,

todo.md

@@ -64,6 +64,7 @@ Rules the API follows:
 | The hold released exactly when the peer was answered: a refused `sendResp()` keeps it, a listener that rejected drops it | `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` |
+| An intermediate delivery notification read as a report marked `intermediate`, and never counted into a merge | `test/dlr.test.ts`, `test/session.test.ts`, `test/session-extras.test.ts` |
 | A listener that throws, or rejects, reaching `sessionError`/`serverError` rather than the process | `test/session.test.ts`, `test/error-from.test.ts` |
 | Cross-checked against node-smpp both ways and over a live session | `test/interop.test.ts` |
 | CI on Node 18/20/22/24, Renovate, tag-triggered publish | `.github/workflows/` |
@@ -131,13 +132,6 @@ session message is a change to every call site.
       and applies it to the other is wrong. A budget type both take would close it. 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
-      SMS. Kannel treats 0x04, 0x08 and 0x20 alike as report-bearing. Against it: a non-final report
-      would take a segment's slot in `DlrMerger` and complete the group early. Raised by review,
-      2026-08-27; needs a decision.
-
 - [ ] **`once()` is copied into four test files, and two copies never give up.**
       `session-extras.test.ts` and `readme.test.ts` reject after 5000 ms; `session.test.ts` and
       `tls.test.ts` wait forever, so an event that never fires still hangs the run the way an