Bind as SMPP 3.4 by default, with interfaceVersion to override it

README.md

@@ -77,7 +77,8 @@ Every one is optional.
 | `host` / `port` | `localhost` / `2775` | Where to connect. |
 | `username` / `password` | `user` / `pass` | Bind credentials (`system_id` and `password`). |
 | `bindType` | `transceiver` | `transceiver`, `transmitter` or `receiver`. |
-| `systemType`, `addressRange`, `addrTon`, `addrNpi`, `interfaceVersion` | `''`, `''`, `0`, `0`, `0x50` | The remaining bind fields, for operators that require them. |
+| `interfaceVersion` | `0x34` | The SMPP version declared at bind. `0x50` for an SMSC that requires SMPP 5.0. |
+| `systemType`, `addressRange`, `addrTon`, `addrNpi` | `''`, `''`, `0`, `0` | The remaining bind fields, for operators that require them. |
 | `tls` | `false` | `true` for defaults, or a `tls.ConnectionOptions` object for a private CA or a client certificate. |
 | `enquireLinkInterval` | `20000` | How often to send `enquire_link` on a quiet link. |
 | `responseTimeout` | `30000` | How long to wait for a response before giving up on it. |
@@ -275,8 +276,9 @@ have worked around any of these, remove the workaround:
   reported the full length, so it went out corrupt. In UCS2 that is any message ending in a
   character like 一 (U+4E00), which made the bug routine for CJK text.
 - Short or malformed PDUs threw out of the codec instead of being reported as a parse failure.
-- Binds now declare `interface_version` 0x50. 0.4.0 declared 0x00, because the default in its own
-  command table was never applied. Pass `interfaceVersion: 0x34` to bind as SMPP 3.4.
+- Binds now declare `interface_version` 0x34. 0.4.0 declared 0x00, which tells the SMSC the ESME
+  speaks SMPP 3.3 or earlier — and a spec-following SMSC then withholds every optional parameter,
+  including the TLVs delivery receipts are carried in.
 - `submit_multi` was missing its `sm_length` field, so its `short_message` never round-tripped.
 
 The corrected framing is cross-checked against [node-smpp](https://github.com/farhadi/node-smpp), an

src/client.ts

@@ -33,8 +33,8 @@ const defaults = {
 	bindType: 'transceiver',
 	enquireLinkInterval: 20_000,
 	host: 'localhost',
-	/** SMPP 5.0. 0.4.0 declared 0x00 because its per-parameter default was never applied. */
-	interfaceVersion: 0x50,
+	/** SMPP 3.4. The 3.4 spec reserves every value above it, so 0x50 is undefined to a 3.4 SMSC. */
+	interfaceVersion: 0x34,
 	password: 'pass',
 	port: 2775,
 	username: 'user',

test/interop.test.ts

@@ -69,7 +69,7 @@ describe('our encoder against the reference parser', () => {
 		const parsed = referenceParse(ourBuffer({
 			cmdName: 'bind_transceiver',
 			params: {
-				interface_version: 0x50,
+				interface_version: 0x34,
 				password: 'bar',
 				system_id: 'foo',
 				system_type: 'smpp',
@@ -80,7 +80,7 @@ describe('our encoder against the reference parser', () => {
 		assert.equal(parsed.command, 'bind_transceiver');
 		assert.equal(parsed.system_id, 'foo');
 		assert.equal(parsed.password, 'bar');
-		assert.equal(parsed.interface_version, 0x50);
+		assert.equal(parsed.interface_version, 0x34);
 	});
 
 	test('a deliver_sm carrying delivery receipt TLVs', () => {

test/session.test.ts

@@ -5,6 +5,7 @@ import type { Session } from '../src/session.ts';
 import type { Sms } from '../src/sms.ts';
 import type { SmppServer } from '../src/server.ts';
 import { client } from '../src/client.ts';
+import { isCommand } from '../src/pdu.ts';
 import { server } from '../src/server.ts';
 
 async function startServer(options: Parameters<typeof server>[0] = {}): Promise<SmppServer> {
@@ -93,6 +94,30 @@ describe('bind', () => {
 		assert.equal(await responded, '00000010800000150000000400000001');
 		await smpp.close();
 	});
+
+	test('declares SMPP 3.4 by default and the version the caller asks for', async () => {
+		const smpp = await startServer();
+		const declared: (number | undefined)[] = [];
+
+		smpp.on('session', session => {
+			session.on('incomingPduObj', pduObj => {
+				if (isCommand(pduObj, 'bind_transceiver')) {
+					declared.push(pduObj.params.interface_version);
+				}
+			});
+		});
+
+		const { session: byDefault } = await connect(smpp);
+		const { session: asFive } = await connect(smpp, { interfaceVersion: 0x50 });
+
+		assert.ok(byDefault);
+		assert.ok(asFive);
+		assert.deepEqual(declared, [0x34, 0x50]);
+
+		await byDefault.unbind();
+		await asFive.unbind();
+		await smpp.close();
+	});
 });
 
 describe('sending', () => {

todo.md

@@ -5,7 +5,7 @@ rules there constrain every item below.
 
 ## Status
 
-The rewrite is **feature complete and green**: 136 tests, lint and typecheck clean, verified on Node
+The rewrite is **feature complete and green**: 137 tests, lint and typecheck clean, verified on Node
 18, 20, 22 and 24. What is left is release work and a few things worth adding before or after 1.0.0.
 
 ```bash
@@ -62,10 +62,6 @@ Every defect listed in the AGENTS.md table has a regression test naming the beha
 
 ## Before publishing 1.0.0
 
-- [ ] **Decide the `interface_version` default.** Binds now declare 0x50, which is what 0.4.0's own
-      command table intended but never applied — it actually sent 0x00. 0x34 (SMPP 3.4) is the more
-      conservative choice and is what most SMSCs implement. Flagged to the maintainer; the README
-      documents 0x50 and the `interfaceVersion` option overrides it either way.
 - [ ] Create the `@larvit/smpp` package on npm and add `NPM_TOKEN` to the repository secrets, which
       `.github/workflows/release.yaml` needs.
 - [ ] Tag `v1.0.0` to publish.
@@ -78,6 +74,10 @@ Every defect listed in the AGENTS.md table has a regression test naming the beha
 - [ ] **In-flight sends across a reconnect.** They currently fail with "Session closed before a
       response arrived" and the caller retries. Re-queueing them automatically would be friendlier
       but risks duplicate delivery, so it needs a decision before it is built.
+- [ ] **The server never returns the `sc_interface_version` TLV.** The 3.4 spec has an ESME read its
+      absence from a bind response as "this SMSC does not support optional parameters", and ours
+      does send DLR TLVs. Returning it has to be conditional: a peer that declared below 0x34 must
+      not be sent optional parameters at all.
 - [ ] **TLS is untested.** The code path is right (`tls.connect` / `tls.createServer`, options
       passed through) but no test exercises a handshake. Needs a self-signed certificate fixture.
 - [ ] **`submit_multi` and the broadcast commands** encode and decode, but nothing exercises them