Read a delivery receipt's body as the octets that arrived (#81)

* Regression tests for a receipt body read under a data_coding it is not written in

* Read a delivery receipt's body as the octets that arrived, not by its data_coding

* Assert SMPPSim's UCS2 receipt body parses like every other segment's

* Record the receipt-body defect as fixed

* Retain a multipart segment's octets once, not twice

* Sort the new type import into its file's order

test/pdu.test.ts

@@ -1,6 +1,8 @@
 import assert from 'node:assert/strict';
 import test, { describe } from 'node:test';
-import { PduRefusedError, isCommand, isResp, objToPdu, pduReturn, pduToObj, refusalAnswer } from '../src/pdu.ts';
+import { PduRefusedError, refusalAnswer } from '../src/pdu-refusal.ts';
+import { isCommand, isResp, objToPdu, pduReturn, pduToObj } from '../src/pdu.ts';
+import { paramText } from '../src/defs/types.ts';
 
 function encode(...args: Parameters<typeof objToPdu>): Buffer {
 	const { buffer, err } = objToPdu(...args);
@@ -206,6 +208,40 @@ describe('encoding submit_sm', () => {
 	});
 });
 
+describe('decoding short_message', () => {
+	function deliverSm(dataCoding: number, message: Buffer | string) {
+		return decode(encode({
+			cmdName: 'deliver_sm',
+			params: {
+				data_coding: dataCoding,
+				destination_addr: '46709771337',
+				short_message: message,
+				source_addr: '46701113311',
+			},
+			seqNr: 3,
+		}));
+	}
+
+	test('reads an inbound message with the data_coding the PDU declares', () => {
+		const binary = Buffer.from([0x00, 0x1B, 0x60, 0x80, 0xFF]);
+
+		assert.equal(deliverSm(0x08, 'hej 一').params.short_message, 'hej 一');
+		assert.equal(deliverSm(0x03, Buffer.from([0xE1, 0xE7, 0xDA])).params.short_message, 'áçÚ');
+		assert.deepEqual(
+			Buffer.from(paramText(deliverSm(0x04, binary).params.short_message), 'latin1'),
+			binary,
+		);
+	});
+
+	// A delivery receipt is read from these rather than from the text above, since its body is
+	// Appendix B's fixed format whatever the data_coding the peer inherited onto it says.
+	test('keeps the octets that arrived alongside the text they decoded to', () => {
+		const pduObj = deliverSm(0x08, 'hej 一');
+
+		assert.deepEqual(pduObj.shortMessageOctets, Buffer.from('hej 一', 'utf16le').swap16());
+	});
+});
+
 describe('encoding submit_multi', () => {
 	const dest = { dest_addr_npi: 1, dest_addr_ton: 1, destination_addr: '46709771337' };