Add PDU framing and delivery receipt parsing

test/pdu-framer.test.ts

@@ -0,0 +1,87 @@
+import assert from 'node:assert/strict';
+import test, { describe } from 'node:test';
+import { PduFramer } from '../src/pdu-framer.ts';
+import { objToPdu } from '../src/pdu.ts';
+
+function pdu(seqNr: number): Buffer {
+	const { buffer } = objToPdu({ cmdName: 'enquire_link', seqNr });
+
+	assert.ok(buffer);
+
+	return buffer;
+}
+
+describe('PduFramer', () => {
+	test('yields nothing until a whole PDU has arrived', () => {
+		const framer = new PduFramer();
+		const whole = pdu(1);
+
+		framer.push(whole.subarray(0, 8));
+		assert.deepEqual(framer.next(), { pdus: [] });
+
+		framer.push(whole.subarray(8));
+		assert.deepEqual(framer.next(), { pdus: [whole] });
+	});
+
+	test('splits several PDUs delivered in one chunk', () => {
+		const framer = new PduFramer();
+
+		framer.push(Buffer.concat([pdu(1), pdu(2), pdu(3)]));
+
+		const { pdus } = framer.next();
+
+		assert.ok(pdus);
+		assert.equal(pdus.length, 3);
+		assert.deepEqual(pdus[2], pdu(3));
+	});
+
+	test('reassembles a PDU dribbled one octet at a time', () => {
+		const framer = new PduFramer();
+		const whole = pdu(42);
+
+		for (const octet of whole) {
+			framer.push(Buffer.from([octet]));
+		}
+
+		assert.deepEqual(framer.next(), { pdus: [whole] });
+		assert.equal(framer.buffered, 0);
+	});
+
+	test('keeps a trailing partial PDU buffered for the next chunk', () => {
+		const framer = new PduFramer();
+		const second = pdu(2);
+
+		framer.push(Buffer.concat([pdu(1), second.subarray(0, 4)]));
+
+		const first = framer.next();
+
+		assert.ok(first.pdus);
+		assert.equal(first.pdus.length, 1);
+		assert.equal(framer.buffered, 4);
+
+		framer.push(second.subarray(4));
+		assert.deepEqual(framer.next(), { pdus: [second] });
+	});
+
+	// 0.4.0 read a command length of 0 as "discard the buffer" and looped; anything absurd was
+	// simply trusted and allocated.
+	test('reports an impossible command length instead of trusting it', () => {
+		const zero = new PduFramer();
+		const huge = new PduFramer();
+
+		zero.push(Buffer.alloc(16));
+		assert.ok(zero.next().err instanceof Error);
+
+		huge.push(Buffer.from('ffffffff0000001500000000000000ff', 'hex'));
+		assert.ok(huge.next().err instanceof Error);
+	});
+
+	test('ignores empty chunks', () => {
+		const framer = new PduFramer();
+
+		framer.push(Buffer.alloc(0));
+
+		assert.equal(framer.buffered, 0);
+		assert.deepEqual(framer.next(), { pdus: [] });
+	});
+});