diagnostics_channel.js
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diagnostics_channel.js
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	import { test, testThrows, testDeep, summary } from './helpers.js';
	import diagnosticsChannel from 'node:diagnostics_channel';

	console.log('diagnostics_channel\n');

	function collectEvents(tracing) {
	const events = [];

	for (const name of ['start', 'end', 'asyncStart', 'asyncEnd', 'error']) {
	tracing[name].subscribe(message => {
	events.push({ name, message: { ...message } });
	});
	}

	return events;
	}

	test('exports channel', typeof diagnosticsChannel.channel, 'function');
	test('exports tracingChannel', typeof diagnosticsChannel.tracingChannel, 'function');

	const symbolName = Symbol('diagnostics');
	test(
	'channel caches string names',
	diagnosticsChannel.channel('spec:diagnostics:string') === diagnosticsChannel.channel('spec:diagnostics:string'),
	true
	);
	test('channel accepts symbol names', diagnosticsChannel.channel(symbolName).name, symbolName);

	testThrows('channel rejects invalid names', () => diagnosticsChannel.channel(123));
	testThrows('subscribe rejects non-functions', () => diagnosticsChannel.channel('spec:diagnostics:invalid-subscription').subscribe(123));

	const storeChannel = diagnosticsChannel.channel('spec:diagnostics:store');
	const store = {
	run(_value, fn) {
	return fn();
	}
	};
	test('hasSubscribers starts false', storeChannel.hasSubscribers, false);
	storeChannel.bindStore(store);
	test('bindStore contributes to hasSubscribers', storeChannel.hasSubscribers, true);
	storeChannel.unbindStore(store);
	test('unbindStore clears hasSubscribers', storeChannel.hasSubscribers, false);

	const snapshotChannel = diagnosticsChannel.channel('spec:diagnostics:snapshot');
	const snapshotCalls = [];
	const lateSubscriber = () => snapshotCalls.push('late');
	snapshotChannel.subscribe(() => {
	snapshotCalls.push('first');
	snapshotChannel.subscribe(lateSubscriber);
	});
	snapshotChannel.subscribe(() => snapshotCalls.push('second'));
	snapshotChannel.publish({});
	snapshotChannel.publish({});
	testDeep('publish snapshots subscribers', snapshotCalls, ['first', 'second', 'first', 'second', 'late']);

	const syncTracing = diagnosticsChannel.tracingChannel('spec:diagnostics:sync');
	const syncEvents = collectEvents(syncTracing);
	test(
	'traceSync returns result',
	syncTracing.traceSync(() => 42, { phase: 'sync' }),
	42
	);
	testDeep('traceSync publishes start/end', syncEvents, [
	{ name: 'start', message: { phase: 'sync' } },
	{ name: 'end', message: { phase: 'sync', result: 42 } }
	]);

	const promiseTracing = diagnosticsChannel.tracingChannel('spec:diagnostics:promise');
	const promiseEvents = collectEvents(promiseTracing);
	test('tracePromise resolves result', await promiseTracing.tracePromise(() => Promise.resolve(7), { phase: 'promise' }), 7);
	testDeep('tracePromise publishes end before async events', promiseEvents, [
	{ name: 'start', message: { phase: 'promise' } },
	{ name: 'end', message: { phase: 'promise' } },
	{ name: 'asyncStart', message: { phase: 'promise', result: 7 } },
	{ name: 'asyncEnd', message: { phase: 'promise', result: 7 } }
	]);

	const callbackTracing = diagnosticsChannel.tracingChannel('spec:diagnostics:callback');
	const callbackEvents = collectEvents(callbackTracing);
	let callbackError = '';
	const callbackReturn = callbackTracing.traceCallback(
	callback => {
	try {
	callback(null, 9);
	} catch (err) {
	callbackError = err.message;
	}
	return 'outer-result';
	},
	-1,
	{ phase: 'callback' },
	undefined,
	() => {
	throw new Error('callback boom');
	}
	);
	test('traceCallback returns outer result', callbackReturn, 'outer-result');
	test('traceCallback uses the last argument by default', callbackError, 'callback boom');
	testDeep('traceCallback still publishes asyncEnd when callback throws', callbackEvents, [
	{ name: 'start', message: { phase: 'callback' } },
	{ name: 'asyncStart', message: { phase: 'callback', result: 9 } },
	{ name: 'asyncEnd', message: { phase: 'callback', result: 9 } },
	{ name: 'end', message: { phase: 'callback', result: 9 } }
	]);

	summary();

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