Better scope management for async code

[rhcarvalho]

Currently, the @sentry/browser SDK has no mechanism to automatically clone the Hub (and, consequently, Scope), unlike @sentry/node that automatically clones a new hub per Node Domain -- and we use that to isolate state for Node server handling concurrent requests.

This means that, in particular for @sentry/browser, any kind of async code may end up accidentally mixing up state unless hubs are manually cloned and used per unit of concurrency.

This issue tracks improving automatic hub/scope management/propagation in @sentry/browser. As a possible solution we may use (an optional support for) Zone.js.

For example:

setTag('a', 'tag');
withScope((scope) => {
  setTimeout(() => {
    captureMessage('test'); // no tags
  }, 0);
});
getCurrentHub().getScope().clear();

hub.withScope(async scope => {
  console.log('scope1', scope);
  scope.setTag('me', 'you');
  hub.withScope(async scope => {
    // will have tag me: you
    console.log('scope2', scope);
    await asyncOperation();
    hub.withScope(async scope => {
      // won't have tag me: you
      console.log('scope3', scope);
      await asyncOperation();
    });
  });
});

The problem is apparent when some code needs to get something from the current scope, for example here is our fetch instrumentation:

sentry-javascript/packages/tracing/src/browser/request.ts

Lines 169 to 178 in 61eda62

	const activeTransaction = getActiveTransaction();
	if (activeTransaction) {
	const span = activeTransaction.startChild({
	data: {
	...handlerData.fetchData,
	type: 'fetch',
	},
	description: `${handlerData.fetchData.method} ${handlerData.fetchData.url}`,
	op: 'http',
	});

sentry-javascript/packages/tracing/src/utils.ts

Lines 54 to 56 in 61eda62

	export function getActiveTransaction<T extends Transaction>(hub: Hub = getCurrentHub()): T | undefined {
	return hub?.getScope()?.getTransaction() as T | undefined;
	}

Because fetch is async, the "current scope" is not necessarily in the state that one would expect. In the example above, when we call getActiveTransaction(), the current hub/scope may have changed and lost reference to the current transaction.

[github-actions]

This issue has gone three weeks without activity. In another week, I will close it.

But! If you comment or otherwise update it, I will reset the clock, and if you label it Status: Backlog or Status: In Progress, I will leave it alone ... forever!

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"A weed is but an unloved flower." ― Ella Wheeler Wilcox 🥀

[hanayashiki]

hope this can get some attention