feat(core): Add continueTrace method

[mydea]

This adds a new continueTrace method which can be used to continue a trace from headers.

This method has the following signature:

function continueTrace<V>(
  {
    sentryTrace,
    baggage,
  }: {
    sentryTrace: Parameters<typeof tracingContextFromHeaders>[0];
    baggage: Parameters<typeof tracingContextFromHeaders>[1];
  },
  callback: (transactionContext: Partial<TransactionContext>) => V,
): V

In practice, this can be used like this:

const transaction = continueTrace({ sentryTrace, baggage }, transactionContext => {
  return startTransaction({
    ...transactionContext,
    name: 'my transaction',
    op: 'my op',
    metadata: {
      ...transactionContext.metadata,
      source: 'route',
    }
  });
});

Closes #9011

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser (incl. Tracing, Replay) - Webpack (gzipped)	84.24 KB (0%)
@sentry/browser (incl. Tracing) - Webpack (gzipped)	31.41 KB (0%)
@sentry/browser - Webpack (gzipped)	22 KB (0%)
@sentry/browser (incl. Tracing, Replay) - ES6 CDN Bundle (gzipped)	78.77 KB (+0.11% 🔺)
@sentry/browser (incl. Tracing) - ES6 CDN Bundle (gzipped)	28.59 KB (+0.26% 🔺)
@sentry/browser - ES6 CDN Bundle (gzipped)	21 KB (+2.03% 🔺)
@sentry/browser (incl. Tracing, Replay) - ES6 CDN Bundle (minified & uncompressed)	254.38 KB (+0.1% 🔺)
@sentry/browser (incl. Tracing) - ES6 CDN Bundle (minified & uncompressed)	86.66 KB (+0.28% 🔺)
@sentry/browser - ES6 CDN Bundle (minified & uncompressed)	62.35 KB (+1.84% 🔺)
@sentry/browser (incl. Tracing) - ES5 CDN Bundle (gzipped)	31.45 KB (+0.24% 🔺)
@sentry/react (incl. Tracing, Replay) - Webpack (gzipped)	84.27 KB (0%)
@sentry/react - Webpack (gzipped)	22.05 KB (0%)
@sentry/nextjs Client (incl. Tracing, Replay) - Webpack (gzipped)	102.23 KB (-0.02% 🔽)
@sentry/nextjs Client - Webpack (gzipped)	50.99 KB (-0.03% 🔽)

[AbhiPrasad]

This is really elegant, it means we can use it with startSpan also.

[Lms24]

Do we also export this in the browser SDKs? I believe we should, for meta tags.
(If there's a reason not to, disregard my other comment).

[Lms24]

l: I'd add meta tags here for the backend->frontend use case.

Suggested change

	/**
	* Continue a trace from a sentryTrace & baggage header.
	* This method takes a sentryTrace, baggage, and an optional request,
	* and will continue tracing from the context provided.
	* It takes a callback that receives a transactionContext that may be used for `startTransaction` or `startSpan`.
	*/
	export function continueTrace<V>(
	/**
	* Continue a trace from a `sentry-trace` and `baggage` values.
	* These values can be obtained from incoming request headers or, in the browser, from `<meta name="sentry-trace">` and `<meta name="baggage">` HTML tags.
	*
	* This function takes a `sentry-trace`, `baggage`, and optionally, a `request` object.
	* It will continue tracing from the context provided.
	*
	* It takes a callback that receives a transactionContext that may be used for `startTransaction` or `startSpan`.
	*/
	export function continueTrace<V>(

[mydea]

I updated the comment to reflect this 👍

[mydea]

Do we also export this in the browser SDKs? I believe we should, for meta tags.
(If there's a reason not to, disregard my other comment).

Oops, missed that - added it to browser exports as well!

[lforst]

I am a bit in favor of removing the request option. It seems a bit off encapsulation wise. While they are often related, continuing a trace should have nothing to do with a request.

[mydea]

I am a bit in favor of removing the request option. It seems a bit off encapsulation wise. While they are often related, continuing a trace should have nothing to do with a request.

I'll remove the request then. I have no strong feelings and was also not sure. Maybe we can also streamline around just always setting scope.setSDKProcessingMetadata({ request: req }); everywhere and stop also setting this directly on the event, as actually this is redundant and not really needed.