Add tracing #1100

This package provides high level tracing APIs tailored to k6 browser needs, defining methods that allow to correlate async events with the pages to which they belong to.

Adds a new traces registry which will hold the references for every iteration root span and wrapping context. This span will be extended for every instrumented method call during the iteration execution.

The traces registry has to be held per VU scope, as it stores traces indexed per iteration, which are only unique per VU. Therefore keep it under browser registry so we can use it to handle traces generation based on iter events. Because VU.State is nil when the browser registry is initialized, we have to initialize the traces registry on the first VU iteration so we can get access to the k6 TracerProvider. This is done within a sync.Once so we ensure the traces registry is only initialized once per VU.

This also sets the trace context, wrapping the iteration's root span, as the context for browser, which will be inherited by the other components such as browser context, page, etc.

Only stop the traces registry if it has been previously initialized, which won't happen for the initial VU. When stopping, ensure any active live span is ended before exiting.

This is so the tracer can be retrieved by the other components which inherit the browser context (BrowserContext, Page, etc) and use it to generate spans that represent their actions.

Generate a span from onFrameNavigated async event parsing. We must also keep a reference to the last active span for the main frame so we can end it when FrameSession.ctx is Done so the span is flushed before exiting.

Allows to run JS code in the global object instead of a specific execution context.

In order to be able to correlate the Web Vitals events to the navigation span to which they belong to, we have to add a reference to that span in the page context, so it can be retrieved by our Web Vitals script that is executed in the page before pushing the WV metrics to k6 browser through the set up binding. The JS code to set the spanID in the page context is executed through the EvaluateGlobal method as otherwise it would be executed in the current frame context. The problem is that, because we are processing a navigation event, the frame context has actually already changed in the browser but our event parsing goroutine will not process that until we exit the onFrameNavigated method and receive the onExecutionContextCreated event. This would result in an error when evaluating the JS code due to "execution context changed". In this case, because the JS code sets a property in the global object (window), it is OK to just execute it in the global context. Additionally the EvaluateGlobal method has to be called in a separate goroutine to avoid deadlocking the event parsing goroutine when the frame loading generates CDP events that have to be acted on for the loading process to continue, such as when the frame contains a JS initiated dialog (alert, confirm, prompt, or onbeforeunload) which we have to parse and respond with an explicit accept/dismiss action (see onEventJavascriptDialogOpening).

To be able to associate a web vital to the PageNavigation span, we need to inject the span's id that was previously set in the page in onFrameNavigated to the WV event so that the measurement can be correctly linked to the page navigation span.

Generate a span that represents a WebVital measurement.

Defines a tracer interface with only the methods required for the common package tracing. This also allows us to implement higher level helper functions that will automatically retrieve the Tracer from a given context and use it to generate a span, or return a noop span if no tracer is found in the context, avoiding a possible NPE.

This functions will try to call the same method they implement from the tracer contained in the given context. If the tracer is not found in the context, they return a noop Span. This makes the code in the common package cleaner and avoids dealing with possible NPEs. At the sime time avoids having to mock the tracer in tests.

Allows to set a specific TracerProvider for the test VU implementation. If not set, it defaults to NoopTracerProvider.

Reduces nested levels.

Modifies the browser registry constructor to accept a context that will be used in order to build the browser context which will eventually be inherited by the other browser components.

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Add tracing #1100

Add tracing #1100

Commits on Dec 11, 2023