Best way to set trace parent

[kenfinnigan]

I'm working on adding OpenTelemetry to Quarkus and have an issue on a "clean" way to do something.

I need to extract the trace from incoming HTTP headers, which is fine, but extract() returns a Context whether there was anything there or not. Though it makes sense, there then doesn't appear to be a way to know that the returned Context is the root context without doing an equals() check on it, which seems ugly.

I'm doing this because I want to call setParent() when it's an incoming context, but call setNoParent() when it isn't for span creation.

Am I missing a cleaner way to achieve this?

[Oberon00]

You can call extract with Context.root instead of Context.current.

[Oberon00]

I think it gets set to Context.current, which could be completely different.

In which case do you think it does get set to current?

What is routingContext? And, if it is a context, is it what is passed to extract? Why do you need a tracer there?

As the return is not null, it calls setParent(), which sets the root to false causing the current context to be used as the parent.

If setParent is called, the current context is never accessed by span creation. Instead, the context you passed to setParent is used as-is.

[Oberon00]

A clarification: Even though spanBuilder.setNoParent() is currently implemented in a more complicated way (a code cleanup opportunity @jkwatson ?), it boils down to being exactly equivalent to spanBuilder.setParent(Context.root()).

[jkwatson]

I vaguely recall trying to clean that code up in the past and running into difficulties, but I don't remember any of the details, so I might be making it up. :)

[trask]

👍 this is definitely a case where reading (and trusting) the javadoc is better than reading the code:

opentelemetry-java/api/all/src/main/java/io/opentelemetry/api/trace/SpanBuilder.java

Lines 113 to 114 in 7c73ddb

	* <p>If no {@link Span} is available in the specified {@code Context}, the resulting {@code Span}
	* will become a root instance, as if {@link #setNoParent()} had been called.

[kenfinnigan]

Thanks @trask and @Oberon00, I think I'd got lost somewhere and was inferring something else was happening.