Allow skipping reporting through context flag

[OrkhanAlikhanov]

Describe the feature

From the code it looks like there is no way to skip tracing once the plugin is enabled. I suggest having ability to skip this conditionally based on a value set on context.

Motivation

I have a web request that starts background work. The DB spans are recorded under request, but the DB spans from background task are reported individually, I'm not interested in the background task DB spans and would like to skip it

Related Issues

N/A

[OrkhanAlikhanov]

Workaround that I can think of is starting a span but not sending it

[zstone12]

@OrkhanAlikhanov maybe you can do it with define a filterProcessor. with context get special value then skip export span. demo code like this.

type filterProcessor struct {
sdktrace.SpanProcessor
}

func (p *filterProcessor) OnStart(ctx context.Context, s sdktrace.ReadWriteSpan) {
if skip, ok := ctx.Value("skip-db-spans").(bool); !ok || !skip {
p.SpanProcessor.OnStart(ctx, s)
}
}

provider := sdktrace.NewTracerProvider(
sdktrace.WithSpanProcessor(&filterProcessor{existingProcessor}),
)

[iamfanic]

@OrkhanAlikhanov You can also try customizing a sampler to impose restrictions on the reporting

type filterSampler struct{}

func (fs filterSampler) ShouldSample(p sdktrace.SamplingParameters) sdktrace.SamplingResult {
	enable := p.ParentContext.Value("enable-trace")
	if enable == nil || enable.(bool) == false {
		return sdktrace.SamplingResult{
			Decision: sdktrace.Drop,
		}
	}

	return sdktrace.SamplingResult{
		Decision: sdktrace.RecordAndSample,
	}
}

func (fs filterSampler) Description() string {
	return "filterSampler"
}

func init()  {
	tp := sdktrace.NewTracerProvider(sdktrace.WithSampler(filterSampler{}))
	otel.SetTracerProvider(tp)
}

And make sure to set the context value at the places that need to be reported

ctx := context.WithValue(context.Background(), "enable-trace", true)
ctx, span := tracer.Start(ctx, r.URL.Path)
defer span.End()