[Feature]: In Collector, expose droppedSpanHandler as an option

[vprithvi]

Requirement

As a Jaeger operator, I'd like to have customized handling when spans are dropped due to incoming queue being full on Jaeger Collector.

Problem

The droppedItemHandler is configured inside newSpanProcessor.

jaeger/cmd/collector/app/span_processor.go

Lines 90 to 100 in fa94007

	func newSpanProcessor(spanWriter spanstore.Writer, additional []ProcessSpan, opts ...Option) *spanProcessor {
	options := Options.apply(opts...)
	handlerMetrics := NewSpanProcessorMetrics(
	options.serviceMetrics,
	options.hostMetrics,
	options.extraFormatTypes)
	droppedItemHandler := func(item interface{}) {
	handlerMetrics.SpansDropped.Inc(1)
	}
	boundedQueue := queue.NewBoundedQueue(options.queueSize, droppedItemHandler)

Proposal

Use the existing Options struct to add a new OnDroppedSpan, use a type assertion internally to convert the interface{} to a *model.Span.

type OnDroppedSpan func(span *model.Span)

func newSpanProcessor(...

	droppedItemHandler := func(item interface{}) {
		handlerMetrics.SpansDropped.Inc(1)
	}

	if options.onDroppedSpan != nil {
		droppedItemHandler = func(iSpan interface{}) {
			options.onDroppedSpan(iSpan.(*model.Span))
		}
	}

Open questions

No response

[eshwarhs]

Hi, I would like to take this up. Can you assign it to me @yurishkuro

[yurishkuro]

https://github.com/jaegertracing/jaeger/blob/main/CONTRIBUTING_GUIDELINES.md#assigning-issues