creating a new context with an existing trace context is not working as expected

[HeenaBansal20]

I am looking for the way to create a new context with an existing context but with updated TraceFlags.

I am writting my own extract() function and trying to understand how I can create new context with the current context.

For example if my propagator FIELDS has 3 headers x-span , x-trace and x-sampled.
If only the x-sampled header is present, the function should extract the context and keep the existing traceid and spanid (if available) but update the sampled flag.

I am trying this way but I am getting currentContext as null:

public function extract($carrier, ?PropagationGetterInterface $getter = null, ?ContextInterface $context = null): ContextInterface
    {
        $getter ??= ArrayAccessGetterSetter::getInstance();
        $context ??= Context::getCurrent();
        
        $spanContext = self::extractImpl($carrier, $getter, $context);
        if (!$spanContext->isValid()) {
            return $context;
        }

        return $context->withContextValue(Span::wrap($spanContext));
    }
  private static function extractImpl($carrier, PropagationGetterInterface $getter, ContextInterface $context): SpanContextInterface
    {
        $traceId = self::readHeader($carrier, $getter, self::INSTANA_TRACE_ID_HEADER);
        $spanId = self::readHeader($carrier, $getter, self::INSTANA_SPAN_ID_HEADER);
        $sampled = self::getSampledValue($carrier, $getter);
$currentspanContext = Span::fromContext($context)->getContext();
if ((!$traceId &&  !$spanId) && $sampled != null) {
            echo "I am in this condition";
           
            $updatedSpanContext = SpanContext::createFromRemoteParent(
                $currentSpanContext->getTraceId(),
                $currentSpanContext->getSpanId(),
                $isSampled ? TraceFlags::SAMPLED : TraceFlags::DEFAULT
            );
            return updatedSpanContext;

Tetscase:

public function test_extract_context_with_no_trace_and_span_headers(): void
     {
         $carrier = [
             'X-INSTANA-L' => '0',
         ];

         $this->assertEquals(
             SpanContext::createFromRemoteParent(SpanContextValidator::ff000000000000000000000000000041,
             SpanContextValidator::ff00000000000041),
             $this->getSpanContext($this->instanaMultiPropagator->extract($carrier))
         );
     }

[brettmc]

I am trying this way but I am getting currentContext as null

Do you mean this this line null? $context ??= Context::getCurrent();

If I have understood correctly, you want to use an existing context propagation mechanism (for example the otel TraceParent one), and then selectively apply Instana headers on top of that?

[HeenaBansal20]

@brettmc , this line returns null.
$currentspanContext = Span::fromContext($context)->getContext();

I want to keep the current traceid and spanid from the span context and update the trace flags only as part of instana headers.

For example
if my carrier has only this
$carrier = [
'X-INSTANA-L' => '1',
];

I should be able to create a new remote parent from root traceid and spanid but trace flags to be 1. New span should be
$updatedSpanContext = SpanContext::createFromRemoteParent(
$currentSpanContext->getTraceId(),
$currentSpanContext->getSpanId(),
$isSampled ? TraceFlags::SAMPLED : TraceFlags::DEFAULT
);

[brettmc]

I think what you're hoping for is that the TraceContextPropagator has run before your propagator, then your propagator may make some changes.
Have you tried using MultiTextMapPropagator? You'd have to be careful that they are registered in the correct order, but I think it can do what you want. First TraceContextPropagator will extract context, and that context will be passed in to subsequent propagators, ie yours.

[HeenaBansal20]

@brettmc , I reconsidered the requirement with respect to only one INSTANA header in carrier.
I need not to go to that route.
please take a look at my PR here .
#1582

[brettmc]

I think this can be closed now, since you've taken a different path in the PR.