From de269fa7218bdcf98e1ab361c37d0fed5e9ae382 Mon Sep 17 00:00:00 2001
From: Chris Danis <cdanis@wikimedia.org>
Date: Thu, 19 Dec 2024 17:24:32 -0500
Subject: Setup: parse incoming traceparent header

If present and valid, connect our root span to the
input parent span.

Bug: T340552
Change-Id: I3530c3b6be95c7b4a8960ad25929f795c4514db0
---
 includes/Setup.php | 11 ++++++++---
 1 file changed, 8 insertions(+), 3 deletions(-)

(limited to 'includes/Setup.php')

diff --git a/includes/Setup.php b/includes/Setup.php
index ec6ba6e9c1f3..e40056e9aca2 100644
--- a/includes/Setup.php
+++ b/includes/Setup.php
@@ -78,6 +78,7 @@ use MediaWiki\Title\Title;
 use MediaWiki\User\User;
 use Psr\Log\LoggerInterface;
 use Wikimedia\RequestTimeout\RequestTimeout;
+use Wikimedia\Telemetry\SpanContext;
 use Wikimedia\Telemetry\SpanInterface;
 use Wikimedia\Telemetry\TracerState;
 
@@ -346,9 +347,13 @@ call_user_func( static function (): void {
 	// Avoid high cardinality URL path as root span name, instead safely use the HTTP method.
 	// Per OTEL Semantic Conventions, https://opentelemetry.io/docs/specs/semconv/http/http-spans/
 	$spanName = $request->getMethod();
-	$rootSpan =
-		$tracer->createRootSpan( $spanName )
-			->setSpanKind( SpanInterface::SPAN_KIND_SERVER )
+	$incomingSpanContext = SpanContext::newFromTraceparentHeader( $request->getHeader( 'traceparent' ) );
+	if ( $incomingSpanContext ) {
+		$rootSpan = $tracer->createSpanWithParent( $spanName, $incomingSpanContext );
+	} else {
+		$rootSpan = $tracer->createRootSpan( $spanName );
+	}
+	$rootSpan->setSpanKind( SpanInterface::SPAN_KIND_SERVER )
 			->setAttributes( array_filter( [
 				'http.request.method' => $request->getMethod(),
 				'url.path' => $request->getRequestURL(),
-- 
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