From a4313d5748fa99bad6f1198e9b8f4a4e02babbc2 Mon Sep 17 00:00:00 2001
From: Vcode2407 <vkslog69@gmail.com>
Date: Mon, 9 Nov 2026 19:11:59 +0530
Subject: [PATCH] Preserve repeated tracestate header fields

Signed-off-by: Vcode2407 <vkslog69@gmail.com>
---
 .../W3CTraceContextPropagator.java            | 18 ++++++++--
 .../W3CTraceContextPropagatorTest.java        | 33 +++++++++++++++++++
 2 files changed, 49 insertions(+), 2 deletions(-)

diff --git a/api/all/src/main/java/io/opentelemetry/api/trace/propagation/W3CTraceContextPropagator.java b/api/all/src/main/java/io/opentelemetry/api/trace/propagation/W3CTraceContextPropagator.java
index 393439518df..f37aaf0f19a 100644
--- a/api/all/src/main/java/io/opentelemetry/api/trace/propagation/W3CTraceContextPropagator.java
+++ b/api/all/src/main/java/io/opentelemetry/api/trace/propagation/W3CTraceContextPropagator.java
@@ -25,6 +25,7 @@
 import java.util.Collection;
 import java.util.Collections;
 import java.util.HashSet;
+import java.util.Iterator;
 import java.util.List;
 import java.util.Set;
 import java.util.logging.Logger;
@@ -165,8 +166,21 @@ private static <C> SpanContext extractImpl(@Nullable C carrier, TextMapGetter<C>
       return contextFromParentHeader;
     }
 
-    String traceStateHeader = getter.get(carrier, TRACE_STATE);
-    if (traceStateHeader == null || traceStateHeader.isEmpty()) {
+    Iterator<String> traceStateHeaders = getter.getAll(carrier, TRACE_STATE);
+    if (traceStateHeaders == null || !traceStateHeaders.hasNext()) {
+      return contextFromParentHeader;
+    }
+
+    String traceStateHeader = traceStateHeaders.next();
+    if (traceStateHeaders.hasNext()) {
+      // W3C Trace Context requires combining repeated fields in the order received.
+      StringBuilder combined = new StringBuilder(traceStateHeader);
+      while (traceStateHeaders.hasNext()) {
+        combined.append(',').append(traceStateHeaders.next());
+      }
+      traceStateHeader = combined.toString();
+    }
+    if (traceStateHeader.isEmpty()) {
       return contextFromParentHeader;
     }
 
diff --git a/api/all/src/test/java/io/opentelemetry/api/trace/propagation/W3CTraceContextPropagatorTest.java b/api/all/src/test/java/io/opentelemetry/api/trace/propagation/W3CTraceContextPropagatorTest.java
index 851d278e73f..87429cc737a 100644
--- a/api/all/src/test/java/io/opentelemetry/api/trace/propagation/W3CTraceContextPropagatorTest.java
+++ b/api/all/src/test/java/io/opentelemetry/api/trace/propagation/W3CTraceContextPropagatorTest.java
@@ -21,7 +21,9 @@
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.HashMap;
+import java.util.Iterator;
 import java.util.LinkedHashMap;
+import java.util.List;
 import java.util.Map;
 import java.util.stream.Stream;
 import javax.annotation.Nullable;
@@ -249,6 +251,37 @@ void extract_SampledContext_WithTraceState() {
                 TRACE_ID_BASE16, SPAN_ID_BASE16, TraceFlags.getSampled(), TRACE_STATE));
   }
 
+  @Test
+  void extract_multipleTraceStateHeaders() {
+    Map<String, List<String>> carrier = new HashMap<>();
+    carrier.put(
+        W3CTraceContextPropagator.TRACE_PARENT,
+        Collections.singletonList(TRACEPARENT_HEADER_SAMPLED));
+    carrier.put(W3CTraceContextPropagator.TRACE_STATE, Arrays.asList("bar=baz", "foo=bar"));
+    TextMapGetter<Map<String, List<String>>> multiGetter =
+        new TextMapGetter<Map<String, List<String>>>() {
+          @Override
+          @Nullable
+          public String get(Map<String, List<String>> headers, String key) {
+            return headers.getOrDefault(key, Collections.emptyList()).stream()
+                .findFirst()
+                .orElse(null);
+          }
+
+          @Override
+          public Iterator<String> getAll(Map<String, List<String>> headers, String key) {
+            return headers.getOrDefault(key, Collections.emptyList()).iterator();
+          }
+        };
+
+    Context context = w3cTraceContextPropagator.extract(Context.root(), carrier, multiGetter);
+
+    assertThat(getSpanContext(context))
+        .isEqualTo(
+            SpanContext.createFromRemoteParent(
+                TRACE_ID_BASE16, SPAN_ID_BASE16, TraceFlags.getSampled(), TRACE_STATE));
+  }
+
   @Test
   void extract_NotSampledContext_WithTraceState() {
     Map<String, String> carrier = new LinkedHashMap<>();