Do not overwrite existing baggage with empty baggage in JaegerPropagator

CHANGELOG.md

@@ -2,6 +2,14 @@
 
 ## Unreleased
 
+### API
+
+#### Extensions
+
+* Trace propagators: Fix `JaegerPropagator` overwriting existing baggage when the `jaeger-baggage`
+  header has no parsable entries
+  ([#8632](https://github.com/open-telemetry/opentelemetry-java/pull/8632))
+
 ### SDK
 
 #### Exporters

extensions/trace-propagators/src/main/java/io/opentelemetry/extension/trace/propagation/JaegerPropagator.java

@@ -291,7 +291,11 @@ private static <C> Baggage getBaggageFromHeader(@Nullable C carrier, TextMapGett
         }
       }
     }
-    return builder == null ? null : builder.build();
+    if (builder == null) {
+      return null;
+    }
+    Baggage baggage = builder.build();
+    return baggage.isEmpty() ? null : baggage;
   }
 
   /** Returns a two-element array of {@code [entriesAdded, bytesAdded]}. */

extensions/trace-propagators/src/test/java/io/opentelemetry/extension/trace/propagation/JaegerPropagatorTest.java

@@ -443,6 +443,26 @@ void extract_baggageOnly_withHeader_invalid() {
         .isEqualTo(Baggage.empty());
   }
 
+  @ParameterizedTest
+  @MethodSource
+  void extract_baggageOnly_withHeader_invalid_keepsExistingBaggage(String headerValue) {
+    Baggage existingBaggage = Baggage.builder().put("user", "alice").build();
+    Map<String, String> carrier = new LinkedHashMap<>();
+    carrier.put(BAGGAGE_HEADER, headerValue);
+
+    Context context = Context.root().with(existingBaggage);
+    assertThat(fromContext(jaegerPropagator.extract(context, carrier, getter)))
+        .isEqualTo(existingBaggage);
+  }
+
+  static Stream<Arguments> extract_baggageOnly_withHeader_invalid_keepsExistingBaggage() {
+    return Stream.of(
+        Arguments.argumentSet("no separator", "nometa+novalue"),
+        Arguments.argumentSet("empty value", "user="),
+        Arguments.argumentSet("empty header", ""),
+        Arguments.argumentSet("too many separators", "a=b=c"));
+  }
+
   @Test
   void extract_baggageOnly_withHeader_andPrefix() {
     Map<String, String> carrier = new LinkedHashMap<>();