changes W3CBaggagePropagator to handle multiple headers for baggage, using new getList() method on the TextMapGetter. Includes tests.

Author: jamesmoessis

api/all/src/main/java/io/opentelemetry/api/baggage/propagation/W3CBaggagePropagator.java

@@ -86,6 +86,12 @@ private static String encodeValue(String value) {
     return URL_ESCAPER.escape(value);
   }
 
+  /**
+   * @param context the {@code Context} used to store the extracted value.
+   * @param carrier holds propagation fields. For example, an outgoing message or http request.
+   * @param getter invoked for each propagation key to get data from the carrier.
+   * @return the extracted context
+   */
   @Override
   public <C> Context extract(Context context, @Nullable C carrier, TextMapGetter<C> getter) {
     if (context == null) {
@@ -95,21 +101,26 @@ public <C> Context extract(Context context, @Nullable C carrier, TextMapGetter<C
       return context;
     }
 
-    String baggageHeader = getter.get(carrier, FIELD);
-    if (baggageHeader == null) {
-      return context;
-    }
-    if (baggageHeader.isEmpty()) {
+    List<String> baggageHeaders = getter.getList(carrier, FIELD);
+    if (baggageHeaders == null || baggageHeaders.isEmpty()) {
       return context;
     }
 
+    boolean extracted = false;
     BaggageBuilder baggageBuilder = Baggage.builder();
-    try {
-      extractEntries(baggageHeader, baggageBuilder);
-    } catch (RuntimeException e) {
-      return context;
+    for (String header : baggageHeaders) {
+      if (header.isEmpty()) {
+        continue;
+      }
+
+      try {
+        extractEntries(header, baggageBuilder);
+        extracted = true;
+      } catch (RuntimeException expected) {
+        // invalid baggage header, continue
+      }
     }
-    return context.with(baggageBuilder.build());
+    return extracted ? context.with(baggageBuilder.build()) : context;
   }
 
   private static void extractEntries(String baggageHeader, BaggageBuilder baggageBuilder) {

api/all/src/test/java/io/opentelemetry/api/baggage/propagation/W3CBaggagePropagatorTest.java

@@ -8,6 +8,7 @@
 import static java.util.Collections.singletonMap;
 import static org.assertj.core.api.Assertions.assertThat;
 
+import com.google.common.collect.ImmutableList;
 import com.google.common.collect.ImmutableMap;
 import io.opentelemetry.api.baggage.Baggage;
 import io.opentelemetry.api.baggage.BaggageEntryMetadata;
@@ -16,6 +17,7 @@
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.LinkedHashMap;
+import java.util.List;
 import java.util.Map;
 import javax.annotation.Nullable;
 import org.junit.jupiter.api.Test;
@@ -36,6 +38,27 @@ public String get(Map<String, String> carrier, String key) {
         }
       };
 
+  private static final TextMapGetter<Map<String, List<String>>> multiGetter =
+      new TextMapGetter<Map<String, List<String>>>() {
+        @Override
+        public Iterable<String> keys(Map<String, List<String>> carrier) {
+          return carrier.keySet();
+        }
+
+        @Nullable
+        @Override
+        public String get(Map<String, List<String>> carrier, String key) {
+          return carrier.getOrDefault(key, Collections.emptyList()).stream()
+              .findFirst()
+              .orElse(null);
+        }
+
+        @Override
+        public List<String> getList(Map<String, List<String>> carrier, String key) {
+          return carrier.getOrDefault(key, Collections.emptyList());
+        }
+      };
+
   @Test
   void fields() {
     assertThat(W3CBaggagePropagator.getInstance().fields()).containsExactly("baggage");
@@ -421,6 +444,73 @@ void extract_nullGetter() {
         .isSameAs(context);
   }
 
+  @Test
+  void extract_multiple_headers() {
+    W3CBaggagePropagator propagator = W3CBaggagePropagator.getInstance();
+
+    Context result =
+        propagator.extract(
+            Context.root(),
+            ImmutableMap.of("baggage", ImmutableList.of("k1=v1", "k2=v2")),
+            multiGetter);
+
+    Baggage expectedBaggage = Baggage.builder().put("k1", "v1").put("k2", "v2").build();
+    assertThat(Baggage.fromContext(result)).isEqualTo(expectedBaggage);
+  }
+
+  @Test
+  void extract_multiple_headers_duplicate_key() {
+    W3CBaggagePropagator propagator = W3CBaggagePropagator.getInstance();
+
+    Context result =
+        propagator.extract(
+            Context.root(),
+            ImmutableMap.of("baggage", ImmutableList.of("k1=v1", "k1=v2")),
+            multiGetter);
+
+    Baggage expectedBaggage = Baggage.builder().put("k1", "v2").build();
+    assertThat(Baggage.fromContext(result)).isEqualTo(expectedBaggage);
+  }
+
+  @Test
+  void extract_multiple_headers_mixed_duplicates_non_duplicates() {
+    W3CBaggagePropagator propagator = W3CBaggagePropagator.getInstance();
+
+    Context result =
+        propagator.extract(
+            Context.root(),
+            ImmutableMap.of("baggage", ImmutableList.of("k1=v1,k2=v0", "k2=v2,k3=v3")),
+            multiGetter);
+
+    Baggage expectedBaggage =
+        Baggage.builder().put("k1", "v1").put("k2", "v2").put("k3", "v3").build();
+    assertThat(Baggage.fromContext(result)).isEqualTo(expectedBaggage);
+  }
+
+  @Test
+  void extract_multiple_headers_all_empty() {
+    W3CBaggagePropagator propagator = W3CBaggagePropagator.getInstance();
+
+    Context result =
+        propagator.extract(
+            Context.root(), ImmutableMap.of("baggage", ImmutableList.of("", "")), multiGetter);
+
+    Baggage expectedBaggage = Baggage.builder().build();
+    assertThat(Baggage.fromContext(result)).isEqualTo(expectedBaggage);
+  }
+
+  @Test
+  void extract_multiple_headers_some_empty() {
+    W3CBaggagePropagator propagator = W3CBaggagePropagator.getInstance();
+
+    Context result =
+        propagator.extract(
+            Context.root(), ImmutableMap.of("baggage", ImmutableList.of("", "k=v")), multiGetter);
+
+    Baggage expectedBaggage = Baggage.builder().put("k", "v").build();
+    assertThat(Baggage.fromContext(result)).isEqualTo(expectedBaggage);
+  }
+
   @Test
   void inject_noBaggage() {
     W3CBaggagePropagator propagator = W3CBaggagePropagator.getInstance();

context/src/main/java/io/opentelemetry/context/propagation/TextMapGetter.java

@@ -37,7 +37,7 @@ public interface TextMapGetter<C> {
   String get(@Nullable C carrier, String key);
 
   /**
-   * If implemented, returns all values for a given {@code key}, in order.
+   * If implemented, returns all values for a given {@code key} in order, or returns an empty list.
    *
    * <p>The default method returns the first value of the given propagation {@code key} as a
    * singleton list, or returns an empty list.