Implement ExtendedTextMapGetter in spring-webmvc-5.3 instrumentation

instrumentation/spring/spring-webmvc/spring-webmvc-5.3/library/src/main/java/io/opentelemetry/instrumentation/spring/webmvc/v5_3/JavaxHttpServletRequestGetter.java

@@ -5,11 +5,15 @@
 
 package io.opentelemetry.instrumentation.spring.webmvc.v5_3;
 
-import io.opentelemetry.context.propagation.TextMapGetter;
+import static java.util.Collections.emptyIterator;
+
+import io.opentelemetry.context.propagation.internal.ExtendedTextMapGetter;
 import java.util.Collections;
+import java.util.Enumeration;
+import java.util.Iterator;
 import javax.servlet.http.HttpServletRequest;
 
-enum JavaxHttpServletRequestGetter implements TextMapGetter<HttpServletRequest> {
+enum JavaxHttpServletRequestGetter implements ExtendedTextMapGetter<HttpServletRequest> {
   INSTANCE;
 
   @Override
@@ -21,4 +25,24 @@ public Iterable<String> keys(HttpServletRequest carrier) {
   public String get(HttpServletRequest carrier, String key) {
     return carrier.getHeader(key);
   }
+
+  @Override
+  public Iterator<String> getAll(HttpServletRequest carrier, String key) {
+    Enumeration<String> values = carrier.getHeaders(key);
+    if (values == null) {
+      return emptyIterator();
+    }
+
+    return new Iterator<String>() {
+      @Override
+      public boolean hasNext() {
+        return values.hasMoreElements();
+      }
+
+      @Override
+      public String next() {
+        return values.nextElement();
+      }
+    };
+  }
 }

instrumentation/spring/spring-webmvc/spring-webmvc-5.3/library/src/test/java/io/opentelemetry/instrumentation/spring/webmvc/v5_3/WebMvcHttpServerTest.java

@@ -53,6 +53,8 @@ protected void configure(HttpServerTestOptions options) {
           }
           return expectedHttpRoute(endpoint, method);
         });
+
+    options.setTestExtractMultiBaggage(true);
   }
 
   @Test

testing-common/src/main/java/io/opentelemetry/instrumentation/testing/junit/http/HttpServerTestOptions.java

@@ -231,6 +231,12 @@ public HttpServerTestOptions useHttp2() {
     return setUseHttp2(true);
   }
 
+  @CanIgnoreReturnValue
+  public HttpServerTestOptions setTestExtractMultiBaggage(boolean testExtractMultiBaggage) {
+    this.testExtractMultiBaggage = testExtractMultiBaggage;
+    return this;
+  }
+
   @FunctionalInterface
   public interface SpanNameMapper {