Fix apachehttpclients so that they accept multiple headers

Author: sarahchen6

dd-java-agent/instrumentation/apache-httpclient-4/src/main/java/datadog/trace/instrumentation/apachehttpclient/ApacheHttpClientDecorator.java

@@ -3,6 +3,8 @@
 import datadog.trace.bootstrap.instrumentation.api.UTF8BytesString;
 import datadog.trace.bootstrap.instrumentation.decorator.HttpClientDecorator;
 import java.net.URI;
+import java.util.ArrayList;
+import java.util.List;
 import org.apache.http.Header;
 import org.apache.http.HttpResponse;
 import org.apache.http.client.methods.HttpUriRequest;
@@ -46,18 +48,26 @@ protected int status(final HttpResponse httpResponse) {
 
   @Override
   protected String getRequestHeader(HttpUriRequest request, String headerName) {
-    Header header = request.getFirstHeader(headerName);
-    if (null != header) {
-      return header.getValue();
+    Header[] headers = request.getHeaders(headerName);
+    List<String> values = new ArrayList<>();
+    if (headers.length > 0) {
+      for (Header header : headers) {
+        values.add(header.getValue());
+      }
+      return String.join(",", values);
     }
     return null;
   }
 
   @Override
   protected String getResponseHeader(HttpResponse response, String headerName) {
-    Header header = response.getFirstHeader(headerName);
-    if (null != header) {
-      return header.getValue();
+    Header[] headers = response.getHeaders(headerName);
+    List<String> values = new ArrayList<>();
+    if (headers.length > 0) {
+      for (Header header : headers) {
+        values.add(header.getValue());
+      }
+      return String.join(",", values);
     }
     return null;
   }

dd-java-agent/instrumentation/apache-httpclient-5/src/main/java/datadog/trace/instrumentation/apachehttpclient5/ApacheHttpClientDecorator.java

@@ -4,6 +4,8 @@
 import datadog.trace.bootstrap.instrumentation.decorator.HttpClientDecorator;
 import java.net.URI;
 import java.net.URISyntaxException;
+import java.util.ArrayList;
+import java.util.List;
 import org.apache.hc.core5.http.Header;
 import org.apache.hc.core5.http.HttpRequest;
 import org.apache.hc.core5.http.HttpResponse;
@@ -49,18 +51,26 @@ protected int status(final HttpResponse httpResponse) {
 
   @Override
   protected String getRequestHeader(HttpRequest request, String headerName) {
-    Header header = request.getFirstHeader(headerName);
-    if (null != header) {
-      return header.getValue();
+    Header[] headers = request.getHeaders(headerName);
+    List<String> values = new ArrayList<>();
+    if (headers.length > 0) {
+      for (Header header : headers) {
+        values.add(header.getValue());
+      }
+      return String.join(",", values);
     }
     return null;
   }
 
   @Override
   protected String getResponseHeader(HttpResponse response, String headerName) {
-    Header header = response.getFirstHeader(headerName);
-    if (null != header) {
-      return header.getValue();
+    Header[] headers = response.getHeaders(headerName);
+    List<String> values = new ArrayList<>();
+    if (headers.length > 0) {
+      for (Header header : headers) {
+        values.add(header.getValue());
+      }
+      return String.join(",", values);
     }
     return null;
   }