Issue #1671 asymmetric trailer usage on MetaData.Request

jetty-server/src/main/java/org/eclipse/jetty/server/HttpChannel.java

@@ -25,6 +25,7 @@ import java.util.List;
 import java.util.concurrent.Executor;
 import java.util.concurrent.atomic.AtomicBoolean;
 import java.util.concurrent.atomic.AtomicLong;
+import java.util.function.Supplier;
 
 import javax.servlet.DispatcherType;
 import javax.servlet.RequestDispatcher;
@@ -75,9 +76,18 @@ public class HttpChannel implements Runnable, HttpOutput.Interceptor
     private final HttpChannelState _state;
     private final Request _request;
     private final Response _response;
+    private final Supplier<HttpFields> _trailerSupplier = new Supplier<HttpFields>()
+    {
+        @Override
+        public HttpFields get()
+        {
+            return _trailers;
+        }
+    };
     private MetaData.Response _committedMetaData;
     private RequestLog _requestLog;
     private long _oldIdleTimeout;
+    private HttpFields _trailers;
 
     /** Bytes written after interception (eg after compression) */
     private long _written;
@@ -581,6 +591,7 @@ public class HttpChannel implements Runnable, HttpOutput.Interceptor
         if (idleTO>=0 && _oldIdleTimeout!=idleTO)
             setIdleTimeout(idleTO);
 
+        request.setTrailerSupplier(_trailerSupplier);
         _request.setMetaData(request);
 
         if (LOG.isDebugEnabled())
@@ -608,7 +619,7 @@ public class HttpChannel implements Runnable, HttpOutput.Interceptor
     {
         if (LOG.isDebugEnabled())
             LOG.debug("{} onTrailers {}", this, trailers);
-        _request.setTrailers(trailers);
+        _trailers = trailers;
     }
 
     public boolean onRequestComplete()

jetty-server/src/main/java/org/eclipse/jetty/server/Request.java

@@ -39,6 +39,7 @@ import java.util.EventListener;
 import java.util.List;
 import java.util.Locale;
 import java.util.Map;
+import java.util.function.Supplier;
 import java.util.stream.Collectors;
 
 import javax.servlet.AsyncContext;
@@ -199,7 +200,6 @@ public class Request implements HttpServletRequest
     private long _timeStamp;
     private MultiPartInputStreamParser _multiPartInputStream; //if the request is a multi-part mime
     private AsyncContextState _async;
-    private HttpFields _trailers;
 
     /* ------------------------------------------------------------ */
     public Request(HttpChannel channel, HttpInput input)
@@ -215,9 +215,12 @@ public class Request implements HttpServletRequest
         return metadata==null?null:metadata.getFields();
     }
 
+    /* ------------------------------------------------------------ */
     public HttpFields getTrailers()
     {
-        return _trailers;
+        MetaData.Request metadata=_metaData;
+        Supplier<HttpFields> trailers =  metadata==null?null:metadata.getTrailerSupplier();
+        return trailers==null?null:trailers.get();
     }
 
     /* ------------------------------------------------------------ */
@@ -1859,7 +1862,6 @@ public class Request implements HttpServletRequest
         _multiPartInputStream = null;
         _remote=null;
         _input.recycle();
-        _trailers = null;
     }
 
     /* ------------------------------------------------------------ */
@@ -2228,11 +2230,6 @@ public class Request implements HttpServletRequest
         _scope = scope;
     }
 
-    public void setTrailers(HttpFields trailers)
-    {
-        _trailers = trailers;
-    }
-
     /* ------------------------------------------------------------ */
     @Override
     public AsyncContext startAsync() throws IllegalStateException