Converted writeTrailers to a static method

jetty-core/jetty-http2/jetty-http2-tests/src/test/java/org/eclipse/jetty/http2/tests/TrailersTest.java

@@ -415,7 +415,7 @@ public void process(Request request, Response response, Callback callback)
             {
                 HttpFields.Mutable trailers = HttpFields.build();
                 response.setTrailersSupplier(() -> trailers);
-                Content.copy(request, response, response::writeTrailers, callback);
+                Content.copy(request, response, Response.newTrailersChunkProcessor(response), callback);
             }
         });
 

jetty-core/jetty-io/src/main/java/org/eclipse/jetty/io/Content.java

@@ -21,7 +21,6 @@
 import java.nio.charset.StandardCharsets;
 import java.util.Objects;
 import java.util.concurrent.Flow;
-import java.util.function.BiPredicate;
 import java.util.function.Consumer;
 
 import org.eclipse.jetty.io.content.ContentSinkOutputStream;
@@ -80,12 +79,12 @@ public static void copy(Source source, Sink sink, Callback callback)
      *
      * @param source the source to copy from
      * @param sink the sink to copy to
-     * @param chunkHandler a (possibly {@code null}) predicate to handle the current chunk and its callback
+     * @param chunkProcessor a (possibly {@code null}) predicate to handle the current chunk and its callback
      * @param callback the callback to notify when the copy is complete
      */
-    public static void copy(Source source, Sink sink, BiPredicate<Chunk, Callback> chunkHandler, Callback callback)
+    public static void copy(Source source, Sink sink, Chunk.Processor chunkProcessor, Callback callback)
     {
-        new ContentCopier(source, sink, chunkHandler, callback).iterate();
+        new ContentCopier(source, sink, chunkProcessor, callback).iterate();
     }
 
     /**
@@ -683,5 +682,21 @@ public boolean release()
                 return true;
             }
         }
+
+        /**
+         * <p>Implementations of this interface may process {@link Chunk}s being copied by the
+         * {@link Content#copy(Source, Sink, Processor, Callback)} method, so that
+         * {@link Chunk}s of unknown types can be copied.
+         * @see Content#copy(Source, Sink, Processor, Callback)
+         */
+        interface Processor
+        {
+            /**
+             * @param chunk The chunk to be considered for processing.
+             * @param callback The callback that will be called once the accepted chunk is processed.
+             * @return True if the chunk will be process and the callback will be called (or may have already been called), false otherwise.
+             */
+            boolean process(Chunk chunk, Callback callback);
+        }
     }
 }

jetty-core/jetty-io/src/main/java/org/eclipse/jetty/io/internal/ContentCopier.java

@@ -13,8 +13,6 @@
 
 package org.eclipse.jetty.io.internal;
 
-import java.util.function.BiPredicate;
-
 import org.eclipse.jetty.io.Content;
 import org.eclipse.jetty.util.Callback;
 import org.eclipse.jetty.util.IteratingNestedCallback;
@@ -23,16 +21,16 @@ public class ContentCopier extends IteratingNestedCallback
 {
     private final Content.Source source;
     private final Content.Sink sink;
-    private final BiPredicate<Content.Chunk, Callback> chunkHandler;
+    private final Content.Chunk.Processor chunkProcessor;
     private Content.Chunk current;
     private boolean terminated;
 
-    public ContentCopier(Content.Source source, Content.Sink sink, BiPredicate<Content.Chunk, Callback> chunkHandler, Callback callback)
+    public ContentCopier(Content.Source source, Content.Sink sink, Content.Chunk.Processor chunkProcessor, Callback callback)
     {
         super(callback);
         this.source = source;
         this.sink = sink;
-        this.chunkHandler = chunkHandler;
+        this.chunkProcessor = chunkProcessor;
     }
 
     @Override
@@ -55,7 +53,7 @@ protected Action process() throws Throwable
             return Action.IDLE;
         }
 
-        if (chunkHandler != null && chunkHandler.test(current, this))
+        if (chunkProcessor != null && chunkProcessor.process(current, this))
             return Action.SCHEDULED;
 
         if (current instanceof Error error)

jetty-core/jetty-server/src/main/java/org/eclipse/jetty/server/Response.java

@@ -65,24 +65,49 @@ public interface Response extends Content.Sink
 
     CompletableFuture<Void> writeInterim(int status, HttpFields headers);
 
-    // TODO: make it static, otherwise we must override it in Wrapper.
-    default boolean writeTrailers(Content.Chunk chunk, Callback ignored)
+    /**
+     * <p>Return chunk processor suitable to be passed to the
+     * {@link Content#copy(Content.Source, Content.Sink, Content.Chunk.Processor, Callback)}
+     * method, that will handles {@link Trailers} chunks
+     * by adding the their fields to the {@link HttpFields} supplied by
+     * {@link Response#getTrailersSupplier()}.</p>
+     * <p>This is specifically useful for writing trailer that have been received via
+     * the {@link Content.Source#read()} API, for example when echoing a request to a response:</p>
+     * <pre>
+     *   Content.copy(request, response, Response.asTrailerChunkHandler(response), callback);
+     * </pre>
+     * @param response The response for which to process trailer chunks.
+     *                 If the {@link Response#setTrailersSupplier(Supplier)}
+     *                 method has not been called prior to this method, then a noop processor is returned.
+     * @return A chunk processor that will add trailer chunks to the response's trailer supplied fields.
+     * @see Content#copy(Content.Source, Content.Sink, Content.Chunk.Processor, Callback)
+     * @see Trailers
+     */
+    static Content.Chunk.Processor newTrailersChunkProcessor(Response response)
     {
-        if (chunk instanceof Trailers trailers)
+        Supplier<HttpFields> supplier = response.getTrailersSupplier();
+        if (supplier == null)
+            return (chunk, callback) -> false;
+
+        return (chunk, callback) ->
         {
-            HttpFields requestTrailers = trailers.getTrailers();
-            if (requestTrailers != null)
+            if (chunk instanceof Trailers trailers)
             {
-                Supplier<HttpFields> supplier = getTrailersSupplier();
-                if (supplier != null)
+                HttpFields requestTrailers = trailers.getTrailers();
+                if (requestTrailers != null)
                 {
+                    // Call supplier in lambda to get latest responseTrailers
                     HttpFields responseTrailers = supplier.get();
                     if (responseTrailers instanceof HttpFields.Mutable mutable)
+                    {
                         mutable.add(requestTrailers);
+                        callback.succeeded();
+                        return true;
+                    }
                 }
             }
-        }
-        return false;
+            return false;
+        };
     }
 
     @SuppressWarnings("unchecked")

jetty-core/jetty-server/src/test/java/org/eclipse/jetty/server/handler/EchoHandler.java

@@ -48,7 +48,7 @@ public void process(Request request, Response response, Callback callback)
             response.getHeaders().putLongField(HttpHeader.CONTENT_LENGTH, contentLength);
 
         if (contentLength > 0 || contentLength == -1 && request.getHeaders().contains(HttpHeader.TRANSFER_ENCODING))
-            Content.copy(request, response, response::writeTrailers, callback);
+            Content.copy(request, response, Response.newTrailersChunkProcessor(response), callback);
         else
             callback.succeeded();
     }