feat: send TE trailers on HTTP/2

changes.md

@@ -72,6 +72,8 @@ Changes log
           continues to be written on a virtual thread.
         - Active client requests can be aborted; HTTP stream failures surface as I/O errors and a
           communication-error response callback.
+        - HTTP/2 and HTTP/3 requests advertise `te: trailers`; stream header names are normalized
+          to lowercase at the HTTP boundary.
     - Bugs fixed
         - Slf4j bridge reports wrong line number and caller class in log4j. Issue #233.
         - When GET is an allowed method of a server resource, HEAD is now also listed (e.g. in the Allow header of a 405 response). Issue #266.

org.restlet/src/main/java/org/restlet/engine/netty/NettyClientCall.java

@@ -30,6 +30,7 @@
 import java.io.InterruptedIOException;
 import java.io.PushbackInputStream;
 import java.net.ConnectException;
+import java.util.Locale;
 import java.util.Map;
 import java.util.concurrent.CompletableFuture;
 import java.util.concurrent.TimeUnit;
@@ -590,7 +591,11 @@ private void writeRequest(Representation entity) throws IOException {
         if (!requestTrailers.isEmpty()) {
             DefaultLastHttpContent withTrailers = new DefaultLastHttpContent(Unpooled.EMPTY_BUFFER);
             for (Header trailer : requestTrailers) {
-                withTrailers.trailingHeaders().add(trailer.getName(), trailer.getValue());
+                String name =
+                        kind.isStream()
+                                ? trailer.getName().toLowerCase(Locale.ROOT)
+                                : trailer.getName();
+                withTrailers.trailingHeaders().add(name, trailer.getValue());
             }
             lastContent = withTrailers;
         }
@@ -620,6 +625,9 @@ private HttpRequest newRequestHead() {
             String name = header.getName();
             if (!HeaderConstants.HEADER_CONTENT_LENGTH.equalsIgnoreCase(name)
                     && !HeaderConstants.HEADER_TRANSFER_ENCODING.equalsIgnoreCase(name)) {
+                if (kind.isStream()) {
+                    name = name.toLowerCase(Locale.ROOT);
+                }
                 headers.add(name, header.getValue());
             }
         }
@@ -632,6 +640,7 @@ private HttpRequest newRequestHead() {
         if (kind.isStream()) {
             headers.remove(HttpHeaderNames.CONNECTION);
             headers.remove("Keep-Alive");
+            headers.set("te", "trailers");
             // The HTTP/2 and HTTP/3 codecs read the ":scheme" pseudo-header from their extension
             // header.
             headers.set(
@@ -715,7 +724,8 @@ private void awaitHead() throws IOException {
      */
     void onResponseHead(HttpResponse response) {
         for (Map.Entry<String, String> entry : response.headers()) {
-            String name = entry.getKey();
+            String name =
+                    kind.isStream() ? entry.getKey().toLowerCase(Locale.ROOT) : entry.getKey();
             if (!name.regionMatches(true, 0, "x-http2-", 0, 8)
                     && !name.regionMatches(true, 0, "x-http3-", 0, 8)) {
                 responseHeaders.add(name, entry.getValue());
@@ -770,7 +780,11 @@ void onResponseComplete(io.netty.handler.codec.http.HttpHeaders trailers) {
         org.restlet.Response currentResponse = response;
         if (currentResponse != null) {
             for (Map.Entry<String, String> trailer : trailers) {
-                currentResponse.getTrailers().add(trailer.getKey(), trailer.getValue());
+                String name =
+                        kind.isStream()
+                                ? trailer.getKey().toLowerCase(Locale.ROOT)
+                                : trailer.getKey();
+                currentResponse.getTrailers().add(name, trailer.getValue());
             }
         }
         ChannelInputStream stream = this.body;

org.restlet/src/main/java/org/restlet/engine/netty/NettyServerCall.java

@@ -41,6 +41,7 @@
 import java.util.Arrays;
 import java.util.HexFormat;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.logging.Level;
 import java.util.logging.Logger;
@@ -151,24 +152,30 @@
         this.request = request;
         this.requestBody = requestBody;
         this.confidential = confidential;
-        this.requestHeaders = copyHeaders(request);
+        this.requestHeaders = copyHeaders(request, kind.isStream());
     }
 
     /**
      * Copies the Netty request headers, except the HTTP/2 pseudo-headers. HTTP/2 and HTTP/3 carry
      * the host in the ":authority" pseudo-header, mapped to a "Host" header when absent.
      */
-    private static Series<Header> copyHeaders(HttpRequest request) {
+    private static Series<Header> copyHeaders(HttpRequest request, boolean lowerCaseNames) {
         Series<Header> result = new Series<>(Header.class);
         for (Map.Entry<String, String> header : request.headers()) {
             if (!header.getKey().startsWith(":")) {
-                result.add(header.getKey(), header.getValue());
+                String name =
+                        lowerCaseNames ? header.getKey().toLowerCase(Locale.ROOT) : header.getKey();
+                result.add(name, header.getValue());
             }
         }
         if (result.getFirstValue(HeaderConstants.HEADER_HOST, true) == null) {
             String authority = request.headers().get(":authority");
             if (authority != null) {
-                result.add(HeaderConstants.HEADER_HOST, authority);
+                result.add(
+                        lowerCaseNames
+                                ? HeaderConstants.HEADER_HOST.toLowerCase(Locale.ROOT)
+                                : HeaderConstants.HEADER_HOST,
+                        authority);
             }
         }
         return result;
@@ -266,7 +273,9 @@
     /** Copies the request trailing headers before the body stream is ended. */
     void setRequestTrailers(HttpHeaders trailers) {
         for (Map.Entry<String, String> trailer : trailers) {
-            requestTrailers.add(trailer.getKey(), trailer.getValue());
+            String name =
+                    kind.isStream() ? trailer.getKey().toLowerCase(Locale.ROOT) : trailer.getKey();
+            requestTrailers.add(name, trailer.getValue());
         }
     }
 
@@ -524,7 +533,7 @@
      *
      * @param emptyBody True if no body follows.
      */
     private void writeHead(boolean emptyBody) {
         if (responseHeadWritten) {
             return;
         }
@@ -539,11 +548,13 @@
         HttpResponse head = new DefaultHttpResponse(HttpVersion.HTTP_1_1, status);
 
         for (Header header : responseHeaders) {
-            head.headers().add(header.getName(), header.getValue());
+            String name =
+                    kind.isStream() ? header.getName().toLowerCase(Locale.ROOT) : header.getName();
+            head.headers().add(name, header.getValue());
         }
 
         if (altSvc != null && !head.headers().contains("Alt-Svc")) {
-            head.headers().set("Alt-Svc", altSvc);
+            head.headers().set(kind.isStream() ? "alt-svc" : "Alt-Svc", altSvc);
         }
 
         boolean hasTrailers = !responseTrailers.isEmpty();
@@ -612,7 +623,7 @@
         LastHttpContent lastContent = LastHttpContent.EMPTY_LAST_CONTENT;
         if (responseTrailersEnabled) {
             DefaultLastHttpContent withTrailers = new DefaultLastHttpContent(Unpooled.EMPTY_BUFFER);
-            copyHeaders(responseTrailers, withTrailers.trailingHeaders());
+            copyHeaders(responseTrailers, withTrailers.trailingHeaders(), kind.isStream());
             lastContent = withTrailers;
         }
         ChannelFuture future = channel.writeAndFlush(lastContent);
@@ -639,9 +650,13 @@
     }
 
     private static void copyHeaders(
-            Series<Header> source, io.netty.handler.codec.http.HttpHeaders target) {
+            Series<Header> source,
+            io.netty.handler.codec.http.HttpHeaders target,
+            boolean lowerCaseNames) {
         for (Header header : source) {
-            target.add(header.getName(), header.getValue());
+            String name =
+                    lowerCaseNames ? header.getName().toLowerCase(Locale.ROOT) : header.getName();
+            target.add(name, header.getValue());
         }
     }
 

org.restlet/src/test/java/org/restlet/engine/connector/Http2TrailerHeadersTestCase.java

@@ -0,0 +1,107 @@
+/**
+ * Copyright 2005-2026 Qlik
+ *<p>
+ * The content of this file is subject to the terms of the Apache 2.0 open
+ * source license available at https://www.opensource.org/licenses/apache-2.0
+ *<p>
+ * Restlet is a registered trademark of QlikTech International AB.
+ */
+package org.restlet.engine.connector;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.util.List;
+import java.util.Locale;
+import java.util.concurrent.atomic.AtomicReference;
+import org.junit.jupiter.api.AfterEach;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.restlet.Client;
+import org.restlet.Context;
+import org.restlet.Request;
+import org.restlet.Response;
+import org.restlet.Restlet;
+import org.restlet.Server;
+import org.restlet.data.Header;
+import org.restlet.data.MediaType;
+import org.restlet.data.Method;
+import org.restlet.data.Protocol;
+import org.restlet.engine.Engine;
+
+class Http2TrailerHeadersTestCase {
+
+    private final AtomicReference<String> receivedTe = new AtomicReference<>();
+
+    private final AtomicReference<List<String>> receivedHeaderNames = new AtomicReference<>();
+
+    private Server server;
+
+    private Client client;
+
+    @BeforeEach
+    void setUp() {
+        Engine.clearThreadLocalVariables();
+        Engine.register(false);
+        Engine.getInstance().getRegisteredServers().add(new HttpServerHelper(null));
+        Engine.getInstance().getRegisteredClients().add(new HttpClientHelper(null));
+    }
+
+    @AfterEach
+    void tearDown() throws Exception {
+        if (client != null) {
+            client.stop();
+        }
+        if (server != null) {
+            server.stop();
+        }
+        Engine.clearThreadLocalVariables();
+    }
+
+    @Test
+    void sendsTeTrailersAndNormalizesHttp2HeaderNames() throws Exception {
+        Restlet echo =
+                new Restlet() {
+                    @Override
+                    public void handle(Request request, Response response) {
+                        receivedTe.set(request.getHeaders().getFirstValue("te", true));
+                        receivedHeaderNames.set(
+                                request.getHeaders().stream().map(Header::getName).toList());
+                        response.getHeaders().add(new Header("X-Response-Header", "response"));
+                        response.getTrailers().add(new Header("X-Response-Trailer", "response"));
+                        response.setEntity("ok", MediaType.TEXT_PLAIN);
+                    }
+                };
+        Context serverContext = new Context();
+        serverContext.getParameters().add("http.transport.protocol", "HTTP2");
+        server = new Server(serverContext, Protocol.HTTP, 0, echo);
+        server.start();
+
+        Context clientContext = new Context();
+        clientContext.getParameters().add("httpClientTransportMode", "HTTP2");
+        client = new Client(clientContext, Protocol.HTTP);
+        client.start();
+
+        Request request =
+                new Request(Method.GET, "http://localhost:" + server.getActualPort() + "/");
+        request.getHeaders().add(new Header("X-Request-Header", "request"));
+
+        Response response = client.handle(request);
+
+        assertEquals("trailers", receivedTe.get());
+        assertTrue(
+                receivedHeaderNames.get().stream()
+                        .allMatch(name -> name.equals(name.toLowerCase(Locale.ROOT))));
+        assertEquals("ok", response.getEntityAsText());
+        assertTrue(
+                response.getHeaders().stream()
+                        .allMatch(
+                                header ->
+                                        header.getName()
+                                                .equals(
+                                                        header.getName()
+                                                                .toLowerCase(Locale.ROOT))));
+        assertEquals("response", response.getTrailers().getFirstValue("x-response-trailer", true));
+        assertEquals("x-response-trailer", response.getTrailers().get(0).getName());
+    }
+}