Add HttpProtocol#HTTP3

reactor-netty-http/src/main/java/reactor/netty/http/HttpProtocol.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018-2023 VMware, Inc. or its affiliates, All Rights Reserved.
+ * Copyright (c) 2018-2024 VMware, Inc. or its affiliates, All Rights Reserved.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -48,5 +48,11 @@ public enum HttpProtocol {
 	 * require {@literal Connection: Upgrade} handshake between a client and server but
 	 * fallback to HTTP/1.1 will not be supported.
 	 */
-	H2C
+	H2C,
+
+	/**
+	 * HTTP/3.0 support.
+	 * @since 1.2.0
+	 */
+	HTTP3
 }

reactor-netty-http/src/main/java/reactor/netty/http/internal/Http3.java

@@ -0,0 +1,50 @@
+/*
+ * Copyright (c) 2024 VMware, Inc. or its affiliates, All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *   https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package reactor.netty.http.internal;
+
+/**
+ * Utility class around HTTP/3.
+ * <p><strong>Note:</strong> This utility class is for internal use only. It can be removed at any time.
+ *
+ * @author Violeta Georgieva
+ * @since 1.2.0
+ */
+public final class Http3 {
+
+	static final boolean isHttp3Available;
+	static {
+		boolean http3;
+		try {
+			Class.forName("io.netty.incubator.codec.http3.Http3");
+			http3 = true;
+		}
+		catch (Throwable t) {
+			http3 = false;
+		}
+		isHttp3Available = http3;
+	}
+
+	/**
+	 * Check if the current runtime supports HTTP/3, by verifying if {@code netty-incubator-codec-http3} is on the classpath.
+	 *
+	 * @return true if {@code netty-incubator-codec-http3} is available
+	 */
+	public static boolean isHttp3Available() {
+		return isHttp3Available;
+	}
+
+	private Http3() {}
+}

reactor-netty-http/src/main/java/reactor/netty/http/server/HttpServer.java

@@ -58,6 +58,8 @@
 import reactor.util.context.Context;
 
 import static reactor.netty.ReactorNetty.format;
+import static reactor.netty.http.internal.Http3.isHttp3Available;
+import static reactor.netty.http.server.HttpServerConfig.h3;
 
 /**
  * An HttpServer allows building in a safe immutable way an HTTP server that is
@@ -836,6 +838,11 @@ public final HttpServer protocol(HttpProtocol... supportedProtocols) {
 		Objects.requireNonNull(supportedProtocols, "supportedProtocols");
 		HttpServer dup = duplicate();
 		dup.configuration().protocols(supportedProtocols);
+		if ((dup.configuration()._protocols & h3) == h3 && !isHttp3Available()) {
+			throw new UnsupportedOperationException(
+					"To enable HTTP/3 support, you must add the dependency `io.netty.incubator:netty-incubator-codec-http3`" +
+							" to the class path first");
+		}
 		return dup;
 	}
 

reactor-netty-http/src/main/java/reactor/netty/http/server/HttpServerBind.java

@@ -71,6 +71,10 @@ public Mono<? extends DisposableServer> bind() {
 								"Use a Clear-Text H2 protocol via HttpServer#protocol or configure TLS " +
 								"via HttpServer#secure"));
 			}
+			else if ((config._protocols & HttpServerConfig.h3) == HttpServerConfig.h3) {
+				return Mono.error(new IllegalArgumentException(
+						"Configured H3 protocol without TLS. Configure TLS via HttpServer#secure"));
+			}
 		}
 		return super.bind();
 	}

reactor-netty-http/src/main/java/reactor/netty/http/server/HttpServerConfig.java

@@ -415,6 +415,9 @@ else if (p == HttpProtocol.H2) {
 			else if (p == HttpProtocol.H2C) {
 				_protocols |= h2c;
 			}
+			else if (p == HttpProtocol.HTTP3) {
+				_protocols |= h3;
+			}
 		}
 		this._protocols = _protocols;
 	}
@@ -796,6 +799,8 @@ else if (metricsRecorder instanceof ContextAwareHttpServerMetricsRecorder) {
 
 	static final boolean ACCESS_LOG = Boolean.parseBoolean(System.getProperty(ACCESS_LOG_ENABLED, "false"));
 
+	static final int h3 = 0b1000;
+
 	static final int h2 = 0b010;
 
 	static final int h2c = 0b001;