1. About the Documentation

This section provides a brief overview of Reactor Netty reference documentation. You do not need to read this guide in a linear fashion. Each piece stands on its own, though they often refer to other pieces.

The Reactor Netty reference guide is available as HTML documents. The latest copy is available at https://projectreactor.io/docs/netty/release/reference/index.html

Copies of this document may be made for your own use and for distribution to others, provided that you do not charge any fee for such copies and further provided that each copy contains this Copyright Notice, whether distributed in print or electronically.

1.2. Contributing to the Documentation

The reference guide is written in Asciidoc, and you can find its sources at https://github.com/reactor/reactor-netty/tree/master/src/docs/asciidoc.

If you have an improvement, we will be happy to get a pull request from you!

We recommend that you check out a local copy of the repository so that you can generate the documentation by using the asciidoctor Gradle task and checking the rendering. Some of the sections rely on included files, so GitHub rendering is not always complete.

To facilitate documentation edits, most sections have a link at the end that opens an edit UI directly on GitHub for the main source file for that section. These links are only present in the HTML5 version of this reference guide. They look like the following link: Suggest Edit to About the Documentation.

1.3. Getting Help

There are several ways to reach out for help with Reactor Netty. You can:

  • Get in touch with the community on Gitter.

  • Ask a question on stackoverflow.com at reactor-netty.

  • Report bugs in Github issues. The repository is the following: reactor-netty.

All of Reactor Netty is open source, including this documentation.

2. Getting Started

This section contains information that should help you get going with Reactor Netty. It includes the following information:

2.1. Introducing Reactor Netty

Suited for Microservices Architecture, Reactor Netty offers backpressure-ready network engines for HTTP (including Websockets), TCP, and UDP.

2.2. Prerequisites

Reactor Netty runs on Java 8 and above.

It has transitive dependencies on:

  • Reactive Streams v1.0.2

  • Reactor Core v3.x

  • Netty v4.1.x

2.3. Understanding the BOM

Reactor Netty is part of the Project Reactor BOM (since the Aluminium release train). This curated list groups artifacts that are meant to work well together, providing the relevant versions despite potentially divergent versioning schemes in these artifacts.

The BOM (Bill of Materials) is itself versioned, using a release train scheme with a codename followed by a qualifier. The following list shows a few examples:

Aluminium-RELEASE
Californium-BUILD-SNAPSHOT
Aluminium-SR1
Bismuth-RELEASE
Californium-SR32

The codenames represent what would traditionally be the MAJOR.MINOR number. They (mostly) come from the Periodic Table of Elements, in increasing alphabetical order.

The qualifiers are (in chronological order):

  • BUILD-SNAPSHOT

  • M1..N: Milestones or developer previews

  • RELEASE: The first GA (General Availability) release in a codename series

  • SR1..N: The subsequent GA releases in a codename series (equivalent to PATCH number — SR stands for Service Release).

2.4. Getting Reactor Netty

As mentioned earlier, the easiest way to use Reactor Netty in your core is to use the BOM and add the relevant dependencies to your project. Note that, when adding such a dependency, you must omit the version so that the version gets picked up from the BOM.

However, if you want to force the use of a specific artifact’s version, you can specify it when adding your dependency as you usually would. You can also forgo the BOM entirely and specify dependencies by their artifact versions.

2.4.1. Maven Installation

The BOM concept is natively supported by Maven. First, you need to import the BOM by adding the following snippet to your pom.xml. If the top section (dependencyManagement) already exists in your pom, add only the contents.

<dependencyManagement> (1)
    <dependencies>
        <dependency>
            <groupId>io.projectreactor</groupId>
            <artifactId>reactor-bom</artifactId>
            <version>Californium-RELEASE</version>
            <type>pom</type>
            <scope>import</scope>
        </dependency>
    </dependencies>
</dependencyManagement>
1 Notice the dependencyManagement tag. This is in addition to the regular dependencies section.

Next, add your dependencies to the relevant reactor projects, as usual (except without a <version>). The following listing shows how to do so:

<dependencies>
    <dependency>
        <groupId>io.projectreactor.netty</groupId>
        <artifactId>reactor-netty</artifactId> (1)
        (2)
    </dependency>
</dependencies>
1 Dependency on Reactor Netty
2 No version tag here

2.4.2. Gradle Installation

Gradle has no core support for Maven BOMs, but you can use Spring’s gradle-dependency-management plugin.

First, apply the plugin from the Gradle Plugin Portal. The following example shows how to do so:

plugins {
    id "io.spring.dependency-management" version "1.0.7.RELEASE" (1)
}
1 as of this writing, 1.0.7.RELEASE is the latest version of the plugin. Check for updates.

Then use it to import the BOM. The following listing shows how to do so:

dependencyManagement {
     imports {
          mavenBom "io.projectreactor:reactor-bom:Californium-RELEASE"
     }
}

Finally, add a dependency to your project, without a version number. The following listing shows how to do so:

dependencies {
     compile 'io.projectreactor.netty:reactor-netty' (1)
}
1 There is no third : separated section for the version. It is taken from the BOM.

2.4.3. Milestones and Snapshots

Milestones and developer previews are distributed through the Spring Milestones repository rather than Maven Central. To add it to your build configuration file, use the following snippet:

Milestones in Maven
<repositories>
	<repository>
		<id>spring-milestones</id>
		<name>Spring Milestones Repository</name>
		<url>https://repo.spring.io/milestone</url>
	</repository>
</repositories>

For Gradle, use the following snippet:

Milestones in Gradle
repositories {
  maven { url 'https://repo.spring.io/milestone' }
  mavenCentral()
}

Similarly, snapshots are also available in a separate dedicated repository (for both Maven and Gradle):

BUILD-SNAPSHOTs in Maven
<repositories>
	<repository>
		<id>spring-snapshots</id>
		<name>Spring Snapshot Repository</name>
		<url>https://repo.spring.io/snapshot</url>
	</repository>
</repositories>
BUILD-SNAPSHOTs in Gradle
repositories {
  maven { url 'https://repo.spring.io/snapshot' }
  mavenCentral()
}

3. TCP Server

Reactor Netty provides an easy to use and configure TcpServer. It hides most of the Netty functionality that is needed to create a TCP server and adds Reactive Streams backpressure.

3.1. Starting and Stopping

To start a TCP server, you must create and configure a TcpServer instance. By default, the host is configured for any local address, and the system picks up an ephemeral port when the bind operation is invoked. The folloiwng example shows how to create and configure a TcpServer instance:

import reactor.netty.DisposableServer;
import reactor.netty.tcp.TcpServer;

public class Application {

    public static void main(String[] args) {
        DisposableServer server =
                TcpServer.create()   (1)
                         .bindNow(); (2)

        server.onDispose()
              .block();
    }
}
1 Creates a TcpServer instance that is ready for configuring.
2 Starts the server in a blocking fashion and waits for it to finish initializing.

The returned DisposableServer offers a simple server API, including disposeNow(), which shuts the server down in a blocking fashion.

3.1.1. Host and Port

To serve on a specific host and port, you can apply the following configuration to the TCP server:

import reactor.netty.DisposableServer;
import reactor.netty.tcp.TcpServer;

public class Application {

    public static void main(String[] args) {
        DisposableServer server =
                TcpServer.create()
                         .host("localhost") (1)
                         .port(8080)        (2)
                         .bindNow();

        server.onDispose()
              .block();
    }
}
1 Configures the TCP server host
2 Configures the TCP server port

3.2. Writing Data

In order to send data to a connected client, you must attach an I/O handler. The I/O handler has access to NettyOutbound to be able to write data. The following example shows how to attach an I/O handler:

import reactor.core.publisher.Mono;
import reactor.netty.DisposableServer;
import reactor.netty.tcp.TcpServer;

public class Application {

    public static void main(String[] args) {
        DisposableServer server =
                TcpServer.create()
                         .handle((inbound, outbound) -> outbound.sendString(Mono.just("hello"))) (1)
                         .bindNow();

        server.onDispose()
              .block();
    }
}
1 Sends hello string to the connected clients

3.3. Consuming Data

In order to receive data from a connected client, you must attach an I/O handler. The I/O handler has access to NettyInbound to be able to read data. The following example shows how to use it:

import reactor.netty.DisposableServer;
import reactor.netty.tcp.TcpServer;

public class Application {

    public static void main(String[] args) {
        DisposableServer server =
                TcpServer.create()
                         .handle((inbound, outbound) -> inbound.receive().then()) (1)
                         .bindNow();

        server.onDispose()
              .block();
    }
}
1 Receives data from the connected clients

3.4. Lifecycle Callbacks

The following lifecycle callbacks are provided to let you extend the TCP server:

  • doOnBind: Invoked when the server channel is about to bind.

  • doOnBound: Invoked when the server channel is bound.

  • doOnConnection: Invoked when a remote client is connected

  • doOnUnbound: Invoked when the server channel is unbound.

  • doOnLifecycle: Sets up all lifecycle callbacks.

The following example uses the doOnConnection callback:

import io.netty.handler.timeout.ReadTimeoutHandler;
import reactor.netty.DisposableServer;
import reactor.netty.tcp.TcpServer;
import java.util.concurrent.TimeUnit;

public class Application {

    public static void main(String[] args) {
        DisposableServer server =
                TcpServer.create()
                         .doOnConnection(conn ->
                                 conn.addHandler(new ReadTimeoutHandler(10, TimeUnit.SECONDS))) (1)
                         .bindNow();

        server.onDispose()
              .block();
    }
}
1 Netty pipeline is extended with ReadTimeoutHandler when a remote client is connected.

3.5. TCP-level Configurations

This section describes three kinds of configuration that you can use at the TCP level:

3.5.1. Setting Channel Options

By default, the TCP server is configured with the following options:

/../../main/java/reactor/netty/tcp/TcpServerBind.java
ServerBootstrap createServerBootstrap() {
	return new ServerBootstrap()
			.option(ChannelOption.SO_REUSEADDR, true)
			.childOption(ChannelOption.AUTO_READ, false)
			.childOption(ChannelOption.TCP_NODELAY, true)
			.localAddress(new InetSocketAddress(DEFAULT_PORT));
}

If additional options are necessary or changes to the current options, you can apply the following configuration:

import io.netty.channel.ChannelOption;
import reactor.netty.DisposableServer;
import reactor.netty.tcp.TcpServer;

public class Application {

    public static void main(String[] args) {
        DisposableServer server =
                TcpServer.create()
                         .option(ChannelOption.CONNECT_TIMEOUT_MILLIS, 10000)
                         .bindNow();

        server.onDispose()
              .block();
    }
}

You can find more about Netty channel options at the following links:

3.5.2. Using a Wire Logger

Reactor Netty provides wire logging for when the traffic between the peers has to be inspected. By default, wire logging is disabled. To enable it, you must set the logger reactor.netty.tcp.TcpServer level to DEBUG and apply the following configuration;

import reactor.netty.DisposableServer;
import reactor.netty.tcp.TcpServer;

public class Application {

    public static void main(String[] args) {
        DisposableServer server =
                TcpServer.create()
                         .wiretap(true) (1)
                         .bindNow();

        server.onDispose()
              .block();
    }
}
1 Enables the wire logging

3.5.3. Using an Event Loop Group

By default, the TCP server uses an “Event Loop Group,” where the number of the worker threads equals the number of processors available to the runtime on initialization (but with a minimum value of 4). When you need a different configuration, you can use one of the LoopResource#create methods.

The default configuration for the Event Loop Group is the following:

/../../main/java/reactor/netty/ReactorNetty.java
/**
 * Default worker thread count, fallback to available processor
 * (but with a minimum value of 4)
 */
public static final String IO_WORKER_COUNT = "reactor.netty.ioWorkerCount";
/**
 * Default selector thread count, fallback to -1 (no selector thread)
 */
public static final String IO_SELECT_COUNT = "reactor.netty.ioSelectCount";
/**
 * Default worker thread count for UDP, fallback to available processor
 * (but with a minimum value of 4)
 */
public static final String UDP_IO_THREAD_COUNT = "reactor.netty.udp.ioThreadCount";


/**
 * Default value whether the native transport (epoll, kqueue) will be preferred,
 * fallback it will be preferred when available
 */
public static final String NATIVE = "reactor.netty.native";

If changes to the these settings are needed, you can apply the following configuration:

import reactor.netty.DisposableServer;
import reactor.netty.resources.LoopResources;
import reactor.netty.tcp.TcpServer;

public class Application {

    public static void main(String[] args) {
        LoopResources loop = LoopResources.create("event-loop", 1, 4, true);
        DisposableServer server =
                TcpServer.create()
                         .runOn(loop)
                         .bindNow();

        server.onDispose()
              .block();
    }
}

3.6. SSL/TLS

When you need SSL or TLS, you can apply the configuration shown in the next listing. By default, if OpenSSL is available, SslProvider.OPENSSL provider is used as a provider. Otherwise SslProvider.JDK is used. Switching the provider can be done through SslContextBuilder or by setting -Dio.netty.handler.ssl.noOpenSsl=true.

The following example uses SslContextBuilder:

import io.netty.handler.ssl.SslContextBuilder;
import reactor.netty.DisposableServer;
import reactor.netty.tcp.TcpServer;
import java.io.File;

public class Application {

    public static void main(String[] args) {
        DisposableServer server =
                TcpServer.create()
                         .secure(spec ->
                                 SslContextBuilder.forServer(new File("certificate.crt"),
                                                             new File("private.key")))
                         .bindNow();

        server.onDispose()
              .block();
    }
}

4. TCP Client

Reactor Netty provides the easy-to-use and easy-to-configure TcpClient. It hides most of the Netty functionality that is needed in order to create a TCP client and adds Reactive Streams backpressure.

4.1. Connect and Disconnect

To connect the TCP client to a given endpoint, you must create and configure a TcpClient instance. By default, the host is localhost and the port is 12012. The following example shows how to create a TcpClient:

import reactor.netty.Connection;
import reactor.netty.tcp.TcpClient;

public class Application {

    public static void main(String[] args) {
        Connection connection =
                TcpClient.create()      (1)
                         .connectNow(); (2)

        connection.onDispose()
                  .block();
    }
}
1 Creates a TcpClient instance that is ready for configuring.
2 Connects the client in a blocking fashion and waits for it to finish initializing.

The returned Connection offers a simple connection API, including to disposeNow(), which shuts the client down in a blocking fashion.

4.1.1. Host and Port

To connect to a specific host and port, you can apply the following configuration to the TCP client. The following example shows how to do so:

import reactor.netty.Connection;
import reactor.netty.tcp.TcpClient;

public class Application {

    public static void main(String[] args) {
        Connection connection =
                TcpClient.create()
                         .host("example.com") (1)
                         .port(80)            (2)
                         .connectNow();

        connection.onDispose()
                  .block();
    }
}
1 Configures the HTTP host
2 Configures the HTTP port

4.2. Writing Data

To send data to a given endpoint, you must attach an I/O handler. The I/O handler has access to NettyOutbound to be able to write data.

import reactor.core.publisher.Mono;
import reactor.netty.Connection;
import reactor.netty.tcp.TcpClient;

public class Application {

    public static void main(String[] args) {
        Connection connection =
                TcpClient.create()
                         .host("example.com")
                         .port(80)
                         .handle((inbound, outbound) -> outbound.sendString(Mono.just("hello"))) (1)
                         .connectNow();

        connection.onDispose()
                  .block();
    }
}
1 Sends hello string to the endpoint.

4.3. Consuming Data

To receive data from a given endpoint, you must attach an I/O handler. The I/O handler has access to NettyInbound to be able to read data. The following example shows how to do so:

import reactor.netty.Connection;
import reactor.netty.tcp.TcpClient;

public class Application {

    public static void main(String[] args) {
        Connection connection =
                TcpClient.create()
                         .host("example.com")
                         .port(80)
                         .handle((inbound, outbound) -> inbound.receive().then()) (1)
                         .connectNow();

        connection.onDispose()
                  .block();
    }
}
1 Receives data from a given endpoint

4.4. Lifecycle Callbacks

The following lifecycle callbacks are provided to let you extend the TCP client.

  • doOnConnect: Invoked when the channel is about to connect.

  • doOnConnected: Invoked after the channel has been connected.

  • doOnDisconnected: Invoked after the channel has been disconnected.

  • doOnLifecycle: Sets up all lifecycle callbacks.

The following example uses the doOnConnected callback:

import io.netty.handler.timeout.ReadTimeoutHandler;
import reactor.netty.Connection;
import reactor.netty.tcp.TcpClient;
import java.util.concurrent.TimeUnit;

public class Application {

    public static void main(String[] args) {
        Connection connection =
                TcpClient.create()
                         .host("example.com")
                         .port(80)
                         .doOnConnected(conn ->
                                 conn.addHandler(new ReadTimeoutHandler(10, TimeUnit.SECONDS))) (1)
                         .connectNow();

        connection.onDispose()
                  .block();
    }
}
1 Netty pipeline is extended with ReadTimeoutHandler when the channel has been connected.

4.5. TCP-level Configurations

This section describes three kinds of configuration that you can use at the TCP level:

4.5.1. Channel Options

By default, the TCP client is configured with the following options:

/../../main/java/reactor/netty/tcp/TcpClient.java
static final Bootstrap DEFAULT_BOOTSTRAP =
		new Bootstrap().option(ChannelOption.AUTO_READ, false)
		               .remoteAddress(InetSocketAddressUtil.createUnresolved(NetUtil.LOCALHOST.getHostAddress(), DEFAULT_PORT));

If additional options are necessary or changes to the current options, you can apply the following configuration:

import io.netty.channel.ChannelOption;
import reactor.netty.Connection;
import reactor.netty.tcp.TcpClient;

public class Application {

    public static void main(String[] args) {
        Connection connection =
                TcpClient.create()
                         .host("example.com")
                         .port(80)
                         .option(ChannelOption.CONNECT_TIMEOUT_MILLIS, 10000)
                         .connectNow();

        connection.onDispose()
                  .block();
    }
}

You can find more about Netty channel options at the following links:

4.5.2. Wire Logger

Reactor Netty provides wire logging for when the traffic between the peers has to be inspected. By default, wire logging is disabled. To enable it, you must set the logger reactor.netty.tcp.TcpClient level to DEBUG and apply the following configuration:

import reactor.netty.Connection;
import reactor.netty.tcp.TcpClient;

public class Application {

    public static void main(String[] args) {
        Connection connection =
                TcpClient.create()
                         .wiretap(true) (1)
                         .host("example.com")
                         .port(80)
                         .connectNow();

        connection.onDispose()
                  .block();
    }
}
1 Enables the wire logging

4.5.3. Event Loop Group

By default the TCP client uses an “Event Loop Group”, where the number of the worker threads equals the number of processors available to the runtime on initialization (but with a minimum value of 4). When you need a different configuration, you can use one of the LoopResource#create methods.

The following listing shows the default configuration for the Event Loop Group:

/../../main/java/reactor/netty/ReactorNetty.java
/**
 * Default worker thread count, fallback to available processor
 * (but with a minimum value of 4)
 */
public static final String IO_WORKER_COUNT = "reactor.netty.ioWorkerCount";
/**
 * Default selector thread count, fallback to -1 (no selector thread)
 */
public static final String IO_SELECT_COUNT = "reactor.netty.ioSelectCount";
/**
 * Default worker thread count for UDP, fallback to available processor
 * (but with a minimum value of 4)
 */
public static final String UDP_IO_THREAD_COUNT = "reactor.netty.udp.ioThreadCount";


/**
 * Default value whether the native transport (epoll, kqueue) will be preferred,
 * fallback it will be preferred when available
 */
public static final String NATIVE = "reactor.netty.native";

If you need changes to the these settings, you can apply the following configuration:

import reactor.netty.Connection;
import reactor.netty.resources.LoopResources;
import reactor.netty.tcp.TcpClient;

public class Application {

    public static void main(String[] args) {
        LoopResources loop = LoopResources.create("event-loop", 1, 4, true);
        Connection connection =
                TcpClient.create()
                         .host("example.com")
                         .port(80)
                         .runOn(loop)
                         .connectNow();

        connection.onDispose()
                  .block();
    }
}

4.6. Connection Pool

By default, the TCP client uses a “fixed” connection pool with 500 as the maximum number of the channels and 45s as the acquisition timeout. This means that the implementation creates a new channel if someone tries to acquire a channel but none is in the pool. When the maximum number of the channels in the pool is reached, new tries to acquire a channel are delayed until a channel is returned to the pool again. The implementation uses FIFO order for channels in the pool regardless of whether it is “elastic” or “fixed”. By default, there is no idle time specified for the channels in the pool.

If you need an “elastic” connection pool, you can apply the following configuration by using ConnectionProvider. The following example shows how to do so:

import reactor.netty.Connection;
import reactor.netty.resources.ConnectionProvider;
import reactor.netty.tcp.TcpClient;

public class Application {

    public static void main(String[] args) {
        ConnectionProvider provider = ConnectionProvider.elastic("fixed");
        Connection connection =
                TcpClient.create(provider)
                         .host("example.com")
                         .port(80)
                         .connectNow();

        connection.onDispose()
                  .block();
    }
}

If you need to disable the connection pool, you can apply the following configuration:

import reactor.netty.Connection;
import reactor.netty.tcp.TcpClient;

public class Application {

    public static void main(String[] args) {
        Connection connection =
                TcpClient.newConnection()
                         .host("example.com")
                         .port(80)
                         .connectNow();

        connection.onDispose()
                  .block();
    }
}

If you need to specify an idle time for the channels in the connection pool, you can apply the following configuration:

import reactor.netty.Connection;
import reactor.netty.resources.ConnectionProvider;
import reactor.netty.tcp.TcpClient;
import java.time.Duration;

public class Application {

    public static void main(String[] args) {
        ConnectionProvider provider = ConnectionProvider.fixed("fixed", 50, 30000, Duration.ofSeconds(60));
        Connection connection =
                TcpClient.create(provider)
                         .host("example.com")
                         .port(80)
                         .connectNow();

        connection.onDispose()
                  .block();
    }
}
Be cautious with an “elastic” connection pool when you expect a high load. You might experience reactor.netty.http.client.PrematureCloseException exception with a root cause "Connect Timeout" due to too many concurrent connections opened/acquired.

4.7. SSL and TLS

When you need SSL or TLS, you can apply the following configuration. By default, if OpenSSL is available, the SslProvider.OPENSSL provider is used as a provider. Otherwise, the provider is SslProvider.JDK. You can switch the provider by using SslContextBuilder or by setting -Dio.netty.handler.ssl.noOpenSsl=true.

The following example uses SslContextBuilder:

import io.netty.handler.ssl.SslContextBuilder;
import reactor.netty.Connection;
import reactor.netty.tcp.TcpClient;

public class Application {

    public static void main(String[] args) {
        Connection connection =
                TcpClient.create()
                         .host("example.com")
                         .port(443)
                         .secure(spec -> spec.sslContext(SslContextBuilder.forClient()))
                         .connectNow();

        connection.onDispose()
                  .block();
    }
}

4.8. Proxy Support

The TCP client supports the proxy functionality provided by Netty and provides a way to specify “non proxy hosts” through the ProxyProvider builder. The following example uses ProxyProvider:

import reactor.netty.Connection;
import reactor.netty.tcp.ProxyProvider;
import reactor.netty.tcp.TcpClient;

public class Application {

    public static void main(String[] args) {
        Connection connection =
                TcpClient.create()
                         .host("example.com")
                         .port(80)
                         .proxy(spec -> spec.type(ProxyProvider.Proxy.SOCKS4)
                                            .host("proxy")
                                            .port(8080)
                                            .nonProxyHosts("localhost"))
                         .connectNow();

        connection.onDispose()
                  .block();
    }
}

5. HTTP Server

Reactor Netty provides the easy-to-use and easy-to-configure HttpServer class. It hides most of the Netty functionality that is needed in order to create a HTTP server and adds Reactive Streams backpressure.

5.1. Starting and Stopping

To start an HTTP server, you must create and configure a HttpServer instance. By default, the host is configured for any local address, and the system picks up an ephemeral port when the bind operation is invoked. The following example shows how to create an HttpServer instance:

import reactor.netty.DisposableServer;
import reactor.netty.http.server.HttpServer;

public class Application {

    public static void main(String[] args) {
        DisposableServer server =
                HttpServer.create()   (1)
                          .bindNow(); (2)

        server.onDispose()
              .block();
    }
}
1 Creates an HttpServer instance ready for configuring.
2 Starts the server in a blocking fashion and waits for it to finish initializing.

The returned DisposableServer offers a simple server API, including to disposeNow(), which shuts the server down in a blocking fashion.

5.1.1. Host and Port

To serve on a specific host and port, you can apply the following configuration to the HTTP server:

import reactor.netty.DisposableServer;
import reactor.netty.http.server.HttpServer;

public class Application {

    public static void main(String[] args) {
        DisposableServer server =
                HttpServer.create()
                          .host("localhost") (1)
                          .port(8080)        (2)
                          .bindNow();

        server.onDispose()
              .block();
    }
}
1 Configures the HTTP server host
2 Configures the HTTP server port

5.2. Routing HTTP

Defining routes for the HTTP server requires configuring the provided HttpServerRoutes builder. The following example shows how to do so:

import reactor.core.publisher.Mono;
import reactor.netty.DisposableServer;
import reactor.netty.http.server.HttpServer;

public class Application {

    public static void main(String[] args) {
        DisposableServer server =
                HttpServer.create()
                          .route(routes ->
                              routes.get("/hello",        (1)
                                         (request, response) -> response.sendString(Mono.just("Hello World!")))
                                    .post("/echo",        (2)
                                         (request, response) -> response.send(request.receive().retain()))
                                    .get("/path/{param}", (3)
                                         (request, response) -> response.sendString(Mono.just(request.param("param"))))
                                    .ws("/ws",            (4)
                                         (wsInbound, wsOutbound) -> wsOutbound.send(wsInbound.receive().retain())))
                          .bindNow();

        server.onDispose()
              .block();
    }
}
1 Serves a GET request to /hello and returns Hello World!
2 Serves a POST request to /echo and returns the received request body as a response.
3 Serves a GET request to /path/{param} and returns the value of the path parameter.
4 Serves websocket to /ws and returns the received incoming data as outgoing data.
The server routes are unique and only the first matching in order of declaration is invoked.

5.2.1. SSE

The following code shows how you can configure the HTTP server to serve Server-Sent Events:

import com.fasterxml.jackson.databind.ObjectMapper;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.ByteBufAllocator;
import org.reactivestreams.Publisher;
import reactor.core.publisher.Flux;
import reactor.netty.DisposableServer;
import reactor.netty.http.server.HttpServer;
import reactor.netty.http.server.HttpServerRequest;
import reactor.netty.http.server.HttpServerResponse;

import java.io.ByteArrayOutputStream;
import java.nio.charset.Charset;
import java.time.Duration;
import java.util.function.BiFunction;

public class Application {

    public static void main(String[] args) {
        DisposableServer server =
                HttpServer.create()
                          .route(routes -> routes.get("/sse", serveSse()))
                          .bindNow();

        server.onDispose()
              .block();
    }

    /**
     * Prepares SSE response
     * The "Content-Type" is "text/event-stream"
     * The flushing strategy is "flush after every element" emitted by the provided Publisher
     */
    private static BiFunction<HttpServerRequest, HttpServerResponse, Publisher<Void>> serveSse() {
        Flux<Long> flux = Flux.interval(Duration.ofSeconds(10));
        return (request, response) ->
            response.sse()
                    .send(flux.map(Application::toByteBuf), b -> true);
    }

    /**
     * Transforms the Object to ByteBuf following the expected SSE format.
     */
    private static ByteBuf toByteBuf(Object any) {
        ByteArrayOutputStream out = new ByteArrayOutputStream();
        try {
            out.write("data: ".getBytes(Charset.defaultCharset()));
            MAPPER.writeValue(out, any);
            out.write("\n\n".getBytes(Charset.defaultCharset()));
        }
        catch (Exception e) {
            throw new RuntimeException(e);
        }
        return ByteBufAllocator.DEFAULT
                               .buffer()
                               .writeBytes(out.toByteArray());
    }

    private static final ObjectMapper MAPPER = new ObjectMapper();
}

5.2.2. Static Resources

The following code shows how you can configure the HTTP server to serve static resources:

import reactor.netty.DisposableServer;
import reactor.netty.http.server.HttpServer;

public class Application {

    public static void main(String[] args) {
        DisposableServer server =
                HttpServer.create()
                          .route(routes -> routes.file("/index.html", pathToFile))
                          .bindNow();

        server.onDispose()
              .block();
    }
}

5.3. Writing Data

To send data to a connected client, you must attach an I/O handler by using either handle(…​) or route(…​). The I/O handler has access to HttpServerResponse, to be able to write data. The following example uses the handle(…​) method:

import reactor.core.publisher.Mono;
import reactor.netty.DisposableServer;
import reactor.netty.http.server.HttpServer;

public class Application {

    public static void main(String[] args) {
        DisposableServer server =
                HttpServer.create()
                          .handle((request, response) -> response.sendString(Mono.just("hello"))) (1)
                          .bindNow();

        server.onDispose()
              .block();
    }
}
1 Sends hello string to the connected clients

5.3.1. Adding Headers and Other Metadata

When you send data to the connected clients, you may need to send additional headers, cookies, status code, and other metadata. You can provide this additional metadata by using HttpServerResponse. The following example shows how to do so:

import io.netty.handler.codec.http.HttpHeaderNames;
import io.netty.handler.codec.http.HttpResponseStatus;
import reactor.core.publisher.Mono;
import reactor.netty.DisposableServer;
import reactor.netty.http.server.HttpServer;

public class Application {

    public static void main(String[] args) {
        DisposableServer server =
                HttpServer.create()
                          .route(routes ->
                              routes.get("/hello",
                                         (request, response) ->
                                             response.status(HttpResponseStatus.OK)
                                                     .header(HttpHeaderNames.CONTENT_LENGTH, "12")
                                                     .sendString(Mono.just("Hello World!"))))
                          .bindNow();

        server.onDispose()
              .block();
    }
}

5.3.2. Compression

You can configure the HTTP server to send a compressed response, depending on the request header Accept-Encoding or (in the case of websocket) the Sec-Websocket-Extensions header.

Reactor Netty provides three different strategies for compressing the outgoing data:

  • compress(boolean): Depending on the boolean that is provided, the compression is enabled (true) or disabled (false).

  • compress(int): The compression is performed once the response size exceeds the given value (in bytes).

  • compress(BiPredicate<HttpServerRequest, HttpServerResponse>): The compression is performed if the predicate returns true.

The following example uses the compress method (set to true) to enable compression:

import reactor.netty.DisposableServer;
import reactor.netty.http.server.HttpServer;

public class Application {

    public static void main(String[] args) {
        DisposableServer server =
                HttpServer.create()
                          .compress(true)
                          .route(routes -> routes.file("/index.html", pathToFile))
                          .bindNow();

        server.onDispose()
              .block();
    }
}

5.4. Consuming Data

To receive data from a connected client, you must attach an I/O handler by using either handle(…​) or route(…​). The I/O handler has access to HttpServerRequest, to be able to read data.

The following example uses the handle(…​) method:

import reactor.netty.DisposableServer;
import reactor.netty.http.server.HttpServer;

public class Application {

    public static void main(String[] args) {
        DisposableServer server =
                HttpServer.create()
                          .handle((request, response) -> request.receive().then()) (1)
                          .bindNow();

        server.onDispose()
              .block();
    }
}
1 Receives data from the connected clients

5.4.1. Reading Headers, URI Params, and other Metadata

When you receive data from the connected clients, you might need to check request headers, parameters, and other metadata. You can obtain this additional metadata by using HttpServerRequest. The following example shows how to do so:

import reactor.core.publisher.Mono;
import reactor.netty.DisposableServer;
import reactor.netty.http.server.HttpServer;

public class Application {

    public static void main(String[] args) {
        DisposableServer server =
                HttpServer.create()
                          .route(routes ->
                              routes.get("/{param}",
                                         (request, response) -> {
                                             if (request.requestHeaders().contains("Some-Header")) {
                                                 return response.sendString(Mono.just(request.param("param")));
                                             }
                                             return response.sendNotFound();
                                         }))
                          .bindNow();

        server.onDispose()
              .block();
    }
}
Obtaining the Remote (Client) Address

In addition to the metadata that you can obtain from the request, you can also receive the host (server) address, the remote (client) address and the scheme. Depending on the chosen factory method, you can retrieve the information directly from the channel or by using the Forwarded or X-Forwarded-* HTTP request headers. The following example shows how to do so:

import reactor.core.publisher.Mono;
import reactor.netty.DisposableServer;
import reactor.netty.http.server.HttpServer;

public class Application {

    public static void main(String[] args) {
        DisposableServer server =
                HttpServer.create()
                          .forwarded(true) (1)
                          .route(routes ->
                              routes.get("/clientip",
                                         (request, response) ->
                                             response.sendString(Mono.just(request.remoteAddress() (2)
                                                                                  .getHostString()))))
                          .bindNow();

        server.onDispose()
              .block();
    }
}
1 Specifies that the information about the connection is to be obtained from the Forwarded and X-Forwarded-* HTTP request headers, if possible.
2 Returns the address of the remote (client) peer.

5.4.2. HTTP Request Decoder

By default, Netty configures some restrictions for the incoming requests, such as:

  • The maximum length of the initial line.

  • The maximum length of all headers.

  • The maximum length of the content or each chunk.

For more information, see HttpRequestDecoder

By default, the HTTP server is configured with the following settings:

/../../main/java/reactor/netty/http/HttpDecoderSpec.java
public static final int DEFAULT_MAX_INITIAL_LINE_LENGTH = 4096;
public static final int DEFAULT_MAX_HEADER_SIZE         = 8192;
public static final int DEFAULT_MAX_CHUNK_SIZE          = 8192;
public static final boolean DEFAULT_VALIDATE_HEADERS    = true;
public static final int DEFAULT_INITIAL_BUFFER_SIZE     = 128;

When you need to change these default settings, you can configure the HTTP server as follows:

import reactor.core.publisher.Mono;
import reactor.netty.DisposableServer;
import reactor.netty.http.server.HttpServer;

public class Application {

    public static void main(String[] args) {
        DisposableServer server =
                HttpServer.create()
                          .httpRequestDecoder(spec -> spec.maxHeaderSize(16384)) (1)
                          .handle((request, response) -> response.sendString(Mono.just("hello")))
                          .bindNow();

        server.onDispose()
              .block();
    }
}
1 The maximum length of all headers will be 16384. When this value is exceeded, a TooLongFrameException is raised.

5.5. TCP-level Configurations

When you need to change configuration on the TCP level, you can use the following snippet to extend the default TCP server configuration:

import io.netty.channel.ChannelOption;
import reactor.netty.DisposableServer;
import reactor.netty.http.server.HttpServer;

public class Application {

    public static void main(String[] args) {
        DisposableServer server =
                HttpServer.create()
                          .tcpConfiguration(tcpServer ->
                                  tcpServer.option(ChannelOption.CONNECT_TIMEOUT_MILLIS, 10000))
                          .bindNow();

        server.onDispose()
              .block();
    }
}

See TCP Server for more detail about TCP-level configuration.

5.5.1. Wire Logger

Reactor Netty provides wire logging for when you need to inspect the traffic between the peers. By default, wire logging is disabled. To enable it, you must set the logger reactor.netty.http.server.HttpServer level to DEBUG and apply the following configuration:

import reactor.netty.DisposableServer;
import reactor.netty.http.server.HttpServer;

public class Application {

    public static void main(String[] args) {
        DisposableServer server =
                HttpServer.create()
                          .wiretap(true) (1)
                          .bindNow();

        server.onDispose()
              .block();
    }
}
1 Enables the wire logging

5.6. SSL and TLS

When you need SSL or TLS, you can apply the configuration shown in the next example. By default, if OpenSSL is available, SslProvider.OPENSSL provider is used as a provider. Otherwise SslProvider.JDK is used. You can switch the provider by using SslContextBuilder or by setting -Dio.netty.handler.ssl.noOpenSsl=true.

The following example uses SslContextBuilder:

import io.netty.handler.ssl.SslContextBuilder;
import reactor.netty.DisposableServer;
import reactor.netty.http.server.HttpServer;
import java.io.File;

public class Application {

    public static void main(String[] args) {
        File cert = new File("certificate.crt");
        File key = new File("private.key");
        DisposableServer server =
                HttpServer.create()
                          .secure(spec -> spec.sslContext(SslContextBuilder.forServer(cert,key)))
                          .bindNow();

        server.onDispose()
              .block();
    }
}

5.7. HTTP Access Log

The current logging support provides only the Common Log Format.

You can use -Dreactor.netty.http.server.accessLogEnabled=true to enable the HTTP access log. By default, it is disabled.

You can use the following configuration (for Logback or similar logging frameworks) to have a separate HTTP access log file:

<appender name="accessLog" class="ch.qos.logback.core.FileAppender">
    <file>access_log.log</file>
    <encoder>
        <pattern>%msg%n</pattern>
    </encoder>
</appender>
<appender name="async" class="ch.qos.logback.classic.AsyncAppender">
    <appender-ref ref="accessLog" />
</appender>

<logger name="reactor.netty.http.server.AccessLog" level="INFO" additivity="false">
    <appender-ref ref="async"/>
</logger>

5.8. HTTP/2

By default, the HTTP server supports HTTP/1.1. If you need HTTP/2, you can get it through configuration. In addition to the protocol configuration, if you need H2 but not H2C (cleartext), you must also configure SSL.

As that protocol is not supported “out-of-the-box” by JDK8, you need an additional dependency to a native library that supports it — for example, netty-tcnative-boringssl-static.

The following listing presents a simple H2 example:

import io.netty.handler.ssl.SslContextBuilder;
import reactor.core.publisher.Mono;
import reactor.netty.DisposableServer;
import reactor.netty.http.HttpProtocol;
import reactor.netty.http.server.HttpServer;
import java.io.File;

public class Application {

    public static void main(String[] args) {
        DisposableServer server =
                HttpServer.create()
                          .port(8080)
                          .protocol(HttpProtocol.H2) (1)
                          .secure(spec ->            (2)
                                  SslContextBuilder.forServer(new File("certificate.crt"),
                                                              new File("private.key")))
                          .handle((request, response) -> response.sendString(Mono.just("hello")))
                          .bindNow();

        server.onDispose()
              .block();
    }
}
1 Configures the server to support only HTTP/2
2 Configures SSL

The application should now behave as follows:

$ curl --http2 https://localhost:8080 -i
HTTP/2 200

hello

The following listing presents a simple H2C example:

import reactor.core.publisher.Mono;
import reactor.netty.DisposableServer;
import reactor.netty.http.HttpProtocol;
import reactor.netty.http.server.HttpServer;

public class Application {

    public static void main(String[] args) {
        DisposableServer server =
                HttpServer.create()
                          .port(8080)
                          .protocol(HttpProtocol.H2C)
                          .handle((request, response) -> response.sendString(Mono.just("hello")))
                          .bindNow();

        server.onDispose()
              .block();
    }
}

The application should now behave as follows:

$ curl --http2-prior-knowledge http://localhost:8080 -i
HTTP/2 200

hello

6. HTTP Client

Reactor Netty provides the easy-to-use and easy-to-configure HttpClient. It hides most of the Netty functionality that is required to create a HTTP client and adds Reactive Streams backpressure.

6.1. Connect

To connect the HTTP client to a given HTTP endpoint, you must create and configure a HttpClient instance. The following example shows how to do so:

import reactor.netty.http.client.HttpClient;
import reactor.netty.http.client.HttpClientResponse;

public class Application {

    public static void main(String[] args) {
        HttpClientResponse response =
                HttpClient.create()                   (1)
                          .get()                      (2)
                          .uri("http://example.com/") (3)
                          .response()                 (4)
                          .block();
    }
}
1 Creates a HttpClient instance ready for configuring.
2 Specifies that GET method will be used.
3 Specifies the path.
4 Obtains the response HttpClientResponse

The following example uses WebSocket:

import io.netty.buffer.Unpooled;
import io.netty.util.CharsetUtil;
import reactor.core.publisher.Flux;
import reactor.netty.http.client.HttpClient;

public class Application {

    public static void main(String[] args) {
        HttpClient.create()
                  .websocket()
                  .uri("wss://echo.websocket.org")
                  .handle((inbound, outbound) -> {
                      inbound.receive()
                             .asString()
                             .take(1)
                             .subscribe(System.out::println);

                      final byte[] msgBytes = "hello".getBytes(CharsetUtil.ISO_8859_1);
                      return outbound.send(Flux.just(Unpooled.wrappedBuffer(msgBytes), Unpooled.wrappedBuffer(msgBytes)),
                                           b -> true)
                                     .neverComplete();
                  })
                  .blockLast();
    }
}

6.1.1. Host and Port

In order to connect to a specific host and port, you can apply the following configuration to the HTTP client:

import reactor.netty.http.client.HttpClient;
import reactor.netty.http.client.HttpClientResponse;

public class Application {

    public static void main(String[] args) {
        HttpClientResponse response =
                HttpClient.create()
                          .tcpConfiguration(tcpClient -> tcpClient.host("example.com")) (1)
                          .port(80)                                                     (2)
                          .get()
                          .uri("/")
                          .response()
                          .block();
    }
}
1 Configures the HTTP host
2 Configures the HTTP port

6.2. Writing Data

To send data to a given HTTP endpoint, you can provide a Publisher by using the send(Publisher) method. By default, Transfer-Encoding: chunked is applied for those HTTP methods for which a request body is expected. Content-Length provided through request headers disables Transfer-Encoding: chunked, if necessary. The following example sends hello:

import reactor.core.publisher.Mono;
import reactor.netty.ByteBufFlux;
import reactor.netty.http.client.HttpClient;
import reactor.netty.http.client.HttpClientResponse;

public class Application {

    public static void main(String[] args) {
        HttpClientResponse response =
                HttpClient.create()
                          .post()
                          .uri("http://example.com/")
                          .send(ByteBufFlux.fromString(Mono.just("hello"))) (1)
                          .response()
                          .block();
    }
}
1 Sends a hello string to the given HTTP endpoint

6.2.1. Adding Headers and Other Metadata

When sending data to a given HTTP endpoint, you may need to send additional headers, cookies and other metadata. You can use the following configuration to do so:

import io.netty.handler.codec.http.HttpHeaderNames;
import reactor.core.publisher.Mono;
import reactor.netty.ByteBufFlux;
import reactor.netty.http.client.HttpClient;
import reactor.netty.http.client.HttpClientResponse;

public class Application {

    public static void main(String[] args) {
        HttpClientResponse response =
                HttpClient.create()
                          .headers(h -> h.set(HttpHeaderNames.CONTENT_LENGTH, 5)) (1)
                          .post()
                          .uri("http://example.com/")
                          .send(ByteBufFlux.fromString(Mono.just("hello")))
                          .response()
                          .block();
    }
}
1 Disables Transfer-Encoding: chunked and provides Content-Length header.
Compression

You can enable compression on the HTTP client, which means the request header Accept-Encoding (or, in the case of WebSocket, the Sec-Websocket-Extensions header) is added to the request headers. The following example shows how to do so:

import reactor.netty.http.client.HttpClient;
import reactor.netty.http.client.HttpClientResponse;

public class Application {

    public static void main(String[] args) {
        HttpClientResponse response =
                HttpClient.create()
                          .compress(true)
                          .get()
                          .uri("http://example.com/")
                          .response()
                          .block();
    }
}
Auto-Redirect Support

You can configure the HTTP client to enable auto-redirect support.

Reactor Netty provides two different strategies for auto-redirect support:

  • followRedirect(boolean): Specifies whether HTTP auto-redirect support is enabled for statuses 301|302|307|308.

  • followRedirect(BiPredicate<HttpClientRequest, HttpClientResponse>): Enables auto-redirect support if the supplied predicate matches.

The following example uses followRedirect(true):

import reactor.netty.http.client.HttpClient;
import reactor.netty.http.client.HttpClientResponse;

public class Application {

    public static void main(String[] args) {
        HttpClientResponse response =
                HttpClient.create()
                          .followRedirect(true)
                          .get()
                          .uri("http://example.com/")
                          .response()
                          .block();
    }
}

6.3. Consuming Data

To receive data from a given HTTP endpoint, you can use one of the methods from HttpClient.ResponseReceiver. The following example uses the responseContent method:

import reactor.netty.http.client.HttpClient;

public class Application {

    public static void main(String[] args) {
        String response =
                HttpClient.create()
                          .get()
                          .uri("http://example.com/")
                          .responseContent() (1)
                          .aggregate()       (2)
                          .asString()        (3)
                          .block();
    }
}
1 Receives data from a given HTTP endpoint
2 Aggregates the data
3 Transforms the data as string

6.3.1. Reading Headers and Other Metadata

When receiving data from a given HTTP endpoint, you can check response headers, status code, and other metadata. You can obtain this additional metadata by using HttpClientResponse. The following example shows how to do so.

import reactor.netty.http.client.HttpClient;

public class Application {

    public static void main(String[] args) {
        String response =
                HttpClient.create()
                          .get()
                          .uri("http://example.com/")
                          .responseSingle((resp, bytes) -> {
                              System.out.println(resp.status()); (1)
                              return bytes.asString();
                          })
                          .block();
    }
}
1 Obtains the status code.

6.3.2. HTTP Response Decoder

By default, Netty configures some restrictions for the incoming responses, such as:

  • The maximum length of the initial line.

  • The maximum length of all headers.

  • The maximum length of the content or each chunk.

For more information, see HttpResponseDecoder

By default, the HTTP client is configured with the following settings:

/../../main/java/reactor/netty/http/HttpDecoderSpec.java
public static final int DEFAULT_MAX_INITIAL_LINE_LENGTH = 4096;
public static final int DEFAULT_MAX_HEADER_SIZE         = 8192;
public static final int DEFAULT_MAX_CHUNK_SIZE          = 8192;
public static final boolean DEFAULT_VALIDATE_HEADERS    = true;
public static final int DEFAULT_INITIAL_BUFFER_SIZE     = 128;
/../../main/java/reactor/netty/http/client/HttpResponseDecoderSpec.java
public static final boolean DEFAULT_FAIL_ON_MISSING_RESPONSE         = false;
public static final boolean DEFAULT_PARSE_HTTP_AFTER_CONNECT_REQUEST = false;

When you need to change these default settings, you can configure the HTTP client as follows:

import reactor.netty.http.client.HttpClient;

public class Application {

    public static void main(String[] args) {
        String response =
                HttpClient.create()
                        .httpResponseDecoder(spec -> spec.maxHeaderSize(16384)) (1)
                        .get()
                        .uri("http://example.com/")
                        .responseContent()
                          .aggregate()
                          .asString()
                          .block();
    }
}
1 The maximum length of all headers will be 16384. When this value is exceeded, a TooLongFrameException is raised.

6.4. TCP-level Configurations

When you need configurations on a TCP level, you can use the following snippet to extend the default TCP client configuration:

import io.netty.channel.ChannelOption;
import reactor.netty.http.client.HttpClient;
import reactor.netty.http.client.HttpClientResponse;

public class Application {

    public static void main(String[] args) {
        HttpClientResponse response =
                HttpClient.create()
                          .tcpConfiguration(tcpClient ->
                                  tcpClient.option(ChannelOption.CONNECT_TIMEOUT_MILLIS, 10000))
                          .get()
                          .uri("http://example.com/")
                          .response()
                          .block();
    }
}

See TCP Client for more about TCP level configurations.

6.4.1. Wire Logger

Reactor Netty provides wire logging for when the traffic between the peers needs to be inspected. By default, wire logging is disabled. To enable it, you must set the logger reactor.netty.http.client.HttpClient level to DEBUG and apply the following configuration:

import reactor.netty.http.client.HttpClient;
import reactor.netty.http.client.HttpClientResponse;

public class Application {

    public static void main(String[] args) {
        HttpClientResponse response =
                HttpClient.create()
                          .wiretap(true) (1)
                          .get()
                          .uri("http://example.com/")
                          .response()
                          .block();
    }
}
1 Enables the wire logging

6.5. SSL andTLS

When you need SSL or TLS, you can apply the configuration shown in the next example. By default, if OpenSSL is available, a SslProvider.OPENSSL provider is used as a provider. Otherwise a SslProvider.JDK provider is used You can switch the provider by using SslContextBuilder or by setting -Dio.netty.handler.ssl.noOpenSsl=true. The following example uses SslContextBuilder:

import io.netty.handler.ssl.SslContextBuilder;
import reactor.netty.http.client.HttpClient;
import reactor.netty.http.client.HttpClientResponse;

public class Application {

    public static void main(String[] args) {
        HttpClientResponse response =
                HttpClient.create()
                          .secure(spec -> spec.sslContext(SslContextBuilder.forClient()))
                          .get()
                          .uri("https://example.com/")
                          .response()
                          .block();
    }
}

6.6. Retry Strategies

By default, the HTTP client retries the request once if it was aborted on the TCP level.

7. UDP Server

Reactor Netty provides the easy-to-use and easy-to-configure UdpServer. It hides most of the Netty functionality that is required to create a UDP server and adds Reactive Streams backpressure.

7.1. Starting and Stopping

To start a UDP server, a UdpServer instance has to be created and configured. By default, the host is configured to be localhost and the port is 12012. The following example shows how to create and start a UDP server:

import reactor.netty.Connection;
import reactor.netty.udp.UdpServer;
import java.time.Duration;

public class Application {

    public static void main(String[] args) {
        Connection server =
                UdpServer.create()                         (1)
                         .bindNow(Duration.ofSeconds(30)); (2)

        server.onDispose()
              .block();
    }
}
1 Creates a UdpServer instance that is ready for configuring.
2 Starts the server in a blocking fashion and waits for it to finish initializing.

The returned Connection offers a simple server API, including to disposeNow(), which shuts the server down in a blocking fashion.

7.1.1. Host and Port

In order to serve on a specific host and port, you can apply the following configuration to the UDP server:

import reactor.netty.Connection;
import reactor.netty.udp.UdpServer;
import java.time.Duration;

public class Application {

    public static void main(String[] args) {
        Connection server =
                UdpServer.create()
                         .host("localhost") (1)
                         .port(8080)        (2)
                         .bindNow(Duration.ofSeconds(30));

        server.onDispose()
              .block();
    }
}
1 Configures the UDP server host
2 Configures the UDP server port

7.2. Writing Data

To send data to the remote peer, you must attach an I/O handler. The I/O handler has access to UdpOutbound, to be able to write data. The following example shows how to send hello:

import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.socket.DatagramPacket;
import io.netty.util.CharsetUtil;
import reactor.core.publisher.Mono;
import reactor.netty.Connection;
import reactor.netty.udp.UdpServer;

import java.time.Duration;

public class Application {

    public static void main(String[] args) {
        Connection server =
                UdpServer.create()
                         .handle((in, out) ->
                             out.sendObject(
                                 in.receiveObject()
                                   .map(o -> {
                                       if (o instanceof DatagramPacket) {
                                           DatagramPacket p = (DatagramPacket) o;
                                           ByteBuf buf = Unpooled.copiedBuffer("hello", CharsetUtil.UTF_8);
                                           return new DatagramPacket(buf, p.sender()); (1)
                                       }
                                       else {
                                           return Mono.error(
                                               new Exception("Unexpected type of the message: " + o));
                                       }
                                   })))
                         .bindNow(Duration.ofSeconds(30));

        server.onDispose()
              .block();
    }
}
1 Sends a hello string to the remote peer

7.3. Consuming Data

To receive data from a remote peer, you must attach an I/O handler. The I/O handler has access to UdpInbound, to be able to read data. The following example shows how to consume data:

import io.netty.channel.socket.DatagramPacket;
import reactor.core.publisher.Mono;
import reactor.netty.Connection;
import reactor.netty.udp.UdpServer;

import java.time.Duration;

public class Application {

    public static void main(String[] args) {
        Connection server =
                UdpServer.create()
                         .handle((in, out) ->
                             out.sendObject(
                                 in.receiveObject()
                                   .map(o -> {
                                       if (o instanceof DatagramPacket) {
                                           DatagramPacket p = (DatagramPacket) o;
                                           return new DatagramPacket(p.content().retain(), p.sender()); (1)
                                       }
                                       else {
                                           return Mono.error(new Exception("Unexpected type of the message: " + o));
                                       }
                                   })))
                         .bindNow(Duration.ofSeconds(30));

        server.onDispose()
              .block();
    }
}
1 Receives data from the remote peer

7.4. Lifecycle Callbacks

The following lifecycle callbacks are provided to let you extend the UDP server:

  • doOnBind: Invoked when the server channel is about to bind.

  • doOnBound: Invoked when the server channel is bound.

  • doOnUnbound: Invoked when the server channel is unbound.

  • doOnLifecycle: Sets up all lifecycle callbacks.

The following example uses the doOnBound method:

import io.netty.handler.codec.LineBasedFrameDecoder;
import reactor.netty.Connection;
import reactor.netty.udp.UdpServer;
import java.time.Duration;

public class Application {

    public static void main(String[] args) {
        Connection server =
                UdpServer.create()
                         .doOnBound(conn -> conn.addHandler(new LineBasedFrameDecoder(8192))) (1)
                         .bindNow(Duration.ofSeconds(30));

        server.onDispose()
              .block();
    }
}
1 Netty pipeline is extended with LineBasedFrameDecoder when the server channel is bound.

7.5. Connection Configurations

This section describes three kinds of configuration that you can use at the TCP level:

7.5.1. Channel Options

By default, the UDP server is configured with the following options:

/../../main/java/reactor/netty/udp/UdpServer.java
static final Bootstrap DEFAULT_BOOTSTRAP =
		new Bootstrap().option(ChannelOption.AUTO_READ, false)
		               .localAddress(NetUtil.LOCALHOST, DEFAULT_PORT);

If you need additional options or need to change the current options, you can apply the following configuration:

import io.netty.channel.ChannelOption;
import reactor.netty.Connection;
import reactor.netty.udp.UdpServer;
import java.time.Duration;

public class Application {

    public static void main(String[] args) {
        Connection server =
                UdpServer.create()
                         .option(ChannelOption.CONNECT_TIMEOUT_MILLIS, 10000)
                         .bindNow(Duration.ofSeconds(30));

        server.onDispose()
              .block();
    }
}

For more about Netty channel options, see the following links:

7.5.2. Wire Logger

Reactor Netty provides wire logging for when the traffic between the peers has to be inspected. By default, wire logging is disabled. To enable it, you must set the logger reactor.netty.udp.UdpServer level to DEBUG and apply the following configuration:

import reactor.netty.Connection;
import reactor.netty.udp.UdpServer;
import java.time.Duration;

public class Application {

    public static void main(String[] args) {
        Connection server =
                UdpServer.create()
                         .wiretap(true) (1)
                         .bindNow(Duration.ofSeconds(30));

        server.onDispose()
              .block();
    }
}
1 Enables the wire logging

7.5.3. Event Loop Group

By default, the UDP server uses “Event Loop Group,” where the number of the worker threads equals the number of processors available to the runtime on initialization (but with a minimum value of 4). When you need a different configuration, you can use one of the LoopResource#create methods.

The default configuration for the “Event Loop Group” is the following:

/../../main/java/reactor/netty/ReactorNetty.java
/**
 * Default worker thread count, fallback to available processor
 * (but with a minimum value of 4)
 */
public static final String IO_WORKER_COUNT = "reactor.netty.ioWorkerCount";
/**
 * Default selector thread count, fallback to -1 (no selector thread)
 */
public static final String IO_SELECT_COUNT = "reactor.netty.ioSelectCount";
/**
 * Default worker thread count for UDP, fallback to available processor
 * (but with a minimum value of 4)
 */
public static final String UDP_IO_THREAD_COUNT = "reactor.netty.udp.ioThreadCount";


/**
 * Default value whether the native transport (epoll, kqueue) will be preferred,
 * fallback it will be preferred when available
 */
public static final String NATIVE = "reactor.netty.native";

If you need changes to the these settings, you can apply the following configuration:

import reactor.netty.Connection;
import reactor.netty.resources.LoopResources;
import reactor.netty.udp.UdpServer;
import java.time.Duration;

public class Application {

    public static void main(String[] args) {
        LoopResources loop = LoopResources.create("event-loop", 1, 4, true);
        Connection server =
                UdpServer.create()
                         .runOn(loop)
                         .bindNow(Duration.ofSeconds(30));

        server.onDispose()
              .block();
    }
}

8. UDP Client

Reactor Netty provides the easy-to-use and easy-to-configure UdpClient. It hides most of the Netty functionality that is required to create a UDP client and adds Reactive Streams backpressure.

8.1. Connecting and Disconnecting

To connect the UDP client to a given endpoint, you must create and configure a UdpClient instance. By default, the host is configured for localhost and the port is 12012. The following example shows how to create and connect a UDP client:

import reactor.netty.Connection;
import reactor.netty.udp.UdpClient;
import java.time.Duration;

public class Application {

    public static void main(String[] args) {
        Connection connection =
                UdpClient.create()                            (1)
                         .connectNow(Duration.ofSeconds(30)); (2)

        connection.onDispose()
                  .block();
    }
}
1 Creates a UdpClient instance that is ready for configuring.
2 Connects the client in a blocking fashion and waits for it to finish initializing.

The returned Connection offers a simple connection API, including to disposeNow(), which shuts the client down in a blocking fashion.

8.1.1. Host and Port

To connect to a specific host and port, you can apply the following configuration to the UDP client:

import reactor.netty.Connection;
import reactor.netty.udp.UdpClient;
import java.time.Duration;

public class Application {

    public static void main(String[] args) {
        Connection connection =
                UdpClient.create()
                         .host("example.com") (1)
                         .port(80)            (2)
                         .connectNow(Duration.ofSeconds(30));

        connection.onDispose()
                  .block();
    }
}
1 Configures the host to which this client should connect
2 Configures the port to which this client should connect

8.2. Writing Data

To send data to a given peer, you must attach an I/O handler. The I/O handler has access to UdpOutbound, to be able to write data.

The following example shows how to send hello:

import reactor.core.publisher.Mono;
import reactor.netty.Connection;
import reactor.netty.udp.UdpClient;

import java.time.Duration;

public class Application {

    public static void main(String[] args) {
        Connection connection =
                UdpClient.create()
                         .host("example.com")
                         .port(80)
                         .handle((udpInbound, udpOutbound) -> udpOutbound.sendString(Mono.just("hello"))) (1)
                         .connectNow(Duration.ofSeconds(30));

        connection.onDispose()
                  .block();
    }
}
1 Sends hello string to the remote peer.

8.3. Consuming Data

To receive data from a given peer, you must attach an I/O handler. The I/O handler has access to UdpInbound, to be able to read data. The following example shows how to consume data:

import reactor.netty.Connection;
import reactor.netty.udp.UdpClient;
import java.time.Duration;

public class Application {

    public static void main(String[] args) {
        Connection connection =
                UdpClient.create()
                         .host("example.com")
                         .port(80)
                         .handle((udpInbound, udpOutbound) -> udpInbound.receive().then()) (1)
                         .connectNow(Duration.ofSeconds(30));

        connection.onDispose()
                  .block();
    }
}
1 Receives data from a given peer

8.4. Lifecycle Callbacks

The following lifecycle callbacks are provided to let you extend the UDP client:

  • doOnConnect: Invoked when the channel is about to connect.

  • doOnConnected: Invoked after the channel has been connected.

  • doOnDisconnected: Invoked after the channel has been disconnected.

  • doOnLifecycle: Sets up all lifecycle callbacks.

The following example uses the doOnConnected method:

import io.netty.handler.codec.LineBasedFrameDecoder;
import reactor.netty.Connection;
import reactor.netty.udp.UdpClient;
import java.time.Duration;

public class Application {

    public static void main(String[] args) {
        Connection connection =
                UdpClient.create()
                         .host("example.com")
                         .port(80)
                         .doOnConnected(conn -> conn.addHandler(new LineBasedFrameDecoder(8192))) (1)
                         .connectNow(Duration.ofSeconds(30));

        connection.onDispose()
                  .block();
    }
}
1 The Netty pipeline is extended with LineBasedFrameDecoder when the channel has been connected.

8.5. Connection Configurations

This section describes three kinds of configuration that you can use at the TCP level:

8.5.1. Channel Options

By default, the UDP client is configured with the following options:

/../../main/java/reactor/netty/udp/UdpClient.java
static final Bootstrap DEFAULT_BOOTSTRAP =
		new Bootstrap().option(ChannelOption.AUTO_READ, false)
		               .remoteAddress(NetUtil.LOCALHOST, DEFAULT_PORT);

If you need additional options or need to change the current options, you can apply the following configuration:

import io.netty.channel.ChannelOption;
import reactor.netty.Connection;
import reactor.netty.udp.UdpClient;
import java.time.Duration;

public class Application {

    public static void main(String[] args) {
        Connection connection =
                UdpClient.create()
                         .host("example.com")
                         .port(80)
                         .option(ChannelOption.CONNECT_TIMEOUT_MILLIS, 10000)
                         .connectNow(Duration.ofSeconds(30));

        connection.onDispose()
                  .block();
    }
}

You can find more about Netty channel options at the following links:

8.5.2. Wire Logger

Reactor Netty provides wire logging for when the traffic between the peers has to be inspected. By default, wire logging is disabled. To enable it, you must set the logger reactor.netty.udp.UdpClient level to DEBUG and apply the following configuration:

import reactor.netty.Connection;
import reactor.netty.udp.UdpClient;
import java.time.Duration;

public class Application {

    public static void main(String[] args) {
        Connection connection =
                UdpClient.create()
                         .host("example.com")
                         .port(80)
                         .wiretap(true) (1)
                         .connectNow(Duration.ofSeconds(30));

        connection.onDispose()
                  .block();
    }
}
1 Enables the wire logging

8.5.3. Event Loop Group

By default, the UDP client uses “Event Loop Group,” where the number of the worker threads equals the number of processors available to the runtime on initialization (but with a minimum value of 4). When you need a different configuration, you can use one of the LoopResources#create methods.

The following listing shows the default configuration for the “Event Loop Group”:

/../../main/java/reactor/netty/ReactorNetty.java
/**
 * Default worker thread count, fallback to available processor
 * (but with a minimum value of 4)
 */
public static final String IO_WORKER_COUNT = "reactor.netty.ioWorkerCount";
/**
 * Default selector thread count, fallback to -1 (no selector thread)
 */
public static final String IO_SELECT_COUNT = "reactor.netty.ioSelectCount";
/**
 * Default worker thread count for UDP, fallback to available processor
 * (but with a minimum value of 4)
 */
public static final String UDP_IO_THREAD_COUNT = "reactor.netty.udp.ioThreadCount";


/**
 * Default value whether the native transport (epoll, kqueue) will be preferred,
 * fallback it will be preferred when available
 */
public static final String NATIVE = "reactor.netty.native";

If you need changes to the these settings, you can apply the following configuration:

import reactor.netty.Connection;
import reactor.netty.resources.LoopResources;
import reactor.netty.udp.UdpClient;
import java.time.Duration;

public class Application {

    public static void main(String[] args) {
        LoopResources loop = LoopResources.create("event-loop", 1, 4, true);
        Connection connection =
                UdpClient.create()
                         .host("example.com")
                         .port(80)
                         .runOn(loop)
                         .connectNow(Duration.ofSeconds(30));

        connection.onDispose()
                  .block();
    }
}