# QUIC Client

Reactor Netty provides the easy-to-use and easy-to-configure `QuicClient`. It hides most of the Netty functionality that is required to create a `QUIC` client and add Reactive Streams backpressure.

## 1. Connecting and Disconnecting

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

github.com/reactor/reactor-netty/tree/main/reactor-netty-examples/src/main/java/reactor/netty/examples/documentation/quic/client/create/Application.java

    import reactor.netty.Connection;
    import reactor.netty.quic.QuicClient;

    import java.time.Duration;

    public class Application {

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

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

1 | Creates a `QuicClient` instance that is ready for configuring.
2 | Connects the client in a blocking fashion and waits for it to finish initializing.

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

### 1.1. Host and Port

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

github.com/reactor/reactor-netty/tree/main/reactor-netty-examples/src/main/java/reactor/netty/examples/documentation/quic/client/address/Application.java

    import reactor.netty.Connection;
    import reactor.netty.quic.QuicClient;

    import java.net.InetSocketAddress;

    public class Application {

    	public static void main(String[] args) {
    		Connection connection =
    				QuicClient.create()
    				          .remoteAddress(() -> new InetSocketAddress("127.0.0.1", 8080)) (1)
    				          .connectNow();

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

1 | Configures the `host` and `port` to which this client should connect

| The port can be specified also with QUIC_PORT environment variable.

## 2. Secure Connection

To configure the `QUIC` client with SSL, you must apply the following configuration:

github.com/reactor/reactor-netty/tree/main/reactor-netty-examples/src/main/java/reactor/netty/examples/documentation/quic/client/security/Application.java

    import io.netty.handler.codec.quic.QuicSslContext;
    import io.netty.handler.codec.quic.QuicSslContextBuilder;
    import reactor.netty.Connection;
    import reactor.netty.quic.QuicClient;

    public class Application {

    	public static void main(String[] args) {
    		QuicSslContext clientCtx =
    				QuicSslContextBuilder.forClient()
    				                     .applicationProtocols("http/1.1")
    				                     .build();

    		Connection connection =
    				QuicClient.create()
    				          .secure(clientCtx) (1)
    				          .connectNow();

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

1 | Configures the SSL context to use for the secure connection

## 3. Initial Settings

`QUIC` allows configuring various settings for the connection. You can apply the following configuration:

github.com/reactor/reactor-netty/tree/main/reactor-netty-examples/src/main/java/reactor/netty/examples/documentation/quic/client/settings/Application.java

    import reactor.netty.Connection;
    import reactor.netty.quic.QuicClient;

    public class Application {

    	public static void main(String[] args) {
    		Connection connection =
    				QuicClient.create()
    				          .initialSettings(spec ->                           (1)
    				              spec.maxData(10000000)                         (2)
    				                  .maxStreamDataBidirectionalLocal(1000000)  (3)
    				                  .maxStreamDataBidirectionalRemote(1000000) (4)
    				                  .maxStreamDataUnidirectional(1000000)      (5)
    				                  .maxStreamsBidirectional(100)              (6)
    				                  .maxStreamsUnidirectional(100))            (7)
    				          .connectNow();

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

1 | Configures the initial settings for the `QUIC` connection
2 | Sets the maximum amount of data that can be sent on the connection
3 | Sets the maximum amount of data that can be sent on a bidirectional stream initiated by the local endpoint
4 | Sets the maximum amount of data that can be sent on a bidirectional stream initiated by the remote endpoint
5 | Sets the maximum amount of data that can be sent on a unidirectional stream
6 | Sets the maximum number of concurrent bidirectional streams
7 | Sets the maximum number of concurrent unidirectional streams

## 4. Opening Streams

To open a stream to the remote peer, you can use the following approach:

github.com/reactor/reactor-netty/tree/main/reactor-netty-examples/src/main/java/reactor/netty/examples/documentation/quic/client/stream/Application.java

    import io.netty.handler.codec.quic.QuicSslContext;
    import io.netty.handler.codec.quic.QuicSslContextBuilder;
    import reactor.core.publisher.Mono;
    import reactor.netty.quic.QuicClient;
    import reactor.netty.quic.QuicConnection;

    import java.net.InetSocketAddress;
    import java.time.Duration;
    import java.util.concurrent.CountDownLatch;

    public class Application {

    	public static void main(String[] args) throws InterruptedException {
    		QuicSslContext clientCtx =
    				QuicSslContextBuilder.forClient()
    				                     .applicationProtocols("http/1.1")
    				                     .build();

    		QuicConnection connection =
    				QuicClient.create()
    				          .bindAddress(() -> new InetSocketAddress(0))
    				          .remoteAddress(() -> new InetSocketAddress("127.0.0.1", 8080))
    				          .secure(clientCtx)
    				          .idleTimeout(Duration.ofSeconds(5))
    				          .initialSettings(spec ->
    				              spec.maxData(10000000)
    				                  .maxStreamDataBidirectionalLocal(1000000))
    				          .connectNow();

    		CountDownLatch latch = new CountDownLatch(1);
    		connection.createStream((in, out) ->             (1)
    		              out.sendString(Mono.just("Hello")) (2)
    		                 .then(in.receive()              (3)
    		                         .asString()
    		                         .doOnNext(s -> {
    		                             System.out.println("CLIENT RECEIVED: " + s);
    		                             latch.countDown();
    		                         })
    		                         .then()))
    		          .subscribe();

    		latch.await();

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

1 | Creates a new bidirectional stream
2 | Sends data to the remote peer
3 | Receives data from the remote peer

## 5. Lifecycle Callbacks

The following lifecycle callbacks are provided to let you extend the `QuicClient`:

Callback | Description
--- | ---
`doOnBind` | Invoked when the client is about to bind.
`doOnBound` | Invoked when the client has been bound.
`doOnChannelInit` | Invoked when initializing the channel.
`doOnConnect` | Invoked when the client is about to connect to the remote address.
`doOnConnected` | Invoked after the client has been connected.
`doOnDisconnected` | Invoked after the client has been disconnected.
`doOnUnbound` | Invoked when the client has been unbound.

The following example uses the `doOnConnected` callback:

github.com/reactor/reactor-netty/tree/main/reactor-netty-examples/src/main/java/reactor/netty/examples/documentation/quic/client/lifecycle/Application.java

    import reactor.netty.Connection;
    import reactor.netty.quic.QuicClient;

    public class Application {

    	public static void main(String[] args) throws InterruptedException {
    		Connection connection =
    				QuicClient.create()
    				          .doOnConnected(quicConnection -> System.out.println("Connected!")) (1)
    				          .connectNow();

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

1 | Invoked after the client has been connected

## 6. Connection Configuration

This section describes three kinds of configuration that you can use at the `QUIC` client level:

- Channel Options

- Wire Logger

- Event Loop Group

### 6.1. Channel Options

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

github.com/reactor/reactor-netty/tree/main/reactor-netty-examples/src/main/java/reactor/netty/examples/documentation/quic/client/channeloptions/Application.java

    import io.netty.channel.ChannelOption;
    import io.netty.handler.codec.quic.QLogConfiguration;
    import io.netty.handler.codec.quic.QuicChannelOption;
    import reactor.netty.Connection;
    import reactor.netty.quic.QuicClient;

    public class Application {

    	public static void main(String[] args) throws InterruptedException {
    		Connection connection =
    				QuicClient.create()
    				          .option(ChannelOption.CONNECT_TIMEOUT_MILLIS, 10000)             (1)
    				          .option(QuicChannelOption.QLOG,
    				              new QLogConfiguration("path", "logTitle", "logDescription")) (2)
    				          .connectNow();

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

1 | Configures the connect timeout
2 | Enables `QLOG` for the `QUIC` connection

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

- Common ChannelOption

- Quic ChannelOption

### 6.2. 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.quic.QuicClient` level to `DEBUG` and apply the following configuration:

github.com/reactor/reactor-netty/tree/main/reactor-netty-examples/src/main/java/reactor/netty/examples/documentation/quic/client/wiretap/Application.java

    import reactor.netty.Connection;
    import reactor.netty.quic.QuicClient;

    public class Application {

    	public static void main(String[] args) {
    		Connection connection =
    				QuicClient.create()
    				          .wiretap(true) (1)
    				          .connectNow();

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

1 | Enables the wire logging

#### 6.2.1. Wire Logger formatters

Reactor Netty supports 3 different formatters:

- AdvancedByteBufFormat#HEX_DUMP - the default

github.com/reactor/reactor-netty/tree/main/reactor-netty-core/src/main/java/reactor/netty/transport/logging/AdvancedByteBufFormat.java

    	/**
    	 * When wire logging is enabled with this format, both events and content will be logged.
    	 * The content will be in hex format.
    	 * <p>Examples:</p>
    	 * <pre>
    	 * {@code
    	 * reactor.netty.http.HttpTests - [d5230a14, L:/0:0:0:0:0:0:0:1:60267 - R:/0:0:0:0:0:0:0:1:60269] REGISTERED
    	 * reactor.netty.http.HttpTests - [d5230a14, L:/0:0:0:0:0:0:0:1:60267 - R:/0:0:0:0:0:0:0:1:60269] ACTIVE
    	 * reactor.netty.http.HttpTests - [d5230a14, L:/0:0:0:0:0:0:0:1:60267 - R:/0:0:0:0:0:0:0:1:60269] READ: 145B
    	 *          +-------------------------------------------------+
    	 *          |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
    	 * +--------+-------------------------------------------------+----------------+
    	 * |00000000| 50 4f 53 54 20 2f 74 65 73 74 2f 57 6f 72 6c 64 |POST /test/World|
    	 * |00000010| 20 48 54 54 50 2f 31 2e 31 0d 0a 43 6f 6e 74 65 | HTTP/1.1..Conte|
    	 * |00000020| 6e 74 2d 54 79 70 65 3a 20 74 65 78 74 2f 70 6c |nt-Type: text/pl|
    	 * |00000030| 61 69 6e 0d 0a 75 73 65 72 2d 61 67 65 6e 74 3a |ain..user-agent:|
    	 * |00000040| 20 52 65 61 63 74 6f 72 4e 65 74 74 79 2f 64 65 | ReactorNetty/de|
    	 * ...
    	 * reactor.netty.http.HttpTests - [d5230a14, L:/0:0:0:0:0:0:0:1:60267 - R:/0:0:0:0:0:0:0:1:60269] WRITE: 38B
    	 *          +-------------------------------------------------+
    	 *          |  0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f |
    	 * +--------+-------------------------------------------------+----------------+
    	 * |00000000| 48 54 54 50 2f 31 2e 31 20 32 30 30 20 4f 4b 0d |HTTP/1.1 200 OK.|
    	 * |00000010| 0a 63 6f 6e 74 65 6e 74 2d 6c 65 6e 67 74 68 3a |.content-length:|
    	 * |00000020| 20 30 0d 0a 0d 0a                               | 0....          |
    	 * +--------+-------------------------------------------------+----------------+
    	 * }
    	 * </pre>
    	 */

- AdvancedByteBufFormat#SIMPLE

github.com/reactor/reactor-netty/tree/main/reactor-netty-core/src/main/java/reactor/netty/transport/logging/AdvancedByteBufFormat.java

    	/**
    	 * When wire logging is enabled with this format, only the events will be logged.
    	 * <p>Examples:</p>
    	 * <pre>
    	 * {@code
    	 * reactor.netty.http.HttpTests - [230d3686, L:/0:0:0:0:0:0:0:1:60241 - R:/0:0:0:0:0:0:0:1:60245] REGISTERED
    	 * reactor.netty.http.HttpTests - [230d3686, L:/0:0:0:0:0:0:0:1:60241 - R:/0:0:0:0:0:0:0:1:60245] ACTIVE
    	 * reactor.netty.http.HttpTests - [230d3686, L:/0:0:0:0:0:0:0:1:60241 - R:/0:0:0:0:0:0:0:1:60245] READ: 145B
    	 * reactor.netty.http.HttpTests - [230d3686, L:/0:0:0:0:0:0:0:1:60241 - R:/0:0:0:0:0:0:0:1:60245] WRITE: 38B
    	 * }
    	 * </pre>
    	 */

- AdvancedByteBufFormat#TEXTUAL

github.com/reactor/reactor-netty/tree/main/reactor-netty-core/src/main/java/reactor/netty/transport/logging/AdvancedByteBufFormat.java

    	/**
    	 * When wire logging is enabled with this format, both events and content will be logged.
    	 * The content will be in plain text format.
    	 * <p>Examples:</p>
    	 * <pre>
    	 * {@code
    	 * reactor.netty.http.HttpTests - [02c3db6c, L:/0:0:0:0:0:0:0:1:60317 - R:/0:0:0:0:0:0:0:1:60319] REGISTERED
    	 * reactor.netty.http.HttpTests - [02c3db6c, L:/0:0:0:0:0:0:0:1:60317 - R:/0:0:0:0:0:0:0:1:60319] ACTIVE
    	 * reactor.netty.http.HttpTests - [02c3db6c, L:/0:0:0:0:0:0:0:1:60317 - R:/0:0:0:0:0:0:0:1:60319] READ: 145B POST /test/World HTTP/1.1
    	 * Content-Type: text/plain
    	 * user-agent: ReactorNetty/dev
    	 * ...
    	 * reactor.netty.http.HttpTests - [02c3db6c, L:/0:0:0:0:0:0:0:1:60317 - R:/0:0:0:0:0:0:0:1:60319] WRITE: 38B HTTP/1.1 200 OK
    	 * content-length: 0
    	 * }
    	 * </pre>
    	 */

When you need to change the default formatter you can configure it as follows:

github.com/reactor/reactor-netty/tree/main/reactor-netty-examples/src/main/java/reactor/netty/examples/documentation/quic/client/wiretap/custom/Application.java

    import io.netty.handler.logging.LogLevel;
    import reactor.netty.Connection;
    import reactor.netty.quic.QuicClient;
    import reactor.netty.transport.logging.AdvancedByteBufFormat;

    public class Application {

    	public static void main(String[] args) {
    		Connection connection =
    				QuicClient.create()
    				          .wiretap("logger-name", LogLevel.DEBUG, AdvancedByteBufFormat.TEXTUAL) (1)
    				          .connectNow();

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

1 | Enables the wire logging, AdvancedByteBufFormat#TEXTUAL is used for printing the content.

### 6.3. Event Loop Group

By default `Reactor Netty` 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). This “Event Loop Group” is shared between all servers and clients in one JVM. 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:

github.com/reactor/reactor-netty/tree/main/reactor-netty-core/src/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)
    	 * <p><strong>Note:</strong> In most use cases using a worker thread also as a selector thread works well.
    	 * A possible use case for specifying a separate selector thread might be when the worker threads are too busy
    	 * and connections cannot be accepted fast enough.
    	 * <p><strong>Note:</strong> Although more than 1 can be configured as a selector thread count, in reality
    	 * only 1 thread will be used as a 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 quiet period that guarantees that the disposal of the underlying LoopResources
    	 * will not happen, fallback to 2 seconds.
    	 */
    	public static final String SHUTDOWN_QUIET_PERIOD = "reactor.netty.ioShutdownQuietPeriod";
    	/**
    	 * Default maximum amount of time to wait until the disposal of the underlying LoopResources
    	 * regardless if a task was submitted during the quiet period, fallback to 15 seconds.
    	 */
    	public static final String SHUTDOWN_TIMEOUT = "reactor.netty.ioShutdownTimeout";

    	/**
    	 * Default value whether the native transport (epoll, io_uring, kqueue) will be preferred,
    	 * fallback it will be preferred when available.
    	 * <p><strong>Note:</strong> On {@code Linux}, {@code Epoll} will be preferred by default.
    	 * If {@code IO_Uring} needs to be configured, a dependency to {@code io.netty:netty-transport-native-io_uring}
    	 * has to be added.
    	 */
    	public static final String NATIVE = "reactor.netty.native";

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

github.com/reactor/reactor-netty/tree/main/reactor-netty-examples/src/main/java/reactor/netty/examples/documentation/quic/client/eventloop/Application.java

    import reactor.netty.Connection;
    import reactor.netty.quic.QuicClient;
    import reactor.netty.resources.LoopResources;

    public class Application {

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

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

#### 6.3.1. Disposing Event Loop Group

- If you use the default `Event Loop Group` provided by Reactor Netty, invoke `HttpResources``#disposeLoopsAndConnections`/`#disposeLoopsAndConnectionsLater` method.

| Disposing `HttpResources` means that every server/client that is using it, will not be able to use it anymore!

- If you use custom `LoopResources`, invoke `LoopResources``#dispose`/`#disposeLater` method.

| Disposing the custom `LoopResources` means that every server/client that is configured to use it, will not be able to use it anymore!

## 7. Metrics

When `QUIC` client metrics are needed for an integration with a system as `Micrometer`, you can provide your own metrics recorder, as follows:

github.com/reactor/reactor-netty/tree/main/reactor-netty-examples/src/main/java/reactor/netty/examples/documentation/quic/client/metrics/Application.java

    import reactor.netty.Connection;
    import reactor.netty.channel.ChannelMetricsRecorder;
    import reactor.netty.quic.QuicClient;

    import java.net.SocketAddress;
    import java.time.Duration;

    public class Application {

    	public static void main(String[] args) {
    		Connection connection =
    				QuicClient.create()
    				          .metrics(true, CustomChannelMetricsRecorder::new) (1)
    				          .connectNow();

    		connection.onDispose()
    		          .block();
    	}

1 | Enables `QUIC` client metrics and provides `ChannelMetricsRecorder` implementation.

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  - Reactor Netty
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