InterceptingServer.java

/*
 * Copyright 2016 Netflix, Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 */

package io.reactivex.netty.examples.tcp.interceptors.simple;

import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandler;
import io.reactivex.netty.examples.ExamplesEnvironment;
import io.reactivex.netty.examples.tcp.interceptors.transformation.TransformingInterceptorsServer;
import io.reactivex.netty.protocol.tcp.server.ConnectionHandler;
import io.reactivex.netty.protocol.tcp.server.TcpServer;
import io.reactivex.netty.protocol.tcp.server.TcpServerInterceptorChain;
import io.reactivex.netty.protocol.tcp.server.TcpServerInterceptorChain.Interceptor;
import rx.Observable;

import java.nio.charset.Charset;

/**
 * A TCP echo server that follows a simple text based, new line delimited message protocol.
 * The server sends a "Hello" as the first message and then the echo of what it receives from the client. <p>
 *
 * This example demonstrates the usage of simple server side interceptors which does not do any data transformations.
 * For interceptors requiring data transformation see {@link TransformingInterceptorsServer}
 *
 * This example just aims to demonstrate how to write the simplest TCP server, it is however, not of much use in general
 * primarily because it reads unstructured data i.e. there are no boundaries that define what constitutes "a message".
 * In order to define such boundaries, one would typically add a {@link ChannelHandler} that converts the read raw
 * {@code ByteBuffer} to a structured message.
 */
public final class InterceptingServer {

    public static void main(final String[] args) {

        ExamplesEnvironment env = ExamplesEnvironment.newEnvironment(InterceptingServer.class);

        TcpServer<ByteBuf, ByteBuf> server;

        /*Starts a new TCP server on an ephemeral port.*/
        server = TcpServer.newServer(0)
                          .start(TcpServerInterceptorChain.startRaw(sendHello())
                                                          .end(echoHandler()));

        /*Wait for shutdown if not called from the client (passed an arg)*/
        if (env.shouldWaitForShutdown(args)) {
            server.awaitShutdown();
        }

        /*If not waiting for shutdown, assign the ephemeral port used to a field so that it can be read and used by
        the caller, if any.*/
        env.registerServerAddress(server.getServerAddress());
    }

    /**
     * Sends a hello on accepting a new connection.
     */
    private static Interceptor<ByteBuf, ByteBuf> sendHello() {
        return in -> newConnection -> newConnection.writeString(Observable.just("Hello\n"))
                                                   .concatWith(in.handle(newConnection));
    }

    /**
     * New {@link ConnectionHandler} that echoes all data received.
     *
     * @return Connection handler.
     */
    private static ConnectionHandler<ByteBuf, ByteBuf> echoHandler() {
        return conn -> conn.writeStringAndFlushOnEach(
                conn.getInput().map(msg -> "echo => " + msg.toString(Charset.defaultCharset()) + "\n"));
    }
}