Migrate reactivesocket-load-balancer into reactivesocket-java (#93)

**Problem**
The multi-repo structure is difficult to use in a context of rapid
short iterations.

**Solution**
Migrate the reactivesocket-load-balancer repo inside reactivesocket-java.
The submodules have been renamed like this:

- reactivesocket-load-balancer-builder -> reactivesocket-client
- reactivesocket-load-balancer-core -> reactivesocket-client
- reactivesocket-load-balancer-eureka -> reactivesocket-discovery-eureka
- reactivesocket-load-balancer-servo -> reactivesocket-stats-servo

I also added a simple module `reactivesocket-examples`, which only contains
one file so far. The goal of this module is to demonstrate simple examples.

Author: stevegury

reactivesocket-client/build.gradle

@@ -0,0 +1,4 @@
+dependencies {
+    compile project(':reactivesocket-core')
+    testCompile project(':reactivesocket-test')
+}

reactivesocket-client/src/main/java/io/reactivesocket/client/Builder.java

@@ -0,0 +1,263 @@
+/**
+ * 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.reactivesocket.client;
+
+import io.reactivesocket.ReactiveSocket;
+import io.reactivesocket.ReactiveSocketConnector;
+import io.reactivesocket.ReactiveSocketFactory;
+import io.reactivesocket.client.filter.*;
+import org.reactivestreams.Publisher;
+import org.reactivestreams.Subscriber;
+import org.reactivestreams.Subscription;
+
+import java.net.SocketAddress;
+import java.util.*;
+import java.util.concurrent.Executors;
+import java.util.concurrent.ScheduledExecutorService;
+import java.util.concurrent.ThreadFactory;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicInteger;
+import java.util.function.Function;
+import java.util.stream.Collectors;
+
+public class Builder {
+    private static AtomicInteger counter = new AtomicInteger(0);
+    private final String name;
+
+    private final ScheduledExecutorService executor;
+
+    private final long requestTimeout;
+    private final TimeUnit requestTimeoutUnit;
+
+    private final long connectTimeout;
+    private final TimeUnit connectTimeoutUnit;
+
+    private final double backupQuantile;
+
+    private final int retries;
+
+    private final ReactiveSocketConnector<SocketAddress> connector;
+    private final Function<Throwable, Boolean> retryThisException;
+
+    private final Publisher<List<SocketAddress>> source;
+
+    private Builder(
+        String name,
+        ScheduledExecutorService executor,
+        long requestTimeout, TimeUnit requestTimeoutUnit,
+        long connectTimeout, TimeUnit connectTimeoutUnit,
+        double backupQuantile,
+        int retries, Function<Throwable, Boolean> retryThisException,
+        ReactiveSocketConnector<SocketAddress> connector,
+        Publisher<List<SocketAddress>> source
+    ) {
+        this.name = name;
+        this.executor = executor;
+        this.requestTimeout = requestTimeout;
+        this.requestTimeoutUnit = requestTimeoutUnit;
+        this.connectTimeout = connectTimeout;
+        this.connectTimeoutUnit = connectTimeoutUnit;
+        this.backupQuantile = backupQuantile;
+        this.retries = retries;
+        this.connector = connector;
+        this.retryThisException = retryThisException;
+        this.source = source;
+    }
+
+    public Builder withRequestTimeout(long timeout, TimeUnit unit) {
+        return new Builder(
+            name,
+            executor,
+            timeout, unit,
+            connectTimeout, connectTimeoutUnit,
+            backupQuantile,
+            retries, retryThisException,
+            connector,
+            source
+        );
+    }
+
+    public Builder withConnectTimeout(long timeout, TimeUnit unit) {
+        return new Builder(
+            name,
+            executor,
+            requestTimeout, requestTimeoutUnit,
+            timeout, unit,
+            backupQuantile,
+            retries, retryThisException,
+            connector,
+            source
+        );
+    }
+
+    public  Builder withBackupRequest(double quantile) {
+        return new Builder(
+            name,
+            executor,
+            requestTimeout, requestTimeoutUnit,
+            connectTimeout, connectTimeoutUnit,
+            quantile,
+            retries, retryThisException,
+            connector,
+            source
+        );
+    }
+
+    public  Builder withExecutor(ScheduledExecutorService executor) {
+        return new Builder(
+            name,
+            executor,
+            requestTimeout, requestTimeoutUnit,
+            connectTimeout, connectTimeoutUnit,
+            backupQuantile,
+            retries, retryThisException,
+            connector,
+            source
+        );
+    }
+
+    public  Builder withConnector(ReactiveSocketConnector<SocketAddress> connector) {
+        return new Builder(
+            name,
+            executor,
+            requestTimeout, requestTimeoutUnit,
+            connectTimeout, connectTimeoutUnit,
+            backupQuantile,
+            retries, retryThisException,
+            connector,
+            source
+        );
+    }
+
+    public Builder withSource(Publisher<List<SocketAddress>> source) {
+        return new Builder(
+            name,
+            executor,
+            requestTimeout, requestTimeoutUnit,
+            connectTimeout, connectTimeoutUnit,
+            backupQuantile,
+            retries, retryThisException,
+            connector,
+            source
+        );
+    }
+
+    public Builder withRetries(int nbOfRetries, Function<Throwable, Boolean> retryThisException) {
+        return new Builder(
+            name,
+            executor,
+            requestTimeout, requestTimeoutUnit,
+            connectTimeout, connectTimeoutUnit,
+            backupQuantile,
+            nbOfRetries, retryThisException,
+            connector,
+            source
+        );
+    }
+
+    public ReactiveSocket build() {
+        if (source == null) {
+            throw new IllegalStateException("Please configure the source!");
+        }
+        if (connector == null) {
+            throw new IllegalStateException("Please configure the connector!");
+        }
+
+        ReactiveSocketConnector<SocketAddress> filterConnector = connector
+            .chain(socket -> new TimeoutSocket(socket, requestTimeout, requestTimeoutUnit, executor))
+            .chain(DrainingSocket::new);
+
+        Publisher<List<ReactiveSocketFactory<SocketAddress>>> factories =
+            sourceToFactory(source, filterConnector);
+
+        ReactiveSocket socket = new LoadBalancer(factories);
+        if (0.0 < backupQuantile && backupQuantile < 1.0) {
+            socket = new BackupRequestSocket(socket, backupQuantile, executor);
+        }
+        if (retries > 0) {
+            socket = new RetrySocket(socket, retries, t -> true);
+        }
+        return socket;
+    }
+
+    private Publisher<List<ReactiveSocketFactory<SocketAddress>>> sourceToFactory(
+        Publisher<List<SocketAddress>> source,
+        ReactiveSocketConnector<SocketAddress> connector
+    ) {
+        return subscriber ->
+            source.subscribe(new Subscriber<List<SocketAddress>>() {
+                private Map<SocketAddress, ReactiveSocketFactory<SocketAddress>> current;
+
+                @Override
+                public void onSubscribe(Subscription s) {
+                    subscriber.onSubscribe(s);
+                    current = new HashMap<>();
+                }
+
+                @Override
+                public void onNext(List<SocketAddress> socketAddresses) {
+                    socketAddresses.stream()
+                        .filter(sa -> !current.containsKey(sa))
+                        .map(connector::toFactory)
+                        .map(factory -> new TimeoutFactory<>(factory, connectTimeout, connectTimeoutUnit, executor))
+                        .map(FailureAwareFactory::new)
+                        .forEach(factory -> current.put(factory.remote(), factory));
+
+                    Set<SocketAddress> addresses = new HashSet<>(socketAddresses);
+                    Iterator<Map.Entry<SocketAddress, ReactiveSocketFactory<SocketAddress>>> it =
+                        current.entrySet().iterator();
+                    while (it.hasNext()) {
+                        SocketAddress sa = it.next().getKey();
+                        if (! addresses.contains(sa)) {
+                            it.remove();
+                        }
+                    }
+
+                    List<ReactiveSocketFactory<SocketAddress>> factories =
+                        current.values().stream().collect(Collectors.toList());
+                    subscriber.onNext(factories);
+                }
+
+                @Override
+                public void onError(Throwable t) { subscriber.onError(t); }
+
+                @Override
+                public void onComplete() { subscriber.onComplete(); }
+            });
+    }
+
+    public static Builder instance() {
+        return new Builder(
+            "rs-loadbalancer-" + counter.incrementAndGet(),
+            Executors.newScheduledThreadPool(4, new ThreadFactory() {
+                @Override
+                public Thread newThread(Runnable r) {
+                    Thread thread = new Thread(r);
+                    thread.setName("reactivesocket-scheduler-thread");
+                    thread.setDaemon(true);
+                    return thread;
+                }
+            }),
+            1, TimeUnit.SECONDS,
+            10, TimeUnit.SECONDS,
+            0.99,
+            3, t -> true,
+            null,
+            null
+        );
+    }
+}
+