First take on adding an EventListener to the API (square#6)

extend the builder and OkHttpClient to take either an EventListener or an EventListenerFactory

okhttp/src/main/java/okhttp3/OkHttpClient.java

@@ -216,6 +216,8 @@ public void apply(ConnectionSpec tlsConfiguration, SSLSocket sslSocket, boolean
   final int readTimeout;
   final int writeTimeout;
   final int pingInterval;
+  final EventListener eventListener;
+  final EventListener.Factory eventListenerFactory;
 
   public OkHttpClient() {
     this(new Builder());
@@ -233,6 +235,8 @@ public OkHttpClient() {
     this.cache = builder.cache;
     this.internalCache = builder.internalCache;
     this.socketFactory = builder.socketFactory;
+    this.eventListener = builder.eventListener;
+    this.eventListenerFactory = builder.eventListenerFactory;
 
     boolean isTLS = false;
     for (ConnectionSpec spec : connectionSpecs) {
@@ -404,6 +408,14 @@ public List<Interceptor> networkInterceptors() {
     return networkInterceptors;
   }
 
+  public EventListener eventListener() {
+    return eventListener;
+  }
+
+  public EventListener.Factory eventListenerFactory() {
+    return eventListenerFactory;
+  }
+
   /**
    * Prepares the {@code request} to be executed at some point in the future.
    */
@@ -451,6 +463,8 @@ public static final class Builder {
     int readTimeout;
     int writeTimeout;
     int pingInterval;
+    EventListener eventListener;
+    EventListener.Factory eventListenerFactory;
 
     public Builder() {
       dispatcher = new Dispatcher();
@@ -472,6 +486,8 @@ public Builder() {
       readTimeout = 10_000;
       writeTimeout = 10_000;
       pingInterval = 0;
+      eventListener = EventListener.NULL_EVENT_LISTENER;
+      eventListenerFactory = null;
     }
 
     Builder(OkHttpClient okHttpClient) {
@@ -501,6 +517,8 @@ public Builder() {
       this.readTimeout = okHttpClient.readTimeout;
       this.writeTimeout = okHttpClient.writeTimeout;
       this.pingInterval = okHttpClient.pingInterval;
+      this.eventListener = okHttpClient.eventListener;
+      this.eventListenerFactory = okHttpClient.eventListenerFactory;
     }
 
     /**
@@ -878,6 +896,16 @@ public Builder addNetworkInterceptor(Interceptor interceptor) {
       return this;
     }
 
+    public Builder addEventListener(EventListener listener) {
+      eventListener = listener;
+      return this;
+    }
+
+    public Builder addEventListenerFactory(EventListener.Factory listenerFactory) {
+      eventListenerFactory = listenerFactory;
+      return this;
+    }
+
     public OkHttpClient build() {
       return new OkHttpClient(this);
     }

okhttp/src/main/java/okhttp3/RealCall.java

@@ -33,6 +33,7 @@
 final class RealCall implements Call {
   final OkHttpClient client;
   final RetryAndFollowUpInterceptor retryAndFollowUpInterceptor;
+  final EventListener eventListener;
 
   /** The application's original request unadulterated by redirects or auth headers. */
   final Request originalRequest;
@@ -42,10 +43,17 @@ final class RealCall implements Call {
   private boolean executed;
 
   RealCall(OkHttpClient client, Request originalRequest, boolean forWebSocket) {
+    final EventListener.Factory eventListenerFactory = client.eventListenerFactory();
+
     this.client = client;
     this.originalRequest = originalRequest;
     this.forWebSocket = forWebSocket;
     this.retryAndFollowUpInterceptor = new RetryAndFollowUpInterceptor(client, forWebSocket);
+    if (null == eventListenerFactory) {
+      this.eventListener = client.eventListener();
+    } else {
+      this.eventListener = eventListenerFactory.create(this);
+    }
   }
 
   @Override public Request request() {