Add HTTP transport startup hook (elastic#130812)

This commit introduces a `startInternal()` method to
`AbstractHttpServerTransport` and makes `doStart()` a final method so
that we can customize the startup behaviour of the HTTP transport in a
follow-up without needing cooperation from subclasses.

Relates ES-12223

Author: DaveCTurner

modules/transport-netty4/src/main/java/org/elasticsearch/http/netty4/Netty4HttpServerTransport.java

@@ -165,7 +165,7 @@ public Settings settings() {
     }
 
     @Override
-    protected void doStart() {
+    protected void startInternal() {
         boolean success = false;
         try {
             sharedGroup = sharedGroupFactory.getHttpGroup();

server/src/main/java/org/elasticsearch/http/AbstractHttpServerTransport.java

@@ -235,6 +235,13 @@ private TransportAddress bindAddress(final InetAddress hostAddress) {
 
     protected abstract HttpServerChannel bind(InetSocketAddress hostAddress) throws Exception;
 
+    @Override
+    protected final void doStart() {
+        startInternal();
+    }
+
+    protected abstract void startInternal();
+
     /**
      * Gracefully shut down.  If {@link HttpTransportSettings#SETTING_HTTP_SERVER_SHUTDOWN_GRACE_PERIOD} is zero, the default, then
      * forcefully close all open connections immediately.
@@ -251,7 +258,7 @@ private TransportAddress bindAddress(final InetAddress hostAddress) {
      * </ol>
      */
     @Override
-    protected void doStop() {
+    protected final void doStop() {
         synchronized (httpServerChannels) {
             if (httpServerChannels.isEmpty() == false) {
                 try {

server/src/test/java/org/elasticsearch/http/AbstractHttpServerTransportTests.java

@@ -211,14 +211,10 @@ protected HttpServerChannel bind(InetSocketAddress hostAddress) {
                 }
 
                 @Override
-                protected void doStart() {
-
-                }
+                protected void startInternal() {}
 
                 @Override
-                protected void stopInternal() {
-
-                }
+                protected void stopInternal() {}
 
                 @Override
                 public HttpStats stats() {
@@ -295,14 +291,10 @@ protected HttpServerChannel bind(InetSocketAddress hostAddress) {
                 }
 
                 @Override
-                protected void doStart() {
-
-                }
+                protected void startInternal() {}
 
                 @Override
-                protected void stopInternal() {
-
-                }
+                protected void stopInternal() {}
 
                 @Override
                 public HttpStats stats() {
@@ -385,7 +377,7 @@ protected HttpServerChannel bind(InetSocketAddress hostAddress) {
                 }
 
                 @Override
-                protected void doStart() {}
+                protected void startInternal() {}
 
                 @Override
                 protected void stopInternal() {}
@@ -516,7 +508,7 @@ protected HttpServerChannel bind(InetSocketAddress hostAddress) {
             }
 
             @Override
-            protected void doStart() {}
+            protected void startInternal() {}
 
             @Override
             protected void stopInternal() {}
@@ -567,9 +559,7 @@ protected HttpServerChannel bind(InetSocketAddress hostAddress) {
                 }
 
                 @Override
-                protected void doStart() {
-
-                }
+                protected void startInternal() {}
 
                 @Override
                 protected void stopInternal() {
@@ -710,14 +700,10 @@ protected HttpServerChannel bind(InetSocketAddress hostAddress) {
                 }
 
                 @Override
-                protected void doStart() {
-
-                }
+                protected void startInternal() {}
 
                 @Override
-                protected void stopInternal() {
-
-                }
+                protected void stopInternal() {}
 
                 @Override
                 public HttpStats stats() {
@@ -774,7 +760,7 @@ protected HttpServerChannel bind(InetSocketAddress hostAddress) {
                 }
 
                 @Override
-                protected void doStart() {}
+                protected void startInternal() {}
 
                 @Override
                 protected void stopInternal() {}
@@ -856,7 +842,7 @@ protected HttpServerChannel bind(InetSocketAddress hostAddress) {
                 }
 
                 @Override
-                protected void doStart() {}
+                protected void startInternal() {}
 
                 @Override
                 protected void stopInternal() {}
@@ -1226,7 +1212,7 @@ protected HttpServerChannel bind(InetSocketAddress hostAddress) {
         }
 
         @Override
-        protected void doStart() {
+        protected void startInternal() {
             bindServer();
         }