Preloading support in browser

	   Apps like the QSB can request the browser to preload a
	   web page.
           - preloaded pages are not added to the browser history
	     if they'r not seen by the user
	   - when a request is received, a new tab is created for the
	     preloaded page, but not added to the tab list
 	   - upon receiving the view intent for the preloaded page
             the tab is added to the tab list, and shown
	   - if several pages are preloaded consecutively in the same tab,
             the back stack is cleared before it is displayed
           - preloaded pages use the main browser cookie jar, so pages that
             have never been viewed by the user can drop cookies

Change-Id: I9ed21f2c9560fda0ed042b460b73bb33988a2e8a

1 files changed, 137 insertions, 0 deletions

diff --git a/src/com/android/browser/Preloader.java b/src/com/android/browser/Preloader.java
new file mode 100644
index 000000000..5a5f6873b
--- /dev/null
+++ b/src/com/android/browser/Preloader.java
@@ -0,0 +1,137 @@
+/*
+ * Copyright (C) 2011 The Android Open Source Project
+ *
+ * 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 com.android.browser;
+
+import android.content.Context;
+import android.os.Handler;
+import android.os.Looper;
+import android.util.AttributeSet;
+import android.util.Log;
+import android.webkit.WebView;
+
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * Singleton class for handling preload requests.
+ */
+public class Preloader {
+
+    private final static String LOGTAG = "browser.preloader";
+    private final static boolean LOGD_ENABLED = true;//com.android.browser.Browser.LOGD_ENABLED;
+
+    private static final int PRERENDER_TIMEOUT_MILLIS = 30 * 1000; // 30s
+
+    private static Preloader sInstance;
+
+    private final Context mContext;
+    private final Handler mHandler;
+    private final BrowserWebViewFactory mFactory;
+    private final HashMap<String, PreloaderSession> mSessions;
+
+    public static void initialize(Context context) {
+        sInstance = new Preloader(context);
+    }
+
+    public static Preloader getInstance() {
+        return sInstance;
+    }
+
+    private Preloader(Context context) {
+        mContext = context;
+        mHandler = new Handler(Looper.getMainLooper());
+        mSessions = new HashMap<String, PreloaderSession>();
+        mFactory = new BrowserWebViewFactory(context);
+
+    }
+
+    private PreloaderSession getSession(String id) {
+        PreloaderSession s = mSessions.get(id);
+        if (s == null) {
+            if (LOGD_ENABLED) Log.d(LOGTAG, "Create new preload session " + id);
+            s = new PreloaderSession(id);
+            mSessions.put(id, s);
+        }
+        return s;
+    }
+
+    private PreloaderSession takeSession(String id) {
+        PreloaderSession s = mSessions.remove(id);
+        if (s != null) {
+            s.cancelTimeout();
+        }
+        return s;
+    }
+
+    public void handlePreloadRequest(String id, String url, Map<String, String> headers) {
+        PreloaderSession s = getSession(id);
+        s.touch(); // reset timer
+        if (LOGD_ENABLED) Log.d(LOGTAG, "Preloading " + url);
+        s.getTab().loadUrl(url, headers);
+    }
+
+    public void discardPreload(String id) {
+        PreloaderSession s = takeSession(id);
+        if (s != null) {
+            if (LOGD_ENABLED) Log.d(LOGTAG, "Discard preload session " + id);
+            Tab t = s.getTab();
+            t.destroy();
+        }
+    }
+
+    /**
+     * Return a preloaded tab, and remove it from the preloader. This is used when the
+     * view is about to be displayed.
+     */
+    public Tab getPreloadedTab(String id) {
+        PreloaderSession s = takeSession(id);
+        if (LOGD_ENABLED) Log.d(LOGTAG, "Showing preload session " + id + "=" + s);
+        return s == null ? null : s.getTab();
+    }
+
+    private class PreloaderSession {
+        private final String mId;
+        private final Tab mTab;
+
+        private final Runnable mTimeoutTask = new Runnable(){
+            @Override
+            public void run() {
+                if (LOGD_ENABLED) Log.d(LOGTAG, "Preload session timeout " + mId);
+                discardPreload(mId);
+            }};
+
+        public PreloaderSession(String id) {
+            mId = id;
+            mTab = new Tab(new PreloadController(mContext), mFactory.createWebView(false));
+            touch();
+        }
+
+        public void cancelTimeout() {
+            mHandler.removeCallbacks(mTimeoutTask);
+        }
+
+        public void touch() {
+            cancelTimeout();
+            mHandler.postDelayed(mTimeoutTask, PRERENDER_TIMEOUT_MILLIS);
+        }
+
+        public Tab getTab() {
+            return mTab;
+        }
+
+    }
+
+}