Generate license html file from xml files of partitions

Treble-ization requires each partner to store their license information
into their own partition because each partition can be updated
individually.
So each partition will have its own NOTICE.xml.gz, and Settings should
be able to generate license html from xml files of partitions.

Test: building succeeded and tested on sailfish.
  make ROBOTEST_FILTER=LicenseHtmlGeneratorFromXmlTest RunSettingsRoboTests
  make ROBOTEST_FILTER=LicenseHtmlLoaderTest RunSettingsRoboTests
  make ROBOTEST_FILTER=SettingsLicenseActivityTest RunSettingsRoboTests
Bug: 37099941
Change-Id: If797759d300ee20dd43ad8efd7d17b4f7e0c4537

src/com/android/settings/LicenseHtmlLoader.java

@@ -0,0 +1,110 @@
+/*
+ * Copyright (C) 2017 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.settings;
+
+import android.content.Context;
+import android.support.annotation.VisibleForTesting;
+import android.util.Log;
+
+import com.android.settings.utils.AsyncLoader;
+
+import java.io.File;
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * LicenseHtmlLoader is a loader which loads a license html file from default license xml files.
+ */
+class LicenseHtmlLoader extends AsyncLoader<File> {
+    private static final String TAG = "LicenseHtmlLoader";
+
+    private static final String[] DEFAULT_LICENSE_XML_PATHS = {
+                "/system/etc/NOTICE.xml.gz",
+                "/vendor/etc/NOTICE.xml.gz",
+                "/odm/etc/NOTICE.xml.gz",
+                "/oem/etc/NOTICE.xml.gz"};
+    private static final String NOTICE_HTML_FILE_NAME = "NOTICE.html";
+
+    private Context mContext;
+
+    public LicenseHtmlLoader(Context context) {
+        super(context);
+        mContext = context;
+    }
+
+    @Override
+    public File loadInBackground() {
+        return generateHtmlFromDefaultXmlFiles();
+    }
+
+    @Override
+    protected void onDiscardResult(File f) {
+    }
+
+    private File generateHtmlFromDefaultXmlFiles() {
+        final List<File> xmlFiles = getVaildXmlFiles();
+        if (xmlFiles.isEmpty()) {
+            Log.e(TAG, "No notice file exists.");
+            return null;
+        }
+
+        File cachedHtmlFile = getCachedHtmlFile();
+        if(!isCachedHtmlFileOutdated(xmlFiles, cachedHtmlFile) ||
+                generateHtmlFile(xmlFiles, cachedHtmlFile)) {
+            return cachedHtmlFile;
+        }
+
+        return null;
+    }
+
+    @VisibleForTesting
+    List<File> getVaildXmlFiles() {
+        final List<File> xmlFiles = new ArrayList();
+        for (final String xmlPath : DEFAULT_LICENSE_XML_PATHS) {
+            File file = new File(xmlPath);
+            if (file.exists() && file.length() != 0) {
+                xmlFiles.add(file);
+            }
+        }
+        return xmlFiles;
+    }
+
+    @VisibleForTesting
+    File getCachedHtmlFile() {
+        return new File(mContext.getCacheDir(), NOTICE_HTML_FILE_NAME);
+    }
+
+    @VisibleForTesting
+    boolean isCachedHtmlFileOutdated(List<File> xmlFiles, File cachedHtmlFile) {
+        boolean outdated = true;
+        if (cachedHtmlFile.exists() && cachedHtmlFile.length() != 0) {
+            outdated = false;
+            for (File file : xmlFiles) {
+                if (cachedHtmlFile.lastModified() < file.lastModified()) {
+                    outdated = true;
+                    break;
+                }
+            }
+        }
+        return outdated;
+    }
+
+    @VisibleForTesting
+    boolean generateHtmlFile(List<File> xmlFiles, File htmlFile) {
+        return LicenseHtmlGeneratorFromXml.generateHtml(xmlFiles, htmlFile);
+    }
+}