lint/libs/lint-checks/src/main/java/com/android/tools/lint/checks/AppLinksAutoVerifyDetector.java - platform/tools/base - Git at Google

 /*
  * Copyright (C) 2015 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.tools.lint.checks;

 import static com.android.SdkConstants.ANDROID_URI;
 import static com.android.SdkConstants.ATTR_HOST;
 import static com.android.SdkConstants.ATTR_SCHEME;
 import static com.android.SdkConstants.MANIFEST_PLACEHOLDER_PREFIX;
 import static com.android.SdkConstants.MANIFEST_PLACEHOLDER_SUFFIX;
 import static com.android.SdkConstants.UTF_8;
 import static com.android.xml.AndroidManifest.ATTRIBUTE_NAME;
 import static com.android.xml.AndroidManifest.NODE_ACTION;
 import static com.android.xml.AndroidManifest.NODE_CATEGORY;
 import static com.android.xml.AndroidManifest.NODE_DATA;
 import static com.android.xml.AndroidManifest.NODE_INTENT;

 import com.android.SdkConstants;
 import com.android.annotations.NonNull;
 import com.android.annotations.Nullable;
 import com.android.tools.lint.detector.api.Category;
 import com.android.tools.lint.detector.api.Detector;
 import com.android.tools.lint.detector.api.Implementation;
 import com.android.tools.lint.detector.api.Issue;
 import com.android.tools.lint.detector.api.Scope;
 import com.android.tools.lint.detector.api.Severity;
 import com.android.tools.lint.detector.api.XmlContext;
 import com.android.tools.lint.detector.api.XmlScanner;
 import com.android.tools.lint.model.LintModelVariant;
 import com.google.common.annotations.VisibleForTesting;
 import com.google.common.collect.Lists;
 import com.google.common.collect.Maps;
 import com.google.gson.JsonArray;
 import com.google.gson.JsonElement;
 import com.google.gson.JsonObject;
 import com.google.gson.JsonParser;
 import com.google.gson.JsonSyntaxException;
 import java.io.BufferedReader;
 import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.io.InputStream;
 import java.io.InputStreamReader;
 import java.net.HttpURLConnection;
 import java.net.MalformedURLException;
 import java.net.URL;
 import java.net.UnknownHostException;
 import java.util.List;
 import java.util.Map;
 import java.util.concurrent.ExecutorService;
 import java.util.concurrent.Executors;
 import java.util.concurrent.Future;
 import org.w3c.dom.Attr;
 import org.w3c.dom.Document;
 import org.w3c.dom.Element;
 import org.w3c.dom.Node;
 import org.w3c.dom.NodeList;

 /** Check if the App Link which needs auto verification is correctly set. */
 public class AppLinksAutoVerifyDetector extends Detector implements XmlScanner {

     private static final Implementation IMPLEMENTATION =
             new Implementation(AppLinksAutoVerifyDetector.class, Scope.MANIFEST_SCOPE);

     public static final Issue ISSUE_ERROR =
             Issue.create(
                             "AppLinksAutoVerifyError",
                             "App Links Auto Verification Failure",
                             "Ensures that app links are correctly set and associated with website.",
                             Category.CORRECTNESS,
                             5,
                             Severity.ERROR,
                             IMPLEMENTATION)
                     .addMoreInfo("https://g.co/appindexing/applinks")
                     .setEnabledByDefault(false);

     public static final Issue ISSUE_WARNING =
             Issue.create(
                             "AppLinksAutoVerifyWarning",
                             "Potential App Links Auto Verification Failure",
                             "Ensures that app links are correctly set and associated with website.",
                             Category.CORRECTNESS,
                             5,
                             Severity.WARNING,
                             IMPLEMENTATION)
                     .addMoreInfo("https://g.co/appindexing/applinks")
                     .setEnabledByDefault(false);

     private static final String ATTRIBUTE_AUTO_VERIFY = "autoVerify";
     private static final String JSON_RELATIVE_PATH = "/.well-known/assetlinks.json";

     @VisibleForTesting static final int STATUS_HTTP_CONNECT_FAIL = -1;
     @VisibleForTesting static final int STATUS_MALFORMED_URL = -2;
     @VisibleForTesting static final int STATUS_UNKNOWN_HOST = -3;
     @VisibleForTesting static final int STATUS_NOT_FOUND = -4;
     @VisibleForTesting static final int STATUS_WRONG_JSON_SYNTAX = -5;
     @VisibleForTesting static final int STATUS_JSON_PARSE_FAIL = -6;
     @VisibleForTesting static final int STATUS_HTTP_OK = 200;

     /* Maps website host url to a future task which will send HTTP request to fetch the JSON file
      * and also return the status code during the fetching process. */
     private final Map<String, Future<HttpResult>> mFutures = Maps.newHashMap();

     /* Maps website host url to host attribute in AndroidManifest.xml. */
     private final Map<String, Attr> mJsonHost = Maps.newHashMap();

     @Override
     public void visitDocument(@NonNull XmlContext context, @NonNull Document document) {

         // This check sends http request. Only done in batch mode.
         if (!context.getScope().contains(Scope.ALL_JAVA_FILES)) {
             return;
         }

         if (document.getDocumentElement() != null) {
             List<Element> intents = getTags(document.getDocumentElement(), NODE_INTENT);
             if (!needAutoVerification(intents)) {
                 return;
             }

             for (Element intent : intents) {
                 boolean actionView =
                         hasNamedSubTag(intent, NODE_ACTION, "android.intent.action.VIEW");
                 boolean browsableCategory =
                         hasNamedSubTag(intent, NODE_CATEGORY, "android.intent.category.BROWSABLE");
                 if (!actionView || !browsableCategory) {
                     continue;
                 }
                 mJsonHost.putAll(getJsonUrl(context, intent));
             }
         }

         Map<String, HttpResult> results = getJsonFileAsync();

         String packageName = context.getProject().getPackage();
         for (Map.Entry<String, HttpResult> result : results.entrySet()) {
             if (result.getValue() == null) {
                 continue;
             }
             Attr host = mJsonHost.get(result.getKey());
             if (host == null) {
                 continue;
             }
             String jsonPath = result.getKey() + JSON_RELATIVE_PATH;
             switch (result.getValue().mStatus) {
                 case STATUS_HTTP_OK:
                     List<String> packageNames = getPackageNameFromJson(result.getValue().mJsonFile);
                     if (!packageNames.contains(packageName)) {
                         context.report(
                                 ISSUE_ERROR,
                                 host,
                                 context.getLocation(host),
                                 String.format(
                                         "This host does not support app links to your app. Checks the Digital Asset Links JSON file: %s",
                                         jsonPath));
                     }
                     break;
                 case STATUS_HTTP_CONNECT_FAIL:
                     context.report(
                             ISSUE_WARNING,
                             host,
                             context.getLocation(host),
                             String.format(
                                     "Connection to Digital Asset Links JSON file %s fails",
                                     jsonPath));
                     break;
                 case STATUS_MALFORMED_URL:
                     context.report(
                             ISSUE_ERROR,
                             host,
                             context.getLocation(host),
                             String.format(
                                     "Malformed URL of Digital Asset Links JSON file: %s. An unknown protocol is specified",
                                     jsonPath));
                     break;
                 case STATUS_UNKNOWN_HOST:
                     context.report(
                             ISSUE_WARNING,
                             host,
                             context.getLocation(host),
                             String.format(
                                     "Unknown host: %s. Check if the host exists, and check your network connection",
                                     result.getKey()));
                     break;
                 case STATUS_NOT_FOUND:
                     context.report(
                             ISSUE_ERROR,
                             host,
                             context.getLocation(host),
                             String.format(
                                     "Digital Asset Links JSON file %s is not found on the host",
                                     jsonPath));
                     break;
                 case STATUS_WRONG_JSON_SYNTAX:
                     context.report(
                             ISSUE_ERROR,
                             host,
                             context.getLocation(host),
                             String.format("%s has incorrect JSON syntax", jsonPath));
                     break;
                 case STATUS_JSON_PARSE_FAIL:
                     context.report(
                             ISSUE_ERROR,
                             host,
                             context.getLocation(host),
                             String.format("Parsing JSON file %s fails", jsonPath));
                     break;
                 default:
                     context.report(
                             ISSUE_WARNING,
                             host,
                             context.getLocation(host),
                             String.format(
                                     "HTTP request for Digital Asset Links JSON file %1$s fails. HTTP response code: %2$s",
                                     jsonPath, result.getValue().mStatus));
             }
         }
     }

     /**
      * Gets all the tag elements with a specific tag name, within a parent tag element.
      *
      * @param element The parent tag element.
      * @return List of tag elements found.
      */
     @NonNull
     private static List<Element> getTags(@NonNull Element element, @NonNull String tagName) {
         List<Element> tagList = Lists.newArrayList();
         if (element.getTagName().equalsIgnoreCase(tagName)) {
             tagList.add(element);
         } else {
             NodeList children = element.getChildNodes();
             for (int i = 0; i < children.getLength(); i++) {
                 Node child = children.item(i);
                 if (child instanceof Element) {
                     tagList.addAll(getTags((Element) child, tagName));
                 }
             }
         }
         return tagList;
     }

     /**
      * Checks if auto verification is needed. i.e. any intent tag element's autoVerify attribute is
      * set to true.
      *
      * @param intents The intent tag elements.
      * @return true if auto verification is needed.
      */
     private static boolean needAutoVerification(@NonNull List<Element> intents) {
         for (Element intent : intents) {
             if (intent.getAttributeNS(ANDROID_URI, ATTRIBUTE_AUTO_VERIFY)
                     .equals(SdkConstants.VALUE_TRUE)) {
                 return true;
             }
         }
         return false;
     }

     /**
      * Checks if the element has a sub tag with specific name and specific name attribute.
      *
      * @param element The tag element.
      * @param tagName The name of the sub tag.
      * @param nameAttrValue The value of the name attribute.
      * @return If the element has such a sub tag.
      */
     private static boolean hasNamedSubTag(
             @NonNull Element element, @NonNull String tagName, @NonNull String nameAttrValue) {
         NodeList children = element.getElementsByTagName(tagName);
         for (int i = 0; i < children.getLength(); i++) {
             Element e = (Element) children.item(i);
             if (e.getAttributeNS(ANDROID_URI, ATTRIBUTE_NAME).equals(nameAttrValue)) {
                 return true;
             }
         }
         return false;
     }

     /**
      * Gets the urls of all the host from which Digital Asset Links JSON files will be fetched.
      *
      * @param intent The intent tag element.
      * @return List of JSON file urls.
      */
     @NonNull
     private static Map<String, Attr> getJsonUrl(
             @NonNull XmlContext context, @NonNull Element intent) {
         List<String> schemes = Lists.newArrayList();
         List<Attr> hosts = Lists.newArrayList();
         NodeList dataTags = intent.getElementsByTagName(NODE_DATA);
         for (int k = 0; k < dataTags.getLength(); k++) {
             Element dataTag = (Element) dataTags.item(k);
             String scheme = dataTag.getAttributeNS(ANDROID_URI, ATTR_SCHEME);
             if (scheme.equals("http") || scheme.equals("https")) {
                 schemes.add(scheme);
             }
             if (dataTag.hasAttributeNS(ANDROID_URI, ATTR_HOST)) {
                 Attr host = dataTag.getAttributeNodeNS(ANDROID_URI, ATTR_HOST);
                 hosts.add(host);
             }
         }
         Map<String, Attr> urls = Maps.newHashMap();
         for (String scheme : schemes) {
             for (Attr host : hosts) {
                 String hostname = host.getValue();
                 if (hostname.startsWith(SdkConstants.MANIFEST_PLACEHOLDER_PREFIX)) {
                     hostname = resolvePlaceHolder(context, hostname);
                     if (hostname == null) {
                         continue;
                     }
                 }
                 urls.put(scheme + "://" + hostname, host);
             }
         }
         return urls;
     }

     @Nullable
     private static String resolvePlaceHolder(
             @NonNull XmlContext context, @NonNull String hostname) {
         assert hostname.startsWith(SdkConstants.MANIFEST_PLACEHOLDER_PREFIX);
         LintModelVariant variant = context.getProject().getBuildVariant();
         if (variant != null) {
             Map<String, String> placeHolders = variant.getManifestPlaceholders();
             String name =
                     hostname.substring(
                             MANIFEST_PLACEHOLDER_PREFIX.length(),
                             hostname.length() - MANIFEST_PLACEHOLDER_SUFFIX.length());
             return placeHolders.get(name);
         }
         return null;
     }

     /* Normally null. Used for testing. */
     @Nullable @VisibleForTesting static Map<String, HttpResult> sMockData;

     /**
      * Gets all the Digital Asset Links JSON file asynchronously.
      *
      * @return The map between the host url and the HTTP result.
      */
     private Map<String, HttpResult> getJsonFileAsync() {
         if (sMockData != null) {
             return sMockData;
         }

         ExecutorService executorService = Executors.newCachedThreadPool();
         for (final Map.Entry<String, Attr> url : mJsonHost.entrySet()) {
             Future<HttpResult> future =
                     executorService.submit(() -> getJson(url.getKey() + JSON_RELATIVE_PATH));
             mFutures.put(url.getKey(), future);
         }
         executorService.shutdown();

         Map<String, HttpResult> jsons = Maps.newHashMap();
         for (Map.Entry<String, Future<HttpResult>> future : mFutures.entrySet()) {
             try {
                 jsons.put(future.getKey(), future.getValue().get());
             } catch (Exception e) {
                 jsons.put(future.getKey(), null);
             }
         }
         return jsons;
     }

     /**
      * Gets the Digital Asset Links JSON file on the website host.
      *
      * @param url The URL of the host on which JSON file will be fetched.
      */
     @NonNull
     private static HttpResult getJson(@NonNull String url) {
         try {
             URL urlObj = new URL(url);
             HttpURLConnection connection = (HttpURLConnection) urlObj.openConnection();
             if (connection == null) {
                 return new HttpResult(STATUS_HTTP_CONNECT_FAIL, null);
             }
             try {
                 InputStream inputStream = connection.getInputStream();
                 if (inputStream == null) {
                     return new HttpResult(connection.getResponseCode(), null);
                 }
                 try (BufferedReader reader =
                         new BufferedReader(new InputStreamReader(inputStream, UTF_8))) {
                     String line;
                     StringBuilder response = new StringBuilder();
                     while ((line = reader.readLine()) != null) {
                         response.append(line);
                         response.append('\n');
                     }

                     try {
                         JsonElement jsonFile = new JsonParser().parse(response.toString());
                         return new HttpResult(connection.getResponseCode(), jsonFile);
                     } catch (JsonSyntaxException e) {
                         return new HttpResult(STATUS_WRONG_JSON_SYNTAX, null);
                     } catch (RuntimeException e) {
                         return new HttpResult(STATUS_JSON_PARSE_FAIL, null);
                     }
                 }
             } finally {
                 connection.disconnect();
             }
         } catch (MalformedURLException e) {
             return new HttpResult(STATUS_MALFORMED_URL, null);
         } catch (UnknownHostException e) {
             return new HttpResult(STATUS_UNKNOWN_HOST, null);
         } catch (FileNotFoundException e) {
             return new HttpResult(STATUS_NOT_FOUND, null);
         } catch (IOException e) {
             return new HttpResult(STATUS_HTTP_CONNECT_FAIL, null);
         }
     }

     /**
      * Gets the package names of all the apps from the Digital Asset Links JSON file.
      *
      * @param element The JsonElement of the json file.
      * @return All the package names.
      */
     private static List<String> getPackageNameFromJson(JsonElement element) {
         List<String> packageNames = Lists.newArrayList();
         if (element instanceof JsonArray) {
             JsonArray jsonArray = (JsonArray) element;
             for (int i = 0; i < jsonArray.size(); i++) {
                 JsonElement app = jsonArray.get(i);
                 if (app instanceof JsonObject) {
                     JsonObject target = ((JsonObject) app).getAsJsonObject("target");
                     if (target != null) {
                         // Checks namespace to ensure it is an app statement.
                         JsonElement namespace = target.get("namespace");
                         JsonElement packageName = target.get("package_name");
                         if (namespace != null
                                 && namespace.getAsString().equals("android_app")
                                 && packageName != null) {
                             packageNames.add(packageName.getAsString());
                         }
                     }
                 }
             }
         }
         return packageNames;
     }

     /* For storing the result of getting Digital Asset Links Json File */
     @VisibleForTesting
     static final class HttpResult {

         /* HTTP response code or others errors related to HTTP connection, JSON file parsing. */
         private final int mStatus;
         private final JsonElement mJsonFile;

         @VisibleForTesting
         HttpResult(int status, JsonElement jsonFile) {
             mStatus = status;
             mJsonFile = jsonFile;
         }
     }
 }
	/*
	* Copyright (C) 2015 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.tools.lint.checks;

	import static com.android.SdkConstants.ANDROID_URI;
	import static com.android.SdkConstants.ATTR_HOST;
	import static com.android.SdkConstants.ATTR_SCHEME;
	import static com.android.SdkConstants.MANIFEST_PLACEHOLDER_PREFIX;
	import static com.android.SdkConstants.MANIFEST_PLACEHOLDER_SUFFIX;
	import static com.android.SdkConstants.UTF_8;
	import static com.android.xml.AndroidManifest.ATTRIBUTE_NAME;
	import static com.android.xml.AndroidManifest.NODE_ACTION;
	import static com.android.xml.AndroidManifest.NODE_CATEGORY;
	import static com.android.xml.AndroidManifest.NODE_DATA;
	import static com.android.xml.AndroidManifest.NODE_INTENT;

	import com.android.SdkConstants;
	import com.android.annotations.NonNull;
	import com.android.annotations.Nullable;
	import com.android.tools.lint.detector.api.Category;
	import com.android.tools.lint.detector.api.Detector;
	import com.android.tools.lint.detector.api.Implementation;
	import com.android.tools.lint.detector.api.Issue;
	import com.android.tools.lint.detector.api.Scope;
	import com.android.tools.lint.detector.api.Severity;
	import com.android.tools.lint.detector.api.XmlContext;
	import com.android.tools.lint.detector.api.XmlScanner;
	import com.android.tools.lint.model.LintModelVariant;
	import com.google.common.annotations.VisibleForTesting;
	import com.google.common.collect.Lists;
	import com.google.common.collect.Maps;
	import com.google.gson.JsonArray;
	import com.google.gson.JsonElement;
	import com.google.gson.JsonObject;
	import com.google.gson.JsonParser;
	import com.google.gson.JsonSyntaxException;
	import java.io.BufferedReader;
	import java.io.FileNotFoundException;
	import java.io.IOException;
	import java.io.InputStream;
	import java.io.InputStreamReader;
	import java.net.HttpURLConnection;
	import java.net.MalformedURLException;
	import java.net.URL;
	import java.net.UnknownHostException;
	import java.util.List;
	import java.util.Map;
	import java.util.concurrent.ExecutorService;
	import java.util.concurrent.Executors;
	import java.util.concurrent.Future;
	import org.w3c.dom.Attr;
	import org.w3c.dom.Document;
	import org.w3c.dom.Element;
	import org.w3c.dom.Node;
	import org.w3c.dom.NodeList;

	/** Check if the App Link which needs auto verification is correctly set. */
	public class AppLinksAutoVerifyDetector extends Detector implements XmlScanner {

	private static final Implementation IMPLEMENTATION =
	new Implementation(AppLinksAutoVerifyDetector.class, Scope.MANIFEST_SCOPE);

	public static final Issue ISSUE_ERROR =
	Issue.create(
	"AppLinksAutoVerifyError",
	"App Links Auto Verification Failure",
	"Ensures that app links are correctly set and associated with website.",
	Category.CORRECTNESS,
	5,
	Severity.ERROR,
	IMPLEMENTATION)
	.addMoreInfo("https://g.co/appindexing/applinks")
	.setEnabledByDefault(false);

	public static final Issue ISSUE_WARNING =
	Issue.create(
	"AppLinksAutoVerifyWarning",
	"Potential App Links Auto Verification Failure",
	"Ensures that app links are correctly set and associated with website.",
	Category.CORRECTNESS,
	5,
	Severity.WARNING,
	IMPLEMENTATION)
	.addMoreInfo("https://g.co/appindexing/applinks")
	.setEnabledByDefault(false);

	private static final String ATTRIBUTE_AUTO_VERIFY = "autoVerify";
	private static final String JSON_RELATIVE_PATH = "/.well-known/assetlinks.json";

	@VisibleForTesting static final int STATUS_HTTP_CONNECT_FAIL = -1;
	@VisibleForTesting static final int STATUS_MALFORMED_URL = -2;
	@VisibleForTesting static final int STATUS_UNKNOWN_HOST = -3;
	@VisibleForTesting static final int STATUS_NOT_FOUND = -4;
	@VisibleForTesting static final int STATUS_WRONG_JSON_SYNTAX = -5;
	@VisibleForTesting static final int STATUS_JSON_PARSE_FAIL = -6;
	@VisibleForTesting static final int STATUS_HTTP_OK = 200;

	/* Maps website host url to a future task which will send HTTP request to fetch the JSON file
	* and also return the status code during the fetching process. */
	private final Map<String, Future<HttpResult>> mFutures = Maps.newHashMap();

	/* Maps website host url to host attribute in AndroidManifest.xml. */
	private final Map<String, Attr> mJsonHost = Maps.newHashMap();

	@Override
	public void visitDocument(@NonNull XmlContext context, @NonNull Document document) {

	// This check sends http request. Only done in batch mode.
	if (!context.getScope().contains(Scope.ALL_JAVA_FILES)) {
	return;
	}

	if (document.getDocumentElement() != null) {
	List<Element> intents = getTags(document.getDocumentElement(), NODE_INTENT);
	if (!needAutoVerification(intents)) {
	return;
	}

	for (Element intent : intents) {
	boolean actionView =
	hasNamedSubTag(intent, NODE_ACTION, "android.intent.action.VIEW");
	boolean browsableCategory =
	hasNamedSubTag(intent, NODE_CATEGORY, "android.intent.category.BROWSABLE");
	if (!actionView \|\| !browsableCategory) {
	continue;
	}
	mJsonHost.putAll(getJsonUrl(context, intent));
	}
	}

	Map<String, HttpResult> results = getJsonFileAsync();

	String packageName = context.getProject().getPackage();
	for (Map.Entry<String, HttpResult> result : results.entrySet()) {
	if (result.getValue() == null) {
	continue;
	}
	Attr host = mJsonHost.get(result.getKey());
	if (host == null) {
	continue;
	}
	String jsonPath = result.getKey() + JSON_RELATIVE_PATH;
	switch (result.getValue().mStatus) {
	case STATUS_HTTP_OK:
	List<String> packageNames = getPackageNameFromJson(result.getValue().mJsonFile);
	if (!packageNames.contains(packageName)) {
	context.report(
	ISSUE_ERROR,
	host,
	context.getLocation(host),
	String.format(
	"This host does not support app links to your app. Checks the Digital Asset Links JSON file: %s",
	jsonPath));
	}
	break;
	case STATUS_HTTP_CONNECT_FAIL:
	context.report(
	ISSUE_WARNING,
	host,
	context.getLocation(host),
	String.format(
	"Connection to Digital Asset Links JSON file %s fails",
	jsonPath));
	break;
	case STATUS_MALFORMED_URL:
	context.report(
	ISSUE_ERROR,
	host,
	context.getLocation(host),
	String.format(
	"Malformed URL of Digital Asset Links JSON file: %s. An unknown protocol is specified",
	jsonPath));
	break;
	case STATUS_UNKNOWN_HOST:
	context.report(
	ISSUE_WARNING,
	host,
	context.getLocation(host),
	String.format(
	"Unknown host: %s. Check if the host exists, and check your network connection",
	result.getKey()));
	break;
	case STATUS_NOT_FOUND:
	context.report(
	ISSUE_ERROR,
	host,
	context.getLocation(host),
	String.format(
	"Digital Asset Links JSON file %s is not found on the host",
	jsonPath));
	break;
	case STATUS_WRONG_JSON_SYNTAX:
	context.report(
	ISSUE_ERROR,
	host,
	context.getLocation(host),
	String.format("%s has incorrect JSON syntax", jsonPath));
	break;
	case STATUS_JSON_PARSE_FAIL:
	context.report(
	ISSUE_ERROR,
	host,
	context.getLocation(host),
	String.format("Parsing JSON file %s fails", jsonPath));
	break;
	default:
	context.report(
	ISSUE_WARNING,
	host,
	context.getLocation(host),
	String.format(
	"HTTP request for Digital Asset Links JSON file %1$s fails. HTTP response code: %2$s",
	jsonPath, result.getValue().mStatus));
	}
	}
	}

	/**
	* Gets all the tag elements with a specific tag name, within a parent tag element.
	*
	* @param element The parent tag element.
	* @return List of tag elements found.
	*/
	@NonNull
	private static List<Element> getTags(@NonNull Element element, @NonNull String tagName) {
	List<Element> tagList = Lists.newArrayList();
	if (element.getTagName().equalsIgnoreCase(tagName)) {
	tagList.add(element);
	} else {
	NodeList children = element.getChildNodes();
	for (int i = 0; i < children.getLength(); i++) {
	Node child = children.item(i);
	if (child instanceof Element) {
	tagList.addAll(getTags((Element) child, tagName));
	}
	}
	}
	return tagList;
	}

	/**
	* Checks if auto verification is needed. i.e. any intent tag element's autoVerify attribute is
	* set to true.
	*
	* @param intents The intent tag elements.
	* @return true if auto verification is needed.
	*/
	private static boolean needAutoVerification(@NonNull List<Element> intents) {
	for (Element intent : intents) {
	if (intent.getAttributeNS(ANDROID_URI, ATTRIBUTE_AUTO_VERIFY)
	.equals(SdkConstants.VALUE_TRUE)) {
	return true;
	}
	}
	return false;
	}

	/**
	* Checks if the element has a sub tag with specific name and specific name attribute.
	*
	* @param element The tag element.
	* @param tagName The name of the sub tag.
	* @param nameAttrValue The value of the name attribute.
	* @return If the element has such a sub tag.
	*/
	private static boolean hasNamedSubTag(
	@NonNull Element element, @NonNull String tagName, @NonNull String nameAttrValue) {
	NodeList children = element.getElementsByTagName(tagName);
	for (int i = 0; i < children.getLength(); i++) {
	Element e = (Element) children.item(i);
	if (e.getAttributeNS(ANDROID_URI, ATTRIBUTE_NAME).equals(nameAttrValue)) {
	return true;
	}
	}
	return false;
	}

	/**
	* Gets the urls of all the host from which Digital Asset Links JSON files will be fetched.
	*
	* @param intent The intent tag element.
	* @return List of JSON file urls.
	*/
	@NonNull
	private static Map<String, Attr> getJsonUrl(
	@NonNull XmlContext context, @NonNull Element intent) {
	List<String> schemes = Lists.newArrayList();
	List<Attr> hosts = Lists.newArrayList();
	NodeList dataTags = intent.getElementsByTagName(NODE_DATA);
	for (int k = 0; k < dataTags.getLength(); k++) {
	Element dataTag = (Element) dataTags.item(k);
	String scheme = dataTag.getAttributeNS(ANDROID_URI, ATTR_SCHEME);
	if (scheme.equals("http") \|\| scheme.equals("https")) {
	schemes.add(scheme);
	}
	if (dataTag.hasAttributeNS(ANDROID_URI, ATTR_HOST)) {
	Attr host = dataTag.getAttributeNodeNS(ANDROID_URI, ATTR_HOST);
	hosts.add(host);
	}
	}
	Map<String, Attr> urls = Maps.newHashMap();
	for (String scheme : schemes) {
	for (Attr host : hosts) {
	String hostname = host.getValue();
	if (hostname.startsWith(SdkConstants.MANIFEST_PLACEHOLDER_PREFIX)) {
	hostname = resolvePlaceHolder(context, hostname);
	if (hostname == null) {
	continue;
	}
	}
	urls.put(scheme + "://" + hostname, host);
	}
	}
	return urls;
	}

	@Nullable
	private static String resolvePlaceHolder(
	@NonNull XmlContext context, @NonNull String hostname) {
	assert hostname.startsWith(SdkConstants.MANIFEST_PLACEHOLDER_PREFIX);
	LintModelVariant variant = context.getProject().getBuildVariant();
	if (variant != null) {
	Map<String, String> placeHolders = variant.getManifestPlaceholders();
	String name =
	hostname.substring(
	MANIFEST_PLACEHOLDER_PREFIX.length(),
	hostname.length() - MANIFEST_PLACEHOLDER_SUFFIX.length());
	return placeHolders.get(name);
	}
	return null;
	}

	/* Normally null. Used for testing. */
	@Nullable @VisibleForTesting static Map<String, HttpResult> sMockData;

	/**
	* Gets all the Digital Asset Links JSON file asynchronously.
	*
	* @return The map between the host url and the HTTP result.
	*/
	private Map<String, HttpResult> getJsonFileAsync() {
	if (sMockData != null) {
	return sMockData;
	}

	ExecutorService executorService = Executors.newCachedThreadPool();
	for (final Map.Entry<String, Attr> url : mJsonHost.entrySet()) {
	Future<HttpResult> future =
	executorService.submit(() -> getJson(url.getKey() + JSON_RELATIVE_PATH));
	mFutures.put(url.getKey(), future);
	}
	executorService.shutdown();

	Map<String, HttpResult> jsons = Maps.newHashMap();
	for (Map.Entry<String, Future<HttpResult>> future : mFutures.entrySet()) {
	try {
	jsons.put(future.getKey(), future.getValue().get());
	} catch (Exception e) {
	jsons.put(future.getKey(), null);
	}
	}
	return jsons;
	}

	/**
	* Gets the Digital Asset Links JSON file on the website host.
	*
	* @param url The URL of the host on which JSON file will be fetched.
	*/
	@NonNull
	private static HttpResult getJson(@NonNull String url) {
	try {
	URL urlObj = new URL(url);
	HttpURLConnection connection = (HttpURLConnection) urlObj.openConnection();
	if (connection == null) {
	return new HttpResult(STATUS_HTTP_CONNECT_FAIL, null);
	}
	try {
	InputStream inputStream = connection.getInputStream();
	if (inputStream == null) {
	return new HttpResult(connection.getResponseCode(), null);
	}
	try (BufferedReader reader =
	new BufferedReader(new InputStreamReader(inputStream, UTF_8))) {
	String line;
	StringBuilder response = new StringBuilder();
	while ((line = reader.readLine()) != null) {
	response.append(line);
	response.append('\n');
	}

	try {
	JsonElement jsonFile = new JsonParser().parse(response.toString());
	return new HttpResult(connection.getResponseCode(), jsonFile);
	} catch (JsonSyntaxException e) {
	return new HttpResult(STATUS_WRONG_JSON_SYNTAX, null);
	} catch (RuntimeException e) {
	return new HttpResult(STATUS_JSON_PARSE_FAIL, null);
	}
	}
	} finally {
	connection.disconnect();
	}
	} catch (MalformedURLException e) {
	return new HttpResult(STATUS_MALFORMED_URL, null);
	} catch (UnknownHostException e) {
	return new HttpResult(STATUS_UNKNOWN_HOST, null);
	} catch (FileNotFoundException e) {
	return new HttpResult(STATUS_NOT_FOUND, null);
	} catch (IOException e) {
	return new HttpResult(STATUS_HTTP_CONNECT_FAIL, null);
	}
	}

	/**
	* Gets the package names of all the apps from the Digital Asset Links JSON file.
	*
	* @param element The JsonElement of the json file.
	* @return All the package names.
	*/
	private static List<String> getPackageNameFromJson(JsonElement element) {
	List<String> packageNames = Lists.newArrayList();
	if (element instanceof JsonArray) {
	JsonArray jsonArray = (JsonArray) element;
	for (int i = 0; i < jsonArray.size(); i++) {
	JsonElement app = jsonArray.get(i);
	if (app instanceof JsonObject) {
	JsonObject target = ((JsonObject) app).getAsJsonObject("target");
	if (target != null) {
	// Checks namespace to ensure it is an app statement.
	JsonElement namespace = target.get("namespace");
	JsonElement packageName = target.get("package_name");
	if (namespace != null
	&& namespace.getAsString().equals("android_app")
	&& packageName != null) {
	packageNames.add(packageName.getAsString());
	}
	}
	}
	}
	}
	return packageNames;
	}

	/* For storing the result of getting Digital Asset Links Json File */
	@VisibleForTesting
	static final class HttpResult {

	/* HTTP response code or others errors related to HTTP connection, JSON file parsing. */
	private final int mStatus;
	private final JsonElement mJsonFile;

	@VisibleForTesting
	HttpResult(int status, JsonElement jsonFile) {
	mStatus = status;
	mJsonFile = jsonFile;
	}
	}
	}