preview/features/app-linking.jd

page.title=App Links
page.image=images/cards/card-app-linking_2x.png
page.keywords=applinking, deeplinks, intents
@jd:body

<div id="qv-wrapper">
  <div id="qv">
    <h2>In this document</h2>
      <ol>
        <li><a href="#url-handling">Understanding URL Request Handling</a> </li>
        <li><a href="#intent-handler">Create an Intent Handler for URLs</a></li>
        <li><a href="#request-verify">Request App Links Verification</a></li>
        <li><a href="#web-assoc">Declare Website Associations</a></li>
        <li><a href="#testing">Testing App Links</a></li>
      </ol>
  </div>
</div>


<p>
  The M Developer Preview introduces a new option for handling web site links, allowing clicked
  links to go directly to the website's official app, instead of asking the user to chose how to
  handle the link. This feature saves the user time and helps developers deliver a better
  experience. Users can also select whether an app should always open specific types of links
  automatically or prompt the user each time.
</p>

<p>
  Handling links automatically requires the cooperation of app developers and website owners.
  Developers must configure their apps to declare connections with websites and request
  verification. Website owners can publish a
  Digital Asset Links file
  to allow Android to verify the association of apps with their sites. The general steps for
  creating verified app links are as follows:
</p>

<ol>
  <li>Create intent filters within your app for your website URLs</li>
  <li>Configure your app to request verification of app links</li>
  <li>Publish a Digital Asset Links JSON file on your websites</li>
</ol>

<h2 id="url-handling">Understanding URL Request Handling</h2>

<p>
  The app links feature allows your app to become the default handler for your website URLs, as
  long as the user has not already chosen an app to handle that URL pattern. When a web URI intent
  is invoked through a clicked link or programatic request, the Android system determines what app
  is used to handle the intent. The system use these criteria, in order, to determine how to handle
  the request:
</p>

<ol>
  <li>
    <strong>User has set app link associations</strong>: If the user has designated an app to
    handle app links, the system passes the web URI request to that app. Users set this association
    by opening <strong>Settings &gt; Apps &gt; Configure apps (gear icon) &gt; App links</strong>,
    then selecting an app to use and configuring it's <strong>App links</strong> property to the
    <em>Open in this app</em> option.
  </li>

  <li>
    <strong>No association set by user and a single supporting app</strong>: If the user
    has not set a preference that matches the web URI request, and there is only one app declaring
    support for the intents URI pattern, the system passes the request to that app.
  </li>

  <li>
    <strong>No association set by user and multiple supporting apps</strong>: If there is
    no explicit user preference and there are multiple apps declaring support for the web URI
    pattern, the system prompts the user to select one of the available apps
  </li>
</ol>

<p>
  In case #2 (no user setting and no other app handlers), if an app is newly installed and verified
  as a handler for this type of link, the system sets it as the default handler. In the other two
  cases, the system behavior is the same, regardless of the presence of a verified app link
  handler.
</p>


<h2 id="intent-handler">Create an Intent Handler for URLs</h2>

<p>
  App links are based on the <a href="{@docRoot}guide/components/intents-filters.html">Intent</a>
  framework, which enables apps to handle requests from the system or other apps. Multiple apps may
  declare matching web link URI patterns in their intent filters. When a user clicks on a web link
  that does not have a default launch handler, the platform selects an app to handle the request,
  based on the criteria described in the previous section.
</p>

<p>
  To enable your app to handle links, use intent filters in your app manifest to declare the URI
  patterns to be handled by your app. The following sample code shows an intent filter that can
  handle links to {@code http://www.android.com} and {@code https://www.android.com}:
</p>

<pre>
  &lt;activity ...&gt;
      &lt;intent-filter&gt;
          &lt;action android:name="android.intent.action.VIEW" /&gt;
          &lt;category android:name="android.intent.category.DEFAULT" /&gt;
          &lt;category android:name="android.intent.category.BROWSABLE" /&gt;
          &lt;data android:scheme="http" /&gt;
          &lt;data android:scheme="https" /&gt;
          &lt;data android:host="www.android.com" /&gt;
      &lt;/intent-filter&gt;
  &lt;/activity&gt;
</pre>

<p>
  As shown in the example above, intent filters for app links must declare an {@code android:scheme}
  value of either {@code http} or {@code https}, or both. The filter should not declare
  any other schemes. The filter must also include the {@code android.intent.action.VIEW}; and
  {@code android.intent.category.BROWSABLE} category names.
</p>

<p>
  This manifest declaration defines the connection between your app and a website. However, in
  order to have the system treat your app as the default handler for a set of URLs, you must
  also request that the system verify this connection, which is explained in the next section.
</p>


<h2 id="request-verify">Request App Links Verification</h2>

<p>
  In addition to declaring an association between your app and a web site using intent filters,
  your app must also request automatic verification with an additional manifest declaration. When
  this declaration is set, the Android system attempts to verify your app after it is installed.
  If the verification succeeds, and the user has not set a preference for your website URLs, the
  system automatically routes those URL requests to your app.
</p>

<p>
  The system performs app link verifications by comparing the host names in the data elements of
  the apps intent filters against the Digital Asset Links files ({@code assetlinks.json}) hosted
  on the respective web domains. To enable the system to verify a host, make sure that your intent
  filter declarations include the {@code android.intent.action.VIEW} intent action and {@code
  android.intent.category.BROWSABLE} intent category.
</p>


<h3 id="config-verify">Enabling automatic verification</h3>

<p>
  To enable link handling verification for your app, set the {@code android:autoVerify} attribute to
  {@code true} on at least one of the web URI intent filters in your app manifest, as shown in the
  following manifest code snippet:
</p>

<pre>
&lt;activity ...&gt;

    &lt;intent-filter <strong>android:autoVerify="true"</strong>&gt;
        &lt;action android:name="android.intent.action.VIEW" /&gt;
        &lt;category android:name="android.intent.category.DEFAULT"gt;
        &lt;category android:name="android.intent.category.BROWSABLE" /&gt;
        &lt;data android:scheme="http" android:host="www.android.com" /&gt;
        &lt;data android:scheme="https" android:host="www.android.com" /&gt;
    &lt;/intent-filter&gt;

&lt;/activity&gt;
</pre>

<p>
  When the {@code android:autoVerify} attribute is set, the system attempts to verify all hosts
  associated with web URIs in all of your app's intent filters when the app is installed. The
  system treats your app as the default handler for the specified URI pattern only if it
  successfully verifies <em>all</em> app link patterns declared in your manifest.
</p>


<h3 id="multi-host">Supporting app linking for multiple hosts</h3>

<p>
  The system must be able to verify each host specified in the apps web URI intent filters data
  elements against the Digital Asset Links files hosted on the respective web domains. If any
  verification fails, the app is not verified to be a default handler for any of the web URL
  patterns defined in its intent filters. For example, an app with the following intent filters
  would fail verification if an {@code assetlinks.json} file were not found at both
  {@code https://www.domain1.com/.well-known/assetlinks.json} and
  {@code https://www.domain2.com/.well-known/assetlinks.json}:
</p>

<pre>
&lt;application&gt;

  &lt;activity android:name=MainActivity&gt;
    &lt;intent-filter <strong>android:autoVerify="true"</strong>&gt;
      &lt;action android:name="android.intent.action.VIEW" /&gt;
      &lt;category android:name="android.intent.category.DEFAULT" /&gt;
      &lt;category android:name="android.intent.category.BROWSABLE" /&gt;
      &lt;data android:scheme="http" android:host="www.domain1.com" /&gt;
      &lt;data android:scheme="https" android:host="www.domain1.com" /&gt;
    &lt;/intent-filter&gt;
  &lt;/activity&gt;
  &lt;activity android:name=SecondActivity&gt;
    &lt;intent-filter&gt;
      &lt;action android:name="android.intent.action.VIEW" /&gt;
      &lt;category android:name="android.intent.category.DEFAULT" /&gt;
      &lt;category android:name="android.intent.category.BROWSABLE" /&gt;
      &lt;data android:scheme="https" android:host="www.domain2.com" /&gt;
    &lt;/intent-filter&gt;
  &lt;/activity&gt;

&lt;/application
</pre>


<h3 id="multi-subdomain">Supporting app linking for multiple subdomains</h3>

<p>
  The Digital Asset Links protocol treats subdomains as unique, separate hosts. If your intent
  filter lists both the {@code www.example.com} and {@code mobile.example.com} subdomains as
  schemes, you must host separate {@code assetlink.json} file on each subdomain. For example, an
  app with the following intent filter declaration would pass verification only if the website
  owner published valid {@code assetlinks.json} files at both
  {@code https://www.example.com/.well-known/assetlinks.json} and
  {@code https://mobile.example.com/.well-known/assetlinks.json}:
</p>

<pre>
&lt;application&gt;
  &lt;activity android:name=MainActivity&gt;
    &lt;intent-filter <strong>android:autoVerify="true"</strong>&gt;
      &lt;action android:name="android.intent.action.VIEW" /&gt;
      &lt;category android:name="android.intent.category.DEFAULT" /&gt;
      &lt;category android:name="android.intent.category.BROWSABLE" /&gt;
      &lt;data android:scheme="http" android:host="www.example.com" /&gt;
      &lt;data android:scheme="https" android:host="mobile.example.com" /&gt;
    &lt;/intent-filter&gt;
  &lt;/activity&gt;
&lt;/application&gt;
</pre>


<h2 id="web-assoc">Declare Website Associations</h2>

<p>
  For app link verification to be successful, website owners must declare associations
  with apps. A site owner declares the relationship to an app by hosting a Digital Asset Links JSON
  file, with the name {@code assetlinks.json}, at the following well-known location on the domain:
</p>

<pre>
  https://<em>domain</em>[:<em>optional_port</em>]/.well-known/assetlinks.json
</pre>

<p class="note">
  <strong>Important:</strong> With M Preview 3 and the Android 6.0 (API level 23) release, the JSON
  file is verified via the encrypted HTTPS protocol. Make sure that your hosted file can be
  accessed over an HTTPS connection, regardless of whether your app's intent filter declares an
  {@code android:scheme} setting of {@code http}, {@code https} or both.
</p>

<p>
  A Digital Asset Links JSON file indicates the Android apps that are associated with the web site.
  The JSON file identifies associated apps with the following fields:
</p>

<ul>
  <li>{@code package_name}: The package name declared in the app's manifest.</li>

  <li>{@code sha256_cert_fingerprints}: The SHA256 fingerprints of your apps signing certificate.
    You can use the Java keytool to generate the fingerprint using the following command:
    <pre>keytool -list -v -keystore my-release-key.keystore</pre>
    This field supports multiple fingerprints, which can be used to support different versions
    of your app, such as debug and production builds.
  </li>
</ul>

<p>
  The following example {@code assetlinks.json} file grants link opening rights to a
  {@code com.example} Android application:
</p>

<pre>
  [{
    "relation": ["delegate_permission/common.handle_all_urls"],
    "target": {
      "namespace": "android_app",
      "package_name": "com.example",
      "sha256_cert_fingerprints":
      ["14:6D:E9:83:C5:73:06:50:D8:EE:B9:95:2F:34:FC:64:16:A0:83:42:E6:1D:BE:A8:8A:04:96:B2:3F:CF:44:E5"]
    }
  }]
</pre>


<h3 id="multiple-apps">Associating a website with multiple apps</h3>

<p>
  A website can declare associations with multiple apps within the same {@code assetlinks.json}
  file. The following file listing shows an example of a statement file that declares association
  with two, separate apps and is hosted at
  <code>https://www.example.com/.well-known/assetlinks.json</code>:
</p>

<pre>
[{
  "relation": ["delegate_permission/common.handle_all_urls"],
  "target": {
    "namespace": "android_app",
    "package_name": <strong>"example.com.puppies.app"</strong>,
    "sha256_cert_fingerprints":
    ["<strong>14:6D:E9:83:C5:73:06:50:D8:EE:B9:95:2F:34:FC:64:16:A0:83:42:E6:1D:BE:A8:8A:04:96:B2:3F:CF:44:E5</strong>"]
  }
  },
  {
  "relation": ["delegate_permission/common.handle_all_urls"],
  "target": {
    "namespace": "android_app",
    "package_name": "<strong>example.com.monkeys.app</strong>",
    "sha256_cert_fingerprints":
    ["<strong>14:6D:E9:83:C5:73:06:50:D8:EE:B9:95:2F:34:FC:64:16:A0:83:42:E6:1D:BE:A8:8A:04:96:B2:3F:CF:44:E5</strong>"]
  }
}]
</pre>

<p>
  When multiple apps handle links to the same host, the system determines which one to use for
  a given link based on the intent filters defined in each apps manifest. Different apps may
  handle links for different resources under the same web host. For example, app1 may
  declare an intent filter for {@code https://example.com/articles}, and app2 may declare
  an intent filter for {@code https://example.com/videos}.
</p>

<p class="note">
  <strong>Note:</strong> Multiple apps associated with a domain may be signed with the same or
  different certificates.
</p>


<h3 id="multi-site">Associating multiple websites with a single app</h3>

<p>
  Multiple websites can declare associations with the same app in their respective {@code
  assetlinks.json} files. The following file listings show an example of how to declare the
  association of domain1 and domain2 with app1:
</p>

<pre>
https://www.domain1.com/.well-known/assetlinks.json

[{
  "relation": ["delegate_permission/common.handle_all_urls"],
  "target": {
    "namespace": "android_app",
    "package_name": "<strong>com.mycompany.app1</strong>",
    "sha256_cert_fingerprints":
    ["<strong>14:6D:E9:83:C5:73:06:50:D8:EE:B9:95:2F:34:FC:64:16:A0:83:42:E6:1D:BE:A8:8A:04:96:B2:3F:CF:44:E5</strong>"]
  }
}]
</pre>

<pre>
https://www.domain2.com/.well-known/assetlinks.json

[{
  "relation": ["delegate_permission/common.handle_all_urls"],
  "target": {
    "namespace": "android_app",
    "package_name": "<strong>com.mycompany.app1</strong>",
    "sha256_cert_fingerprints":
    ["<strong>14:6D:E9:83:C5:73:06:50:D8:EE:B9:95:2F:34:FC:64:16:A0:83:42:E6:1D:BE:A8:8A:04:96:B2:3F:CF:44:E5</strong>"]
  }
}]
</pre>


<h2 id="testing">Testing App Links</h2>

<p>
  When implementing the app linking feature, you should test the linking functionality to
  make your app can be successfully associated with your websites and handle URL requests
  as you expect.
</p>


<h3 id="test-hosts">Confirm the list of hosts to verify</h3>

<p>
  When testing, you should confirm the list of associated hosts that the system should verify
  for your app. Make a list of all web URIs in intent-filters in your manifest that
  includes the following:
</p>

<ul>
  <li>{@code android:scheme} attribute with a value of {@code http} or {@code https}
  </li>
  <li>{@code android:host} attribute with a domain URI pattern
  </li>
  <li>{@code android.intent.action.VIEW} category element
  </li>
  <li>{@code android.intent.category.BROWSABLE} category element
  </li>
</ul>

<p>
  Use this list to check that a Digital Asset Links JSON file is provided on each named host
  and subdomain.
</p>


<h3 id="test-dal-files">Confirm the Digital Asset Links files</h3>

<p>
  For each website, confirm that the Digital Asset Links JSON file is properly hosted and
  defined by using the Digital Asset Links API:
</p>

<pre>
https://digitalassetlinks.googleapis.com/v1/statements:list?
   source.web.site=https://<strong>&lt;domain1&gt;:&lt;port&gt;</strong>&amp;
   relation=delegate_permission/common.handle_all_urls
</pre>


<h3 id="test-intent">Testing a web URI intent</h3>

<p>
  Once you have confirmed the list of websites to associate with your app, and you have confirmed
  that the hosted JSON file is valid, install the app on your device. Wait at least 20 seconds for
  the asynchronous verification process to complete. Use the following command to check
  if the system verified your app and set the correct link handling policies:
</p>

<pre>
adb shell am start -a android.intent.action.VIEW \
    -c android.intent.category.BROWSABLE \
    -d "http://<domain1>:<port>;"
</pre>


<h3 id="check-link-policies">Check link policies</h3>

<p>
  As part of your testing process, you can check the current system settings for link handling.
  Use the following command to get a listing of link-handling policies for all applications:
</p>

<pre>
  adb shell dumpsys package domain-preferred-apps
  --or--
  adb shell dumpsys package d
</pre>

<p class="note">
  <strong>Note:</strong> Make sure you wait at least 20 seconds after installation of your app to
  allow for the system to complete the verification process.
</p>

<p>
  The command returns a listing of each user or profile defined on the device,
  indicated by a header in the following format:
</p>

<pre>
App linkages for user 0:
</pre>

<p>
  Following this heading, the output lists the link-handling settings for that user in this format:
</p>

<pre>
Package: com.android.vending
Domains: play.google.com market.android.com
Status: always : 200000002
</pre>

<p>This listing indicates the what apps are associated with what domains for that user, as
  described below:</p>

<ul>
  <li>{@code Package} - Identifies an app by its package name, as declared in its manifest.
  </li>
  <li>{@code Domains} - Shows the full list of hosts whose web links this app handles.
  </li>
  <li>{@code Status} - Shows the current link-handling setting for this app. An app that set {@code
  android:autoVerify="true"} value and passed verification is shown with a status of {@code
  always}. The hexadecimal number after this status is related to the Android system's record of
  the users app linkage preferences. This value is not relevant for interpreting whether the
  verification operation passed.
  </li>
</ul>

<p class="note">
  <strong>Note:</strong>It is possible for a user to change the app link settings for an app
  before the verification operation has completed. If this
  situation occurs, you may see a false positive for a successful verification, even though
  verification has failed. However, the user has already explicitly enabled the app to open
  supported links without asking. In this case, no dialog is shown and the link goes directly to
  your app, but only because explicit user preferences take precedence.
</p>


<h3 id="test-example">Test example</h3>

<p>
  For app link verification to succeed, the system must be able to verify your app with all of
  the websites referenced in your apps intent filters, that meet the criteria for app links.
  The following example manifest snippet shows app configuration with several app links defined:
</p>

<pre>
  &lt;application&gt;

      &lt;activity android:name=MainActivity&gt;
          &lt;intent-filter <strong>android:autoVerify="true"</strong>&gt;
              &lt;action android:name="android.intent.action.VIEW" /&gt;
              &lt;category android:name="android.intent.category.DEFAULT" /&gt;
              &lt;category android:name="android.intent.category.BROWSABLE" /&gt;
              &lt;data android:scheme="http" android:host="www.example.com" /&gt;
              &lt;data android:scheme="https" android:host="mobile.example.com" /&gt;
          &lt;/intent-filter&gt;
          &lt;intent-filter&gt;
              &lt;action android:name="android.intent.action.VIEW" /&gt;
              &lt;category android:name="android.intent.category.BROWSABLE" /&gt;
              &lt;data android:scheme="http" android:host="www.example2.com" /&gt;
          &lt;/intent-filter&gt;
      &lt;/activity&gt;

      &lt;activity android:name=SecondActivity&gt;
          &lt;intent-filter&gt;
              &lt;action android:name="android.intent.action.VIEW" /&gt;
              &lt;category android:name="android.intent.category.DEFAULT" /&gt;
              &lt;category android:name="android.intent.category.BROWSABLE" /&gt;
              &lt;data android:scheme="http" android:host="account.example.com" /&gt;
          &lt;/intent-filter&gt;
      &lt;/activity&gt;

      &lt;activity android:name=ThirdActivity&gt;
        &lt;intent-filter&gt;
            &lt;action android:name="android.intent.action.VIEW" /&gt;
            &lt;category android:name="android.intent.category.DEFAULT" /&gt;
            &lt;data android:scheme="http" android:host="map.example.com" /&gt;
        &lt;/intent-filter&gt;
        &lt;intent-filter&gt;
            &lt;action android:name="android.intent.action.VIEW" /&gt;
            &lt;category android:name="android.intent.category.BROWSABLE" /&gt;
            &lt;data android:scheme="market" android:host="example.com" /&gt;
        &lt;/intent-filter&gt;
      &lt;/activity&gt;

  &lt;/application&gt;
</pre>

<p>
  The list of hosts that the platform would attempt to verify from the above manifest is:
</p>

<pre>
  www.example.com
  mobile.example.com
  www.example2.com
  account.example.com
</pre>

<p>
  The list of hosts that the platform would not attempt to verify from the above manifest is:
</p>

<pre>
  map.example.com (it does not have android.intent.category.BROWSABLE)
  market://example.com (it does not have either an http or https scheme)
</pre>