Some gotchas when using Firebase Dynamic Links

The last couple of weeks I have been trying to add Firebase Dynamic Links into an app and it took me way longer than I had originally planned. In this post, I wanted to share some of the lessons learned.

First: note that there are 2 kinds of links that you can use:

1. Dynamic links that you generate on the Dynamic Links section of your Firebase project. These will be the same for every user and are great to link to universally same sections of your app. These are quick to set up and are probably a good idea to try before generating the second kind of deep links
2. Dynamic links generated by a user for another user on a client application. These would be custom links only relevant for unique users and so cannot be generated via the project dashboard.

In my case, I was trying to get #2 working and it proved to be a real bear.

The problem is that when generating a unique URL, you are essentially doing a couple of handoffs: The first link is managed completely by Firebase (usually with a *.page.link URL). This link checks to see if the app is installed on the device the link is launched on and links to the app-install page if not. If that is fine, the link redirects to the second link that you actually are trying to get to. The second link is often a web address on your own domain which needs to be correctly configured for that page, or else the link will just open that webpage which is probably not what you want to do.

Gotcha 1: [Android] Make sure you have the SHA256 signature saved in your Firebase project

For the longest time, I didn’t realize that I had only the SHA1 key saved in my project. Deep links don’t work without SHA256 values for your project. Thanks to this answer from StackOverflow.

Gotcha 2: [Android] Make sure you have /.well-known/assetlinks.json correctly configured

It took me a while to get this document correctly deployed (mostly my fault). I really should have read the documentation on verified site associations on Android more carefully. You can verify your assetlinks setup via this URL (just replace the domain and, if applicable, port values):

https://digitalassetlinks.googleapis.com/v1/statements:list?source.web.site=https://domain1:port&relation=delegate_permission/common.handle_all_urls

Also remember, if you are using Google Play Store to sign and release your app, your assetlinks should refer to their key’s SHA256 signatures. Conveniently, you can copy the assetlinks file from the Play Store itself under the Setup > App Integrity section of the developer console

Gotcha 3: [Android] Make sure “autoverify” attribute in your intent-filter is set to true

Not sure how I missed this but, this took a long time to find

 <intent-filter android:autoVerify="true">
    <action android:name="android.intent.action.VIEW" />
    <category android:name="android.intent.category.DEFAULT" />
     <category android:name="android.intent.category.BROWSABLE" />
     <data
          android:scheme="https"
          android:host="my.app.com" />
 </intent-filter>

iOS:

Surprisingly, as frustrating as getting the Android version to work was, the iOS integration was much simpler. Just following this video helped a lot!

Hope some of this info helps you if you are using dynamic links in your app

Author: Arpit Mathur

Arpit Mathur is a Principal Engineer at Comcast Labs where he is currently working on a variety of topics including Machine Learning, Affective Computing, and Blockchain applications. Arpit has also worked extensively on Android and iOS applications, Virtual Reality apps as well as with web technologies like JavaScript, HTML and Ruby on Rails. He also spent a couple of years in the User Experience team as a Creative Technologist. View all posts by Arpit Mathur