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Troubleshooting Google Digital Asset Links for Seamless Android App Linking

  ·   3 min read

We all want to provide a seamless experience for the users of our app. Android app links are a great way to launch users straight into the app when they click on a link.

There are different types of links that you can create in an Android app.

  • Deep Links

  • Web Links

  • App Links

I’ve been working on a product for which we needed to use app links. Here I’ll discuss solving issues with setting up Android app links.

If you are new and implementing app links from scratch, I suggest you look through android-app-links.

In order to use app links we need to prove the ownership of the domain by uploading assetlinks.json to .well-known directory in the root of the domain.

https://<mydomain.com>/.well-known/assetlinks.json

Here is an example of Uber’s assetlinks.json https://uber.com/.well-known/assetlinks.json

Our product was using Webflow to host the website and it did not support adding Google digital asset links.

Setup reverse proxy

The options were either to download the content and host it ourselves or set up a reverse proxy, chose the latter.

Used Nginx for this and the config is as follows:

server {
	listen 80 default_server;
	listen [::]:80 default_server;

	root /var/www/html;

	# Add index.php to the list if you are using PHP
	index index.html index.htm index.nginx-debian.html;

	server_name _;
	location /health {
		access_log off;
		return 200 "OK";
		add_header Content-Type text/plain;
	}

	location /.well-known/ {
        alias /var/www/html/.well-known/;
		add_header Content-Type application/json;
    }

	location / {
		
        proxy_pass https://<web.mydomain.com>;
        proxy_busy_buffers_size   512k;
 		proxy_buffers   4 512k;
 		proxy_buffer_size   256k;
		proxy_ssl_server_name on; 
        proxy_set_header  X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
	}
}

Following are the steps followed to set this up.

  1. Changed the configured domain in Webflow from https://<mydomain.com> to https://<web.mydomain.com> .

  2. Brought a reverse proxy in between this and served the https://<mydomain.com> site through this.

  3. Copied the assetlinks.json file to /var/www/html/.well-known/ path of the Nginx container while building the Docker image for Nginx.

  4. Now assetlinks.json was available at https://<mydomain.com>/.well-known/assetlinks.json

  5. But when validated using google-digital-asset-links-tester, it failed.

When the network was inspected, it was throwing

unavailable: Redirect encountered while fetching statements from 
https://<mydomain.com>/.well-known/assetlinks.json (which is 
equivalent to https://<mydomain.com>/.well-known/assetlinks.json): 
redirects are disallowed for security reasons 
(NOT_FOLLOWED_MAX_FORWARDS)

As per google official doc,

The assetlinks.json file must be served as Content-Type: application/json in the HTTP headers, and it cannot be a redirect (that is, 301 or 302 response codes are not followed).

In our case, initially assetlinks.json was served via a redirect as shown below.

Since redirects were a security restriction, modified the flow as follows:

Initially, we had a redirect in order to handle some use cases for certain paths, in the updated flow this was included in the Nginx conf so that assetlinks.json can be served without redirects.

Now validated again using google-digital-asset-links-tester, my domain was able to grant deep linking permission to my app.

Let me know if you have faced similar issues with Android app links in the comments.

References

This blog was originally published here

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