How to share file from browser to my app and return worked file using app links

I need to create the application which can process the file shared from a browser and to return the result file. The required action I can retreive from the link. But I can't figure out how to get the file content.

I have set up Intent Filters in AndroidManifest.xml:

<activity android:name="activity">
    <intent-filter>
        <action android:name="android.intent.action.VIEW" />
        <category android:name="android.intent.category.DEFAULT" />
        <category android:name="android.intent.category.BROWSABLE" />
        <data
            android:scheme="app"
            android:host="action" />
    </intent-filter>
</activity>

And I've added the processing code in the Activity.

And I've made the following HTML prototype:

        document.getElementById('sendButton').addEventListener('click', function() {
            const fileInput = document.getElementById('fileInput');
            if (fileInput.files.length > 0) {
                const file = fileInput.files[0];
                const url = app://action?operation=sign&filename=${encodeURIComponent(file.name)};
                
              window.location.href = url;
            } else {
                alert('Please select a file first.');
            }
        });

But it doesn't work. When I press the button, nothing happens (in logcat also nothing). But when I check deep link with adb the app wakes up.

I don't fully understand whether it could work or there's another way to get this done. Where to start investigation the problem?

Looks to me like you just need to aexport the activity from the manifest file. Also you should not need to specify a host - try a path instead.

You are using a private-use URI scheme URL to link to the application. These are often also used to receive OAuth responses in mobile apps. Here is some example syntax to conpare against:

<activity
    android:name=".oauth.LoginRequestResponseActivity"
    android:exported="true"
    android:launchMode="singleTask"
    android:configChanges="orientation|screenSize">

    <intent-filter>
        <action android:name="android.intent.action.VIEW" />
        <category android:name="android.intent.category.DEFAULT"/>
        <category android:name="android.intent.category.BROWSABLE"/>
        <data android:scheme="com.example.demoapp" android:path="/callback" />
    </intent-filter>
</activity>