Android App Links

Android App Links

Configuring App Links on Android with assetlinks.json

The app side is one more intent filter on MainActivity, next to the booknest scheme filter of App Lifecycle. android:autoVerify="true" asks Android to verify the host at install time:

The App Links intent filter in android/app/src/main/AndroidManifest.xmlXML

<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="booknest.example.com" />
</intent-filter>

The web side is https://booknest.example.com/.well-known/assetlinks.json, served as application/json without redirects. It names the package and the SHA-256 fingerprint of the signing certificate, here the debug keystore's, as keytool -list -v -keystore ~/.android/debug.keystore printed it:

deploy/.well-known/assetlinks.jsonJSON

[
  {
    "relation": ["delegate_permission/common.handle_all_urls"],
    "target": {
      "namespace": "android_app",
      "package_name": "com.example.booknest",
      "sha256_cert_fingerprints": [
"DA:B3:86:A8:49:8D:6E:02:BA:EE:02:5F:CC:09:BB:F6:80:A7:50:94:01:E4:2E:1C:A8:4F:69:12:03:2F:72:50"
      ]
    }
  }
]

A release needs the release fingerprint too; with Play App Signing that is Google's key, shown in the Play Console 1 (Play App Signing). example.com is reserved, so verification here was bound to fail, as pm shows:

Re-running verification, then approving the domain for testingShell

adb -s emulator-5558 shell pm verify-app-links --re-verify com.example.booknest
adb -s emulator-5558 shell pm get-app-links com.example.booknest | tail -1
adb -s emulator-5558 shell pm set-app-links --package com.example.booknest \
  2 booknest.example.com
adb -s emulator-5558 shell pm get-app-links com.example.booknest | tail -1

Output

      booknest.example.com: legacy_failure
      booknest.example.com: approved

legacy_failure: the verifier could not confirm the file. State 2, STATE_APPROVED, is a testing override. The same link, sent with am start -a android.intent.action.VIEW -d, before and after:

The App Link before verification opens Chrome 1 (at its first-run screen on this fresh emulator), and after the domain is approved opens BookNest directly on the book page

Since Android 12 an unverified link goes straight to the browser, so re-verify after every deployment.

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