Flutter Web how to serve file assetlinks.json for Android App Links verification

It is enough to add the .well-know folder and the file to the web folder of your Flutter project.

And to change the firebase.json adding headers and rewrites entries.

{
  "hosting": {
    "public": "build/web",
    "appAssociation": "NONE",
    "ignore": ["firebase.json", "**/.*", "**/node_modules/**"],
    "headers": [
      {
        "source": "/.well-known/assetlinks.json",
        "headers": [
          {
            "key": "Content-Type",
            "value": "application/json"
          }
        ]
      }
    ],
    "rewrites": [
      {
        "source": "/.well-known/assetlinks.json",
        "destination": "/.well-known/assetlinks.json"
      },
      {
        "source": "**",
        "destination": "/index.html"
      }
    ]
  }
}

build and deploy again and the file is now accessible!

Thanks for the easy guide to https://blog.bam.tech/developer-news/universal-links-firebase-hosting-and-flutter-web

Firebase Hosting automatically generates assetlinks.json and apple-app-site-association files when they are requested. It doesn't require any extra configuration.

You just need to make sure that your app details (package, SHA256 certificate fingerprints, etc.) are correctly setup in the Project Settings and make sure that in your firebase.json the property appAssociation is set to "AUTO" (or omitted, as AUTO is the default value).

Example firebase.json:

{
  "hosting": {
    "public": "build/web",
    "ignore": [
      "firebase.json",
      "**/.*",
      "**/node_modules/**"
    ],
    "appAssociation": "AUTO",
    "rewrites": [
      {
        "source": "**",
        "destination": "/index.html"
      }
    ]
  }
}

Ref: https://firebase.google.com/docs/hosting/full-config#rewrite-dynamic-links

If I am not mistaken, Firebase stores files in a so called bucket. The bucket can be directly exposed to the internet or you can use the API to pull the file you need and put it somewhere public on your domain:

https://firebase.google.com/docs/storage/web/list-files

To see how to publish files in a gloud bucket, here is a good answer:

How do you make many files public in Google Cloud Storage?

Be aware the method described provides public access, so make sure you only expose what you want.