Database SDK should warn when it builds databaseUrl from projectId

[samtstern]

[READ] Step 1: Are you in the right place?

Yep

[REQUIRED] Step 2: Describe your environment

• Android Studio version: all
• Firebase Component: Database
• Component version: 19.6.0

[REQUIRED] Step 3: Describe the problem

Steps to reproduce:

1. Create a new project
2. Add an Android app
3. Download google-services.json
4. Create the default RTDB instance on the project, choose Europe location

Because (3) precedes (4) the json file will not contain the firebase_url key and therefore the RTDB SDK will try and make up the database URL:

  public static FirebaseDatabase getInstance(@NonNull FirebaseApp app) {
    String databaseUrl = app.getOptions().getDatabaseUrl();
    if (databaseUrl == null) {
      if (app.getOptions().getProjectId() == null) {
        throw new DatabaseException(
            "Failed to get FirebaseDatabase instance: Can't determine Firebase Database URL. "
                + "Be sure to include a Project ID in your configuration.");
      }
      databaseUrl = "https://" + app.getOptions().getProjectId() + "-default-rtdb.firebaseio.com";
    }
    return getInstance(app, databaseUrl);
  }

However it doesn't print any warning when it does this, and for anyone who chooses Europe this is the wrong URL. See developer pain here:
firebase/codelab-friendlychat-android#137

Relevant Code:

See above

[schmidt-sebastian]

@jfdt - Do you have thoughts here?

[jsdt]

We can improve the error message to make it clear that the database is in a different region (and needs a different URL). I don't think we need to have a warning if the url is inferred and works correctly though.

[fredzqm]

Just to be clear even if the google-services.json is redownloaded after the database is created, it won't contain databaseUrl. Any non-us-central default databases must be connected with its full url passed into getInstance().

Thanks for bringing this up. We should work on improving the public documentation and surface a better error message in the SDK.

[fredzqm]

Sorry, I take it back. Creating the databaseUrl today will change the config.
I was confused because the decision settled a while ago was to discourage config redownloads.

[samtstern]

FYI there are a lot of conversations going on about this topic, the future of the JSON plugin, etc. So before making any changes here make sure to talk to Mike D at least.

@jsdt that would imply that the warning only happens after the first failed operation, right? Or does the RTDB SDK eagerly try to connect to the backend when instantiated?

[schmidt-sebastian]

The Android SDK only connects to the backend when there is work to do.