using the dart firebase package on my laptop.

fbtest.dart

/*
 * pubspec.yaml:
 *
 * name: dconsole1
 * version: 0.0.1
 * description: A simple console application.
 * dependencies:
 *  firebase: '^3.0.0'
 *  http: '^0.11.3'
 *  googleapis_auth: any
 *
 * CREDENTIALS is a file downloaded from
 * https://console.firebase.google.com/ => your project => gear =>
 * project settings => service accounts => generate new private key
 */

import 'dart:io';
import 'package:googleapis_auth/auth_io.dart';
import 'package:firebase/firebase_io.dart';

const String CREDENTIALS = "project-42-firebase-adminsdk-2ftwd-something.json";
const String PATH = "https://project-42.firebaseio.com/messages.json";
final List<String> SCOPES = [
  "https://www.googleapis.com/auth/firebase.database",
  "https://www.googleapis.com/auth/userinfo.email"];

main(List<String> args) {
  print('Hello world!');

  // withFutures();
  withA();
}

void withFutures() {
  final File credsfile = new File(CREDENTIALS);
  credsfile.readAsString().then((contents) {
    final credentials = new ServiceAccountCredentials.fromJson(contents);

    clientViaServiceAccount(credentials, SCOPES).then((client) {
      var fb = new FirebaseClient(client.credentials.accessToken.data);
      fb.get(PATH).then((thing) => print(thing));

      client.close();
    });
  });
}

withA() async {
  final File credsfile = new File(CREDENTIALS);
  final contents = await credsfile.readAsString();
  final credentials = new ServiceAccountCredentials.fromJson(contents);
  final client = await clientViaServiceAccount(credentials, SCOPES);
  final fb = new FirebaseClient(client.credentials.accessToken.data);
  var data = await fb.get(PATH);

  // type is _InternalLinkedHashMap
  print(data);
}