Google Cloud Dart API pubsub example code. I'm sharing this code to help those that will try to use this lib on dart and maybe will find the docs poor to achieve this example.

pubsub_google_cloud_example.dart

import 'package:googleapis/pubsub/v1.dart';
import 'package:googleapis_auth/auth_io.dart';
import 'credentials.dart';

const _SCOPES = const [PubsubApi.PubsubScope];

Future<PublishResponse> pubsubExample(Map<String, String> data) =>
    clientViaServiceAccount(PUBLISH_PUBSUB_CREDENTIALS, _SCOPES).then((http) {
      PubsubMessage msg = PubsubMessage();
      msg.attributes = data;
      PublishRequest publishRequest = PublishRequest();
      publishRequest.messages = [msg];
      String topic = 'projects/<YOUR PROJECT>/topics/<YOUR_TOPIC>';
      PubsubApi pubsubApi = PubsubApi(http);

      return pubsubApi.projects.topics
          .publish(publishRequest, topic)
          .then((publishResponse) => publishResponse);
    });




"credentials.dart':
import 'package:googleapis_auth/auth_io.dart';

final PUBLISH_PUBSUB_CREDENTIALS = ServiceAccountCredentials.fromJson({
  "type": "service_account",
  "project_id": "YOUR PROJECT ID",
  "private_key_id": "YOUR PRIVATE KEY ID",
  "private_key":"YOUR PRIVATE KEY"
  "client_email": "YOUR EMAIL",
  "client_id": "YOUR ID",
  "auth_uri": "https://accounts.google.com/o/oauth2/auth",
  "token_uri": "https://oauth2.googleapis.com/token",
  "auth_provider_x509_cert_url": "https://www.googleapis.com/oauth2/v1/certs",
  "client_x509_cert_url":
      "https://www.googleapis.com/robot/v1/metadata/x509/user-publish%40ligre-dev.iam.gserviceaccount.com"
});