Dart

Refresh Access Token on 401 Unauthorized and Retry (Service Account)

See more Google Cloud Storage Examples

Demonstrates how to handle an expired access token error, refresh the token, and retry the request. (In this case, the request is to download an object from Google Cloud Storage.) Dart

import 'package:chilkat/chilkat.dart';

void main() {
  var success = false;

  // This example requires the Chilkat API to have been previously unlocked.
  // See Global Unlock Sample for sample code.

  // This example uses a previously obtained access token having permission for the 
  // scope "https://www.googleapis.com/auth/cloud-platform"

  // In this example, Get Google Cloud Storage OAuth2 Access Token, 
  // the service account access token was saved to a text file.  This example fetches the access token from the file..
  final sbToken = CkStringBuilder();
  try {
    sbToken.loadFile('qa_data/tokens/googleCloudStorageAccessToken.txt', 'utf-8');
  } on ChilkatException {
    print('Failed to load access token.');
    return;
  }

  final http = CkHttp();

  http.authToken = sbToken.getAsString();

  // Construct a URL to download an object named "starfish.jpg" from the "chilkat-ocean" bucket.
  http.setUrlVar('bucket_name', 'chilkat-ocean');
  http.setUrlVar('object_name', 'starfish.jpg');
  final url = 'https://www.googleapis.com/storage/v1/b/{\$bucket_name}/o/{\$object_name}?alt=media';

  // If there is an error response, then we didn't actually download the file data,
  // but instead we downloaded an error response..
  final fileData = CkBinData();
  success = true;
  try {
    http.downloadBd(url, fileData);
  } on ChilkatException {
    success = false;
  }
  final responseCode = http.lastStatus;
  if ((!success) && (responseCode != 401)) {
    print(http.lastErrorText);
    return;
  }

  if (responseCode == 401) {
    print('Received 401 Unauthorized response. Attempting to refresh the access token...');

    // May be that the access token expired.
    // Load our JSON key and request a new access token, then retry the original request.
    final fac = CkFileAccess();
    final String jsonKey;
    try {
      jsonKey = fac.readEntireTextFile('qa_data/googleApi/ChilkatCloud-13a07a2e8b3f.json', 'utf-8');
    } on ChilkatException catch (e) {
      print(e.lastErrorText);
      return;
    }

    final gAuth = CkAuthGoogle();
    gAuth.jsonKey = jsonKey;
    gAuth.scope = 'https://www.googleapis.com/auth/cloud-platform';
    gAuth.expireNumSeconds = 3600;
    gAuth.subEmailAddress = '';

    final tlsSock = CkSocket();
    try {
      tlsSock.connect('www.googleapis.com', 443, true, 5000);
    } on ChilkatException catch (e) {
      print(e.lastErrorText);
      return;
    }

    try {
      gAuth.obtainAccessToken(tlsSock);
    } on ChilkatException catch (e) {
      print(e.lastErrorText);
      return;
    }

    fac.writeEntireTextFile('qa_data/tokens/googleCloudStorageAccessToken.txt', gAuth.accessToken, 'utf-8', false);

    // Retry the original request.
    http.authToken = gAuth.accessToken;
    try {
      http.downloadBd(url, fileData);
    } on ChilkatException catch (e) {
      print(e.lastErrorText);
      return;
    }
  }

  if (responseCode != 200) {
    // Get the error response
    final sbErrorResponse = CkStringBuilder();
    sbErrorResponse.appendBd(fileData, 'utf-8', 0, 0);
    print('Error response code = $responseCode');
    print('Error:');
    print(sbErrorResponse.getAsString());
    return;
  }

  print('Success.');

  // Save the downloaded data to a file.
  success = true;
  try {
    fileData.writeFile('qa_output/starfish.jpg');
  } on ChilkatException {
    success = false;
  }
}