Google App Engine App failed to access Google Cloud Storage bucket - google-app-engine

Question

Unable to access default Google Cloud Storage bucket from Appengine Project. This project was created with App engine SDK version prior to 1.9.0. I've created the bucket manually, as per GCS Documentation it was said by default the bucket is accessible to Appengine Projects, but its not accessible in my case. This is the code snippet that tries to create a file..
...
GcsService gcsService = GcsServiceFactory.createGcsService();
GcsFilename file = new GcsFilename(getGcsDefaultBucketName(), fileName);
GcsFileOptions.Builder builder = new GcsFileOptions.Builder();
GcsFileOptions options = builder.mimeType(mimeType).build();
GcsOutputChannel channel = gcsService.createOrReplace(file, options); //erroring in this line
...
Error found in Logs:
: com.google.appengine.tools.cloudstorage.NonRetriableException: java.lang.RuntimeException: Server replied with 403, verify ACLs are set correctly on the object and bucket: Request: POST https://storage.googleapis.com/1-ebilly.appspot.com/SERVICESTAGEREPORT-DEVICENAME-LYF2-CREATEDDATE-01012017-CREATEDDATE-19022017-.ZIP
: User-Agent: AppEngine-Java-GCS
: Content-Length: 0
: x-goog-resumable: start
: Content-Type: application/zip
:
: no content: Response: 403 with 212 bytes of content
: X-GUploader-UploadID: AEnB2Upq0Lhtfy5pbt06pVib8J0-L0XiGqW4JpB0G9PL87keY3WV7RCMVLCPeclD-D4UATEddvvwpAG2qeeIxUJx--brKxdQFw
: Content-Type: application/xml; charset=UTF-8
: Content-Length: 212
: Vary: Origin
: <?xml version='1.0' encoding='UTF-8'?><Error><Code>AccessDenied</Code><Message>Access denied.</Message><Details>Caller does not have storage.objects.create access to bucket myprojectID.appspot.com.</Details></Error>
:
: at com.google.appengine.tools.cloudstorage.RetryHelper.doRetry(RetryHelper.java:120)
: at com.google.appengine.tools.cloudstorage.RetryHelper.runWithRetries(RetryHelper.java:166)
: at com.google.appengine.tools.cloudstorage.RetryHelper.runWithRetries(RetryHelper.java:156)
: at com.google.appengine.tools.cloudstorage.GcsServiceImpl.createOrReplace(GcsServiceImpl.java:70)
PS: I've tried to create a new Google Appengine Project and deployed the app init. This project is automatically created with a default GCS bucket and the same code is working fine without any error. My old project has lots of DB data which I want to retain and continue to use the same project without disposing it.
Please help with your thoughts to make the GCS bucket accessible in old project.

Answer 1

Resolved the issue by adding IAM permissin for appengine project. After reading the IAM "Access Control at the Project Level" document and comparing old project and new project permissions came to know that Appengine project level permission is not found in old project. After adding the permission the same code started to access the default bucket.
IAM Permissions before fix screenshot
IAM Permissions after fix screenshot

Answer 2

Try this:-
GcsService gcsService = GcsServiceFactory.createGcsService(RetryParams.getDefaultInstance());
GcsFileOptions options = new GcsFileOptions.Builder().mimeType(mime).build();
GcsFilename gcsfilename = new GcsFilename(BUCKET_NAME, fileName);
GcsOutputChannel outputChannel = gcsService.createOrReplace(gcsfilename, options);