Storage: FakeStorageRpc states it supports generations, but generationMatch option unsupported on Blob creation.

[SanjayVas]

Environment details

1. Specify the API at the beginning of the title. For example, "BigQuery: ...").
   General, Core, and Other are also allowed as types
2. OS type and version: Debian 11
3. Java version: 11
4. storage_nio version(s): HEAD

Steps to reproduce

1. Init Storage using LocalStorageHelper.
2. Call create with BlobInfo and BlobTargetOption.generationMatch.

Code example

val bucketName = "bucket"
val blobKey = "blob-key"
val storage = LocalStorageHelper.getOptions().service
storage.create(
  BlobInfo.newBuilder(bucketName, blobKey, 0L).build(),
  Storage.BlobTargetOption.generationMatch()
)

Stack trace

java.lang.UnsupportedOperationException
com.google.cloud.storage.StorageException: 
	at com.google.cloud.storage.StorageException.translateAndThrow(StorageException.java:81)
	at com.google.cloud.storage.StorageImpl.internalCreate(StorageImpl.java:229)
	at com.google.cloud.storage.StorageImpl.create(StorageImpl.java:157)

Caused by: 
	at com.google.cloud.storage.contrib.nio.testing.FakeStorageRpc.potentiallyThrow(FakeStorageRpc.java:446)
	at com.google.cloud.storage.contrib.nio.testing.FakeStorageRpc.create(FakeStorageRpc.java:96)
	at com.google.cloud.storage.StorageImpl$3.call(StorageImpl.java:221)
	at com.google.cloud.storage.StorageImpl$3.call(StorageImpl.java:218)
	at com.google.api.gax.retrying.DirectRetryingExecutor.submit(DirectRetryingExecutor.java:105)
	at com.google.cloud.RetryHelper.run(RetryHelper.java:76)
	at com.google.cloud.RetryHelper.runWithRetries(RetryHelper.java:50)
	at com.google.cloud.storage.StorageImpl.internalCreate(StorageImpl.java:217)
	... 40 more

External references such as API reference guides

https://github.com/googleapis/java-storage-nio/blob/main/google-cloud-nio/src/main/java/com/google/cloud/storage/contrib/nio/testing/FakeStorageRpc.java

Any additional information below

FakeStorageRpc appears to handle generations for some operations using the checkGeneration private method. For Blob create however, it just calls potentiallyThrow. It seems like it should be a relatively simple change to check the generation if the appropriate option is set, with two wrinkles:

1. What should the behavior be w.r.t. throwIfOption? Should it still throw for any option, or just unsupported ones?
2. What's the right error code? Currently checkGeneration uses 404, but that's likely not correct for create. Does the real Cloud Storage implementation return 412 - Precondition failed in this case?

[cojenco]

Thanks for the detailed report! As noted in our readme, this is a known limitation and is considered a feature request. We welcome pull requests in case you want to add support 😄

The error code that is returned by live GCS, in this case, is 412 Precondition Failed. There are specific cases where the server returns 404, more details here. I’m not sure what the behavior throwIfOption should be and will check with the team.

[SanjayVas]

Thanks for the info.

Does the class documentation for FakeStorageRpc need to be fixed then? It states generations are supported there.

[cojenco]

I'll update the documentation shortly. Thanks for bringing this to our attention.