chore: ensure generation is included when a grpc ReadObject is retried (#2741)

If a read is opened without a generation, we want to ensure we restart for the same generation. We have this behavior for json This is mainly to avoid a race condition of reading an object (gen=1), that object being replaced (gen=2) then retry attempts to read it again we need to read gen=1 otherwise we will return corrupted data.

Author: BenWhitehead

google-cloud-storage/src/main/java/com/google/cloud/storage/GapicUnbufferedReadableByteChannel.java

@@ -264,12 +264,15 @@ private void ensureStreamOpen() {
  alg,
  () -> {
  ReadObjectObserver tmp = new ReadObjectObserver();
- ReadObjectRequest request = req;
+ ReadObjectRequest.Builder builder = req.toBuilder();
  long currentFetchOffset = fetchOffset.get();
- if (request.getReadOffset() != currentFetchOffset) {
- request = req.toBuilder().setReadOffset(currentFetchOffset).build();
+ if (req.getReadOffset() != currentFetchOffset) {
+ builder.setReadOffset(currentFetchOffset);
  }
- read.call(request, tmp);
+ if (metadata != null && req.getGeneration() == 0) {
+ builder.setGeneration(metadata.getGeneration());
+ }
+ read.call(builder.build(), tmp);
  ApiExceptions.callAndTranslateApiException(tmp.open);
  return tmp;
  },

google-cloud-storage/src/test/java/com/google/cloud/storage/ITGapicUnbufferedReadableByteChannelTest.java

@@ -66,7 +66,8 @@ public final class ITGapicUnbufferedReadableByteChannelTest {
 
  private final ReadObjectRequest req1 =
  ReadObjectRequest.newBuilder().setObject(objectName).setReadOffset(0).build();
- private final ReadObjectRequest req2 = req1.toBuilder().setReadOffset(20).build();
+ private final ReadObjectRequest req2 =
+ req1.toBuilder().setGeneration(3L).setReadOffset(20).build();
  private final ReadObjectResponse resp1 =
  ReadObjectResponse.newBuilder()
  .setMetadata(expectedResult)