Azure Storage - Download a blob with conditions

Question

I've been having trouble assigning read conditions on blobs when trying to download them when using the Azure Storage SDK .

Basically, what I am trying to do goes like this:

1. Upload a blob ( WORKS )
2. Download the blob ( WORKS )
3. Get the Etag of the blob with blobRef.GetProperties().Etag ( WORKS )
4. Use the Etag to try to download the blob again expecting a RequestFailedException e where the e.ErrorCode == ConditionNotMet ( FAILS )

This is the code:

var condition = new Azure.Storage.Blobs.Models.BlobRequestConditions
{
    IfNoneMatch = new Azure.ETag(previousEtagString),
};

//blobRef is a valid instance of Azure.Storage.Blobs.BlobClient
//target is the filePath

blobRef.DownloadTo(target, conditions: condition); // this should throw RequestFailedException

Notes:

1. When I try to compare the Etag fetched from step 3 (which is converted to a string) with the one I am sending in step 4, it returns they are the same blobRef.GetProperties().Etag == new Azure.Etag(blobRef.GetProperties().Etag.ToString()) -> true

2. I also opened the question at the GitHub Repo

3. Passing test cases with v11:

    var blobRef = _blobContainer.GetBlockBlobReference(identifier); blobRef.DownloadTo(target, AccessCondition.GenerateIfNoneMatchCondition(stringEtag)); //throws StorageException

4. Just noticed that the blob downloaded the second time, does not contain any data. It's empty. The first one has data. Are the read conditions partially working, but not throwing the exception?

Thanks

Answer 1

Use the Etag to try to download the blob again expecting a RequestFailedException e where the e.ErrorCode == ConditionNotMet

This is not the expected behavior because Etag only changes when a blob is updated.

If a blob is not updated, Etag value remains the same. So if you do not update the blob, you can perform a conditional download multiple times without getting the precondition failure error.