private static async Task <FunctionDataCacheKey> GetFunctionDataCacheKey(BlobWithContainer <BlobBaseClient> blob, CancellationToken cancellationToken)
{
// To be strongly consistent, first check the latest version present in blob storage;
// query for that particular version in the cache.
BlobProperties properties = await blob.BlobClient.FetchPropertiesOrNullIfNotExistAsync(cancellationToken).ConfigureAwait(false);
if (properties == null)
{
return(null);
}
string eTag = properties.ETag.ToString();
string id = blob.BlobClient.Uri.AbsoluteUri;
FunctionDataCacheKey cacheKey = new FunctionDataCacheKey(id, eTag);
return(cacheKey);
}
public static async Task <ICacheAwareReadObject> TryBindCacheAwareAsync(BlobWithContainer <BlobBaseClient> blob, ValueBindingContext context, IFunctionDataCache functionDataCache)
{
try
{
// Generate the cache key for this blob
FunctionDataCacheKey cacheKey = await GetFunctionDataCacheKey(blob, context.CancellationToken).ConfigureAwait(false);
if (cacheKey == null)
{
return(null);
}
// Check if it exists in the cache
if (functionDataCache.TryGet(cacheKey, isIncrementActiveReference: true, out SharedMemoryMetadata sharedMemoryMeta))
{
// CACHE HIT
return(new CacheableReadBlob(cacheKey, sharedMemoryMeta, functionDataCache));
}
// CACHE MISS
// Wrap the blob's stream along with the cache key so it can be inserted in the cache later using the above generated key for this blob
Stream innerStream = await TryBindStreamAsync(blob.BlobClient, context.CancellationToken, cacheKey.Version).ConfigureAwait(false);
return(new CacheableReadBlob(cacheKey, innerStream, functionDataCache));
}
catch (RequestFailedException exception)
{
// Testing generic error case since specific error codes are not available for FetchAttributes
// (HEAD request), including OpenRead.
if (!exception.IsNotFound())
{
throw;
}
return(null);
}
}