private async Task <T> LoadAuxiliaryFileAsync <T>(
string blobName,
Func <JsonReader, T> loadData) where T : class
{
_logger.LogInformation(
"Attempted to load blob {BlobName} as {TypeName}.",
blobName,
typeof(T).FullName);
var stopwatch = Stopwatch.StartNew();
var blob = Container.GetBlobReference(blobName);
using (var stream = await blob.OpenReadAsync(AccessCondition.GenerateEmptyCondition()))
using (var textReader = new StreamReader(stream))
using (var jsonReader = new JsonTextReader(textReader))
{
var data = loadData(jsonReader);
stopwatch.Stop();
_telemetryService.TrackAuxiliaryFileDownloaded(blobName, stopwatch.Elapsed);
_logger.LogInformation(
"Loaded blob {BlobName}. Took {Duration}.",
blobName,
stopwatch.Elapsed);
return(data);
};
}
private async Task <T> LoadAuxiliaryFileAsync <T>(
string blobName,
Func <JsonReader, T> loadData) where T : class
{
// Retry on HTTP 412 because it's possible CloudBlockBlob.OpenReadyAsync throws a 412 while reading the
// resulting stream. This is because the WindowsAzure.Storage SDK implements the streaming read with a
// series of range requests with If-Match, presumably to keep memory consumption at a minimum. During these
// reads, the file can be modified which will cause an HTTP 412 Precondition Failed.
var data = default(T);
await Retry.IncrementalAsync(
async() =>
{
_logger.LogInformation(
"Attempted to load blob {BlobName} as {TypeName}.",
blobName,
typeof(T).FullName);
var stopwatch = Stopwatch.StartNew();
var blob = Container.GetBlobReference(blobName);
using (var stream = await blob.OpenReadAsync(AccessCondition.GenerateEmptyCondition()))
using (var textReader = new StreamReader(stream))
using (var jsonReader = new JsonTextReader(textReader))
{
data = loadData(jsonReader);
stopwatch.Stop();
_telemetryService.TrackAuxiliaryFileDownloaded(blobName, stopwatch.Elapsed);
_logger.LogInformation(
"Loaded blob {BlobName}. Took {Duration}.",
blobName,
stopwatch.Elapsed);
};
},
ex => ex is StorageException se && se.IsPreconditionFailedException(),
maxRetries : 5,
initialWaitInterval : TimeSpan.Zero,
waitIncrement : TimeSpan.FromSeconds(10));
return(data);
}