public async Task <bool> CheckIfBlobExistsAsync(string blobPath)
{
string url = $"{FeedContainerUrl}/{blobPath}?comp=metadata";
using (HttpClient client = new HttpClient())
{
const int MaxAttempts = 15;
// add a bit of randomness to the retry delay.
var rng = new Random();
int retryCount = MaxAttempts;
// Used to make sure TaskCancelledException comes from timeouts.
CancellationTokenSource cancelTokenSource = new CancellationTokenSource();
while (true)
{
try
{
client.DefaultRequestHeaders.Clear();
var request = AzureHelper.RequestMessage("GET", url, AccountName, AccountKey).Invoke();
using (HttpResponseMessage response = await client.SendAsync(request, cancelTokenSource.Token))
{
if (response.IsSuccessStatusCode)
{
Log.LogMessage(
MessageImportance.Low,
$"Blob {blobPath} exists for {AccountName}: Status Code:{response.StatusCode} Status Desc: {await response.Content.ReadAsStringAsync()}");
}
else
{
Log.LogMessage(
MessageImportance.Low,
$"Blob {blobPath} does not exist for {AccountName}: Status Code:{response.StatusCode} Status Desc: {await response.Content.ReadAsStringAsync()}");
}
return(response.IsSuccessStatusCode);
}
}
catch (HttpRequestException toLog)
{
if (retryCount <= 0)
{
Log.LogError($"Unable to check for existence of blob {blobPath} in {AccountName} after {MaxAttempts} retries.");
throw;
}
else
{
Log.LogWarning("Exception thrown while trying to detect if blob already exists in feed:");
Log.LogWarningFromException(toLog, true);
}
}
catch (TaskCanceledException possibleTimeoutToLog)
{
// Detect timeout.
if (possibleTimeoutToLog.CancellationToken != cancelTokenSource.Token)
{
if (retryCount <= 0)
{
Log.LogError($"Unable to check for existence of blob {blobPath} in {AccountName} after {MaxAttempts} retries.");
throw;
}
else
{
Log.LogWarning("Exception thrown while trying to detect if blob already exists in feed:");
Log.LogWarningFromException(possibleTimeoutToLog, true);
}
}
else
{
throw;
}
}
--retryCount;
Log.LogWarning($"Failed to check for existence of blob {blobPath}. {retryCount} attempts remaining");
int delay = (MaxAttempts - retryCount) * rng.Next(1, 7);
await Task.Delay(delay * 1000);
}
}
}
public static async Task<HttpResponseMessage> RequestWithRetry(TaskLoggingHelper loggingHelper, HttpClient client,
Func<HttpRequestMessage> createRequest, Func<HttpResponseMessage, bool> validationCallback = null, int retryCount = 5,
int retryDelaySeconds = 5)
{
if (loggingHelper == null)
throw new ArgumentNullException(nameof(loggingHelper));
if (client == null)
throw new ArgumentNullException(nameof(client));
if (createRequest == null)
throw new ArgumentNullException(nameof(createRequest));
if (retryCount < 1)
throw new ArgumentException(nameof(retryCount));
if (retryDelaySeconds < 1)
throw new ArgumentException(nameof(retryDelaySeconds));
int retries = 0;
HttpResponseMessage response = null;
// add a bit of randomness to the retry delay
var rng = new Random();
while (retries < retryCount)
{
if (retries > 0)
{
if (response != null)
{
response.Dispose();
response = null;
}
int delay = retryDelaySeconds * retries * rng.Next(1, 5);
loggingHelper.LogMessage(MessageImportance.Low, "Waiting {0} seconds before retry", delay);
await System.Threading.Tasks.Task.Delay(delay * 1000);
}
try
{
using (var request = createRequest())
response = await client.SendAsync(request);
}
catch (Exception e)
{
loggingHelper.LogWarningFromException(e, true);
// if this is the final iteration let the exception bubble up
if (retries + 1 == retryCount)
throw;
}
// response can be null if we fail to send the request
if (response != null)
{
if (validationCallback == null)
{
// check if the response code is within the range of failures
if (IsWithinRetryRange(response.StatusCode))
{
loggingHelper.LogWarning("Request failed with status code {0}", response.StatusCode);
}
else
{
loggingHelper.LogMessage(MessageImportance.Low, "Response completed with status code {0}", response.StatusCode);
return response;
}
}
else
{
bool isSuccess = validationCallback(response);
if (!isSuccess)
{
loggingHelper.LogMessage("Validation callback returned retry for status code {0}", response.StatusCode);
}
else
{
loggingHelper.LogMessage("Validation callback returned success for status code {0}", response.StatusCode);
return response;
}
}
}
++retries;
}
// retry count exceeded
loggingHelper.LogWarning("Retry count {0} exceeded", retryCount);
// set some default values in case response is null
var statusCode = "None";
var contentStr = "Null";
if (response != null)
{
statusCode = response.StatusCode.ToString();
contentStr = await response.Content.ReadAsStringAsync();
response.Dispose();
}
throw new HttpRequestException(string.Format("Request failed with status {0} response {1}", statusCode, contentStr));
}
