Which status codes should I expect when using Azure Table Storage - azure

Question

I want to do something when/if an insert operation on Azure Table Storage fails. Assume that I want to return false from the below code when I receive an error. _table is of type CloudTable and the code below works.
public bool InsertEntity(TableEntity entity)
{
var insertOperation = TableOperation.Insert(entity);
var result = _table.Execute(insertOperation);
return (result.HttpStatusCode == (int)System.Net.HttpStatusCode.OK);
}
I get the result 203 when the operation succeeds. But there are other possible results like "200 OK".
How can I write a piece of code that will allow me to understand from the status code that something went wrong?

Answer 1

Using the .NET SDK, any situation that needs to be handled will throw an exception. i.e. Any status code that is not 2xx will cause an exception.
To handle situations where something went wrong, I don't have to manually check the status code of the result for every request. All I have to do is to write exception handling code. Like below:
try
{
var result = _table.Execute(insertOperation);
}
catch (Exception)
{
Log("Something went wrong in table operation.");
}

Answer 2

From this page:
REST API operations for Azure storage services return standard HTTP
status codes, as defined in the HTTP/1.1 Status Code Definitions.
So every successful operation against table service will return 2XX status code. To find out about the exact code returned, I would recommend checking out each operation on the REST API Documentation page. For example, Create Table operation returns 201 status code if the operation is successful.
Similarly, for errors in table service you will get error code in 400 range (that would mean you provided incorrect data e.g. 409 (Conflict) error if you're trying to create a table which already exists) or in 500 range (for example, table service is unavailable). You can find the list of all Table Service Error Codes here: https://msdn.microsoft.com/en-us/library/azure/dd179438.aspx.

Answer 3

Basically, any return in 2xx is "OK". In this example:
https://msdn.microsoft.com/en-us/library/system.net.httpstatuscode%28v=vs.110%29.aspx
203 Non-Authoritative Information:
Indicates that the returned metainformation is from a cached copy
instead of the
origin server and therefore may be incorrect.
This Azure white paper elaborates further:
http://go.microsoft.com/fwlink/?LinkId=153401
9.6.5 Error handling and reporting
The REST API is designed to look like a standard HTTP server interacting with existing HTTP clients
(e.g., browsers, HTTP client libraries, proxies, caches, and so on).
To ensure the HTTP clients handle errors properly, we map each Windows
Azure Table error to an HTTP status code.
HTTP status codes are less expressive than Windows Azure Table error
codes and contain less information about the error. Although the HTTP
status codes contain less information about the error, clients that
understand HTTP will usually handle the error correctly.
Therefore, when handling errors or reporting Windows Azure Table
errors to end users, use the Windows Azure Table error code along with
the HTTP status code as it contains more information about the error.
Additionally, when debugging your application, you should also consult
the human readable element of the XML error
response.
These links are also useful:
Microsoft Azure: Status and Error Codes
Clean way to catch errors from Azure Table (other than string match?)

Answer 4

If you are using Azure Storage SDK accessing Azure Table Storage, the SDK would throw a StorageException on the client side for unexpected Http Status Codes returned from the table storage service. To extract the actual HttpStatusCode you would need to wrap your code in a try {} catch(StorageException ex){} block. And then parse the actual exception object to extract the HttpStatusCode embedded in it.
Have a look at Azure Storage Exception parser I implemented in Nuget:
https://www.nuget.org/packages/AzureStorageExceptionParser/
This extracts HttpStatusCode and many other useful fields from Azure StorageExceptions. You can use the same library accross table, blob, queue clients etc. as they all follow the same StorageException pattern.
Note that there will be some exceptions thrown by the Azure Storage SDK that are not StorageExceptions, those are mostly client side request validation type of exceptions and naturally they do not contain any HttpStatusCode. (Hence you would need to have a catch for specifically StorageExceptions to extract HttpStatusCode s).
As a separate note, Azure Storage SDK has a fairly robust retry mechanism for failed requests. Below is the snippet from SDK source code where they decide if the failed response is retrieable or not.
https://github.com/Azure/azure-storage-net/blob/master/Lib/Common/RetryPolicies/ExponentialRetry.cs
if ((statusCode >= 300 && statusCode < 500 && statusCode != 408)
|| statusCode == 501 // Not Implemented
|| statusCode == 505 // Version Not Supported
|| lastException.Message == SR.BlobTypeMismatch)
{
return false; //aka. do not Retry if w are here otherwise Retry if within max retry count..
}