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Configure proxy for Azure Storage / CloudTableClient in .NET Core

under Azure | D comments | edit

For a project I’m working on I needed to specify a outgoing proxy for accessing Azure Table Storage in a .NET console application.

Unfortunately the default way of setting a proxy in the app.config of classic .NET applications doesn’t work for .NET core.

After fiddling around for a bit I found the solution for setting it in a .NET core application (based on a answer on stackoverflow). If you use the Microsoft.Azure.Cosmos.Table Nuget package, instead of the old WindowsAzure.Storage package (I’m using version 1.0.1), the CloudTableClient allows you to pass in a TableClientConfiguration with a DelegatingHandler:

public TableStorage(string accountName, string keyValue, IWebProxy proxy)
{
	_storageAccount = new CloudStorageAccount(new StorageCredentials(accountName, keyValue), true);
    var storageDelegatingHandler = new StorageDelegatingHandler(proxy);
    _tableClient = _storageAccount.CreateCloudTableClient(
        new TableClientConfiguration
        {
            RestExecutorConfiguration = new RestExecutorConfiguration
            {
                DelegatingHandler = storageDelegatingHandler
            } 
        });

    /// further config
}

In the DelegatingHandler you can set the proxy for the HttpClientHandler:

public class StorageDelegatingHandler : DelegatingHandler
{
  private readonly IWebProxy _proxy;

  private bool _firstCall = true;

  public StorageDelegatingHandler() 
  : base()
  {
  }

  public StorageDelegatingHandler(HttpMessageHandler httpMessageHandler)
  : base(httpMessageHandler)
  {
  }

  public StorageDelegatingHandler(IWebProxy proxy)
  {
  	_proxy = proxy;
  }

  protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
  {
    if (_firstCall && _proxy != null)
    {
      HttpClientHandler inner = (HttpClientHandler)InnerHandler;
      inner.Proxy = _proxy;
    }

    _firstCall = false;
    return base.SendAsync(request, cancellationToken);
  }
}

Now you can configure the proxy where you’re setting up dependency injection:

public class ProxySettings
{
  public bool Use => !string.IsNullOrWhiteSpace(Address);

  public string Address { get; set; }

  public bool BypassOnLocal { get; set; }
}

var proxySettings = Configuration
                .GetSection(nameof(ProxySettings))
                .Get<ProxySettings>();

IWebProxy proxy = null;
if (proxySettings != null && proxySettings.Use)
{
	proxy = new WebProxy(proxySettings.Address, proxySettings.BypassOnLocal);
	WebRequest.DefaultWebProxy = proxy;
}

services.AddSingleton<IStorage>(new TableStorage(Configuration["StorageAccountName"], Configuration["StorageAccountKey"], proxy));

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