RetryAfter Read Headers

Policy.cs

private TimeSpan getServerWaitDuration(DelegateResult<HttpResponseMessage> response)
{
	var retryAfter = response?.Result?.Headers?.RetryAfter;
	if (retryAfter == null)
		return TimeSpan.Zero;
	
	return retryAfter.Date.HasValue
		? retryAfter.Date.Value - DateTime.UtcNow
		: retryAfter.Delta.GetValueOrDefault(TimeSpan.Zero);
}

var retryAfterPolicy = Policy
	.HandleResult<HttpResponseMessage>(r => r?.Headers?.RetryAfter != null) // EDIT: .Net Framework only: https://msdn.microsoft.com/en-us/library/system.net.http.headers.httpresponseheaders.aspx;  not yet in this form in .NET Core?
	.WaitAndRetryAsync(
		retryCount: numRetries,
		sleepDurationProvider: (retryCount, response, context) => getServerWaitDuration(response)
        );
        
 //Wrap with a Timeout so it doesn't run forever...
 
Policy timeoutPolicy = Policy.TimeoutAsync(30, TimeoutStrategy.Optimistic);
var executionPolicy = timeoutPolicy.WrapAsync(retryAfterPolicy);


//Call with below. Remember - Policies are thread safe.
/*If the code executed through the policy is your own code, the recommended pattern is to call cancellationToken.ThrowIfCancellationRequested() at suitable intervals in the cancellable work.*/

var result = await executionPolicy
    .ExecuteAsync(
        async ct => await httpClient.GetAsync(requestEndpoint, ct), // Execute a delegate which responds to a CancellationToken input parameter.
        CancellationToken.None // CancellationToken.None here indicates you have no independent cancellation control you wish to add to the cancellation provided by TimeoutPolicy.
    );