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// Copyright (C) 2018, The Duplicati Team
// http://www.duplicati.com, info@duplicati.com
//
// This library is free software; you can redistribute it and/or modify
// it under the terms of the GNU Lesser General Public License as
// published by the Free Software Foundation; either version 2.1 of the
// License, or (at your option) any later version.
//
// This library is distributed in the hope that it will be useful, but
// WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
// Lesser General Public License for more details.
//
// You should have received a copy of the GNU Lesser General Public
// License along with this library; if not, write to the Free Software
// Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
using Duplicati.Library.Logging;
using Duplicati.Library.Utility;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Net.Http.Headers;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
namespace Duplicati.Library
{
public class RetryAfterHelper
{
private static readonly string LOGTAG = Log.LogTagFromType<RetryAfterHelper>();
// Whenever a response includes a Retry-After header, we'll update this timestamp with when we can next
// send a request. And before sending any requests, we'll make sure to wait until at least this time.
// Since this may be read and written by multiple threads, it is stored as a long and updated using Interlocked.Exchange.
private long retryAfter = DateTimeOffset.MinValue.UtcTicks;
public void SetRetryAfter(RetryConditionHeaderValue retryAfter)
{
if (retryAfter != null)
{
DateTimeOffset? delayUntil = null;
if (retryAfter.Delta.HasValue)
{
delayUntil = DateTimeOffset.UtcNow + retryAfter.Delta.Value;
}
else if (retryAfter.Date.HasValue)
{
delayUntil = retryAfter.Date.Value;
}
if (delayUntil.HasValue)
{
// Set the retry timestamp to the UTC version of the timestamp.
long newRetryAfter = delayUntil.Value.UtcTicks;
// Update the persisted retry after timestamp
long replacedRetryAfter;
long currentRetryAfter;
do
{
currentRetryAfter = Interlocked.Read(ref this.retryAfter);
if (newRetryAfter < currentRetryAfter)
{
// If the current retry after is already past the new value, then no need to update it again.
break;
}
else
{
replacedRetryAfter = Interlocked.CompareExchange(ref this.retryAfter, newRetryAfter, currentRetryAfter);
}
}
while (replacedRetryAfter != currentRetryAfter);
}
}
}
public void WaitForRetryAfter()
{
this.WaitForRetryAfterAsync(CancellationToken.None).Await();
}
public async Task WaitForRetryAfterAsync(CancellationToken cancelToken)
{
TimeSpan delay = this.GetDelayTime();
if (delay > TimeSpan.Zero)
{
Log.WriteProfilingMessage(
LOGTAG,
"RetryAfterWait",
"Waiting for {0} to respect Retry-After header",
delay);
await Task.Delay(delay).ConfigureAwait(false);
}
}
private TimeSpan GetDelayTime()
{
// Make sure this is thread safe in case multiple calls are made concurrently to this backend
// This is done by reading the value into a local value which is then parsed and operated on locally.
long retryAfterTicks = Interlocked.Read(ref this.retryAfter);
DateTimeOffset delayUntil = new DateTimeOffset(retryAfterTicks, TimeSpan.Zero);
TimeSpan delay;
DateTimeOffset now = DateTimeOffset.UtcNow;
// Make sure delayUntil is in the future and delay until then if so
if (delayUntil >= now)
{
delay = delayUntil - now;
}
else
{
// If the date given was in the past then don't wait at all
delay = TimeSpan.Zero;
}
return delay;
}
}
}
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