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RateLimitedHttpMessageHandler.cs
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RateLimitedHttpMessageHandler.cs
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// Copyright (c) 2021 .NET Foundation and Contributors. All rights reserved.
// Licensed to the .NET Foundation under one or more agreements.
// The .NET Foundation licenses this file to you under the MIT license.
// See the LICENSE file in the project root for full license information.
using System;
using System.Collections.Generic;
using System.Diagnostics.CodeAnalysis;
using System.Globalization;
using System.IO;
using System.Linq;
using System.Net.Http;
using System.Reactive.Linq;
using System.Reactive.Threading.Tasks;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using Punchclock;
namespace Fusillade
{
/// <summary>
/// A http handler which will limit the rate at which we can read.
/// </summary>
public class RateLimitedHttpMessageHandler : LimitingHttpMessageHandler
{
private readonly int _priority;
private readonly OperationQueue? _opQueue;
private readonly Dictionary<string, InflightRequest> _inflightResponses =
new Dictionary<string, InflightRequest>();
private readonly Func<HttpRequestMessage, HttpResponseMessage, string, CancellationToken, Task>? _cacheResult;
private long? _maxBytesToRead;
/// <summary>
/// Initializes a new instance of the <see cref="RateLimitedHttpMessageHandler"/> class.
/// </summary>
/// <param name="handler">The handler we are wrapping.</param>
/// <param name="basePriority">The base priority of the request.</param>
/// <param name="priority">The priority of the request.</param>
/// <param name="maxBytesToRead">The maximum number of bytes we can reead.</param>
/// <param name="opQueue">The operation queue on which to run the operation.</param>
/// <param name="cacheResultFunc">A method that is called if we need to get cached results.</param>
public RateLimitedHttpMessageHandler(HttpMessageHandler handler, Priority basePriority, int priority = 0, long? maxBytesToRead = null, OperationQueue? opQueue = null, Func<HttpRequestMessage, HttpResponseMessage, string, CancellationToken, Task>? cacheResultFunc = null)
: base(handler)
{
_priority = (int)basePriority + priority;
_maxBytesToRead = maxBytesToRead;
_opQueue = opQueue;
_cacheResult = cacheResultFunc;
}
/// <summary>
/// Generates a unique key for a <see cref="HttpRequestMessage"/>.
/// This assists with the caching.
/// </summary>
/// <param name="request">The request to generate a unique key for.</param>
/// <returns>The unique key.</returns>
public static string UniqueKeyForRequest(HttpRequestMessage request)
{
if (request is null)
{
throw new ArgumentNullException(nameof(request));
}
var ret = new[]
{
request.RequestUri!.ToString(),
request.Method.Method,
request.Headers.Accept.ConcatenateAll(x => x.CharSet + x.MediaType),
request.Headers.AcceptEncoding.ConcatenateAll(x => x.Value),
(request.Headers.Referrer ?? new Uri("http://example")).AbsoluteUri,
request.Headers.UserAgent.ConcatenateAll(x => x.Product != null ? x.Product.ToString() : x.Comment!),
}.Aggregate(
new StringBuilder(),
(acc, x) =>
{
acc.AppendLine(x);
return acc;
});
if (request.Headers.Authorization != null)
{
ret.Append(request.Headers.Authorization.Parameter).AppendLine(request.Headers.Authorization.Scheme);
}
return "HttpSchedulerCache_" + ret.ToString().GetHashCode().ToString("x", CultureInfo.InvariantCulture);
}
/// <inheritdoc />
public override void ResetLimit(long? maxBytesToRead = null)
{
_maxBytesToRead = maxBytesToRead;
}
/// <inheritdoc />
protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
{
if (request is null)
{
throw new ArgumentNullException(nameof(request));
}
var method = request.Method;
if (method != HttpMethod.Get && method != HttpMethod.Head && method != HttpMethod.Options)
{
return base.SendAsync(request, cancellationToken);
}
var cacheResult = _cacheResult;
if (cacheResult == null && NetCache.RequestCache != null)
{
cacheResult = NetCache.RequestCache.Save;
}
if (_maxBytesToRead < 0)
{
var tcs = new TaskCompletionSource<HttpResponseMessage>();
tcs.SetCanceled();
return tcs.Task;
}
var key = UniqueKeyForRequest(request);
var realToken = new CancellationTokenSource();
var ret = new InflightRequest(() =>
{
lock (_inflightResponses)
{
_inflightResponses.Remove(key);
}
realToken.Cancel();
});
lock (_inflightResponses)
{
if (_inflightResponses.ContainsKey(key))
{
var val = _inflightResponses[key];
val.AddRef();
cancellationToken.Register(val.Cancel);
return val.Response.ToTask(cancellationToken);
}
_inflightResponses[key] = ret;
}
cancellationToken.Register(ret.Cancel);
var queue = _opQueue ?? NetCache.OperationQueue;
queue.Enqueue(
_priority,
null!,
async () =>
{
try
{
var resp = await base.SendAsync(request, realToken.Token).ConfigureAwait(false);
if (_maxBytesToRead != null && resp.Content?.Headers.ContentLength != null)
{
_maxBytesToRead -= resp.Content.Headers.ContentLength;
}
if (cacheResult != null && resp.Content != null)
{
var ms = new MemoryStream();
var stream = await resp.Content.ReadAsStreamAsync().ConfigureAwait(false);
await stream.CopyToAsync(ms, 32 * 1024, realToken.Token).ConfigureAwait(false);
realToken.Token.ThrowIfCancellationRequested();
var newResp = new HttpResponseMessage();
foreach (var kvp in resp.Headers)
{
newResp.Headers.Add(kvp.Key, kvp.Value);
}
var newContent = new ByteArrayContent(ms.ToArray());
foreach (var kvp in resp.Content.Headers)
{
newContent.Headers.Add(kvp.Key, kvp.Value);
}
newResp.Content = newContent;
resp = newResp;
await cacheResult(request, resp, key, realToken.Token).ConfigureAwait(false);
}
return resp;
}
finally
{
lock (_inflightResponses)
{
_inflightResponses.Remove(key);
}
}
},
realToken.Token).ToObservable().Subscribe(ret.Response);
return ret.Response.ToTask(cancellationToken);
}
}
}