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70 lines
2.8 KiB
C
70 lines
2.8 KiB
C
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// Copyright 2018 The Chromium Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#ifndef NET_HTTP_PROXY_FALLBACK_H_
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#define NET_HTTP_PROXY_FALLBACK_H_
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// ------------------------------------------------------------
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// Proxy Fallback Overview
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// ------------------------------------------------------------
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//
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// Proxy fallback is a feature that is split between the proxy resolution layer
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// and the HTTP layers.
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//
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// The proxy resolution layer is responsible for:
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// * Obtaining a list of proxies to use
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// (ProxyResolutionService::ResolveProxy). Proxy lists are (usually) the
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// result of having evaluated a PAC script, such as:
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// return "PROXY foobar1:8080; HTTPS foobar2:8080; DIRECT";
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//
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// * Re-ordering the proxy list such that proxies that have recently failed
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// are given lower priority (ProxyInfo::DeprioritizeBadProxies)
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//
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// * Maintaining the expiring cache of proxies that have recently failed.
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//
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//
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// The HTTP layer is responsible for:
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// * Attempting to issue the URLRequest through each of the
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// proxies, in the order specified by the list.
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//
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// * Deciding whether this attempt was successful, whether it was a failure
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// but should keep trying other proxies, or whether it was a failure and
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// should stop trying other proxies.
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//
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// * Upon successful completion of an attempt though a proxy, calling
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// ProxyResolutionService::ReportSuccess to inform it of all the failed
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// attempts that were made. (A proxy is only considered to be "bad"
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// if the request was able to be completed through some other proxy).
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//
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//
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// Exactly how to interpret the proxy lists returned by PAC is not specified by
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// a standard. The justifications for what errors are considered for fallback
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// are given beside the implementation.
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#include "net/base/net_export.h"
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namespace net {
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class ProxyServer;
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// Returns true if a failed request issued through a proxy server should be
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// re-tried using the next proxy in the fallback list.
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//
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// The proxy fallback logic is a compromise between compatibility and
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// increasing odds of success, and may choose not to retry a request on the
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// next proxy option, even though that could work.
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//
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// - |proxy| is the proxy server that failed the request.
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// - |error| is the error for the request when it was sent through |proxy|.
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// - |final_error| is an out parameter that is set with the "final" error to
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// report to the caller. The error is only re-written in cases where
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// CanFalloverToNextProxy() returns false.
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NET_EXPORT bool CanFalloverToNextProxy(const ProxyServer& proxy,
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int error,
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int* final_error);
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} // namespace net
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#endif // NET_HTTP_PROXY_FALLBACK_H_
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