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