Implement exponential back-off mechanism and enforce it at the URLRequestHttpJob level.

net/url_request/request_throttler_entry_interface.h

+// Copyright (c) 2010 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.
+
+#ifndef NET_URL_REQUEST_REQUEST_THROTTLER_ENTRY_INTERFACE_H_
+#define NET_URL_REQUEST_REQUEST_THROTTLER_ENTRY_INTERFACE_H_
+
+#include "base/basictypes.h"
+#include "base/ref_counted.h"
+#include "base/time.h"
+
+class RequestThrottlerHeaderInterface;
+
+// Interface provided on entries of the request throttler manager.
+class RequestThrottlerEntryInterface
+    : public base::RefCounted<RequestThrottlerEntryInterface> {
+ public:
+  RequestThrottlerEntryInterface() {}
+
+  // Returns true when we have encountered server errors and are doing
+  // exponential back-off.
+  // URLRequestHttpJob checks this method prior to every request; it cancels
+  // requests if this method returns true.
+  virtual bool IsDuringExponentialBackoff() const = 0;
+
+  // Calculates a recommended sending time for the next request and reserves it.
+  // The sending time is not earlier than the current exponential back-off
+  // release time or |earliest_time|. Moreover, the previous results of
+  // the method are taken into account, in order to make sure they are spread
+  // properly over time.
+  // Returns the recommended delay before sending the next request, in
+  // milliseconds. The return value is always positive or 0.
+  // Although it is not mandatory, respecting the value returned by this method
+  // is helpful to avoid traffic overload.
+  virtual int64 ReserveSendingTimeForNextRequest(
+      const base::TimeTicks& earliest_time) = 0;
+
+  // Returns the time after which requests are allowed.
+  virtual base::TimeTicks GetExponentialBackoffReleaseTime() const = 0;
+
+  // This method needs to be called each time a response is received.
+  virtual void UpdateWithResponse(
+      const RequestThrottlerHeaderInterface* response) = 0;
+
+  // Lets higher-level modules, that know how to parse particular response
+  // bodies, notify of receiving malformed content for the given URL. This will
+  // be handled by the throttler as if an HTTP 5xx response had been received to
+  // the request, i.e. it will count as a failure.
+  virtual void ReceivedContentWasMalformed() = 0;
+
+ protected:
+  virtual ~RequestThrottlerEntryInterface() {}
+
+ private:
+  friend class base::RefCounted<RequestThrottlerEntryInterface>;
+  DISALLOW_COPY_AND_ASSIGN(RequestThrottlerEntryInterface);
+};
+
+#endif  // NET_URL_REQUEST_REQUEST_THROTTLER_ENTRY_INTERFACE_H_