net/url_request/url_request_backoff_manager.h

   1 // Copyright 2015 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef NET_URL_REQUEST_URL_REQUEST_BACKOFF_MANAGER_H_
   6 #define NET_URL_REQUEST_URL_REQUEST_BACKOFF_MANAGER_H_
   7
   8 #include <map>
   9 #include <string>
  10
  11 #include "base/basictypes.h"
  12 #include "base/threading/non_thread_safe.h"
  13 #include "base/time/time.h"
  14 #include "net/base/net_export.h"
  15 #include "net/base/network_change_notifier.h"
  16 #include "url/gurl.h"
  17
  18 namespace net {
  19
  20 class HttpResponseHeaders;
  21
  22 // Class that manages information on Backoff headers. URL requests for HTTPS
  23 // contents should update their URLs in this manager on each response.
  24 //
  25 // Design doc:
  26 // https://docs.google.com/document/d/1aAxwXK7Vw3VigFd6MmrItbAIgMdKAf-XxXXbhWXdID0/edit?usp=sharing
  27 //
  28 // URLRequestBackoffManager maintains a map of URL IDs to
  29 // URLRequestBackoffManager::Entry. It creates an entry when a request receives
  30 // a Backoff header, and does garbage collection from time to time in order to
  31 // clean out outdated entries. URL ID consists of lowercased scheme, host, port
  32 // and path. A newer request with the same ID will override the old entry.
  33 //
  34 // Note that the class does not implement logic to retry a request at random
  35 // with uniform distribution.
  36 // TODO(xunjieli): Expose release time so that the caller can retry accordingly.
  37 class NET_EXPORT URLRequestBackoffManager
  38     : NON_EXPORTED_BASE(public base::NonThreadSafe),
  39       public NetworkChangeNotifier::IPAddressObserver,
  40       public NetworkChangeNotifier::ConnectionTypeObserver {
  41  public:
  42   // Minimum number of seconds that a Backoff header can specify.
  43   static const uint16 kMinimumBackoffInSeconds;
  44   // Maximum number of seconds that a Backoff header can specify.
  45   static const uint16 kMaximumBackoffInSeconds;
  46   // Number of throttled requests that will be made between garbage collection.
  47   static const uint16 kNewEntriesBetweenCollecting;
  48
  49   URLRequestBackoffManager();
  50   ~URLRequestBackoffManager() override;
  51
  52   // Updates internal states with a response.
  53   void UpdateWithResponse(const GURL& url,
  54                           HttpResponseHeaders* headers,
  55                           const base::Time& response_time);
  56
  57   // Returns whether the request should be rejected because of a Backoff header.
  58   bool ShouldRejectRequest(const GURL& url, const base::Time& request_time);
  59
  60   // IPAddressObserver implementation.
  61   void OnIPAddressChanged() override;
  62
  63   // ConnectionTypeObserver implementation.
  64   void OnConnectionTypeChanged(
  65       NetworkChangeNotifier::ConnectionType type) override;
  66
  67   // Used by tests.
  68   int GetNumberOfEntriesForTests() const;
  69
  70  private:
  71   // An struct that holds relevant information obtained from a Backoff header.
  72   struct Entry {
  73     Entry(const base::Time& time1, const base::Time& time2)
  74         : throttled_time(time1), release_time(time2), used(false) {}
  75     ~Entry() {}
  76
  77     // Returns whether this entry is outdated.
  78     bool IsOutDated() { return base::Time::Now() >= release_time; }
  79
  80     // Before this time, requests with the same URL ID should be throttled.
  81     const base::Time throttled_time;
  82
  83     // Only one request with the same URL ID should be allowed in
  84     // [|throttled_time|, |release_time|).
  85     // After this time, all requests with the same URL ID are allowed.
  86     const base::Time release_time;
  87
  88     // Indicates whether a request has been made in
  89     // [|throttled_time|, |release_time|).
  90     bool used;
  91   };
  92
  93   // From each URL, generate an ID composed of the scheme, host, port and path
  94   // that allows unique mapping an entry to it.
  95   typedef std::map<std::string, Entry*> UrlEntryMap;
  96
  97   // Method that ensures the map gets cleaned from time to time. The period at
  98   // which garbage collecting happens is adjustable with the
  99   // kNewEntriesBetweenCollecting constant.
 100   void GarbageCollectEntriesIfNecessary();
 101
 102   // Return true if there is a well-formed Backoff header key-value pair,
 103   // and write the Backoff header value in |result|. Return false if no header
 104   // is found or the value is invalid (i.e. less than kMinimumBackoffInSeconds
 105   // or greater than kMaximumBackoffInSeconds).
 106   bool GetBackoffTime(HttpResponseHeaders* headers,
 107                       base::TimeDelta* result) const;
 108
 109   // Method that transforms a URL into an ID that can be used in the map.
 110   // Resulting IDs will be lowercase and consist of the scheme, host, port
 111   // and path (without query string, fragment, etc.).
 112   // If the URL is invalid, the invalid spec will be returned, without any
 113   // transformation.
 114   std::string GetIdFromUrl(const GURL& url) const;
 115
 116   // When switching from online to offline or change IP addresses,
 117   // clear all back-off history. This is a precaution in case the change in
 118   // online state now allows communicating without errors with servers that
 119   // were previously returning Backoff headers.
 120   void OnNetworkChange();
 121
 122   UrlEntryMap url_entries_;
 123
 124   // Keeps track of how many new entries are created since last garbage
 125   // collection.
 126   unsigned int new_entries_since_last_gc_;
 127
 128   // Valid after construction.
 129   GURL::Replacements url_id_replacements_;
 130
 131   DISALLOW_COPY_AND_ASSIGN(URLRequestBackoffManager);
 132 };
 133
 134 }  // namespace net
 135
 136 #endif  // NET_URL_REQUEST_URL_REQUEST_BACKOFF_MANAGER_H_