Implement URLRequestBackoffManager for managing Backoff headers

net/url_request/url_request_backoff_manager.h

Index: net/url_request/url_request_backoff_manager.h
diff --git a/net/url_request/url_request_backoff_manager.h b/net/url_request/url_request_backoff_manager.h
new file mode 100644
index 0000000000000000000000000000000000000000..232ebdc02b664f1e95057500a022f8039999f3d4
--- /dev/null
+++ b/net/url_request/url_request_backoff_manager.h
@@ -0,0 +1,136 @@
+// Copyright 2015 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_URL_REQUEST_BACKOFF_MANAGER_H_
+#define NET_URL_REQUEST_URL_REQUEST_BACKOFF_MANAGER_H_
+
+#include <map>
+#include <string>
+
+#include "base/basictypes.h"
+#include "base/threading/non_thread_safe.h"
+#include "base/time/time.h"
+#include "net/base/net_export.h"
+#include "net/base/network_change_notifier.h"
+#include "url/gurl.h"
+
+namespace net {
+
+class HttpResponseHeaders;
+
+// Class that manages information on Backoff headers. URL requests for HTTPS
+// contents should update their URLs in this manager on each response.
+//
+// Design doc:
+// https://docs.google.com/document/d/1aAxwXK7Vw3VigFd6MmrItbAIgMdKAf-XxXXbhWXdID0/edit?usp=sharing
+//
+// URLRequestBackoffManager maintains a map of URL IDs to
+// URLRequestBackoffManager::Entry. It creates an entry when a request receives
+// a Backoff header, and does garbage collection from time to time in order to
+// clean out outdated entries. URL ID consists of lowercased scheme, host, port
+// and path. A newer request with the same ID will override the old entry.
+//
+// Note that the class does not implement logic to retry a request at random
+// with uniform distribution.
+// TODO(xunjieli): Expose release time so that the caller can retry accordingly.
+class NET_EXPORT URLRequestBackoffManager
+    : NON_EXPORTED_BASE(public base::NonThreadSafe),
+      public NetworkChangeNotifier::IPAddressObserver,
+      public NetworkChangeNotifier::ConnectionTypeObserver {
+ public:
+  // Minimum number of seconds that a Backoff header can specify.
+  static const uint16 kMinimumBackoffInSeconds;
+  // Maximum number of seconds that a Backoff header can specify.
+  static const uint16 kMaximumBackoffInSeconds;
+  // Number of throttled requests that will be made between garbage collection.
+  static const uint16 kNewEntriesBetweenCollecting;
+
+  URLRequestBackoffManager();
+  ~URLRequestBackoffManager() override;
+
+  // Updates internal states with a response.
+  void UpdateWithResponse(const GURL& url,
+                          HttpResponseHeaders* headers,
+                          const base::Time& response_time);
+
+  // Returns whether the request should be rejected because of a Backoff header.
+  bool ShouldRejectRequest(const GURL& url, const base::Time& request_time);
+
+  // IPAddressObserver implementation.
+  void OnIPAddressChanged() override;
+
+  // ConnectionTypeObserver implementation.
+  void OnConnectionTypeChanged(
+      NetworkChangeNotifier::ConnectionType type) override;
+
+  // Used by tests.
+  int GetNumberOfEntriesForTests() const;
+
+ private:
+  // An struct that holds relevant information obtained from a Backoff header.
+  struct Entry {
+    Entry(const base::Time& time1, const base::Time& time2)
+        : throttled_time(time1), release_time(time2), used(false) {}
+    ~Entry() {}
+
+    // Returns whether this entry is outdated.
+    bool IsOutDated() { return base::Time::Now() >= release_time; }
+
+    // Before this time, requests with the same URL ID should be throttled.
+    const base::Time throttled_time;
+
+    // Only one request with the same URL ID should be allowed in
+    // [|throttled_time|, |release_time|).
+    // After this time, all requests with the same URL ID are allowed.
+    const base::Time release_time;
+
+    // Indicates whether a request has been made in
+    // [|throttled_time|, |release_time|).
+    bool used;
+  };
+
+  // From each URL, generate an ID composed of the scheme, host, port and path
+  // that allows unique mapping an entry to it.
+  typedef std::map<std::string, Entry*> UrlEntryMap;
+
+  // Method that ensures the map gets cleaned from time to time. The period at
+  // which garbage collecting happens is adjustable with the
+  // kNewEntriesBetweenCollecting constant.
+  void GarbageCollectEntriesIfNecessary();
+
+  // Return true if there is a well-formed Backoff header key-value pair,
+  // and write the Backoff header value in |result|. Return false if no header
+  // is found or the value is invalid (i.e. less than kMinimumBackoffInSeconds
+  // or greater than kMaximumBackoffInSeconds).
+  bool GetBackoffTime(HttpResponseHeaders* headers,
+                      base::TimeDelta* result) const;
+
+  // Method that transforms a URL into an ID that can be used in the map.
+  // Resulting IDs will be lowercase and consist of the scheme, host, port
+  // and path (without query string, fragment, etc.).
+  // If the URL is invalid, the invalid spec will be returned, without any
+  // transformation.
+  std::string GetIdFromUrl(const GURL& url) const;
+
+  // When switching from online to offline or change IP addresses,
+  // clear all back-off history. This is a precaution in case the change in
+  // online state now allows communicating without errors with servers that
+  // were previously returning Backoff headers.
+  void OnNetworkChange();
+
+  UrlEntryMap url_entries_;
+
+  // Keeps track of how many new entries are created since last garbage
+  // collection.
+  unsigned int new_entries_since_last_gc_;
+
+  // Valid after construction.
+  GURL::Replacements url_id_replacements_;
+
+  DISALLOW_COPY_AND_ASSIGN(URLRequestBackoffManager);
+};
+
+}  // namespace net
+
+#endif  // NET_URL_REQUEST_URL_REQUEST_BACKOFF_MANAGER_H_