Allow fallback from https to http for component update checks.

components/update_client/request_sender.h

 // Copyright 2014 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 COMPONENTS_UPDATE_CLIENT_REQUEST_SENDER_H_
 #define COMPONENTS_UPDATE_CLIENT_REQUEST_SENDER_H_
 
+#include <stdint.h>
+
 #include <string>
 #include <vector>
 
 #include "base/callback.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/threading/thread_checker.h"
 #include "net/url_request/url_fetcher_delegate.h"
 #include "url/gurl.h"
 
 namespace net {
 class URLFetcher;
 }
 
 namespace update_client {
 
 class ClientUpdateProtocolEcdsa;
 class Configurator;
 
 // Sends a request to one of the urls provided. The class implements a chain
 // of responsibility design pattern, where the urls are tried in the order they
 // are specified, until the request to one of them succeeds or all have failed.
 // CUP signing is optional.
 class RequestSender : public net::URLFetcherDelegate {
  public:
   // If |error| is 0, then the response is provided in the |response| parameter.
-  using RequestSenderCallback =
-      base::Callback<void(int error, const std::string& response)>;
+  // |retry_after_sec| contains the value of the X-Retry-After response header,
+  // when the response was received from a cryptografically secure URL. The
+  // range for this value is [0, 86400], where the upper bound represents one
+  // day, and 0 means that no retry policy should be in effect.
+  using RequestSenderCallback = base::Callback<
+      void(int error, const std::string& response, int retry_after_sec)>;
 
   static int kErrorResponseNotTrusted;
 
   explicit RequestSender(const scoped_refptr<Configurator>& config);
   ~RequestSender() override;
 
   // |use_signing| enables CUP signing of protocol messages exchanged using
   // this class.
   void Send(bool use_signing,
             const std::string& request_body,
             const std::vector<GURL>& urls,
             const RequestSenderCallback& request_sender_callback);
 
  private:
   // Combines the |url| and |query_params| parameters.
   static GURL BuildUpdateUrl(const GURL& url, const std::string& query_params);
 
   // Decodes and returns the public key used by CUP.
   static std::string GetKey(const char* key_bytes_base64);
 
-  // Returns the Etag of the server response or an empty string if the
-  // Etag is not available.
-  static std::string GetServerETag(const net::URLFetcher* source);
+  // Returns the string value of a header of the server response or an empty
+  // string if the header is not available.
+  static std::string GetStringHeaderValue(const net::URLFetcher* source,
+                                          const char* header_name);
+
+  // Returns the integral value of a header of the server response or -1 if
+  // if the header is not available or a conversion error has occured.
+  static int64_t GetInt64HeaderValue(const net::URLFetcher* source,
+                                     const char* header_name);
 
   // Overrides for URLFetcherDelegate.
   void OnURLFetchComplete(const net::URLFetcher* source) override;
 
   // Implements the error handling and url fallback mechanism.
   void SendInternal();
 
   // Called when SendInternal complets. |response_body|and |response_etag|
   // contain the body and the etag associated with the HTTP response.
   void SendInternalComplete(int error,
                             const std::string& response_body,
-                            const std::string& response_etag);
+                            const std::string& response_etag,
+                            int retry_after_sec);
 
   // Helper function to handle a non-continuable error in Send.
-  void HandleSendError(int error);
+  void HandleSendError(int error, int retry_after_sec);
 
   base::ThreadChecker thread_checker_;
 
   const scoped_refptr<Configurator> config_;
   bool use_signing_;
   std::vector<GURL> urls_;
   std::string request_body_;
   RequestSenderCallback request_sender_callback_;
 
   std::string public_key_;
   std::vector<GURL>::const_iterator cur_url_;
   scoped_ptr<net::URLFetcher> url_fetcher_;
   scoped_ptr<ClientUpdateProtocolEcdsa> signer_;
 
   DISALLOW_COPY_AND_ASSIGN(RequestSender);
 };
 
 }  // namespace update_client
 
 #endif  // COMPONENTS_UPDATE_CLIENT_REQUEST_SENDER_H_