Add GetExpirationTimes() to HttpResponseHeader.

net/http/http_response_headers.h

 // Copyright (c) 2012 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_HTTP_HTTP_RESPONSE_HEADERS_H_
 #define NET_HTTP_HTTP_RESPONSE_HEADERS_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 172 matching lines @@
   bool GetCharset(std::string* charset) const;
 
   // Returns true if this response corresponds to a redirect.  The target
   // location of the redirect is optionally returned if location is non-null.
   bool IsRedirect(std::string* location) const;
 
   // Returns true if the HTTP response code passed in corresponds to a
   // redirect.
   static bool IsRedirectResponseCode(int response_code);
 
-  // Returns true if the response cannot be reused without validation.  The
-  // result is relative to the current_time parameter, which is a parameter to
-  // support unit testing.  The request_time parameter indicates the time at
-  // which the request was made that resulted in this response, which was
-  // received at response_time.
-  bool RequiresValidation(const base::Time& request_time,
-                          const base::Time& response_time,
-                          const base::Time& current_time) const;
+  // Returns the time from which this resource can no longer be reused without
+  // validation. |request_time| is the local time at which the request that
+  // resulted in this response was made. |response_time| is the local time at
+  // which we received this response.
+  base::Time GetFreshnessExpiry(base::Time request_time,
+                                base::Time response_time) const;
 
   // Returns the amount of time the server claims the response is fresh from
-  // the time the response was generated.  See section 13.2.4 of RFC 2616.  See
-  // RequiresValidation for a description of the response_time parameter.
-  base::TimeDelta GetFreshnessLifetime(const base::Time& response_time) const;
+  // the time the response was generated.  See section 13.2.4 of RFC 2616.
+  // |response_time| is the local time at which we received this response. If
+  // a finite (possibly zero) freshness lifetime exists, it is returned in the
+  // output parameter |finite_freshness_lifetime|, and |was_finite| is set to
+  // false. If |was_finite| is true, the resource is fresh indefinitely, and
+  // |finite_freshness_lifetime| has an undefined value.
+  void GetFreshnessLifetime(base::Time response_time,
+                            base::TimeDelta* finite_freshness_lifetime,
+                            bool* was_finite) const;
 
-  // Returns the age of the response.  See section 13.2.3 of RFC 2616.
-  // See RequiresValidation for a description of this method's parameters.
-  base::TimeDelta GetCurrentAge(const base::Time& request_time,
-                                const base::Time& response_time,
-                                const base::Time& current_time) const;
+  // Returns the time at which this resource had age zero. |request_time| is the
+  // local time at which the request that resulted in this response was made.
+  // |response_time| is the local time at which we received this response.
+  base::Time GetFreshnessOrigin(base::Time request_time,
+                                base::Time response_time) const;
 

[rvargas (doing something else), 2014/02/06 22:39:58]

How about adding a new method instead:

Time HttpResponseHeaders::GetFreshnessLimit(const Time& request_time,
                                            const Time& response_time,
                                            const Time& current_time) const {
  TimeDelta lifetime = GetFreshnessLifetime(response_time);
  if (lifetime == TimeDelta())
    return current_time;

  TimeDelta age = GetCurrentAge(request_time, response_time, current_time);
  if (lifetime <= age)
    return current_time;

  return current_time + lifetime - age;
}

If you don't like the small code duplication we can have:

bool HttpResponseHeaders::RequiresValidation(const Time& request_time,
                                             const Time& response_time,
                                             const Time& current_time) const {
  return GetFreshnessLimit(request_time, response_time, current_time) ==
         current_time;
}

[gavinp, 2014/02/07 15:59:18]

I originally considered this second idea, of keeping a RequiresValidation()
method so that we wouldn't have to change the call sites. I decided against that
approach for two reasons:

1. API surface area. The call sites don't benefit very much from the
RequiresValidation() call; and so changing the call sites seemed preferable to
having a second method that isn't needed if we make those few changes.

2. The benefit of removing "current_time" parameter. The documentation claimed
it was only for testing, and certainly every call site except the unit test was
passing in Time::Now(). Using FreshnessExpiry meant that this extra parameter
wasn't necessary even for testing, so that's a simplification of the API.

   // The following methods extract values from the response headers.  If a
   // value is not present, then false is returned.  Otherwise, true is returned
   // and the out param is assigned to the corresponding value.
   bool GetMaxAgeValue(base::TimeDelta* value) const;
   bool GetAgeValue(base::TimeDelta* value) const;
   bool GetDateValue(base::Time* value) const;
   bool GetLastModifiedValue(base::Time* value) const;
   bool GetExpiresValue(base::Time* value) const;
 
   // Extracts the time value of a particular header.  This method looks for the
@@ skipping 176 matching lines @@
 
   // The parsed http version number (not normalized).
   HttpVersion parsed_http_version_;
 
   DISALLOW_COPY_AND_ASSIGN(HttpResponseHeaders);
 };
 
 }  // namespace net
 
 #endif  // NET_HTTP_HTTP_RESPONSE_HEADERS_H_