Add GetExpirationTimes() to HttpResponseHeader.

net/http/http_response_headers.cc

 // 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.
 
 // The rules for header parsing were borrowed from Firefox:
 // http://lxr.mozilla.org/seamonkey/source/netwerk/protocol/http/src/nsHttpResponseHead.cpp
 // The rules for parsing content-types were also borrowed from Firefox:
 // http://lxr.mozilla.org/mozilla/source/netwerk/base/src/nsURLHelper.cpp#834
 
 #include "net/http/http_response_headers.h"
@@ skipping 926 matching lines @@
 bool HttpResponseHeaders::IsRedirectResponseCode(int response_code) {
   // Users probably want to see 300 (multiple choice) pages, so we don't count
   // them as redirects that need to be followed.
   return (response_code == 301 ||
           response_code == 302 ||
           response_code == 303 ||
           response_code == 307 ||
           response_code == 308);
 }
 
-// From RFC 2616 section 13.2.4:
+// We calculate and return |corrected_response_time|, defined by:
 //
-// The calculation to determine if a response has expired is quite simple:
+//   current_age = now - corrected_response_time
 //
-//   response_is_fresh = (freshness_lifetime > current_age)
+// So a caller can store an ExpirationTimes object and use it to determine
+// freshness throughout the objects lifetime.
 //
 // Of course, there are other factors that can force a response to always be
 // validated or re-fetched.
-//
-// From RFC 5861 section 3, a stale response may be used while revalidation is
-// performed in the background if
-//
-//   freshness_lifetime + stale_while_revalidate > current_age
-//
-ValidationType HttpResponseHeaders::RequiresValidation(
+HttpResponseHeaders::ExpirationTimes HttpResponseHeaders::GetExpirationTimes(
     const Time& request_time,
-    const Time& response_time,
-    const Time& current_time) const {
-  FreshnessLifetimes lifetimes = GetFreshnessLifetimes(response_time);
-  if (lifetimes.freshness.is_zero() && lifetimes.staleness.is_zero())
-    return VALIDATION_SYNCHRONOUS;
+    const Time& response_time) const {
+  // From RFC 2616 section 13.2.3:
+  //
+  // Summary of age calculation algorithm, when a cache receives a response:
+  //
+  //   /*
+  //    * age_value
+  //    *      is the value of Age: header received by the cache with
+  //    *              this response.
+  //    * date_value
+  //    *      is the value of the origin server's Date: header
+  //    * request_time
+  //    *      is the (local) time when the cache made the request
+  //    *              that resulted in this cached response
+  //    * response_time
+  //    *      is the (local) time when the cache received the
+  //    *              response
+  //    * now
+  //    *      is the current (local) time
+  //    */
+  //   apparent_age = max(0, response_time - date_value);
+  //   corrected_received_age = max(apparent_age, age_value);
+  //   response_delay = response_time - request_time;
+  //   corrected_initial_age = corrected_received_age + response_delay;
+  //   resident_time = now - response_time;
+  //   current_age   = corrected_initial_age + resident_time;
 
-  TimeDelta age = GetCurrentAge(request_time, response_time, current_time);
+  // If there is no Date header, then assume that the server response was
+  // generated at the time when we received the response.
+  Time date_value;
+  if (!GetDateValue(&date_value))
+    date_value = response_time;
 
-  if (lifetimes.freshness > age)
-    return VALIDATION_NONE;
+  // If there is no Age header, then assume age is zero.  GetAgeValue does not
+  // modify its out param if the value does not exist.
+  TimeDelta age_value;
+  GetAgeValue(&age_value);
 
-  if (lifetimes.freshness + lifetimes.staleness > age)
-    return VALIDATION_ASYNCHRONOUS;
+  TimeDelta apparent_age = std::max(TimeDelta(), response_time - date_value);
+  TimeDelta corrected_received_age = std::max(apparent_age, age_value);
+  TimeDelta response_delay = response_time - request_time;
+  TimeDelta corrected_initial_age = corrected_received_age + response_delay;
 
-  return VALIDATION_SYNCHRONOUS;
+  // From the age calculation algorithm above, we can derive the corrected
+  // response time, the |now| for which |current_age == 0|. Substituting into
+  // the RFC 2616 13.2.3 equations above, and simplyfing:
+  //
+  //    corrected_initial_age + resident_time == 0
+  //    corrected_initial_age + corrected_response_time - response_time == 0
+  //    corrected_response_time == response_time - corrected_initial_age
+
+  ExpirationTimes expirations;
+  expirations.corrected_response_time = response_time - corrected_initial_age;
+  CalculateLifetimes(response_time, &expirations.freshness_lifetime,
+                     &expirations.staleness_lifetime);
+  return expirations;
 }
 
 // From RFC 2616 section 13.2.4:
 //
 // The max-age directive takes priority over Expires, so if max-age is present
 // in a response, the calculation is simply:
 //
 //   freshness_lifetime = max_age_value
 //
 // Otherwise, if Expires is present in the response, the calculation is:
 //
 //   freshness_lifetime = expires_value - date_value
 //
 // Note that neither of these calculations is vulnerable to clock skew, since
 // all of the information comes from the origin server.
 //
 // Also, if the response does have a Last-Modified time, the heuristic
 // expiration value SHOULD be no more than some fraction of the interval since
 // that time. A typical setting of this fraction might be 10%:
 //
 //   freshness_lifetime = (date_value - last_modified_value) * 0.10
 //
 // If the stale-while-revalidate directive is present, then it is used to set
 // the |staleness| time, unless it overridden by another directive.
 //
-HttpResponseHeaders::FreshnessLifetimes
-HttpResponseHeaders::GetFreshnessLifetimes(const Time& response_time) const {
-  FreshnessLifetimes lifetimes;
+void HttpResponseHeaders::CalculateLifetimes(
+    const Time& response_time,
+    TimeDelta* out_freshness_lifetime,
+    TimeDelta* out_staleness_lifetime) const {
+  *out_freshness_lifetime = TimeDelta();
+  *out_staleness_lifetime = TimeDelta();
+
   // Check for headers that force a response to never be fresh.  For backwards
   // compat, we treat "Pragma: no-cache" as a synonym for "Cache-Control:
   // no-cache" even though RFC 2616 does not specify it.
   if (HasHeaderValue("cache-control", "no-cache") ||
       HasHeaderValue("cache-control", "no-store") ||
       HasHeaderValue("pragma", "no-cache") ||
       // Vary: * is never usable: see RFC 2616 section 13.6.
       HasHeaderValue("vary", "*")) {
-    return lifetimes;
+    return;
   }
 
   // Cache-Control directive must_revalidate overrides stale-while-revalidate.
   bool must_revalidate = HasHeaderValue("cache-control", "must-revalidate");
 
-  if (must_revalidate || !GetStaleWhileRevalidateValue(&lifetimes.staleness)) {
-    DCHECK_EQ(TimeDelta(), lifetimes.staleness);
+  if (must_revalidate ||
+      !GetStaleWhileRevalidateValue(out_staleness_lifetime)) {
+    DCHECK_EQ(TimeDelta(), *out_staleness_lifetime);
   }
 
   // NOTE: "Cache-Control: max-age" overrides Expires, so we only check the
   // Expires header after checking for max-age in GetFreshnessLifetimes.  This
   // is important since "Expires: <date in the past>" means not fresh, but
   // it should not trump a max-age value.
-  if (GetMaxAgeValue(&lifetimes.freshness))
-    return lifetimes;
+  if (GetMaxAgeValue(out_freshness_lifetime))
+    return;
 
   // If there is no Date header, then assume that the server response was
   // generated at the time when we received the response.
   Time date_value;
   if (!GetDateValue(&date_value))
     date_value = response_time;
 
   Time expires_value;
   if (GetExpiresValue(&expires_value)) {
     // The expires value can be a date in the past!
     if (expires_value > date_value) {
-      lifetimes.freshness = expires_value - date_value;
-      return lifetimes;
+      *out_freshness_lifetime = expires_value - date_value;
+      return;
     }
 
-    DCHECK_EQ(TimeDelta(), lifetimes.freshness);
-    return lifetimes;
+    DCHECK_EQ(TimeDelta(), *out_freshness_lifetime);
+    return;
   }
 
   // From RFC 2616 section 13.4:
   //
   //   A response received with a status code of 200, 203, 206, 300, 301 or 410
   //   MAY be stored by a cache and used in reply to a subsequent request,
   //   subject to the expiration mechanism, unless a cache-control directive
   //   prohibits caching.
   //   ...
   //   A response received with any other status code (e.g. status codes 302
@@ skipping 13 matching lines @@
   // https://datatracker.ietf.org/doc/draft-reschke-http-status-308/ is an
   // experimental RFC that adds 308 permanent redirect as well, for which "any
   // future references ... SHOULD use one of the returned URIs."
   if ((response_code_ == 200 || response_code_ == 203 ||
        response_code_ == 206) && !must_revalidate) {
     // TODO(darin): Implement a smarter heuristic.
     Time last_modified_value;
     if (GetLastModifiedValue(&last_modified_value)) {
       // The last-modified value can be a date in the future!
       if (last_modified_value <= date_value) {
-        lifetimes.freshness = (date_value - last_modified_value) / 10;
-        return lifetimes;
+        *out_freshness_lifetime = (date_value - last_modified_value) / 10;
+        return;
       }
     }
   }
 
   // These responses are implicitly fresh (unless otherwise overruled):
   if (response_code_ == 300 || response_code_ == 301 || response_code_ == 308 ||
       response_code_ == 410) {
-    lifetimes.freshness = TimeDelta::Max();
-    lifetimes.staleness = TimeDelta();  // It should never be stale.
-    return lifetimes;
+    *out_freshness_lifetime = TimeDelta::Max();
+    *out_staleness_lifetime = TimeDelta();  // It should never be stale.
+    return;
   }
 
   // Our heuristic freshness estimate for this resource is 0 seconds, in
   // accordance with common browser behaviour. However, stale-while-revalidate
   // may still apply.
-  DCHECK_EQ(TimeDelta(), lifetimes.freshness);
-  return lifetimes;
-}
-
-// From RFC 2616 section 13.2.3:
-//
-// Summary of age calculation algorithm, when a cache receives a response:
-//
-//   /*
-//    * age_value
-//    *      is the value of Age: header received by the cache with
-//    *              this response.
-//    * date_value
-//    *      is the value of the origin server's Date: header
-//    * request_time
-//    *      is the (local) time when the cache made the request
-//    *              that resulted in this cached response
-//    * response_time
-//    *      is the (local) time when the cache received the
-//    *              response
-//    * now
-//    *      is the current (local) time
-//    */
-//   apparent_age = max(0, response_time - date_value);
-//   corrected_received_age = max(apparent_age, age_value);
-//   response_delay = response_time - request_time;
-//   corrected_initial_age = corrected_received_age + response_delay;
-//   resident_time = now - response_time;
-//   current_age   = corrected_initial_age + resident_time;
-//
-TimeDelta HttpResponseHeaders::GetCurrentAge(const Time& request_time,
-                                             const Time& response_time,
-                                             const Time& current_time) const {
-  // If there is no Date header, then assume that the server response was
-  // generated at the time when we received the response.
-  Time date_value;
-  if (!GetDateValue(&date_value))
-    date_value = response_time;
-
-  // If there is no Age header, then assume age is zero.  GetAgeValue does not
-  // modify its out param if the value does not exist.
-  TimeDelta age_value;
-  GetAgeValue(&age_value);
-
-  TimeDelta apparent_age = std::max(TimeDelta(), response_time - date_value);
-  TimeDelta corrected_received_age = std::max(apparent_age, age_value);
-  TimeDelta response_delay = response_time - request_time;
-  TimeDelta corrected_initial_age = corrected_received_age + response_delay;
-  TimeDelta resident_time = current_time - response_time;
-  TimeDelta current_age = corrected_initial_age + resident_time;
-
-  return current_age;
+  DCHECK_EQ(TimeDelta(), *out_freshness_lifetime);
+  return;
 }
 
 bool HttpResponseHeaders::GetMaxAgeValue(TimeDelta* result) const {
   return GetCacheControlDirective("max-age", result);
 }
 
 bool HttpResponseHeaders::GetAgeValue(TimeDelta* result) const {
   std::string value;
   if (!EnumerateHeader(nullptr, "Age", &value))
     return false;
@@ skipping 306 matching lines @@
   return true;
 }
 
 bool HttpResponseHeaders::IsChunkEncoded() const {
   // Ignore spurious chunked responses from HTTP/1.0 servers and proxies.
   return GetHttpVersion() >= HttpVersion(1, 1) &&
       HasHeaderValue("Transfer-Encoding", "chunked");
 }
 
 }  // namespace net