stale-while-revalidate experimental implementation.

net/http/http_response_headers.h

Index: net/http/http_response_headers.h
diff --git a/net/http/http_response_headers.h b/net/http/http_response_headers.h
index ddab798c0a2c0795556d1b2da0a583574c581553..e6bbf2e58d6c33d357e87b9e1b8f8b3a217b1124 100644
--- a/net/http/http_response_headers.h
+++ b/net/http/http_response_headers.h
@@ -43,6 +43,25 @@ class NET_EXPORT HttpResponseHeaders
   static const PersistOptions PERSIST_SANS_RANGES = 1 << 4;
   static const PersistOptions PERSIST_SANS_SECURITY_STATE = 1 << 5;
 
+  enum ValidationType {
+    VALIDATION_NONE = 0,      // the resource is fresh
+    VALIDATION_ASYNCHRONOUS,  // the resource requires async revalidation
+    VALIDATION_SYNCHRONOUS    // the resource requires sync revalidation
+  };
+
+  struct Freshness {
+    // Construct an "unusable" Freshness entry (lifetime = 0, usable = false)
+    Freshness();
+    // Construct a "usable" Freshness entry (lifetime >= 0, usable = true)
+    explicit Freshness(const base::TimeDelta& lifetime);
+    ~Freshness();
+
+    // True if the response might be usable (depending on freshness).
+    const bool usable;
+    // Invariant: if usable is false, lifetime is 0.
+    const base::TimeDelta lifetime;
+  };
+
   static const char kContentRange[];
 
   // Parses the given raw_headers.  raw_headers should be formatted thus:
@@ -201,19 +220,26 @@ class NET_EXPORT HttpResponseHeaders
   // 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 amount of time the server claims the response is fresh from
+  // Returns VALIDATION_NONE if the response can be reused without
+  // validation. VALIDATION_ASYNCHRONOUS means the response can be re-used, but
+  // asynchronous revalidation must be performed. VALIDATION_SYNCHRONOUS means
+  // that the result cannot be reused without revalidation.
+  // 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.
+  ValidationType RequiresValidation(const base::Time& request_time,
+                                    const base::Time& response_time,
+                                    const base::Time& current_time) const;
+
+  // Calculates 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;
+  // RequiresValidation for a description of the response_time parameter.  Sets
+  // |Freshness.usable| to false and |Freshness.lifetime| to zero if there is a
+  // header that prohibits the use of the response. This allows us to
+  // distinguish cases when a stale response cannot be used by
+  // stale-while-revalidate.
+  Freshness GetFreshnessLifetime(const base::Time& response_time) 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.