DNS: Expose stale results through HostResolverImpl.

net/dns/host_resolver_impl.h

Index: net/dns/host_resolver_impl.h
diff --git a/net/dns/host_resolver_impl.h b/net/dns/host_resolver_impl.h
index 5c3124cba5962bce899455a799e9e77e65a10bd4..d23f64f2f219a049309fd6593cc7c9a24708929f 100644
--- a/net/dns/host_resolver_impl.h
+++ b/net/dns/host_resolver_impl.h
@@ -137,12 +137,16 @@ class NET_EXPORT HostResolverImpl
               const CompletionCallback& callback,
               RequestHandle* out_req,
               const BoundNetLog& source_net_log) override;
-  int ResolveFromCache(const RequestInfo& info,
-                       AddressList* addresses,
-                       const BoundNetLog& source_net_log) override;
   void ChangeRequestPriority(RequestHandle req,
                              RequestPriority priority) override;
   void CancelRequest(RequestHandle req) override;
+  int ResolveFromCache(const RequestInfo& info,
+                       AddressList* addresses,
+                       const BoundNetLog& source_net_log) override;
+  int ResolveStaleFromCache(const RequestInfo& info,
+                            AddressList* addresses,
+                            HostCache::EntryStaleness* stale_info,
+                            const BoundNetLog& source_net_log) override;
   void SetDnsClientEnabled(bool enabled) override;
   HostCache* GetHostCache() override;
   std::unique_ptr<base::Value> GetDnsConfigAsValue() const override;
@@ -170,10 +174,15 @@ class NET_EXPORT HostResolverImpl
   // ERR_NAME_NOT_RESOLVED if either hostname is invalid or IP literal is
   // incompatible, ERR_DNS_CACHE_MISS if entry was not found in cache and
   // HOSTS and is not localhost.
+  //
+  // If |stale_info| is non-null, then stale cache entries can be returned, and
+  // |*stale_info| will be filled in with details of the entry's staleness (if
+  // an entry, fresh or stale, was returned).

[Randy Smith (Not in Mondays), 2016/05/07 01:36:31]

(I'll remark in passing that I'm twitchy about the nullity of an output
parameter control a function's behavior and I'd rather have the control done
some other way (maybe a separate function?), but given this is a well
documented, private, helper function that doesn't really even rise to the level
of suggestion; I'm good with you making your own decision.  But I wanted to
express my discomfort :-}.)

[Julia Tuttle, 2016/05/11 20:19:48]

Done.

   int ResolveHelper(const Key& key,
                     const RequestInfo& info,
                     const IPAddress* ip_address,
                     AddressList* addresses,
+                    HostCache::EntryStaleness* stale_info,
                     const BoundNetLog& request_net_log);
 
   // Tries to resolve |key| as an IP, returns true and sets |net_error| if
@@ -187,10 +196,15 @@ class NET_EXPORT HostResolverImpl
   // If |key| is not found in cache returns false, otherwise returns
   // true, sets |net_error| to the cached error code and fills |addresses|
   // if it is a positive entry.
+  //
+  // If |stale_info| is non-null, then stale cache entries can be returned, and
+  // |*stale_info| will be filled in with details of the entry's staleness (if
+  // an entry, fresh or stale, was returned).
   bool ServeFromCache(const Key& key,
                       const RequestInfo& info,
                       int* net_error,
-                      AddressList* addresses);
+                      AddressList* addresses,
+                      HostCache::EntryStaleness* stale_info);
 
   // If we have a DnsClient with a valid DnsConfig, and |key| is found in the
   // HOSTS file, returns true and fills |addresses|. Otherwise returns false.