DNS: Expose stale results through HostResolverImpl.

net/dns/host_resolver.h

Index: net/dns/host_resolver.h
diff --git a/net/dns/host_resolver.h b/net/dns/host_resolver.h
index 840aeb80e35de806ec97caa2ef86e07825b78e3b..3581889b13daad628630ccda019fe16748dcaa2f 100644
--- a/net/dns/host_resolver.h
+++ b/net/dns/host_resolver.h
@@ -18,6 +18,7 @@
 #include "net/base/net_export.h"
 #include "net/base/prioritized_dispatcher.h"
 #include "net/base/request_priority.h"
+#include "net/dns/host_cache.h"
 
 namespace base {
 class Value;
@@ -27,7 +28,6 @@ namespace net {
 
 class AddressList;
 class BoundNetLog;
-class HostCache;
 class HostResolverProc;
 class NetLog;
 
@@ -155,14 +155,6 @@ class NET_EXPORT HostResolver {
                       RequestHandle* out_req,
                       const BoundNetLog& net_log) = 0;
 
-  // Resolves the given hostname (or IP address literal) out of cache or HOSTS
-  // file (if enabled) only. This is guaranteed to complete synchronously.
-  // This acts like |Resolve()| if the hostname is IP literal, or cached value
-  // or HOSTS entry exists. Otherwise, ERR_DNS_CACHE_MISS is returned.
-  virtual int ResolveFromCache(const RequestInfo& info,
-                               AddressList* addresses,
-                               const BoundNetLog& net_log) = 0;
-
   // Changes the priority of the specified request. |req| is the handle returned
   // by Resolve(). ChangeRequestPriority must NOT be called after the request's
   // completion callback has already run or the request was canceled.
@@ -175,6 +167,52 @@ class NET_EXPORT HostResolver {
   // has already run or the request was canceled.
   virtual void CancelRequest(RequestHandle req) = 0;
 
+  // Resolves the given hostname (or IP address literal) out of cache or HOSTS
+  // file (if enabled) only. This is guaranteed to complete synchronously.
+  // This acts like |Resolve()| if the hostname is IP literal, or cached value
+  // or HOSTS entry exists. Otherwise, ERR_DNS_CACHE_MISS is returned.
+  virtual int ResolveFromCache(const RequestInfo& info,
+                               AddressList* addresses,
+                               const BoundNetLog& net_log) = 0;
+
+  // Like |ResolveFromCache()|, but can return a stale result if the
+  // implementation supports it. Fills in |*stale_info| if a response is
+  // returned to indicate how stale (or not) it is.
+  virtual int ResolveStaleFromCache(const RequestInfo& info,
+                                    AddressList* addresses,
+                                    HostCache::EntryStaleness* stale_info,
+                                    const BoundNetLog& net_log);
+
+  // Uses |ResolveStaleFromCache| and |Resolve| to get fresh data (either from
+  // the cache or from the network) but also return stale data if any is
+  // available.
+  //
+  // If a fresh result is available in cache, populates |addresses| and returns
+  // it synchronously.
+  //
+  // Otherwise, starts a network request, returns ERR_IO_PENDING, and:
+  //
+  // If a stale result is available in cache, returns it through
+  // |*stale_error|, |*stale_addresses|, and |*stale_info|.
+  //
+  // If no result is available in cache, sets |*stale_error| to
+  // ERR_DNS_CACHE_MISS.
+  //
+  // In either asynchronous case:
+  //
+  // If |out_req| is non-NULL, then |*out_req| will be filled with a handle to
+  // the async request. This handle is not valid after the request has
+  // completed.
+  int ResolveStale(const RequestInfo& info,
+                   RequestPriority priority,
+                   AddressList* addresses,
+                   const CompletionCallback& callback,
+                   RequestHandle* out_req,
+                   int* stale_error,
+                   AddressList* stale_addresses,
+                   HostCache::EntryStaleness* stale_info,
+                   const BoundNetLog& net_log);
+
   // Enable or disable the built-in asynchronous DnsClient.
   virtual void SetDnsClientEnabled(bool enabled);