[net] HostResolverImpl + DnsTransaction + DnsConfigService = Asynchronous DNS ready for experiments.

net/base/host_resolver_impl.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_BASE_HOST_RESOLVER_IMPL_H_
 #define NET_BASE_HOST_RESOLVER_IMPL_H_
 #pragma once
 
 #include <map>
 #include <vector>
 
 #include "base/basictypes.h"
 #include "base/gtest_prod_util.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/memory/weak_ptr.h"
 #include "base/threading/non_thread_safe.h"
 #include "base/time.h"
 #include "net/base/capturing_net_log.h"
 #include "net/base/host_cache.h"
 #include "net/base/host_resolver.h"
 #include "net/base/host_resolver_proc.h"
 #include "net/base/net_export.h"
 #include "net/base/net_log.h"
 #include "net/base/network_change_notifier.h"
 #include "net/base/prioritized_dispatcher.h"
+#include "net/dns/dns_config_service.h"
 
 namespace net {
 
+class DnsTransactionFactory;
+
 // For each hostname that is requested, HostResolver creates a
-// HostResolverImpl::Job. When this job gets dispatched it creates a ProcJob
+// HostResolverImpl::Job. When this job gets dispatched it creates a ProcTask
 // which runs the given HostResolverProc on a WorkerPool thread. If requests for
 // that same host are made during the job's lifetime, they are attached to the
 // existing job rather than creating a new one. This avoids doing parallel
 // resolves for the same host.
 //
 // The way these classes fit together is illustrated by:
 //
 //
 //            +----------- HostResolverImpl -------------+
 //            |                    |                     |
 //           Job                  Job                   Job
 //    (for host1, fam1)    (for host2, fam2)     (for hostx, famx)
 //       /    |   |            /   |   |             /   |   |
 //   Request ... Request  Request ... Request   Request ... Request
 //  (port1)     (port2)  (port3)      (port4)  (port5)      (portX)
 //
 // When a HostResolverImpl::Job finishes, the callbacks of each waiting request
 // are run on the origin thread.
 //
 // Thread safety: This class is not threadsafe, and must only be called
 // from one thread!
 //
 // The HostResolverImpl enforces limits on the maximum number of concurrent
 // threads using PrioritizedDispatcher::Limits.
 //
 // Jobs are ordered in the queue based on their priority and order of arrival.
 //
+// TODO(szym): Change DnsConfigService::Observer to Callback.
 class NET_EXPORT HostResolverImpl
     : public HostResolver,
       NON_EXPORTED_BASE(public base::NonThreadSafe),
       public NetworkChangeNotifier::IPAddressObserver,
       public NetworkChangeNotifier::DNSObserver,
+      public DnsConfigService::Observer,

[cbentzel, 2012/02/10 19:51:08]

NON_EXPORTED_BASE needed. 

[szym, 2012/02/10 21:49:36]

In the long run, I don't think we should be keeping the Observer pattern given
that HostResolverImpl owns the DnsConfigService.

[cbentzel, 2012/02/10 22:18:49]

Agree. But it doesn't compile without this on a component build.

[szym, 2012/02/11 00:01:37]

Oh yes, absolutely, that is fixed in the next patch.

       public base::SupportsWeakPtr<HostResolverImpl> {
  public:
   // Parameters for ProcTask which resolves hostnames using HostResolveProc.
   //
   // |resolver_proc| is used to perform the actual resolves; it must be
   // thread-safe since it is run from multiple worker threads. If
   // |resolver_proc| is NULL then the default host resolver procedure is
   // used (which is SystemHostResolverProc except if overridden).
   //
   // For each attempt, we could start another attempt if host is not resolved
@@ skipping 25 matching lines @@
     uint32 retry_factor;
   };
 
   // Creates a HostResolver that first uses the local cache |cache|, and then
   // falls back to |proc_params.resolver_proc|.
   //
   // If |cache| is NULL, then no caching is used. Otherwise we take
   // ownership of the |cache| pointer, and will free it during destruction.
   //
   // |job_limits| specifies the maximum number of jobs that the resolver will
-  // run at once (not counting potential duplicate attempts).
+  // run at once. This upper-bounds the total number of outstanding
+  // DNS transactions (not counting retransmissions and retries).
+  //
+  // |proc_job_limits| specifies the maximum number of calls to
+  // SystemHostResolverProc the resolver will make on WorkerPool (not counting
+  // retries).
+  //
+  // |dns_config_service| will be used to obtain DnsConfig for
+  // DnsTransactionFactory.
   //
   // |net_log| must remain valid for the life of the HostResolverImpl.
   // TODO(szym): change to scoped_ptr<HostCache>.
   HostResolverImpl(HostCache* cache,
                    const PrioritizedDispatcher::Limits& job_limits,
+                   const PrioritizedDispatcher::Limits& proc_limits,
                    const ProcTaskParams& proc_params,
+                   scoped_ptr<DnsConfigService> dns_config_service,
                    NetLog* net_log);
 
   // If any completion callbacks are pending when the resolver is destroyed,
   // the host resolutions are cancelled, and the completion callbacks will not
   // be called.
   virtual ~HostResolverImpl();
 
   // Configures maximum number of Jobs in the queue. Exposed for testing.
   // Only allowed when the queue is empty.
   void SetMaxQueuedJobs(size_t value);
@@ skipping 10 matching lines @@
   virtual void CancelRequest(RequestHandle req) OVERRIDE;
   virtual void SetDefaultAddressFamily(AddressFamily address_family) OVERRIDE;
   virtual AddressFamily GetDefaultAddressFamily() const OVERRIDE;
   virtual void ProbeIPv6Support() OVERRIDE;
   virtual HostCache* GetHostCache() OVERRIDE;
 
  private:
   class Job;
   class ProcTask;
   class IPv6ProbeJob;
+  class DnsTask;
   class Request;
   typedef HostCache::Key Key;
   typedef std::map<Key, Job*> JobMap;
   typedef std::vector<Request*> RequestsList;
 
   // Helper used by |Resolve()| and |ResolveFromCache()|.  Performs IP
   // literal and cache lookup, returns OK if successful,
   // 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.
   int ResolveHelper(const Key& key,
@@ skipping 23 matching lines @@
   // Callback from IPv6 probe activity.
   void IPv6ProbeSetDefaultAddressFamily(AddressFamily address_family);
 
   // Returns the (hostname, address_family) key to use for |info|, choosing an
   // "effective" address family by inheriting the resolver's default address
   // family when the request leaves it unspecified.
   Key GetEffectiveKeyForRequest(const RequestInfo& info) const;
 
   // Called by |job| when it has finished running. Records the result in cache
   // if necessary and dispatches another job if possible.
-  void OnJobFinished(Job* job, const AddressList& addrlist);
+  void OnJobFinished(Job* job,
+                     const AddressList& addrlist,

[cbentzel, 2012/02/10 19:51:08]

Should ttl be part of the AddressList?

[szym, 2012/02/10 21:49:36]

An excellent question. Makes sense for HostCache and DnsTask, but not quite for
HostResolverProc and getaddrinfo. (There's no explicit permission in POSIX to
cache the results of getaddrinfo.)

+                     base::TimeDelta ttl);
 
   // Removes |job| from |jobs_|.
   void RemoveJob(Job* job);
 
   // Aborts all in progress jobs and notifies their requests.
   // Might start new jobs.
   void AbortAllInProgressJobs();
 
-  // NetworkChangeNotifier::IPAddressObserver methods:
+  // NetworkChangeNotifier::IPAddressObserver interface.

[cbentzel, 2012/02/10 19:51:08]

Nit: the examples on http://dev.chromium.org/developers/coding-style show

// NetworkChangeNotifier::IPAddressObserver:

   virtual void OnIPAddressChanged() OVERRIDE;
 
-  // NetworkChangeNotifier::OnDNSChanged methods:
+  // NetworkChangeNotifier::DNSObserver interface.
   virtual void OnDNSChanged() OVERRIDE;
 
+  // DnsConfigService::Observer interface.
+  virtual void OnConfigChanged(const DnsConfig& dns_config) OVERRIDE;
+
   // Cache of host resolution results.
   scoped_ptr<HostCache> cache_;
 
   // Map from HostCache::Key to a Job.
   JobMap jobs_;
 
   // Starts Jobs according to their priority and the configured limits.
   PrioritizedDispatcher dispatcher_;
 
+  // Starts ProcTask if DnsTask fails. Enforces tighter limits than
+  // |dispatcher_|.
+  PrioritizedDispatcher proc_dispatcher_;
+
   // Limit on the maximum number of jobs queued in |dispatcher_|.
   size_t max_queued_jobs_;
 
   // Parameters for ProcTask.
   ProcTaskParams proc_params_;
 
+  scoped_ptr<DnsTransactionFactory> dns_transaction_factory_;
+
   // Address family to use when the request doesn't specify one.
   AddressFamily default_address_family_;
 
+  scoped_ptr<DnsConfigService> dns_config_service_;
+
   // Indicate if probing is done after each network change event to set address
   // family.
   // When false, explicit setting of address family is used.
   bool ipv6_probe_monitoring_;
 
   // The last un-cancelled IPv6ProbeJob (if any).
   scoped_refptr<IPv6ProbeJob> ipv6_probe_job_;
 
   // Any resolver flags that should be added to a request by default.
   HostResolverFlags additional_resolver_flags_;
 
   NetLog* net_log_;
 
   DISALLOW_COPY_AND_ASSIGN(HostResolverImpl);
 };
 
 }  // namespace net
 
 #endif  // NET_BASE_HOST_RESOLVER_IMPL_H_