Refactorings surrounding HostResolver:...

net/base/host_resolver_impl.h

Index: net/base/host_resolver_impl.h
===================================================================
--- net/base/host_resolver_impl.h	(revision 20435)
+++ net/base/host_resolver_impl.h	(working copy)
@@ -2,39 +2,21 @@
 // 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_H_
-#define NET_BASE_HOST_RESOLVER_H_
+#ifndef NET_BASE_HOST_RESOLVER_IMPL_H_
+#define NET_BASE_HOST_RESOLVER_IMPL_H_
 
 #include <string>
 #include <vector>
 
-#include "base/basictypes.h"
-#include "base/lock.h"
-#include "base/ref_counted.h"
-#include "googleurl/src/gurl.h"
-#include "net/base/completion_callback.h"
 #include "net/base/host_cache.h"
+#include "net/base/host_resolver.h"
+#include "net/base/host_resolver_proc.h"
 
-class MessageLoop;
-
 namespace net {
 
-class AddressList;
-class HostMapper;
-
-// This class represents the task of resolving hostnames (or IP address
-// literal) to an AddressList object.
-//
-// HostResolver handles multiple requests at a time, so when cancelling a
-// request the Request* handle that was returned by Resolve() needs to be
-// given.  A simpler alternative for consumers that only have 1 outstanding
-// request at a time is to create a SingleRequestHostResolver wrapper around
-// HostResolver (which will automatically cancel the single request when it
-// goes out of scope).
-//
 // For each hostname that is requested, HostResolver creates a
-// HostResolver::Job. This job gets dispatched to a thread in the global
-// WorkerPool, where it runs "getaddrinfo(hostname)". If requests for that same
+// HostResolverImpl::Job. This job gets dispatched to a thread in the global
+// WorkerPool, where it runs SystemHostResolverProc(). If requests for that same
 // host are made while the job is already outstanding, then they are attached
 // to the existing job rather than creating a new one. This avoids doing
 // parallel resolves for the same host.
@@ -42,7 +24,7 @@
 // The way these classes fit together is illustrated by:
 //
 //
-//            +------------- HostResolver ---------------+
+//            +----------- HostResolverImpl -------------+
 //            |                    |                     |
 //           Job                  Job                   Job
 //       (for host1)          (for host2)           (for hostX)
@@ -51,126 +33,52 @@
 //  (port1)     (port2)  (port3)      (port4)  (port5)      (portX)
 //
 //
-// When a HostResolver::Job finishes its work in the threadpool, the callbacks
-// of each waiting request are run on the origin thread.
+// When a HostResolverImpl::Job finishes its work in the threadpool, 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!
 //
-class HostResolver : public base::RefCounted<HostResolver> {
+class HostResolverImpl : public HostResolver {
  public:
-  // The parameters for doing a Resolve(). |hostname| and |port| are required,
-  // the rest are optional (and have reasonable defaults).
-  class RequestInfo {
-   public:
-    RequestInfo(const std::string& hostname, int port)
-        : hostname_(hostname),
-          port_(port),
-          allow_cached_response_(true),
-          is_speculative_(false) {}
-
-    const int port() const { return port_; }
-    const std::string& hostname() const { return hostname_; }
-
-    bool allow_cached_response() const { return allow_cached_response_; }
-    void set_allow_cached_response(bool b) { allow_cached_response_ = b; }
-
-    bool is_speculative() const { return is_speculative_; }
-    void set_is_speculative(bool b) { is_speculative_ = b; }
-
-    const GURL& referrer() const { return referrer_; }
-    void set_referrer(const GURL& referrer) { referrer_ = referrer; }
-
-   private:
-    // The hostname to resolve.
-    std::string hostname_;
-
-    // The port number to set in the result's sockaddrs.
-    int port_;
-
-    // Whether it is ok to return a result from the host cache.
-    bool allow_cached_response_;
-
-    // Whether this request was started by the DNS prefetcher.
-    bool is_speculative_;
-
-    // Optional data for consumption by observers. This is the URL of the
-    // page that lead us to the navigation, for DNS prefetcher's benefit.
-    GURL referrer_;
-  };
-
-  // Interface for observing the requests that flow through a HostResolver.
-  class Observer {
-   public:
-    virtual ~Observer() {}
-
-    // Called at the start of HostResolver::Resolve(). |id| is a unique number
-    // given to the request, so it can be matched up with a corresponding call
-    // to OnFinishResolutionWithStatus() or OnCancelResolution().
-    virtual void OnStartResolution(int id, const RequestInfo& info) = 0;
-
-    // Called on completion of request |id|. Note that if the request was
-    // cancelled, OnCancelResolution() will be called instead.
-    virtual void OnFinishResolutionWithStatus(int id, bool was_resolved,
-                                              const RequestInfo& info) = 0;
-
-    // Called when request |id| has been cancelled. A request is "cancelled"
-    // if either the HostResolver is destroyed while a resolution is in
-    // progress, or HostResolver::CancelRequest() is called.
-    virtual void OnCancelResolution(int id, const RequestInfo& info) = 0;
-  };
-
   // Creates a HostResolver that caches up to |max_cache_entries| for
-  // |cache_duration_ms| milliseconds.
-  //
-  // TODO(eroman): Get rid of the default parameters as it violate google
-  // style. This is temporary to help with refactoring.
-  HostResolver(int max_cache_entries = 100, int cache_duration_ms = 60000);
+  // |cache_duration_ms| milliseconds. |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)
+  HostResolverImpl(HostResolverProc* resolver_proc,
+                   int max_cache_entries,
+                   int cache_duration_ms);
 
   // If any completion callbacks are pending when the resolver is destroyed,
   // the host resolutions are cancelled, and the completion callbacks will not
   // be called.
-  ~HostResolver();
+  virtual ~HostResolverImpl();
 
-  // Opaque type used to cancel a request.
-  class Request;
+  // HostResolver methods:
+  virtual int Resolve(const RequestInfo& info, AddressList* addresses,
+                      CompletionCallback* callback, RequestHandle* out_req);
+  virtual void CancelRequest(RequestHandle req);
+  virtual void AddObserver(Observer* observer);
+  virtual void RemoveObserver(Observer* observer);
 
-  // Resolves the given hostname (or IP address literal), filling out the
-  // |addresses| object upon success.  The |info.port| parameter will be set as
-  // the sin(6)_port field of the sockaddr_in{6} struct.  Returns OK if
-  // successful or an error code upon failure.
-  //
-  // When callback is null, the operation completes synchronously.
-  //
-  // When callback is non-null, the operation will be performed asynchronously.
-  // ERR_IO_PENDING is returned if it has been scheduled successfully. Real
-  // result code will be passed to the completion callback. If |req| is
-  // non-NULL, then |*req| will be filled with a handle to the async request.
-  // This handle is not valid after the request has completed.
-  int Resolve(const RequestInfo& info, AddressList* addresses,
-              CompletionCallback* callback, Request** req);
-
-  // Cancels the specified request. |req| is the handle returned by Resolve().
-  // After a request is cancelled, its completion callback will not be called.
-  void CancelRequest(Request* req);
-
-  // Adds an observer to this resolver. The observer will be notified of the
-  // start and completion of all requests (excluding cancellation). |observer|
-  // must remain valid for the duration of this HostResolver's lifetime.
-  void AddObserver(Observer* observer);
-
-  // Unregisters an observer previously added by AddObserver().
-  void RemoveObserver(Observer* observer);
-
   // TODO(eroman): temp hack for http://crbug.com/15513
-  void Shutdown();
+  virtual void Shutdown();
 
  private:
   class Job;
+  class Request;
   typedef std::vector<Request*> RequestsList;
   typedef base::hash_map<std::string, scoped_refptr<Job> > JobMap;
   typedef std::vector<Observer*> ObserversList;
 
+  // Returns the HostResolverProc to use for this instance.
+  HostResolverProc* effective_resolver_proc() const {
+    return resolver_proc_ ?
+        resolver_proc_.get() : HostResolverProc::GetDefault();
+  }
+
   // Adds a job to outstanding jobs list.
   void AddOutstandingJob(Job* job);
 
@@ -213,88 +121,16 @@
   // Observers are the only consumers of this ID number.
   int next_request_id_;
 
+  // The procedure to use for resolving host names. This will be NULL, except
+  // in the case of unit-tests which inject custom host resolving behaviors.
+  scoped_refptr<HostResolverProc> resolver_proc_;
+
   // TODO(eroman): temp hack for http://crbug.com/15513
   bool shutdown_;
 
-  DISALLOW_COPY_AND_ASSIGN(HostResolver);
+  DISALLOW_COPY_AND_ASSIGN(HostResolverImpl);
 };
 
-// This class represents the task of resolving a hostname (or IP address
-// literal) to an AddressList object.  It wraps HostResolver to resolve only a
-// single hostname at a time and cancels this request when going out of scope.
-class SingleRequestHostResolver {
- public:
-  explicit SingleRequestHostResolver(HostResolver* resolver);
-
-  // If a completion callback is pending when the resolver is destroyed, the
-  // host resolution is cancelled, and the completion callback will not be
-  // called.
-  ~SingleRequestHostResolver();
-
-  // Resolves the given hostname (or IP address literal), filling out the
-  // |addresses| object upon success. See HostResolver::Resolve() for details.
-  int Resolve(const HostResolver::RequestInfo& info,
-              AddressList* addresses, CompletionCallback* callback);
-
- private:
-  // Callback for when the request to |resolver_| completes, so we dispatch
-  // to the user's callback.
-  void OnResolveCompletion(int result);
-
-  // The actual host resolver that will handle the request.
-  scoped_refptr<HostResolver> resolver_;
-
-  // The current request (if any).
-  HostResolver::Request* cur_request_;
-  CompletionCallback* cur_request_callback_;
-
-  // Completion callback for when request to |resolver_| completes.
-  net::CompletionCallbackImpl<SingleRequestHostResolver> callback_;
-
-  DISALLOW_COPY_AND_ASSIGN(SingleRequestHostResolver);
-};
-
-// A helper class used in unit tests to alter hostname mappings.  See
-// SetHostMapper for details.
-class HostMapper : public base::RefCountedThreadSafe<HostMapper> {
- public:
-  virtual ~HostMapper() {}
-
-  // Returns possibly altered hostname, or empty string to simulate
-  // a failed lookup.
-  virtual std::string Map(const std::string& host) = 0;
-
- protected:
-  // Ask previous host mapper (if set) for mapping of given host.
-  std::string MapUsingPrevious(const std::string& host);
-
- private:
-  friend class ScopedHostMapper;
-
-  // Set mapper to ask when this mapper doesn't want to modify the result.
-  void set_previous_mapper(HostMapper* mapper) {
-    previous_mapper_ = mapper;
-  }
-
-  scoped_refptr<HostMapper> previous_mapper_;
-};
-
-#ifdef UNIT_TEST
-// This function is designed to allow unit tests to override the behavior of
-// HostResolver.  For example, a HostMapper instance can force all hostnames
-// to map to a fixed IP address such as 127.0.0.1.
-//
-// The previously set HostMapper (or NULL if there was none) is returned.
-//
-// NOTE: This function is not thread-safe, so take care to only call this
-// function while there are no outstanding HostResolver instances.
-//
-// NOTE: In most cases, you should use ScopedHostMapper instead, which is
-// defined in host_resolver_unittest.h
-//
-HostMapper* SetHostMapper(HostMapper* host_mapper);
-#endif
-
 }  // namespace net
 
-#endif  // NET_BASE_HOST_RESOLVER_H_
+#endif  // NET_BASE_HOST_RESOLVER_IMPL_H_