text: // 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 CHROME_BROWSER_EXTENSIONS_API_DNS_HOST_RESOLVER_WRAPPER_H_
  #define CHROME_BROWSER_EXTENSIONS_API_DNS_HOST_RESOLVER_WRAPPER_H_
  
  #include "base/memory/singleton.h"
  #include "net/base/host_resolver.h"
  
  namespace extensions {
  
  // Used for testing. In production code, this class does nothing interesting.
  // This class is a singleton that holds a pointer to a mock HostResolver, or
  // else to NULL. API classes that need to resolve hostnames ask this class for
  // the correct HostResolver to use, passing in the one that they want to use,
  // thereby avoiding most lifetime issues, and it will reply with either that
  // same one, or else the test version to use instead.
  //
  // This is a pretty complicated way to replace a single pointer with another.
  // TODO(miket): make the previous statement obsolete.
  class HostResolverWrapper {
   public:
    static HostResolverWrapper* GetInstance();
  
    // Given a pointer to a real host resolver, returns the same pointer or else
    // a substitute MockHostResolver to use instead. If
    // SetHostResolverForTesting() hasn't been called, then this method returns
    // the supplied argument as its result.
    net::HostResolver* GetHostResolver(net::HostResolver* real_resolver);
  
    // Sets the MockHostResolver to return in GetHostResolver().
    void SetHostResolverForTesting(net::HostResolver* mock_resolver);
  
   private:
    HostResolverWrapper();
    friend struct DefaultSingletonTraits<HostResolverWrapper>;
  
    net::HostResolver* resolver_;
  
    DISALLOW_COPY_AND_ASSIGN(HostResolverWrapper);
  };
  
  }  // namespace extensions
  
  #endif  // CHROME_BROWSER_EXTENSIONS_API_DNS_HOST_RESOLVER_WRAPPER_H_
  