Adds support for the DHCP portion of the WPAD (proxy auto-discovery) protocol.

net/proxy/dhcp_proxy_script_fetcher_factory.h

Index: net/proxy/dhcp_proxy_script_fetcher_factory.h
diff --git a/net/proxy/dhcp_proxy_script_fetcher_factory.h b/net/proxy/dhcp_proxy_script_fetcher_factory.h
new file mode 100644
index 0000000000000000000000000000000000000000..10aea406ecc829bbfd1fa2d708f477d96a0ed769
--- /dev/null
+++ b/net/proxy/dhcp_proxy_script_fetcher_factory.h
@@ -0,0 +1,72 @@
+// Copyright (c) 2011 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_PROXY_DHCP_SCRIPT_FETCHER_FACTORY_H_
+#define NET_PROXY_DHCP_SCRIPT_FETCHER_FACTORY_H_
+#pragma once
+
+#include "base/basictypes.h"
+#include "base/memory/singleton.h"
+#include "net/base/completion_callback.h"
+#include "net/url_request/url_request_context.h"
+
+namespace net {
+
+class DhcpProxyScriptFetcher;
+
+// Factory for creating the appropriate concrete base class of
+// DhcpProxyScriptFetcher for your operating system and settings.
+//
+// You might think we could just implement a DHCP client at the protocol
+// level and have cross-platform support for retrieving PAC configuration
+// from DHCP, but unfortunately the DHCP protocol assumes there is a single
+// client per machine (specifically per network interface card), and there
+// is an implicit state machine between the client and server, so adding a
+// second client to the machine would not be advisable (see e.g. some
+// discussion of what can happen at this URL:
+// http://www.net.princeton.edu/multi-dhcp-one-interface-handling.html).
+//
+// Therefore, we have platform-specific implementations, and so we use
+// this factory to select the right one.
+class DhcpProxyScriptFetcherFactory {
+ public:
+  // This object is used as a Singleton by production code.
+  static DhcpProxyScriptFetcherFactory* GetInstance();

[eroman, 2011/04/21 05:22:48]

We can avoid singletons here by passing this as a dependency to
InitProxyResolver, when it is constructed on the chrome side of things
(similarly, we can test the command line flags to decide whether it should be
enabled or not at construction time).

[Jói, 2011/05/03 21:20:59]

I've changed this class to just have the static flag and static functions,
rather than being a singleton.  After looking at what it would take to provide
the configuration in URLRequestContext, I disagree that every callsite should
pass the flag.  I think it localizes responsibilities better to have flag
parsing outside of chrome/net, and receiving configuration via browser_main is
already done for many components of net in InitializeNetworkOptions().  So for
now, I'm leaving initialization of the "feature enabled" flag in
InitializeNetworkOptions.

+
+  // Ownership is transferred to the caller. url_request_context must be valid
+  // and its lifetime must exceed that of the returned DhcpProxyScriptFetcher.
+  //
+  // Note that while a request is in progress, the fetcher may be holding a
+  // reference to |url_request_context|. Be careful not to create cycles
+  // between the fetcher and the context; you can break such cycles by calling
+  // Cancel().
+  DhcpProxyScriptFetcher* Create(URLRequestContext* url_request_context) const;
+
+  // Attempts to enable/disable the DHCP WPAD feature.  Does nothing
+  // if |IsSupported()| returns false.
+  //
+  // The feature is disabled by default, for now.
+  void SetEnabled(bool enabled);
+
+  // Returns true if the DHCP WPAD feature is enabled.  Always returns
+  // false if |IsSupported()| is false.
+  bool IsEnabled() const;
+
+  // Returns true if the DHCP WPAD feature is supported on the current
+  // operating system.
+  static bool IsSupported();
+
+ protected:
+  DhcpProxyScriptFetcherFactory();
+  ~DhcpProxyScriptFetcherFactory();
+  friend struct DefaultSingletonTraits<DhcpProxyScriptFetcherFactory>;
+
+  bool feature_enabled_;
+
+  DISALLOW_COPY_AND_ASSIGN(DhcpProxyScriptFetcherFactory);
+};
+
+}  // namespace net
+
+#endif  // NET_PROXY_DHCP_SCRIPT_FETCHER_FACTORY_H_