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

This is Windows-only for now, and is disabled by default.  Start
Chrome with the flag --enable-dhcp-wpad to enable the feature.  See
discussion in comment on DhcpProxyScriptFetcherFactory for why this
needs to be done in a per-platform way rather than cross-platform.
The code is factored so that adding other platform implementations
will be straight forward.

Most of the implementation is stand-alone and extends the
ScriptProxyFetcher class hierarchy (and makes its interface slightly
more generic).  The integration point into existing code is in
InitProxyResolver, which previously handled fallback from DNS
auto-detect to custom PAC URL and now does fallback from DHCP to DNS
to custom PAC URL.

BUG=18575
TEST=net_unittests has good coverage for the new and changed code, but
manual tests on a network with a PAC URL configured in DHCP are also
needed.

Review URL: http://codereview.chromium.org/6831025

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@85646 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 98 insertions, 0 deletions

diff --git a/net/proxy/dhcp_proxy_script_fetcher.h b/net/proxy/dhcp_proxy_script_fetcher.h
new file mode 100644
index 0000000..adb011d
--- /dev/null
+++ b/net/proxy/dhcp_proxy_script_fetcher.h
@@ -0,0 +1,98 @@
+// 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_H_
+#define NET_PROXY_DHCP_SCRIPT_FETCHER_H_
+#pragma once
+
+#include "base/basictypes.h"
+#include "base/compiler_specific.h"
+#include "base/string16.h"
+#include "net/base/completion_callback.h"
+#include "net/proxy/proxy_script_fetcher.h"
+#include "net/url_request/url_request_context.h"
+
+namespace net {
+
+// Interface for classes that can fetch a proxy script as configured via DHCP.
+//
+// The Fetch method on this interface tries to retrieve the most appropriate
+// PAC script configured via DHCP.
+//
+// Normally there are zero or one DHCP scripts configured, but in the
+// presence of multiple adapters with DHCP enabled, the fetcher resolves
+// which PAC script to use if one or more are available.
+class DhcpProxyScriptFetcher {
+ public:
+  // Destruction should cancel any outstanding requests.
+  virtual ~DhcpProxyScriptFetcher();
+
+  // Attempts to retrieve the most appropriate PAC script configured via DHCP,
+  // and invokes |callback| on completion.
+  //
+  // Returns OK on success, otherwise the error code. If the return code is
+  // ERR_IO_PENDING, then the request completes asynchronously, and |callback|
+  // will be invoked later with the final error code.
+  //
+  // After synchronous or asynchronous completion with a result code of OK,
+  // |*utf16_text| is filled with the response. On failure, the result text is
+  // an empty string, and the result code is a network error. Some special
+  // network errors that may occur are:
+  //
+  //    ERR_PAC_NOT_IN_DHCP   -- no script configured in DHCP.
+  //
+  //    The following all indicate there was one or more script configured
+  //    in DHCP but all failed to download, and the error for the most
+  //    preferred adapter that had a script configured was what the error
+  //    code says:
+  //
+  //      ERR_TIMED_OUT         -- fetch took too long to complete.
+  //      ERR_FILE_TOO_BIG      -- response body was too large.
+  //      ERR_PAC_STATUS_NOT_OK -- script failed to download.
+  //      ERR_NOT_IMPLEMENTED   -- script required authentication.
+  //
+  // If the request is cancelled (either using the "Cancel()" method or by
+  // deleting |this|), then no callback is invoked.
+  //
+  // Only one fetch is allowed to be outstanding at a time.
+  virtual int Fetch(string16* utf16_text,
+                    CompletionCallback* callback) = 0;
+
+  // Aborts the in-progress fetch (if any).
+  virtual void Cancel() = 0;
+
+  // After successful completion of |Fetch()|, this will return the URL
+  // retrieved from DHCP.  It is reset if/when |Fetch()| is called again.
+  virtual const GURL& GetPacURL() const = 0;
+
+  // Intended for unit tests only, so they can test that factories return
+  // the right types under given circumstances.
+  virtual std::string GetFetcherName() const;
+
+ protected:
+  DhcpProxyScriptFetcher();
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(DhcpProxyScriptFetcher);
+};
+
+// A do-nothing retriever, always returns synchronously with
+// ERR_NOT_IMPLEMENTED result and empty text.
+class DoNothingDhcpProxyScriptFetcher : public DhcpProxyScriptFetcher {
+ public:
+  DoNothingDhcpProxyScriptFetcher();
+  virtual ~DoNothingDhcpProxyScriptFetcher();
+
+  virtual int Fetch(string16* utf16_text,
+                    CompletionCallback* callback) OVERRIDE;
+  virtual void Cancel() OVERRIDE;
+  virtual const GURL& GetPacURL() const OVERRIDE;
+ private:
+  GURL gurl_;
+  DISALLOW_COPY_AND_ASSIGN(DoNothingDhcpProxyScriptFetcher);
+};
+
+}  // namespace net
+
+#endif  // NET_PROXY_DHCP_SCRIPT_FETCHER_H_