When talking to a SOCKS v5 proxy, default to sending addresses as raw domains...

net/socket/socks5_client_socket.h

 // Copyright (c) 2009 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_SOCKET_SOCKS5_CLIENT_SOCKET_H_
 #define NET_SOCKET_SOCKS5_CLIENT_SOCKET_H_
 
 #include <string>
 
 #include "base/logging.h"
@@ skipping 13 matching lines @@
 
 // This ClientSocket is used to setup a SOCKSv5 handshake with a socks proxy.
 // Currently no SOCKSv5 authentication is supported.
 class SOCKS5ClientSocket : public ClientSocket {
  public:
   // Takes ownership of the |transport_socket|, which should already be
   // connected by the time Connect() is called.
   //
   // |req_info| contains the hostname and port to which the socket above will
   // communicate to via the SOCKS layer.
+  //
+  // SOCKS5 supports three modes of specifying connection endpoints:
+  //  (1) as an IPv4 address.
+  //  (2) as an IPv6 address.
+  //  (3) as a hostname string.
+  //
+  // To select mode (3), pass NULL for |host_resolver|.
+  //
+  // Otherwise if a non-NULL |host_resolver| is given, Connect() will first
+  // try to resolve the hostname using |host_resolver|, and pass that
+  // resolved address to the proxy server. If the resolve failed, Connect()
+  // will fall-back to mode (3) and simply send the unresolved hosname string
+  // to the SOCKS v5 proxy server.
+  //
+  // Passing NULL for |host_resolver| is the recommended default.
   SOCKS5ClientSocket(ClientSocket* transport_socket,
                      const HostResolver::RequestInfo& req_info,
                      HostResolver* host_resolver);
 
   // On destruction Disconnect() is called.
   virtual ~SOCKS5ClientSocket();
 
   // ClientSocket methods:
 
   // Does the SOCKS handshake and completes the protocol.
@@ skipping 91 matching lines @@
   // This becomes true when the SOCKS handshake has completed and the
   // overlying connection is free to communicate.
   bool completed_handshake_;
 
   // These contain the bytes sent / received by the SOCKS handshake.
   size_t bytes_sent_;
   size_t bytes_received_;
 
   size_t read_header_size;
 
-  // Used to resolve the hostname to which the SOCKS proxy will connect.
-  SingleRequestHostResolver host_resolver_;
+  // If non-NULL, we will use this host resolver to resolve DNS client-side
+  // (and fall back to proxy-side resolving if it fails).
+  // Otherwise, we will do proxy-side DNS resolving.
+  scoped_ptr<SingleRequestHostResolver> host_resolver_;
   AddressList addresses_;
   HostResolver::RequestInfo host_request_info_;
 
   scoped_refptr<LoadLog> load_log_;
 
   DISALLOW_COPY_AND_ASSIGN(SOCKS5ClientSocket);
 };
 
 }  // namespace net
 
 #endif  // NET_SOCKET_SOCKS5_CLIENT_SOCKET_H_