DnsClient refactoring + features (timeout, suffix search, server rotation).

net/dns/dns_client.h

-// 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_DNS_DNS_CLIENT_H_
-#define NET_DNS_DNS_CLIENT_H_
-#pragma once
-
-#include <string>
-
-#include "base/basictypes.h"
-#include "base/callback.h"
-#include "base/memory/weak_ptr.h"
-#include "base/string_piece.h"
-#include "net/base/net_export.h"
-
-namespace net {
-
-class BoundNetLog;
-class ClientSocketFactory;
-class DnsResponse;
-class DnsSession;
-
-// DnsClient performs asynchronous DNS queries. DnsClient takes care of
-// retransmissions, DNS server fallback (or round-robin), suffix search, and
-// simple response validation ("does it match the query") to fight poisoning.
-// It does NOT perform caching, aggregation or prioritization of requests.
-//
-// Destroying DnsClient does NOT affect any already created Requests.
-//
-// TODO(szym): consider adding flags to MakeRequest to indicate options:
-// -- don't perform suffix search
-// -- query both A and AAAA at once
-// -- accept truncated response (and/or forbid TCP)
-class NET_EXPORT_PRIVATE DnsClient {
- public:
-  class Request;
-  // Callback for complete requests. Note that DnsResponse might be NULL if
-  // the DNS server(s) could not be reached.
-  typedef base::Callback<void(Request* req,
-                              int result,
-                              const DnsResponse* resp)> RequestCallback;
-
-  // A data-holder for a request made to the DnsClient.
-  // Destroying the request cancels the underlying network effort.
-  class NET_EXPORT_PRIVATE Request {
-   public:
-    Request(const base::StringPiece& qname,
-            uint16 qtype,
-            const RequestCallback& callback);
-    virtual ~Request();
-
-    const std::string& qname() const { return qname_; }
-
-    uint16 qtype() const { return qtype_; }
-
-    virtual int Start() = 0;
-
-    void DoCallback(int result, const DnsResponse* response) {
-      callback_.Run(this, result, response);
-    }
-
-   private:
-    std::string qname_;
-    uint16 qtype_;
-    RequestCallback callback_;
-
-    DISALLOW_COPY_AND_ASSIGN(Request);
-  };
-
-  virtual ~DnsClient() {}
-
-  // Makes asynchronous DNS query for the given |qname| and |qtype| (assuming
-  // QCLASS == IN). The caller is responsible for destroying the returned
-  // request whether to cancel it or after its completion.
-  // (Destroying DnsClient does not abort the requests.)
-  virtual Request* CreateRequest(
-      const base::StringPiece& qname,
-      uint16 qtype,
-      const RequestCallback& callback,
-      const BoundNetLog& source_net_log) WARN_UNUSED_RESULT = 0;
-
-  // Creates a socket-based DnsClient using the |session|.
-  static DnsClient* CreateClient(DnsSession* session) WARN_UNUSED_RESULT;
-};
-
-}  // namespace net
-
-#endif  // NET_DNS_DNS_CLIENT_H_
-