Isolates generic DnsClient from AsyncHostResolver.

DnsClient provides a generic DNS client that allows fetching resource records. 
DnsClient is very lightweight and does not support aggregation, queuing or 
prioritization of requests. 

This is the first CL in a series to merge AsyncHostResolver into 
HostResolverImpl. 

Also introduces general-purpose BigEndianReader/Writer. 

BUG=90881
TEST=./net_unittests


Review URL: http://codereview.chromium.org/8762001

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@113282 0039d316-1c4b-4281-b951-d872f2087c98

1 files changed, 93 insertions, 0 deletions

diff --git a/net/dns/dns_client.h b/net/dns/dns_client.h
new file mode 100644
index 0000000..af75cf6
--- /dev/null
+++ b/net/dns/dns_client.h
@@ -0,0 +1,93 @@
+// 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 "net/base/net_export.h"
+
+namespace base {
+class StringPiece;
+}
+
+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_
+