Added DnsQuery class

net/base/dns_query.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_BASE_DNS_QUERY_H_
+#define NET_BASE_DNS_QUERY_H_
+#pragma once
+
+#include <string>
+
+#include "net/base/address_family.h"
+#include "net/base/io_buffer.h"
+#include "net/base/net_util.h"
+
+namespace net{
+
+// A class that encapsulates bits and pieces related to DNS request processing.
+class DnsQuery {
+ public:
+  // Constructs an object containing an IOBuffer with raw DNS query string
+  // for |hostname| with the given |address_family|; |port| is here due to
+  // legacy -- getaddrinfo() takes service name, which is mapped to some
+  // port and returns sockaddr_in structures with ports filled in, so do we
+  // -- look at DnsResponse::Parse() to see where it is used.
+  DnsQuery(const std::string& hostname, AddressFamily address_family, int port);
+
+  // Returns true if the constructed object was valid.
+  bool IsValid() const { return io_buffer_.get() != NULL; }
+
+  // DnsQuery field accessors.
+  int port() const;
+  uint16 id() const;
+  uint16 qtype() const;
+  uint16 qclass() const;

[agl, 2011/05/30 18:35:30]

Classes are a really obscure corner of DNS. I'd tend to keep this private unless
there's a need for it that I haven't got to in the code yet.

[agayev, 2011/05/31 15:19:06]

DnsResponse was using it to match the Question part, but this can be hardcoded
to IN for the foreseeable future.

[agayev, 2011/06/01 15:58:24]

Hardcoded class to IN.

+  const std::string& hostname() const;
+
+  // Returns the size of the query in number of bytes.
+  int size() const;

[agl, 2011/05/30 18:35:30]

size_t for sizes?

[agayev, 2011/05/31 15:19:06]

Originally, I had it size_t, but eventually, I needed to compare these to number
of bytes read/written, which is a result from read/write calls, hence ints.  I
try to avoid casts, so decided to change it to int instead, but if the
convention is to use size_t and do casting, I can change that.

+
+  // IOBuffer accessor to be used for writing out the query.  This has a
+  // side effect of randomizing the ID portion of a query buffer.
+  IOBuffer* io_buffer();

[agl, 2011/05/30 18:35:30]

IOBuffers are refcounted, but returning a raw pointer allows callers to forget
this. I'd suggest:
  void io_buffer(scoped_refptr<IOBuffer>* out);
As a way to ensure that nobody ever makes that mistake while still minimizing
copy constructors and atomic ops.

[agayev, 2011/05/31 15:19:06]

I agree that it's an error-prone API, however, the way I use it is
udp_socket->Write(dns_query->io_buffer(), dns_query->size(), callback) and Write
expects a raw pointer.  Would it be better to return a scoped_refptr and do an
explicit get on it?

+
+ private:
+  FRIEND_TEST_ALL_PREFIXES(DnsQueryTest, ConstructorTest);
+  FRIEND_TEST_ALL_PREFIXES(DnsQueryTest, IOBufferAccessRandomizesIdTest);
+  FRIEND_TEST_ALL_PREFIXES(DnsResponseTest, ResponseWithCnameA);
+
+  // Randomizes ID field in the IOBuffer, also sets |id_|.
+  void RandomizeId();
+
+  // Gives access to the query bytes without randomizing ID field, used by
+  // tests.
+  char* data() const;

[agl, 2011/05/30 18:35:30]

const char*?

[agayev, 2011/05/31 15:19:06]

Will do.

+
+  // Port to be used by corresponding DnsResponse when filling sockaddr_ins
+  // to be returned.
+  int port_;
+
+  // ID of the query; changes on each io_buffer_ access.
+  uint16 id_;
+
+  // Type of query, currently, either A or AAAA.
+  uint16 qtype_;
+
+  // Class of query, currently fixed to IN class.

[agl, 2011/05/30 18:35:30]

This is so unlikely to ever change I wouldn't make it a variable even.

[agayev, 2011/05/31 15:19:06]

Will do.

+  uint16 qclass_;
+
+  // Hostname for we are trying to resolve.

[agl, 2011/05/30 18:35:30]

s/for/that/

[agayev, 2011/05/31 15:19:06]

Will do.

+  std::string hostname_;
+
+  // Contains query bytes to be consumed by higher level Write() call.
+  scoped_refptr<IOBufferWithSize> io_buffer_;
+
+  DISALLOW_COPY_AND_ASSIGN(DnsQuery);
+};
+
+}  // namespace net
+
+#endif  // NET_BASE_DNS_QUERY_H_