Added DnsQuery class

net/base/dns_query.cc

+// 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.
+
+#include "net/base/dns_query.h"
+
+#include <string>
+
+#include "base/rand_util.h"
+#include "net/base/address_family.h"
+#include "net/base/dns_util.h"
+
+#include <iostream>
+
+namespace net {
+
+namespace {
+
+void PackUint16BE(char buf[2], uint16 v) {
+  buf[0] = v >> 8;
+  buf[1] = v & 0xff;
+}
+
+uint16 QTypeFromAddressFamily(AddressFamily address_family) {
+  switch (address_family) {
+    case ADDRESS_FAMILY_IPV4:
+      return kDNS_A;
+    case ADDRESS_FAMILY_IPV6:
+      return kDNS_AAAA;
+    default:
+      NOTREACHED() << "Bad address family";
+      return kDNS_A;
+  }
+}
+
+}

[cbentzel, 2011/06/01 17:17:03]

Nit: // namespace to indicate end of anonymous namespace block.

[agayev, 2011/06/01 19:15:01]

Done.

+
+// DNS query consists of a 12-byte header followed by a question section.
+// For details, see RFC 1035 section 4.1.1.  This header template sets RD
+// bit, which directs the name server to pursue query recursively, and sets
+// the QDCOUNT to 1, meaning the question section has a single entry.  The
+// first two bytes of the header form a 16-bit query ID to be copied in the
+// corresponding reply by the name server; it's set to 0 here and is
+// randomized every time the underlying buffer is fetched.
+static const char kHeader[] = {0x00, 0x00, 0x01, 0x00, 0x00, 0x01,
+                               0x00, 0x00, 0x00, 0x00, 0x00, 0x00};
+static const size_t kHeaderLen = arraysize(kHeader);
+
+DnsQuery::DnsQuery(const std::string& hostname,
+                   AddressFamily address_family,
+                   int port)
+    : port_(port),
+      id_(0),
+      qtype_(QTypeFromAddressFamily(address_family)),
+      hostname_(hostname) {
+  std::string qname;
+  if (!net::DNSDomainFromDot(hostname, &qname))
+    return;
+
+  size_t query_size = kHeaderLen + qname.size() +
+    sizeof(qtype_) + sizeof(kClassIN);
+
+  io_buffer_ = new IOBufferWithSize(query_size);
+
+  int iterator = 0;

[cbentzel, 2011/06/01 17:17:03]

nit: byte_offset instead of iterator?

Also, maybe retain a char* buffer_head = io_buffer_->data() variable?

[agayev, 2011/06/01 19:15:01]

Done.

+  memcpy(&io_buffer_->data()[iterator], kHeader, kHeaderLen);
+  iterator += kHeaderLen;
+  memcpy(&io_buffer_->data()[iterator], &qname[0], qname.size());
+  iterator += qname.size();
+  PackUint16BE(&io_buffer_->data()[iterator], qtype_);
+  iterator += sizeof(qtype_);
+  PackUint16BE(&io_buffer_->data()[iterator], kClassIN);
+  iterator += sizeof(kClassIN);
+
+  RandomizeId();

[cbentzel, 2011/06/01 17:17:03]

Should you just do this in io_buffer()

[agayev, 2011/06/01 19:15:01]

That would lead to a construction of a degenerate DnsQuery with 0 id.

[cbentzel, 2011/06/01 19:41:21]

We talked and decided to have io_buffer() mutate the id. That way the DnsQuery
is constant post-construction, and we don't have to worry about how clients
order calls to id or io_buffer, or be surprised that the io_buffer bytes change
underneath them. 

+}
+
+void DnsQuery::RandomizeId() {
+  DCHECK(IsValid());
+  id_ = base::RandUint64() & 0xffff;
+  PackUint16BE(io_buffer_->data(), id_);
+}
+
+int DnsQuery::port() const {
+  DCHECK(IsValid());
+  return port_;
+}
+
+uint16 DnsQuery::id() const {
+  DCHECK(IsValid());
+  return id_;
+}
+
+uint16 DnsQuery::qtype() const {
+  DCHECK(IsValid());
+  return qtype_;
+}
+
+const std::string& DnsQuery::hostname() const {
+  DCHECK(IsValid());
+  return hostname_;
+}
+
+int DnsQuery::size() const {
+  DCHECK(IsValid());
+  return io_buffer_->size();
+}
+
+IOBuffer* DnsQuery::io_buffer() {
+  DCHECK(IsValid());
+  RandomizeId();
+  return io_buffer_.get();
+}
+
+const char* DnsQuery::data() const {
+  DCHECK(IsValid());
+  return io_buffer_->data();
+}
+
+}  // namespace net