net: read the dns query id in terms of base::ReadBigEndian() function

This allow us to write DnsQuery::id() function without the
reinterpret_cast. To be able to do that, we added a pointer to
dns_protocol::Header in DnsQuery. That allowed us to also remove
the header() function.

BUG=None
TEST=net_unittests --gtest_filter=*Dns*
R=ttuttle@chromium.org

Review URL: https://codereview.chromium.org/1597463005

Cr-Commit-Position: refs/heads/master@{#370227}

net/dns/dns_query.cc

@@ -17,14 +17,15 @@ namespace net {
 // bit, which directs the name server to pursue query recursively, and sets
 // the QDCOUNT to 1, meaning the question section has a single entry.
 DnsQuery::DnsQuery(uint16_t id, const base::StringPiece& qname, uint16_t qtype)
-    : qname_size_(qname.size()) {
+    : qname_size_(qname.size()),
+      io_buffer_(
+          new IOBufferWithSize(sizeof(dns_protocol::Header) + question_size())),
+      header_(reinterpret_cast<dns_protocol::Header*>(io_buffer_->data())) {
   DCHECK(!DNSDomainToString(qname).empty());
-  io_buffer_ = new IOBufferWithSize(sizeof(dns_protocol::Header) +
-                                    question_size());
-  *header() = {};
-  header()->id = base::HostToNet16(id);
-  header()->flags = base::HostToNet16(dns_protocol::kFlagRD);
-  header()->qdcount = base::HostToNet16(1);
+  *header_ = {};
+  header_->id = base::HostToNet16(id);
+  header_->flags = base::HostToNet16(dns_protocol::kFlagRD);
+  header_->qdcount = base::HostToNet16(1);
 
   // Write question section after the header.
   base::BigEndianWriter writer(
@@ -42,9 +43,7 @@ scoped_ptr<DnsQuery> DnsQuery::CloneWithNewId(uint16_t id) const {
 }
 
 uint16_t DnsQuery::id() const {
-  const dns_protocol::Header* header =
-      reinterpret_cast<const dns_protocol::Header*>(io_buffer_->data());
-  return base::NetToHost16(header->id);
+  return base::NetToHost16(header_->id);
 }
 
 base::StringPiece DnsQuery::qname() const {
@@ -65,19 +64,16 @@ base::StringPiece DnsQuery::question() const {
 }
 
 void DnsQuery::set_flags(uint16_t flags) {
-  header()->flags = flags;
+  header_->flags = flags;
 }
 
 DnsQuery::DnsQuery(const DnsQuery& orig, uint16_t id) {
   qname_size_ = orig.qname_size_;
   io_buffer_ = new IOBufferWithSize(orig.io_buffer()->size());
   memcpy(io_buffer_.get()->data(), orig.io_buffer()->data(),
          io_buffer_.get()->size());
-  header()->id = base::HostToNet16(id);
-}
-
-dns_protocol::Header* DnsQuery::header() {
-  return reinterpret_cast<dns_protocol::Header*>(io_buffer_->data());
+  header_ = reinterpret_cast<dns_protocol::Header*>(io_buffer_->data());
+  header_->id = base::HostToNet16(id);
 }
 
 }  // namespace net

net/dns/dns_query.h

@@ -51,9 +51,6 @@ class NET_EXPORT_PRIVATE DnsQuery {
  private:
   DnsQuery(const DnsQuery& orig, uint16_t id);
 
-  // Convenience for header access.
-  dns_protocol::Header* header();
-
   // Returns the size of the question section.
   size_t question_size() const {
     // QNAME + QTYPE + QCLASS
@@ -67,6 +64,9 @@ class NET_EXPORT_PRIVATE DnsQuery {
   // Contains query bytes to be consumed by higher level Write() call.
   scoped_refptr<IOBufferWithSize> io_buffer_;
 
+  // Pointer to the dns header section.
+  dns_protocol::Header* header_;
+
   DISALLOW_COPY_AND_ASSIGN(DnsQuery);
 };