net: add a convenience getter accessor for dns Header to DnsQuery

net/dns/dns_query.h

Index: net/dns/dns_query.h
diff --git a/net/dns/dns_query.h b/net/dns/dns_query.h
index 14c5b5be8cc467f5007e5e1999627d05e316c4d5..9c44cc841ef38fe5bd8e6d18e03d514695edbcf5 100644
--- a/net/dns/dns_query.h
+++ b/net/dns/dns_query.h
@@ -16,6 +16,10 @@
 
 namespace net {
 
+namespace dns_protocol {
+struct Header;
+}
+
 class IOBufferWithSize;
 
 // Represents on-the-wire DNS query message as an object.
@@ -47,6 +51,9 @@ class NET_EXPORT_PRIVATE DnsQuery {
  private:
   DnsQuery(const DnsQuery& orig, uint16_t id);
 
+  // Convenience for header access.
+  dns_protocol::Header* header();

[pauljensen, 2015/12/29 12:38:02]

I'm not really a fan of making something hacky (the reinterpret_cast) easier to
use.

[tfarina, 2015/12/29 13:57:43]

dns_response.h already has an accessor like this. I don't consider something
from the C++ cast-system like reinterpret_cast a hack.

[pauljensen, 2015/12/29 15:06:22]

Casting something to a different type and dereferencing is a hack in my book. 
It violates C aliasing rules and optimizing compiler are apt to reinterpret the
code in unforseen ways.

+
   // Size of the DNS name (*NOT* hostname) we are trying to resolve; used
   // to calculate offsets.
   size_t qname_size_;