Add simple non-response-based question parsing for mDNS passive listening

net/dns/dns_response.h

 // Copyright (c) 2012 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_RESPONSE_H_
 #define NET_DNS_DNS_RESPONSE_H_
 
 #include <string>
 
 #include "base/basictypes.h"
@@ skipping 49 matching lines @@
   // is stored in the dotted form, e.g., "example.com". Returns number of bytes
   // consumed or 0 on failure.
   // This is exposed to allow parsing compressed names within RRDATA for TYPEs
   // such as NS, CNAME, PTR, MX, SOA.
   // See RFC 1035 section 4.1.4.
   unsigned ReadName(const void* pos, std::string* out) const;
 
   // Parses the next resource record into |record|. Returns true if succeeded.
   bool ReadRecord(DnsResourceRecord* record);
 
+  // Skip a question section, returns true if succeeded.
+  bool SkipQuestion();
+
  private:
   const char* packet_;
   size_t length_;
   // Current offset within the packet.
   const char* cur_;
 };
 
 // Buffer-holder for the DNS response allowing easy access to the header fields
 // and resource records. After reading into |io_buffer| must call InitParse to
 // position the RR parser.
@@ skipping 28 matching lines @@
   ~DnsResponse();
 
   // Internal buffer accessor into which actual bytes of response will be
   // read.
   IOBufferWithSize* io_buffer() { return io_buffer_.get(); }
 
   // Assuming the internal buffer holds |nbytes| bytes, returns true iff the
   // packet matches the |query| id and question.
   bool InitParse(int nbytes, const DnsQuery& query);
 
+  // Assuming the internal buffer holds |nbytes| bytes, initialize the parser
+  // without matching it against an existing query.
+  bool InitParseWithoutQuery(int nbytes);
+
   // Returns true if response is valid, that is, after successful InitParse.
   bool IsValid() const;
 
   // All of the methods below are valid only if the response is valid.
 
   // Accessors for the header.
   uint16 flags() const;  // excluding rcode
   uint8 rcode() const;
   unsigned answer_count() const;
 
@@ skipping 23 matching lines @@
   // Iterator constructed after InitParse positioned at the answer section.
   // It is never updated afterwards, so can be used in accessors.
   DnsRecordParser parser_;
 
   DISALLOW_COPY_AND_ASSIGN(DnsResponse);
 };
 
 }  // namespace net
 
 #endif  // NET_DNS_DNS_RESPONSE_H_