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 97 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 InitParse(int nbytes);

[szym, 2013/04/17 22:11:12]

I suggest keeping it distinct, e.g., InitParseWithoutQuery(...) since the
semantics are substantially different from InitParse.

The comment should also indicate that the parser is still positioned after the
question section.

[szym, 2013/04/17 23:30:27]

After some more thinking, I suggest InitParseIgnoreQuery.
I'd also be OK if you used InitParse here and InitParseMatchQuery for the other
method.

[Noam Samuel, 2013/04/18 19:03:17]

Done.

+
   // 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;
 
   // Accessors to the question. The qname is unparsed.
   base::StringPiece qname() const;
   uint16 qtype() const;
 
   // Returns qname in dotted format.
   std::string GetDottedName() const;
 
+  // Returns the offset of the response.
+  size_t GetResponseOffset() const;

[szym, 2013/04/17 22:11:12]

"Response" is confusing. (This is DnsResponse.) I suggest "answer" in reference
to "answer section".

That said, I don't think this is needed, see comments in .cc

[Noam Samuel, 2013/04/18 19:03:17]

Made irrelevant.

On 2013/04/17 22:11:12, szym wrote:

+
   // Returns an iterator to the resource records in the answer section.
   // The iterator is valid only in the scope of the DnsResponse.
   // This operation is idempotent.
   DnsRecordParser Parser() const;
 
   // Extracts an AddressList from this response. Returns SUCCESS if succeeded.
   // Otherwise returns a detailed error number.
   Result ParseToAddressList(AddressList* addr_list, base::TimeDelta* ttl) const;
 
  private:
   // Convenience for header access.
   const dns_protocol::Header* header() const;
 
   // Buffer into which response bytes are read.
   scoped_refptr<IOBufferWithSize> io_buffer_;
 
   // 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_