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

net/dns/dns_response.cc

 // 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.
 
 #include "net/dns/dns_response.h"
 
+#include <climits>
+
 #include "base/string_util.h"
 #include "base/sys_byteorder.h"
 #include "net/base/address_list.h"
 #include "net/base/big_endian.h"
 #include "net/base/dns_util.h"
 #include "net/base/io_buffer.h"
 #include "net/base/net_errors.h"
 #include "net/dns/dns_protocol.h"
 #include "net/dns/dns_query.h"
 
@@ skipping 151 matching lines @@
     return false;
   }
 
   // Construct the parser.
   parser_ = DnsRecordParser(io_buffer_->data(),
                             nbytes,
                             hdr_size + question.size());
   return true;
 }
 
+bool DnsResponse::InitParseNoQuery(int nbytes) {

[gene, 2013/04/16 21:55:22]

nit: you may consider naming this InitParse() as well.

[Noam Samuel, 2013/04/16 23:28:19]

Done.

+  if (nbytes >= io_buffer_->size())
+    return false;
+
+  const size_t hdr_size = sizeof(dns_protocol::Header);
+
+  // Construct the parser.
+  parser_ = DnsRecordParser(io_buffer_->data(),
+                            nbytes,
+                            hdr_size + GetQuestionSectionSize());
+  return true;
+}
+
 bool DnsResponse::IsValid() const {
   return parser_.IsValid();
 }
 
 uint16 DnsResponse::flags() const {
   DCHECK(parser_.IsValid());
   return base::NetToHost16(header()->flags) & ~(dns_protocol::kRcodeMask);
 }
 
 uint8 DnsResponse::rcode() const {
@@ skipping 22 matching lines @@
   const size_t type_offset = parser_.GetOffset() - 2 * sizeof(uint16);
   uint16 type;
   ReadBigEndian<uint16>(io_buffer_->data() + type_offset, &type);
   return type;
 }
 
 std::string DnsResponse::GetDottedName() const {
   return DNSDomainToString(qname());
 }
 
+size_t DnsResponse::GetQuestionSectionSize() const {

[gene, 2013/04/16 21:55:22]

nit: You may consider changing this function to GetResponseOffset(), this will
simplify your InitParseNoQuery() a bit

[Noam Samuel, 2013/04/16 23:28:19]

Done.

+  uint16 qdcount = base::NetToHost16(header()->qdcount);
+  size_t hdr_size = sizeof(dns_protocol::Header);
+  const char* data = io_buffer_->data();
+  size_t data_size = io_buffer_->size();
+  size_t pos = hdr_size;
+
+  for (uint16 i = 0; i < qdcount; i++) {
+    while (pos < data_size && data[pos]) {

[gene, 2013/04/16 21:55:22]

data[pos] -> data[pos] != 0
you can make it more explicit and easy to read with () && ()

[Noam Samuel, 2013/04/16 23:28:19]

Done.

+      // Traversal and checks adapted from DNSDomainToString.
+
+      // Handling pointers, which have both high bits set and an extra
+      // byte trailing them to indicate a location in the buffer.
+      if (static_cast<unsigned>(data[pos]) >= 192) {

[gene, 2013/04/16 21:55:22]

could you please make a new variable
usigned txt_len = static_cast<unsigned>(data[pos]);

+        pos+=2;
+        continue;
+      }
+
+#if CHAR_MIN < 0
+      if (data[pos] < 0)
+        return 0;
+#endif
+      if (data[pos] > 63) {
+        return 0;
+      }
+
+      if (static_cast<int>(data[pos] + pos + 1 > data_size))

[gene, 2013/04/16 21:55:22]

why do you need static_cast here?
btw, you may move this check to the outside of this loop

[Noam Samuel, 2013/04/16 23:28:19]

Done.

+        return 0;
+
+      pos += data[pos]+1;

[gene, 2013/04/16 21:55:22]

need spaces aroud +

[Noam Samuel, 2013/04/16 23:28:19]

Done.

+    }
+
+    pos += 5;  // 2 for qtype, 2 for qclass, 1 for null char

[gene, 2013/04/16 21:55:22]

Comment is a bit misleading, I think it should be
// 1 for 0-length text, 2 for qtype, 2 for qclass

[Noam Samuel, 2013/04/16 23:28:19]

Done.

+  }
+  return pos - hdr_size;
+}
+
 DnsRecordParser DnsResponse::Parser() const {
   DCHECK(parser_.IsValid());
   // Return a copy of the parser.
   return parser_;
 }
 
 const dns_protocol::Header* DnsResponse::header() const {
   return reinterpret_cast<const dns_protocol::Header*>(io_buffer_->data());
 }
 
@@ skipping 56 matching lines @@
 
   // getcanonname in eglibc returns the first owner name of an A or AAAA RR.
   // If the response passed all the checks so far, then |expected_name| is it.
   *addr_list = AddressList::CreateFromIPAddressList(ip_addresses,
                                                     expected_name);
   *ttl = base::TimeDelta::FromSeconds(ttl_sec);
   return DNS_PARSE_OK;
 }
 
 }  // namespace net