Isolates generic DnsClient from AsyncHostResolver.

net/dns/dns_response.h

 // Copyright (c) 2011 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_
 #pragma once
 
+#include <string>
+
+#include "base/basictypes.h"
 #include "base/memory/ref_counted.h"
+#include "base/string_piece.h"
 #include "net/base/net_export.h"
 #include "net/base/net_util.h"
+#include "net/dns/dns_protocol.h"
 
 namespace net{
 
 class DnsQuery;
 class IOBufferWithSize;
 
-// Represents on-the-wire DNS response as an object; allows extracting
-// records.
+// Parsed resource record.
+struct NET_EXPORT_PRIVATE DnsResourceRecord {
+  std::string name;  // in dotted form
+  uint16 type;
+  uint16 klass;
+  uint32 ttl;
+  base::StringPiece rdata;  // points to the original response buffer
+};
+
+// Iterator to walk over resource records of the DNS response packet.
+class NET_EXPORT_PRIVATE DnsRecordParser {
+ public:
+  // Construct an uninitialized iterator.
+  DnsRecordParser();
+
+  // Construct an iterator to process the |packet| of given |length|.
+  // |offset| points to the beginning of the answer section.
+  DnsRecordParser(const void* packet, size_t length, size_t offset);
+
+  bool IsValid() const { return packet_ != NULL; }

[mmenke, 2011/12/06 18:08:39]

Should add a comment that this validates the parser, not the data it's parsing.

Also, are this and the uninitialized constructor even necessary?

[szym, 2011/12/06 19:05:51]

Done.
It makes DnsResponse::Parser() a bit easier to implement. Could remove it if
it's distracting.

+
+  // Returns |true| if no more bytes remain in the packet.
+  bool AtEnd() const { return cur_ == packet_ + length_; }
+
+  // Parses a (possibly compressed) DNS name from the packet starting at
+  // |pos|. Stores output (even partial) in |out| unless |out| is NULL. |out|
+  // 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.
+  int ParseName(const void* pos, std::string* out) const;
+
+  // Parses the next resource record. Returns true if succeeded.
+  bool ParseRecord(DnsResourceRecord* record);
+
+ 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.
 class NET_EXPORT_PRIVATE DnsResponse {
  public:
   // Constructs an object with an IOBuffer large enough to read
   // one byte more than largest possible response, to detect malformed
-  // responses; |query| is a pointer to the DnsQuery for which |this|
-  // is supposed to be a response.
-  explicit DnsResponse(DnsQuery* query);
+  // responses.
+  DnsResponse();
+  // Constructs response from |data|. Used for testing purposes only!
+  DnsResponse(const void* data, size_t length, size_t answer_offset);
   ~DnsResponse();
 
   // Internal buffer accessor into which actual bytes of response will be
   // read.
   IOBufferWithSize* io_buffer() { return io_buffer_.get(); }
 
-  // Parses response of size nbytes and puts address into |ip_addresses|,
-  // returns net_error code in case of failure.
-  int Parse(int nbytes, IPAddressList* ip_addresses);
+  // Returns false if the packet is shorter than the header or does not match
+  // |query| id or question.
+  bool InitParse(int nbytes, const DnsQuery& query);
+
+  // Accessors for the header.
+  uint8 flags0() const;  // first byte of flags
+  uint8 flags1() const;  // second byte of flags excluding rcode
+  uint8 rcode() const;
+  int answer_count() const;
+
+  // Returns an iterator to the resource records in the answer section. Must be
+  // called after InitParse. The iterator is valid only in the scope of the
+  // DnsResponse.
+  DnsRecordParser Parser() const { return parser_; }
 
  private:
-  // The matching query; |this| is the response for |query_|.  We do not
-  // own it, lifetime of |this| should be within the limits of lifetime of
-  // |query_|.
-  const DnsQuery* const query_;
+  // 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.
+  DnsRecordParser parser_;
+
   DISALLOW_COPY_AND_ASSIGN(DnsResponse);
 };
 
 }  // namespace net
 
 #endif  // NET_DNS_DNS_RESPONSE_H_