net/dns/dns_response.h

   1 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
   2 // Use of this source code is governed by a BSD-style license that can be
   3 // found in the LICENSE file.
   4
   5 #ifndef NET_DNS_DNS_RESPONSE_H_
   6 #define NET_DNS_DNS_RESPONSE_H_
   7
   8 #include <string>
   9
  10 #include "base/basictypes.h"
  11 #include "base/memory/ref_counted.h"
  12 #include "base/strings/string_piece.h"
  13 #include "base/time/time.h"
  14 #include "net/base/net_export.h"
  15 #include "net/base/net_util.h"
  16
  17 namespace net {
  18
  19 class AddressList;
  20 class DnsQuery;
  21 class IOBufferWithSize;
  22
  23 namespace dns_protocol {
  24 struct Header;
  25 }
  26
  27 // Parsed resource record.
  28 struct NET_EXPORT_PRIVATE DnsResourceRecord {
  29   DnsResourceRecord();
  30   ~DnsResourceRecord();
  31
  32   std::string name;  // in dotted form
  33   uint16 type;
  34   uint16 klass;
  35   uint32 ttl;
  36   base::StringPiece rdata;  // points to the original response buffer
  37 };
  38
  39 // Iterator to walk over resource records of the DNS response packet.
  40 class NET_EXPORT_PRIVATE DnsRecordParser {
  41  public:
  42   // Construct an uninitialized iterator.
  43   DnsRecordParser();
  44
  45   // Construct an iterator to process the |packet| of given |length|.
  46   // |offset| points to the beginning of the answer section.
  47   DnsRecordParser(const void* packet, size_t length, size_t offset);
  48
  49   // Returns |true| if initialized.
  50   bool IsValid() const { return packet_ != NULL; }
  51
  52   // Returns |true| if no more bytes remain in the packet.
  53   bool AtEnd() const { return cur_ == packet_ + length_; }
  54
  55   // Returns current offset into the packet.
  56   size_t GetOffset() const { return cur_ - packet_; }
  57
  58   // Parses a (possibly compressed) DNS name from the packet starting at
  59   // |pos|. Stores output (even partial) in |out| unless |out| is NULL. |out|
  60   // is stored in the dotted form, e.g., "example.com". Returns number of bytes
  61   // consumed or 0 on failure.
  62   // This is exposed to allow parsing compressed names within RRDATA for TYPEs
  63   // such as NS, CNAME, PTR, MX, SOA.
  64   // See RFC 1035 section 4.1.4.
  65   unsigned ReadName(const void* pos, std::string* out) const;
  66
  67   // Parses the next resource record into |record|. Returns true if succeeded.
  68   bool ReadRecord(DnsResourceRecord* record);
  69
  70   // Skip a question section, returns true if succeeded.
  71   bool SkipQuestion();
  72
  73  private:
  74   const char* packet_;
  75   size_t length_;
  76   // Current offset within the packet.
  77   const char* cur_;
  78 };
  79
  80 // Buffer-holder for the DNS response allowing easy access to the header fields
  81 // and resource records. After reading into |io_buffer| must call InitParse to
  82 // position the RR parser.
  83 class NET_EXPORT_PRIVATE DnsResponse {
  84  public:
  85   // Possible results from ParseToAddressList.
  86   enum Result {
  87     DNS_PARSE_OK = 0,
  88     DNS_MALFORMED_RESPONSE,    // DnsRecordParser failed before the end of
  89                                // packet.
  90     DNS_MALFORMED_CNAME,       // Could not parse CNAME out of RRDATA.
  91     DNS_NAME_MISMATCH,         // Got an address but no ordered chain of CNAMEs
  92                                // leads there.
  93     DNS_SIZE_MISMATCH,         // Got an address but size does not match.
  94     DNS_CNAME_AFTER_ADDRESS,   // Found CNAME after an address record.
  95     DNS_ADDRESS_TTL_MISMATCH,  // OBSOLETE. No longer used.
  96     DNS_NO_ADDRESSES,          // OBSOLETE. No longer used.
  97     // Only add new values here.
  98     DNS_PARSE_RESULT_MAX,      // Bounding value for histograms.
  99   };
 100
 101   // Constructs a response buffer large enough to store one byte more than
 102   // largest possible response, to detect malformed responses.
 103   DnsResponse();
 104
 105   // Constructs a response buffer of given length. Used for TCP transactions.
 106   explicit DnsResponse(size_t length);
 107
 108   // Constructs a response from |data|. Used for testing purposes only!
 109   DnsResponse(const void* data, size_t length, size_t answer_offset);
 110
 111   ~DnsResponse();
 112
 113   // Internal buffer accessor into which actual bytes of response will be
 114   // read.
 115   IOBufferWithSize* io_buffer() { return io_buffer_.get(); }
 116
 117   // Assuming the internal buffer holds |nbytes| bytes, returns true iff the
 118   // packet matches the |query| id and question.
 119   bool InitParse(int nbytes, const DnsQuery& query);
 120
 121   // Assuming the internal buffer holds |nbytes| bytes, initialize the parser
 122   // without matching it against an existing query.
 123   bool InitParseWithoutQuery(int nbytes);
 124
 125   // Returns true if response is valid, that is, after successful InitParse.
 126   bool IsValid() const;
 127
 128   // All of the methods below are valid only if the response is valid.
 129
 130   // Accessors for the header.
 131   uint16 flags() const;  // excluding rcode
 132   uint8 rcode() const;
 133
 134   unsigned answer_count() const;
 135   unsigned additional_answer_count() const;
 136
 137   // Accessors to the question. The qname is unparsed.
 138   base::StringPiece qname() const;
 139   uint16 qtype() const;
 140
 141   // Returns qname in dotted format.
 142   std::string GetDottedName() const;
 143
 144   // Returns an iterator to the resource records in the answer section.
 145   // The iterator is valid only in the scope of the DnsResponse.
 146   // This operation is idempotent.
 147   DnsRecordParser Parser() const;
 148
 149   // Extracts an AddressList from this response. Returns SUCCESS if succeeded.
 150   // Otherwise returns a detailed error number.
 151   Result ParseToAddressList(AddressList* addr_list, base::TimeDelta* ttl) const;
 152
 153  private:
 154   // Convenience for header access.
 155   const dns_protocol::Header* header() const;
 156
 157   // Buffer into which response bytes are read.
 158   scoped_refptr<IOBufferWithSize> io_buffer_;
 159
 160   // Iterator constructed after InitParse positioned at the answer section.
 161   // It is never updated afterwards, so can be used in accessors.
 162   DnsRecordParser parser_;
 163
 164   DISALLOW_COPY_AND_ASSIGN(DnsResponse);
 165 };
 166
 167 }  // namespace net
 168
 169 #endif  // NET_DNS_DNS_RESPONSE_H_