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