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_ 170
