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// 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 <string>
#include "base/basictypes.h"
#include "base/memory/ref_counted.h"
#include "base/string_piece.h"
#include "base/time.h"
#include "net/base/net_export.h"
#include "net/base/net_util.h"
namespace net {
class AddressList;
class DnsQuery;
class IOBufferWithSize;
namespace dns_protocol {
struct Header;
// 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 {
// Construct an uninitialized iterator.
// 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);
// Returns |true| if initialized.
bool IsValid() const { return packet_ != NULL; }
// Returns |true| if no more bytes remain in the packet.
bool AtEnd() const { return cur_ == packet_ + length_; }
// Returns current offset into the packet.
size_t GetOffset() const { return cur_ - packet_; }
// 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., "". 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.
unsigned ReadName(const void* pos, std::string* out) const;
// Parses the next resource record into |record|. Returns true if succeeded.
bool ReadRecord(DnsResourceRecord* record);
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 {
// Possible results from ParseToAddressList.
enum Result {
DNS_MALFORMED_RESPONSE, // DnsRecordParser failed before the end of
// packet.
DNS_MALFORMED_CNAME, // Could not parse CNAME out of RRDATA.
DNS_NAME_MISMATCH, // Got an address but no ordered chain of CNAMEs
// leads there.
DNS_SIZE_MISMATCH, // Got an address but size does not match.
DNS_CNAME_AFTER_ADDRESS, // Found CNAME after an address record.
DNS_NO_ADDRESSES, // OBSOLETE. No longer used.
// Only add new values here.
DNS_PARSE_RESULT_MAX, // Bounding value for histograms.
// Constructs an object with an IOBuffer large enough to read
// one byte more than largest possible response, to detect malformed
// responses.
// Constructs response from |data|. Used for testing purposes only!
DnsResponse(const void* data, size_t length, size_t answer_offset);
// Internal buffer accessor into which actual bytes of response will be
// read.
IOBufferWithSize* io_buffer() { return io_buffer_.get(); }
// 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);
// Returns true if response is valid, that is, after successful InitParse.
bool IsValid() const;
// All of the methods below are valid only if the response is valid.
// Accessors for the header.
uint16 flags() const; // excluding rcode
uint8 rcode() const;
unsigned answer_count() const;
// Accessors to the question. The qname is unparsed.
base::StringPiece qname() const;
uint16 qtype() const;
// Returns qname in dotted format.
std::string GetDottedName() const;
// Returns an iterator to the resource records in the answer section.
// The iterator is valid only in the scope of the DnsResponse.
// This operation is idempotent.
DnsRecordParser Parser() const;
// Extracts an AddressList from this response. Returns SUCCESS if succeeded.
// Otherwise returns a detailed error number.
Result ParseToAddressList(AddressList* addr_list, base::TimeDelta* ttl) const;
// 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.
// It is never updated afterwards, so can be used in accessors.
DnsRecordParser parser_;
} // namespace net