258 lines
9.4 KiB
C
258 lines
9.4 KiB
C
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// Copyright 2012 The Chromium Authors
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// Use of this source code is governed by a BSD-style license that can be
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// found in the LICENSE file.
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#ifndef NET_DNS_DNS_RESPONSE_H_
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#define NET_DNS_DNS_RESPONSE_H_
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#include <stddef.h>
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#include <stdint.h>
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#include <string>
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#include <vector>
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#include "base/containers/span.h"
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#include "base/memory/scoped_refptr.h"
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#include "base/strings/string_piece.h"
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#include "net/base/net_export.h"
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#include "net/dns/dns_response_result_extractor.h"
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#include "net/dns/public/dns_protocol.h"
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#include "third_party/abseil-cpp/absl/types/optional.h"
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namespace base {
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class BigEndianWriter;
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} // namespace base
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namespace net {
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class DnsQuery;
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class IOBuffer;
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namespace dns_protocol {
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struct Header;
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} // namespace dns_protocol
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// Structure representing a Resource Record as specified in RFC 1035, Section
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// 4.1.3.
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struct NET_EXPORT_PRIVATE DnsResourceRecord {
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DnsResourceRecord();
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DnsResourceRecord(const DnsResourceRecord& other);
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DnsResourceRecord(DnsResourceRecord&& other);
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~DnsResourceRecord();
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DnsResourceRecord& operator=(const DnsResourceRecord& other);
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DnsResourceRecord& operator=(DnsResourceRecord&& other);
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// A helper to set |owned_rdata| that also sets |rdata| to point to it. The
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// |value| must be non-empty. See the definition of |owned_rdata| below.
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void SetOwnedRdata(std::string value);
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// NAME (variable length) + TYPE (2 bytes) + CLASS (2 bytes) + TTL (4 bytes) +
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// RDLENGTH (2 bytes) + RDATA (variable length)
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//
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// Uses |owned_rdata| for RDATA if non-empty.
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size_t CalculateRecordSize() const;
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std::string name; // in dotted form
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uint16_t type = 0;
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uint16_t klass = 0;
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uint32_t ttl = 0;
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// Points to the original response buffer or otherwise to |owned_rdata|.
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base::StringPiece rdata;
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// Used to construct a DnsResponse from data. This field is empty if |rdata|
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// points to the response buffer.
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std::string owned_rdata;
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};
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// Iterator to walk over resource records of the DNS response packet.
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class NET_EXPORT_PRIVATE DnsRecordParser {
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public:
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// Construct an uninitialized iterator.
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DnsRecordParser();
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// Construct an iterator to process the `packet` of given `length`.
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// `offset` points to the beginning of the answer section. `ReadRecord()` will
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// fail if called more than `num_records` times, no matter whether or not
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// there is additional data at the end of the buffer that may appear to be a
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// valid record.
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DnsRecordParser(const void* packet,
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size_t length,
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size_t offset,
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size_t num_records);
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// Returns |true| if initialized.
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bool IsValid() const { return packet_ != nullptr; }
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// Returns |true| if no more bytes remain in the packet.
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bool AtEnd() const { return cur_ == packet_ + length_; }
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// Returns current offset into the packet.
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size_t GetOffset() const { return cur_ - packet_; }
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// Parses a (possibly compressed) DNS name from the packet starting at
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// |pos|. Stores output (even partial) in |out| unless |out| is NULL. |out|
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// is stored in the dotted form, e.g., "example.com". Returns number of bytes
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// consumed or 0 on failure.
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// This is exposed to allow parsing compressed names within RRDATA for TYPEs
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// such as NS, CNAME, PTR, MX, SOA.
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// See RFC 1035 section 4.1.4.
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unsigned ReadName(const void* pos, std::string* out) const;
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// Parses the next resource record into |record|. Returns true if succeeded.
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bool ReadRecord(DnsResourceRecord* record);
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// Read a question section, returns true if succeeded. In `DnsResponse`,
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// expected to be called during parse, after which the current offset will be
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// after all questions.
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bool ReadQuestion(std::string& out_dotted_qname, uint16_t& out_qtype);
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private:
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const char* packet_ = nullptr;
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size_t length_ = 0;
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size_t num_records_ = 0;
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size_t num_records_parsed_ = 0;
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// Current offset within the packet.
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const char* cur_ = nullptr;
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};
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// Buffer-holder for the DNS response allowing easy access to the header fields
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// and resource records. After reading into |io_buffer| must call InitParse to
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// position the RR parser.
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class NET_EXPORT_PRIVATE DnsResponse {
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public:
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// Constructs a response buffer large enough to store one byte more than
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// largest possible response, to detect malformed responses.
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DnsResponse();
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// Constructs a response message from `answers` and the originating `query`.
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// After the successful construction, and the parser is also initialized.
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//
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// If `validate_records` is false, DCHECKs validating the correctness of
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// records will be skipped. Intended for tests to allow creation of malformed
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// responses.
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DnsResponse(uint16_t id,
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bool is_authoritative,
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const std::vector<DnsResourceRecord>& answers,
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const std::vector<DnsResourceRecord>& authority_records,
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const std::vector<DnsResourceRecord>& additional_records,
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const absl::optional<DnsQuery>& query,
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uint8_t rcode = dns_protocol::kRcodeNOERROR,
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bool validate_records = true,
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bool validate_names_as_internet_hostnames = true);
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// Constructs a response buffer of given length. Used for TCP transactions.
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explicit DnsResponse(size_t length);
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// Constructs a response from the passed buffer.
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DnsResponse(scoped_refptr<IOBuffer> buffer, size_t size);
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// Constructs a response from |data|. Used for testing purposes only!
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DnsResponse(const void* data, size_t length, size_t answer_offset);
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static DnsResponse CreateEmptyNoDataResponse(uint16_t id,
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bool is_authoritative,
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base::span<const uint8_t> qname,
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uint16_t qtype);
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// Move-only.
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DnsResponse(DnsResponse&& other);
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DnsResponse& operator=(DnsResponse&& other);
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~DnsResponse();
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// Internal buffer accessor into which actual bytes of response will be
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// read.
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IOBuffer* io_buffer() { return io_buffer_.get(); }
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const IOBuffer* io_buffer() const { return io_buffer_.get(); }
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// Size of the internal buffer.
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size_t io_buffer_size() const { return io_buffer_size_; }
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// Assuming the internal buffer holds |nbytes| bytes, returns true iff the
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// packet matches the |query| id and question. This should only be called if
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// the response is constructed from a raw buffer.
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bool InitParse(size_t nbytes, const DnsQuery& query);
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// Assuming the internal buffer holds |nbytes| bytes, initialize the parser
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// without matching it against an existing query. This should only be called
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// if the response is constructed from a raw buffer.
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bool InitParseWithoutQuery(size_t nbytes);
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// Does not require the response to be fully parsed and valid, but will return
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// nullopt if the ID is unknown. The ID will only be known if the response is
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// successfully constructed from data or if InitParse...() has been able to
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// parse at least as far as the ID (not necessarily a fully successful parse).
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absl::optional<uint16_t> id() const;
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// Returns true if response is valid, that is, after successful InitParse, or
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// after successful construction of a new response from data.
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bool IsValid() const;
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// All of the methods below are valid only if the response is valid.
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// Accessors for the header.
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uint16_t flags() const; // excluding rcode
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uint8_t rcode() const;
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unsigned question_count() const;
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unsigned answer_count() const;
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unsigned authority_count() const;
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unsigned additional_answer_count() const;
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const std::vector<uint16_t>& qtypes() const {
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DCHECK(parser_.IsValid());
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DCHECK_EQ(question_count(), qtypes_.size());
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return qtypes_;
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}
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const std::vector<std::string>& dotted_qnames() const {
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DCHECK(parser_.IsValid());
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DCHECK_EQ(question_count(), dotted_qnames_.size());
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return dotted_qnames_;
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}
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// Shortcuts to get qtype or qname for single-query responses. Should only be
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// used in cases where there is known to be exactly one question (e.g. because
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// that has been validated by `InitParse()`).
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uint16_t GetSingleQType() const;
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base::StringPiece GetSingleDottedName() const;
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// Returns an iterator to the resource records in the answer section.
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// The iterator is valid only in the scope of the DnsResponse.
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// This operation is idempotent.
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DnsRecordParser Parser() const;
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private:
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bool WriteHeader(base::BigEndianWriter* writer,
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const dns_protocol::Header& header);
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bool WriteQuestion(base::BigEndianWriter* writer, const DnsQuery& query);
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bool WriteRecord(base::BigEndianWriter* writer,
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const DnsResourceRecord& record,
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bool validate_record,
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bool validate_name_as_internet_hostname);
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bool WriteAnswer(base::BigEndianWriter* writer,
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const DnsResourceRecord& answer,
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const absl::optional<DnsQuery>& query,
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bool validate_record,
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bool validate_name_as_internet_hostname);
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// Convenience for header access.
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const dns_protocol::Header* header() const;
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// Buffer into which response bytes are read.
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scoped_refptr<IOBuffer> io_buffer_;
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// Size of the buffer.
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size_t io_buffer_size_;
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// Iterator constructed after InitParse positioned at the answer section.
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// It is never updated afterwards, so can be used in accessors.
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DnsRecordParser parser_;
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bool id_available_ = false;
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std::vector<std::string> dotted_qnames_;
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std::vector<uint16_t> qtypes_;
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};
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} // namespace net
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#endif // NET_DNS_DNS_RESPONSE_H_
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