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// Copyright 2012 The Chromium Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#include <stddef.h>
#include <stdint.h>
#include <optional>
#include <string>
#include <string_view>
#include <vector>
#include "base/compiler_specific.h"
#include "base/containers/span.h"
#include "base/containers/span_writer.h"
#include "base/memory/scoped_refptr.h"
#include "net/base/net_export.h"
#include "net/dns/dns_response_result_extractor.h"
#include "net/dns/public/dns_protocol.h"
namespace net {
class DnsQuery;
class IOBuffer;
namespace dns_protocol {
struct Header;
} // namespace dns_protocol
// Structure representing a Resource Record as specified in RFC 1035, Section
// 4.1.3.
struct NET_EXPORT_PRIVATE DnsResourceRecord {
DnsResourceRecord(const DnsResourceRecord& other);
DnsResourceRecord(DnsResourceRecord&& other);
DnsResourceRecord& operator=(const DnsResourceRecord& other);
DnsResourceRecord& operator=(DnsResourceRecord&& other);
// A helper to set |owned_rdata| that also sets |rdata| to point to it. The
// |value| must be non-empty. See the definition of |owned_rdata| below.
void SetOwnedRdata(std::string value);
// NAME (variable length) + TYPE (2 bytes) + CLASS (2 bytes) + TTL (4 bytes) +
// RDLENGTH (2 bytes) + RDATA (variable length)
// Uses |owned_rdata| for RDATA if non-empty.
size_t CalculateRecordSize() const;
std::string name; // in dotted form
uint16_t type = 0;
uint16_t klass = 0;
uint32_t ttl = 0;
// Points to the original response buffer or otherwise to |owned_rdata|.
std::string_view rdata;
// Used to construct a DnsResponse from data. This field is empty if |rdata|
// points to the response buffer.
std::string owned_rdata;
// 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`.
// `offset` points to the beginning of the answer section. `ReadRecord()` will
// fail if called more than `num_records` times, no matter whether or not
// there is additional data at the end of the buffer that may appear to be a
// valid record.
DnsRecordParser(base::span<const uint8_t> packet,
size_t offset,
size_t num_records);
// TODO( Deprecated, use the span-based constructor.
UNSAFE_BUFFER_USAGE DnsRecordParser(const void* packet,
size_t length,
size_t offset,
size_t num_records);
// Returns |true| if initialized.
bool IsValid() const { return !packet_.empty(); }
// Returns |true| if no more bytes remain in the packet.
bool AtEnd() const { return cur_ == packet_.size(); }
// Returns current offset into the packet.
size_t GetOffset() const { return cur_; }
// 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);
// Read a question section, returns true if succeeded. In `DnsResponse`,
// expected to be called during parse, after which the current offset will be
// after all questions.
bool ReadQuestion(std::string& out_dotted_qname, uint16_t& out_qtype);
base::span<const uint8_t> packet_;
size_t num_records_ = 0u;
size_t num_records_parsed_ = 0u;
// Current offset within the packet.
size_t cur_ = 0u;
// 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 {
// Constructs a response buffer large enough to store one byte more than
// largest possible response, to detect malformed responses.
// Constructs a response message from `answers` and the originating `query`.
// After the successful construction, and the parser is also initialized.
// If `validate_records` is false, DCHECKs validating the correctness of
// records will be skipped. Intended for tests to allow creation of malformed
// responses.
DnsResponse(uint16_t id,
bool is_authoritative,
const std::vector<DnsResourceRecord>& answers,
const std::vector<DnsResourceRecord>& authority_records,
const std::vector<DnsResourceRecord>& additional_records,
const std::optional<DnsQuery>& query,
uint8_t rcode = dns_protocol::kRcodeNOERROR,
bool validate_records = true,
bool validate_names_as_internet_hostnames = true);
// Constructs a response buffer of given length. Used for TCP transactions.
explicit DnsResponse(size_t length);
// Constructs a response from the passed buffer.
DnsResponse(scoped_refptr<IOBuffer> buffer, size_t size);
// Constructs a response from |data|. Used for testing purposes only!
DnsResponse(const void* data, size_t length, size_t answer_offset);
static DnsResponse CreateEmptyNoDataResponse(uint16_t id,
bool is_authoritative,
base::span<const uint8_t> qname,
uint16_t qtype);
// Move-only.
DnsResponse(DnsResponse&& other);
DnsResponse& operator=(DnsResponse&& other);
// Internal buffer accessor into which actual bytes of response will be
// read.
IOBuffer* io_buffer() { return io_buffer_.get(); }
const IOBuffer* io_buffer() const { return io_buffer_.get(); }
// Size of the internal buffer.
size_t io_buffer_size() const { return io_buffer_size_; }
// Assuming the internal buffer holds |nbytes| bytes, returns true iff the
// packet matches the |query| id and question. This should only be called if
// the response is constructed from a raw buffer.
bool InitParse(size_t nbytes, const DnsQuery& query);
// Assuming the internal buffer holds |nbytes| bytes, initialize the parser
// without matching it against an existing query. This should only be called
// if the response is constructed from a raw buffer.
bool InitParseWithoutQuery(size_t nbytes);
// Does not require the response to be fully parsed and valid, but will return
// nullopt if the ID is unknown. The ID will only be known if the response is
// successfully constructed from data or if InitParse...() has been able to
// parse at least as far as the ID (not necessarily a fully successful parse).
std::optional<uint16_t> id() const;
// Returns true if response is valid, that is, after successful InitParse, or
// after successful construction of a new response from data.
bool IsValid() const;
// All of the methods below are valid only if the response is valid.
// Accessors for the header.
uint16_t flags() const; // excluding rcode
uint8_t rcode() const;
unsigned question_count() const;
unsigned answer_count() const;
unsigned authority_count() const;
unsigned additional_answer_count() const;
const std::vector<uint16_t>& qtypes() const {
DCHECK_EQ(question_count(), qtypes_.size());
return qtypes_;
const std::vector<std::string>& dotted_qnames() const {
DCHECK_EQ(question_count(), dotted_qnames_.size());
return dotted_qnames_;
// Shortcuts to get qtype or qname for single-query responses. Should only be
// used in cases where there is known to be exactly one question (e.g. because
// that has been validated by `InitParse()`).
uint16_t GetSingleQType() const;
std::string_view GetSingleDottedName() 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;
bool WriteHeader(base::SpanWriter<uint8_t>* writer,
const dns_protocol::Header& header);
bool WriteQuestion(base::SpanWriter<uint8_t>* writer, const DnsQuery& query);
bool WriteRecord(base::SpanWriter<uint8_t>* writer,
const DnsResourceRecord& record,
bool validate_record,
bool validate_name_as_internet_hostname);
bool WriteAnswer(base::SpanWriter<uint8_t>* writer,
const DnsResourceRecord& answer,
const std::optional<DnsQuery>& query,
bool validate_record,
bool validate_name_as_internet_hostname);
// Convenience for header access.
const dns_protocol::Header* header() const;
// Buffer into which response bytes are read.
scoped_refptr<IOBuffer> io_buffer_;
// Size of the buffer.
size_t io_buffer_size_;
// Iterator constructed after InitParse positioned at the answer section.
// It is never updated afterwards, so can be used in accessors.
DnsRecordParser parser_;
bool id_available_ = false;
std::vector<std::string> dotted_qnames_;
std::vector<uint16_t> qtypes_;
} // namespace net