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dns_utils.cpp
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#include "net/dns_utils.h"
#include <algorithm>
#include <atomic>
#include <cstring>
#include <ldns/ldns.h>
namespace ag {
static std::atomic<uint16_t> g_next_request_id = 1;
static std::string rdf_to_string(const ldns_rdf *rdf) {
DeclPtr<char, &free> name{ldns_rdf2str(rdf)};
std::string_view n = name.get();
if (ldns_dname_str_absolute(name.get())) {
n.remove_suffix(1); // drop trailing dot
}
return std::string(n);
}
static void add_name_to_answer(dns_utils::DecodedReply &answer, const ldns_rdf *rdf) {
std::string n = rdf_to_string(rdf);
if (std::none_of(answer.names.begin(), answer.names.end(), [n](const std::string &i) {
return n == i;
})) {
answer.names.emplace_back(std::move(n));
}
}
static std::optional<dns_utils::RecordType> ldns_to_utils_rr_type(ldns_rr_type x) {
switch (x) {
case LDNS_RR_TYPE_A:
return dns_utils::RT_A;
case LDNS_RR_TYPE_AAAA:
return dns_utils::RT_AAAA;
default:
return std::nullopt;
}
}
static dns_utils::DecodeResult decode_request(ldns_pkt *pkt) {
const ldns_rr_list *question = ldns_pkt_question(pkt);
if (ldns_rr_list_rr_count(question) == 0) {
return dns_utils::InapplicablePacket{ldns_pkt_id(pkt)};
}
const ldns_rr *question_rr = ldns_rr_list_rr(question, 0);
return dns_utils::DecodedRequest{
.id = ldns_pkt_id(pkt),
.question_type = ldns_to_utils_rr_type(ldns_rr_get_type(question_rr)),
.name = rdf_to_string(ldns_rr_owner(question_rr)),
};
}
static dns_utils::DecodeResult decode_reply(dns_utils::LdnsPktPtr pkt) {
if (ldns_pkt_get_rcode(pkt.get()) != LDNS_RCODE_NOERROR) {
return dns_utils::InapplicablePacket{ldns_pkt_id(pkt.get())};
}
const ldns_rr_list *question = ldns_pkt_question(pkt.get());
if (ldns_rr_list_rr_count(question) == 0) {
return dns_utils::InapplicablePacket{ldns_pkt_id(pkt.get())};
}
dns_utils::DecodedReply decoded_answer = {
.id = ldns_pkt_id(pkt.get()),
.question_type = ldns_to_utils_rr_type(ldns_rr_get_type(ldns_rr_list_rr(question, 0))),
};
const ldns_rr_list *answer = ldns_pkt_answer(pkt.get());
for (size_t i = 0; i < ldns_rr_list_rr_count(answer); ++i) {
switch (const ldns_rr *a = ldns_rr_list_rr(answer, i); ldns_rr_get_type(a)) {
case LDNS_RR_TYPE_A:
case LDNS_RR_TYPE_AAAA: {
const ldns_rdf *rd = ldns_rr_rdf(a, 0);
if (rd == nullptr) {
continue;
}
size_t rd_size = ldns_rdf_size(rd);
if (rd_size != 4 && rd_size != 16) {
continue;
}
add_name_to_answer(decoded_answer, ldns_rr_owner(a));
const uint8_t *ip = ldns_rdf_data(rd);
decoded_answer.addresses.push_back({{ip, ip + rd_size}, std::chrono::seconds(ldns_rr_ttl(a))});
break;
}
case LDNS_RR_TYPE_CNAME: {
const ldns_rdf *rd = ldns_rr_rdf(a, 0);
if (rd == nullptr) {
continue;
}
add_name_to_answer(decoded_answer, ldns_rr_owner(a));
// ignoring TTL of CNAMEs for simplicity
add_name_to_answer(decoded_answer, rd);
break;
}
case LDNS_RR_TYPE_HTTPS:
case LDNS_RR_TYPE_SVCB:
add_name_to_answer(decoded_answer, ldns_rr_owner(a));
break;
default:
break;
}
}
decoded_answer.pkt = std::move(pkt);
return decoded_answer;
}
dns_utils::DecodeResult dns_utils::decode_packet(U8View packet) {
LdnsPktPtr pkt;
{
ldns_pkt *p = nullptr;
if (ldns_status s = ldns_wire2pkt(&p, packet.data(), packet.size()); s != LDNS_STATUS_OK) {
return Error{ldns_get_errorstr_by_id(s)};
}
pkt.reset(p);
}
if (ldns_pkt_qr(pkt.get())) {
return decode_reply(std::move(pkt));
}
return decode_request(pkt.get());
}
dns_utils::EncodeResult dns_utils::encode_request(const dns_utils::Request &request) {
std::string name{request.name};
if (!ldns_dname_str_absolute(name.c_str())) {
name.push_back('.');
}
LdnsPktPtr pkt{ldns_pkt_query_new(ldns_dname_new_frm_str(name.c_str()),
(request.type == RT_A) ? LDNS_RR_TYPE_A : LDNS_RR_TYPE_AAAA, LDNS_RR_CLASS_IN, LDNS_RD)};
ldns_pkt_set_id(pkt.get(), g_next_request_id.fetch_add(1, std::memory_order::relaxed));
uint8_t *buffer; // NOLINT(cppcoreguidelines-init-variables)
size_t pkt_size; // NOLINT(cppcoreguidelines-init-variables)
if (ldns_status s = ldns_pkt2wire(&buffer, pkt.get(), &pkt_size); s != LDNS_STATUS_OK) {
return dns_utils::Error{ldns_get_errorstr_by_id(s)};
}
std::vector<uint8_t> raw = {buffer, buffer + pkt_size};
free(buffer); // NOLINT(cppcoreguidelines-no-malloc,hicpp-no-malloc)
return EncodedRequest{ldns_pkt_id(pkt.get()), std::move(raw)};
}
dns_utils::LdnsPktPtr dns_utils::decode_pkt(U8View message) {
ldns_pkt *pkt;
if (ldns_status status = ldns_wire2pkt(&pkt, message.data(), message.size()); status == LDNS_STATUS_OK) {
return LdnsPktPtr{pkt};
}
return nullptr;
}
dns_utils::LdnsBufferPtr dns_utils::encode_pkt(const ldns_pkt *pkt) {
LdnsBufferPtr buffer{ldns_buffer_new(ldns_pkt_size(pkt))};
if (ldns_status status = ldns_pkt2buffer_wire(buffer.get(), pkt); status == LDNS_STATUS_OK) {
return buffer;
}
return nullptr;
}
bool dns_utils::remove_svcparam_echconfig(ldns_pkt *response) {
bool modified = false;
for (size_t i = 0; i < ldns_pkt_ancount(response); ++i) {
ldns_rr *rr = ldns_rr_list_rr(ldns_pkt_answer(response), i);
if (auto type = ldns_rr_get_type(rr);
(type != LDNS_RR_TYPE_SVCB && type != LDNS_RR_TYPE_HTTPS) || (ldns_rr_rd_count(rr) != 3)) {
continue;
}
ldns_rdf *params = ldns_rr_rdf(rr, 2);
if (ldns_rdf_get_type(params) != LDNS_RDF_TYPE_SVCPARAMS) {
continue;
}
uint8_t *current_param_start = nullptr;
uint16_t key; // NOLINT(*-init-variables)
uint16_t len; // NOLINT(*-init-variables)
U8View params_tail = {ldns_rdf_data(params), ldns_rdf_size(params)};
while (params_tail.size() >= sizeof(key)) {
current_param_start = (uint8_t *) params_tail.data();
std::memcpy(&key, params_tail.data(), sizeof(key));
params_tail.remove_prefix(sizeof(key));
if (params_tail.size() < sizeof(len)) {
break;
}
std::memcpy(&len, params_tail.data(), sizeof(len));
params_tail.remove_prefix(sizeof(len));
key = ntohs(key);
len = ntohs(len);
if (params_tail.size() < len) {
break;
}
params_tail.remove_prefix(len);
if (key == LDNS_SVCPARAM_KEY_ECHCONFIG) {
std::memmove(current_param_start, params_tail.data(), params_tail.size());
ldns_rdf_set_size(params, ldns_rdf_size(params) - sizeof(key) - sizeof(len) - len);
modified = true;
break;
}
}
}
return modified;
}
} // namespace ag