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/*
* Copyright (c) 2021, Sergey Bugaev <bugaevc@serenityos.org>
*
* SPDX-License-Identifier: BSD-2-Clause
*/
#include "MulticastDNS.h"
#include "DNSPacket.h"
#include <AK/IPv4Address.h>
#include <AK/JsonArray.h>
#include <AK/JsonObject.h>
#include <AK/JsonValue.h>
#include <AK/String.h>
#include <LibCore/File.h>
#include <poll.h>
#include <sys/socket.h>
#include <unistd.h>
namespace LookupServer {
MulticastDNS::MulticastDNS(Object* parent)
: Core::UDPServer(parent)
, m_hostname("courage.local")
{
char buffer[HOST_NAME_MAX];
if (gethostname(buffer, sizeof(buffer)) < 0) {
perror("gethostname");
} else {
m_hostname = String::formatted("{}.local", buffer);
}
u8 zero = 0;
if (setsockopt(fd(), IPPROTO_IP, IP_MULTICAST_LOOP, &zero, 1) < 0)
perror("setsockopt(IP_MULTICAST_LOOP)");
ip_mreq mreq = {
mdns_addr.sin_addr,
{ htonl(INADDR_ANY) },
};
if (setsockopt(fd(), IPPROTO_IP, IP_ADD_MEMBERSHIP, &mreq, sizeof(mreq)) < 0)
perror("setsockopt(IP_ADD_MEMBERSHIP)");
bind(IPv4Address(), 5353);
on_ready_to_receive = [this]() {
handle_packet();
};
// TODO: Announce on startup. We cannot just call announce() here,
// because it races with the network interfaces getting configured.
}
void MulticastDNS::handle_packet()
{
auto buffer = receive(1024);
auto optional_packet = DNSPacket::from_raw_packet(buffer.data(), buffer.size());
if (!optional_packet.has_value()) {
dbgln("Got an invalid mDNS packet");
return;
}
auto& packet = optional_packet.value();
if (packet.is_query())
handle_query(packet);
}
void MulticastDNS::handle_query(const DNSPacket& packet)
{
bool should_reply = false;
for (auto& question : packet.questions())
if (question.name() == m_hostname)
should_reply = true;
if (!should_reply)
return;
announce();
}
void MulticastDNS::announce()
{
DNSPacket response;
response.set_is_response();
response.set_code(DNSPacket::Code::NOERROR);
response.set_authoritative_answer(true);
response.set_recursion_desired(false);
response.set_recursion_available(false);
for (auto& address : local_addresses()) {
auto raw_addr = address.to_in_addr_t();
DNSAnswer answer {
m_hostname,
DNSRecordType::A,
DNSRecordClass::IN,
120,
String { (const char*)&raw_addr, sizeof(raw_addr) },
true,
};
response.add_answer(answer);
}
if (emit_packet(response) < 0)
perror("Failed to emit response packet");
}
ssize_t MulticastDNS::emit_packet(const DNSPacket& packet, const sockaddr_in* destination)
{
auto buffer = packet.to_byte_buffer();
if (!destination)
destination = &mdns_addr;
return sendto(fd(), buffer.data(), buffer.size(), 0, (const sockaddr*)destination, sizeof(*destination));
}
Vector<IPv4Address> MulticastDNS::local_addresses() const
{
auto file = Core::File::construct("/proc/net/adapters");
if (!file->open(Core::OpenMode::ReadOnly)) {
dbgln("Failed to open /proc/net/adapters: {}", file->error_string());
return {};
}
auto file_contents = file->read_all();
auto json = JsonValue::from_string(file_contents);
VERIFY(json.has_value());
Vector<IPv4Address> addresses;
json.value().as_array().for_each([&addresses](auto& value) {
auto if_object = value.as_object();
auto address = if_object.get("ipv4_address").to_string();
auto ipv4_address = IPv4Address::from_string(address);
// Skip unconfigured interfaces.
if (!ipv4_address.has_value())
return;
// Skip loopback adapters.
if (ipv4_address.value()[0] == IN_LOOPBACKNET)
return;
addresses.append(ipv4_address.value());
});
return addresses;
}
Vector<DNSAnswer> MulticastDNS::lookup(const DNSName& name, DNSRecordType record_type)
{
DNSPacket request;
request.set_is_query();
request.set_recursion_desired(false);
request.add_question({ name, record_type, DNSRecordClass::IN, false });
if (emit_packet(request) < 0) {
perror("failed to emit request packet");
return {};
}
Vector<DNSAnswer> answers;
// FIXME: It would be better not to block
// the main loop while we wait for a response.
while (true) {
pollfd pfd { fd(), POLLIN, 0 };
auto rc = poll(&pfd, 1, 1000);
if (rc < 0) {
perror("poll");
} else if (rc == 0) {
// Timed out.
return {};
}
auto buffer = receive(1024);
if (buffer.is_empty())
return {};
auto optional_packet = DNSPacket::from_raw_packet(buffer.data(), buffer.size());
if (!optional_packet.has_value()) {
dbgln("Got an invalid mDNS packet");
continue;
}
auto& packet = optional_packet.value();
if (packet.is_query())
continue;
for (auto& answer : packet.answers())
if (answer.name() == name && answer.type() == record_type)
answers.append(answer);
if (!answers.is_empty())
return answers;
}
}
}
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