Martin Michelsen
118 lines
3.5 KiB
C++
118 lines
3.5 KiB
C++
#include "DNSServer.hh"
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#include <stdio.h>
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#include <string.h>
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#include <unistd.h>
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#include <poll.h>
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#include <netinet/in.h>
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#include <phosg/Encoding.hh>
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#include <phosg/Network.hh>
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#include <phosg/Strings.hh>
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#include <vector>
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#include <string>
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#include "NetworkAddresses.hh"
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using namespace std;
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DNSServer::DNSServer(shared_ptr<struct event_base> base,
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uint32_t local_connect_address, uint32_t external_connect_address) :
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base(base), local_connect_address(local_connect_address),
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external_connect_address(external_connect_address) { }
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DNSServer::~DNSServer() {
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for (const auto& it : this->fd_to_receive_event) {
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close(it.first);
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}
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}
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void DNSServer::listen(const std::string& socket_path) {
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this->add_socket(::listen(socket_path, 0, 0));
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}
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void DNSServer::listen(const std::string& addr, int port) {
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this->add_socket(::listen(addr, port, 0));
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}
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void DNSServer::listen(int port) {
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this->add_socket(::listen("", port, 0));
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}
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void DNSServer::add_socket(int fd) {
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unique_ptr<struct event, void(*)(struct event*)> e(event_new(this->base.get(),
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fd, EV_READ | EV_PERSIST, &DNSServer::dispatch_on_receive_message,
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this), event_free);
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event_add(e.get(), nullptr);
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this->fd_to_receive_event.emplace(fd, move(e));
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}
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void DNSServer::dispatch_on_receive_message(evutil_socket_t fd,
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short events, void* ctx) {
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reinterpret_cast<DNSServer*>(ctx)->on_receive_message(fd, events);
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}
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string DNSServer::response_for_query(
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const void* vdata, size_t size, uint32_t resolved_address) {
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if (size < 0x0C) {
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throw invalid_argument("query too small");
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}
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const char* data = reinterpret_cast<const char*>(vdata);
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size_t name_len = strlen(&data[12]) + 1;
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be_uint32_t be_resolved_address = resolved_address;
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string response;
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response.append(data, 2);
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response.append("\x81\x80\x00\x01\x00\x01\x00\x00\x00\x00", 10);
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response.append(&data[12], name_len);
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response.append("\x00\x01\x00\x01\xC0\x0C\x00\x01\x00\x01\x00\x00\x00\x3C\x00\x04", 16);
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response.append(reinterpret_cast<const char*>(&be_resolved_address), 4);
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return response;
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}
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string DNSServer::response_for_query(
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const string& query, uint32_t resolved_address) {
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return DNSServer::response_for_query(query.data(), query.size(), resolved_address);
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}
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void DNSServer::on_receive_message(int fd, short) {
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for (;;) {
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sockaddr_in remote;
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socklen_t remote_size = sizeof(sockaddr_in);
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memset(&remote, 0, remote_size);
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string input(2048, 0);
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ssize_t bytes = recvfrom(fd, const_cast<char*>(input.data()), input.size(),
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0, reinterpret_cast<sockaddr*>(&remote), &remote_size);
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if (bytes < 0) {
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if (errno != EAGAIN) {
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log(INFO, "[DNSServer] input error %d", errno);
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throw runtime_error("cannot read from udp socket");
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}
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break;
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} else if (bytes == 0) {
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break;
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} else if (bytes < 0x0C) {
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log(WARNING, "[DNSServer] input query too small");
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print_data(stderr, input);
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} else {
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input.resize(bytes);
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uint32_t remote_address = ntohl(remote.sin_addr.s_addr);
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uint32_t connect_address = is_local_address(remote_address)
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? this->local_connect_address
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: this->external_connect_address;
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string response = this->response_for_query(input, connect_address);
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sendto(fd, response.data(), response.size(), 0,
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reinterpret_cast<const sockaddr*>(&remote), remote_size);
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}
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}
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}
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