flycast/core/hw/modem/dns.cpp

/*
	Created on: Sep 24, 2018

	Copyright 2018 flyinghead

	This file is part of reicast.

    reicast is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 2 of the License, or
    (at your option) any later version.

    reicast is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with reicast.  If not, see <https://www.gnu.org/licenses/>.
 */

#include <stdio.h>
#include <errno.h>
#ifndef _WIN32
#include <sys/socket.h>
#include <arpa/inet.h>
#include <netinet/in.h>
#include <unistd.h>
#endif

extern "C" {
#include <pico_stack.h>
#include <pico_ipv4.h>
#include <pico_dns_common.h>
}

void get_host_by_name(const char *name, struct pico_ip4 dnsaddr);
int get_dns_answer(struct pico_ip4 *address, struct pico_ip4 dnsaddr);
char *read_name(char *reader, char *buffer, int *count);
void set_non_blocking(int fd);

static int sock_fd = -1;
static unsigned short qid = PICO_TIME_MS();
static int qname_len;

void get_host_by_name(const char *host, struct pico_ip4 dnsaddr)
{
    if (sock_fd < 0)
    {
    	sock_fd = socket(AF_INET , SOCK_DGRAM , IPPROTO_UDP);
    	set_non_blocking(sock_fd);
    }

    struct sockaddr_in dest;
    dest.sin_family = AF_INET;
    dest.sin_port = htons(53);
    dest.sin_addr.s_addr = dnsaddr.addr;

    // DNS Packet header
	char buf[1024];
    pico_dns_packet *dns = (pico_dns_packet *)&buf;

    dns->id = qid++;
    dns->qr = PICO_DNS_QR_QUERY;
    dns->opcode = PICO_DNS_OPCODE_QUERY;
    dns->aa = PICO_DNS_AA_NO_AUTHORITY;
    dns->tc = PICO_DNS_TC_NO_TRUNCATION;
    dns->rd = PICO_DNS_RD_IS_DESIRED;
    dns->ra = PICO_DNS_RA_NO_SUPPORT;
    dns->z = 0;
    dns->rcode = PICO_DNS_RCODE_NO_ERROR;
    dns->qdcount = htons(1);	// One question
    dns->ancount = 0;
    dns->nscount = 0;
    dns->arcount = 0;

    char *qname = &buf[sizeof(pico_dns_packet)];

    strcpy(qname + 1, host);
    pico_dns_name_to_dns_notation(qname, 128);
	qname_len = strlen(qname) + 1;

	struct pico_dns_question_suffix *qinfo = (struct pico_dns_question_suffix *) &buf[sizeof(pico_dns_packet) + qname_len]; //fill it
    qinfo->qtype = htons(PICO_DNS_TYPE_A);		// Address record
    qinfo->qclass = htons(PICO_DNS_CLASS_IN);

    if (sendto(sock_fd, buf, sizeof(pico_dns_packet) + qname_len + sizeof(struct pico_dns_question_suffix), 0, (struct sockaddr *)&dest, sizeof(dest)) < 0)
    	perror("DNS sendto failed");
}

int get_dns_answer(struct pico_ip4 *address, struct pico_ip4 dnsaddr)
{
	struct sockaddr_in peer;
	socklen_t peer_len = sizeof(peer);
    char buf[1024];

    int r = recvfrom(sock_fd, buf, sizeof(buf), 0, (struct sockaddr*)&peer , &peer_len);
    if (r < 0)
    {
    	if (errno != EAGAIN && errno != EWOULDBLOCK)
    		perror("DNS recvfrom failed");
    	return -1;
    }
    if (peer.sin_addr.s_addr != dnsaddr.addr)
    	return -1;

    pico_dns_packet *dns = (pico_dns_packet*) buf;

    // move to the first answer
    char *reader = &buf[sizeof(pico_dns_packet) + qname_len + sizeof(struct pico_dns_question_suffix)];

    int stop = 0;

    for (int i = 0; i < ntohs(dns->ancount); i++)
    {
    	// FIXME Check name?
        free(read_name(reader, buf, &stop));
        reader = reader + stop;

        struct pico_dns_record_suffix *record = (struct pico_dns_record_suffix *)reader;
        reader = reader + sizeof(struct pico_dns_record_suffix);

        if (ntohs(record->rtype) == PICO_DNS_TYPE_A) // Address record
        {
            memcpy(&address->addr, reader, 4);

            return 0;
        }
        reader = reader + ntohs(record->rdlength);
    }
    return -1;
}

char *read_name(char *reader, char *buffer, int *count)
{
	char *name = (char *)malloc(128);
	if ((uint8_t)reader[0] & 0xC0)
	{
		int offset = (((uint8_t)reader[0] & ~0xC0) << 8) + (uint8_t)reader[1];
		reader = &buffer[offset];
		*count = 2;
	}
	else
	{
		*count = strlen(reader) + 1;
	}
	pico_dns_notation_to_name(reader, 128);
	strcpy(name, reader + 1);

	return name;
}