/**
 * Copyright (C) 2012-2013 Steven Barth <steven@midlink.org>
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License v2 as published by
 * the Free Software Foundation.
 *
 * This program 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.
 *
 */

#include <time.h>
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <resolv.h>
#include <getopt.h>
#include <stddef.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <signal.h>
#include <stdbool.h>
#include <syslog.h>
#include <alloca.h>

#include <arpa/inet.h>
#include <net/if.h>
#include <netinet/ip6.h>
#include <netpacket/packet.h>
#include <linux/netlink.h>

#include <sys/socket.h>
#include <sys/ioctl.h>
#include <sys/epoll.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/syscall.h>

#include <libubox/uloop.h>
#include "odhcpd.h"

static int ioctl_sock = -1;
static int urandom_fd = -1;

static void sighandler(_unused int signal)
{
	uloop_end();
}

static void print_usage(const char *app)
{
	printf(
	"== %s Usage ==\n\n"
	"  -h, --help   Print this help\n"
	"  -l level     Specify log level 0..7 (default %d)\n",
		app, config.log_level
	);
}

static bool ipv6_enabled(void)
{
	int fd = socket(AF_INET6, SOCK_DGRAM, 0);

	if (fd < 0)
		return false;

	close(fd);

	return true;
}

int main(int argc, char **argv)
{
	openlog("odhcpd", LOG_PERROR | LOG_PID, LOG_DAEMON);
	int opt;

	while ((opt = getopt(argc, argv, "hl:")) != -1) {
		switch (opt) {
		case 'h':
			print_usage(argv[0]);
			return 0;
		case 'l':
			config.log_level = (atoi(optarg) & LOG_PRIMASK);
			fprintf(stderr, "Log level set to %d\n", config.log_level);
			break;
		}
	}
	setlogmask(LOG_UPTO(config.log_level));
	uloop_init();

	if (getuid() != 0) {
		syslog(LOG_ERR, "Must be run as root!");
		return 2;
	}

	ioctl_sock = socket(AF_INET, SOCK_DGRAM | SOCK_CLOEXEC, 0);

	if (ioctl_sock < 0)
		return 4;

	if ((urandom_fd = open("/dev/urandom", O_RDONLY | O_CLOEXEC)) < 0)
		return 4;

	signal(SIGUSR1, SIG_IGN);
	signal(SIGINT, sighandler);
	signal(SIGTERM, sighandler);

	if (netlink_init())
		return 4;

	if (ipv6_enabled()) {
		if (router_init())
			return 4;

		if (dhcpv6_init())
			return 4;

		if (ndp_init())
			return 4;
	}
#ifndef DHCPV4_SUPPORT
	else
		return 4;
#else
	if (dhcpv4_init())
		return 4;
#endif

	odhcpd_run();
	return 0;
}


/* Read IPv6 MTU for interface */
int odhcpd_get_interface_config(const char *ifname, const char *what)
{
	char buf[64];
	
	snprintf(buf, sizeof(buf), "/proc/sys/net/ipv6/conf/%s/%s", ifname, what);

	int fd = open(buf, O_RDONLY);
	if (fd < 0)
		return -1;

	ssize_t len = read(fd, buf, sizeof(buf) - 1);
	close(fd);

	if (len < 0)
		return -1;

	buf[len] = 0;
	return atoi(buf);
}


/* Read IPv6 MAC for interface */
int odhcpd_get_mac(const struct interface *iface, uint8_t mac[6])
{
	struct ifreq ifr;

	memset(&ifr, 0, sizeof(ifr));
	strncpy(ifr.ifr_name, iface->ifname, sizeof(ifr.ifr_name) - 1);
	if (ioctl(ioctl_sock, SIOCGIFHWADDR, &ifr) < 0)
		return -1;

	memcpy(mac, ifr.ifr_hwaddr.sa_data, 6);
	return 0;
}

int odhcpd_get_flags(const struct interface *iface)
{
	struct ifreq ifr;

	memset(&ifr, 0, sizeof(ifr));
	strncpy(ifr.ifr_name, iface->ifname, sizeof(ifr.ifr_name) - 1);
	if (ioctl(ioctl_sock, SIOCGIFFLAGS, &ifr) < 0)
		return -1;

	return ifr.ifr_flags;
}


/* Forwards a packet on a specific interface */
ssize_t odhcpd_send(int socket, struct sockaddr_in6 *dest,
		struct iovec *iov, size_t iov_len,
		const struct interface *iface)
{
	/* Construct headers */
	uint8_t cmsg_buf[CMSG_SPACE(sizeof(struct in6_pktinfo))] = {0};
	struct msghdr msg = {
		.msg_name = (void *) dest,
		.msg_namelen = sizeof(*dest),
		.msg_iov = iov,
		.msg_iovlen = iov_len,
		.msg_control = cmsg_buf,
		.msg_controllen = sizeof(cmsg_buf),
		.msg_flags = 0
	};

	/* Set control data (define destination interface) */
	struct cmsghdr *chdr = CMSG_FIRSTHDR(&msg);
	chdr->cmsg_level = IPPROTO_IPV6;
	chdr->cmsg_type = IPV6_PKTINFO;
	chdr->cmsg_len = CMSG_LEN(sizeof(struct in6_pktinfo));
	struct in6_pktinfo *pktinfo = (struct in6_pktinfo*)CMSG_DATA(chdr);
	pktinfo->ipi6_ifindex = iface->ifindex;

	/* Also set scope ID if link-local */
	if (IN6_IS_ADDR_LINKLOCAL(&dest->sin6_addr)
			|| IN6_IS_ADDR_MC_LINKLOCAL(&dest->sin6_addr))
		dest->sin6_scope_id = iface->ifindex;

	char ipbuf[INET6_ADDRSTRLEN];
	inet_ntop(AF_INET6, &dest->sin6_addr, ipbuf, sizeof(ipbuf));

	ssize_t sent = sendmsg(socket, &msg, MSG_DONTWAIT);
	if (sent < 0)
		syslog(LOG_ERR, "Failed to send to %s%%%s@%s (%m)",
				ipbuf, iface->name, iface->ifname);
	else
		syslog(LOG_DEBUG, "Sent %zd bytes to %s%%%s@%s",
				sent, ipbuf, iface->name, iface->ifname);
	return sent;
}


static int odhcpd_get_linklocal_interface_address(int ifindex, struct in6_addr *lladdr)
{
	int ret = -1;
	struct sockaddr_in6 addr;
	socklen_t alen = sizeof(addr);
	int sock = socket(AF_INET6, SOCK_RAW, IPPROTO_ICMPV6);

	if (sock < 0)
		return -1;

	memset(&addr, 0, sizeof(addr));
	addr.sin6_family = AF_INET6;
	inet_pton(AF_INET6, ALL_IPV6_ROUTERS, &addr.sin6_addr);
	addr.sin6_scope_id = ifindex;

	if (!connect(sock, (struct sockaddr*)&addr, sizeof(addr)) &&
			!getsockname(sock, (struct sockaddr*)&addr, &alen)) {
		*lladdr = addr.sin6_addr;
		ret = 0;
	}

	close(sock);
	return ret;
}

/*
 * DNS address selection criteria order :
 * - use IPv6 address with valid lifetime if none is yet selected
 * - use IPv6 address with a preferred lifetime if the already selected IPv6 address is deprecated
 * - use an IPv6 ULA address if the already selected IPv6 address is not an ULA address
 * - use the IPv6 address with the longest preferred lifetime
 */
int odhcpd_get_interface_dns_addr(const struct interface *iface, struct in6_addr *addr)
{
	time_t now = odhcpd_time();
	ssize_t m = -1;

	if (!iface->dns_service)
		return -1;

	for (size_t i = 0; i < iface->addr6_len; ++i) {
		if (iface->addr6[i].valid_lt <= (uint32_t)now)
			continue;

		if (m < 0) {
			m = i;
			continue;
		}

		if (iface->addr6[m].preferred_lt >= (uint32_t)now &&
				iface->addr6[i].preferred_lt < (uint32_t)now)
			continue;

		if (IN6_IS_ADDR_ULA(&iface->addr6[i].addr.in6)) {
			if (!IN6_IS_ADDR_ULA(&iface->addr6[m].addr.in6)) {
				m = i;
				continue;
			}
		} else if (IN6_IS_ADDR_ULA(&iface->addr6[m].addr.in6))
			continue;

		if (iface->addr6[i].preferred_lt > iface->addr6[m].preferred_lt)
			m = i;
	}

	if (m >= 0) {
		*addr = iface->addr6[m].addr.in6;
		return 0;
	}

	return odhcpd_get_linklocal_interface_address(iface->ifindex, addr);
}

struct interface* odhcpd_get_interface_by_index(int ifindex)
{
	struct interface *iface;

	avl_for_each_element(&interfaces, iface, avl) {
		if (iface->ifindex == ifindex)
			return iface;
	}

	return NULL;
}

/* Convenience function to receive and do basic validation of packets */
static void odhcpd_receive_packets(struct uloop_fd *u, _unused unsigned int events)
{
	struct odhcpd_event *e = container_of(u, struct odhcpd_event, uloop);

	uint8_t data_buf[8192], cmsg_buf[128];
	union {
		struct sockaddr_in6 in6;
		struct sockaddr_in in;
		struct sockaddr_ll ll;
		struct sockaddr_nl nl;
	} addr;

	if (u->error) {
		int ret = -1;
		socklen_t ret_len = sizeof(ret);

		u->error = false;
		if (e->handle_error && getsockopt(u->fd, SOL_SOCKET, SO_ERROR, &ret, &ret_len) == 0)
			e->handle_error(e, ret);
	}

	if (e->recv_msgs) {
		e->recv_msgs(e);
		return;
	}

	while (true) {
		struct iovec iov = {data_buf, sizeof(data_buf)};
		struct msghdr msg = {
			.msg_name = (void *) &addr,
			.msg_namelen = sizeof(addr),
			.msg_iov = &iov,
			.msg_iovlen = 1,
			.msg_control = cmsg_buf,
			.msg_controllen = sizeof(cmsg_buf),
			.msg_flags = 0
		};

		ssize_t len = recvmsg(u->fd, &msg, MSG_DONTWAIT);
		if (len < 0) {
			if (errno == EAGAIN)
				break;
			else
				continue;
		}


		/* Extract destination interface */
		int destiface = 0;
		int *hlim = NULL;
		void *dest = NULL;
		struct in6_pktinfo *pktinfo;
		struct in_pktinfo *pkt4info;
		for (struct cmsghdr *ch = CMSG_FIRSTHDR(&msg); ch != NULL; ch = CMSG_NXTHDR(&msg, ch)) {
			if (ch->cmsg_level == IPPROTO_IPV6 &&
					ch->cmsg_type == IPV6_PKTINFO) {
				pktinfo = (struct in6_pktinfo*)CMSG_DATA(ch);
				destiface = pktinfo->ipi6_ifindex;
				dest = &pktinfo->ipi6_addr;
			} else if (ch->cmsg_level == IPPROTO_IP &&
					ch->cmsg_type == IP_PKTINFO) {
				pkt4info = (struct in_pktinfo*)CMSG_DATA(ch);
				destiface = pkt4info->ipi_ifindex;
				dest = &pkt4info->ipi_addr;
			} else if (ch->cmsg_level == IPPROTO_IPV6 &&
					ch->cmsg_type == IPV6_HOPLIMIT) {
				hlim = (int*)CMSG_DATA(ch);
			}
		}

		/* Check hoplimit if received */
		if (hlim && *hlim != 255)
			continue;

		/* Detect interface for packet sockets */
		if (addr.ll.sll_family == AF_PACKET)
			destiface = addr.ll.sll_ifindex;

		char ipbuf[INET6_ADDRSTRLEN] = "kernel";
		if (addr.ll.sll_family == AF_PACKET &&
				len >= (ssize_t)sizeof(struct ip6_hdr))
			inet_ntop(AF_INET6, &data_buf[8], ipbuf, sizeof(ipbuf));
		else if (addr.in6.sin6_family == AF_INET6)
			inet_ntop(AF_INET6, &addr.in6.sin6_addr, ipbuf, sizeof(ipbuf));
		else if (addr.in.sin_family == AF_INET)
			inet_ntop(AF_INET, &addr.in.sin_addr, ipbuf, sizeof(ipbuf));

		/* From netlink */
		if (addr.nl.nl_family == AF_NETLINK) {
			syslog(LOG_DEBUG, "Received %zd Bytes from %s%%netlink", len,
					ipbuf);
			e->handle_dgram(&addr, data_buf, len, NULL, dest);
			return;
		} else if (destiface != 0) {
			struct interface *iface;

			avl_for_each_element(&interfaces, iface, avl) {
				if (iface->ifindex != destiface)
					continue;

				syslog(LOG_DEBUG, "Received %zd Bytes from %s%%%s@%s", len,
						ipbuf, iface->name, iface->ifname);

				e->handle_dgram(&addr, data_buf, len, iface, dest);
			}
		}


	}
}

/* Register events for the multiplexer */
int odhcpd_register(struct odhcpd_event *event)
{
	event->uloop.cb = odhcpd_receive_packets;
	return uloop_fd_add(&event->uloop, ULOOP_READ |
			((event->handle_error) ? ULOOP_ERROR_CB : 0));
}

int odhcpd_deregister(struct odhcpd_event *event)
{
	event->uloop.cb = NULL;
	return uloop_fd_delete(&event->uloop);
}

void odhcpd_process(struct odhcpd_event *event)
{
	odhcpd_receive_packets(&event->uloop, 0);
}

int odhcpd_urandom(void *data, size_t len)
{
	return read(urandom_fd, data, len);
}


time_t odhcpd_time(void)
{
	struct timespec ts;
	clock_gettime(CLOCK_MONOTONIC, &ts);
	return ts.tv_sec;
}


static const char hexdigits[] = "0123456789abcdef";
static const int8_t hexvals[] = {
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -2, -2, -1, -1, -2, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -2, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
     0,  1,  2,  3,  4,  5,  6,  7,  8,  9, -1, -1, -1, -1, -1, -1,
    -1, 10, 11, 12, 13, 14, 15, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, 10, 11, 12, 13, 14, 15, -1, -1, -1, -1, -1, -1, -1, -1, -1,
    -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1, -1,
};

ssize_t odhcpd_unhexlify(uint8_t *dst, size_t len, const char *src)
{
	size_t c;
	for (c = 0; c < len && src[0] && src[1]; ++c) {
		int8_t x = (int8_t)*src++;
		int8_t y = (int8_t)*src++;
		if (x < 0 || (x = hexvals[x]) < 0
				|| y < 0 || (y = hexvals[y]) < 0)
			return -1;
		dst[c] = x << 4 | y;
		while (((int8_t)*src) < 0 ||
				(*src && hexvals[(uint8_t)*src] < 0))
			src++;
	}

	return c;
}


void odhcpd_hexlify(char *dst, const uint8_t *src, size_t len)
{
	for (size_t i = 0; i < len; ++i) {
		*dst++ = hexdigits[src[i] >> 4];
		*dst++ = hexdigits[src[i] & 0x0f];
	}
	*dst = 0;
}

const char *odhcpd_print_mac(const uint8_t *mac, const size_t len)
{
	static char buf[32];

	snprintf(buf, sizeof(buf), "%02x", mac[0]);
	for (size_t i = 1, j = 2; i < len && j < sizeof(buf); i++, j += 3)
		snprintf(buf + j, sizeof(buf) - j, ":%02x", mac[i]);

	return buf;
}

int odhcpd_bmemcmp(const void *av, const void *bv, size_t bits)
{
	const uint8_t *a = av, *b = bv;
	size_t bytes = bits / 8;
	bits %= 8;

	int res = memcmp(a, b, bytes);
	if (res == 0 && bits > 0)
		res = (a[bytes] >> (8 - bits)) - (b[bytes] >> (8 - bits));

	return res;
}


void odhcpd_bmemcpy(void *av, const void *bv, size_t bits)
{
	uint8_t *a = av;
	const uint8_t *b = bv;

	size_t bytes = bits / 8;
	bits %= 8;
	memcpy(a, b, bytes);

	if (bits > 0) {
		uint8_t mask = (1 << (8 - bits)) - 1;
		a[bytes] = (a[bytes] & mask) | ((~mask) & b[bytes]);
	}
}


int odhcpd_netmask2bitlen(bool inet6, void *mask)
{
	int bits;
	struct in_addr *v4;
	struct in6_addr *v6;

	if (inet6)
		for (bits = 0, v6 = mask;
		     bits < 128 && (v6->s6_addr[bits / 8] << (bits % 8)) & 128;
		     bits++);
	else
		for (bits = 0, v4 = mask;
		     bits < 32 && (ntohl(v4->s_addr) << bits) & 0x80000000;
		     bits++);

	return bits;
}

bool odhcpd_bitlen2netmask(bool inet6, unsigned int bits, void *mask)
{
	uint8_t b;
	struct in_addr *v4;
	struct in6_addr *v6;

	if (inet6)
	{
		if (bits > 128)
			return false;

		v6 = mask;

		for (unsigned int i = 0; i < sizeof(v6->s6_addr); i++)
		{
			b = (bits > 8) ? 8 : bits;
			v6->s6_addr[i] = (uint8_t)(0xFF << (8 - b));
			bits -= b;
		}
	}
	else
	{
		if (bits > 32)
			return false;

		v4 = mask;
		v4->s_addr = bits ? htonl(~((1 << (32 - bits)) - 1)) : 0;
	}

	return true;
}

bool odhcpd_valid_hostname(const char *name)
{
#define MAX_LABEL	63
	const char *c, *label, *label_end;
	int label_sz = 0;

	for (c = name, label_sz = 0, label = name, label_end = name + strcspn(name, ".") - 1;
			*c && label_sz <= MAX_LABEL; c++) {
		if ((*c >= '0' && *c <= '9') ||
		    (*c >= 'A' && *c <= 'Z') ||
		    (*c >= 'a' && *c <= 'z')) {
			label_sz++;
			continue;
		}

		if ((*c == '_' || *c == '-') && c != label && c != label_end) {
			label_sz++;
			continue;
		}

		if (*c == '.') {
			if (*(c + 1)) {
				label = c + 1;
				label_end = label + strcspn(label, ".") - 1;
				label_sz = 0;
			}
			continue;
		}

		return false;
	}

	return (label_sz && label_sz <= MAX_LABEL ? true : false);
}