path: root/minecproxy/idle.c

#include <inttypes.h>
#include <sys/socket.h>
#include <netinet/ip.h>
#include <arpa/inet.h>
#include <string.h>
#include <ctype.h>
#include <errno.h>

#include "main.h"
#include "uring.h"
#include "server.h"
#include "idle.h"
#include "ptimer.h"

struct idle {
	struct ptimer_task ptask;
	struct uring_task task;
};

static inline void
write_byte(char **pos, char byte)
{
	assert_return(pos && *pos);

	**pos = byte;
	(*pos)++;
}

#define MC_HELO 0x00
#define MC_NEXT_STATE_STATUS 0x01
#define MC_GET_STATUS 0x00
#define MC_VARINT_MAX_BYTES 5
#define MC_STATUS_REPLY 0x00
#define MC_UNDEFINED_VERSION -1

static inline void
write_varint(char **pos, int32_t orig)
{
	assert_return(pos && *pos);

	uint32_t val = (uint32_t)orig;

	while (val) {
		**pos = val & 0x7f;
		val >>= 7;
		if (val > 0)
			**pos |= 0x80;
		(*pos)++;
	}
}

/*
 * return value:
 * positive = varint parsed
 * zero = need more bytes
 * negative = error
 */
static inline int
read_varint(char **pos, size_t *remain, int32_t *res)
{
	unsigned consumed;
	uint32_t val = 0;

	assert_return(pos && *pos && remain && res, -1);

	for (consumed = 1; consumed <= *remain; consumed++) {
		uint32_t tmp;

		tmp = **pos & 0x7f;
		val += (tmp << (7 * (consumed - 1)));
		(*pos)++;

		if (!(tmp & 0x80))
			break;
	}

	if (consumed > *remain)
		return 0;
	else if (consumed > MC_VARINT_MAX_BYTES)
		return -1;

	*remain -= consumed;
	*res = (int32_t)val;
	return 1;
}

static inline void
write_bytes(char **pos, const char *bytes, size_t n)
{
	assert_return(pos && *pos && bytes && n > 0);

	memcpy(*pos, bytes, n);
	*pos += n;
}

static inline void
write_str(char **pos, const char *str)
{
	size_t len;

	assert_return(pos && *pos && !empty_str(str));

	len = strlen(str);
	write_varint(pos, len);
	write_bytes(pos, str, len);
}

static inline void
write_cmd(char **pos, const char *begin, const char *end)
{
	assert_return(pos && *pos && begin && end && end > begin);

	write_varint(pos, end - begin);
	write_bytes(pos, begin, end - begin);
}

static int
idle_check_handshake_complete(struct uring_task *task, _unused_ int res)
{
	size_t remain;
	char *pos;
	int32_t mclen;
	int r;

	assert_return(task, -EINVAL);
	assert_task_alive_or(DBG_IDLE, task, return -EINTR);

	remain = task->tbuf->len;
	pos = task->tbuf->buf;

	r = read_varint(&pos, &remain, &mclen);
	if (r < 0) {
		error("failed to parse message length");
		return -EINVAL;
	} else if (r == 0) {
		return 0;
	} else if (mclen < 2) {
		error("short MC message");
		return -EINVAL;
	}

	if (mclen < remain) {
		debug(DBG_IDLE, "short MC message - len: %" PRIi32 ", remain: %zu",
		      mclen, remain);
		return 0;
	} 

	debug(DBG_IDLE, "Complete message");
	return 1;
}

#define ONLINE_NEEDLE "\"online\""
static int
get_player_count(const char *pos, size_t remain)
{
	/*
	 * Example JSON (line breaks added):
	 * {"description":{
	 *	"text":"A Minecraft Server"},
	 *	"players":{"max":20,"online":0},
	 *	"version":{"name":"1.15.2","protocol":578}
	 * }
	 */
	char *online;
	char *end;
	unsigned count;

	assert_return(pos && remain > 0, -1);

	online = memmem(pos, remain, ONLINE_NEEDLE, STRLEN(ONLINE_NEEDLE));
	if (!online) {
		error("could not find online count in JSON");
		return -1;
	}

	remain -= (online - pos);

	end = memchr(online, '}', remain);
	if (!end) {
		error("could not parse JSON (no end)");
		return -1;
	}
	*end = '\0';

	if (sscanf(online, ONLINE_NEEDLE " : %u", &count) != 1) {
		error("could not parse JSON (online count)");
		return -1;
	}

	return count;
}

static void
idle_check_handshake_reply(struct uring_task *task, int res)
{
	struct server *server = container_of(task, struct server, idle_task);
	int32_t mclen;
	int32_t jsonlen;
	char *pos;
	size_t remain;
	int player_count = -1;
	int r;

	assert_return(task);
	assert_task_alive(DBG_IDLE, task);

	debug(DBG_IDLE, "res: %i", res);
	if (res < 0)
		goto out;

	/*
	fprintf(stderr, "Received MC message (%i bytes):", res);
	for (int i = 0; i < res; i++)
		fprintf(stderr, "0x%02hhx ", idle->remotebuf[i]);
	fprintf(stderr, "n");
	*/

	remain = server->idle_buf.len;
	pos = server->idle_buf.buf;

	r = read_varint(&pos, &remain, &mclen);
	if (r <= 0 || mclen < 2 || mclen < remain) {
		/* Should not happen since the msg has been checked already */
		error("invalid message");
		goto out;
	}

	debug(DBG_IDLE, "MC message - len: %" PRIi32 ", remain: %zu",
	      mclen, remain);

	if (*pos != MC_STATUS_REPLY) {
		error("unknown server reply (0x%02hhx)", *pos);
		goto out;
	}

	pos++;
	remain--;

	r = read_varint(&pos, &remain, &jsonlen);
	if (r <= 0) {
		error("could not read JSON length");
		goto out;
	}

	debug(DBG_IDLE, "MC - json len: %" PRIi32 ", remain: %zu",
	      jsonlen, remain);

	if (jsonlen < remain) {
		error("invalid JSON length");
		goto out;
	}

	/*
	fprintf(stderr, "JSON: ");
	for (int i = 0; i < jsonlen; i++)
		fprintf(stderr, "%c", pos[i]);
	*/

	player_count = get_player_count(pos, remain);

out:
	uring_task_close_fd(task);
	server_set_active_players(server, player_count);
	return;
}

static void
idle_check_handshake_sent(struct uring_task *task, int res)
{
	assert_return(task);
	assert_task_alive(DBG_IDLE, task);

	debug(DBG_IDLE, "sent %i bytes", res);
	if (res < 0) {
		uring_task_close_fd(task);
		return;
	}

	uring_tbuf_read_until(task,
			      idle_check_handshake_complete,
			      idle_check_handshake_reply);
}

void
idle_check_get_player_count(struct server *server, struct connection *conn)
{
	char buf[1024];
	char *pos;
	char *cmdbuf = server->idle_buf.buf;
	uint16_t port;
	char hostname[INET6_ADDRSTRLEN];

	assert_return(server && conn && server->idle_task.priv);

	port = saddr_port(&conn->remote);
	saddr_addr(&conn->remote, hostname, sizeof(hostname));

	pos = buf;
	write_byte(&pos, MC_HELO);
	write_varint(&pos, MC_UNDEFINED_VERSION);
	write_str(&pos, hostname);
	write_byte(&pos, (port >> 8) & 0xff);
	write_byte(&pos, (port >> 0) & 0xff);
	write_byte(&pos, MC_NEXT_STATE_STATUS);
	write_cmd(&cmdbuf, buf, pos);

	pos = buf;
	write_byte(&pos, MC_GET_STATUS);
	write_cmd(&cmdbuf, buf, pos);

	server->idle_buf.len = (cmdbuf - server->idle_buf.buf);
	debug(DBG_IDLE, "sending MC message (%zu bytes)", server->idle_buf.len);

	uring_tbuf_write(&server->idle_task, idle_check_handshake_sent);
}

static void
idle_cb(struct ptimer_task *ptask)
{
	struct idle *idle = container_of(ptask, struct idle, ptask);
	struct server *server;

	assert_return(ptask);
	assert_task_alive(DBG_IDLE, &idle->task);

	debug(DBG_IDLE, "timer fired");

	list_for_each_entry(server, &cfg->servers, list)
		server_idle_check(server);
}

static void
idle_free(struct uring_task *task)
{
	struct idle *idle = container_of(task, struct idle, task);

	assert_return(task);
	debug(DBG_IDLE, "task %p, idle %p", task, idle);
	xfree(idle);
}

void
idle_refdump()
{
	assert_return_silent(cfg->idle);

	uring_task_refdump(&cfg->idle->task);
}

void
idle_delete()
{
	assert_return(cfg->idle);

	debug(DBG_IDLE, "closing fd %i", cfg->idle->task.fd);
	ptimer_del_task(&cfg->idle->ptask);
	uring_task_destroy(&cfg->idle->task);
	cfg->idle = NULL;
}

void
idle_init()
{
	struct idle *idle;

	assert_return(!cfg->idle);

	idle = zmalloc(sizeof(*idle));
	if (!idle)
		die("malloc: %m");

	ptask_init(&idle->ptask, 60, 0, idle_cb);
	uring_task_init(&idle->task, "idle", uring_parent(), idle_free);
	ptimer_add_task(&idle->ptask);
	cfg->idle = idle;
}