Create a shared mc protocol implementation and use it in the proxy and cmd line tool

3 files changed, 296 insertions, 0 deletions

diff --git a/shared/mc-protocol.c b/shared/mc-protocol.c
new file mode 100644
index 0000000..afc9b38
--- /dev/null
+++ b/shared/mc-protocol.c
@@ -0,0 +1,282 @@
+#include <stdint.h>
+#include <inttypes.h>
+#include <strings.h>
+
+#include "utils.h"
+
+#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 unsigned
+write_byte(char **pos, char byte)
+{
+	if (pos && *pos) {
+		**pos = byte;
+		(*pos)++;
+	}
+	return 1;
+}
+static inline unsigned
+write_varint(char **pos, int32_t v)
+{
+	uint32_t u = (uint32_t)v;
+	unsigned rv = 0;
+
+	do {
+		char x;
+
+		x = u & 0x7f;
+		if (u >>= 7)
+			x |= 0x80;
+		if (pos && *pos)
+			*((*pos)++) = x;
+		rv++;
+	} while (u);
+
+	return rv;
+}
+
+static inline unsigned
+write_bytes(char **pos, const char *bytes, size_t n)
+{
+	if (pos && *pos) {
+		memcpy(*pos, bytes, n);
+		*pos += n;
+	}
+
+	return n;
+}
+
+static inline unsigned
+write_str(char **pos, const char *str, size_t len)
+{
+	unsigned rv;
+
+	rv = write_varint(pos, len);
+	rv += write_bytes(pos, str, len);
+
+	return rv;
+}
+
+/*
+ * return value:
+ * > 0 = varint parsed
+ *   0 = need more bytes
+ * < 0 = error
+ */
+static inline int
+read_varint(const char **from, size_t *remain, int32_t *res)
+{
+	unsigned consumed;
+	uint32_t val = 0;
+
+	assert_return(from && *from && remain && res, -1);
+
+	for (consumed = 1; consumed <= *remain; consumed++) {
+		uint32_t tmp;
+
+		tmp = **from & 0x7f;
+		val += (tmp << (7 * (consumed - 1)));
+		(*from)++;
+
+		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;
+}
+
+/*
+ * return value:
+ * > 0 = varint parsed
+ *   0 = need more bytes
+ * < 0 = error
+ */
+int
+mc_is_handshake_complete(const char *buf, size_t len)
+{
+	int32_t mclen;
+	int r;
+
+	assert_return(buf && len > 0, -1);
+
+	r = read_varint(&buf, &len, &mclen);
+	if (r < 0) {
+		error("failed to parse message length");
+		return -1;
+	} else if (r == 0) {
+		return 0;
+	} else if (mclen < 2) {
+		error("short MC message");
+		return -1;
+	}
+
+	if (mclen < len) {
+		debug(DBG_IDLE, "short MC message - len: %" PRIi32 ", remain: %zu",
+		      mclen, len);
+		return 0;
+	} 
+
+	debug(DBG_IDLE, "Complete message");
+	return 1;
+}
+
+#define PLAYERS_NEEDLE	"\"players\""
+#define MAX_NEEDLE	"\"max\""
+#define ONLINE_NEEDLE	"\"online\""
+static bool
+mc_get_player_count(const char *buf, size_t remain,
+		    unsigned *ronline, unsigned *rmax)
+{
+	/*
+	 * Example JSON (line breaks added):
+	 * {"description":{
+	 *	"text":"A Minecraft Server"},
+	 *	"players":{"max":20,"online":0},
+	 *	"version":{"name":"1.15.2","protocol":578}
+	 * }
+	 */
+	char *players;
+	char *pmax;
+	char *ponline;
+	unsigned online, max;
+
+	assert_return(buf && remain > 0, false);
+
+	players = memmem(buf, remain, PLAYERS_NEEDLE, STRLEN(PLAYERS_NEEDLE));
+	if (!players)
+		goto error;
+
+	remain -= (players - buf);
+
+	pmax = memmem(players, remain, MAX_NEEDLE, STRLEN(MAX_NEEDLE));
+	ponline = memmem(players, remain, ONLINE_NEEDLE, STRLEN(ONLINE_NEEDLE));
+	if (!pmax || !ponline)
+		goto error;
+
+	if ((sscanf(pmax, MAX_NEEDLE " : %u", &max) != 1) ||
+	    (sscanf(ponline, ONLINE_NEEDLE " : %u", &online) != 1))
+		goto error;
+
+	if (ronline)
+		*ronline = online;
+
+	if (rmax)
+		*rmax = max;
+
+	return true;
+
+error:
+	error("could not parse server status reply");
+	return false;
+}
+
+bool
+mc_protocol_parse_status_reply(const char *buf, size_t len,
+			       unsigned *online, unsigned *max)
+{
+	const char *from = buf;
+	size_t remain = len;
+	int32_t mclen;
+	int32_t jsonlen;
+	int r;
+
+	assert_return(buf && len > 0, -1);
+
+	r = read_varint(&from, &remain, &mclen);
+	if (r <= 0 || mclen < 2 || mclen < remain) {
+		/* Should not happen since the msg has been checked already */
+		error("invalid message");
+		return false;
+	}
+
+	debug(DBG_IDLE, "MC message - len: %" PRIi32 ", remain: %zu",
+	      mclen, remain);
+
+	if (*from != MC_STATUS_REPLY) {
+		error("unknown server reply (0x%02hhx)", *from);
+		return false;
+	}
+
+	from++;
+	remain--;
+
+	r = read_varint(&from, &remain, &jsonlen);
+	if (r <= 0) {
+		error("could not read JSON length");
+		return false;
+	}
+
+	debug(DBG_IDLE, "MC - json len: %" PRIi32 ", remain: %zu",
+	      jsonlen, remain);
+
+	if (jsonlen < remain) {
+		error("invalid JSON length");
+		return false;
+	}
+
+	if (mc_get_player_count(from, remain, online, max))
+		return true;
+
+	return false;
+}
+
+bool
+mc_protocol_create_status_request(char *buf, size_t len, size_t *rlen,
+				  struct saddr *saddr)
+{
+	uint16_t port;
+	char hostname[INET6_ADDRSTRLEN];
+	size_t bodylen, hostlen, packetlen;
+	char *to = buf;
+
+	assert_return(buf && len > 0 && rlen && saddr, false);
+
+	port = saddr_port(saddr);
+	saddr_addr(saddr, hostname, sizeof(hostname));
+	hostlen = strlen(hostname);
+
+	/* First, a handshake, calculate body length... */
+	bodylen  = write_byte(NULL, MC_HELO);
+	bodylen += write_varint(NULL, MC_UNDEFINED_VERSION);
+	bodylen += write_str(NULL, hostname, hostlen);
+	bodylen += write_byte(NULL, (port >> 8) & 0xff);
+	bodylen += write_byte(NULL, (port >> 0) & 0xff);
+	bodylen += write_byte(NULL, MC_NEXT_STATE_STATUS);
+
+	/* ...check buffer size... */
+	if (len < (MC_VARINT_MAX_BYTES + bodylen + 2 /* = status req */))
+		return false;
+
+	/* ...write header... */
+	packetlen = write_varint(&to, bodylen);
+
+	/* ...write body... */
+	packetlen += write_byte(&to, MC_HELO);
+	packetlen += write_varint(&to, MC_UNDEFINED_VERSION);
+	packetlen += write_str(&to, hostname, hostlen);
+	packetlen += write_byte(&to, (port >> 8) & 0xff);
+	packetlen += write_byte(&to, (port >> 0) & 0xff);
+	packetlen += write_byte(&to, MC_NEXT_STATE_STATUS);
+
+	/* ...then a status request, again with a header... */
+	packetlen += write_varint(&to, 1);
+
+	/* ...and body */
+	packetlen += write_byte(&to, MC_GET_STATUS);
+
+	*rlen = packetlen;
+	return true;
+}
+
diff --git a/shared/mc-protocol.h b/shared/mc-protocol.h
new file mode 100644
index 0000000..8ecc02a
--- /dev/null
+++ b/shared/mc-protocol.h
@@ -0,0 +1,13 @@
+#ifndef foomcprotocolhfoo
+#define foomcprotocolhfoo
+
+int mc_is_handshake_complete(const char *buf, size_t len);
+
+bool mc_protocol_parse_status_reply(const char *buf, size_t len,
+				    unsigned *online, unsigned *max);
+
+bool mc_protocol_create_status_request(char *buf, size_t len, size_t *rlen,
+				       struct saddr *saddr);
+
+#endif
+
diff --git a/shared/meson.build b/shared/meson.build
index ccfad4a..5b15c05 100644
--- a/shared/meson.build
+++ b/shared/meson.build
@@ -1,5 +1,6 @@
 srcs_libshared = [
 	'rcon-protocol.c',
+	'mc-protocol.c',
 	'config-parser.c',
 	'utils.c',
 ]