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#include "a2s.h"
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <errno.h>
#include <sys/types.h>
#include <sys/socket.h>
#include <netdb.h>
#include <arpa/inet.h>
/*
* A2S_INFO — Valve Source Engine server query protocol (UDP).
*
* Reference: https://developer.valvesoftware.com/wiki/Server_queries
*
* Wire protocol (modern Source, post-Orange Box):
*
* Request:
* FF FF FF FF 54 "Source Engine Query" 00
*
* Some servers issue a challenge before responding:
* FF FF FF FF 41 <4-byte challenge>
* In that case resend the request with the challenge appended.
*
* Response (type 0x49 = 'I'):
* FF FF FF FF 49
* <byte> protocol
* <string> name
* <string> map ← we want this
* <string> folder
* <string> game
* <short> appid
* <byte> players ← we want this
* <byte> max_players ← we want this
* ... (remaining fields not parsed)
*/
/* ── helpers ─────────────────────────────────────────────────────────────── */
/* Read a null-terminated string from buf starting at *pos.
* Advances *pos past the null byte.
* Returns 0 on success, -1 if the buffer would be overrun. */
static int read_string(const uint8_t *buf, int buf_len,
int *pos, char *out, int out_size)
{
int start = *pos;
while (*pos < buf_len && buf[*pos] != '\0')
(*pos)++;
if (*pos >= buf_len)
return -1; /* no null terminator found */
int len = *pos - start;
if (len >= out_size)
len = out_size - 1;
memcpy(out, buf + start, len);
out[len] = '\0';
(*pos)++; /* skip null byte */
return 0;
}
/* ── a2s_query ───────────────────────────────────────────────────────────── */
int a2s_query(const char *host, uint16_t port, int timeout_ms, A2SInfo *out)
{
memset(out, 0, sizeof(*out));
out->players = -1;
out->max_players = -1;
/* Resolve host */
struct addrinfo hints, *res, *rp;
memset(&hints, 0, sizeof(hints));
hints.ai_family = AF_UNSPEC;
hints.ai_socktype = SOCK_DGRAM;
char port_str[8];
snprintf(port_str, sizeof(port_str), "%u", port);
if (getaddrinfo(host, port_str, &hints, &res) != 0)
return -1;
int fd = -1;
for (rp = res; rp; rp = rp->ai_next) {
fd = socket(rp->ai_family, rp->ai_socktype, rp->ai_protocol);
if (fd < 0) continue;
if (connect(fd, rp->ai_addr, rp->ai_addrlen) == 0) break;
close(fd);
fd = -1;
}
freeaddrinfo(res);
if (fd < 0) return -1;
/* Set receive timeout */
struct timeval tv;
tv.tv_sec = timeout_ms / 1000;
tv.tv_usec = (timeout_ms % 1000) * 1000;
setsockopt(fd, SOL_SOCKET, SO_RCVTIMEO, &tv, sizeof(tv));
setsockopt(fd, SOL_SOCKET, SO_SNDTIMEO, &tv, sizeof(tv));
/* Build initial A2S_INFO request */
static const uint8_t a2s_prefix[] = {
0xFF, 0xFF, 0xFF, 0xFF, 0x54
};
static const char a2s_payload[] = "Source Engine Query";
/* Full request: prefix + payload + null byte */
uint8_t req[32];
int req_len = 0;
memcpy(req + req_len, a2s_prefix, sizeof(a2s_prefix));
req_len += sizeof(a2s_prefix);
memcpy(req + req_len, a2s_payload, sizeof(a2s_payload)); /* includes \0 */
req_len += sizeof(a2s_payload);
uint8_t resp[2048];
int resp_len;
int attempts = 0;
retry:
if (attempts++ >= 2) {
close(fd);
return -1;
}
if (send(fd, req, req_len, 0) != req_len) {
close(fd);
return -1;
}
resp_len = recv(fd, resp, sizeof(resp), 0);
if (resp_len < 5) {
close(fd);
return -1;
}
/* Check for challenge response: FF FF FF FF 41 <4 bytes> */
if (resp_len >= 9 &&
resp[0] == 0xFF && resp[1] == 0xFF &&
resp[2] == 0xFF && resp[3] == 0xFF &&
resp[4] == 0x41)
{
/* Append the 4-byte challenge to the request and resend */
if (req_len + 4 > (int)sizeof(req)) {
close(fd);
return -1;
}
memcpy(req + req_len, resp + 5, 4);
req_len += 4;
goto retry;
}
/* Expect response type 0x49 ('I') */
if (resp[0] != 0xFF || resp[1] != 0xFF ||
resp[2] != 0xFF || resp[3] != 0xFF ||
resp[4] != 0x49)
{
close(fd);
return -1;
}
close(fd);
/* Parse response body starting after the 5-byte header */
int pos = 5;
/* Skip protocol version (1 byte) */
if (pos + 1 > resp_len) return -1;
pos++;
/* Skip name string */
char scratch[256];
if (read_string(resp, resp_len, &pos, scratch, sizeof(scratch)) != 0)
return -1;
/* Map string — this is what we want */
if (read_string(resp, resp_len, &pos, out->map, sizeof(out->map)) != 0)
return -1;
/* Skip folder string */
if (read_string(resp, resp_len, &pos, scratch, sizeof(scratch)) != 0)
return -1;
/* Skip game string */
if (read_string(resp, resp_len, &pos, scratch, sizeof(scratch)) != 0)
return -1;
/* Skip app ID (2 bytes) */
if (pos + 2 > resp_len) return -1;
pos += 2;
/* Players (1 byte) */
if (pos + 1 > resp_len) return -1;
out->players = resp[pos++];
/* Max players (1 byte) */
if (pos + 1 > resp_len) return -1;
out->max_players = resp[pos++];
return 0;
}
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