1#define _GNU_SOURCE
 2#include <sys/socket.h>
 3#include <netinet/in.h>
 4#include <netdb.h>
 5#include <inttypes.h>
 6#include <errno.h>
 7#include <string.h>
 8#include <stdlib.h>
 9
10int getservbyport_r(int port, const char *prots,
11	struct servent *se, char *buf, size_t buflen, struct servent **res)
12{
13	int i;
14	struct sockaddr_in sin = {
15		.sin_family = AF_INET,
16		.sin_port = port,
17	};
18
19	if (!prots) {
20		int r = getservbyport_r(port, "tcp", se, buf, buflen, res);
21		if (r) r = getservbyport_r(port, "udp", se, buf, buflen, res);
22		return r;
23	}
24	*res = 0;
25
26	/* Align buffer */
27	i = (uintptr_t)buf & sizeof(char *)-1;
28	if (!i) i = sizeof(char *);
29	if (buflen <= 3*sizeof(char *)-i)
30		return ERANGE;
31	buf += sizeof(char *)-i;
32	buflen -= sizeof(char *)-i;
33
34	if (strcmp(prots, "tcp") && strcmp(prots, "udp")) return EINVAL;
35
36	se->s_port = port;
37	se->s_proto = (char *)prots;
38	se->s_aliases = (void *)buf;
39	buf += 2*sizeof(char *);
40	buflen -= 2*sizeof(char *);
41	se->s_aliases[1] = 0;
42	se->s_aliases[0] = se->s_name = buf;
43
44	switch (getnameinfo((void *)&sin, sizeof sin, 0, 0, buf, buflen,
45		strcmp(prots, "udp") ? 0 : NI_DGRAM)) {
46	case EAI_MEMORY:
47	case EAI_SYSTEM:
48		return ENOMEM;
49	case EAI_OVERFLOW:
50		return ERANGE;
51	default:
52		return ENOENT;
53	case 0:
54		break;
55	}
56
57	/* A numeric port string is not a service record. */
58	if (strtol(buf, 0, 10)==ntohs(port)) return ENOENT;
59
60	*res = se;
61	return 0;
62}