source: asp3_tinet_ecnl_rx/trunk/musl-1.1.18/src/network/getservbyport_r.c@ 337

#define _GNU_SOURCE
#include <sys/socket.h>
#include <netinet/in.h>
#include <netdb.h>
#include <inttypes.h>
#include <errno.h>
#include <string.h>
#include <stdlib.h>

int getservbyport_r(int port, const char *prots,
        struct servent *se, char *buf, size_t buflen, struct servent **res)
{
        int i;
        struct sockaddr_in sin = {
                .sin_family = AF_INET,
                .sin_port = port,
        };

        if (!prots) {
                int r = getservbyport_r(port, "tcp", se, buf, buflen, res);
                if (r) r = getservbyport_r(port, "udp", se, buf, buflen, res);
                return r;
        }
        *res = 0;

        /* Align buffer */
        i = (uintptr_t)buf & sizeof(char *)-1;
        if (!i) i = sizeof(char *);
        if (buflen < 3*sizeof(char *)-i)
                return ERANGE;
        buf += sizeof(char *)-i;
        buflen -= sizeof(char *)-i;

        if (strcmp(prots, "tcp") && strcmp(prots, "udp")) return EINVAL;

        se->s_port = port;
        se->s_proto = (char *)prots;
        se->s_aliases = (void *)buf;
        buf += 2*sizeof(char *);
        buflen -= 2*sizeof(char *);
        se->s_aliases[1] = 0;
        se->s_aliases[0] = se->s_name = buf;

        switch (getnameinfo((void *)&sin, sizeof sin, 0, 0, buf, buflen,
                strcmp(prots, "udp") ? 0 : NI_DGRAM)) {
        case EAI_MEMORY:
        case EAI_SYSTEM:
                return ENOMEM;
        default:
                return ENOENT;
        case 0:
                break;
        }

        /* A numeric port string is not a service record. */
        if (strtol(buf, 0, 10)==ntohs(port)) return ENOENT;

        *res = se;
        return 0;
}