source: azure_iot_hub/trunk/musl-1.1.18/src/network/getservbyname_r.c@ 388

#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>
#include "lookup.h"

#define ALIGN (sizeof(struct { char a; char *b; }) - sizeof(char *))

int getservbyname_r(const char *name, const char *prots,
        struct servent *se, char *buf, size_t buflen, struct servent **res)
{
        struct service servs[MAXSERVS];
        int cnt, proto, align;

        *res = 0;

        /* Don't treat numeric port number strings as service records. */
        char *end = "";
        strtoul(name, &end, 10);
        if (!*end) return ENOENT;

        /* Align buffer */
        align = -(uintptr_t)buf & ALIGN-1;
        if (buflen < 2*sizeof(char *)+align)
                return ERANGE;
        buf += align;

        if (!prots) proto = 0;
        else if (!strcmp(prots, "tcp")) proto = IPPROTO_TCP;
        else if (!strcmp(prots, "udp")) proto = IPPROTO_UDP;
        else return EINVAL;

        cnt = __lookup_serv(servs, name, proto, 0, 0);
        if (cnt<0) switch (cnt) {
        case EAI_MEMORY:
        case EAI_SYSTEM:
                return ENOMEM;
        default:
                return ENOENT;
        }

        se->s_name = (char *)name;
        se->s_aliases = (void *)buf;
        se->s_aliases[0] = se->s_name;
        se->s_aliases[1] = 0;
        se->s_port = htons(servs[0].port);
        se->s_proto = servs[0].proto == IPPROTO_TCP ? "tcp" : "udp";

        *res = se;
        return 0;
}