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

  /* 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;
  }

  *res = se;
  return 0;
}