Socket.gethostname

static VALUE
sock_gethostname(VALUE obj)
{
#if defined(NI_MAXHOST)
#  define RUBY_MAX_HOST_NAME_LEN NI_MAXHOST
#elif defined(HOST_NAME_MAX)
#  define RUBY_MAX_HOST_NAME_LEN HOST_NAME_MAX
#else
#  define RUBY_MAX_HOST_NAME_LEN 1024
#endif

    long len = RUBY_MAX_HOST_NAME_LEN;
    VALUE name;

    name = rb_str_new(0, len);
    while (gethostname(RSTRING_PTR(name), len) < 0) {
        int e = errno;
        switch (e) {
          case ENAMETOOLONG:
#ifdef __linux__
          case EINVAL:
            /* glibc before version 2.1 uses EINVAL instead of ENAMETOOLONG */
#endif
            break;
          default:
            rb_syserr_fail(e, "gethostname(3)");
        }
        rb_str_modify_expand(name, len);
        len += len;
    }
    char *s = RSTRING_PTR(name), *p = memchr(s, 0, len);
    if (p) rb_str_resize(name, (long)(p - s));
    return name;
}