test

                ssize_t n = readlink(out, target, sizeof target - 1);

                if (n < 0) return nullptr;

                target[n] = 0;

                // new rest = target + remaining

                // new rest = target + remaining; the remaining part is

                // empty or starts with '/' (no '/' of its own: a link as

                // the last component must not look like "target/", which

                // the directory check below would refuse for a file)

                size_t remain = strlen(rest + pos);

                if ((size_t)n + 1 + remain >= sizeof rest) { errno = ENAMETOOLONG; return nullptr; }

                if ((size_t)n + remain >= sizeof rest) { errno = ENAMETOOLONG; return nullptr; }

                char tmp[PATH_MAX];

                memcpy(tmp, target, (size_t)n);

                tmp[n] = '/';

                memcpy(tmp + n + 1, rest + pos, remain + 1);

                memcpy(rest, tmp, (size_t)n + 1 + remain + 1);

                memcpy(tmp + n, rest + pos, remain + 1);

                memcpy(rest, tmp, (size_t)n + remain + 1);

                pos = 0;

                if (target[0] == '/') { out[0] = '/'; out[1] = 0; olen = 1; }

                else { olen = prev; out[olen] = 0; }