public class Minimal
{
    public static void main(String[] args) throws IOException, InterruptedException
    {
        System.out.println("https://github.com/apache/mina-sshd/issues/800");

        SshServer sshd = SshServer.setUpDefaultServer();

        sshd.setPort(40_000);

        sshd.setKeyPairProvider(new SimpleGeneratorHostKeyProvider(Path.of("hostkey.ser")));

        sshd.setPasswordAuthenticator((u, p, s) -> true);

        sshd.setUserAuthFactories(List.of(new UserAuthNoneFactory()));

        sshd.setSubsystemFactories(List.of(new SftpSubsystemFactory()));

        sshd.setFileSystemFactory(new FileSystemFactory()
        {
            @Override
            public Path getUserHomeDir(SessionContext session) throws IOException
            {
                return Path.of("/");
            }

            @Override
            public FileSystem createFileSystem(SessionContext session) throws IOException
            {
                System.out.println("filesystem created");
                return new MyFileSystem();
            }
        });

        sshd.start();

        System.out.println("Ready!");

        Thread.sleep(Integer.MAX_VALUE);
    }

    private static class MyFileSystem extends FileSystem
    {
        @Override
        public FileSystemProvider provider()
        {
            System.out.println("this is never called?");
            return null;
        }

        @Override
        public void close() throws IOException
        {
            // do nothing
        }

        @Override
        public boolean isOpen()
        {
            return true;
        }

        @Override
        public boolean isReadOnly()
        {
            return false;
        }

        @Override
        public String getSeparator()
        {
            return "/";
        }

        @Override
        public Iterable<Path> getRootDirectories()
        {
            return List.of(Path.of("/"));
        }

        @Override
        public Iterable<FileStore> getFileStores()
        {
            return List.of();
        }

        @Override
        public Set<String> supportedFileAttributeViews()
        {
            return Set.of();
        }

        @Override
        public Path getPath(String first, String... more)
        {
            Path result = Path.of(first);
            for (String chunk : more)
            {
                result = result.resolve(chunk);
            }
            return result;
        }

        @Override
        public PathMatcher getPathMatcher(String syntaxAndPattern)
        {
            return null;
        }

        @Override
        public UserPrincipalLookupService getUserPrincipalLookupService()
        {
            return null;
        }

        @Override
        public WatchService newWatchService() throws IOException
        {
            return null;
        }
    }
}