How to write file into Apache SSHD server?

EXPLANATION:

I am building a test tool for my colleagues. I have several "mock" in-memory back-ends that they will need to use to run integration tests.

Therefore, I need to run SSH Server with the ability to upload/download a file.

The basic use-cases are the following:

• Upload a file, download file via Apache Camel route
• Upload a file, transfer file to a different folder via Apache Camel route, download file to verify transformation, content

QUESTION:

I have Apache SSHD Server written:

Server implementation example SshServer.java:

package com.example.sshd;

import org.apache.sshd.server.SshServer;
import org.apache.sshd.server.keyprovider.SimpleGeneratorHostKeyProvider;
import org.apache.sshd.server.scp.ScpCommandFactory;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.IOException;
import java.nio.file.Files;

public class SSHServer {

    private SshServer sshServer;
    private static final Logger logger = LoggerFactory.getLogger(SSHServer.class);

    public SSHServer() throws IOException {
        sshServer = SshServer.setUpDefaultServer();
        sshServer.setHost("127.0.0.1");
        sshServer.setKeyPairProvider(new SimpleGeneratorHostKeyProvider(Files.createTempFile("host_file", ".ser").toAbsolutePath()));
        sshServer.setCommandFactory(new ScpCommandFactory());
        sshServer.setPasswordAuthenticator((username, password, serverSession) -> {
            logger.debug("authenticating: {} password: {}", username, password);
            return username != null && "changeit".equals(password);
        });
    }

    public void startServer() throws IOException{
        sshServer.start();
    }

    public void stopServer() throws IOException {
        sshServer.stop();
    }
}

I tried:

• Find JavaDoc
• Find similar questions/solutions on StackOverflow
• Read Apache SSHD documentation on GitHub

I couldn't find an answer so far. I found this post, and it looks like I need to have SSH Client as well. Am I on the right track?

• Do I need SSH Client to write a file to SSH Server?
• How can I write a file while running the Apache SSHD server?

Apparently yes.

As I didn't have an SSH client, I have to create both client and server.

Example of file upload in Kotlin:

fun upload(file: File) {
    val creator = ScpClientCreator.instance()
    val scpClient = creator.createScpClient(session())
    scpClient.upload(Paths.get(file.absolutePath), file.name)
}

SSH Server creation:

fun setupServer(host: String, port: Int, rootDir: File, userName: String, pwd: String): SshServer {
    val sshd = SshServer.setUpDefaultServer()
    sshd.keyPairProvider = SimpleGeneratorHostKeyProvider(File(rootDir, "sshd_key.ser").toPath())
    sshd.fileSystemFactory = VirtualFileSystemFactory(Paths.get(rootDir.absolutePath))
    sshd.port = port
    sshd.host = host
    sshd.passwordAuthenticator = PasswordAuthenticator { username: String, password: String, _: ServerSession? -> username == userName && password == pwd }
    sshd.commandFactory = ScpCommandFactory()
    val factoryList: MutableList<SubsystemFactory> = ArrayList()
    factoryList.add(SftpSubsystemFactory())
    sshd.subsystemFactories = factoryList
    return sshd
}

SSH Client creation:

fun setupClient(): SshClient {
    return SshClient.setUpDefaultClient()
}

// Session for scp client
fun session(): ClientSession {
    val session = client.connect(userName, server.host, server.port).verify().session
    session.addPasswordIdentity(password)
    session.auth().verify().isSuccess
    return session
}