Wouldn’t it be nice to have a possibility to connect you application securely via SSH with a secret user/password and communicate with it within the application specific shell? That was my first idea as I found the Apache’s SSHD project.
Apache SSHD is a 100% pure java library to support the SSH protocols on both the client and server side. This library is based on Apache MINA, a scalable and high performance asynchronous IO library.
This blog post demonstrates how is it possible to create a application shell using Apache SSHD and JLine projects.
mvn archetype:generate \ -DgroupId=net.javaforge.blog \ -DartifactId=sshd-daemon-demo \ -DarchetypeArtifactId=maven-archetype-quickstart \ -DinteractiveMode=false
<dependency> <groupId>org.apache.sshd</groupId> <artifactId>sshd-core</artifactId> <version>0.9.0</version> </dependency> <dependency> <groupId>jline</groupId> <artifactId>jline</artifactId> <version>2.11</version> </dependency> <!-- not really necessary, just to simplify logging in this demo --> <dependency> <groupId>org.slf4j</groupId> <artifactId>slf4j-simple</artifactId> <version>1.6.6</version> </dependency>
public class InAppPasswordAuthenticator implements PasswordAuthenticator {
@Override
public boolean authenticate(String username, String password, ServerSession session) {
return username != null && username.equals(password);
}
}
public class InAppShellFactory implements Factory {
public Command create() {
return new InAppShell();
}
private static class InAppShell implements Command, Runnable {
private static final Logger log = LoggerFactory.getLogger(InAppShell.class);
public static final boolean IS_MAC_OSX = System.getProperty("os.name").startsWith("Mac OS X");
private static final String SHELL_THREAD_NAME = "InAppShell";
private static final String SHELL_PROMPT = "app> ";
private static final String SHELL_CMD_QUIT = "quit";
private static final String SHELL_CMD_EXIT = "exit";
private static final String SHELL_CMD_VERSION = "version";
private static final String SHELL_CMD_HELP = "help";
private InputStream in;
private OutputStream out;
private OutputStream err;
private ExitCallback callback;
private Environment environment;
private Thread thread;
private ConsoleReader reader;
private PrintWriter writer;
public InputStream getIn() {
return in;
}
public OutputStream getOut() {
return out;
}
public OutputStream getErr() {
return err;
}
public Environment getEnvironment() {
return environment;
}
public void setInputStream(InputStream in) {
this.in = in;
}
public void setOutputStream(OutputStream out) {
this.out = out;
}
public void setErrorStream(OutputStream err) {
this.err = err;
}
public void setExitCallback(ExitCallback callback) {
this.callback = callback;
}
public void start(Environment env) throws IOException {
environment = env;
thread = new Thread(this, SHELL_THREAD_NAME);
thread.start();
}
public void destroy() {
if (reader != null)
reader.shutdown();
thread.interrupt();
}
@Override
public void run() {
try {
reader = new ConsoleReader(in, new FilterOutputStream(out) {
@Override
public void write(final int i) throws IOException {
super.write(i);
// workaround for MacOSX!! reset line after CR..
if (IS_MAC_OSX && i == ConsoleReader.CR.toCharArray()[0]) {
super.write(ConsoleReader.RESET_LINE);
}
}
});
reader.setPrompt(SHELL_PROMPT);
reader.addCompleter(new StringsCompleter(SHELL_CMD_QUIT,
SHELL_CMD_EXIT, SHELL_CMD_VERSION, SHELL_CMD_HELP));
writer = new PrintWriter(reader.getOutput());
// output welcome banner on ssh session startup
writer.println("****************************************************");
writer.println("* Welcome to Application Shell. *");
writer.println("****************************************************");
writer.flush();
String line;
while ((line = reader.readLine()) != null) {
handleUserInput(line.trim());
}
} catch (InterruptedIOException e) {
// Ignore
} catch (Exception e) {
log.error("Error executing InAppShell...", e);
} finally {
callback.onExit(0);
}
}
private void handleUserInput(String line) throws InterruptedIOException {
if (line.equalsIgnoreCase(SHELL_CMD_QUIT)
|| line.equalsIgnoreCase(SHELL_CMD_EXIT))
throw new InterruptedIOException();
String response;
if (line.equalsIgnoreCase(SHELL_CMD_VERSION))
response = "InApp version 1.0.0";
else if (line.equalsIgnoreCase(SHELL_CMD_HELP))
response = "Help is not implemented yet...";
else
response = "======> \"" + line + "\"";
writer.println(response);
writer.flush();
}
}
}
public class App {
public static void main(String[] args) throws Throwable {
SshServer sshd = SshServer.setUpDefaultServer();
sshd.setPort(5222);
sshd.setKeyPairProvider(new SimpleGeneratorHostKeyProvider("hostkey.ser"));
sshd.setPasswordAuthenticator(new InAppPasswordAuthenticator());
sshd.setShellFactory(new InAppShellFactory());
sshd.start();
}
}
The KeyPairProvider above is used on the server side to provide the host key.
Now after starting our SSH daemon we can connect it using ordinary SSH client. Find below a screenshot of my session with the InAppShell:
The project source code is hosted on GitHub under https://github.com/bigpuritz/javaforge-blog/tree/master/sshd-daemon-demo
