Posh Devcon2009

Posh: an OSGi Shell
RFC132 in action!
Derek Baum
Paremus Limited
Posh OSGi Shell Copyright © 2009 Paremus Limited. All rights reserved. June 2009

The (Draft) Specification


RFC132: Problem Description
No standard way for user to interact with an
OSGi-based system.
• Different commands for common tasks
– install, start, stop, status
• Different API to add commands
– Commands are not reusable
• No script support


Equinox & Felix Shells
$ java -jar org.eclipse.osgi_3.4.3.R34x_v20081215-1030.jar
$ java -jar org.eclipse.osgi_3.4.3.R34x_v20081215-1030.jar -console
osgi> ss
Framework is launched.
id State Bundle
0 ACTIVE org.eclipse.osgi_3.4.3.R34x_v20081215-1030
osgi> ^D$

$ java -jar bin/felix.jar
-> ss
Command not found.
-> ps
START LEVEL 1
ID State Level Name
[ 0] [Active ] [ 0] System Bundle (1.8.0)
[ 1] [Active ] [ 1] Apache Felix Shell Service (1.2.0)
[ 2] [Active ] [ 1] Apache Felix Shell TUI (1.2.0)
[ 3] [Active ] [ 1] Apache Felix Bundle Repository (1.4.0)
-> ^DShellTUI: No standard input...exiting.
^C$

Hello, Equinox
import org.eclipse.osgi.framework.console.CommandInterpreter;
import org.eclipse.osgi.framework.console.CommandProvider;

public class Commands implements CommandProvider {

public void _hello(CommandInterpreter ci) {
ci.print("Hello, " + ci.nextArgument());
}

public String getHelp() {
return "thello - say hellon";
}
}


Hello, Felix
import org.apache.felix.shell.Command;

public class HelloCommand implements Command {

public void execute(String s, PrintStream out, PrintStream err) {
String[] args = s.split(“s+”);

if (args.length < 2) {
err.println(“Usage: ” + getUsage());
}
else {
out.println(“Hello, “ + args[1]);
}
}

public String getName() { return "hello";}
public String getUsage() { return "hello name";}
public String getShortDescription() { return "say hello";}
}


Hello, RFC132
public class Commands {

public boolean hello(String name) {
System.out.println(“Hello, “ + name);
return name != null;
}

}


RFC132 Command Interface
• Simple & lightweight to add commands
– Promotes adding commands in any bundle

• Access to input and output streams
• Shared session state between commands
• Small (core runtime < 50Kb)


Architecture
Console Telnet ...
Session Session Session

CommandProvider

CommandSessionImpl ThreadIO

CommandSession
command providers
Converter scope=xxx, function=yyy

Basic Basic ...
Conversions Commands Commands


CommandProcessor
package org.osgi.service.command;

public interface CommandProcessor {
CommandSession createSession(InputStream in, PrintStream out,
PrintStream err);
}


CommandSession

public interface CommandSession {
Object execute(CharSequence program) throws Exception;
void close();

InputStream getKeyboard();
PrintStream getConsole();

Object get(String name);
void put(String name, Object value);

CharSequence format(Object target, int level);
Object convert(Class<?> type, Object instance);
}


Command Provider
• There is no CommandProvider interface
• Parameters are coerced using reflection
• Any service can provide commands

public void start(BundleContext ctx) {
Commands cmd = new Commands();
String functions[] = {“hello”, “goodbye”};
Dictionary dict = new Dictionary();
dict.put(“osgi.command.scope”, “myscope”);
dict.put(“osgi.command.function”, functions);
ctx.registerService(cmd.getClass().getName,() cmd, dict);
}


Any Command Interface
public boolean grep(String[] args) throws IOException;

public URI cd(CommandSession session, String dir);
public URI pwd(CommandSession session);

public void addCommand(String scope, Object target);
public void addCommand(String scope, Object target, Class<?> fc);
public void addCommand(String scope, Object target, String func);

public Bundle getBundle(long id);
public Bundle[] getBundles();
public ServiceRegistration registerService(
String clazz, Object svcObj, Dictionary dict);


Grep command
public boolean grep(CommandSession session, List<String> args)
throws IOException {
Pattern pattern = Pattern.compile(args.remove(0));

for (String arg : args) {
InputStream in =
Directory.resolve(session,arg).toURL().openStream();
Reader rdr = new BufferedReader(new InputStreamReader(in));
String s;

while ((s = rdr.readLine()) != null) {
if (pattern.matcher(s).find()) {
match = true;
System.out.println(s);
}
}
}

return match;
}


Interactive Shell Language
• Interactive shell requirements differ from
those for scripting languages
– Easy for users to type
– Minimum parenthesis, semi-colons etc
– Compatibility with Unix shells like bash

• Existing JVM languages not good for shell
– Jacl: needs own TCL-derived library
– BeanShell: syntax too verbose


Tiny Shell Language - TSL
• Easy to use – no unnecessary syntax
• Provides lists, pipes and closures
• Leverages Java capabilities
– Method calls using reflection
– Argument coercion

• Commands can provide control primitives
• Small size (<50Kb)


Closures implement Function
public interface Function {
Object execute(CommandSession session, List<Object> arguments)
throws Exception;
}


Add Control Primitives
public void each(CommandSession session, Collection<Object> list,
Function closure) throws Exception {

List<Object> args = new ArrayList<Object>();
args.add(null);

for (Object x : list) {
args.set(0, x);
closure.execute(session, args);
}
}

% each [a, b, 1, 2] { echo $it }
a
b
1
2


RFC132: What's missing?
• Commands in osgi: scope are not defined
• Search order for unscoped commands
• List available commands and variables
• Script execution
• Command editing, history and completion


Posh: in action!


Posh in action!
Builds on basic RFC132 runtime
• Adds SCOPE path
• Shell builtins: set, type
• Script execution
• Command editing, history & completion
• Control-C interrupt handling
• And more…


Links

RFC132 Draft Specification
www.osgi.org/download/osgi-4.2-early-draft.pdf

Posh “devcon” binary download
www.paremus.com/devcon2009download/

derek.baum@paremus.com


Posh Devcon2009

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