Crosshair

Issue commands to your python app and reload its code on demand using SSH.

Features

• RPC-like control over an SSH interface
• Code management through a plugin manager that supports reloading at runtime

Using the SSH Server

So, you want to start your ssh server so you can issue commands to your application? Great! There are a couple of things you need to do before you start.

Set up keys

Generate a host key in RSA, DSA, or ECDSA format. Put this in a safe place on disk, for example, /home/crosshair/keys/id_host_rsa

Now you'll need to set up at least one key so you can access the server. Create a directory to store user keys, for example, /home/crosshair/keys/users/ Then put each user's public key in that directory in a file named username.pub, for example, the user nicola would have her key in /home/crosshair/keys/users/nicola.pub

Now you're all set with the keys you need to run a crosshair SSH server.

Public keys can be added or removed at any time, the server does not need to restart to pick up changes.

Running the SSH Server

crosshair.ssh.SSHServer takes the following arguments to __init__

• host_key_fname: the filename of the host key
• public_keys_path: the path to where user's public keys are stored
• address: two tuple of address and port to listen on

Example:

from crosshair import ssh

server = ssh.SSHServer(
    host_key_fname = '/home/crosshair/keys/host_rsa.key',
    public_keys_path = '/home/crosshair/keys/public_keys/',
    address = ('192.168.0.42', 9045))

Now you have your SSH Server ready! You probably want to load the core plugins next:

from crosshair import plugins

plugins.load('crosshair.commands')

Now start your server with:

server.serve_forever()

Client usage example:

$ ssh -p 9045 -i ./admin admin@192.168.0.42 list-commands
help
list-commands
reload-plugins
$ ssh -p 9045 -i ./admin admin@192.168.0.42 help list-commands
usage: list-commands
$ ssh -p 9045 -i ./admin admin@192.168.0.42 reload-plugins
Plugins reloaded.

Commands and Plugins

Built in commands

If you have loaded the crosshair.commands plugin, you will have these commands available:

• list-commands: Lists the available commands
• help : displays help for the specified command
• reload-plugins: reloads all crosshair plugins from disk

Writing Command Plugins

Commands should extend crosshair.commands.Command, and implement the following methods:

• execute(self, channel): run the command, sending any output to channel using channel.send
• setup_parser(self): Initialise self.parser with an argument parser that extends crosshair.commands.ArgumentParser, which is a standard Python argparse.ArgumentParser with slightly altered error handling

Once you have written your commands, register them with the plugin handler.

Example:

myplugin.py

from crosshair import plugins
from crosshair import commands


class HelloWorldCommand(commands.Command):
    def execute(self, channel):
        channel.send('Hello, world!\n')


plugins.register_command_handler('hello-world', HelloWorldCommand)

Remember to load your command plugin like this:

from crosshair import plugins

plugins.load('myplugin')