Added new XEP-0050 implementation.

Backward incompatibility alert!

Please see examples/adhoc_provider.py for how to use the new
plugin implementation, or the test examples in the files
tests/test_stream_xep_0050.py and tests/test_stanza_xep_0050.py.

Major changes:
    - May now have zero-step commands. Useful if a command is
      intended to be a dynamic status report that doesn't
      require any user input.
    - May use payloads other than data forms, such as a
      completely custom stanza type.
    - May include multiple payload items, such as multiple
      data forms, or a form and a custom stanza type.
    - Includes a command user API for calling adhoc commands
      on remote agents and managing the workflow.
    - Added support for note elements.

Todo:
    - Add prev action support.

You may use register_plugin('old_0050') to continue using the
previous XEP-0050 implementation.

3 files changed, 788 insertions, 0 deletions

diff --git a/sleekxmpp/plugins/xep_0050/__init__.py b/sleekxmpp/plugins/xep_0050/__init__.py
new file mode 100644
index 00000000..99f44f2a
--- /dev/null
+++ b/sleekxmpp/plugins/xep_0050/__init__.py
@@ -0,0 +1,10 @@
+"""
+    SleekXMPP: The Sleek XMPP Library
+    Copyright (C) 2011 Nathanael C. Fritz, Lance J.T. Stout
+    This file is part of SleekXMPP.
+
+    See the file LICENSE for copying permission.
+"""
+
+from sleekxmpp.plugins.xep_0050.stanza import Command
+from sleekxmpp.plugins.xep_0050.adhoc import xep_0050
diff --git a/sleekxmpp/plugins/xep_0050/adhoc.py b/sleekxmpp/plugins/xep_0050/adhoc.py
new file mode 100644
index 00000000..fe964e96
--- /dev/null
+++ b/sleekxmpp/plugins/xep_0050/adhoc.py
@@ -0,0 +1,593 @@
+"""
+    SleekXMPP: The Sleek XMPP Library
+    Copyright (C) 2011 Nathanael C. Fritz, Lance J.T. Stout
+    This file is part of SleekXMPP.
+
+    See the file LICENSE for copying permission.
+"""
+
+import logging
+import time
+
+from sleekxmpp import Iq
+from sleekxmpp.xmlstream.handler import Callback
+from sleekxmpp.xmlstream.matcher import StanzaPath
+from sleekxmpp.xmlstream import register_stanza_plugin, JID
+from sleekxmpp.plugins.base import base_plugin
+from sleekxmpp.plugins.xep_0050 import stanza
+from sleekxmpp.plugins.xep_0050 import Command
+
+
+log = logging.getLogger(__name__)
+
+
+class xep_0050(base_plugin):
+
+    """
+    XEP-0050: Ad-Hoc Commands
+
+    XMPP's Adhoc Commands provides a generic workflow mechanism for
+    interacting with applications. The result is similar to menu selections
+    and multi-step dialogs in normal desktop applications. Clients do not
+    need to know in advance what commands are provided by any particular
+    application or agent. While adhoc commands provide similar functionality
+    to Jabber-RPC, adhoc commands are used primarily for human interaction.
+
+    Also see <http://xmpp.org/extensions/xep-0050.html>
+
+    Configuration Values:
+        threaded -- Indicates if command events should be threaded.
+                    Defaults to True.
+
+    Events:
+        command_execute  -- Received a command with action="execute"
+        command_next     -- Received a command with action="next"
+        command_complete -- Received a command with action="complete"
+        command_cancel   -- Received a command with action="cancel"
+
+    Attributes:
+        threaded -- Indicates if command events should be threaded.
+                    Defaults to True.
+        commands -- A dictionary mapping JID/node pairs to command
+                    names and handlers.
+        sessions -- A dictionary or equivalent backend mapping
+                    session IDs to dictionaries containing data
+                    relevant to a command's session.
+
+    Methods:
+        plugin_init       -- Overrides base_plugin.plugin_init
+        post_init         -- Overrides base_plugin.post_init
+        new_session       -- Return a new session ID.
+        prep_handlers     -- Placeholder. May call with a list of handlers
+                             to prepare them for use with the session storage
+                             backend, if needed.
+        set_backend       -- Replace the default session storage with some
+                             external storage mechanism, such as a database.
+                             The provided backend wrapper must be able to
+                             act using the same syntax as a dictionary.
+        add_command       -- Add a command for use by external entitites.
+        get_commands      -- Retrieve a list of commands provided by a
+                             remote agent.
+        send_command      -- Send a command request to a remote agent.
+        start_command     -- Command user API: initiate a command session
+        continue_command  -- Command user API: proceed to the next step
+        cancel_command    -- Command user API: cancel a command
+        complete_command  -- Command user API: finish a command
+        terminate_command -- Command user API: delete a command's session
+    """
+
+    def plugin_init(self):
+        """Start the XEP-0050 plugin."""
+        self.xep = '0050'
+        self.description = 'Ad-Hoc Commands'
+        self.stanza = stanza
+
+        self.threaded = self.config.get('threaded', True)
+        self.commands = {}
+        self.sessions = self.config.get('session_db', {})
+
+        self.xmpp.register_handler(
+                Callback("Ad-Hoc Execute",
+                         StanzaPath('iq@type=set/command'),
+                         self._handle_command))
+
+        self.xmpp.register_handler(
+                Callback("Ad-Hoc Result",
+                         StanzaPath('iq@type=result/command'),
+                         self._handle_command_result))
+
+        self.xmpp.register_handler(
+                Callback("Ad-Hoc Error",
+                         StanzaPath('iq@type=error/command'),
+                         self._handle_command_result))
+
+        register_stanza_plugin(Iq, stanza.Command)
+
+        self.xmpp.add_event_handler('command_execute',
+                                    self._handle_command_start,
+                                    threaded=self.threaded)
+        self.xmpp.add_event_handler('command_next',
+                                    self._handle_command_next,
+                                    threaded=self.threaded)
+        self.xmpp.add_event_handler('command_cancel',
+                                    self._handle_command_cancel,
+                                    threaded=self.threaded)
+        self.xmpp.add_event_handler('command_complete',
+                                    self._handle_command_complete,
+                                    threaded=self.threaded)
+
+    def post_init(self):
+        """Handle cross-plugin interactions."""
+        base_plugin.post_init(self)
+        self.xmpp['xep_0030'].add_feature(Command.namespace)
+
+    def set_backend(self, db):
+        """
+        Replace the default session storage dictionary with
+        a generic, external data storage mechanism.
+
+        The replacement backend must be able to interact through
+        the same syntax and interfaces as a normal dictionary.
+
+        Arguments:
+            db -- The new session storage mechanism.
+        """
+        self.sessions = db
+
+    def prep_handlers(self, handlers, **kwargs):
+        """
+        Prepare a list of functions for use by the backend service.
+
+        Intended to be replaced by the backend service as needed.
+
+        Arguments:
+            handlers -- A list of function pointers
+            **kwargs -- Any additional parameters required by the backend.
+        """
+        pass
+
+    # =================================================================
+    # Server side (command provider) API
+
+    def add_command(self, jid=None, node=None, name='', handler=None):
+        """
+        Make a new command available to external entities.
+
+        Access control may be implemented in the provided handler.
+
+        Command workflow is done across a sequence of command handlers. The
+        first handler is given the intial Iq stanza of the request in order
+        to support access control. Subsequent handlers are given only the
+        payload items of the command. All handlers will receive the command's
+        session data.
+
+        Arguments:
+            jid     -- The JID that will expose the command.
+            node    -- The node associated with the command.
+            name    -- A human readable name for the command.
+            handler -- A function that will generate the response to the
+                       initial command request, as well as enforcing any
+                       access control policies.
+        """
+        if jid is None:
+            jid = self.xmpp.boundjid
+        elif isinstance(jid, str):
+            jid = JID(jid)
+        item_jid = jid.full
+
+        # Client disco uses only the bare JID
+        if self.xmpp.is_component:
+            jid = jid.full
+        else:
+            jid = jid.bare
+
+        self.xmpp['xep_0030'].add_identity(category='automation',
+                                           itype='command-list',
+                                           name='Ad-Hoc commands',
+                                           node=Command.namespace,
+                                           jid=jid)
+        self.xmpp['xep_0030'].add_item(jid=item_jid,
+                                       name=name,
+                                       node=Command.namespace,
+                                       subnode=node,
+                                       ijid=jid)
+        self.xmpp['xep_0030'].add_identity(category='automation',
+                                           itype='command-node',
+                                           name=name,
+                                           node=node,
+                                           jid=jid)
+        self.xmpp['xep_0030'].add_feature(Command.namespace, None, jid)
+
+        self.commands[(item_jid, node)] = (name, handler)
+
+    def new_session(self):
+        """Return a new session ID."""
+        return str(time.time()) + '-' + self.xmpp.new_id()
+
+    def _handle_command(self, iq):
+        """Raise command events based on the command action."""
+        self.xmpp.event('command_%s' % iq['command']['action'], iq)
+
+    def _handle_command_start(self, iq):
+        """
+        Process an initial request to execute a command.
+
+        Arguments:
+            iq -- The command execution request.
+        """
+        sessionid = self.new_session()
+        node = iq['command']['node']
+        key = (iq['to'].full, node)
+        name, handler = self.commands.get(key, ('Not found', None))
+        if not handler:
+            log.debug('Command not found: %s, %s' % (key, self.commands))
+
+        initial_session = {'id': sessionid,
+                           'from': iq['from'],
+                           'to': iq['to'],
+                           'node': node,
+                           'payload': None,
+                           'interfaces': '',
+                           'payload_classes': None,
+                           'notes': None,
+                           'has_next': False,
+                           'allow_complete': False,
+                           'allow_prev': False,
+                           'past': [],
+                           'next': None,
+                           'prev': None,
+                           'cancel': None}
+
+        session = handler(iq, initial_session)
+
+        self._process_command_response(iq, session)
+
+    def _handle_command_next(self, iq):
+        """
+        Process a request for the next step in the workflow
+        for a command with multiple steps.
+
+        Arguments:
+            iq -- The command continuation request.
+        """
+        sessionid = iq['command']['sessionid']
+        session = self.sessions[sessionid]
+
+        handler = session['next']
+        interfaces = session['interfaces']
+        results = []
+        for stanza in iq['command']['substanzas']:
+            if stanza.plugin_attrib in interfaces:
+                results.append(stanza)
+        if len(results) == 1:
+            results = results[0]
+
+        session = handler(results, session)
+
+        self._process_command_response(iq, session)
+
+    def _process_command_response(self, iq, session):
+        """
+        Generate a command reply stanza based on the
+        provided session data.
+
+        Arguments:
+            iq      -- The command request stanza.
+            session -- A dictionary of relevant session data.
+        """
+        sessionid = session['id']
+
+        payload = session['payload']
+        if not isinstance(payload, list):
+            payload = [payload]
+
+        session['interfaces'] = [item.plugin_attrib for item in payload]
+        session['payload_classes'] = [item.__class__ for item in payload]
+
+        self.sessions[sessionid] = session
+
+        for item in payload:
+            register_stanza_plugin(Command, item.__class__, iterable=True)
+
+        iq.reply()
+        iq['command']['node'] = session['node']
+        iq['command']['sessionid'] = session['id']
+
+        if session['next'] is None:
+            iq['command']['actions'] = []
+            iq['command']['status'] = 'completed'
+        elif session['has_next']:
+            actions = ['next']
+            if session['allow_complete']:
+                actions.append('complete')
+            if session['allow_prev']:
+                actions.append('prev')
+            iq['command']['actions'] = actions
+            iq['command']['status'] = 'executing'
+        else:
+            iq['command']['actions'] = ['complete']
+            iq['command']['status'] = 'executing'
+
+        iq['command']['notes'] = session['notes']
+
+        for item in payload:
+            iq['command'].append(item)
+
+        iq.send()
+
+    def _handle_command_cancel(self, iq):
+        """
+        Process a request to cancel a command's execution.
+
+        Arguments:
+            iq -- The command cancellation request.
+        """
+        node = iq['command']['node']
+        sessionid = iq['command']['sessionid']
+        session = self.sessions[sessionid]
+        handler = session['cancel']
+
+        if handler:
+            handler(iq, session)
+
+        try:
+            del self.sessions[sessionid]
+        except:
+            pass
+
+        iq.reply()
+        iq['command']['node'] = node
+        iq['command']['sessionid'] = sessionid
+        iq['command']['status'] = 'canceled'
+        iq['command']['notes'] = session['notes']
+        iq.send()
+
+    def _handle_command_complete(self, iq):
+        """
+        Process a request to finish the execution of command
+        and terminate the workflow.
+
+        All data related to the command session will be removed.
+
+        Arguments:
+            iq -- The command completion request.
+        """
+        node = iq['command']['node']
+        sessionid = iq['command']['sessionid']
+        session = self.sessions[sessionid]
+        handler = session['next']
+        interfaces = session['interfaces']
+        results = []
+        for stanza in iq['command']['substanzas']:
+            if stanza.plugin_attrib in interfaces:
+                results.append(stanza)
+        if len(results) == 1:
+            results = results[0]
+
+        if handler:
+            handler(results, session)
+
+        iq.reply()
+        iq['command']['node'] = node
+        iq['command']['sessionid'] = sessionid
+        iq['command']['actions'] = []
+        iq['command']['status'] = 'completed'
+        iq['command']['notes'] = session['notes']
+        iq.send()
+
+        del self.sessions[sessionid]
+
+
+    # =================================================================
+    # Client side (command user) API
+
+    def get_commands(self, jid, **kwargs):
+        """
+        Return a list of commands provided by a given JID.
+
+        Arguments:
+            jid      -- The JID to query for commands.
+            local    -- If true, then the query is for a JID/node
+                        combination handled by this Sleek instance and
+                        no stanzas need to be sent.
+                        Otherwise, a disco stanza must be sent to the
+                        remove JID to retrieve the items.
+            ifrom    -- Specifiy the sender's JID.
+            block    -- If true, block and wait for the stanzas' reply.
+            timeout  -- The time in seconds to block while waiting for
+                        a reply. If None, then wait indefinitely.
+            callback -- Optional callback to execute when a reply is
+                        received instead of blocking and waiting for
+                        the reply.
+            iterator -- If True, return a result set iterator using
+                        the XEP-0059 plugin, if the plugin is loaded.
+                        Otherwise the parameter is ignored.
+        """
+        return self.xmpp['xep_0030'].get_items(jid=jid,
+                                               node=Command.namespace,
+                                               **kwargs)
+
+    def send_command(self, jid, node, ifrom=None, action='execute',
+                    payload=None, sessionid=None, **kwargs):
+        """
+        Create and send a command stanza, without using the provided
+        workflow management APIs.
+
+        Arguments:
+            jid       -- The JID to send the command request or result.
+            node      -- The node for the command.
+            ifrom     -- Specify the sender's JID.
+            action    -- May be one of: execute, cancel, complete,
+                         or cancel.
+            payload   -- Either a list of payload items, or a single
+                         payload item such as a data form.
+            sessionid -- The current session's ID value.
+            block     -- Specify if the send call will block until a
+                         response is received, or a timeout occurs.
+                         Defaults to True.
+            timeout   -- The length of time (in seconds) to wait for a
+                         response before exiting the send call
+                         if blocking is used. Defaults to
+                         sleekxmpp.xmlstream.RESPONSE_TIMEOUT
+            callback  -- Optional reference to a stream handler
+                         function. Will be executed when a reply
+                         stanza is received.
+        """
+        iq = self.xmpp.Iq()
+        iq['type'] = 'set'
+        iq['to'] = jid
+        if ifrom:
+            iq['from'] = ifrom
+        iq['command']['node'] = node
+        iq['command']['action'] = action
+        if sessionid is not None:
+            iq['command']['sessionid'] = sessionid
+        if payload is not None:
+            if not isinstance(payload, list):
+                payload = [payload]
+            for item in payload:
+                iq['command'].append(item)
+        return iq.send(**kwargs)
+
+    def start_command(self, jid, node, session, ifrom=None):
+        """
+        Initiate executing a command provided by a remote agent.
+
+        The workflow provided is always non-blocking.
+
+        The provided session dictionary should contain:
+            next  -- A handler for processing the command result.
+            error -- A handler for processing any error stanzas
+                     generated by the request.
+
+        Arguments:
+            jid     -- The JID to send the command request.
+            node    -- The node for the desired command.
+            session -- A dictionary of relevant session data.
+            ifrom   -- Optionally specify the sender's JID.
+        """
+        session['jid'] = jid
+        session['node'] = node
+        session['timestamp'] = time.time()
+        session['payload'] = None
+        iq = self.xmpp.Iq()
+        iq['type'] = 'set'
+        iq['to'] = jid
+        if ifrom:
+            iq['from'] = ifrom
+            session['from'] = ifrom
+        iq['command']['node'] = node
+        iq['command']['action'] = 'execute'
+        sessionid = 'client:pending_' + iq['id']
+        session['id'] = sessionid
+        self.sessions[sessionid] = session
+        iq.send(block=False)
+
+    def continue_command(self, session):
+        """
+        Execute the next action of the command.
+
+        Arguments:
+            session -- All stored data relevant to the current
+                       command session.
+        """
+        sessionid = 'client:' + session['id']
+        self.sessions[sessionid] = session
+
+        self.send_command(session['jid'],
+                          session['node'],
+                          ifrom=session.get('from', None),
+                          action='next',
+                          payload=session.get('payload', None),
+                          sessionid=session['id'])
+
+    def cancel_command(self, session):
+        """
+        Cancel the execution of a command.
+
+        Arguments:
+            session -- All stored data relevant to the current
+                       command session.
+        """
+        sessionid = 'client:' + session['id']
+        self.sessions[sessionid] = session
+
+        self.send_command(session['jid'],
+                          session['node'],
+                          ifrom=session.get('from', None),
+                          action='cancel',
+                          payload=session.get('payload', None),
+                          sessionid=session['id'])
+
+    def complete_command(self, session):
+        """
+        Finish the execution of a command workflow.
+
+        Arguments:
+            session -- All stored data relevant to the current
+                       command session.
+        """
+        sessionid = 'client:' + session['id']
+        self.sessions[sessionid] = session
+
+        self.send_command(session['jid'],
+                          session['node'],
+                          ifrom=session.get('from', None),
+                          action='complete',
+                          payload=session.get('payload', None),
+                          sessionid=session['id'])
+
+    def terminate_command(self, session):
+        """
+        Delete a command's session after a command has completed
+        or an error has occured.
+
+        Arguments:
+            session -- All stored data relevant to the current
+                       command session.
+        """
+        try:
+            del self.sessions[session['id']]
+        except:
+            pass
+
+    def _handle_command_result(self, iq):
+        """
+        Process the results of a command request.
+
+        Will execute the 'next' handler stored in the session
+        data, or the 'error' handler depending on the Iq's type.
+
+        Arguments:
+            iq -- The command response.
+        """
+        sessionid = 'client:' + iq['command']['sessionid']
+        pending = False
+
+        if sessionid not in self.sessions:
+            pending = True
+            pendingid = 'client:pending_' + iq['id']
+            if pendingid not in self.sessions:
+                return
+            sessionid = pendingid
+
+        session = self.sessions[sessionid]
+        sessionid = 'client:' + iq['command']['sessionid']
+        session['id'] = iq['command']['sessionid']
+
+        self.sessions[sessionid] = session
+
+        if pending:
+            del self.sessions[pendingid]
+
+        handler_type = 'next'
+        if iq['type'] == 'error':
+            handler_type = 'error'
+        handler = session.get(handler_type, None)
+        if handler:
+            handler(iq, session)
+        elif iq['type'] == 'error':
+            self.terminate_command(session)
+
+        if iq['command']['status']  == 'completed':
+            self.terminate_command(session)
diff --git a/sleekxmpp/plugins/xep_0050/stanza.py b/sleekxmpp/plugins/xep_0050/stanza.py
new file mode 100644
index 00000000..31a4a5d5
--- /dev/null
+++ b/sleekxmpp/plugins/xep_0050/stanza.py
@@ -0,0 +1,185 @@
+"""
+    SleekXMPP: The Sleek XMPP Library
+    Copyright (C) 2011 Nathanael C. Fritz, Lance J.T. Stout
+    This file is part of SleekXMPP.
+
+    See the file LICENSE for copying permission.
+"""
+
+from sleekxmpp.xmlstream import ElementBase, ET
+
+
+class Command(ElementBase):
+
+    """
+    XMPP's Adhoc Commands provides a generic workflow mechanism for
+    interacting with applications. The result is similar to menu selections
+    and multi-step dialogs in normal desktop applications. Clients do not
+    need to know in advance what commands are provided by any particular
+    application or agent. While adhoc commands provide similar functionality
+    to Jabber-RPC, adhoc commands are used primarily for human interaction.
+
+    Also see <http://xmpp.org/extensions/xep-0050.html>
+
+    Example command stanzas:
+      <iq type="set">
+        <command xmlns="http://jabber.org/protocol/commands"
+                 node="run_foo"
+                 action="execute" />
+      </iq>
+
+      <iq type="result">
+        <command xmlns="http://jabber.org/protocol/commands"
+                 node="run_foo"
+                 sessionid="12345"
+                 status="executing">
+          <actions>
+            <complete />
+          </actions>
+          <note type="info">Information!</note>
+          <x xmlns="jabber:x:data">
+            <field var="greeting"
+                   type="text-single"
+                   label="Greeting" />
+          </x>
+        </command>
+      </iq>
+
+    Stanza Interface:
+        action    -- The action to perform.
+        actions   -- The set of allowable next actions.
+        node      -- The node associated with the command.
+        notes     -- A list of tuples for informative notes.
+        sessionid -- A unique identifier for a command session.
+        status    -- May be one of: canceled, completed, or executing.
+
+    Attributes:
+        actions      -- A set of allowed action values.
+        statuses     -- A set of allowed status values.
+        next_actions -- A set of allowed next action names.
+
+    Methods:
+        get_action  -- Return the requested action.
+        get_actions -- Return the allowable next actions.
+        set_actions -- Set the allowable next actions.
+        del_actions -- Remove the current set of next actions.
+        get_notes   -- Return a list of informative note data.
+        set_notes   -- Set informative notes.
+        del_notes   -- Remove any note data.
+        add_note    -- Add a single note.
+    """
+
+    name = 'command'
+    namespace = 'http://jabber.org/protocol/commands'
+    plugin_attrib = 'command'
+    interfaces = set(('action', 'sessionid', 'node',
+                      'status', 'actions', 'notes'))
+    actions = set(('cancel', 'complete', 'execute', 'next', 'prev'))
+    statuses = set(('canceled', 'completed', 'executing'))
+    next_actions = set(('prev', 'next', 'complete'))
+
+    def get_action(self):
+        """
+        Return the value of the action attribute.
+
+        If the Iq stanza's type is "set" then use a default
+        value of "execute".
+        """
+        if self.parent()['type'] == 'set':
+            return self._get_attr('action', default='execute')
+        return self._get_attr('action')
+
+    def set_actions(self, values):
+        """
+        Assign the set of allowable next actions.
+
+        Arguments:
+            values -- A list containing any combination of:
+                        'prev', 'next', and 'complete'
+        """
+        self.del_actions()
+        if values:
+            self._set_sub_text('{%s}actions' % self.namespace, '', True)
+            actions = self.find('{%s}actions' % self.namespace)
+            for val in values:
+                if val in self.next_actions:
+                    action = ET.Element('{%s}%s' % (self.namespace, val))
+                    actions.append(action)
+
+    def get_actions(self):
+        """
+        Return the set of allowable next actions.
+        """
+        actions = []
+        actions_xml = self.find('{%s}actions' % self.namespace)
+        if actions_xml is not None:
+            for action in self.next_actions:
+                action_xml = actions_xml.find('{%s}%s' % (self.namespace,
+                                                          action))
+                if action_xml is not None:
+                    actions.append(action)
+        return actions
+
+    def del_actions(self):
+        """
+        Remove all allowable next actions.
+        """
+        self._del_sub('{%s}actions' % self.namespace)
+
+    def get_notes(self):
+        """
+        Return a list of note information.
+
+        Example:
+            [('info', 'Some informative data'),
+             ('warning', 'Use caution'),
+             ('error', 'The command ran, but had errors')]
+        """
+        notes = []
+        notes_xml = self.findall('{%s}note' % self.namespace)
+        for note in notes_xml:
+            notes.append((note.attrib.get('type', 'info'),
+                          note.text))
+        return notes
+
+    def set_notes(self, notes):
+        """
+        Add multiple notes to the command result.
+
+        Each note is a tuple, with the first item being one of:
+        'info', 'warning', or 'error', and the second item being
+        any human readable message.
+
+        Example:
+            [('info', 'Some informative data'),
+             ('warning', 'Use caution'),
+             ('error', 'The command ran, but had errors')]
+
+
+        Arguments:
+            notes -- A list of tuples of note information.
+        """
+        self.del_notes()
+        for note in notes:
+            self.add_note(note[1], note[0])
+
+    def del_notes(self):
+        """
+        Remove all notes associated with the command result.
+        """
+        notes_xml = self.findall('{%s}note' % self.namespace)
+        for note in notes_xml:
+            self.xml.remove(note)
+
+    def add_note(self, msg='', ntype='info'):
+        """
+        Add a single note annotation to the command.
+
+        Arguments:
+            msg   -- A human readable message.
+            ntype -- One of: 'info', 'warning', 'error'
+        """
+        xml = ET.Element('{%s}note' % self.namespace)
+        xml.attrib['type'] = ntype
+        xml.text = msg
+        self.xml.append(xml)