status-bot/modules/ffpb.py

# -*- coding: utf-8 -*-
from __future__ import print_function
import willie

from datetime import datetime, timedelta
import difflib
from email.utils import mktime_tz
from fnmatch import fnmatch
import git
import netaddr
import json
import urllib2
import re
import os
import random
import shelve
import subprocess
import sys
import time

import dns.resolver, dns.reversename
import SocketServer
import threading

# ensure our directory is on path (in order to load batcave module)
__my_dir = os.path.dirname(__file__)
if __my_dir not in sys.path:
    sys.path.append(__my_dir)

from batcave import BatcaveClient

msgserver = None
peers_repo = None

nodeaccess = None

__batcave = None

ffpb_resolver = dns.resolver.Resolver()
ffpb_resolver.nameservers = ['10.132.254.53']


class MsgHandler(SocketServer.BaseRequestHandler):
    """Reads line from TCP stream and forwards it to configured IRC channels."""

    def handle(self):
        data = self.request.recv(2048).strip()
        sender = self.resolve_name(self.client_address[0])

        bot = self.server.bot
        if bot is None:
            print("ERROR: No bot in handle() :-(")
            return

        target = bot.config.core.owner
        if bot.config.has_section('ffpb'):
            is_public = data.lstrip().lower().startswith("public:")

            if is_public and not bot.config.ffpb.msg_target_public is None:
                data = data[7:].lstrip()
                target = bot.config.ffpb.msg_target_public
            elif not bot.config.ffpb.msg_target is None:
                target = bot.config.ffpb.msg_target

        bot.msg(target, "[{0}] {1}".format(sender, str(data)))

    def resolve_name(self, ipaddr):
        """
        Resolves the host name of the given IP address
        and strips away the suffix (.infra)?.ffpb
        """

        if ipaddr.startswith("127."):
            return "localhost"

        try:
            addr = dns.reversename.from_address(ipaddr)
            return re.sub("(.infra)?.ffpb.", "", str(ffpb_resolver.query(addr, "PTR")[0]))
        except dns.resolver.NXDOMAIN:
            return ipaddr


class ThreadingTCPServer(SocketServer.ThreadingMixIn, SocketServer.TCPServer):
    """Defines a threaded TCP socket server."""
    bot = None


def setup(bot):
    """Called by willie upon loading this plugin."""

    global __batcave, msgserver, peers_repo, nodeaccess

    # signal begin of setup routine
    bot.memory['ffpb_in_setup'] = True

    # load list of seen nodes from disk
    seen_nodes = shelve.open('nodes.seen', writeback=True)
    bot.memory['seen_nodes'] = seen_nodes

    # load list of node ACL from disk (used in playitsafe())
    nodeaccess = shelve.open('nodes.acl', writeback=True)

    # no need to configure anything else if the ffpb config section is missing
    if not bot.config.has_section('ffpb'):
        bot.memory['ffpb_in_setup'] = False
        return

    # open the git repository containing the peers files
    if not bot.config.ffpb.peers_directory is None:
        peers_repo = git.Repo(bot.config.ffpb.peers_directory)
        assert peers_repo.bare is False

    # if configured, start the messaging server
    if int(bot.config.ffpb.msg_enable) == 1:
        host = "localhost"
        port = 2342
        if not bot.config.ffpb.msg_host is None:
            host = bot.config.ffpb.msg_host
        if not bot.config.ffpb.msg_port is None:
            port = int(bot.config.ffpb.msg_port)

        msgserver = ThreadingTCPServer((host, port), MsgHandler)
        msgserver.bot = bot
        ipaddr, port = msgserver.server_address
        print("Messaging server listening on {}:{}".format(ipaddr, port))

        msgserver_thread = threading.Thread(target=msgserver.serve_forever)
        msgserver_thread.daemon = True
        msgserver_thread.start()

    # initialize BATCAVE
    __batcave = BatcaveClient(bot.config.ffpb.batcave_url)

    # signal end of setup routine
    bot.memory['ffpb_in_setup'] = False


def shutdown(bot):
    global msgserver, nodeaccess

    # store node acl
    if not nodeaccess is None:
        nodeaccess.sync()
        nodeaccess.close()
        nodeaccess = None

    # store seen nodes
    if 'seen_nodes' in bot.memory and bot.memory['seen_nodes'] != None:
        bot.memory['seen_nodes'].close()
        bot.memory['seen_nodes'] = None
        del bot.memory['seen_nodes']

    # shutdown messaging server
    if not msgserver is None:
        msgserver.shutdown()
        print("Closed messaging server.")
        msgserver = None


@willie.module.commands("help")
@willie.module.commands("hilfe")
@willie.module.commands("man")
def ffpb_help(bot, trigger):
    """Display commony ulsed functions."""

    functions = {
        "!ping <knoten>": "Prüfe ob der Knoten erreichbar ist.",
        "!status": "Aktuellen Status des Netzwerks (insb. Anzahl Knoten und Clients) ausgegeben.",
        "!highscore": "Höchstwerte von Anzahl Knoten und Clients",
        "!info <knoten>": "Allgemeine Information zu dem Knoten anzeigen.",
        "!link <knoten>": "MAC-Adresse und Link zur Status-Seite des Knotens anzeigen.",
        "!mesh <knoten>": "Zeige Mesh-Partner eines Knotens",
        "!lastseen <knoten>": "Zeitpunkt an dem der Knoten zuletzt gesehen wurde",
    }

    param = trigger.group(2)
    if param is None:
        bot.say("Funktionen: " + str.join(", ", sorted(functions.keys())))
        return

    if param.startswith("!"):
        param = param[1:]

    for fun in functions.keys():
        if fun.startswith("!" + param + " "):
            bot.say("Hilfe zu '" + fun + "': " + functions[fun])
            return

    bot.say("Allgemeine Hilfe gibt's mit !help - ohne Parameter.")


def playitsafe(bot, trigger,
               botadmin=False, admin_channel=False,
               via_channel=False, via_privmsg=False, need_op=False,
               node=None, reply_directly=True,
               debug_user=None, debug_ignorebotadmin=False):
    """
    helper: checks that the triggering user has the necessary rights

    Returns true if everything is okay.
    If it's not, a reply is send via the bot and false is returned.
    """

    if via_channel and via_privmsg:
        raise Exception('Der Entwickler ist ein dummer, dummer Junge. ' +
                        '(playitsafe: via_channel && via_privmsg).')

    user = trigger.nick if debug_user is None else debug_user
    user = user.lower()

    # botadmin: you need to be configured as a bot admin
    if botadmin and not trigger.admin:
        if reply_directly:
            bot.say('Du brauchst Super-Kuh-Kräfte um dieses Kommando auszuführen.')
        return False

    # via_channel: the request must not be a private conversation
    if via_channel and trigger.is_privmsg:
        if reply_directly:
            bot.say('Bitte per Channel - mehr Transparenz wagen und so!')
        return False

    # via_privmsg: the request must be a private conversation
    if via_privmsg and not trigger.is_privmsg:
        if reply_directly:
            bot.say('Solche Informationen gibt es nur per PM, ' +
                    'da bin ich ja schon ein klein wenig sensibel ...')
        return False

    # need_op: if the message is in a channel, check that the user has OP there
    if need_op and (not trigger.is_privmsg) and \
       (not user in bot.ops[trigger.sender]):
        if reply_directly:
            bot.say('Keine Zimtschnecke, keine Kekse.')
        return False

    # node: check that the user is whitelisted (or is admin)
    if not node is None and (debug_ignorebotadmin or not trigger.admin):
        acluser = [x for x in nodeaccess if x.lower() == user]
        acluser = acluser[0] if len(acluser) == 1 else None
        if nodeaccess is None or acluser is None:
            if reply_directly:
                bot.reply('You! Shall! Not! Access!')
            return False

        nodeid = node['node_id'] if 'node_id' in node else None
        matched = False
        for x in nodeaccess[acluser]:
            if x == nodeid or fnmatch(node['hostname'], x):
                matched = True
                break

        if not matched:
            if reply_directly:
                bot.reply('Mach das doch bitte auf deinen Knoten, kthxbye.')
            return False

    return True


@willie.module.commands('nodeacl')
def ffpb_nodeacl(bot, trigger):
    """Configure ACL for nodes."""

    if not playitsafe(bot, trigger, botadmin=True):
        # the check function already gives a bot reply, just exit here
        return

    # ensure the user gave arguments
    if trigger.group(2) is None or len(trigger.group(2)) == 0:
        bot.say('Sag doch was du willst ... einmal mit Profis arbeiten, ey -.-')
        return

    # read additional arguments
    cmd = trigger.group(3).lower()

    if cmd == 'list':
        user = trigger.group(4)
        if user is None:
            usernames = [x for x in nodeaccess]
            bot.say('ACLs gesetzt für die User: ' + ', '.join(usernames))
            return

        user = user.lower()
        uid = [x for x in nodeaccess if x.lower() == user]
        if len(uid) == 0:
            bot.say('Für \'{0}\' ist keine Node ACL gesetzt.'.format(user))
            return

        bot.say('Node ACL für \'{0}\' = \'{1}\''.format(
            uid[0],
            '\', \''.join(nodeaccess[uid[0]]))
        )
        return

    if cmd in ['add', 'del', 'check']:
        user = trigger.group(4)
        value = trigger.group(5)

        if user is None or value is None:
            bot.say('Du bist eine Pappnase - User und Knoten, bitte.')
            return

        user = str(user)
        print('NodeACL ' + cmd + ' \'' + value + '\' for user \'' + user + '\'')
        uid = [x for x in nodeaccess if x == user or x.lower() == user]
        if cmd == 'add':
            uid = uid[0] if len(uid) > 0 else user
            if not uid in nodeaccess:
                nodeaccess[uid] = []
            if not value in nodeaccess[uid]:
                nodeaccess[uid].append(value)
                bot.say("201 nodeACL '{0}' +'{1}'".format(uid, value))
            else:
                bot.say("304 nodeACL '{0}' contains '{1}'".format(uid, value))

        elif cmd == 'del':
            if len(uid) == 0:
                bot.say("404 nodeACL '{0}'".format(uid))
                return
            if value in nodeaccess[uid]:
                nodeaccess[uid].remove(value)
                bot.say("200 nodeACL '{0}' -'{1}'".format(uid, value))
            else:
                bot.say("404 nodeACL '{0}' has no '{1}'".format(uid, value))

        elif cmd == 'check':
            if len(uid) == 0:
                bot.say('Nope, keine ACL gesetzt.')
                return

            node = ffpb_findnode(value)
            if node is None:
                bot.say('Nope, kein Plan was für ein Knoten das ist.')
                return

            result = playitsafe(bot, trigger,
                                debug_user=uid[0], debug_ignorebotadmin=True,
                                node=node, reply_directly=False)
            if result is True:
                bot.say('Jupp.')
            elif result is False:
                bot.say('Nope.')
            else:
                bot.say('Huh? result=' + str(result))

        return

    bot.say('Unbekanntes Kommando. Probier ' +
            '"list [user]", "add user value" oder "del user value". ' +
            'Value kann node_id oder hostname-Maske sein.')


def ffpb_ensurenodeid(nodedata):
    """Makes sure that the given dict has a 'node_id' field."""

    if 'node_id' in nodedata:
        return nodedata

    # derive node's id
    nodeid = None
    if 'network' in nodedata and 'mac' in nodedata['network']:
        nodeid = nodedata['network']['mac'].replace(':', '')

    # assemble extended data
    result = {'node_id': nodeid}
    for key in nodedata:
        result[key] = nodedata[key]

    return result


def ffpb_findnode(name, allow_fuzzymatching=True):
    """helper: try to identify the node the user meant by the given name"""

    # no name, no node
    if name is None or len(name) == 0:
        return None

    name = str(name).strip()

    # disable fuzzy matching if name is enclosed in quotes
    if name.startswith('\'') and name.endswith('\'') or \
       name.startswith('"') and name.endswith('"'):
        name = name[1:-1]
        allow_fuzzymatching = False

    # try to match MAC
    m = re.search("^([0-9a-fA-F][0-9a-fA-F]:){5}[0-9a-fA-F][0-9a-fA-F]$", name)
    if not m is None:
        mac = m.group(0).lower()
        node = __batcave.find_node_by_mac(mac)

        if node is not None:
            return node

        else:
            nodeid = mac.replace(':', '').lower()
            return {
                'node_id': nodeid,
                'hostname': '?-' + nodeid,
                'network': {
                    'addresses': [mac2ipv6(mac, 'fdca:ffee:ff12:132:')],
                    'mac': mac,
                },
                'hardware': {
                    'model': 'derived-from-mac',
                },
            }

    # try to find by NAME
    node = __batcave.find_node_by_name(name, fuzzymatch=allow_fuzzymatching)
    if node is not None:
        return __batcave.get_node(node['id'])

    # not found in ALFRED data -> try peers_repo
    if not peers_repo is None:
        peer_name = None
        peer_mac = None
        peer_file = None

        for b in peers_repo.heads.master.commit.tree.blobs:
            if b.name.lower() == name.lower():
                peer_name = b.name
                peer_file = b.abspath
                break

        if (not peer_file is None) and os.path.exists(peer_file):
            peerfile = open(peer_file, "r")
            for line in peerfile:
                if line.startswith("# MAC:"):
                    peer_mac = line[6:].strip()
            peerfile.close()

        if not peer_mac is None:
            return {
                'node_id': peer_mac.replace(':', ''),
                'hostname': peer_name,
                'network': {
                    'addresses': [mac2ipv6(peer_mac, 'fdca:ffee:ff12:132:'), ],
                    'mac': peer_mac,
                },
                'hardware': {
                    'model': 'derived-from-vpnkeys',
                },
            }

    # none of the above was able to identify the requested node
    return None


def ffpb_findnode_from_botparam(bot, name, ensure_recent_alfreddata=True):
    """helper: call ffpb_findnode() and give common answers via bot on error"""

    if name is None or len(name) == 0:
        if not bot is None:
            bot.reply("Grün.")
        return None

    node = ffpb_findnode(name)
    if node is None:
        if not bot is None:
            bot.say("Kein Plan wer oder was mit '" + name + "' gemeint ist :(")

    return node


def mac2ipv6(mac, prefix=None):
    """Calculate IPv6 address from given MAC,
    optionally replacing the fe80:: prefix with a given one."""

    result = str(netaddr.EUI(mac).ipv6_link_local())
    if (not prefix is None) and (result.startswith("fe80::")):
        result = prefix + result[6:]
    return result


def ffpb_notify_newly_seen_nodes(bot, new):
    if not isinstance(bot, dict):
        return
    if len(new) == 0 or bot.memory['ffpb_in_setup']:
        return

    action_msg = None
    if len(new) == 1:
        action_msg = random.choice((
            'bemerkt den neuen Knoten {0}',
            'entdeckt {0}',
            'reibt sich die Augen und erblickt einen verpackungsfrischen Knoten {0}',
            u'heißt {0} im Mesh willkommen',
            'freut sich, dass {0} aufgetaucht ist',
            'traut seinen Augen kaum. {0} sagt zum ersten Mal: Hallo Freifunk Paderborn',
            u'sieht die ersten Herzschläge von {0}',
            u'stellt einen großen Pott Heißgetränk zu {0} und fragt ob es hier Meshpartner gibt.',
        )).format('\'' + str(new[0][1]) + '\'')

        # try to fetch location from BATCAVE in order to add a geomap URL
        location = __batcave.get_nodefield(str.replace(new[0][0], ':', ''), 'location')
        if not location is None:
            action_msg += ' http://map.paderborn.freifunk.net/geomap.html?lat=' + location['latitude'] + '&lon=' + location['longitude']
    else:
        action_msg = random.choice((
            'bemerkt die neuen Knoten {0} und {1}',
            'hat {0} und {1} entdeckt',
            'bewundert {0} sowie {1}',
            'freut sich, dass {0} und {1} nun auch online sind',
            u'heißt {0} und {1} im Mesh willkommen',
            'fragt sich ob die noch jungen Herzen von {0} und {1} synchron schlagen',
        ))
        all_but_last = [str(x[1]) for x in new[0:-1]]
        last = str(new[-1][1])
        action_msg = action_msg.format(
            '\'' + '\', \''.join(all_but_last) + '\'',
            '\'' + last + '\''
        )
    action_target = bot.config.ffpb.msg_target
    if not bot.config.ffpb.msg_target_public is None:
        action_target = bot.config.ffpb.msg_target_public
    bot.msg(action_target, '\x01ACTION %s\x01' % action_msg)


@willie.module.interval(60)
def ffpb_updatepeers(bot):
    """Refresh list of peers and message the diff."""

    if peers_repo is None:
        print('WARNING: peers_repo is None')
        return

    old_head = peers_repo.head.commit
    peers_repo.remotes.origin.pull()
    new_head = peers_repo.head.commit

    if new_head != old_head:
        print('git pull: from ' + str(old_head) + ' to ' + str(new_head))

        added = []
        changed = []
        renamed = []
        deleted = []
        for f in old_head.diff(new_head):
            if f.new_file:
                added.append(f.b_blob.name)

            elif f.deleted_file:
                deleted.append(f.a_blob.name)

            elif f.renamed:
                renamed.append([f.rename_from, f.rename_to])

            else:
                changed.append(f.a_blob.name)

        response = "Knoten-Update (VPN +{0} %{1} -{2}): ".format(
                   len(added), len(renamed)+len(changed), len(deleted))
        for f in added:
            response += " +'{}'".format(f)
        for f in changed:
            response += " %'{}'".format(f)
        for f in renamed:
            response += " '{}'->'{}'".format(f[0], f[1])
        for f in deleted:
            response += " -'{}'".format(f)

        bot.msg(bot.config.ffpb.msg_target, response)


def ffpb_fetch_stats(bot, url, memoryid):
    """Fetch a ffmap-style nodes.json from the given URL and
    store it in the bot's memory."""

    response = urllib2.urlopen(url)

    data = json.load(response)
    nodes_active = 0
    nodes_total = 0
    clients_count = 0

    for node in data['nodes']:
        if node['flags']['gateway'] or node['flags']['client']:
            continue

        nodes_total += 1
        if node['flags']['online']:
            nodes_active += 1

        if 'legacy' in node['flags'] and node['flags']['legacy']:
            clients_count -= 1

    for link in data['links']:
        if link['type'] == 'client':
            clients_count += 1

    if not memoryid in bot.memory:
        bot.memory[memoryid] = {}
    stats = bot.memory[memoryid]
    stats["fetchtime"] = time.time()
    stats["nodes_active"] = nodes_active
    stats["nodes_total"] = nodes_total
    stats["clients"] = clients_count

    return (nodes_active, nodes_total, clients_count)


def pretty_date(timestamp=False):
    """
    Get a datetime object or a int() Epoch timestamp and return a
    pretty string like 'an hour ago', 'Yesterday', '3 months ago',
    'just now', etc
    """
    now = datetime.now()
    compare = None
    if type(timestamp) is int:
        compare = datetime.fromtimestamp(timestamp)
    elif type(timestamp) is float:
        compare = datetime.fromtimestamp(int(timestamp))
    elif isinstance(timestamp, datetime):
        compare = timestamp
    elif not timestamp:
        compare = now
    diff = now - compare
    second_diff = diff.seconds
    day_diff = diff.days

    if day_diff < 0:
        return ''

    if day_diff == 0:
        if second_diff < 10:
            return "gerade eben"
        if second_diff < 60:
            return "vor " + str(second_diff) + " Sekunden"
        if second_diff < 120:
            return "vor einer Minute"
        if second_diff < 3600:
            return "vor " + str(second_diff / 60) + " Minuten"
        if second_diff < 7200:
            return "vor einer Stunde"
        if second_diff < 86400:
            return "vor " + str(second_diff / 3600) + " Stunden"
    if day_diff == 1:
        return "gestern"
    if day_diff < 7:
        return "vor " + str(day_diff) + " Tagen"
    return "am " + compare.strftime('%d.%m.%Y um %H:%M Uhr')


@willie.module.commands('ping')
def ffpb_ping(bot, trigger=None, target_name=None, reply_directly=True):
    """Ping the given node"""

    # identify node or bail out
    if target_name is None:
        target_name = trigger.group(2)
    node = ffpb_findnode_from_botparam(bot, target_name,
                                       ensure_recent_alfreddata=False)
    if node is None:
        return None

    # derive node address from MAC
    node_mac = node.get('mac')
    target = mac2ipv6(node_mac, 'fdca:ffee:ff12:132:')
    target_alias = node["hostname"]

    # execute the actual ping and reply the result
    print("pinging '{0}' at {1} ...".format(target_name, target))
    result = os.system('ping6 -c 2 -W 1 ' + target + ' >/dev/null')

    if result == 0:
        print("ping to '{0}' succeeded".format(target_name))
        if reply_directly:
            bot.say('Knoten "' + target_alias + '" antwortet \\o/')
        return True

    elif result == 1 or result == 256:
        print("ping to '{0}' failed".format(target_name))
        if reply_directly:
            bot.say('Keine Antwort von "' + target_alias + '" :-(')
        return False

    else:
        print("ping to '{0}' broken: result='{1}'".format(target_name, result))
        if reply_directly:
            bot.say('Uh oh, irgendwas ist kaputt. Chef, ping result = ' + str(result) + ' - darf ich das essen?')
        return None


@willie.module.commands('mesh')
def ffpb_nodemesh(bot, trigger):
    """Display mesh partners of the given node."""

    # identify node or bail out
    target_name = trigger.group(2)
    node = ffpb_findnode_from_botparam(bot, target_name,
                                       ensure_recent_alfreddata=False)
    if node is None:
        return None

    # derive node's id
    nodeid = node['node_id'] if 'node_id' in node else None
    if nodeid is None:
        msg = 'Mist, ich habe gerade den Zettel verlegt auf dem die Node-ID' + \
              ' von \'{0}\' steht, bitte frag später noch einmal.'
        bot.say(msg.format(node.get('hostname', target_name)))
        return

    # query BATCAVE for node's neighbours (result is a list of MAC addresses)
    cave_result = node['neighbours']
    if cave_result is None:
        msg = 'Hm, scheinbar liegen zu \'{0}\' keine Daten vor. ' + \
              'Klingt komisch, ist aber so.'
        bot.say(msg.format(node.get('hostname', target_name)))
        return

    # query BATCAVE for neighbour's names
    data = '&'.join([str(n) for n in cave_result])
    req = urllib2.urlopen(bot.config.ffpb.batcave_url + 'idmac2name', data)

    # filter out duplicate names
    neighbours = set()
    gateways = set()
    for line in req:
        ident, name = line.strip().split('=')
    if ident == name and ident.startswith('c0:ff:ee:ba:be:'):
        gateways.add('Gateway ' + ident[len('c0:ff:ee:ba:be:'):])
    else:
        neighbours.add(name)
    neighbours = [x for x in neighbours]
    gateways = sorted([x for x in gateways])

    # respond to the user
    reply = node['hostname']
    if len(neighbours) == 0:
        reply += ' hat keinen Mesh-Partner'
    elif len(neighbours) == 1:
        reply += u' mesht mit \'{0}\''.format(neighbours[0])
    else:
        all_except_last = '\', \''.join(neighbours[:-1])
        last = neighbours[-1]
        reply += ' mesht mit \'{0}\' und \'{1}\''.format(all_except_last, last)

    if len(gateways) > 0:
        if len(neighbours) == 0:
            reply += ', aber hat eine Verbindung zu '
        else:
            reply += ' und hat zudem eine Verbindung zu '

        if len(gateways) == 1:
            reply += gateways[0]
        else:
            all_except_last = '\', \''.join(gateways[:-1])
            last = gateways[-1]
            reply += '{0} und {1}'.format(all_except_last, last)

    bot.say(reply)


@willie.module.commands('exec-on-peer')
def ffpb_remoteexec(bot, trigger):
    """Remote execution on the given node"""

    bot_params = trigger.group(2).split(' ', 1) if trigger.group(2) is not None else []
    if len(bot_params) != 2:
        bot.say('Wenn du nicht sagst wo mach ich remote execution bei dir!')
        bot.say('Tipp: !exec-on-peer <peer> <cmd>')
        return

    target_name = bot_params[0]
    target_cmd = bot_params[1]

    # identify requested node or bail out
    node = ffpb_findnode_from_botparam(bot, target_name,
                                       ensure_recent_alfreddata=False)
    if node is None:
        return

    # check ACL
    if not playitsafe(bot, trigger, via_channel=True, node=node):
        return

    # derive target from node's MAC
    node_mac = node.get('mac')
    target = mac2ipv6(node_mac, 'fdca:ffee:ff12:132:')
    target_alias = node["hostname"]

    # assemble SSH command
    cmd = [
        'ssh',
        '-6n',
        '-l', 'root',
        '-o', 'BatchMode=yes',
        '-o', 'StrictHostKeyChecking=no',
        target,
        target_cmd,
    ]
    print("REMOTE EXEC = " + str(cmd))
    try:
        # call SSH
        result = subprocess.check_output(
            cmd,
            stderr=subprocess.STDOUT,
            shell=False,
        )

        # fetch results and sent at most 8 of them as response
        lines = str(result).splitlines()

        if len(lines) == 0:
            bot.say('exec-on-peer(' + target_alias + '): No output')
            return

        msg = 'exec-on-peer({0}): {1} Zeilen'.format(target_alias, len(lines))
        if len(lines) > 8:
            msg += ' (zeige max. 8)'

        bot.say(msg + ':')

        for line in lines[0:8]:
            bot.say(line)

    except subprocess.CalledProcessError as err:
        bot.say('Fehler {0} bei exec-on-peer({1}): {2}'.format(
            err.returncode,
            target_alias,
            err.output
        ))