Add Tahoe-LAFS module

- Created basic plinth app which starts an introducer and a storage
  node on the FreedomBox.
- Prompt user to set a domain name before creating Tahoe-LAFS nodes.
- Support adding and removing of introducers to the storage node.
- Serve Tahoe-LAFS from a different port.
- Start all nodes and introducers at system startup.
- Add utility class YAMLFile with test cases.

.gitignore

@@ -24,3 +24,4 @@ plinth/tests/coverage/report/
 .idea/
 .DS_Store
 *.box
+.eggs

LICENSES

@@ -44,6 +44,7 @@ otherwise.
 - static/themes/default/img/network-wireless.svg :: [[http://tango.freedesktop.org/][Public Domain]]
 - static/themes/default/icons/deluge.png :: [[https://upload.wikimedia.org/wikipedia/commons/thumb/8/85//Deluge-Logo.svg/2000px-Deluge-Logo.svg.png][GPL]]
 - static/themes/default/icons/diaspora.png :: [[https://upload.wikimedia.org/wikipedia/commons/thumb/8/85//Deluge-Logo.svg/2000px-Deluge-Logo.svg.png][Publc Domain]]
+- static/themes/default/icons/ejabberd.png :: [[https://www.ejabberd.im/][GPL-2]]
 - static/themes/default/icons/infinoted.png :: [[https://github.com/gobby/gobby/blob/master/COPYING][ISC]]
 - static/themes/default/icons/ikiwiki.png :: [[https://ikiwiki.info/][GPL-2+]]
 - static/themes/default/icons/jsxc.png :: -
@@ -58,6 +59,6 @@ otherwise.
 - static/themes/default/icons/roundcube.png :: [[https://roundcube.net/][GPL-3+]]
 - static/themes/default/icons/shaarli.png :: [[https://github.com/shaarli/Shaarli][zlib/libpng]]
 - static/themes/default/icons/syncthing.png :: [[https://github.com/syncthing/syncthing/][Mozilla Public License Version 2.0]]
+- static/themes/default/icons/tahoe.png :: [[https://github.com/thekishanraval/Logos][GPLv3+]]
 - static/themes/default/icons/transmission.png :: [[https://transmissionbt.com/][GPL]]
 - static/themes/default/icons/ttrss.png :: [[https://tt-rss.org/gitlab/fox/tt-rss][GPL]]
-- static/themes/default/icons/ejabberd.png :: [[https://www.ejabberd.im/][GPL-2]]

actions/tahoe-lafs

@@ -0,0 +1,260 @@
+#!/usr/bin/python3
+# -*- mode: python -*-
+#
+# This file is part of Plinth.
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+"""
+Configuration helper for Tahoe-LAFS.
+"""
+
+import argparse
+import augeas
+import grp
+import json
+import pwd
+import shutil
+import subprocess
+
+import os
+import ruamel.yaml
+
+from plinth import action_utils
+from plinth.modules.tahoe import (
+    introducer_name,
+    introducers_file,
+    storage_node_name,
+    tahoe_home,
+    introducer_furl_file)
+from plinth.modules.tahoe.errors import TahoeConfigurationError
+from plinth.utils import YAMLFile
+
+
+domain_name_file = os.path.join(tahoe_home, 'domain_name')
+
+DEFAULT_FILE = '/etc/default/tahoe-lafs'
+
+
+def parse_arguments():
+    """Return parsed command line arguments as dictionary."""
+    parser = argparse.ArgumentParser()
+    subparsers = parser.add_subparsers(dest='subcommand', help='Sub command')
+
+    subparsers.add_parser('enable', help='Enable Tahoe-LAFS')
+    subparsers.add_parser('disable', help='Disable Tahoe-LAFS')
+    setup = subparsers.add_parser('setup',
+                                  help='Set domain name for Tahoe-LAFS')
+    setup.add_argument('--domain-name',
+                       help='The domain name to be used by Tahoe-LAFS')
+    subparsers.add_parser('create-introducer',
+                          help='Create and start the introducer node')
+    subparsers.add_parser('create-storage-node',
+                          help='Create and start the storage node')
+    subparsers.add_parser('autostart',
+                          help="Automatically start all introducers and "
+                               "storage nodes on system startup")
+    intro_parser_add = subparsers.add_parser(
+        'add-introducer', help="Add an introducer to the storage node's list "
+                               "of introducers.")
+    intro_parser_add.add_argument(
+        '--introducer', help="Add an introducer to the storage node's list "
+                             "of introducers Param introducer must be a tuple "
+                             "of (pet_name, furl)")
+    intro_parser_remove = subparsers.add_parser(
+        'remove-introducer', help="Rename the introducer entry in the "
+                                  "introducers.yaml file specified by the "
+                                  "param")
+    intro_parser_remove.add_argument(
+        '--pet-name', help='The domain name that will be used by '
+                           'Tahoe-LAFS')
+    subparsers.add_parser('get-introducers',
+                          help="Return a dictionary of all introducers and "
+                               "their furls added to the storage node running "
+                               "on this FreedomBox.")
+    subparsers.add_parser('get-local-introducer',
+                          help="Return the name and furl of the introducer "
+                               "created on this FreedomBox")
+
+    return parser.parse_args()
+
+
+def subcommand_setup(arguments):
+    """Actions to be performed after installing Tahoe-LAFS."""
+    # Create tahoe group if needed.
+    try:
+        grp.getgrnam('tahoe-lafs')
+    except KeyError:
+        subprocess.run(['addgroup', 'tahoe-lafs'], check=True)
+
+    # Create tahoe user if needed.
+    try:
+        pwd.getpwnam('tahoe-lafs')
+    except KeyError:
+        subprocess.run(
+            [
+                'adduser', '--system', '--ingroup', 'tahoe-lafs',
+                '--home', '/var/lib/tahoe-lafs',
+                '--gecos', 'Tahoe-LAFS distributed file system', 'tahoe-lafs'
+            ],
+            check=True)
+
+    if not os.path.exists(tahoe_home):
+        os.makedirs(tahoe_home, mode=0o755)
+
+    shutil.chown(tahoe_home, user='tahoe-lafs', group='tahoe-lafs')
+
+    if not os.path.exists(domain_name_file):
+        with open(domain_name_file, 'w') as dnf:
+            dnf.write(arguments.domain_name)
+
+
+def subcommand_autostart(_):
+    """Automatically start all introducers and storage nodes on system startup.
+    """
+    aug = augeas.Augeas(flags=augeas.Augeas.NO_LOAD +
+                        augeas.Augeas.NO_MODL_AUTOLOAD)
+    aug.set('/augeas/load/Shellvars/lens', 'Shellvars.lns')
+    aug.set('/augeas/load/Shellvars/incl[last() + 1]', DEFAULT_FILE)
+    aug.load()
+
+    aug.set('/files' + DEFAULT_FILE + '/AUTOSTART', 'all')
+    aug.save()
+
+
+def get_configured_domain_name():
+    """Extract and return the domain name from the domain name file.
+
+    Throws TahoeConfigurationError if the domain name file is not found.
+    """
+    if not os.path.exists(domain_name_file):
+        raise TahoeConfigurationError
+    else:
+        with open(domain_name_file) as dnf:
+            return dnf.read().rstrip()
+
+
+def subcommand_create_introducer(_):
+    """Create a Tahoe-LAFS introducer on this FreedomBox."""
+    os.chdir(tahoe_home)
+
+    if not os.path.exists(os.path.join(tahoe_home, introducer_name)):
+        subprocess.check_call([
+            'tahoe', 'create-introducer', '--port=3456',
+            '--location=tcp:{}:3456'.format(get_configured_domain_name()),
+            introducer_name
+        ])
+
+    subprocess.call(['tahoe', 'start', introducer_name])
+
+
+def subcommand_create_storage_node(_):
+    """Create a Tahoe-LAFS storage node on this FreedomBox."""
+    os.chdir(tahoe_home)
+
+    if not os.path.exists(os.path.join(tahoe_home, storage_node_name)):
+        subprocess.check_call([
+            'tahoe', 'create-node', '--nickname=\"storage_node\"',
+            '--webport=1234',
+            '--hostname={}'.format(get_configured_domain_name()),
+            storage_node_name
+        ])
+        with open(
+                os.path.join(tahoe_home, introducer_name, 'private',
+                             introducer_name + '.furl'), 'r') as furl_file:
+            furl = furl_file.read().rstrip()
+            conf_dict = {'introducers': {introducer_name: {'furl': furl}}}
+            conf_yaml = ruamel.yaml.dump(
+                conf_dict, Dumper=ruamel.yaml.RoundTripDumper)
+            with open(
+                    os.path.join(tahoe_home, storage_node_name, 'private',
+                                 'introducers.yaml'), 'w') as introducers_file:
+                introducers_file.write(conf_yaml)
+
+    subprocess.call(['tahoe', 'start', storage_node_name])
+
+
+def subcommand_add_introducer(arguments):
+    """Add an introducer to the storage node's list of introducers.
+
+    Param introducer must be a tuple of (pet_name, furl).
+    """
+    with YAMLFile(introducers_file, restart_storage_node) as conf:
+        pet_name, furl = arguments.introducer.split(",")
+        conf['introducers'][pet_name] = {'furl': furl}
+
+
+def subcommand_remove_introducer(arguments):
+    """Rename the introducer entry in the introducers.yaml file specified
+    by the param pet_name
+    """
+    with YAMLFile(introducers_file, restart_storage_node) as conf:
+        del conf['introducers'][arguments.pet_name]
+
+
+def subcommand_get_introducers(_):
+    """Return a dictionary of all introducers and their furls.
+
+    The ones added to the storage node running on this FreedomBox.
+    """
+    with open(introducers_file, 'r') as intro_conf:
+        conf = ruamel.yaml.round_trip_load(intro_conf)
+
+    introducers = []
+    for pet_name in conf['introducers'].keys():
+        introducers.append((pet_name, conf['introducers'][pet_name]['furl']))
+
+    print(json.dumps(introducers))
+
+
+def subcommand_get_local_introducer(_):
+    """Return the name and furl of the introducer created on this FreedomBox
+    """
+    with open(introducer_furl_file, 'r') as furl_file:
+        furl = furl_file.read().rstrip()
+
+    print(json.dumps((introducer_name, furl)))
+
+
+def subcommand_enable(_):
+    """Enable web configuration and reload."""
+    action_utils.service_enable('tahoe-lafs')
+    action_utils.webserver_enable('tahoe-plinth')
+
+
+def subcommand_disable(_):
+    """Disable web configuration and reload."""
+    action_utils.webserver_disable('tahoe-plinth')
+    action_utils.service_disable('tahoe-lafs')
+
+
+def restart_storage_node():
+    """Called after exiting context of editing introducers file."""
+    try:
+        subprocess.run(['tahoe', 'restart', 'storage_node'], check=True)
+    except subprocess.CalledProcessError as err:
+        print('Failed to restart storage_node with new configuration: %s', err)
+
+
+def main():
+    """Parse arguments and perform all duties."""
+    arguments = parse_arguments()
+
+    subcommand = arguments.subcommand.replace('-', '_')
+    subcommand_method = globals()['subcommand_' + subcommand]
+    subcommand_method(arguments)
+
+
+if __name__ == '__main__':
+    main()

data/etc/apache2/conf-available/tahoe-plinth.conf

@@ -0,0 +1,14 @@
+# Tahoe-LAFS Storage Node web interface
+
+Listen 5678
+
+# XXX: SSL is not configured?
+# TODO: Use subdomain?
+<VirtualHost *:5678>
+    <Location "/">
+        Include includes/freedombox-auth-ldap.conf
+        Require ldap-group cn=admin,ou=groups,dc=thisbox
+
+        ProxyPass http://localhost:1234/
+    </Location>
+</VirtualHost>

data/etc/plinth/modules-enabled/tahoe

@@ -0,0 +1 @@
+plinth.modules.tahoe

data/usr/lib/firewalld/services/tahoe-plinth.xml

@@ -0,0 +1,7 @@
+<?xml version="1.0" encoding="utf-8"?>
+<service>
+    <short>Tahoe-LAFS</short>
+    <description>Tahoe-LAFS is a distributed file storage system</description>
+    <port protocol="tcp" port="5678"/>
+    <port protocol="tcp" port="3456"/>
+</service>

plinth/actions.py

@@ -98,7 +98,6 @@ import subprocess
 from plinth import cfg
 from plinth.errors import ActionError
 
-
 LOGGER = logging.getLogger(__name__)
 
 
@@ -118,7 +117,17 @@ def superuser_run(action, options=None, input=None, async=False):
     return _run(action, options, input, async, True)
 
 
-def _run(action, options=None, input=None, async=False, run_as_root=False):
+def run_as_user(action, options=None, input=None, async=False,
+                become_user=None):
+    """Run a command as a different user.
+
+    If become_user is None, run as current user.
+    """
+    return _run(action, options, input, async, False, become_user)
+
+
+def _run(action, options=None, input=None, async=False, run_as_root=False,
+         become_user=None):
     """Safely run a specific action as a normal user or root.
 
     Actions are pulled from the actions directory.
@@ -159,6 +168,8 @@ def _run(action, options=None, input=None, async=False, run_as_root=False):
     # Contract 1: commands can run via sudo.
     if run_as_root:
         cmd = ['sudo', '-n'] + cmd
+    elif become_user:
+        cmd = ['sudo', '-n', '-u', become_user] + cmd
 
     LOGGER.info('Executing command - %s', cmd)
 

plinth/forms.py

@@ -22,9 +22,26 @@ Common forms for use by modules.
 from django import forms
 from django.utils.translation import ugettext_lazy as _
 
+from plinth import utils
+
 
 class ServiceForm(forms.Form):
     """Generic configuration form for a service."""
     is_enabled = forms.BooleanField(
         label=_('Enable application'),
         required=False)
+
+
+class DomainSelectionForm(forms.Form):
+    """Form for selecting a domain name to be used for
+    distributed federated applications
+    """
+
+    def __init__(self, *args, **kwargs):
+        super().__init__(*args, **kwargs)
+        self.fields['domain_name'].choices = utils.get_domain_names()
+
+    domain_name = forms.ChoiceField(
+        label=_('Select the domain name to be used for this application'),
+        choices=[]
+    )

plinth/modules/diaspora/__init__.py

@@ -18,7 +18,6 @@ import os
 
 from django.utils.translation import ugettext_lazy as _
 
-from plinth.modules import names
 from plinth.utils import format_lazy
 from plinth import actions, action_utils, frontpage, \
     service as service_module
@@ -66,7 +65,7 @@ description = [
         '<a href="https://diaspora.{host}">diaspora.{host}</a> path on the '
         'web server.'.format(host=get_configured_domain_name()) if is_setup()
         else 'Please register a domain name for your FreedomBox to be able to'
-        ' federate with other diaspora* pods.')
+             ' federate with other diaspora* pods.')
 ]
 
 
@@ -112,19 +111,6 @@ def setup(helper, old_version=None):
     helper.call('post', add_shortcut)
 
 
-def get_domain_names():
-    """Return the domain name(s)"""
-    results = []
-
-    for domain_type, domains in names.domains.items():
-        if domain_type == 'hiddenservice':
-            continue
-        for domain in domains:
-            results.append((domain, domain))
-
-    return results
-
-
 def add_shortcut():
     """Add shortcut to diaspora on the Plinth homepage"""
     if is_setup():

plinth/modules/diaspora/views.py

@@ -25,6 +25,7 @@ from django.views.generic import FormView
 from plinth import actions
 from plinth.modules import diaspora
 from plinth.modules.diaspora.forms import DiasporaForm
+from plinth.utils import get_domain_names
 from plinth.views import ServiceView
 
 
@@ -48,7 +49,7 @@ class DiasporaSetupView(FormView):
         context = super().get_context_data(**kwargs)
         context['description'] = self.description
         context['title'] = self.title
-        context['domain_names'] = diaspora.get_domain_names()
+        context['domain_names'] = get_domain_names()
 
         return context
 

plinth/modules/matrixsynapse/__init__.py

@@ -31,8 +31,6 @@ from plinth import actions
 from plinth import frontpage
 from plinth import service as service_module
 from plinth.menu import main_menu
-from plinth.modules import names
-
 
 version = 1
 
@@ -139,20 +137,6 @@ def diagnose():
     return results
 
 
-def get_domain_names():
-    """Return the domain name(s)."""
-    results = []
-
-    for domain_type, domains in names.domains.items():
-        if domain_type == 'hiddenservice':
-            continue
-
-        for domain in domains:
-            results.append((domain, domain))
-
-    return results
-
-
 def get_configured_domain_name():
     """Return the currently configured domain name."""
     if not is_setup():

plinth/modules/matrixsynapse/forms.py

@@ -22,7 +22,7 @@ Forms for configuring matrix-synapse.
 from django import forms
 from django.utils.translation import ugettext_lazy as _
 
-from plinth.modules import matrixsynapse
+from plinth.utils import get_domain_names
 
 
 class MatrixSynapseForm(forms.Form):
@@ -35,4 +35,4 @@ class MatrixSynapseForm(forms.Form):
     def __init__(self, *args, **kwargs):
         """Initialize the form object."""
         super().__init__(*args, **kwargs)
-        self.fields['domain_name'].choices = matrixsynapse.get_domain_names()
+        self.fields['domain_name'].choices = get_domain_names()

plinth/modules/matrixsynapse/views.py

@@ -27,6 +27,7 @@ from plinth import actions
 from plinth import views
 from plinth.modules import matrixsynapse
 from plinth.modules.matrixsynapse.forms import MatrixSynapseForm
+from plinth.utils import get_domain_names
 
 
 class SetupView(FormView):
@@ -49,7 +50,7 @@ class SetupView(FormView):
 
         context['title'] = matrixsynapse.title
         context['description'] = matrixsynapse.description
-        context['domain_names'] = matrixsynapse.get_domain_names()
+        context['domain_names'] = get_domain_names()
 
         return context
 

plinth/modules/tahoe/__init__.py

@@ -0,0 +1,218 @@
+#
+# This file is part of Plinth.
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+"""
+Plinth module to configure Tahoe-LAFS.
+"""
+
+import json
+import os
+
+from django.utils.translation import ugettext_lazy as _
+
+from plinth import action_utils
+from plinth import actions
+from plinth import cfg
+from plinth import frontpage
+from plinth import service as service_module
+from plinth.menu import main_menu
+from plinth.utils import format_lazy
+
+from .errors import TahoeConfigurationError
+
+version = 1
+
+managed_services = ['tahoe-lafs']
+
+managed_packages = ['tahoe-lafs']
+
+title = _('Distributed File Storage (Tahoe-LAFS)')
+
+service = None
+
+tahoe_home = '/var/lib/tahoe-lafs'
+introducer_name = 'introducer'
+storage_node_name = 'storage_node'
+domain_name_file = os.path.join(tahoe_home, 'domain_name')
+introducers_file = os.path.join(
+    tahoe_home, '{}/private/introducers.yaml'.format(storage_node_name))
+introducer_furl_file = os.path.join(
+    tahoe_home, '{0}/private/{0}.furl'.format(introducer_name))
+
+
+def is_setup():
+    """Check whether Tahoe-LAFS is setup"""
+    return os.path.exists(domain_name_file)
+
+
+def get_configured_domain_name():
+    """Extract and return the domain name from the domain name file.
+    Throws TahoeConfigurationError if the domain name file is not found.
+    """
+    if not os.path.exists(domain_name_file):
+        raise TahoeConfigurationError
+    else:
+        with open(domain_name_file) as dnf:
+            return dnf.read().rstrip()
+
+
+description = [
+    _('Tahoe-LAFS is a decentralized secure file storage system. '
+      'It uses provider independent security to store files over a '
+      'distributed network of storage nodes. Even if some of the nodes fail, '
+      'your files can be retrieved from the remaining nodes.'),
+    format_lazy(
+        _('This {box_name} hosts a storage node and an introducer by default. '
+          'Additional introducers can be added, which will introduce this '
+          'node to the other storage nodes.'),
+        box_name=_(cfg.box_name)),
+]
+
+
+def init():
+    """Intialize the module."""
+    menu = main_menu.get('apps')
+    menu.add_urlname(title, 'glyphicon-hdd', 'tahoe:index')
+
+    global service
+    setup_helper = globals()['setup_helper']
+    if setup_helper.get_state() != 'needs-setup' and is_setup():
+        service = service_module.Service(
+            managed_services[0],
+            title,
+            ports=['tahoe-plinth'],
+            is_external=True,
+            is_enabled=is_enabled,
+            enable=enable,
+            disable=disable,
+            is_running=is_running)
+
+        if is_enabled():
+            add_shortcut()
+
+
+def setup(helper, old_version=None):
+    """Install and configure the module."""
+    helper.install(managed_packages)
+
+
+def post_setup(configured_domain_name):
+    """Actions to be performed after installing tahoe-lafs package."""
+    actions.superuser_run('tahoe-lafs',
+                          ['setup', '--domain-name', configured_domain_name])
+    actions.superuser_run('tahoe-lafs', ['enable'])
+    actions.run_as_user('tahoe-lafs', ['create-introducer'],
+                        become_user='tahoe-lafs')
+    actions.run_as_user('tahoe-lafs', ['create-storage-node'],
+                        become_user='tahoe-lafs')
+    actions.superuser_run('tahoe-lafs', ['autostart'])
+
+    global service
+    if service is None:
+        service = service_module.Service(
+            managed_services[0],
+            title,
+            ports=['tahoe-plinth'],
+            is_external=True,
+            is_enabled=is_enabled,
+            enable=enable,
+            disable=disable,
+            is_running=is_running)
+    service.notify_enabled(None, True)
+    add_shortcut()
+
+
+def add_shortcut():
+    """Helper method to add a shortcut to the front page."""
+    # BUG: Current logo appears squashed on front page.
+    frontpage.add_shortcut(
+        'tahoe-lafs', title,
+        url='https://{}:5678'.format(get_configured_domain_name()),
+        login_required=True)
+
+
+def is_running():
+    """Return whether the service is running."""
+    return action_utils.service_is_running(managed_services[0])
+
+
+def is_enabled():
+    """Return whether the module is enabled."""
+    return (action_utils.service_is_enabled(managed_services[0]) and
+            action_utils.webserver_is_enabled('tahoe-plinth'))
+
+
+def enable():
+    """Enable the module."""
+    actions.superuser_run('tahoe-lafs', ['enable'])
+    add_shortcut()
+
+
+def disable():
+    """Enable the module."""
+    actions.superuser_run('tahoe-lafs', ['disable'])
+    frontpage.remove_shortcut('tahoe-lafs')
+
+
+def diagnose():
+    """Run diagnostics and return the results."""
+    return [action_utils.diagnose_url(
+        'http://localhost:5678', kind='4', check_certificate=False),
+            action_utils.diagnose_url(
+                'http://localhost:5678', kind='6', check_certificate=False),
+            action_utils.diagnose_url(
+                'http://{}:5678'.format(get_configured_domain_name()),
+                kind='4',
+                check_certificate=False)]
+
+
+def add_introducer(introducer):
+    """Add an introducer to the storage node's list of introducers.
+    Param introducer must be a tuple of (pet_name, furl)
+    """
+    actions.run_as_user('tahoe-lafs',
+                        ['add-introducer',
+                         "--introducer",
+                         ",".join(introducer)],
+                        become_user='tahoe-lafs')
+
+
+def remove_introducer(pet_name):
+    """Rename the introducer entry in the introducers.yaml file specified by
+    the param pet_name.
+    """
+    actions.run_as_user('tahoe-lafs',
+                        ['remove-introducer', '--pet-name', pet_name],
+                        become_user='tahoe-lafs')
+
+
+def get_introducers():
+    """Return a dictionary of all introducers and their furls added to the
+    storage node running on this FreedomBox.
+    """
+    introducers = actions.run_as_user('tahoe-lafs', ['get-introducers'],
+                                      become_user='tahoe-lafs')
+
+    return json.loads(introducers)
+
+
+def get_local_introducer():
+    """Return the name and furl of the introducer created on this FreedomBox.
+    """
+    introducer = actions.run_as_user('tahoe-lafs', ['get-local-introducer'],
+                                     become_user='tahoe-lafs')
+
+    return json.loads(introducer)

plinth/modules/tahoe/errors.py

@@ -0,0 +1,27 @@
+#
+# This file is part of Plinth.
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+
+"""
+Errors for Tahoe-LAFS module
+"""
+
+from plinth.errors import PlinthError
+
+
+class TahoeConfigurationError(PlinthError):
+    """Tahoe-LAFS has not been configured for domain name."""
+    pass

plinth/modules/tahoe/templates/tahoe-post-setup.html

@@ -0,0 +1,110 @@
+{% extends "service.html" %}
+{% comment %}
+#
+# This file is part of Plinth.
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see
+<http://www.gnu.org/licenses/>.
+#
+{% endcomment %}
+
+{% load i18n %}
+{% load bootstrap %}
+
+{% block description %}
+
+{% for paragraph in description %}
+<p>{{ paragraph|safe }}</p>
+{% endfor %}
+
+<p>
+    {% url 'config:index' as index_url %}
+    {% blocktrans trimmed with domain_name=domain_name %}
+    The Tahoe-LAFS server domain is set to <b>{{ domain_name }}</b>.
+    Changing the FreedomBox domain name needs a reinstall of
+    Tahoe-LAFS and you WILL LOSE DATA. You can access Tahoe-LAFS at
+    <a href="https://{{domain_name}}:5678">https://{{domain_name}}:5678</a>.
+    {% endblocktrans %}
+</p>
+{% endblock %}
+
+{% block configuration %}
+  <h3>{% trans "Configuration" %}</h3>
+
+  <form class="form" method="post">
+    {% csrf_token %}
+
+    {{ form|bootstrap }}
+
+    <input type="submit" class="btn btn-primary"
+           value="{% trans "Update setup" %}"/>
+  </form>
+  <br/>
+
+  <h4>{% trans "Local introducer" %}</h4>
+  <table class="table table-bordered">
+      <thead>
+          <tr>
+              <th>{% trans "Pet Name" %}</th>
+              <th> furl </th>
+          </tr>
+      </thead>
+      <tr>
+          <td> {{ local_introducer.0 }} </td>
+          <td> {{ local_introducer.1 }} </td>
+      </tr>
+  </table>
+
+  <form class="form" method="post" action="/plinth/apps/tahoe-lafs/add_introducer">
+      {% csrf_token %}
+      <h4>{% trans "Add new introducer" %}</h4>
+
+      <div class="form-group">
+          <label>{% trans "Pet Name" %}:</label>
+          <input type="text" class="form-control" name="pet_name">
+      </div>
+      <div class="form-group">
+          <label>furl:</label>
+          <textarea class="form-control" rows="5" name="furl"></textarea>
+      </div>
+      <input type="submit" class="btn btn-primary"
+             value="{% trans "Add" %}"/>
+  </form>
+
+  <br/>
+
+ <h4>{% trans "Connected introducers" %}</h4>
+  <table class="table table-bordered">
+      <thead>
+          <tr>
+              <th>{% trans "Pet Name" %}</th>
+              <th> furl </th>
+          </tr>
+      </thead>
+      {% for introducer, furl in introducers %}
+      <tr>
+          <td> {{ introducer }} </td>
+          <td> {{ furl }} </td>
+          <form class="form" method="post"
+                action="/plinth/apps/tahoe-lafs/remove_introducer/{{introducer}}" id="introducer_list">
+                 {% csrf_token %}
+              <td><button type="submit" class="btn btn-danger">
+                  {% trans "Remove" %}
+              </button></td>
+          </form>
+      </tr>
+      {% endfor %}
+  </table>
+
+{% endblock %}

plinth/modules/tahoe/templates/tahoe-pre-setup.html

@@ -0,0 +1,62 @@
+{% extends "base.html" %}
+{% comment %}
+#
+# This file is part of Plinth.
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+{% endcomment %}
+
+{% load bootstrap %}
+{% load i18n %}
+
+{% block content %}
+  {% block pagetitle %}
+    <h2>{{ title }}</h2>
+  {% endblock %}
+
+  {% block description %}
+    {% for paragraph in description %}
+    <p>{{ paragraph|safe }}</p>
+    {% endfor %}
+  {% endblock %}
+
+  <p>
+    {% url 'config:index' as index_url %}
+    {% if domain_names|length == 0 %}
+      No domain(s) are set. You can setup your domain on the system at
+      <a href="{{ index_url }}">{% trans "Configure" %}</a> page.
+    {% endif %}
+  </p>
+
+  {% block status %}
+  {% endblock %}
+
+  {% block diagnostics %}
+  {% endblock %}
+
+  {% block configuration %}
+    {% if domain_names|length > 0 %}
+      <h3>{% trans Configuration %}</h3>
+      <form class="form" method="post">
+        {% csrf_token %}
+
+        {{ form|bootstrap }}
+
+        <input type="submit" class="btn btn-primary"
+               value="{% trans "Update setup" %}"/>
+      </form>
+    {% endif %}
+  {% endblock %}
+{% endblock %}

plinth/modules/tahoe/urls.py

@@ -0,0 +1,37 @@
+#
+# This file is part of Plinth.
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+"""
+URLs for the Tahoe-LAFS module.
+"""
+
+from . import views
+
+from django.conf.urls import url
+
+from .views import TahoeSetupView, TahoeServiceView
+
+
+urlpatterns = [
+    url(r'^apps/tahoe-lafs/setup$', TahoeSetupView.as_view(),
+        name='setup'),
+    url(r'^apps/tahoe-lafs/add_introducer$', views.add_introducer,
+        name="add-introducer"),
+    url(r'^apps/tahoe-lafs/remove_introducer/(?P<introducer>[0-9a-zA-Z_]+)$',
+        views.remove_introducer, name="remove-introducer"),
+    url(r'^apps/tahoe-lafs/$', TahoeServiceView.as_view(),
+        name='index')
+]

plinth/modules/tahoe/views.py

@@ -0,0 +1,83 @@
+#
+# This file is part of Plinth.
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Affero General Public License as
+# published by the Free Software Foundation, either version 3 of the
+# License, or (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Affero General Public License for more details.
+#
+# You should have received a copy of the GNU Affero General Public License
+# along with this program.  If not, see <http://www.gnu.org/licenses/>.
+#
+"""
+Views for the Tahoe-LAFS module
+"""
+from django.shortcuts import redirect
+from django.urls import reverse_lazy
+from django.views.generic import FormView
+
+from plinth.forms import DomainSelectionForm
+from plinth.modules import tahoe
+from plinth.utils import get_domain_names
+from plinth.views import ServiceView
+
+
+class TahoeSetupView(FormView):
+    """Show tahoe-lafs setup page."""
+    template_name = 'tahoe-pre-setup.html'
+    form_class = DomainSelectionForm
+    description = tahoe.description
+    title = tahoe.title
+    success_url = reverse_lazy('tahoe:index')
+
+    def form_valid(self, form):
+        domain_name = form.cleaned_data['domain_name']
+        tahoe.post_setup(domain_name)
+        return super().form_valid(form)
+
+    def get_context_data(self, *args, **kwargs):
+        context = super().get_context_data(**kwargs)
+        context['description'] = self.description
+        context['title'] = self.title
+        context['domain_names'] = get_domain_names()
+
+        return context
+
+
+class TahoeServiceView(ServiceView):
+    """Show tahoe-lafs service page."""
+    service_id = tahoe.managed_services[0]
+    template_name = 'tahoe-post-setup.html'
+    description = tahoe.description
+    diagnostics_module_name = 'tahoe'
+
+    def dispatch(self, request, *args, **kwargs):
+        if not tahoe.is_setup():
+            return redirect('tahoe:setup')
+
+        return super().dispatch(request, *args, **kwargs)
+
+    def get_context_data(self, *args, **kwargs):
+        context = super().get_context_data(**kwargs)
+        context['domain_name'] = tahoe.get_configured_domain_name()
+        context['introducers'] = tahoe.get_introducers()
+        context['local_introducer'] = tahoe.get_local_introducer()
+
+        return context
+
+
+def add_introducer(request):
+    if request.method == 'POST':
+        tahoe.add_introducer((request.POST['pet_name'], request.POST['furl']))
+        return redirect('tahoe:index')
+
+
+def remove_introducer(request, introducer):
+    if request.method == 'POST':
+        tahoe.remove_introducer(introducer)
+        return redirect('tahoe:index')

plinth/tests/test_utils.py

@@ -19,11 +19,14 @@
 Test module for Plinth's utilities.
 """
 
+import tempfile
+from unittest import TestCase
 from unittest.mock import Mock, MagicMock
 
-from django.test import TestCase
+import ruamel.yaml
 from django.test.client import RequestFactory
 
+from plinth.utils import YAMLFile
 from plinth.utils import is_user_admin
 
 
@@ -81,3 +84,44 @@ class TestIsAdminUser(TestCase):
         mock.assert_called_once_with()
         session_mock.__getitem__.assert_called_once_with(
             'cache_user_is_admin')
+
+
+class TestYAMLFileUtil(TestCase):
+    """Check updating YAML files"""
+
+    kv_pair = {'key': 'value'}
+
+    def test_update_empty_yaml_file(self):
+        """
+        Update an empty YAML file with content.
+        """
+        fp = tempfile.NamedTemporaryFile()
+        conf = {'property1': self.kv_pair}
+
+        with YAMLFile(fp.name) as file_conf:
+            for key in conf.keys():
+                file_conf[key] = conf[key]
+
+        with open(fp.name, 'r') as retrieved_conf:
+            assert retrieved_conf.read() == ruamel.yaml.round_trip_dump(conf)
+
+    def test_update_non_empty_yaml_file(self):
+        """
+        Update a non-empty YAML file with modifications
+        """
+        fp = tempfile.NamedTemporaryFile()
+
+        with open(fp.name, 'w') as conf_file:
+            conf_file.write(
+                ruamel.yaml.round_trip_dump({
+                    'property1': self.kv_pair
+                }))
+
+        with YAMLFile(fp.name) as file_conf:
+            file_conf['property2'] = self.kv_pair
+
+        with open(fp.name, 'r') as retrieved_conf:
+            file_conf = ruamel.yaml.round_trip_load(retrieved_conf)
+            print(file_conf)
+            assert file_conf == {'property1': self.kv_pair,
+                                 'property2': self.kv_pair}

plinth/utils.py

@@ -20,7 +20,10 @@ Miscellaneous utility methods.
 """
 
 import importlib
+import os
+import ruamel.yaml
 from django.utils.functional import lazy
+from plinth.modules import names
 
 
 def import_from_gi(library, version):
@@ -63,3 +66,49 @@ def is_user_admin(request, cached=False):
     user_is_admin = request.user.groups.filter(name='admin').exists()
     request.session['cache_user_is_admin'] = user_is_admin
     return user_is_admin
+
+
+def get_domain_names():
+    """Return the domain name(s)"""
+    domain_names = []
+
+    for domain_type, domains in names.domains.items():
+        if domain_type == 'hiddenservice':
+            continue
+        for domain in domains:
+            domain_names.append((domain, domain))
+
+    return domain_names
+
+
+class YAMLFile(object):
+    """A context management class for updating YAML files"""
+    def __init__(self, yaml_file, post_exit=None):
+        """Return a context object for the YAML file.
+
+        Parameters:
+        yaml_file - the YAML file to update.
+        post_exit - a function that will be called after updating the YAML file.
+        """
+        self.yaml_file = yaml_file
+        self.post_exit = post_exit
+        self.conf = None
+
+    def __enter__(self):
+        with open(self.yaml_file, 'r') as intro_conf:
+            if not self.is_file_empty():
+                self.conf = ruamel.yaml.round_trip_load(intro_conf)
+            else:
+                self.conf = {}
+
+            return self.conf
+
+    def __exit__(self, typ, value, traceback):
+        with open(self.yaml_file, 'w') as intro_conf:
+            ruamel.yaml.round_trip_dump(self.conf, intro_conf)
+
+        if self.post_exit:
+            self.post_exit()
+
+    def is_file_empty(self):
+        return os.stat(self.yaml_file).st_size == 0