Add action to check if ejabberd is installed.

If not installed, show instructions on how to install it.

actions/xmpp

@@ -0,0 +1,63 @@
+#!/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 the ejabberd service
+"""
+
+import argparse
+import subprocess
+
+
+def parse_arguments():
+    """Return parsed command line arguments as dictionary"""
+    parser = argparse.ArgumentParser()
+    subparsers = parser.add_subparsers(dest='subcommand', help='Sub command')
+
+    # Get whether ejabberd is installed
+    subparsers.add_parser('get-installed',
+                          help='Get whether ejabberd is installed')
+
+    return parser.parse_args()
+
+
+def subcommand_get_installed(_):
+    """Get whether ejabberd is installed"""
+    print('installed' if get_installed() else 'not installed')
+
+
+def get_installed():
+    """Check if ejabberd is installed"""
+    with open('/dev/null', 'w') as file_handle:
+        status = subprocess.call(['which', 'ejabberdctl'], stdout=file_handle)
+
+    return not status
+
+
+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()

plinth/modules/xmpp/xmpp.py

@@ -67,10 +67,23 @@ def init():
 @login_required
 def index(request):
     """Serve XMPP page"""
-    main = "<p>XMPP Server Accounts and Configuration</p>"
+    is_installed = actions.superuser_run(
+        'xmpp',
+        ['get-installed']).strip() == 'installed'
 
-    sidebar_right = render_to_string('menu_block.html', {'menu': SIDE_MENU},
-                                     RequestContext(request))
+    main = "<p>XMPP Server Accounts and Configuration</p>"
+    if not is_installed:
+        main += """
+<p>ejabberd is not installed, please install it. ejabberd comes pre-installed
+with FreedomBox. On any Debian-based system (such as FreedomBox) you may install
+it using the command 'aptitude install ejabberd'</p>
+"""
+
+    if is_installed:
+        sidebar_right = render_to_string('menu_block.html', {'menu': SIDE_MENU},
+                                         RequestContext(request))
+    else:
+        sidebar_right = None
 
     return TemplateResponse(request, 'base.html',
                             {'title': _('XMPP Server'),