RogerBW's Blog

Why have a calendar server in the first place? Because I want to check my schedule from multiple devices, and because I don't want to sell out to Google. (Which of course just means that when Google takes over I won't have been paid.)

I've been running calypso for a while, but it doesn't seem terribly responsive; generally when I load multiple calendars at least one of them doesn't come back fast enough to satisfy the client (Lightning), and I was never able to get it to work with LineageOS at all. I'd tried Xandikos before, which started as a fork of Calypso but has now been completely rewritten, but never managed to get it working; but the recent release of Debian 10, which includes it as a package, inspired me to give it another go.

The documentation is fragmentary, but here's how I got it set up in a "full" configuration, i.e. with Apache and UWSGI rather than direct unauthenticated connection. I was poking radicale and calypso at the same time, and even briefly flirting with Apple's calendar-server (caldavd), so there may be more here than is strictly needed.

Packages needed seem to be xandikos, apache2 (which I was already using), libapache2-mod-proxy-uwsgi, uwsgi and uwsgi-plugin-python3. I needed to set up a xandikos user and group (adduser/addgroup).

Apache gets a virtual server (plain text redirects to SSL, and of course I have a LetsEncrypt certificate, validated by DNS). This handles the authentication.

<VirtualHost *:443>
SSLEngine on # [etc., see best practices]

ServerName calendar.homenet.firedrake.org
ServerAdmin [REDACTED]
DocumentRoot /var/www/nowhere

ProxyPass / uwsgi://127.0.0.1:8001/
<Proxy "*">
    AuthType Basic
    AuthName "Xandikos: Authentication Required"
    AuthBasicProvider file
    AuthUserFile /etc/apache2/passwd/xandikos
    AllowOverride None
    Require valid-user
</Proxy>

ErrorLog ${APACHE_LOG_DIR}/calendar.homenet.firedrake.org-error.log
CustomLog ${APACHE_LOG_DIR}/calendar.homenet.firedrake.org-access.log \
combined
</VirtualHost>

<VirtualHost *:80>
ServerName calendar.homenet.firedrake.org
ServerAdmin webmaster@${_DOMAIN}
DocumentRoot /var/www/nowhere

RedirectMatch permanent ^(?!/.well-known/acme-challenge)(.*) \
https://calendar.homenet.firedrake.org/$1

CustomLog ${APACHE_LOG_DIR}/redirect.log vhost_combined
</VirtualHost>

Xandikos doesn't have multi-user support, so this isn't something to throw open to the world, or even to all local users.

UWSGI gets the other half of this localhost connection in /etc/uwsgi/apps-enabled/xandikos.ini:

[uwsgi]
socket = 127.0.0.1:8001
uid = xandikos
gid = xandikos
umask = 022
master = true
cheaper = 0
processes = 1
plugin = python3
module = xandikos.wsgi:app
env = XANDIKOSPATH=/var/lib/xandikos/collections
env = CURRENT_USER_PRINCIPAL=/user/
env = AUTOCREATE=defaults

I think the default collections got created by the first authenticated connection, or it might have been on uwsgi restart.

New calendars created (MKCALENDAR works as it should), I then copied across the data from the old set - using vdirsyncer, which is a bit odd but seems to get the job done.

I then found that the CalDAV code I'd been using (for example to send me reminders of upcoming events) was taking an illicit short-cut. Calypso allows the user simply to GET a calendar, and receive all the events in it, but that's not the One True Way. I poked around CPAN for a bit, not finding any modules that did the right thing (even Cal::DAV, by the same author whose ICal code I'm already using, has this flaw), but was eventually pointed to a page on CalDAV in practice which goes into enough detail for me to get the job done. (And yes, I suppose there will eventually be a module for this.)

Hint to protocol designers: if you find yourself thinking "this is really complicated, I bet adding five-layers-deep XML structures will make it simpler" you are wrong. (At least JSON doesn't have namespaces. Though it does have schemas.) In particular, if you are thinking "round trips are expensive, I'll allow a bunch of simultaneous requests in a single XML stream, each of which will return its own status information, all packed together in another XML stream" I may have to find you and hurt you.

But I do now have my calendar syncing with LineageOS (across the home network or a VPN, using DAVx5 off F-Droid), without having to rely on any third-party servers.

Note: nothing ever tells you what URL you should feed a client. For Lightning I load up individual remote calendars with the full path ( .../user/calendars/roger-public etc.); for DAVx5 it's higher up (I think it was .../user/calendars) and it syncs all of them.

Colouring calendars imported via DAVx5 requires you to set the Calendar Colour property (which Lightning doesn't use), which is its own special fun…