Caldav sync for Emacs orgmode
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README.md

org-caldav

Caldav sync for Emacs Orgmode

Minimum Emacs version needed: 24.3

CalDAV servers:

  • Owncloud and Nextcloud: Regularly tested.

  • Google Calendar: Should work, but you need to register an application with the Google Developer Console for OAuth2 authentication (see below).

  • Radicale and Baikal: Should work. If you get problems with 'Digest' authentication, switch back to 'Basic' (make sure to use https, though!). If you get asked for password repeatedly, put it in .authinfo file (see below).

  • SOGo and Kolab: Reported to be working (https://kolabnow.com/clients/emacs)

Note that current Emacs releases do not correctly handle https over a proxy connection (https://debbugs.gnu.org/cgi/bugreport.cgi?bug=11788). If you need that, you'll have to use a recent Emacs 26.0.x snapshot.

IMPORTANT: Before using this code, please make sure you have backups of your precious Org files. Also, I strongly suggest to create a new, empty calendar on your server for using this package.

ALSO IMPORTANT: When using this package, possibly all Org entries will get an UID property (see doc-string of org-icalendar-store-UID for further details). If you don't want this, then do not use this package; there is just no way around that. It is the only reliable way to uniquely identify Org entries.

IN A NUTSHELL

  • Create a new calendar; the name does not matter.

  • Set org-caldav-url to the base address of your CalDAV server:

  • Set org-caldav-calendar-id to the calendar-id of your new calendar:

    • Own/NextCloud: Click on that little symbol next to the calendar name and inspect the link of the calendar; the last element of the shown path is the calendar-id. This should usually be the same as the name of the calendar, but not necessarily: Owncloud might replace certain characters (upper- to lowercase, for instance), or it might even be entirely different if the calendar was created by another CalDAV application.
    • Google: Click on 'calendar settings' and the id will be shown next to "Calendar Address". It is of the form ID@group.calendar.google.com. Do not omit the domain!
  • Set org-caldav-inbox to an org filename where new entries from the calendar should be stored. Just to be safe, I suggest using an empty, dedicated Org file for that.

  • Set org-caldav-files to the list of org files you would like to sync. The above org-caldav-inbox will be automatically added, so you don't have to add it here.

  • It is usually a good idea to manually set org-icalendar-timezone to the timezone of your remote calendar. It should be a simple string like "Europe/Berlin". If that doesn't work and your events are shifted by a few hours, try the setting "UTC" (the SOGo calendar server seems to need this).

Please note that org-caldav does not directly control how and which entries are exported, it just uses the org-icalendar exporter. Therefore, you should also take a look at the options from the org-icalendar exporter. Most importantly, take a look at org-icalendar-alarm-time to add a reminder to your entries, and org-icalendar-use-deadline and org-icalendar-use-scheduled to control which timestamps should be used.

Call org-caldav-sync to start the sync. The URL package will ask you for username/password for accessing the calendar. (See below on how to store that password in an authinfo file.)

The first sync can easily take several minutes, depending on the number of calendar items. Especially Google's CalDAV interface is pretty slow. If you have to abort the initial sync for some reason, just start org-caldav-sync again in the same Emacs session and you should get asked if you'd like to resume.

The same goes for sync errors you might get. Especially when using Google Calendar, it is not unusual to get stuff like '409' errors during the initial sync. Only Google knows why. Just run org-caldav-sync again until all events are uploaded.

Syncing to Google Calendar

The new CalDAV endpoint for Google Calendar requires OAuth2 authentication. So first, you need to install the oauth2 library from GNU ELPA, and afterwards you need to acquire an application ID and secret from the Google Developer Console. For details on how to do this, follow the Google documentation at

https://developers.google.com/google-apps/calendar/caldav/v2/guide#creating_your_client_id

Put the client ID and secret into org-caldav-oauth2-client-id and org-caldav-oauth2-client-secret, respectively. Then set org-caldav-url to the symbol 'google, and look up the org-caldav-calendar-id as described above.

On first connection, the oauth2 library should redirect you to the Google OAuth2 authentication site. This requires a javascript enabled browser, so make sure that browse-url-browser-function is set to something like browse-url-firefox (the internal shr or w3m browser will not work). After authentication, you will be given a key that you have to paste into the Emacs prompt. The oauth2 library will save this key in Emacs' secure plist store, which is encrypted with GnuPG. If you have not yet used a secure plist store, you will be asked for its encryption passphrase. In the future, you should only need to enter that passphrase again to connect with Google Calendar.

By default, plstore will not cache your entered password, so it will possibly ask you many times. To activate caching, use

(setq plstore-cache-passphrase-for-symmetric-encryption t)

DETAILS

Compared to earlier versions of this package from 2012, it now does proper two-way syncing, that means it does not matter where and how you change an entry. You can also move Org entries freely from one file to another, as long as they are all listed in org-caldav-files. The org-icalendar package will put a unique ID on each entry with an active timestamp, so that org-caldav can find it. It will also sync deletions, but more on that later.

Org and the iCalendar format

An Org entry can store much more information than an iCalendar entry, so there is no one-to-one correspondence between the two formats which makes syncing a bit difficult.

  • Org to iCalendar

This package uses the org-icalendar package to do the export to the iCalendar format (.ics files). By default, it uses the title of the Org entry as SUMMARY and puts the entry's body into DESCRIPTION, snipping stuff like properties and timestamps (you can override that with properties of the same name, but IMO it makes stuff just more complicated). The variable org-icalendar-include-body denotes how many characters from the body should be included as DESCRIPTION (by default all characters are included).

  • iCalendar to Org

If you create a new iCalendar entry in your calendar, you'll get an Org entry with SUMMARY as heading, DESCRIPTION as body and the timestamp. However, if you change an existing entry in the calendar, things get more complicated and the variable org-caldav-sync-changes-to-org comes into play. Its default is the symbol "title-and-timestamp", which means that only the entry's heading is synced (with SUMMARY) and the timestamp gets updated, but not the entry's body with DESCRIPTION. The simple reason is that you might loose data, since DESCRIPTION is rather limited in what it can store. Still, you can set the variable to the symbol "all", which will completely replace an existing Org entry with the entry that gets generated from the calendar's event. You can also limit syncing to heading and/or timestamp only.

To be extra safe, org-caldav will by default backup entries it changes. See the variable org-caldav-backup-file for details.

  • Org sexp entries

A special case are sexp entries like

%%(diary-anniversary  2 2 1969) Foo's birthday

* Regular meeting
  <%%(diary-float t 4 2)>

As you can see, they can appear in two different ways: plain by themselves, or inside an Org entry. If they are inside an Org entry, there's a good chance they will be exported (see below) and have an ID property, so they can be found by org-caldav. We can sync the title, but syncing the timestamp with the s-expression is just infeasible, so this will generate a sync error (which are not critical; you'll just see them at the end of the sync, just so that you're aware that some stuff wasn't synced properly).

However, sexp-entries are insanely flexible, and there are limits as to what the icalendar exporter will handle. For example, this here

** Regular event
   <%%(memq (calendar-day-of-week date) '(1 3 5))>

will not be exported at all.

If the sexp entry is not inside an Org entry but stands by itself, they still will be exported, but they won't get an ID (since IDs are properties linked to Org entries). In practice, that means that you can delete and change them inside Org and this will be synced, but if you change them in the calendar, this will not get synced back. Org-caldav just cannot find those entires, so this will generate a one-time sync error instead (again: those are not critical, just FIY). If you don't want those entries to be exported at all, just set org-icalendar-include-sexps to nil.

Filtering entries

There are several possibilities to choose which entries should be synced and which not:

  • If you only want to sync manually marked entries, use org-caldav-select-tags, which is directly mapped to org-export-select-tags, so see its doc-string on how it works.

  • If you want to exclude certain tags, use org-caldav-exclude-tags, which is mapped to org-icalendar-exclude tags.

  • If you want more fine grained control, use org-caldav-skip-conditions. The syntax of the conditions is described in the doc-string of org-agenda-skip-if.

Note however that the normal org-agenda-skip-function(-global) will not have any effect on the icalendar exporter (this used to be the case, but changed with the new exporters).

Syncing deletions

If you delete entries in your Org files, the corresponding iCalendar entries will by default get deleted. You can change that behavior with org-caldav-delete-calendar-entries to never delete, or to ask before deletion.

You must be careful to not simply remove previously synced files from org-caldav-files, as org-caldav would view all the entries from those files as deleted and hence by default also delete them from the calendar. However, org-caldav should be able to detect this situation and warn you with the message 'Previously synced file(s) are missing', asking you whether to continue nonetheless.

If you delete events in your calendar, you will by default get asked if you'd like to delete the corresponding Org event. You can change that behavior through org-caldav-delete-org-entries.

If you answer a deletion request with "no", the event should get re-synced to the calendar next time you call org-caldav-sync.

Conflict handling

Now that's an easy one: Org always wins. That means, if you change an entry in Org and in the calendar, the changes in the calendar will be lost. I might implement proper conflict handling some day, but don't hold your breath (patches are welcome, of course).

Storing authentication information in authinfo/netrc

If you don't want to enter your user/password every time, you can store it permanently in an authinfo file. In Emacs, the auth-source package takes care of that, but the syntax for https authentication is a bit peculiar. You have to use a line like the following

machine www.google.com:443 port https login username password secret

Note that you have to specify the port number in the URL and also specify 'https' for the port. This is not a bug. For more information, see (info "auth"), especially section "Help for users".

Since you are storing your password in a file it makes sense to encrypt it using GnuPG. While Emacs supports this, there's a subtle bug which makes this feature unusable for the URL package (see bug 11981). This was fixed in Emacs 24.2, so if you're using an older version, you'll have to upgrade if you want encrypted authinfo files for org-caldav.

Storage of sync information and sync from different computers

The current sync state is stored in a file org-caldav-SOMEID.el in the ~/.emacs.d directory. You can change the location through the variable org-caldav-save-directory. SOMEID directly depends on the calendar id (it's a snipped MD5).

If you sync your Org files across different machines and want to use org-caldav on all of them, don't forget to sync the org sync state, too. Probably your best bet is to set org-caldav-save-directory to the path you have your Org files in, so that it gets copied alongside with them.

Starting from scratch

If your sync state somehow gets broken, you can make a clean slate by doing

C-u M-x org-caldav-delete-everything

The function has to be called with a prefix so that you don't call it by accident. This will delete everything in the calendar along with the current sync state. You can then call org-caldav-sync afterwards and it will completely put all Org events into the now empty calendar. Needless to say, don't do that if you have new events in your calendar which are not synced yet...

Deleting many events can be slow, though; in that case, just delete the calendar and re-create it, delete the sync state file in ~/.emacs.d and restart Emacs.

Syncing with more than one calendar

This can be done by setting the variable org-caldav-calendars. It should be a list of plists (a 'plist' is simply a list with alternating :key's and values). Through these plists, you can override the global values of variables like org-caldav-calendar-id, and calling org-caldav-sync will go through these plists in order.

Example:

(setq org-caldav-calendars
  '((:calendar-id "work@whatever" :files ("~/org/work.org")
     :inbox "~/org/fromwork.org")
    (:calendar-id "stuff@mystuff"
     :files ("~/org/sports.org" "~/org/play.org")
     :skip-conditions (regexp "soccer")
     :inbox "~/org/fromstuff.org")) )

This means that you have two calendars with IDs "work@whatever" and "stuff@mystuff". Both will be accessed through the global value of org-caldav-url, since the key :url isn't specified. The calendar "work@whatever" will be synced with the file 'work.org' and inbox 'fromwork.org', while "stuff@mystuff" with 'sports.org' and 'play.org', unless there's the string 'soccer' in the heading, and and inbox is 'fromstuff.org'. See the doc-string of org-caldav-calendars for more details on which keys you can use.

Additional stuff

See the doc-string of org-caldav-inbox if you want more flexibility in where new items should be put. Instead of simply providing a file, you can also choose an existing entry or headline.

Timezone problems

Timezone handling is plain horrible, and it seems every CalDAV server does it slightly differently, also using non-standard headers like X-WR-TIMEZONE. If you see items being shifted by a few hours, make really really sure you have properly set org-icalendar-timezone, and that your calendar is configured to use the same one.

If it still does not work, you can try setting org-icalendar-timezone to the string "UTC". This will put all events using UTC times and the server should transpose the time to the timezone you have set in your calendar preferences. For some servers (like SOGo) this might work better than setting a "real" timezone.

Troubleshooting

If org-caldav reports a problem with the given URL, please triple-check that the URL is correct. It must point to a valid calendar on your CalDAV server.

If the error is that the URL does not seem to accept DAV requests, you can additionally check with 'curl' by doing

 curl -D - -X OPTIONS --basic -u mylogin:mypassword URL

The output of this command must contain a 'DAV' header like this:

DAV: 1, 3, extended-mkcol, access-control, ... etc. ...

By default, org-caldav will put all kinds of debug output into the buffer *org-caldav-debug*. Look there if you're getting sync errors or if something plain doesn't work. If you're using an authinfo file and authentication doesn't work, set auth-info-debug to t and look in the *Messages* buffer. When you report a bug, please try to post the relevant portion of the *org-caldav-debug* buffer since it might be helpful to see what's going wrong. If Emacs throws an error, do

M-x toggle-debug-on-error

and try to replicate the error to get a backtrace.

You can also turn on excessive debugging by setting the variable org-caldav-debug-level to 2. This will also output the contents of the events into the debug buffer. If you send such a buffer in a bug report, please make very sure you have removed personal information from those events.

Known Bugs

  • Recurring events created or changed on the calendar side cannot be synced (they will work fine as long as you manage them in Org, though).

  • Syncing is currently pretty slow since everything is done synchronously.

  • Pretty much everything besides SUMMARY, DESCRIPTION and time is ignored in iCalendar (like 'LOCATION', for instance).

How syncing happens (a.k.a. my little CalDAV rant)

(This is probably not interesting, so you can just stop reading.)

CalDAV is a mess.

First off, it is based on WebDAV, which has its own fair share of problems. The main design flaw of CalDAV however, is that UID and ressource name (the "filename", if you want) are two different things. I know that there are reasons for that (not everything has a UID, like timezones, and you can put several events in one ressource), but this is typical over-engineering to allow some marginal use cases pretty much no one needs. Another problem is that you have to do additional round-trips to get Etag and sequence number, which makes CalDAV pretty slow.

Org-caldav takes the easy route: it assumes that every ressource contains one event, and that UID and ressource name are identical. In fact, Google's CalDAV interface even enforces the latter. And while Owncloud does not enforce it, at least it just does it if you create items in its web interface.

However, the CalDAV standard does not demand this, so I guess there are servers out there with which org-caldav does not work. Patches welcome.

Now, all this would be bad enough if it weren't for the sloppy server implementations which make implementing a CalDAV client a living hell and led to several rewrites of the code. Especially Google, the 500 pound gorilla in the room, doesn't really care much for CalDAV. I guess they really like their own shiny REST-based calendar API better, and I can't blame them for that.