Send calendar invites via email based on calendar feeds.

Support includes:

• humanity.com
• doodle.com
• ferienwiki.de
• calendarlabs.com

Microsoft Outlook does not display subscribed calendar (ics) feeds to other people even though they have access to the personal calendar. To work around this limitation, this tool fetches feeds for multiple people, turns the feed into seperate events, and sends them as meeting invitation emails. It keeps track of the sent invitations and sends updates or cancellations.

Originally created for a team of 150 people scheduled using humanity.com, the tool supports multiple ics feed publishers thanks to a flexible configuration system. Technically, other actions than sending emails could be triggered based on changes in the feed.

You can run the example as follows:

git clone https://github.com/adrium/icsinviter.git
cd icsinviter/example
echo '{}' > events.json
python ../icsinviter.py config.json
less output.eml

The configuration is read from multiple JSON files and the keys are merged recursively. Files to be loaded are specified as command line parameters.

The configuration can be split into multiple files. This allows for example to set permissions on the cmd parameters, or update part of it easily, such as the feeds list.

A complete example can be found in example/config.json.

All configuration parameters are described in the following sections.

Default: false

Perform a dry run: Download feeds and detect changes, but do not send any emails, nor update the state file.

Filename of the state file.

Copies of sent events and updates to the configured email addresses are written to this JSON file.

The tool removes events:

• After a cancellation is sent
• If they are filtered (see filter parameter)
• For email addresses without an entry in the feeds parameter

Note: The file should be initialized manually with {} as content.

Mapping of configured email addresses to feed links.

Events and updates of the feed are sent to the respective email address. The tool will keep events of unavailable or invalid feeds.

Hint: To temporarily disable a feed, an invalid feed link could be set.

Hint: This parameter could be set in a different configuration file for maintenance by another tool.

External tools to retrieve feeds and send emails.

Non-zero exit codes or messages on stderr are treated as a failure.

Feed retrieval shell command.

• Receives the URL as last parameter
• Is expected to return the content on stdout

Email delivery shell command.

• Receives the content of the email on stdin
• stdout is ignored

Default: "uid"

Event key.

• Events are identified by this property and compared with events in the state file
• New events in the feed are sent
• Missing events in the feed are cancelled
• Filtered events are neither sent nor cancelled

Default: {}

Filter events.

The dict consists of event keys and filters. Filters can be specified as dict with an operator op and a value value keys. Operator can be: < > = ~ (regex search)

It is recommended to only include events in the future:

{ "dtstart": { "op": ">", "value": "%Y%m%d", 'methods': ['request','cancel'] } }

The methods parameter is optional.

Values containing a % are used as a format string for strftime.

Default: []

Detect event updates.

Compare the listed properties and send an event update, if any of those changed.

Note: Comparison should not be done using updated properties.

Default: {}

Static variables for use in the template.

Built-in variables are:

• mail_to contains the email address associated with the feed
• uuid a UUID that is generated for every render operation
• now a datetime object with the start of the program
• ics the ics file

Values containing a % are used as a format string for strftime.

Default: {}

Update event properties.

The dict consists of keys and values with the name of the event property that should be updated. Values are interpolated in the same way as templates.

Default: {}

Update event properties.

The dict consists of keys with the name of the event property and a dict containing a pattern and repl key that will be used as parameters for a regex replacement.

Templates for sending emails.

The configuration parameter is a dict with two keys: request and cancel and a filename as value.

The templates are interpolated using str.format and the var dict. Additionally, all properties of the VCALENDAR and VEVENT properties are available in the templates.

See example/template.eml for ideas.

The included parser can be used seperately:

imc.toDict(imc)
imc.fromDict(imcdict)

IMC stands for Internet Mail Consortium, the original creators of the iCalendar and vCard formats. The parser is flexible and can handle any input that "looks" like any of the formats above.

• Arrays of objects are created with a BEGIN:NAME and a matching END:NAME definition
• Property parameters are stored in a dict named like the property name with the suffix appended

There are some caveats:

• Multiple equally-named properties can not be handled
• Quoting and encodings are not supported

An example can be found in testdata/arbitrary.ics. It will be turned into testdata/arbitrary.json and vice-versa.