simono41 / gocal

ICS file parser in Golang

gocal

Fast (and opinionated) ICAL parser in Golang.

Gocal takes an io.Reader and produces an array of Events from it.

Event are parsed between two given dates (Gocal.Start and Gocal.End, 3 months by default). Any event outside this range will be ignored. This behavior can be disabled by setting SkipBounds to true in the Gocal struct. Please note that the behavior will still be enacted for recurring event, to prevent infinite parsing.

Usage

package main

import (
  "github.com/apognu/gocal"
)

func main() {
  f, _ := os.Open("/tmp/mycalendar.ics")
  defer f.Close()

  start, end := time.Now(), time.Now().Add(12*30*24*time.Hour)

  c := gocal.NewParser(f)
  c.Start, c.End = &start, &end
  c.Parse()

  for _, e := range c.Events {
    fmt.Printf("%s on %s by %s", e.Summary, e.Start, e.Organizer.Cn)
  }
}

Timezones

Timezones specified in TZID attributes are parsed and expected to be parsable by Go's time.LoadLocation() method. If you have an ICS file using some other form of representing timezones, you can specify the mapping to be used with a callback function:

var tzMapping = map[string]string{
  "My Super Zone": "Asia/Tokyo",
  "My Ultra Zone": "America/Los_Angeles",
}

gocal.SetTZMapper(func(s string) (*time.Location, error) {
  if tzid, ok := tzMapping[s]; ok {
    return time.LoadLocation(tzid)
  }
  return nil, fmt.Errorf("")
})

If this callback returns an error, the usual method of parsing the timezone will be tried. If both those methods fail, the date and time will be considered UTC.

Custom X-* properties

Any property starting with X- is considered a custom property and is unmarshalled in the event.CustomAttributes map of string to string. For instance, a X-LABEL would be accessible through event.CustomAttributes["X-LABEL"].

Recurring rules

Recurring rule are automatically parsed and expanded during the period set by Gocal.Start and Gocal.End.

That being said, I try to handle the most common situations for RRULEs, as well as overrides (EXDATEs and RECURRENCE-ID overrides).

This was tested only lightly, I might not cover all the cases.

Strict mode

By default, any error in parsing an event will result in the whole feed being aborted altogether (this includes missing or invalid attributes). You can change strict mode's behavior by changing the Strict.Mode attribute of the Gocal struct, with the following behavior:

• StrictModeFailFeed - default, abort parsing of the whole feed
• StrictModeFailEvent - skip the current event
• StrictModeFailAttribute - skip parsing of the failing attribute, set the Valid attribute of the event to false

Duplicate attribute behavior

The behavior when an attribute is duplicated can be customized with the Duplicate.Mode field. The default is to follow the configured strict mode behavior, but you can relax those rule by instructing Gocal to keep either the first or last value.

• DuplicateModeFailStrict
• DuplicateModeKeepFirst
• DuplicateModeKeepLast

Limitations

I do not pretend this abides by RFC 5545, this only covers parts I needed to be parsed for my own personal use. Among other, most property parameters are not handled by the library, and, for now, only the following properties are parsed:

• UID
• SUMMARY / DESCRIPTION
• DTSTART / DTEND / DURATION (day-long, local, UTC and TZIDd)
• DTSTAMP / CREATED / LAST-MODIFIED
• LOCATION
• STATUS
• ORGANIZER (CN; DIR and value)
• ATTENDEEs (CN, DIR, PARTSTAT and value)
• ATTACH (FILENAME, ENCODING, VALUE, FMTTYPE and value)
• CATEGORIES
• GEO
• RRULE
• X-*

Also, we ignore whatever's not a VEVENT.