iCalDAV

A Kotlin CalDAV client with offline sync and conflict resolution. Sync calendars with iCloud, Nextcloud, and other CalDAV servers.

RFC Compliance

RFC	Title	Status
RFC 5545	iCalendar Core (VEVENT, VTODO, VJOURNAL, RRULE)	✅ Full
RFC 5546	iTIP (iCalendar Transport-Independent Interoperability)	✅ Full
RFC 4918	WebDAV (PROPFIND, REPORT, PUT, DELETE)	✅ Full
RFC 4791	CalDAV (calendar-query, calendar-multiget)	✅ Full
RFC 6578	WebDAV Sync (sync-collection, sync-token)	✅ Full
RFC 3744	WebDAV ACL (access control, privileges)	✅ Full
RFC 6638	CalDAV Scheduling (iTIP delivery, free-busy)	✅ Full
RFC 7986	New iCalendar Properties (COLOR, IMAGE, CONFERENCE)	✅ Full
RFC 9073	Event Publishing Extensions (VLOCATION, PARTICIPANT)	✅ Full
RFC 9074	VALARM Extensions (ACKNOWLEDGED, UID, PROXIMITY)	✅ Full
RFC 9253	iCalendar Relationships (LINK, enhanced RELATED-TO)	✅ Full
RFC 6047	iMIP (email-based scheduling)	⬜ Out of scope

Features

iCalendar (RFC 5545)

• Complete VEVENT, VTODO, and VJOURNAL parsing and generation
• Recurring events (RRULE, RDATE, EXDATE, RECURRENCE-ID)
• Access classification (CLASS property: PUBLIC, PRIVATE, CONFIDENTIAL)
• All-day and multi-day event support
• Timezone handling with VTIMEZONE and timezone distribution service
• Alarms (VALARM) with DISPLAY, EMAIL, and AUDIO actions

CalDAV Protocol

• CalDAV client with automatic server discovery
• WebDAV ACL support (RFC 3744) - read and modify access control
• CalDAV Scheduling (RFC 6638) with iTIP message building
• Sync engine with offline support and conflict resolution
• Provider quirks handling (iCloud, Nextcloud, Radicale, Baikal)

Installation

// build.gradle.kts
dependencies {
    implementation("org.onekash:icaldav-client:2.6.2")

    // Optional: Sync engine with offline support
    implementation("org.onekash:icaldav-sync:2.6.2")

    // Optional: Android CalendarContract mapper (API 21+)
    implementation("org.onekash:icaldav-android:2.6.2")
}

Requirements: JVM 17+, Kotlin 1.9+. Android module requires API 21+.

Quick Start

import org.onekash.icaldav.client.CalDavClient
import org.onekash.icaldav.model.ICalEvent
import org.onekash.icaldav.model.ICalDateTime
import org.onekash.icaldav.model.DavResult
import java.time.Instant
import java.time.temporal.ChronoUnit
import java.util.UUID

// Create client
val client = CalDavClient.forProvider(
    serverUrl = "https://caldav.example.com",
    username = "[email protected]",
    password = "password"
)

// Discover calendars
val discovery = client.discoverAccount("https://caldav.example.com")
if (discovery is DavResult.Success) {
    val calendarUrl = discovery.value.calendars.first().href

    // Create event
    val event = ICalEvent(
        uid = UUID.randomUUID().toString(),
        summary = "Team Meeting",
        dtStart = ICalDateTime.fromInstant(Instant.now()),
        dtEnd = ICalDateTime.fromInstant(Instant.now().plus(1, ChronoUnit.HOURS))
    )

    val createResult = client.createEvent(calendarUrl, event)
    if (createResult is DavResult.Success) {
        val (href, etag) = createResult.value

        // Update event
        val updated = event.copy(summary = "Team Meeting (Updated)")
        client.updateEvent(href, updated, etag)

        // Delete event
        client.deleteEvent(href, etag)
    }

    // Fetch events in date range
    val start = Instant.now()
    val end = Instant.now().plus(30, ChronoUnit.DAYS)
    val events = client.fetchEvents(calendarUrl, start, end)
}

Error Handling

All operations return DavResult<T>:

when (val result = client.fetchEvents(calendarUrl, start, end)) {
    is DavResult.Success -> handleEvents(result.value)
    is DavResult.HttpError -> println("HTTP ${result.code}: ${result.message}")
    is DavResult.NetworkError -> println("Network: ${result.exception.message}")
    is DavResult.ParseError -> println("Parse: ${result.message}")
}

Modules

Module	Purpose
icaldav-core	Parse and generate iCalendar (RFC 5545)
icaldav-client	CalDAV/WebDAV client with discovery and CRUD
icaldav-sync	Sync engine with offline support and conflict resolution
icaldav-android	Android CalendarContract mapper (API 21+)

Tested Providers

Provider	Notes
iCloud	CDATA responses, namespace quirks, regional redirects, app-specific passwords
Nextcloud	Standard CalDAV
Radicale	Direct URL access (skip discovery)
Baikal	sabre/dav based, standard CalDAV

Other CalDAV servers following RFC 4791 should work. Open an issue if you encounter problems.

Links

• Maven Central
• GitHub
• Contributing

License

Apache License 2.0