Adapters

Every adapter sends one request at a time, through no proxy — not even one of the environment's, which would resolve the host past the private network guard —, follows no redirect, bounds the silence of the service to 10 seconds and the whole request to 30, and reads at most 10 MiB of an answer. A 401 or a 403 is ProviderFailed::unauthorized(), another error status ProviderFailed::status(), no answer ProviderFailed::unreachable().

ics: a published feed

IcsFeed reads a calendar published as an iCalendar feed: the secret address Google, Microsoft, Apple or Proton give for a calendar. It only reads.

• Calendar: the address of the feed; webcal:// and webcals:// are read as https://.
• Credentials: none. The address is often the feed's only secret: keep it as a credential.
• Transport: phil/safe-http, which refuses a host on a private network, checks each redirect it follows, and stops at 10 MiB; a feed cut there is refused.

caldav: a CalDAV collection

CalDav reads and writes a calendar collection of a CalDAV server (RFC 4791): Nextcloud, Fastmail, iCloud, Radicale.

• Calendar: the https address of the collection, without a query or a fragment.
• Credentials: a user name and an application password, or a bearer token.
• Busy times: the free-busy-query report (§7.10), which answers with times only. A server that answers 400, 404, 405, 415, 422 or 501 to it is asked a calendar-query for the times of the events — start, end, duration, rule, dates, status, transparency —, expanded by the server; the reader expands them again when the server does not.
• Events: written with PUT at <collection>/<SHA-256 of the identifier>.ics, so no identifier can become a path, and deleted at that address; 404 and 410 to a removal are not errors.
• Transport: Symfony's NoPrivateNetworkHttpClient around the client given, so a host that is or resolves to a private network is refused. resolve pins a host to an address, still checked.
• Multistatus: read with ext-dom, without network access; a document type is refused.

google: Google Calendar

GoogleCalendar reads and writes a Google calendar through the Google Calendar API v3.

• Calendar: the calendar identifier, primary or an address such as abc123@group.calendar.google.com.
• Credentials: an OAuth access token, with the scope calendar.freebusy to read and calendar.events to write.
• Busy times: freeBusy, which answers with times only. An error of the calendar in the answer is ProviderFailed::refused() with Google's reason, such as notFound.
• Events: kept under an identifier derived from the event's, its SHA-256 in hexadecimal, which Google's alphabet admits. A write replaces the event, and inserts it when Google answers 404. A time in a named zone is written in it; a time with an offset only, in UTC.

microsoft: Microsoft Graph

MicrosoftGraph reads and writes an Outlook calendar of a Microsoft 365 or Outlook.com account, through Microsoft Graph v1.0.

• Calendar: the Graph identifier of a calendar of the signed-in user, or primary for their default calendar.
• Credentials: an OAuth access token, with Calendars.ReadBasic to read and Calendars.ReadWrite to write.
• Busy times: the calendar view, asking only for each event's start, end, availability and cancellation, in UTC. Free and "working elsewhere" events and cancelled ones are left out, tentative ones kept as tentative. At most 20 pages of 500 events; a next page is followed only on graph.microsoft.com.
• Events: found again by an extended property that holds the event's identifier, updated when found, created otherwise, deleted when found. Times are written in UTC, whole days as midnight to midnight.