diff --git a/proposals/4175-profile-field-time-zone.md b/proposals/4175-profile-field-time-zone.md new file mode 100644 index 00000000000..f68fff48c01 --- /dev/null +++ b/proposals/4175-profile-field-time-zone.md @@ -0,0 +1,148 @@ +# MSC4175: Profile field for user time zone + +Knowing another user's time zone is useful for knowing whether they are likely +to respond or not. Example uses include: + +* Showing a user's time zone or time zone offset directly. +* Showing a user's local time (with hints of whether it is day or night there). + + +## Proposal + +Profiles can provide an optional `m.tz` field with values equal to names from the +[IANA Time Zone Database](https://www.iana.org/time-zones). +Clients can set and fetch this via the [normal API endpoints](https://spec.matrix.org/v1.14/client-server-api/#profiles). + +* Servers MAY validate that the value is a valid IANA time zone. If deemed invalid + they MUST return a 400 error with error code `M_INVALID_PARAM`. +* Clients MUST handle invalid or unknown values. One approach may be processing the value as though it was never set. + +The rationale for somewhat loose validation is that different clients/servers may have +different understanding of valid time zones, e.g. different versions of the time zone +database. + +If the field is not provided, it SHOULD be interpreted as having no time zone information +for that user. + +An example request to set the time zone would be: + +``` +PUT /_matrix/client/v3/profile/@alice:example.org/m.tz + +{ + "m.tz": "America/New_York" +} +``` + +Similarly when retrieving a user's profile: + +``` +GET /_matrix/client/v3/profile/@alice:example.org + +{ + "displayname": "Alice", + "m.tz": "Europe/Paris" +} +``` + + +## Potential issues + +Clients may need to understand IANA time zone names to show useful information to users. +Some languages make this easy, e.g. JavaScript can handle this using +[`Date.toLocaleString()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date/toLocaleString). +This may cause clients to bundle the IANA time zone database (and thus also keep it +up to date). + +Using the IANA time zone name has the downside that it does now allow arbitrary offsets, +which may be required for time zones which are not internationally recognized. + +Clients will need to manually update the profile field when the user changes time zone. +This could be automated by clients based on location, or left as a manual change to +users. + +Clients may wish to periodically fetch the time zone of other users as it is +liable to change somewhat frequently. Currently, profile data isn't propagated/synchronized +between servers, but that's left to a future MSC to solve. It is recommended that +clients cache the value for 12 - 24 hours. + +There should not be backwards compatibility concerns since clients should be ignoring +unknown profile fields. + + +## Alternatives + +The time zone offset could be included directly (in minutes/seconds or in `[+-]HH:MM` form). +This would require clients to manually update the profile field during daylight +savings. Using the IANA time zone name is robust against this. + + +### Delegate profile fields + +There are several standards related to storing of contact information electronically, +notably vCard and its derivatives (see below). It is unclear if Matrix profile +information is similar enough to the contact information found in vCard to warrant using +that format directly, although there is certainly some overlap. + +Some of the JSON formats for vCard which include time zone information are detailed below: + +[RFC7095: jCard The JSON Format for vCard](https://datatracker.ietf.org/doc/html/rfc7095) +format could be used instead, but this doesn't make much sense unless the entire +profile was replaced. + +[RFC9553](https://datatracker.ietf.org/doc/html/rfc9553) offers an alternative +representation for contacts (which is not backwards compatible with vCard). There +exists `timeZone` field under the `addresses` field which uses an time zone name +from the IANA Time Zone Database. + +Note there's an alternative [jCard](https://microformats.org/wiki/jCard) format +which is a non-standard derivative of [hCard](https://microformats.org/wiki/hcard). + + +### Competitive analysis + +Slack's [`users.info` API call](https://api.slack.com/methods/users.info) includes +3 separate fields: + +* `tz`: the time zone database name (e.g. `"America/New_York"`) +* `tz_label`: a friendly name (e.g. `"Eastern Daylight Time"`) +* `tz_offset`: offset in seconds as an integer (e.g. `-14400`) + +XMPP uses either: + +* [XEP-054](https://xmpp.org/extensions/xep-0054.html) uses vCard + ([RFC2426](https://datatracker.ietf.org/doc/html/rfc2426)) converted to XML via + [draft-dawson-vcard-xml-dtd-01](https://datatracker.ietf.org/doc/html/draft-dawson-vcard-xml-dtd-01) +* [XEP-0292](https://xmpp.org/extensions/xep-0292.html) uses xCard: vCard XML Representation + ([RFC6351](https://datatracker.ietf.org/doc/html/rfc6351)), see also vCard4 + ([RFC6351](https://datatracker.ietf.org/doc/html/rfc6351)) + +Rocket.Chat provides a user's [time zone offset](https://developer.rocket.chat/docs/user) +in the `utcOffset` field. + +Mattermost [returns an object](https://api.mattermost.com/#tag/users/operation/GetUser) +with the user's manual and/or automatic IANA time zone name. + +Discord, Twitter, and IRC don't provide a user's time zone. + + +## Security considerations + +Showing a user's time zone gives some information to their location. There is currently +no way to limit what profile fields other users can see. + +Clients may wish to warn users when providing a time zone and give +the option to not include it in their profile. + + +## Unstable prefix + +`us.cloke.msc4175.tz` should be used in place of `m.tz`. + +Clients may immediately use the stable profile field once this MSC is accepted. This is +a client-to-client protocol and no feature negotiation is necessary. + + +## Dependencies + +Requires [MSC4133](https://github.com/matrix-org/matrix-spec-proposals/pull/4133).