MSC4175: Profile field for user time zone (#4175)
* MSC4175: Profile field for user time zone * Expand security section. * Fix typos. Co-authored-by: Will Hunt <will@half-shot.uk> * Updates. * Update with concerns * Add additional required info * Typo fix * Review comments. Co-authored-by: Travis Ralston <travisr@matrix.org> * Typo fix Co-authored-by: Hubert Chathi <hubert@uhoreg.ca> * Add examples --------- Co-authored-by: Will Hunt <will@half-shot.uk> Co-authored-by: Travis Ralston <travisr@matrix.org> Co-authored-by: Hubert Chathi <hubert@uhoreg.ca>pull/4346/head
Patrick Cloke
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# MSC4175: Profile field for user time zone
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Knowing another user's time zone is useful for knowing whether they are likely
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to respond or not. Example uses include:
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* Showing a user's time zone or time zone offset directly.
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* Showing a user's local time (with hints of whether it is day or night there).
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## Proposal
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Profiles can provide an optional `m.tz` field with values equal to names from the
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[IANA Time Zone Database](https://www.iana.org/time-zones).
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Clients can set and fetch this via the [normal API endpoints](https://spec.matrix.org/v1.14/client-server-api/#profiles).
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* Servers MAY validate that the value is a valid IANA time zone. If deemed invalid
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they MUST return a 400 error with error code `M_INVALID_PARAM`.
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* Clients MUST handle invalid or unknown values. One approach may be processing the value as though it was never set.
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The rationale for somewhat loose validation is that different clients/servers may have
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different understanding of valid time zones, e.g. different versions of the time zone
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database.
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If the field is not provided, it SHOULD be interpreted as having no time zone information
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for that user.
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An example request to set the time zone would be:
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```
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PUT /_matrix/client/v3/profile/@alice:example.org/m.tz
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{
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"m.tz": "America/New_York"
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}
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```
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Similarly when retrieving a user's profile:
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```
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GET /_matrix/client/v3/profile/@alice:example.org
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{
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"displayname": "Alice",
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"m.tz": "Europe/Paris"
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}
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```
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## Potential issues
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Clients may need to understand IANA time zone names to show useful information to users.
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Some languages make this easy, e.g. JavaScript can handle this using
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[`Date.toLocaleString()`](https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date/toLocaleString).
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This may cause clients to bundle the IANA time zone database (and thus also keep it
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up to date).
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Using the IANA time zone name has the downside that it does now allow arbitrary offsets,
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which may be required for time zones which are not internationally recognized.
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Clients will need to manually update the profile field when the user changes time zone.
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This could be automated by clients based on location, or left as a manual change to
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users.
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Clients may wish to periodically fetch the time zone of other users as it is
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liable to change somewhat frequently. Currently, profile data isn't propagated/synchronized
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between servers, but that's left to a future MSC to solve. It is recommended that
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clients cache the value for 12 - 24 hours.
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There should not be backwards compatibility concerns since clients should be ignoring
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unknown profile fields.
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## Alternatives
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The time zone offset could be included directly (in minutes/seconds or in `[+-]HH:MM` form).
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This would require clients to manually update the profile field during daylight
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savings. Using the IANA time zone name is robust against this.
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### Delegate profile fields
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There are several standards related to storing of contact information electronically,
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notably vCard and its derivatives (see below). It is unclear if Matrix profile
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information is similar enough to the contact information found in vCard to warrant using
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that format directly, although there is certainly some overlap.
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Some of the JSON formats for vCard which include time zone information are detailed below:
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[RFC7095: jCard The JSON Format for vCard](https://datatracker.ietf.org/doc/html/rfc7095)
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format could be used instead, but this doesn't make much sense unless the entire
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profile was replaced.
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[RFC9553](https://datatracker.ietf.org/doc/html/rfc9553) offers an alternative
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representation for contacts (which is not backwards compatible with vCard). There
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exists `timeZone` field under the `addresses` field which uses an time zone name
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from the IANA Time Zone Database.
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Note there's an alternative [jCard](https://microformats.org/wiki/jCard) format
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which is a non-standard derivative of [hCard](https://microformats.org/wiki/hcard).
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### Competitive analysis
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Slack's [`users.info` API call](https://api.slack.com/methods/users.info) includes
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3 separate fields:
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* `tz`: the time zone database name (e.g. `"America/New_York"`)
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* `tz_label`: a friendly name (e.g. `"Eastern Daylight Time"`)
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* `tz_offset`: offset in seconds as an integer (e.g. `-14400`)
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XMPP uses either:
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* [XEP-054](https://xmpp.org/extensions/xep-0054.html) uses vCard
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([RFC2426](https://datatracker.ietf.org/doc/html/rfc2426)) converted to XML via
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[draft-dawson-vcard-xml-dtd-01](https://datatracker.ietf.org/doc/html/draft-dawson-vcard-xml-dtd-01)
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* [XEP-0292](https://xmpp.org/extensions/xep-0292.html) uses xCard: vCard XML Representation
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([RFC6351](https://datatracker.ietf.org/doc/html/rfc6351)), see also vCard4
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([RFC6351](https://datatracker.ietf.org/doc/html/rfc6351))
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Rocket.Chat provides a user's [time zone offset](https://developer.rocket.chat/docs/user)
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in the `utcOffset` field.
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Mattermost [returns an object](https://api.mattermost.com/#tag/users/operation/GetUser)
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with the user's manual and/or automatic IANA time zone name.
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Discord, Twitter, and IRC don't provide a user's time zone.
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## Security considerations
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Showing a user's time zone gives some information to their location. There is currently
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no way to limit what profile fields other users can see.
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Clients may wish to warn users when providing a time zone and give
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the option to not include it in their profile.
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## Unstable prefix
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`us.cloke.msc4175.tz` should be used in place of `m.tz`.
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Clients may immediately use the stable profile field once this MSC is accepted. This is
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a client-to-client protocol and no feature negotiation is necessary.
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## Dependencies
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Requires [MSC4133](https://github.com/matrix-org/matrix-spec-proposals/pull/4133).
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