The Time Zone Data Distribution Service (TZDIST) Geolocate Extension
draft-murchison-tzdist-geolocate-02

Abstract

This document defines an extension to the Time Zone Data Distribution Service (RFC 7808) to allow a client to determine the correct time zone for a geographic point location using a 'geo' URI (RFC 5870).

Status of This Memo

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Copyright Notice

Copyright (c) 2018 IETF Trust and the persons identified as the document authors. All rights reserved.

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Table of Contents

• 1. Introduction
• 2. Conventions Used in This Document
• 3. "geolocate" Action
• 3.1. Examples: geolocate action
• 4. Security Considerations
• 5. Privacy Considerations
• 6. IANA Considerations
• 6.1. Service Action Registration
• 6.2. Registration of invalid-location Error URN
• 7. Acknowledgments
• 8. References
• 8.1. Normative References
• 8.2. Informative References
• Appendix A. Change History (To be removed by RFC Editor before publication)
• Author's Address

1. Introduction

Clients using a Time Zone Data Distribution Service (TZDIST), particularly mobile clients, may not have prior knowledge of which time zone is appropriate for a particular geographic region. This specification defines a new TZDIST service action to allow a client to query a server with a geographic point location and have that server determine if the location lies within the boundaries of an existing time zone and return the corresponding time zone identifier.

This specification does not define the source of the time zone boundary data. It is assumed that a reliable and accurate source is available. One such source is the Time Zone Boundary Builder.

2. Conventions Used in This Document

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119].

This specification contains examples of HTTP requests and responses. In some cases, additional line breaks have been introduced into the request or response data to match maximum line-length limits of this document.

3. "geolocate" Action

Name:

geolocate

Request-URI Template:

{/service-prefix,data-prefix}/zones{?location}

Description:

This action allows a client to query the time zone data distribution service for the time zone identifier corresponding to the given geographic point location, specified as a 'geo' URI.

If the 'geo' URI specifies an uncertainty value (";u=" parameter), the server MUST return the time zone identifiers for all time zones whose boundary passes through the radius of uncertainty. In the absence of a client-supplied uncertainty value, the server MAY use an implicit uncertainty to coincide with any uncertainty in the time zone boundary data that it uses.

If the 'geo' URI specifies a coordinate reference system (";crs=" parameter) that is unsupported by the server, the server SHOULD return a JSON "problem details" object in the response body including a "type" member with an "invalid-location" error URN as defined below.

Parameters:

location=<geo-URI>

REQUIRED, and MUST occur only once.

Response:

The response has the same format as the "list" and "find" actions (see [RFC7808] Section 6.2), with one result object for each geolocated time zone. If for any reason the server can not determine a time zone in which the point is located (e.g. uninhabited location), it MUST return a "list" response containing zero time zone objects.

Possible Error Codes

urn:ietf:params:tzdist:error:invalid-location

The "location" URI query parameter has an incorrect or unsupported value or appears more than once.

3.1. Examples: geolocate action

The examples below presume that the timezone context path has been discovered (see [RFC7808] Section 4.2.1) to be "/tzdist".

In this example the client asks for the time zone corresponding to the Royal Observatory, Greenwich.

>> Request <<

GET /tzdist/zones?location=geo:51.47778,0.001388889 HTTP/1.1
Host: tz.example.com

>> Response <<

HTTP/1.1 200 OK
Date: Thu, 09 Nov 2017 13:43:28 GMT
Content-Type: application/json; charset="utf-8"
Content-Length: xxxx

{
  "synctoken": "2860088640-1510059107",
  "timezones": [
    {
      "tzid": "Europe/London",
      "etag": "873664-1510059107",
      "last-modified": "2017-11-07T12:51:47Z",
      "publisher": "IANA Time Zone Database",
      "version": "2017c",
      "aliases": [
        "GB",
        "GB-Eire",
        "Europe/Isle_of_Man",
        "Europe/Guernsey",
        "Europe/Belfast",
        "Europe/Jersey"
      ]
    }
  ]
}

In this example the client asks for the timezone corresponding to the Niagara Falls with an uncertainty of 50m. Note that the cataracts are located on the border of Ontario, Canada, and New York, United States, and therefore straddle a time zone boundary.

>> Request <<

GET /tzdist/zones?location=geo:43.0799,-79.0747;u=50 HTTP/1.1
Host: tz.example.com

>> Response <<

HTTP/1.1 200 OK
Date: Thu, 09 Nov 2017 13:58:07 GMT
Content-Type: application/json; charset="utf-8"
Content-Length: xxxx

{
  "synctoken": "2860088640-1510059107",
  "timezones": [
    {
      "tzid": "America/New_York",
      "etag": "6602582-1510059107",
      "last-modified": "2017-11-07T12:51:47Z",
      "publisher": "IANA Time Zone Database",
      "version": "2017c",
      "aliases": [
        "US/Eastern"
      ]
    },
    {
      "tzid": "America/Toronto",
      "etag": "3297806-1510059107",
      "last-modified": "2017-11-07T12:51:47Z",
      "publisher": "IANA Time Zone Database",
      "version": "2017c",
      "aliases": [
        "America/Montreal",
        "Canada/Eastern"
      ]
    }
  ]
}

4. Security Considerations

This specification does not introduce any additional security concerns beyond those described in Section 8 of [RFC7808]

5. Privacy Considerations

A client that uses this extension will leak the precise location of a user's device. The strategies described in Section 9 of [RFC7808] can be used to diminish the ability of an untrusted server or network observer to track the device.

6. IANA Considerations

6.1. Service Action Registration

This document defines the following new TZDIST Service Action to be added to the registry defined in Section 10.3.1 of [RFC7808]:

6.2. Registration of invalid-location Error URN

This section registers the "urn:ietf:params:tzdist:error:invalid-location" URN in the "TZDIST Identifiers" registry defined in Section 10.4 of [RFC7808].

URN:

urn:ietf:params:tzdist:error:invalid-location

Description:

Error code for incorrect use of the "location" URI query parameter.

Specification:

RFCXXXX, Section 3

Contact:

IESG <iesg@ietf.org>

Index value:

N/A.

7. Acknowledgments

The author would like to thank the following individuals for contributing their ideas and support for writing this specification: Cyrus Daboo and Michael Douglass.

8. References

8.1. Normative References

8.2. Informative References

Appendix A. Change History (To be removed by RFC Editor before publication)

Changes since -01:

• Minor editorial changes.

Changes since -00:

• Updated author information.
• Changed locations used in examples.
• Closed issue "percent-encode 'geo' URI value" as unnecessary.
• Closed issue "advertise supported coordinate reference system" as unnecessary (only "wgs84" is defined for RFC 5870).
• Closed issue "discuss territorial and/or international waters" as unnecessary.
• Added privacy concern.
• Minor editorial changes.

Author's Address