Network Working Group M. Douglass Internet-Draft RPI Intended status: Standards Track C. Daboo Expires: October 24, 2015 Apple April 22, 2015 Time Zone Data Distribution Service draft-ietf-tzdist-service-07 Abstract This document defines a time zone data distribution service that allows reliable, secure and fast delivery of time zone data and leap second rules to client systems such as calendaring and scheduling applications or operating systems. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at http://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on October 24, 2015. Copyright Notice Copyright (c) 2015 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Douglass & Daboo Expires October 24, 2015 [Page 1] Internet-Draft TZDIST Service April 2015 Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Conventions . . . . . . . . . . . . . . . . . . . . . . . 4 2. Architectural Overview . . . . . . . . . . . . . . . . . . . 5 3. General Considerations . . . . . . . . . . . . . . . . . . . 6 3.1. Time Zone . . . . . . . . . . . . . . . . . . . . . . . . 6 3.2. Time Zone Data . . . . . . . . . . . . . . . . . . . . . 7 3.3. Time Zone Meta-Data . . . . . . . . . . . . . . . . . . . 7 3.4. Time Zone Data Server . . . . . . . . . . . . . . . . . . 7 3.5. Observance . . . . . . . . . . . . . . . . . . . . . . . 7 3.6. Time Zone Identifiers . . . . . . . . . . . . . . . . . . 7 3.7. Time Zone Aliases . . . . . . . . . . . . . . . . . . . . 7 3.8. Time Zone Localized Names . . . . . . . . . . . . . . . . 8 3.9. Truncating Time Zones . . . . . . . . . . . . . . . . . . 8 3.10. Time Zone Versions . . . . . . . . . . . . . . . . . . . 9 4. Time Zone Data Distribution Service Protocol . . . . . . . . 10 4.1. Server Protocol . . . . . . . . . . . . . . . . . . . . . 10 4.1.1. Time Zone Queries . . . . . . . . . . . . . . . . . . 11 4.1.2. Time Zone Formats . . . . . . . . . . . . . . . . . . 11 4.1.3. Time Zone Localization . . . . . . . . . . . . . . . 11 4.1.4. Conditional Time Zone Requests . . . . . . . . . . . 12 4.1.5. Expanded Time Zone Data . . . . . . . . . . . . . . . 13 4.1.6. Server Requirements . . . . . . . . . . . . . . . . . 13 4.1.7. Error Responses . . . . . . . . . . . . . . . . . . . 13 4.1.8. Extensions . . . . . . . . . . . . . . . . . . . . . 14 4.2. Client Guidelines . . . . . . . . . . . . . . . . . . . . 14 4.2.1. Discovery . . . . . . . . . . . . . . . . . . . . . . 14 4.2.1.1. Time Zone Data Distribution Service SRV Service Labels . . . . . . . . . . . . . . . . . . . . . 15 4.2.1.2. Time Zone Data Distribution Service TXT records . 15 4.2.1.3. Time Zone Data Distribution Service Well-Known URI . . . . . . . . . . . . . . . . . . . . . . . 16 4.2.1.3.1. Example: well-known URI redirects to actual context path . . . . . . . . . . . . . . . . 16 4.2.2. Synchronization of Time Zones . . . . . . . . . . . . 16 4.2.2.1. Initial Synchronization of All Time Zones . . . . 17 4.2.2.2. Subsequent Synchronization of All Time Zones . . 17 4.2.2.3. Synchronization with Pre-Existing Time Zone Data 17 5. Actions . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 5.1. "capabilities" Action . . . . . . . . . . . . . . . . . . 18 5.1.1. Example: Get Capabilities . . . . . . . . . . . . . . 18 5.2. "list" Action . . . . . . . . . . . . . . . . . . . . . . 21 5.2.1. Example: List time zone identifiers . . . . . . . . . 21 5.3. "get" Action . . . . . . . . . . . . . . . . . . . . . . 22 5.3.1. Example: Get time zone data . . . . . . . . . . . . . 24 5.3.2. Example: Conditional Get time zone data . . . . . . . 24 5.3.3. Example: Get time zone data using a time zone alias . 25 Douglass & Daboo Expires October 24, 2015 [Page 2] Internet-Draft TZDIST Service April 2015 5.3.4. Example: Get truncated time zone data . . . . . . . . 25 5.3.5. Example: Get a non-existent time zone data . . . . . 26 5.4. "expand" Action . . . . . . . . . . . . . . . . . . . . . 27 5.4.1. Example: Expanded JSON Data Format . . . . . . . . . 28 5.5. "find" Action . . . . . . . . . . . . . . . . . . . . . . 29 5.5.1. Example: Find action . . . . . . . . . . . . . . . . 30 5.6. "leapseconds" Action . . . . . . . . . . . . . . . . . . 32 5.6.1. Example: Get leapsecond information . . . . . . . . . 32 6. JSON Definitions . . . . . . . . . . . . . . . . . . . . . . 33 6.1. capabilities action response . . . . . . . . . . . . . . 34 6.2. list/find action response . . . . . . . . . . . . . . . . 36 6.3. expand action response . . . . . . . . . . . . . . . . . 38 6.4. leapseconds action response . . . . . . . . . . . . . . . 40 7. New iCalendar Properties . . . . . . . . . . . . . . . . . . 40 7.1. Time Zone Upper Bound . . . . . . . . . . . . . . . . . . 40 7.2. Time Zone Identifier Alias Property . . . . . . . . . . . 41 8. Security Considerations . . . . . . . . . . . . . . . . . . . 42 9. Privacy Considerations . . . . . . . . . . . . . . . . . . . 43 10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 45 10.1. Service Actions Registration . . . . . . . . . . . . . . 45 10.1.1. Service Actions Registration Procedure . . . . . . . 45 10.1.2. Registration Template for Actions . . . . . . . . . 46 10.2. Initial Time Zone Data Distribution Service Registry . . 46 10.2.1. Actions Registry . . . . . . . . . . . . . . . . . . 46 10.3. timezone Well-Known URI Registration . . . . . . . . . . 47 10.4. Service Name Registrations . . . . . . . . . . . . . . . 47 10.4.1. timezone Service Name Registration . . . . . . . . . 47 10.4.2. timezones Service Name Registration . . . . . . . . 47 10.5. tzdist URN sub-namespace . . . . . . . . . . . . . . . . 48 10.6. iCalendar Property Registrations . . . . . . . . . . . . 48 11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 48 12. References . . . . . . . . . . . . . . . . . . . . . . . . . 49 12.1. Normative References . . . . . . . . . . . . . . . . . . 49 12.2. Informative References . . . . . . . . . . . . . . . . . 51 Appendix A. Change History (to be removed prior to publication as an RFC) . . . . . . . . . . . . . . . . . . . . . 51 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 55 1. Introduction Time zone data typically combines a coordinated universal time (UTC) offset with daylight saving time (DST) rules. Time zones are typically tied to specific geographic and geopolitical regions. Whilst the UTC offset for particular regions changes infrequently, DST rules can change frequently and sometimes with very little notice (maybe hours before a change comes into effect). Douglass & Daboo Expires October 24, 2015 [Page 3] Internet-Draft TZDIST Service April 2015 Calendaring and scheduling systems, such as those that use iCalendar [RFC5545], as well as operating systems, critically rely on time zone data to determine the correct local time. As such they need to be kept up to date with changes to time zone data. To date there has been no fast and easy way to do that. Time zone data is often supplied in the form of a set of data files that have to be "compiled" into a suitable database format for use by the client application or operating system. In the case of operating systems, often those changes only get propagated to client machines when there is an operating system update, which can be infrequent, resulting in inaccurate time zone data being present for significant amounts of time. In some cases, old versions of operating systems stop being supported, but are still in use and thus require users to manually "patch" their system to keep up to date with time zone changes. Along with time zone data, it is also important to track the use of leap seconds to allow a mapping between International Atomic Time (TAI) and UTC. Leap seconds can be added (or possibly removed) at various times of year in an irregular pattern typically determined by precise astronomical observations. The insertion of leap seconds into UTC is currently the responsibility of the International Earth Rotation Service. This specification defines a time zone data distribution service protocol that allows for fast, reliable and accurate delivery of time zone data and leap second information to client systems. This protocol is based on HTTP [RFC7230] using a simple JSON [RFC7159] based API. This specification does not define the source of the time zone data or leap second information. It is assumed that a reliable and accurate source is available. One such source is the IANA hosted time zone database [RFC6557]. Discussion of this document has taken place on the tzdist working group mailing list . 1.1. Conventions The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. Unless otherwise indicated, [RFC3339] UTC date-time values use a "Z" suffix, and not fixed numeric offsets. Douglass & Daboo Expires October 24, 2015 [Page 4] Internet-Draft TZDIST Service April 2015 2. Architectural Overview The overall process for the delivery of time zone data can be visualized via the diagram shown below. ==================== ==================== (a) | Contributors | | Contributors | ==================== ==================== | | ==================== ==================== (b) | Publisher A | | Publisher B | ==================== ==================== \ / ==================== (c) | Root Provider | ==================== / | \ / | \ ====================== | ====================== (d) | Secondary Provider | | | Secondary Provider | ====================== | ====================== | | | | | | | | ========== ========== ========== ========== (e) | Client | | Client | | Client | | Client | ========== ========== ========== ========== Figure 1: Time Zone Data Distribution Service Architecture The overall service is made up of several layers: (a) Contributors: Individuals, governments or organizations which provide information about time zones to the publishing process. There can be many contributors. Note this specification does not address how contributions are made. (b) Publishers: Publishers aggregate information from contributors, determine the reliability of the information and, based on that, generate time zone data. There can be many publishers, each getting information from many different contributors. In some cases a publisher may choose to "re-publish" data from another publisher. (c) Root Providers: Servers which obtain and then provide the time zone data from publishers and make that available to other servers or clients. There can be many root providers. Root providers can choose to supply time zone data from one or more publishers. Douglass & Daboo Expires October 24, 2015 [Page 5] Internet-Draft TZDIST Service April 2015 (d) Secondary Providers: Servers which handle the bulk of the requests and reduce the load on root servers. These will typically be simple caches of the root server, located closer to clients. For example a large Internet Service Provider (ISP) may choose to setup their own secondary provider to allow clients within their network to make requests of that server rather than making requests of servers outside their network. Secondary servers will cache and periodically refresh data from the root servers. (e) Clients: Applications, operating systems etc., that make use of time zone data and retrieve that from either root or secondary providers. Some of those layers may be coalesced by implementors. For example, a vendor may choose to implement the entire service as a single monolithic virtual server with the address embedded in distributed systems. Others may choose to provide a service consisting of multiple layers of providers, many secondary servers and a small number of root servers. This specification is concerned only with the protocol used to exchange data between providers and from provider to client. This specification does not define how contributors pass their information to publishers, nor how those publishers vet that information to obtain trustworthy data, nor the format of the data produced by the publishers. 3. General Considerations This section defines several terms and explains some key concepts used in this specification. 3.1. Time Zone A description of the past and predicted future timekeeping practices of a collection of clocks that are intended to agree. Note that the term "time zone" does not have the common meaning of a region of the world at a specific UTC offset, possibly modified by daylight saving time. For example, the "Central European Time" zone can correspond to several time zones "Europe/Berlin", "Europe/Paris", etc., because subregions have kept time differently in the past. Douglass & Daboo Expires October 24, 2015 [Page 6] Internet-Draft TZDIST Service April 2015 3.2. Time Zone Data Data that defines a single time zone, including an identifier, UTC offset values, DST rules, and other information such as time zone abbreviations. 3.3. Time Zone Meta-Data Data that describes additional properties of a time zone that is not itself including in the time zone data. This can include such things as the publisher name, version identifier, aliases, and localized names (see below). 3.4. Time Zone Data Server A server implementing the Time Zone Data Distribution Service Protocol defined by this specification. 3.5. Observance A time zone with varying rules for the UTC offset will have adjacent periods of time that use different UTC offsets. Such periods of time are called observances, with the total set covering the range of validity of the time zone data. 3.6. Time Zone Identifiers Time zone identifiers are unique names associated with each time zone, as defined by publishers. The iCalendar [RFC5545] specification has a "TZID" property and parameter whose value is set to the corresponding time zone identifier, and used to identify time zone data and relate time zones to start and end dates in events, etc. This specification does not define what format of time zone identifiers should be used. It is possible that time zone identifiers from different publishers overlap, and there might be a need for a provider to distinguish those with some form of "namespace" prefix identifying the publisher. However, development of a standard (global) time zone identifier naming scheme is out of scope for this specification. 3.7. Time Zone Aliases Time zone aliases map a name onto a time zone identifier. For example "US/Eastern" is usually mapped on to "America/New_York". Time zone aliases are typically used interchangeably with time zone identifiers when presenting information to users. Douglass & Daboo Expires October 24, 2015 [Page 7] Internet-Draft TZDIST Service April 2015 A time zone data distribution service needs to maintain time zone alias mapping information, and expose that data to clients as well as allow clients to query for time zone data using aliases. When returning time zone data to a client, the server returns the data with an identifier matching the query, but it can include one or more additional identifiers in the data to provide a hint to the client that alternative identifiers are available. For example, a query for "US/Eastern" could include additional identifiers for "America/ New_York" or "America/Montreal". The set of aliases may vary depending on whether time zone data is truncated (see Section 3.9). For example, a client located in the US state of Michigan may see "US/Eastern" as an alias for "America/ Detroit" whereas a client in the US state of New Jersey may see it as an alias for "America/New_York", and all three names may be aliases if time zones are truncated to post-2013 data. 3.8. Time Zone Localized Names Localized names are names for time zones which can be presented to a user in their own language. Each time zone may have one or more localized names associated with it. Names would typically be unique in their own locale as they might be presented to the user in a list. Localized names are distinct from abbreviations commonly used for UTC offsets within a time zone. For example, the time zone "America/ New_York" may have the localized name "Nueva York" in a Spanish locale, as distinct from the abbreviations "EST" and "EDT" which may or may not have their own localizations. A time zone data distribution service might need to maintain localized name information, for one or more chosen languages, as well as allow clients to query for time zone data using localized names. 3.9. Truncating Time Zones Time zone data can contain information about past and future UTC offsets that may not be relevant for a particular server's intended clients. For example, calendaring and scheduling clients are likely most concerned with time zone data that covers a period for one or two years in the past on into the future, as users typically create only new events for the present and future. Similarly, time zone data might contain a large amount of "future" information about transitions occurring many decades into the future. Again, clients might be concerned only with a smaller range into the future, and data past that point might be redundant. To avoid having to send unnecessary data, servers can choose to truncate time zone data to a range determined by start and end point Douglass & Daboo Expires October 24, 2015 [Page 8] Internet-Draft TZDIST Service April 2015 date and time values, and provide only offsets and rules between those points. If such truncation is done, the server MUST include the ranges it is using in the "capabilities" action response (see Section 6.1), so that clients can take appropriate action if they need time zone data for times outside of those ranges. The truncation points at the start and end of a range are always a UTC date-time value, with the start point being "inclusive" to the overall range, and the end point being "exclusive" to the overall range (i.e., the end value is just past the end of the last valid value in the range). A server will advertise a truncation range for the truncated data it can supply, or provide an indicator that it can truncate at any start or end point to produce arbitrary ranges. In addition, the server can advertise that it supplies untruncated data - that is data that covers the full range of times available from the source publisher. In the absence of any indication of truncated data available on the server, the server will supply only untruncated data. When truncating the start of a "VTIMEZONE" component, the server MUST include exactly one "STANDARD" or "DAYLIGHT" sub-component with a "DTSTART" property value that matches the start point of the truncation range, and appropriate "TZOFFSETFROM" and "TZOFFSETTO" properties to indicate the correct offset in effect right before and after the truncation range start point. This sub-component, which is the first observance defined by the time zone data, represents the earliest valid date-time covered by the time zone data in the truncated "VTIMEZONE" component. When truncating the end of a "VTIMEZONE" component, the server MUST include a "TZUNTIL" iCalendar property (Section 7.1) in the "VTIMEZONE" component to indicate the end point of the truncation range. 3.10. Time Zone Versions Time zone data changes over time and it is important for consumers of that data to stay up to date with the latest versions. As a result it is useful to identify individual time zones with a specific version number or version identifier as supplied by the time zone data publisher. There are two common models which time zone data publishers might use to publish updates to time zone data: a. with the "monolithic" model, the data for all time zones is published in one go, with a single version number or identifier applied to the entire data set. e.g., a publisher producing data several times a year might use version identifiers "2015a", "2015b", etc. Douglass & Daboo Expires October 24, 2015 [Page 9] Internet-Draft TZDIST Service April 2015 b. with the "incremental" model, each time zone has its own version identifier, so that each time zone can be independently updated without impacting any others. e.g., if the initial data has version "A.1" for time zone "A", and "B.1" for time zone "B", and then time zone "B" changes; when the data is next published, time zone "A" will still have version "A.1", but time zone "B" will now have "B.2". A time zone data distribution service needs to ensure that the version identifiers used by the time zone data publisher are available to any client, along with the actual publisher name on a per-time zone basis. This allows clients to compare publisher/ version details on any server, with existing locally cached client data, and only fetch those time zones which have actually changed (see Section 4.2.2 for more details on how clients synchronize data from the server). 4. Time Zone Data Distribution Service Protocol 4.1. Server Protocol The time zone data distribution service protocol uses HTTP [RFC7230] for query and delivery of time zone data and meta-data, and leap second information. The interactions with the HTTP server can be broken down into a set of "actions" that define the overall function being requested (see Section 5). Each action targets a specific HTTP resource using the GET method, with various request-URI parameters altering the behavior as needed. The HTTP resources used for requests will be identified via URI templates [RFC6570]. The overall time zone distribution service has a "context path" request-URI defined as "{/service-prefix}". This "root" prefix is discovered by the client as per Section 4.2.1. Request-URIs that target time zone data directly use the prefix "{/service-prefix,data-prefix}". The second component of the prefix template can be used to introduce additional path segments in the request-URI to allow for alternative ways to "partition" the time zone data. For example, time zone data might be partitioned by publisher release dates, or version identifiers. This specification does not define any partitions, which is left for future extensions. When the "data-prefix" variable is empty, the server is expected to return the current version of time zone data it has for all publishers it supports. All template-URI variable values, and URI request parameters that contain text values, MUST be encoded using the UTF-8 [RFC3629] character set. All responses MUST return data using the UTF-8 [RFC3629] character set. It is important to note that any "/" Douglass & Daboo Expires October 24, 2015 [Page 10] Internet-Draft TZDIST Service April 2015 characters, which are frequently found in time zone identifiers, are percent-encoded when used in the value of a path segment expansion variable in a URI template (as per Section 3.2.6 of [RFC6570]). Thus the time zone identifier "America/New_York" would appear as "America%2FNew_York" when used as the value for the "{/tzid}" URI template variable defined later in this specification. The server provides time zone meta-data in the form of a JSON [RFC7159] object. Clients can directly request the time zone meta- data, or issues queries for subsets of meta-data that match specific criteria. Most security considerations are already handled adequately by HTTP. However, given the nature of the data being transferred and the requirement it be correct, all interactions between client and server SHOULD use an HTTP connection protected with TLS [RFC5246] as defined in [RFC2818]. 4.1.1. Time Zone Queries Time zone identifiers, aliases or localized names can be used to query for time zone data or meta-data. This will be more explicitly defined below for each action. In general however, if a "tzid" URI template variable is used, then the value may be an identifier or an alias. When the "pattern" URI query parameter is used it may be an identifier, an alias or a localized name. 4.1.2. Time Zone Formats The default media type [RFC2046] format for returning time zone data is the iCalendar [RFC5545] data format. In addition, the iCalendar- in-XML [RFC6321], and iCalendar-in-JSON [RFC7265] representations are also available. Clients use the HTTP Accept header field (see Section 5.3.2 of [RFC7231]) to indicate their preference for the returned data format. Servers indicate the available formats that they support via the "capabilities" action response (Section 5.1). 4.1.3. Time Zone Localization As per Section 3.8, time zone data can support localized names. Clients use the HTTP Accept-Language header field (see Section 5.3.5 of [RFC7231]) to indicate their preference for the language used for localized names in the response data. Douglass & Daboo Expires October 24, 2015 [Page 11] Internet-Draft TZDIST Service April 2015 4.1.4. Conditional Time Zone Requests When time zone data or meta-data changes, it needs to be distributed in a timely manner because changes to local time offsets might occur within a few days of the publication of the time zone data changes. Typically, the number of time zones that change is small, whilst the overall number of time zones can be large. Thus, when a client is using more than a few time zones, it is more efficient for the client to be able to download only those time zones that have changed. To support conditional time zone requests, based on whether the underlying time zone data or meta-data has changed, the server supports an opaque token based synchronization mechanism for meta- data synchronization, and HTTP ETag based conditional requests for data synchronization (as per [RFC7232]). Note that time zone meta-data includes the time zone data ETag value. Thus time zone meta-data will always change when the corresponding time zone data changes. However, the converse is not true: it is possible for some piece of the time zone meta-data to change without the corresponding time zone data changing. e.g., for the case of a "monolithic" publisher (see Section 3.10), the version identifier in every time zone meta-data element will change with each new published revision, however, only a small subset of time zone data will actually change. For opaque token based synchronization of meta-data, when a client requests a list of all time zones, an opaque token is returned by the server, and that serves as a synchronization token for later requests. Clients can then use the returned opaque token in a conditional "list" action (see Section 5.2) to limit the results to only time zone meta-data which has changed since the previous request. A new opaque token is then returned with the results, and that can be used in a subsequent request. This allows clients to periodically poll the server for possible changes, using the opaque token value from the previous poll. Note, that for a "monolithic" publisher (see Section 3.10) all corresponding time zone meta-data changes as the version identifier changes for all time zones. However, clients only need to retrieve new time zone data for those time zones whose ETag value is different in the corresponding time zone meta-data. If a client only needs data for one time zone (e.g., a clock in a fixed location), then it can use a conditional HTTP request to determine if the time zone data has changed and retrieve the new data. The full details of HTTP conditional requests are described in [RFC7232], what follows is a brief summary of what a client typically does. When the client retrieves the time zone data from the server Douglass & Daboo Expires October 24, 2015 [Page 12] Internet-Draft TZDIST Service April 2015 using a "get" action (see Section 5.3) the server will include an ETag HTTP header field in the response. The client will store the value of that header field along with the request-URI used for the request. When the client wants to check for an update, it issues another "get" action HTTP request on the original request-URI, but this time it includes an If-None-Match HTTP request header field, with a value set to the ETag from the previous response. If the data for the time zone has not changed, the server will return a 304 (Not Modified) HTTP response. If the data has changed, the server will return a normal HTTP success response which will include the changed data, as well as a new value for the ETag. Thus clients can poll the server for changes, and only retrieve new data when it is actually different from what it got before. Clients SHOULD poll for changes, using an appropriate conditional request, at least once a day. A server acting as a secondary provider, caching time zone data from another server, SHOULD poll for changes once per hour. See Section 8 on expected client and server behavior regarding high request rates. 4.1.5. Expanded Time Zone Data Determining time zone offsets at a particular point in time is often a complicated process, as the rules for daylight saving time can be complex. To help with this, the time zone data distribution service provides an action that allows clients to request the server to expand a time zone into a set of "observances" over a fixed period of time (see Section 5.4). Each of these observances describes a UTC onset time and UTC offsets for the prior time and the observance time. Together, these provide a quick way for "thin" clients to determine an appropriate UTC offset for an arbitrary date without having to do full time zone expansion themselves. 4.1.6. Server Requirements To enable a simple client implementation, servers SHOULD ensure that they provide or cache data for all commonly used time zones, from various publishers. That allows client implementations to configure a single server to get all time zone data. In turn, any server can refresh any of the data from any other server - though the root servers may provide the most up-to-date copy of the data. 4.1.7. Error Responses The following are examples of response codes one would expect to be used by the server. Note, however, that unless explicitly prohibited any 2/3/4/5xx series response code may be used in a response. Douglass & Daboo Expires October 24, 2015 [Page 13] Internet-Draft TZDIST Service April 2015 200 (OK) - The command succeeded. 304 (Not Modified) - The requested data is unchanged. 400 (Bad Request) - The Sender has provided an invalid request parameter. 404 (Not Found) - The time zone was not found. When an HTTP error response is returned to the client, the server SHOULD return a JSON "problem detail" object in the response body, as per [I-D.ietf-appsawg-http-problem]. Every JSON "problem detail" object MUST include a "type" member with a uri value matching the applicable error code (defined for each action in Section 5). 4.1.8. Extensions This protocol is designed to be extensible through a standards based registration mechanism (see Section 10). It is anticipated that other useful time zone actions will be added in the future (e.g., mapping a geographical location to time zone identifiers, getting change history for time zones), and so, servers MUST return a description of their capabilities. This will allow clients to determine if new features have been installed and, if not, fall back on earlier features or disable some client capabilities. 4.2. Client Guidelines 4.2.1. Discovery Client implementations need to either know where the time zone data distribution service is located or discover it through some mechanism. To use a time zone data distribution service, a client needs a fully qualified domain name (FQDN), port and HTTP request-URI path. The request-URI path found via discovery is the "context path" for the service itself. The "context path" is used as the value of the "service-prefix" URI template variable when executing actions (see Section 5). The following sub-sections describe two methods of service discovery using DNS SRV records [RFC2782] and an HTTP "well-known" [RFC5785] resource. However, alternative mechanisms could also be used (e.g., a DHCP server option [RFC2131]). Douglass & Daboo Expires October 24, 2015 [Page 14] Internet-Draft TZDIST Service April 2015 4.2.1.1. Time Zone Data Distribution Service SRV Service Labels [RFC2782] defines a DNS-based service discovery protocol that has been widely adopted as a means of locating particular services within a local area network and beyond, using SRV RR records. This can be used to discover a service's FQDN and port. This specification adds two service types for use with SRV records: timezone: Identifies a Time Zone Data Distribution server that uses HTTP without transport layer security ([RFC2818]). timezones: Identifies a Time Zone Data Distribution server that uses HTTP with transport layer security ([RFC2818]). Clients MUST honor "TTL", "Priority" and "Weight" values in the SRV records, as described by [RFC2782]. Example: service record for server without transport layer security. _timezone._tcp SRV 0 1 80 tz.example.com. Example: service record for server with transport layer security. _timezones._tcp SRV 0 1 443 tz.example.com. 4.2.1.2. Time Zone Data Distribution Service TXT records When SRV RRs are used to advertise a time zone data distribution service, it is also convenient to be able to specify a "context path" in the DNS to be retrieved at the same time. To enable that, this specification uses a TXT RR that follows the syntax defined in Section 6 of [RFC6763] and defines a "path" key for use in that record. The value of the key MUST be the actual "context path" to the corresponding service on the server. A site might provide TXT records in addition to SRV records for each service. When present, clients MUST use the "path" value as the "context path" for the service in HTTP requests. When not present, clients use the ".well-known" URI approach described next. Example: text record for service with transport layer security. _timezones._tcp TXT path=/timezones Douglass & Daboo Expires October 24, 2015 [Page 15] Internet-Draft TZDIST Service April 2015 4.2.1.3. Time Zone Data Distribution Service Well-Known URI A "well-known" URI [RFC5785] is registered by this specification for the Time Zone Data Distribution service, "timezone" (see Section 10). This URI points to a resource that the client can use as the initial "context path" for the service they are trying to connect to. The server MUST redirect HTTP requests for that resource to the actual "context path" using one of the available mechanisms provided by HTTP (e.g., using an appropriate 3xx status response). Clients MUST handle HTTP redirects on the ".well-known" URI. Servers MUST NOT locate the actual time zone data distribution service endpoint at the ".well-known" URI as per Section 1.1 of [RFC5785]. Servers SHOULD set an appropriate Cache-Control header field value (as per Section 5.2 of [RFC7234]) in the redirect response to ensure caching occurs as needed, or as required by the type of response generated. For example, if it is anticipated that the location of the redirect might change over time, then a "no-cache" value would be used. To facilitate "context path's" that might differ from user to user, the server MAY require authentication when a client tries to access the ".well-known" URI (i.e., the server would return a 401 status response to the unauthenticated request from the client, then return the redirect response after a successful authentication by the client). 4.2.1.3.1. Example: well-known URI redirects to actual context path A Time Zone Data Distribution server has a "context path" that is "/servlet/timezone". The client will use "/.well-known/timezone" as the path for the service after it has first found the FQDN and port number via an SRV lookup or via manual entry of information by the user. When the client makes its initial HTTP request against "/.well-known/timezone", the server would issue an HTTP 301 redirect response with a Location response header field using the path "/servlet/timezone". The client would then "follow" this redirect to the new resource and continue making HTTP requests there. 4.2.2. Synchronization of Time Zones This section discusses possible client synchronization strategies using the various protocol elements provided by the server for that purpose. Douglass & Daboo Expires October 24, 2015 [Page 16] Internet-Draft TZDIST Service April 2015 4.2.2.1. Initial Synchronization of All Time Zones When a secondary service or a client wishing to cache all time zone data first starts, or wishes to do a full refresh, it synchronizes with another server by first issuing a "list" action to retrieve all the time zone meta-data. The client would preserve the returned opaque token for subsequent use. The client will store the meta-data for each time zone returned in the response. Time zone data for each corresponding time zone can then be fetched and stored locally. In addition a mapping of aliases to time zones can be built from the meta-data. 4.2.2.2. Subsequent Synchronization of All Time Zones A secondary service or a client caching all time zones needs to periodically synchronize with a server. To do so it would issue a "list" action with the "changedsince" URI query parameter set to the value of the opaque token returned by the last synchronization. The client would again preserve the returned opaque token for subsequent use. The client will update its stored time zone meta-data using the new values returned in the response, which contains just the time zone meta-data for those time zones changed since the last synchronization. In addition, it will compare the "etag" value in each time zone meta-data to the ETag value for the corresponding time zone data resource it has previously cached, and if different, it will fetch the new time zone data. Note that if the client presents the server with a "changedsince" value that the server does not support, all time zone data will be returned, as it would for the case where the request did not include a "changedsince" value. Publishers should take into account the fact that the "outright" deletion of time zone names will cause problems to simple clients and so aliasing a deleted time zone identifier to a suitable alternate one is preferable. 4.2.2.3. Synchronization with Pre-Existing Time Zone Data A client might be pre-provisioned with time zone data from a source other than the time zone data distribution service it is configured to use. In such cases, the client might want to minimize the amount of time zone data it synchronizes by doing an initial "list" action to retrieve all the time zone meta-data, but then only fetch time zone data for those time zones that do not match the publisher and version details for the pre-provisioned data. Douglass & Daboo Expires October 24, 2015 [Page 17] Internet-Draft TZDIST Service April 2015 5. Actions Servers MUST support the following actions. The information below shows details about each action: the request-URI the client targets (in the form of a URI template [RFC6570]) a description, the set of allowed query parameters, the nature of the response, and a set of possible error codes for the response (see Section 4.1.7). For any error not covered by the specific error codes defined below, the "urn:ietf:params:tzdist:error:invalid-action" error code is returned to the client in the JSON "problem details" object. 5.1. "capabilities" Action Name: capabilities Request-URI Template: {/service-prefix}/capabilities Description: This action returns the capabilities of the server, allowing clients to determine if a specific feature has been deployed and/or enabled. Parameters: None Response A JSON object containing a "version" member, an "info" member, and an "actions" member, see Section 6.1. Possible Error Codes No specific code. 5.1.1. Example: Get Capabilities >> Request << GET /capabilities HTTP/1.1 Host: tz.example.com >> Response << HTTP/1.1 200 OK Date: Wed, 4 Jun 2008 09:32:12 GMT Content-Type: application/json; charset="utf-8" Content-Length: xxxx { "version": 1, "info": { "primary-source": "Olson:2011m", Douglass & Daboo Expires October 24, 2015 [Page 18] Internet-Draft TZDIST Service April 2015 "formats": [ "text/calendar", "application/calendar+xml", "application/calendar+json" ], "truncated" : { "any": false, "ranges": [ { "start": "1970-01-01T00:00:00Z", "end": "*" }, { "start":"2010-01-01T00:00:00Z", "end":"2020-01-01T00:00:00Z" } ], "untruncated": true }, "provider-details": "http://tz.example.com/about.html", "contacts": ["mailto:tzs@example.org"] }, "actions": [ { "name": "capabilities", "uri-template": "/capabilities", "parameters": [] }, { "name": "list", "uri-template": "/zones{?changedsince}", "parameters": [ { "name": "changedsince", "required": false, "multi": false } ] }, { "name": "get", "uri-template": "/zones{/tzid}{?start,end}", "parameters": [ { "name": "start", Douglass & Daboo Expires October 24, 2015 [Page 19] Internet-Draft TZDIST Service April 2015 "required": false, "multi": false }, { "name": "end", "required": false, "multi": false } ] }, { "name": "expand", "uri-template": "/zones{/tzid}/observances{?start,end}", "parameters": [ { "name": "start", "required": true, "multi": false }, { "name": "end", "required": true, "multi": false } ] }, { "name": "find", "uri-template": "/zones{?pattern}", "parameters": [ { "name": "pattern", "required": true, "multi": false } ] }, { "name": "leapseconds", "uri-template": "/leapseconds", "parameters": [] } ] } Douglass & Daboo Expires October 24, 2015 [Page 20] Internet-Draft TZDIST Service April 2015 5.2. "list" Action Name: list Request-URI Template: {/service-prefix,data- prefix}/zones{?changedsince} Description: This action lists all time zone identifiers in summary format, with publisher, version, aliases and optional localized data. In addition, it returns an opaque synchronization token for the entire response. If the "changedsince" URI query parameter is present, its value MUST correspond to a previously returned synchronization token value. When "changedsince" is used, the server MUST return only those time zones that have changed since the specified synchronization token. If the "changedsince" value is not supported by the server, the server MUST return all time zones, treating the request as if it had no "changedsince". Parameters: changedsince OPTIONAL, but MUST occur only once. Response: A JSON object containing a "synctoken" member and a "timezones" member, see Section 6.2. Possible Error Codes urn:ietf:params:tzdist:error:invalid-changedsince The "changedsince" URI query parameter appears more than once. 5.2.1. Example: List time zone identifiers Douglass & Daboo Expires October 24, 2015 [Page 21] Internet-Draft TZDIST Service April 2015 In this example the client requests the full set of time zone identifiers. >> Request << GET /zones HTTP/1.1 Host: tz.example.com >> Response << HTTP/1.1 200 OK Date: Wed, 4 Jun 2008 09:32:12 GMT Content-Type: application/json; charset="utf-8" Content-Length: xxxx { "synctoken": "2009-10-11T09:32:11Z", "timezones": [ { "tzid": "America/New_York", "etag": "123456789-000-111", "last-modified": "2009-09-17T01:39:34Z", "publisher": "Example.com", "version": "2015a", "aliases":["US/Eastern"], "local-names": [ { "name": "America/New_York", "lang": "en_US" } ] }, ... ] } 5.3. "get" Action Name: get Request-URI Template: {/service-prefix,data- prefix}/zones{/tzid}{?start,end} The "tzid" variable value is REQUIRED to distinguish this action from the "list" action. Douglass & Daboo Expires October 24, 2015 [Page 22] Internet-Draft TZDIST Service April 2015 Description: This action returns a time zone. The response MUST contain an ETag response header field indicating the current value of the strong entity tag of the time zone resource. In the absence of any Accept HTTP request header field, the server MUST return time zone data with the "text/calendar" media type. If the "tzid" variable value is actually a time zone alias, the server will return the matching time zone data with the alias as the identifier in the time zone data. The server MAY include one or more "TZID-ALIAS-OF" properties (see Section 7.2) in the time zone data to indicate additional identifiers that have the matching time zone identifier as an alias. Parameters: start= OPTIONAL, and MUST occur only once. Specifies the inclusive UTC date-time value at which the returned time zone data is truncated at its start. end= OPTIONAL, and MUST occur only once. Specifies the exclusive UTC date-time value at which the returned time zone data is truncated at its end. Response: A document containing all the requested time zone data in the format specified. Possible Error Codes urn:ietf:params:tzdist:error:tzid-not-found No time zone associated with the specified "tzid" path segment value was found. urn:ietf:params:tzdist:error:invalid-format The Accept request header field supplied by the client did not contain a media type for time zone data supported by the server. urn:ietf:params:tzdist:error:invalid-start The "start" URI query parameter has an incorrect value, or appears more than once, or does not match one of the fixed truncation range start values advertised in the "capabilities" action response. urn:ietf:params:tzdist:error:invalid-end The "end" URI query parameter has an incorrect value, or appears more than once, or has a value less than or equal to the "start" URI query parameter, or does not match one of the fixed truncation range end values advertised in the "capabilities" action response. Douglass & Daboo Expires October 24, 2015 [Page 23] Internet-Draft TZDIST Service April 2015 5.3.1. Example: Get time zone data In this example the client requests the time zone with a specific time zone identifier to be returned. >> Request << GET /zones/America%2FNew_York HTTP/1.1 Host: tz.example.com Accept:text/calendar >> Response << HTTP/1.1 200 OK Date: Wed, 4 Jun 2008 09:32:12 GMT Content-Type: text/calendar; charset="utf-8" Content-Length: xxxx ETag: "123456789-000-111" BEGIN:VCALENDAR ... BEGIN:VTIMEZONE TZID:America/New_York ... END:VTIMEZONE END:VCALENDAR 5.3.2. Example: Conditional Get time zone data In this example the client requests the time zone with a specific time zone identifier to be returned, but uses an If-None-Match header field in the request, set to the value of a previously returned ETag header field, or the value of the "etag" member in a JSON "timezone" object returned from a "list" action response. In this example, the data on the server has not changed, so a 304 response is returned. >> Request << GET /zones/America%2FNew_York HTTP/1.1 Host: tz.example.com Accept:text/calendar If-None-Match: "123456789-000-111" >> Response << HTTP/1.1 304 Not Modified Date: Wed, 4 Jun 2008 09:32:12 GMT Douglass & Daboo Expires October 24, 2015 [Page 24] Internet-Draft TZDIST Service April 2015 5.3.3. Example: Get time zone data using a time zone alias In this example the client requests the time zone with an aliased time zone identifier to be returned, and the server returns the time zone data with that identifier, and two aliases. >> Request << GET /zones/US%2FEastern HTTP/1.1 Host: tz.example.com Accept:text/calendar >> Response << HTTP/1.1 200 OK Date: Wed, 4 Jun 2008 09:32:12 GMT Content-Type: text/calendar; charset="utf-8" Content-Length: xxxx ETag: "123456789-000-111" BEGIN:VCALENDAR ... BEGIN:VTIMEZONE TZID:US/Eastern TZID-ALIAS-OF:America/New_York TZID-ALIAS-OF:America/Montreal ... END:VTIMEZONE END:VCALENDAR 5.3.4. Example: Get truncated time zone data Assume the server advertises a "truncated" object in its "capabilities" response that appears as: "truncated": { "any": false, "ranges": [ {"start": "1970-01-01T00:00:00Z", "end": "*"}, {"start":"2010-01-01T00:00:00Z", "end":"2020-01-01T00:00:00Z"} ], "untruncated": false } Douglass & Daboo Expires October 24, 2015 [Page 25] Internet-Draft TZDIST Service April 2015 In this example the client requests the time zone with a specific time zone identifier truncated at one of the ranges specified by the server, to be returned. Note the presence of a "STANDARD" component that matches the start point of the truncation range (converted to the local time for the UTC offset in effect at the matching UTC time). Also, note the presence of the "TZUNTIL" (Section 7.1) iCalendar property in the "VTIMEZONE" component, indicating the upper bound on the validity of the time zone data. >> Request << GET /zones/America%2FNew_York ?start=2010-01-01T00:00:00Z &end=2020-01-01T00:00:00Z HTTP/1.1 Host: tz.example.com Accept:text/calendar >> Response << HTTP/1.1 200 OK Date: Wed, 4 Jun 2008 09:32:12 GMT Content-Type: text/calendar; charset="utf-8" Content-Length: xxxx ETag: "123456789-000-111" BEGIN:VCALENDAR ... BEGIN:VTIMEZONE TZID:America/New_York TZUNTIL:20200101T000000Z BEGIN:STANDARD DTSTART:20101231T190000 TZNAME:EST TZOFFSETFROM:-0500 TZOFFSETTO:-0500 END:STANDARD ... END:VTIMEZONE END:VCALENDAR 5.3.5. Example: Get a non-existent time zone data Douglass & Daboo Expires October 24, 2015 [Page 26] Internet-Draft TZDIST Service April 2015 In this example the client requests the time zone with a specific time zone identifier to be returned. >> Request << GET /zones/America%2FPittsburgh HTTP/1.1 Host: tz.example.com Accept:application/calendar+json >> Response << HTTP/1.1 404 Not Found Date: Wed, 4 Jun 2008 09:32:12 GMT Content-Type: application/problem+json; charset="utf-8" Content-Language: en Content-Length: xxxx { "type": "urn:ietf:params:tzdist:error:tzid-not-found", "title": "Time zone identifier was not found on this server", "status": 404 } 5.4. "expand" Action Name: expand Request-URI Template: {/service-prefix,data-prefix}/zones{/tzid} /observances{?start,end} The "tzid" variable value is REQUIRED. Description: This action expands the specified time zone into a list of onset start date/time (in UTC) and UTC offsets. The response MUST contain an ETag response header field indicating the current value of the strong entity tag of the time zone being expanded. Parameters: start=: REQUIRED, and MUST occur only once. Specifies the inclusive UTC date-time value for the start of the period of interest. end=: REQUIRED, and MUST occur only once. Specifies the exclusive UTC date-time value for the end of the period of interest. Note that this is the exclusive end value - i.e., it Douglass & Daboo Expires October 24, 2015 [Page 27] Internet-Draft TZDIST Service April 2015 represents the date just after the range of interest. e.g., if a client wants the expanded date just for the year 2014, it would use a start value of "2014-01-01T00:00:00Z" and an end value of "2015-01-01T00:00:00Z". An error occurs if the end value is less than or equal to the start value. Response: A JSON object containing a "tzid" member, and an "observances" member, see Section 6.3. If the time zone being expanded is not fully defined over the requested time range (e.g., because of truncation), then the server MUST include "start" and/ or "end" members in the JSON response to indicate the actual start and end point for the observances being returned. The server MUST include an expanded observance representing the time zone information in effect at the start of the returned observance period. Possible Error Codes urn:ietf:params:tzdist:error:tzid-not-found No time zone associated with the specified "tzid" path segment value was found. urn:ietf:params:tzdist:error:invalid-start The "start" URI query parameter has an incorrect value, or appears more than once, or is missing, or has a value outside any fixed truncation ranges advertised in the "capabilities" action response. urn:ietf:params:tzdist:error:invalid-end The "end" URI query parameter has an incorrect value, or appears more than once, or has a value less than or equal to the "start" URI query parameter, or has a value outside any fixed truncation ranges advertised in the "capabilities" action response.. 5.4.1. Example: Expanded JSON Data Format Douglass & Daboo Expires October 24, 2015 [Page 28] Internet-Draft TZDIST Service April 2015 In this example the client requests a time zone in the expanded form. >> Request << GET /zones/America%2FNew_York/observances ?start=2008-01-01T00:00:00Z &end=2009-01-01T00:00:00Z HTTP/1.1 Host: tz.example.com >> Response << HTTP/1.1 200 OK Date: Mon, 11 Oct 2009 09:32:12 GMT Content-Type: application/json; charset="utf-8" Content-Length: xxxx ETag: "123456789-000-111" { "tzid": "America/New_York", "observances": [ { "name": "Standard", "onset": "2008-01-01T00:00:00Z", "utc-offset-from": -18000, "utc-offset-to": -18000 }, { "name": "Daylight", "onset": "2008-03-09T07:00:00Z", "utc-offset-from": -18000, "utc-offset-to": -14400 }, { "name": "Standard", "onset": "2008-11-02T06:00:00Z", "utc-offset-from": -14400, "utc-offset-to": -18000 }, ] } 5.5. "find" Action Name: find Request-URI Template: {/service-prefix,data-prefix}/zones{?pattern} Douglass & Daboo Expires October 24, 2015 [Page 29] Internet-Draft TZDIST Service April 2015 Description: This action allows a client to query the time zone data distribution service for a matching identifier, alias or localized name, using a simple "glob" style pattern match against the names known to the server (with an asterisk * as the wildcard character). Pattern match strings have the following options: * not present An exact text match is done, e.g., "xyz" * first character only An ends-with text match is done, e.g., "*xyz" * last character only A starts-with text match is done, e.g., "xyz*" * first and last characters only A sub-string text match is done, e.g., "*xyz*" In addition, when matching, underscore characters (0x5F) SHOULD be mapped to a single space character (0x20) prior to string comparison. This allows time zone identifiers such as "America/ New_York" to match a query for "*New York*". ASCII characters in the range 0x41 ("A") through 0x5A ("Z") SHOULD be mapped to their lowercase equivalents. To match characters 0x2A ("*") and 0x5C ("\") in the pattern, a single 0x5C ("\") is prepended to act as an "escaping" mechanism. i.e., a pattern "Test\*" implies an exact match test against the string "Test*". Parameters: pattern= REQUIRED, and MUST occur only once. Response: The response has the same format as the "list" action, with one result object per successful match, see Section 6.2. Possible Error Codes urn:ietf:params:tzdist:error:invalid-pattern The "pattern" URI query parameter has an incorrect value, or appears more than once. 5.5.1. Example: Find action In this example the client asks for data about the time zone "US/ Eastern". Douglass & Daboo Expires October 24, 2015 [Page 30] Internet-Draft TZDIST Service April 2015 >> Request << GET /zones?pattern=US/Eastern HTTP/1.1 Host: tz.example.com >> Response << HTTP/1.1 200 OK Date: Wed, 4 Jun 2008 09:32:12 GMT Content-Type: application/json; charset="utf-8" Content-Length: xxxx { "synctoken": "2009-10-11T09:32:11Z", "timezones": [ { "tzid": "America/New_York", "etag": "123456789-000-111", "last-modified": "2009-09-17T01:39:34Z", "publisher": "Example.com", "version": "2015a", "aliases":["US/Eastern"], "local-names": [ { "name": "America/New_York", "lang": "en_US" } ] }, { "tzid": "America/Detroit", "etag": "123456789-999-222", "last-modified": "2009-09-17T01:39:34Z", "publisher": "Example.com", "version": "2015a", "aliases":["US/Eastern"], "local-names": [ { "name": "America/Detroit", "lang": "en_US" } ] }, ... ] } Douglass & Daboo Expires October 24, 2015 [Page 31] Internet-Draft TZDIST Service April 2015 5.6. "leapseconds" Action Name: leapseconds Request-URI Template: {/service-prefix,data-prefix}/leapseconds Description: This action allows a client to query the time zone data distribution service to retrieve the current leap second information available on the server. Parameters: None Response: A JSON object containing an "expires" member, a "publisher" member, a "version" member, and a "leapseconds" member, see Section 6.4. The "expires" member in the JSON response indicates the latest date covered by leap second information. e.g., (from the example below) if the "expires" value is set to "2014-06-28" and the latest leap second change indicated was at "2012-07-01", then the data indicates that there are no leap seconds added (or removed) between those two dates, and information for leap seconds beyond the "expires" date is not yet available. The "leapseconds" member contains a list of JSON objects each of which contains a "utc-offset" and "onset" member. The "onset" member specifies the date (with the implied time of 00:00:00 UTC) at which the corresponding UTC offset from TAI takes effect. In other words, a leap second is added or removed just prior to time 00:00:00 UTC of the specified onset date. Possible Error Codes No specific code. 5.6.1. Example: Get leapsecond information Douglass & Daboo Expires October 24, 2015 [Page 32] Internet-Draft TZDIST Service April 2015 In this example the client requests the current leap second information from the server. >> Request << GET /leapseconds HTTP/1.1 Host: tz.example.com >> Response << HTTP/1.1 200 OK Date: Wed, 4 Jun 2008 09:32:12 GMT Content-Type: application/json; charset="utf-8" Content-Length: xxxx { "expires": "2014-06-28", "publisher": "Example.com", "version": "2014d", "leapseconds": [ { "utc-offset": 10, "onset": "1972-01-01", }, { "utc-offset": 11, "onset": "1972-07-01", }, ... { "utc-offset": 35, "onset": "2012-07-01", } ] } 6. JSON Definitions [RFC7159] defines the structure of JSON objects using a set of primitive elements. Those elements will be used to describe the structure of JSON objects used by this specification using a set of "rules". The rules used are: OBJECT represents a JSON object, defined in Section 4 of [RFC7159]. "OBJECT" is followed by a parenthesized list of "MEMBER" rule names. If a member rule name is preceded by a "?" (0x3F) character, that member is optional, otherwise all members are required. If two or more member rule names are present, each Douglass & Daboo Expires October 24, 2015 [Page 33] Internet-Draft TZDIST Service April 2015 separated from the other by a "|" (0x7C) character, then only one of those members MUST be present in JSON object. JSON object members are unordered, and thus the order used in the rules is not significant. MEMBER represents a member of a JSON object, defined in Section 4 of [RFC7159]. "MEMBER" is followed by a rule name, then the name of the member, followed by a ":", and then the value. A value can be one of "OBJECT", "ARRAY", "NUMBER", "STRING", or "BOOLEAN" rules. ARRAY represents a JSON array, defined in Section 5 of [RFC7159]. "ARRAY" is followed by a value (one of "OBJECT", "ARRAY", "NUMBER", "STRING", or "BOOLEAN"), indicating the type of items used in the array. NUMBER represents a JSON number, defined in Section 6 of [RFC7159]. STRING represents a JSON string, defined in Section 7 of [RFC7159]. BOOLEAN represents either of the JSON values "true" or "false", defined in Section 3 of [RFC7159]. ; a line starting with a ";" (0x3B) character is a comment. Note, clients MUST ignore any unexpected JSON members in responses from the server. 6.1. capabilities action response Rules for the JSON document returned for a "capabilities" action request. ; root object OBJECT (version, info, actions) ; The version number of the protocol supported - MUST be 1 MEMBER version "version" : NUMBER ; object containing service information ; Only one of primary_source or secondary_source MUST be present MEMBER info "info" : OBJECT ( primary_source | secondary_source, formats, ?truncated, ?provider_details, ?contacts ) Douglass & Daboo Expires October 24, 2015 [Page 34] Internet-Draft TZDIST Service April 2015 ; The source of the time zone data provided by a "primary" server MEMBER primary_source "primary-source" : STRING ; The time zone data server from which data is provided by a ; "secondary" server MEMBER secondary_source "secondary-source" : STRING ; Array of one or more media types for the time zone data formats ; that the server can return MEMBER formats "formats" : ARRAY STRING ; Present if the server is providing truncated time zone data. The ; value is an object providing details of the supported truncation ; modes. MEMBER truncated "truncated" : OBJECT: ( any, ?ranges, ?untruncated ) ; Indicates whether the server can truncate time zone data at any ; start or end point. When set to "true" any start or end point is ; a valid value for use with the "start" and "end" URI query ; parameters in a "get" action request MEMBER any "any" : BOOLEAN ; Indicates which ranges of time the server has truncated data for. ; A value from this list may be used with the "start" and "end" URI ; query parameters in a "get" action request. Not present if "any" ; is set to "true" MEMBER ranges "ranges" : ARRAY OBJECT (range-start, range-end) ; [RFC3339] UTC date-time value for inclusive start of the range, ; or the single character "*" to indicate a value corresponding to ; the lower bound supplied by the publisher of the time zone data MEMBER range-start "start" : STRING ; [RFC3339] UTC date-time value for exclusive end of the range, ; or the single character "*" to indicate a value corresponding to ; the upper bound supplied by the publisher of the time zone data MEMBER range-end "end" : STRING ; Indicates whether the server can can supply untruncated data. When ; set to "true" indicates that, in addition to truncated data being ; available, the server can return untruncated data if a "get" ; action request is executed without a "start" or "end" URI query ; parameter MEMBER untruncated "untruncated" : BOOLEAN Douglass & Daboo Expires October 24, 2015 [Page 35] Internet-Draft TZDIST Service April 2015 ; A URI where human readable details about the time zone service ; is available MEMBER provider_details "provider-details" : STRING ; Array of URIs providing contact details for the server ; administrator MEMBER contacts "contacts" : ARRAY STRING ; Array of actions supported by the server MEMBER actions "actions" : ARRAY OBJECT ( action_name, action_params ) ; Name of the action MEMBER action_name: "name" : STRING ; Array of request-URI query parameters supported by the action MEMBER action_params: "parameters" ARRAY OBJECT ( param_name, ?param_required, ?param_multi, ?param_values ) ; Name of the parameter MEMBER param_name "name" : STRING ; If true the parameter has to be present in the request-URI ; default is false MEMBER param_required "required" : BOOLEAN ; If true the parameter can occur more than once in the request-URI ; default is false MEMBER param_multi "multi" : BOOLEAN, ; An array that defines the allowed set of values for the parameter ; In the absence of this member, any string value is acceptable MEMBER param_values "values" ARRAY STRING 6.2. list/find action response Rules for the JSON document returned for a "list" or "find" action request. ; root object OBJECT (synctoken, timezones) Douglass & Daboo Expires October 24, 2015 [Page 36] Internet-Draft TZDIST Service April 2015 ; Server generated opaque token used for synchronizing changes, MEMBER synctoken "synctoken" : STRING ; Array of time zone objects MEMBER timezones "timezones" : ARRAY OBJECT ( tzid, etag, last_modified, publisher, version, ?aliases, ?local_names, ) ; Time zone identifier MEMBER tzid "tzid" : STRING ; Current ETag for the corresponding time zone data resource MEMBER etag "etag" : STRING ; Date/time when the time zone data was last modified ; [RFC3339] UTC date-time value MEMBER last_modified "last-modified" : STRING ; Time zone data publisher MEMBER publisher "publisher" : STRING ; Current version of the time zone data as defined by the ; publisher MEMBER version "version" : STRING ; An array that lists the set of time zone aliases available ; for the corresponding time zone MEMBER aliases "aliases" : ARRAY STRING ; An array that lists the set of localized names available ; for the corresponding time zone MEMBER local_names "local-names" : ARRAY OBJECT ( lname, lang, ?pref ) ; Language tag for the language of the associated name MEMBER: lang "lang" : STRING ; Localized name MEMBER lname "name" : STRING ; Indicates whether this is the preferred name for the associated Douglass & Daboo Expires October 24, 2015 [Page 37] Internet-Draft TZDIST Service April 2015 ; language default: false MEMBER pref "pref" : BOOLEAN 6.3. expand action response Douglass & Daboo Expires October 24, 2015 [Page 38] Internet-Draft TZDIST Service April 2015 Rules for the JSON document returned for a "expand" action request. ; root object OBJECT ( tzid, ?start, ?end, observances ) ; Time zone identifier MEMBER tzid "tzid" : STRING ; The actual inclusive start point for the returned observances ; if different from the value of the "start" URI query parameter MEMBER start "start" : STRING ; The actual exclusive end point for the returned observances ; if different from the value of the "end" URI query parameter MEMBER end "end" : STRING ; Array of time zone objects MEMBER observances "observances" : ARRAY OBJECT ( oname, ?olocal_names, onset, utc_offset_from, utc_offset_to ) ; Observance name MEMBER oname "name" : STRING ; Array of localized observance names MEMBER olocal_names "local-names" : ARRAY STRING ; [RFC3339] UTC date-time value at which the observance takes effect MEMBER onset "onset" : STRING ; The UTC offset in seconds before the start of this observance MEMBER utc_offset_from "utc-offset-from" : NUMBER ; The UTC offset in seconds at and after the start of this observance MEMBER utc_offset_to "utc-offset-to" : NUMBER Douglass & Daboo Expires October 24, 2015 [Page 39] Internet-Draft TZDIST Service April 2015 6.4. leapseconds action response Rules for the JSON document returned for a "leapseconds" action request. ; root object OBJECT ( expires, publisher, version, leapseconds ) ; Last valid date covered by the data in this response ; [RFC3339] full-date value MEMBER expires "expires" : STRING ; Leap second information publisher MEMBER publisher "publisher" : STRING ; Current version of the leap second information as defined by the ; publisher MEMBER version "version" : STRING ; Array of leap second objects MEMBER leapseconds "leapseconds" : ARRAY OBJECT ( utc_offset, onset ) ; The UTC offset from TAI in seconds in effect at and after the ; specified date MEMBER utc_offset "utc-offset" : NUMBER ; [RFC3339] full-date value at which the new UTC offset takes effect, ; at T00:00:00Z MEMBER onset "onset" : STRING 7. New iCalendar Properties 7.1. Time Zone Upper Bound Property Name: TZUNTIL Purpose: This property specifies an upper bound for the validity of data within a "VTIMEZONE" component. Value Type: DATE-TIME Douglass & Daboo Expires October 24, 2015 [Page 40] Internet-Draft TZDIST Service April 2015 Property Parameters: IANA and non-standard property parameters can be specified on this property. Conformance: This property can be specified zero or one time within "VTIMEZONE" calendar components. Description: The value MUST be specified in the UTC time format. Time zone data in a "VTIMEZONE" component might cover only a fixed period of time. The start of such a period is clearly indicated by the earliest observance defined by the "STANDARD" and "DAYLIGHT" sub-components. However, [RFC5545] does not define a way to indicate an upper bound on the validity of the time zone data, which cannot be simply derived from the observance with the latest onset time. This specification introduces the "TZUNTIL" property for that purpose. It specifies an "exclusive" UTC date- time value that indicates the last time at which the time zone data is to be considered valid. This property is also used by time zone data distribution servers to indicate the truncation range end point of time zone data (as described in Section 3.9). Format Definition: This property is defined by the following notation: tzuntil = "TZUNTIL" tzuntilparam ":" date-time CRLF tzuntilparam = *(";" other-param) Example: Suppose a time zone based on astronomical observations has well-defined onset times through the year 2025, but the first onset in 2026 is currently known only approximately. In that case, the "TZUNTIL" property could be specified as follows: TZUNTIL:20260101T000000Z 7.2. Time Zone Identifier Alias Property Property Name: TZID-ALIAS-OF Purpose: This property specifies a time zone identifier that the main time zone identifier is an alias of. Value Type: TEXT Property Parameters: IANA and non-standard property parameters can be specified on this property. Douglass & Daboo Expires October 24, 2015 [Page 41] Internet-Draft TZDIST Service April 2015 Conformance: This property can be specified zero or more times within "VTIMEZONE" calendar components. Description: When the "VTIMEZONE" component uses a time zone identifier alias for the "TZID" property value, the "TZID-ALIAS- OF" property is used to indicate the time zone identifier of the other time zone (see Section 3.7). Format Definition: This property is defined by the following notation: tzid-alias-of = "TZID-ALIAS-OF" tzidaliasofparam ":" [tzidprefix] text CRLF tzidaliasofparam = *(";" other-param) ;tzidprefix defined in [RFC5545]. Example: The following is an example of this property: TZID-ALIAS-OF:America/New_York 8. Security Considerations Time zone data is critical in determining local or UTC time for devices and in calendaring and scheduling operations. As such, it is vital that a reliable source of time zone data is used. Servers providing a time zone data distribution service MUST support HTTP over Transport Layer Security (TLS) (as defined by [RFC2818] with best practices described in [I-D.ietf-uta-tls-bcp]). Servers MAY support a time zone data distribution service over HTTP without TLS. However, secondary servers MUST use TLS to fetch data from a primary server. Clients that support transport layer security as defined by [RFC2818] SHOULD use the "_timezones" service, but MAY use "_timezone" service. However, clients that have been configured to use the TLS-based service, MUST NOT fall back to using the non-TLS service if the TLS- based service is not available. In additional, clients MUST NOT follow HTTP redirect requests from a TLS service to a non-TLS service. Clients MUST follow the certificate verification process specified in [RFC6125] when the TLS-based service is used. A malicious attacker with access to the DNS server data, or able to get spoofed answers cached in a recursive resolver, can potentially cause clients to connect to any server chosen by the attacker. In the absence of a secure DNS option, clients SHOULD check that the target FQDN returned in the SRV record is the same as the original Douglass & Daboo Expires October 24, 2015 [Page 42] Internet-Draft TZDIST Service April 2015 service domain that was queried, or is a sub-domain of the original service domain. In many cases the client configuration is likely to be handled automatically without any user input and as such, any mismatch between the original service domain and the target FQDN is treated as a failure and the client MUST NOT attempt to connect to the target server. In addition, when transport layer security is being used, the transport layer security certificate SHOULD include an SRV-ID field as per [RFC4985] matching the expected DNS SRV queries clients will use for service discovery. If an SRV-ID field is present in a certificate, clients MUST match the SRV-ID value with the service type and domain that matches the DNS SRV request made by the client to discover the service. Time zone data servers SHOULD protect themselves against errant or malicious clients by throttling high request rates or frequent requests for large amounts of data. Clients can avoid being throttled by using the polling capabilities outlined in Section 4.1.4. Servers MAY require some form of authentication or authorization of clients (including secondary servers) to restrict which clients are allowed to access their service, or provide better identification of errant clients. As such, servers MAY require HTTP- based authentication as per [RFC7235]. 9. Privacy Considerations The type and pattern of requests that a client makes can be used to "fingerprint" specific clients or devices and thus potentially used to track information about what the users of the clients might be doing. In particular, a client that only downloads time zone data on an as needed basis, will leak the fact that a user's device has moved from one time zone to another or that the user is receiving scheduling messages from another user in a different time zone. Clients need to be aware of the potential ways in which an untrusted server or a network observer might be able to track them and take precautions such as the following: 1. Always use TLS to connect to the server. 2. Avoid use of TLS session resumption. 3. Always fetch and synchronize the entire set of time zone data to avoid leaking information about which time zones are actually in use by the client. 4. Randomize the order in which individual time zones are fetched using the "get" action, when retrieving a set of time zones based on a "list" action response. Douglass & Daboo Expires October 24, 2015 [Page 43] Internet-Draft TZDIST Service April 2015 5. Avoid use of conditional HTTP requests [RFC7232] with the "get" action to prevent tracking of clients by servers generating client-specific ETag values. 6. Avoid use of cookies in HTTP requests [RFC6265]. 7. Avoid use of authenticated HTTP requests. 8. When doing periodic polling to check for updates, apply a random (positive or negative) offset to the next poll time to avoid servers being able to identify the client by the specific periodicity of its polling behavior. 9. A server trying to "fingerprint" clients might insert a "fake" time zone into the time zone data, using a unique identifier for each client making a request. The server can then watch for client requests that refer to that "fake" time zone and thus track the activity of each client. It is hard for clients to identify a "fake" time zone given that new time zones are added from time to time. One option to mitigate this would be for the client to make use of two time zone distribution servers from two independent providers, that provide time zone data from the same publisher. The client can then compare the list of time zones from each server (assuming they both have the same version of time zone data from the common publisher) and detect ones that appear to be added on one server and not the other. Alternatively, the client can check the publisher data directly to verify that time zones match the set the publisher has. Note that some of the above recommendations will result in less efficient use of the protocol due to fetching data that might not be relevant to the client. An organization can setup a secondary server within their own domain, and configure their clients to use that server, to protect the organization's users from the possibility of being tracked by an untrusted time zone distribution server. Clients can then use more efficient protocol interactions, free from the concerns above, on the basis that their organization's server is trusted. When doing this, the secondary server would follow the recommendations for clients (listed in the previous paragraph) so that the untrusted server is not able to gain information about the organization as a whole. Note, however, that if client requests to the secondary server are subject to tracking by a network observer so clients ought to apply some of the randomization techniques from the list above. Servers that want to avoid accidentally storing information that could be used to identify clients can take the following precautions: Douglass & Daboo Expires October 24, 2015 [Page 44] Internet-Draft TZDIST Service April 2015 1. Avoid logging client request activity, or anonymize information in any logs (e.g., client IP address, client user-agent details, authentication credentials, etc). 2. Add an unused HTTP response header to each response with a random amount of data in it (e.g., to pad the overall request size to the nearest power-of-2 or 128-byte boundary) to avoid exposing which time zones are being fetched when TLS is being used, via network traffic analysis. 10. IANA Considerations This specification defines a new registry of "actions" for the time zone data distribution service protocol, defines a "well-known" URI using the registration procedure and template from Section 5.1 of [RFC5785], creates two new SRV service label aliases, and defines one new iCalendar property parameter as per the registration procedure in [RFC5545]. It also adds a new "tzdist" sub-namespace to the IETF parameters URN sub-namespace as per [RFC3553] for use with protocol related error codes. 10.1. Service Actions Registration This section defines the process to register new or modified time zone data distribution service actions with IANA. 10.1.1. Service Actions Registration Procedure The IETF will create a mailing list, tzdist-service@ietf.org, which can be used for public discussion of time zone data distribution service actions proposals prior to registration. Use of the mailing list is strongly encouraged. The IESG will appoint a designated expert who will monitor the tzdist-service@ietf.org mailing list and review registrations. Registration of new time zone data distribution service actions MUST be reviewed by the designated expert and published in an RFC. A Standard Track RFC is REQUIRED for the registration of new time zone data distribution service actions. A Standard Track RFC is also REQUIRED for changes to actions previously documented in a Standard Track RFC. The registration procedure begins when a completed registration template, as defined below, is sent to tzdist-service@ietf.org and iana@iana.org. The designated expert is expected to tell IANA and the submitter of the registration within two weeks whether the registration is approved, approved with minor changes, or rejected with cause. When a registration is rejected with cause, it can be Douglass & Daboo Expires October 24, 2015 [Page 45] Internet-Draft TZDIST Service April 2015 re-submitted if the concerns listed in the cause are addressed. Decisions made by the designated expert can be appealed to the IESG Applications Area Director, then to the IESG. They follow the normal appeals procedure for IESG decisions. 10.1.2. Registration Template for Actions An action is defined by completing the following template. Name: The name of the action. Request-URI Template: The URI template used in HTTP requests for the action. Description: A general description of the action, its purpose, etc. Parameters: A list of allowed request URI query parameters, indicating whether they are "REQUIRED" or "OPTIONAL" and whether they can occur only once or multiple times, together with the expected format of the parameter values. Response The nature of the response to the HTTP request, e.g., what format the response data is in. Possible Error Codes Possible error codes reported in a JSON "problem details" object if an HTTP request fails. 10.2. Initial Time Zone Data Distribution Service Registry The IANA is requested to create and maintain the following registry for time zone data distribution service actions with pointers to appropriate reference documents. 10.2.1. Actions Registry The following table is to be used to initialize the actions registry. +---------------+----------+-----------------------+ | Action Name | Status | Reference | +---------------+----------+-----------------------+ | capabilities | Current | RFCXXXX, Section 5.1 | | list | Current | RFCXXXX, Section 5.2 | | get | Current | RFCXXXX, Section 5.3 | | expand | Current | RFCXXXX, Section 5.4 | | find | Current | RFCXXXX, Section 5.5 | | leapseconds | Current | RFCXXXX, Section 5.6 | +---------------+----------+-----------------------+ Douglass & Daboo Expires October 24, 2015 [Page 46] Internet-Draft TZDIST Service April 2015 10.3. timezone Well-Known URI Registration URI suffix: timezone Change controller: IETF. Specification document(s): This RFC. Related information: 10.4. Service Name Registrations This document registers two new service names as per [RFC6335]. Both are defined within this document. 10.4.1. timezone Service Name Registration Service Name: timezone Transport Protocol(s): TCP Assignee: IESG Contact: IETF Chair Description: Time Zone Data Distribution Service - non-TLS Reference: [This Draft] Assignment Note: This is an extension of the http service. Defined TXT keys: path= 10.4.2. timezones Service Name Registration Service Name: timezones Transport Protocol(s): TCP Assignee: IESG Contact: IETF Chair Description: Time Zone Data Distribution Service - over TLS Reference: [This Draft] Assignment Note: This is an extension of the https service. Defined TXT keys: path= Douglass & Daboo Expires October 24, 2015 [Page 47] Internet-Draft TZDIST Service April 2015 10.5. tzdist URN sub-namespace IANA is requested to register a new URN sub-namespace within the IETF URN Sub-namespace for Registered Protocol Parameter Identifiers defined in [RFC3553]. Registry name: tzdist Specification): This RFC Repository: Time Distribution Service protocol elements registry. Index value:: This specification defines the single "error" sub- parameter, which itself has sub-parameters representing specific error codes within the protocol as defined in the list of actions in Section 5 and used in problem reports (Section 4.1.7). 10.6. iCalendar Property Registrations This document defines the following new iCalendar properties to be added to the registry defined in Section 8.2.3 of [RFC5545]: +----------------+----------+-----------------------+ | Property | Status | Reference | +----------------+----------+-----------------------+ | TZUNTIL | Current | RFCXXXX, Section 7.1 | | TZID-ALIAS-OF | Current | RFCXXXX, Section 7.2 | +----------------+----------+-----------------------+ 11. Acknowledgements The authors would like to thank the members of the Calendaring and Scheduling Consortium's Time Zone Technical Committee, and the participants and chairs of the IETF tzdist working group. In particular, the following individuals have made important contributions to this work: Steve Allen, Lester Caine, Stephen Colebourne, Tobias Conradi, Steve Crocker, Paul Eggert, John Haug, Ciny Joy, Bryan Keller, Andrew McMillan, Ken Murchison, Tim Parenti, Arnaud Quillaud, Jose Edvaldo Saraiva, and Dave Thewlis. This specification originated from work at the Calendaring and Scheduling Consortium, which has supported the development and testing of implementations of the specification. Douglass & Daboo Expires October 24, 2015 [Page 48] Internet-Draft TZDIST Service April 2015 12. References 12.1. Normative References [I-D.ietf-appsawg-http-problem] Nottingham, M. and E. Wilde, "Problem Details for HTTP APIs", draft-ietf-appsawg-http-problem-00 (work in progress), September 2014. [I-D.ietf-uta-tls-bcp] Sheffer, Y., Holz, R., and P. Saint-Andre, "Recommendations for Secure Use of TLS and DTLS", draft- ietf-uta-tls-bcp-11 (work in progress), February 2015. [RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types", RFC 2046, November 1996. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. [RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for specifying the location of services (DNS SRV)", RFC 2782, February 2000. [RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818, May 2000. [RFC3339] Klyne, G., Ed. and C. Newman, "Date and Time on the Internet: Timestamps", RFC 3339, July 2002. [RFC3553] Mealling, M., Masinter, L., Hardie, T., and G. Klyne, "An IETF URN Sub-namespace for Registered Protocol Parameters", BCP 73, RFC 3553, June 2003. [RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO 10646", STD 63, RFC 3629, November 2003. [RFC4985] Santesson, S., "Internet X.509 Public Key Infrastructure Subject Alternative Name for Expression of Service Name", RFC 4985, August 2007. [RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS) Protocol Version 1.2", RFC 5246, August 2008. [RFC5545] Desruisseaux, B., "Internet Calendaring and Scheduling Core Object Specification (iCalendar)", RFC 5545, September 2009. Douglass & Daboo Expires October 24, 2015 [Page 49] Internet-Draft TZDIST Service April 2015 [RFC5785] Nottingham, M. and E. Hammer-Lahav, "Defining Well-Known Uniform Resource Identifiers (URIs)", RFC 5785, April 2010. [RFC6125] Saint-Andre, P. and J. Hodges, "Representation and Verification of Domain-Based Application Service Identity within Internet Public Key Infrastructure Using X.509 (PKIX) Certificates in the Context of Transport Layer Security (TLS)", RFC 6125, March 2011. [RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265, April 2011. [RFC6321] Daboo, C., Douglass, M., and S. Lees, "xCal: The XML Format for iCalendar", RFC 6321, August 2011. [RFC6335] Cotton, M., Eggert, L., Touch, J., Westerlund, M., and S. Cheshire, "Internet Assigned Numbers Authority (IANA) Procedures for the Management of the Service Name and Transport Protocol Port Number Registry", BCP 165, RFC 6335, August 2011. [RFC6557] Lear, E. and P. Eggert, "Procedures for Maintaining the Time Zone Database", BCP 175, RFC 6557, February 2012. [RFC6570] Gregorio, J., Fielding, R., Hadley, M., Nottingham, M., and D. Orchard, "URI Template", RFC 6570, March 2012. [RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service Discovery", RFC 6763, February 2013. [RFC7159] Bray, T., "The JavaScript Object Notation (JSON) Data Interchange Format", RFC 7159, March 2014. [RFC7230] Fielding, R. and J. Reschke, "Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing", RFC 7230, June 2014. [RFC7231] Fielding, R. and J. Reschke, "Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content", RFC 7231, June 2014. [RFC7232] Fielding, R. and J. Reschke, "Hypertext Transfer Protocol (HTTP/1.1): Conditional Requests", RFC 7232, June 2014. [RFC7234] Fielding, R., Nottingham, M., and J. Reschke, "Hypertext Transfer Protocol (HTTP/1.1): Caching", RFC 7234, June 2014. Douglass & Daboo Expires October 24, 2015 [Page 50] Internet-Draft TZDIST Service April 2015 [RFC7235] Fielding, R. and J. Reschke, "Hypertext Transfer Protocol (HTTP/1.1): Authentication", RFC 7235, June 2014. [RFC7265] Kewisch, P., Daboo, C., and M. Douglass, "jCal: The JSON Format for iCalendar", RFC 7265, May 2014. 12.2. Informative References [RFC2131] Droms, R., "Dynamic Host Configuration Protocol", RFC 2131, March 1997. Appendix A. Change History (to be removed prior to publication as an RFC) Changes for -07 1. Added comment to check publisher data to see if fake time zone has been used. 2. Tweaked non-DNSSEC SRV text to indicate a service->target match is based on sub-domain and that any mismatch is always a failure. 3. SECDIR: Now recommend that TLS certs include an SRV-ID field. 4. SECDIR: Additional privacy text tweaks. Changes for -06 1. WGLC: Added addition text about problems with operating system only updates. 2. WGLC: Use "Root" and "Secondary" as prefix for "Providers" in Figure 1. 3. WGLC: various editorial tweaks and example fixes. 4. WGLC: "invalid-changedsince" error description fixed. 5. WGLC: use "full-date" to describe RFC3339 date only values. 6. WGLC: changed security considerations to prevent clients from falling back to non-TLS. 7. SECDIR: added Privacy Considerations with a bunch of recommendations for clients. 8. SECDIR: require TLS for server-to-server requests. Douglass & Daboo Expires October 24, 2015 [Page 51] Internet-Draft TZDIST Service April 2015 9. SECDIR: require clients to stick with TLS once they start using it (don't downgrade, redirect etc). 10. SECDIR: added reference to TLS BCP document. Changes for -05 1. Now uses its own rules for defining JSON objects. 2. Added new section on time zone versions. 3. Added publisher/version to the list action response meta-data. 4. Changed conditional request and synchronization sections to better describe how meta-data and data are updated. 5. Added the ability to retrieve leap second information from the server. 6. Added text to require servers to return all data if a "changedsince" value is not supported. 7. Switched TZUNTIL to be exclusive rather than inclusive, so that it now matches the definition of the truncation end point (also exclusive). Changes for -04 1. Tweaked invalid-start/end for action expand to indicate outside truncation range. 2. Added text on use of Accept-Language. 3. Added text on requirement to percent-encode {/tzid}. 4. Moved /observances under /zones{/tzid}. 5. Observances response now includes start/end of actual range returned if different from what was requested. 6. Truncation end and &end= for get action are now exclusive. 7. Added capabilities action in capabilities example response. 8. Added uri-template items to capabilities action definitions. 9. Added start/end items to the observances response. Douglass & Daboo Expires October 24, 2015 [Page 52] Internet-Draft TZDIST Service April 2015 10. Error codes are now URNs (with an IANA registration for a tzdist sub-namespace) and the URNs are used as the type value in JSON problem reports. 11. Removed "changedsince" from expand action - ETag can be used instead. Changes for -03 1. Reworked conditional list section (https://tools.ietf.org/wg/tzdist/trac/ticket/22 & https://tools.ietf.org/wg/tzdist/trac/ticket/33). 2. Moved definitions into General Considerations section. 3. Now makes use of ietf-appsawg-http-problem for error responses. 4. Switched to using a more RESTful design with resources used to identify endpoints for actions (https://tools.ietf.org/wg/tzdist/trac/ticket/29). 5. Tweaked TZUNTIL text to further address (https://tools.ietf.org/wg/tzdist/trac/ticket/15). 6. Tweaked "outright" deletion text to match latest on mailing list (https://tools.ietf.org/wg/tzdist/trac/ticket/18). 7. Added additional text suggesting other discovery mechanisms could be used (https://tools.ietf.org/wg/tzdist/trac/ticket/30). 8. Now require "end" parameter on expand to avoid issues with truncated data upper bounds (https://tools.ietf.org/wg/tzdist/trac/ticket/10). Changes for -02 1. "time zone server" -> "time zone data server". 2. Re-worded some text containing reference to "historical" time zone data, and truncation behavior. 3. Removed "REST". 4. Use "TZID-ALIAS-OF" in place of "EQUIVALENT-TZID". 5. Added \-escape mechanism for find action. Douglass & Daboo Expires October 24, 2015 [Page 53] Internet-Draft TZDIST Service April 2015 6. Revised Section 4.2.3 to address (https://tools.ietf.org/wg/tzdist/trac/ticket/18). Changes for -01 1. Query attribute: "name" -> "pattern" (https://tools.ietf.org/wg/tzdist/trac/ticket/4). 2. UTF-8 used for time zone ids and in all responses. 3. Added glossary term and note for "time zone" (https://tools.ietf.org/wg/tzdist/trac/ticket/12). 4. Glossary term change and alias text from (https://tools.ietf.org/wg/tzdist/trac/ticket/13). 5. "Local Provider" -> "Secondary Provider". 6. Additional security text for (https://tools.ietf.org/wg/tzdist/trac/ticket/25). 7. Added additional text to better describe localized names. 8. Added "tzid" member to expand response. 9. Added optional "provider-details" member to capabilities response, and also made "contacts" optional. 10. Definition of "invalid-action" moved to Section 6, and clarified text related to error responses in Sections 4.1.6 and 6 (https://tools.ietf.org/wg/tzdist/trac/ticket/17). 11. Added "Observance" to glossary. 12. Added "TZUNTIL" iCalendar property (part of https://tools.ietf.org/wg/tzdist/trac/ticket/15). 13. Revamped truncation to always use UTC date-time values and support end points (https://tools.ietf.org/wg/tzdist/trac/ ticket/21, and https://tools.ietf.org/wg/tzdist/trac/ticket/10). 14. Expand always uses UTC date-time values for query parameters, and always returns UTC date-time onset values (https://tools.ietf.org/wg/tzdist/trac/ticket/21). Changes for -00 Douglass & Daboo Expires October 24, 2015 [Page 54] Internet-Draft TZDIST Service April 2015 1. Initial WG draft derived from draft-douglass-timezone-service-11, with some terminology changes to match WG name. 2. Updated references. 3. "timezone" -> "time zone" (https://tools.ietf.org/wg/tzdist/trac/ ticket/6). 4. Glossary tweak (first part of https://tools.ietf.org/wg/tzdist/trac/ticket/13). 5. Fix iCalendar property names: UTC-OFFSET-* -> TZOFFSET*. 6. Fix invalid-truncate error code description. Authors' Addresses Michael Douglass Rensselaer Polytechnic Institute 110 8th Street Troy , NY 12180 USA Email: douglm@rpi.edu URI: http://www.rpi.edu/ Cyrus Daboo Apple Inc. 1 Infinite Loop Cupertino , CA 95014 USA Email: cyrus@daboo.name URI: http://www.apple.com/ Douglass & Daboo Expires October 24, 2015 [Page 55]