| Rfc | 7808 |
|---|
| Title | Time Zone Data Distribution Service |
|---|
| Author | M. Douglass, C. Daboo |
|---|
| Date | March
2016 |
|---|
| Format: | TXT, HTML |
|---|
| Status: | PROPOSED STANDARD |
|---|
|
Internet Engineering Task Force (IETF) M. Douglass
Request for Comments: 7808 Spherical Cow Group
Category: Standards Track C. Daboo
ISSN: 2070-1721 Apple
March 2016
Time Zone Data Distribution Service
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 is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 5741.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
http://www.rfc-editor.org/info/rfc7808.
Copyright Notice
Copyright (c) 2016 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.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Conventions . . . . . . . . . . . . . . . . . . . . . . . 4
2. Architectural Overview . . . . . . . . . . . . . . . . . . . 5
3. General Considerations . . . . . . . . . . . . . . . . . . . 7
3.1. Time Zone . . . . . . . . . . . . . . . . . . . . . . . . 7
3.2. Time Zone Data . . . . . . . . . . . . . . . . . . . . . 7
3.3. Time Zone Metadata . . . . . . . . . . . . . . . . . . . 7
3.4. Time Zone Data Server . . . . . . . . . . . . . . . . . . 7
3.5. Observance . . . . . . . . . . . . . . . . . . . . . . . 7
3.6. Time Zone Identifiers . . . . . . . . . . . . . . . . . . 7
3.7. Time Zone Aliases . . . . . . . . . . . . . . . . . . . . 8
3.8. Time Zone Localized Names . . . . . . . . . . . . . . . . 8
3.9. Truncating Time Zones . . . . . . . . . . . . . . . . . . 9
3.10. Time Zone Versions . . . . . . . . . . . . . . . . . . . 10
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 . . . . . . . . . . . . . . . 12
4.1.4. Conditional Time Zone Requests . . . . . . . . . . . 12
4.1.5. Expanded Time Zone Data . . . . . . . . . . . . . . . 14
4.1.6. Server Requirements . . . . . . . . . . . . . . . . . 14
4.1.7. Error Responses . . . . . . . . . . . . . . . . . . . 14
4.1.8. Extensions . . . . . . . . . . . . . . . . . . . . . 14
4.2. Client Guidelines . . . . . . . . . . . . . . . . . . . . 14
4.2.1. Discovery . . . . . . . . . . . . . . . . . . . . . . 14
4.2.1.1. SRV Service Labels for the Time Zone Data
Distribution Service . . . . . . . . . . . . . . 15
4.2.1.2. TXT Records for a Time Zone Data Distribution
Service . . . . . . . . . . . . . . . . . . . . . 15
4.2.1.3. Well-Known URI for a Time Zone Data Distribution
Service . . . . . . . . . . . . . . . . . . . . . 16
4.2.1.3.1. Example: Well-Known URI Redirects to Actual
Context Path . . . . . . . . . . . . . . . . 17
4.2.2. Synchronization of Time Zones . . . . . . . . . . . . 17
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 Preexisting Time Zone Data . 18
5. Actions . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
5.1. "capabilities" Action . . . . . . . . . . . . . . . . . . 18
5.1.1. Example: get capabilities . . . . . . . . . . . . . . 19
5.2. "list" Action . . . . . . . . . . . . . . . . . . . . . . 21
5.2.1. Example: List Time Zone Identifiers . . . . . . . . . 22
5.3. "get" Action . . . . . . . . . . . . . . . . . . . . . . 23
5.3.1. Example: Get Time Zone Data . . . . . . . . . . . . . 24
5.3.2. Example: Conditional Get Time Zone Data . . . . . . . 25
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).
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-based API
[RFC7159].
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].
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, UTC date-time values as specified in
[RFC3339] use a "Z" suffix, and not fixed numeric offsets.
This specification contains examples of HTTP requests and responses.
In some cases, additional line breaks have been introduced into the
request or response data to match maximum line-length limits of this
document.
2. Architectural Overview
The overall process for the delivery of time zone data can be
visualized via the diagram 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 that
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 "republish" data from another
publisher.
(c) Root Providers: Servers that 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.
(d) Secondary Providers: Servers that 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 set up their own secondary provider to allow clients
within their network to make requests of that server rather than
make 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 time zone is 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.
3.2. Time Zone Data
Time zone data is 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 Metadata
Time zone metadata is data that describes additional properties of a
time zone that is not itself included 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 time zone data server is 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. Each period of time
with a constant UTC offset is called an observance.
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) naming scheme for time zone identifiers 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.
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 that 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
new events only 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 unnecessary.
To avoid having to send unnecessary data, servers can choose to
truncate time zone data to a range determined by start- and end-point
date-time values, and to 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 will 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" subcomponent 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 start point of the truncation range. This subcomponent,
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 that 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. For example, a publisher
producing data several times a year might use version identifiers
"2015a", "2015b", etc.
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. For example, 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 that 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, metadata, 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 data distribution service
has a "context path" request-URI template 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 template "{/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; that 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 URI template 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 "/"
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 metadata in the form of a JSON
[RFC7159] object. Clients can directly request the time zone
metadata or issue queries for subsets of metadata that match specific
criteria.
Security and privacy considerations for this protocol are discussed
in detail in Sections 8 and 9, respectively.
4.1.1. Time Zone Queries
Time zone identifiers, aliases, or localized names can be used to
query for time zone data or metadata. 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
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.
4.1.4. Conditional Time Zone Requests
When time zone data or metadata 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 (an
incremental update).
Clients initially request a full list of time zones from the server
using a "list" action request (see Section 5.2). The response to
that request includes two items the client caches for use with
subsequent "conditional" (incremental update) requests:
1. An opaque synchronization token in the "synctoken" JSON member.
This token changes whenever there is a change to any metadata
associated with one or more time zones (where the metadata is the
information reported in the "list" action response for each time
zone).
2. The HTTP ETag header field value for each time zone returned in
the response. The ETag header field value is returned in the
"etag" JSON member, and it corresponds to the ETag header field
value that would be returned when executing a "get" action
request (see Section 5.3) against the corresponding time zone
data resource.
For subsequent updates to cached data, clients can use the following
procedure:
a. Send a "list" action request with a "changedsince" URI query
parameter with its value set to the last opaque synchronization
token returned by the server. The server will return time zone
metadata for only those time zones that have changed since the
last request.
b. The client will cache the new opaque synchronization token
returned in the response for the next incremental update, along
with the returned time zone metadata information.
c. The client will check each time zone metadata to see if the
"etag" value is different from that of any cached time zone data
it has.
d. The client will use a "get" action request to update any cached
time zone data for those time zones whose ETag header field value
has changed.
Note that time zone metadata 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 metadata 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 metadata element will change with each
new published revision; however, only a small subset of time zone
data will actually change.
If a client needs data for only one or a small set of time zones
(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.
a. When the client retrieves the time zone data from the server
using a "get" action (see Section 5.3), the server will include
an HTTP ETag header field in the response.
b. The client will store the value of that header field along with
the request-URI used for the request.
c. 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 header field value 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 that will include the changed data, as well as a new
value for the ETag header field.
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
When an HTTP error response is returned to the client, the server
SHOULD return a JSON "problem details" object in the response body,
as per [RFC7807]. Every JSON "problem details" 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 subsections 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]).
4.2.1.1. SRV Service Labels for the Time Zone Data Distribution Service
[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. TXT Records for a Time Zone Data Distribution Service
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 in
Section 4.2.1.3.
As per Section 8, the server MAY require authentication when a client
tries to access the path URI specified by the TXT RR (i.e., the
server would return a 401 status response to the unauthenticated
request from the client, then return a redirect response after a
successful authentication by the client).
Example: text record for service with Transport Layer Security.
_timezones._tcp TXT path=/timezones
4.2.1.3. Well-Known URI for a Time Zone Data Distribution Service
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, taking into account
security restrictions on redirects described in Section 8. Servers
MUST NOT locate the actual time zone data distribution service
endpoint at the ".well-known" URI as per Section 1.1 of [RFC5785].
The "well-known" URI MUST be present on the server, even when a TXT
RR (Section 4.2.1.2) is used in the DNS to specify a "context path".
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 an appropriate "max-age"
value would be used.
As per Section 8, 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. The client
would also cache the redirect information, subject to any Cache-
Control directive, for use in subsequent requests.
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.
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 issuing a "list" action to retrieve all the
time zone metadata. The client preserves the returned opaque token
for subsequent use (see "synctoken" in Section 5.2.1). The client
stores the metadata 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 metadata. A typical "list" action response
size is about 50-100 KB of "pretty printed" JSON data, for a service
using the IANA time zone database [RFC6557], as of the time of
publication of this specification.
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 issues a "list"
action with the "changedsince" URI query parameter set to the value
of the opaque token returned by the last synchronization. The client
again preserves the returned opaque token for subsequent use. The
client updates its stored time zone metadata using the new values
returned in the response, which contains just the time zone metadata
for those time zones changed since the last synchronization. In
addition, it compares the "etag" value in each time zone metadata to
the ETag header field value for the corresponding time zone data
resource it has previously cached; if they are different, it fetches
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 is 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 Preexisting 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 metadata, 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.
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.
The examples in the following subsections presume that the timezone
context path has been discovered to be "/servlet/timezone" (as in the
example in Section 4.2.1.3.1).
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 /servlet/timezone/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",
"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": "/servlet/timezone/capabilities",
"parameters": []
},
{
"name": "list",
"uri-template": "/servlet/timezone/zones{?changedsince}",
"parameters": [
{
"name": "changedsince",
"required": false,
"multi": false
}
]
},
{
"name": "get",
"uri-template": "/servlet/timezone/zones{/tzid}{?start,end}",
"parameters": [
{
"name": "start",
"required": false,
"multi": false
},
{
"name": "end",
"required": false,
"multi": false
}
]
},
{
"name": "expand",
"uri-template":
"/servlet/timezone/zones{/tzid}/observances{?start,end}",
"parameters": [
{
"name": "start",
"required": true,
"multi": false
},
{
"name": "end",
"required": true,
"multi": false
}
]
},
{
"name": "find",
"uri-template": "/servlet/timezone/zones{?pattern}",
"parameters": [
{
"name": "pattern",
"required": true,
"multi": false
}
]
},
{
"name": "leapseconds",
"uri-template": "/servlet/timezone/leapseconds",
"parameters": []
}
]
}
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, and MUST NOT occur more than 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
In this example the client requests the full set of time zone
identifiers.
>> Request <<
GET /servlet/timezone/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"
}
]
},
...other time zones...
]
}
5.3. "get" Action
Name: get
Request-URI Template:
{/service-prefix,data-prefix}/zones{/tzid}{?start,end}
The "tzid" variable value is REQUIRED in order to distinguish this
action from the "list" action.
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=<date-time>
OPTIONAL, and MUST NOT occur more than once. Specifies the
inclusive UTC date-time value at which the returned time zone
data is truncated at its start.
end=<date-time>
OPTIONAL, and MUST NOT occur more than 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.
5.3.1. Example: Get Time Zone Data
In this example, the client requests that the time zone with a
specific time zone identifier be returned.
>> Request <<
GET /servlet/timezone/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 that the time zone with a
specific time zone identifier 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 /servlet/timezone/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
5.3.3. Example: Get Time Zone Data Using a Time Zone Alias
In this example, the client requests that the time zone with an
aliased time zone identifier be returned, and the server returns the
time zone data with that identifier and two aliases.
>> Request <<
GET /servlet/timezone/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
}
In this example, the client requests that the time zone with a
specific time zone identifier truncated at one of the ranges
specified by the server 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 period of the time zone
data.
>> Request <<
GET /servlet/timezone/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: Request for a Nonexistent Time Zone
In this example, the client requests that the time zone with a
specific time zone identifier be returned. As it turns out, no time
zone exists with that identifier.
>> Request <<
GET /servlet/timezone/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 values (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=<date-time>: REQUIRED, and MUST occur only once. Specifies
the inclusive UTC date-time value for the start of the period
of interest.
end=<date-time>: 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
represents the date just after the range of interest. For 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 points 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
In this example, the client requests a time zone in the expanded
form.
>> Request <<
GET /servlet/timezone/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}
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 patter match against
the names known to the server (with an asterisk (*) as the
wildcard character). Pattern-match strings (which have to be
percent-encoded and then decoded when used in the URI query
parameter) 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 substring text match is done,
e.g., "*xyz*"
Escaping \ and *: To match 0x2A ("*") and 0x5C ("\") characters
in a time zone identifier, those characters have to be
"escaped" in the pattern by prepending a single 0x5C ("\")
character. For example, a pattern "\*Test\\Time\*Zone\*" is
used for an exact match against the time zone identifier
"*Test\Time*Zone*". An unescaped "*" character MUST NOT appear
in the middle of the string and MUST result in an error. An
unescaped "\" character MUST NOT appear anywhere in the string
and MUST result in an error.
In addition, when matching:
Underscores: Underscore characters (0x5F) in time zone
identifiers MUST be mapped to a single space character (0x20)
prior to string comparison in both the pattern and time zone
identifiers being matched. This allows time zone identifiers
such as "America/New_York" to match a query for "*New York*".
Case mapping: ASCII characters in the range 0x41 ("A") through
0x5A ("Z") MUST be mapped to their lowercase equivalents in
both the pattern and time zone identifiers being matched.
Parameters:
pattern=<text>
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".
>> Request <<
GET /servlet/timezone/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"
}
]
},
...
]
}
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. For example (as in Section 5.6.1), 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. When a leap second is
added, the "utc-offset" value will be incremented by one; when a
leap second is removed, the "utc-offset" value will be decremented
by one.
Possible Error Codes No specific code.
5.6.1. Example: Get Leap-Second Information
In this example, the client requests the current leap-second
information from the server.
>> Request <<
GET /servlet/timezone/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": "2015-12-28",
"publisher": "Example.com",
"version": "2015d",
"leapseconds": [
{
"utc-offset": 10,
"onset": "1972-01-01",
},
{
"utc-offset": 11,
"onset": "1972-07-01",
},
...
{
"utc-offset": 35,
"onset": "2012-07-01",
},
{
"utc-offset": 36,
"onset": "2015-07-01",
}
]
}
6. JSON Definitions
[RFC7159] defines the structure of JSON objects using a set of
primitive elements. The structure of JSON objects used by this
specification is described by the following set of rules:
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
separated from the other by a "|" (0x7C) character, then only one
of those members MUST be present in the 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, the name of the
member, 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
Below are the 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
)
; 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)
; UTC date-time value (per [RFC3339]) 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
; UTC date-time value (per [RFC3339]) 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 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
; 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
Below are the rules for the JSON document returned for a "list" or
"find" action request.
; root object
OBJECT (synctoken, timezones)
; 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
; UTC date-time value as specified in [RFC3339]
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
; language default: false
MEMBER pref "pref" : BOOLEAN
6.3. expand Action Response
Below are the 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
; UTC date-time value (per [RFC3339]) 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
6.4. leapseconds Action Response
Below are the 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
; full-date value as specified in [RFC3339]
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
; full-date value (per [RFC3339]) 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
period of data within a "VTIMEZONE" component.
Value Type: DATE-TIME
Property Parameters: IANA and non-standard property parameters can
be specified on this property.
Conformance: This property can be specified zero times 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" subcomponents. However, an upper bound on the validity
period of the time zone data cannot be simply derived from the
observance with the latest onset time, and [RFC5545] does not
define a way to get such an upper bound. 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 in ABNF [RFC5234]:
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 for which
the main time zone identifier is an alias.
Value Type: TEXT
Property Parameters: IANA and non-standard property parameters can
be specified on this property.
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 in ABNF [RFC5234]:
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] and
[RFC5246], with best practices described in [RFC7525]). 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 SHOULD use Transport Layer Security as defined by [RFC2818],
unless they are specifically configured otherwise. 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 addition, clients MUST NOT follow HTTP redirect requests from a
TLS service to a non-TLS service. When using TLS, clients MUST
verify the identity of the server, using a standard, secure mechanism
such as the certificate verification process specified in [RFC6125]
or DANE [RFC6698].
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
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; 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 poorly
implemented 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), as per
[RFC7235], to restrict which clients are allowed to access their
service or provide better identification of problematic clients.
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.
5. Avoid use of conditional HTTP requests [RFC7232] with the "get"
action to prevent tracking of clients by servers generating
client-specific ETag header field 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
occasionally. One option to mitigate this would be for the
client to make use of two time zone data 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 set up 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 data 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 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:
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 Identifiers Registry" to the
IETF parameters URN sub-namespace as per [RFC3553] for use with
protocol related error codes.
10.1. Service Actions Registration
IANA has created a new top-level category called "Time Zone Data
Distribution Service (TZDIST) Parameters" and has put all the
registries created herein into that category.
IANA has created a new registry called "TZDIST Service Actions", as
defined below.
10.1.1. Service Actions Registration Procedure
This registry uses the "Specification Required" policy defined in
[RFC5226], which makes use of a designated expert to review potential
registrations.
The IETF has created a mailing list, tzdist-service@ietf.org, which
is used for public discussion of time zone data distribution service
actions proposals prior to registration. The IESG has appointed a
designated expert who will monitor the tzdist-service@ietf.org
mailing list and review registrations.
A Standards Track RFC is REQUIRED for changes to actions previously
documented in a Standards Track RFC; otherwise, any public
specification that satisfies the requirements of [RFC5226] is
acceptable.
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 whether the registration is
approved, approved with minor changes, or rejected with cause, within
two weeks. When a registration is rejected with cause, it can be
resubmitted if the concerns listed in the cause are addressed.
Decisions made by the designated expert can be appealed as per
Section 7 of [RFC5226].
The designated expert MUST take the following requirements into
account when reviewing the registration:
1. A valid registration template MUST be provided by the submitter,
with a clear description of what the action does.
2. A proposed new action name MUST NOT conflict with any existing
registered action name. A conflict includes a name that
duplicates an existing one or that appears to be very similar to
an existing one and could be a potential source of confusion.
3. A proposed new action MUST NOT exactly duplicate the
functionality of any existing actions. In cases where the new
action functionality is very close to an existing action, the
designated expert SHOULD clarify whether the submitter is aware
of the existing action, and has an adequate reason for creating a
new action with slight differences from an existing one.
4. If a proposed action is an extension to an existing action, the
changes MUST NOT conflict with the intent of the existing action,
or in a way that could cause interoperability problems for
existing deployments of the protocol.
The IANA registry contains the name of the action ("Action Name") and
a reference to the section of the specification where the action
registration template is defined ("Reference").
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.
10.1.3. Actions Registry
The following table provides the initial content of the actions
registry.
+---------------+------------------------+
| Action Name | Reference |
+---------------+------------------------+
| capabilities | RFC 7808, Section 5.1 |
| list | RFC 7808, Section 5.2 |
| get | RFC 7808, Section 5.3 |
| expand | RFC 7808, Section 5.4 |
| find | RFC 7808, Section 5.5 |
| leapseconds | RFC 7808, Section 5.6 |
+---------------+------------------------+
10.2. timezone Well-Known URI Registration
IANA has added the following to the "Well-Known URIs" [RFC5785]
registry:
URI suffix: timezone
Change controller: IESG.
Specification document(s): RFC 7808
Related information: None.
10.3. Service Name Registrations
IANA has added two new service names to the "Service Name and
Transport Protocol Port Number Registry" [RFC6335], as defined below.
10.3.1. timezone Service Name Registration
Service Name: timezone
Transport Protocol(s): TCP
Assignee: IESG <iesg@ietf.org>
Contact: IETF Chair <chair@ietf.org>
Description: Time Zone Data Distribution Service - non-TLS
Reference: RFC 7808
Assignment Note: This is an extension of the http service. Defined
TXT keys: path=<context path> (as per Section 6 of [RFC6763]).
10.3.2. timezones Service Name Registration
Service Name: timezones
Transport Protocol(s): TCP
Assignee: IESG <iesg@ietf.org>
Contact: IETF Chair <chair@ietf.org>
Description: Time Zone Data Distribution Service - over TLS
Reference: RFC 7808
Assignment Note: This is an extension of the https service. Defined
TXT keys: path=<context path> (as per Section 6 of [RFC6763]).
10.4. TZDIST Identifiers Registry
IANA has registered a new URN sub-namespace within the IETF URN Sub-
namespace for Registered Protocol Parameter Identifiers defined in
[RFC3553].
Registrations in this registry follow the "IETF Review" [RFC5226]
policy.
Registry name: TZDIST Identifiers
URN prefix: urn:ietf:params:tzdist
Specification: RFC 7808
Repository: http://www.iana.org/assignments/tzdist-identifiers
Index value: Values in this registry are URNs or URN prefixes that
start with the prefix "urn:ietf:params:tzdist:". Each is
registered independently. The prefix
"urn:ietf:params:tzdist:error:" is used to represent 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).
Each registration in the "TZDIST Identifiers" registry requires the
following information:
URN: The complete URN that is used or the prefix for that URN.
Description: A summary description for the URN or URN prefix.
Specification: A reference to a specification describing the URN or
URN prefix.
Contact: Email for the person or groups making the registration.
Index Value: As described in [RFC3553], URN prefixes that are
registered include a description of how the URN is constructed.
This is not applicable for specific URNs.
The "TZDIST Identifiers" registry has the initial registrations
included in the following sections.
10.4.1. Registration of invalid-action Error URN
The following URN has been registered in the "tzdist Identifiers"
registry.
URN: urn:ietf:params:tzdist:error:invalid-action
Description: Generic error code for any invalid action.
Specification: RFC 7808, Section 5
Repository: http://www.iana.org/assignments/tzdist-identifiers
Contact: IESG <iesg@ietf.org>
Index value: N/A.
10.4.2. Registration of invalid-changedsince Error URN
The following URN has been registered in the "tzdist Identifiers"
registry.
URN: urn:ietf:params:tzdist:error:invalid-changedsince
Description: Error code for incorrect use of the "changedsince" URI
query parameter.
Specification: RFC 7808, Section 5.2
Repository: http://www.iana.org/assignments/tzdist-identifiers
Contact: IESG <iesg@ietf.org>
Index value: N/A.
10.4.3. Registration of tzid-not-found Error URN
The following URN has been registered in the "tzdist Identifiers"
registry.
URN: urn:ietf:params:tzdist:error:tzid-not-found
Description: Error code for missing time zone identifier.
Specification: RFC 7808, Sections 5.3 and 5.4
Repository: http://www.iana.org/assignments/tzdist-identifiers
Contact: IESG <iesg@ietf.org>
Index value: N/A.
10.4.4. Registration of invalid-format Error URN
The following URN has been registered in the "tzdist Identifiers"
registry.
URN: urn:ietf:params:tzdist:error:invalid-format
Description: Error code for unsupported HTTP Accept request header
field value.
Specification: RFC 7808, Section 5.3
Repository: http://www.iana.org/assignments/tzdist-identifiers
Contact: IESG <iesg@ietf.org>
Index value: N/A.
10.4.5. Registration of invalid-start Error URN
The following URN has been registered in the "tzdist Identifiers"
registry.
URN: urn:ietf:params:tzdist:error:invalid-start
Description: Error code for incorrect use of the "start" URI query
parameter.
Specification: RFC 7808, Sections 5.3 and 5.4
Repository: http://www.iana.org/assignments/tzdist-identifiers
Contact: IESG <iesg@ietf.org>
Index value: N/A.
10.4.6. Registration of invalid-end Error URN
The following URN has been registered in the "tzdist Identifiers"
registry.
URN: urn:ietf:params:tzdist:error:invalid-end
Description: Error code for incorrect use of the "end" URI query
parameter.
Specification: RFC 7808, Sections 5.3 and 5.4
Repository: http://www.iana.org/assignments/tzdist-identifiers
Contact: IESG <iesg@ietf.org>
Index value: N/A.
10.4.7. Registration of invalid-pattern Error URN
The following URN has been registered in the "tzdist Identifiers"
registry.
URN: urn:ietf:params:tzdist:error:invalid-pattern
Description: Error code for incorrect use of the "pattern" URI query
parameter.
Specification: RFC 7808, Section 5.5
Repository: http://www.iana.org/assignments/tzdist-identifiers
Contact: IESG <iesg@ietf.org>
Index value: N/A.
10.5. iCalendar Property Registrations
This document defines the following new iCalendar properties, which
have been added to the "Properties" registry under "iCalendar Element
Registries" [RFC5545]:
+----------------+----------+------------------------+
| Property | Status | Reference |
+----------------+----------+------------------------+
| TZUNTIL | Current | RFC 7808, Section 7.1 |
| TZID-ALIAS-OF | Current | RFC 7808, Section 7.2 |
+----------------+----------+------------------------+
11. References
11.1. Normative References
[RFC2046] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part Two: Media Types", RFC 2046,
DOI 10.17487/RFC2046, November 1996,
<http://www.rfc-editor.org/info/rfc2046>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782,
DOI 10.17487/RFC2782, February 2000,
<http://www.rfc-editor.org/info/rfc2782>.
[RFC2818] Rescorla, E., "HTTP Over TLS", RFC 2818,
DOI 10.17487/RFC2818, May 2000,
<http://www.rfc-editor.org/info/rfc2818>.
[RFC3339] Klyne, G. and C. Newman, "Date and Time on the Internet:
Timestamps", RFC 3339, DOI 10.17487/RFC3339, July 2002,
<http://www.rfc-editor.org/info/rfc3339>.
[RFC3553] Mealling, M., Masinter, L., Hardie, T., and G. Klyne, "An
IETF URN Sub-namespace for Registered Protocol
Parameters", BCP 73, RFC 3553, DOI 10.17487/RFC3553, June
2003, <http://www.rfc-editor.org/info/rfc3553>.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
2003, <http://www.rfc-editor.org/info/rfc3629>.
[RFC4985] Santesson, S., "Internet X.509 Public Key Infrastructure
Subject Alternative Name for Expression of Service Name",
RFC 4985, DOI 10.17487/RFC4985, August 2007,
<http://www.rfc-editor.org/info/rfc4985>.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
DOI 10.17487/RFC5226, May 2008,
<http://www.rfc-editor.org/info/rfc5226>.
[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<http://www.rfc-editor.org/info/rfc5234>.
[RFC5246] Dierks, T. and E. Rescorla, "The Transport Layer Security
(TLS) Protocol Version 1.2", RFC 5246,
DOI 10.17487/RFC5246, August 2008,
<http://www.rfc-editor.org/info/rfc5246>.
[RFC5545] Desruisseaux, B., Ed., "Internet Calendaring and
Scheduling Core Object Specification (iCalendar)",
RFC 5545, DOI 10.17487/RFC5545, September 2009,
<http://www.rfc-editor.org/info/rfc5545>.
[RFC5785] Nottingham, M. and E. Hammer-Lahav, "Defining Well-Known
Uniform Resource Identifiers (URIs)", RFC 5785,
DOI 10.17487/RFC5785, April 2010,
<http://www.rfc-editor.org/info/rfc5785>.
[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, DOI 10.17487/RFC6125, March
2011, <http://www.rfc-editor.org/info/rfc6125>.
[RFC6265] Barth, A., "HTTP State Management Mechanism", RFC 6265,
DOI 10.17487/RFC6265, April 2011,
<http://www.rfc-editor.org/info/rfc6265>.
[RFC6321] Daboo, C., Douglass, M., and S. Lees, "xCal: The XML
Format for iCalendar", RFC 6321, DOI 10.17487/RFC6321,
August 2011, <http://www.rfc-editor.org/info/rfc6321>.
[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, DOI 10.17487/RFC6335, August 2011,
<http://www.rfc-editor.org/info/rfc6335>.
[RFC6557] Lear, E. and P. Eggert, "Procedures for Maintaining the
Time Zone Database", BCP 175, RFC 6557,
DOI 10.17487/RFC6557, February 2012,
<http://www.rfc-editor.org/info/rfc6557>.
[RFC6570] Gregorio, J., Fielding, R., Hadley, M., Nottingham, M.,
and D. Orchard, "URI Template", RFC 6570,
DOI 10.17487/RFC6570, March 2012,
<http://www.rfc-editor.org/info/rfc6570>.
[RFC6698] Hoffman, P. and J. Schlyter, "The DNS-Based Authentication
of Named Entities (DANE) Transport Layer Security (TLS)
Protocol: TLSA", RFC 6698, DOI 10.17487/RFC6698, August
2012, <http://www.rfc-editor.org/info/rfc6698>.
[RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service
Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013,
<http://www.rfc-editor.org/info/rfc6763>.
[RFC7159] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March
2014, <http://www.rfc-editor.org/info/rfc7159>.
[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing",
RFC 7230, DOI 10.17487/RFC7230, June 2014,
<http://www.rfc-editor.org/info/rfc7230>.
[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
DOI 10.17487/RFC7231, June 2014,
<http://www.rfc-editor.org/info/rfc7231>.
[RFC7232] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Conditional Requests", RFC 7232,
DOI 10.17487/RFC7232, June 2014,
<http://www.rfc-editor.org/info/rfc7232>.
[RFC7234] Fielding, R., Ed., Nottingham, M., Ed., and J. Reschke,
Ed., "Hypertext Transfer Protocol (HTTP/1.1): Caching",
RFC 7234, DOI 10.17487/RFC7234, June 2014,
<http://www.rfc-editor.org/info/rfc7234>.
[RFC7235] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Authentication", RFC 7235,
DOI 10.17487/RFC7235, June 2014,
<http://www.rfc-editor.org/info/rfc7235>.
[RFC7265] Kewisch, P., Daboo, C., and M. Douglass, "jCal: The JSON
Format for iCalendar", RFC 7265, DOI 10.17487/RFC7265, May
2014, <http://www.rfc-editor.org/info/rfc7265>.
[RFC7525] Sheffer, Y., Holz, R., and P. Saint-Andre,
"Recommendations for Secure Use of Transport Layer
Security (TLS) and Datagram Transport Layer Security
(DTLS)", BCP 195, RFC 7525, DOI 10.17487/RFC7525, May
2015, <http://www.rfc-editor.org/info/rfc7525>.
[RFC7807] Nottingham, M. and E. Wilde, "Problem Details for HTTP
APIs", RFC 7807, DOI 10.17487/RFC7807, March 2016,
<http://www.rfc-editor.org/info/rfc7807>.
11.2. Informative References
[RFC2131] Droms, R., "Dynamic Host Configuration Protocol",
RFC 2131, DOI 10.17487/RFC2131, March 1997,
<http://www.rfc-editor.org/info/rfc2131>.
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, Daniel Kahn
Gillmor, John Haug, Ciny Joy, Bryan Keller, Barry Leiba, 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.
Authors' Addresses
Michael Douglass
Spherical Cow Group
226 3rd Street
Troy, NY 12180
United States
Email: mdouglass@sphericalcowgroup.com
URI: http://sphericalcowgroup.com
Cyrus Daboo
Apple Inc.
1 Infinite Loop
Cupertino, CA 95014
United States
Email: cyrus@daboo.name
URI: http://www.apple.com/