Timezone

ci maintainability

Accurate current and history timezones for Ruby.

Installation

Use the timezone gem - available on RubyGems. Semantic versioning is used, so if you would like to remain up-to-date and avoid any backwards-incompatible changes, use the following in your Gemfile:

gem 'timezone', '~> 1.0'

RubyDocs

Complete documentation for this gem can be found on RubyDoc.

Simple Timezone Queries

Simple querying of time, in any timezone, is accomplished by first retrieving a Timezone::Zone object and then calling methods on that object.

timezone = Timezone['America/Los_Angeles']
=> #<Timezone::Zone name: "America/Los_Angeles">

timezone.valid?
=> true

timezone.utc_to_local(Time.now)
=> 2011-02-11 17:29:05 UTC

timezone.utc_to_local(Time.utc(2010, 1, 1, 0, 0, 0))
=> 2009-12-31 16:00:00 UTC

timezone.time_with_offset(Time.utc(2010, 1, 1, 0, 0, 0))
=> 2009-12-31 16:00:00 -0800

timezone.abbr(Time.new(2016, 9, 4, 1, 0, 0))
=> "PDT"

NOTE: time is always returned in the UTC timezone when using the utc_to_local function, but it accurately reflects the actual time in the specified timezone. The reason for this is that this function also takes into account daylight savings time and historical changes in timezone, which can alter the offset. If you want a time with the appropriate offset at the given time, then use the time_with_offset function as shown above.

You can use the timezone object to convert local times into the best UTC estimate. The reason this is an estimate is that some local times do not actually map to UTC times (for example when time jumps forward) and some local times map to multiple UTC times (for example when time falls back).

timezone = Timezone.fetch('America/Los_Angeles')
=> #<Timezone::Zone name: "America/Los_Angeles">

timezone.local_to_utc(Time.utc(2015,11,1,1,50,0))
=> 2015-11-01 08:50:00 UTC

You can also query a Timezone::Zone object to determine if it was in Daylight Savings Time.

timezone = Timezone['America/Los_Angeles']
=> #<Timezone::Zone name: "America/Los_Angeles">

timezone.dst?(Time.now)
=> true

timezone.dst?(Time.utc(2010, 1, 1, 0, 0, 0))
=> false

For more information on the ::Timezone::Zone object, see the RubyDocs.

Finding Timezones Based on Latitude and Longitude

timezone has the capacity to query Geonames and Google for timezones based on latitude and longitude. Before querying a timezone API you'll need to configure the API you want to use.

Lookup Configuration with Geonames

  1. Ensure you have a Geonames username. It's free and easy to setup, you can do so here.
  2. Ensure you have enabled web services here.

  3. Configure your lookup. NOTE: in Rails it is recommended that you add this code to an initializer.

    Timezone::Lookup.config(:geonames) do |c|
  c.username = 'your_geonames_username_goes_here'
end

Lookup Configuration with Google

  1. Ensure you have a Google API Key, which you can get here.
  2. Enable the Google Maps Time Zone API.

  3. Configure your lookup. NOTE: in Rails it is recommended that you add this code to an initializer.

    Timezone::Lookup.config(:google) do |c|
  c.api_key = 'your_google_api_key_goes_here'
  c.client_id = 'your_google_client_id' # if using 'Google for Work'
end

Performing Latitude - Longitude Lookups

After configuring the API of your choice, pass the lookup coordinates to Timezone::lookup.

timezone = Timezone.lookup(-34.92771808058, 138.477041423321)
=> #<Timezone::Zone name: "Australia/Adelaide">

timezone.name
=> "Australia/Adelaide"

timezone.utc_to_local(Time.now)
=> 2011-02-12 12:02:13 UTC

Latitude - Longitude Lookups for Etcetera areas

By default both Geonames and Google do not provide results for lookups outside of continents and country borders. For example, if you try coordinates [0, 0] (somewhere in the Atlantic Ocean), you will get an exception.

But there is a way to get lookups for the whole Earth surface working (with Geonames only). Just add the offset_etc_areas option to the lookup configuration:

    Timezone::Lookup.config(:geonames) do |c|
      c.username = 'your_geonames_username_goes_here'
      c.offset_etc_zones = true
    end

Then try to lookup coordinates in Etc area:

timezone = Timezone.lookup(89, 40)
=> #<Timezone::Zone name: "Etc/GMT-3">

timezone.name
=> "Etc/GMT-3"

timezone.utc_offset
=> 10800

NOTE: Etc/GMT zones have POSIX-style signs in their names, with positive signs west of Greenwich. For example, "Etc/GMT-3" zone has a negative sign, but a positive UTC offset (10800 seconds or +3 hours) and its time is ahead of UTC (east of Greenwich) by 3 hours.

Error States and Nil Objects

All exceptions raised by the timezone gem are subclasses of ::Timezone::Error::Base. timezone also provides a default nil timezone object that behaves like a Timezone::Zone except that it is invalid.

Timezone.fetch('foobar')
=> Timezone::Error::InvalidZone

Timezone::Error::InvalidZone < Timezone::Error::Base
=> true

Timezone.fetch('foobar', Timezone['America/Los_Angeles'])
=> #<Timezone::Zone name: "America/Los_Angeles">

Timezone.fetch('foobar'){ |name| "#{name} is invalid" }
=> "foobar is invalid"

zone = Timezone['foo/bar']
=> #<Timezone::NilZone>

zone.valid?
=> false

For more information on errors, check ::Timezone::Error.

For more information on the nil object, check ::Timezone::NilZone.

Latitude - longitude lookups can raise ::Timezone::Error::Lookup exceptions when issues occur with the remote API request. For example, if an API limit is reached. If the request is valid but the result does not return a valid timezone, then an ::Timezone::Error::InvalidZone exception will be raised, or a default value will be returned if you have provided one.

Timezone.lookup(10, 10)
=> Timezone::Error::Geonames: api limit reached

Timezone.lookup(10, 100000)
=> Timezone::Error::InvalidZone

Timezone.lookup(10, 100000, Timezone::NilZone.new)
=> #<Timezone::NilZone>

Timezone.lookup(10, 100000){ |name| "#{name} is invalid" }
=> " is invalid"

Using Geonames and Google Lookups

timezone can be configured to use both Google and Geonames lookups. For instance, you may choose to fallback to Google if a Geonames lookup fails. The return value from a ::Timezone::Lookup.config call can be stored and re-used to trigger lookups for the configured service. For instance:

GEONAMES_LOOKUP = Timezone::Lookup.config(:geonames) { |c| c.username = ... }
GOOGLE_LOOKUP = Timezone::Lookup.config(:google) { |c| c.api_key = ... }

lat, lon = 89, 40

begin
  GEONAMES_LOOKUP.lookup(lat, lon)
rescue ::Timezone::Error::Lookup
  GOOGLE_LOOKUP.lookup(lat, lon)
end

Listing Timezones

Retrieving the complete list of timezones can be accomplished using the ::Timezone::names function. NOTE: the list is not ordered.

Timezone.names
=> ["EST", "Indian/Comoro", "Indian/Christmas", "Indian/Cocos", ...]

Using Your Own HTTP Request Handler

If you have non-standard http request needs or want to have more control over API calls to Geonames and Google, you can write your own http request handler instead of using the built-in client.

Here is a sample request handler that uses open-uri to perform requests.

require 'open-uri'

class MyRequestHandler
  def initialize(config)
    @protocol = config.protocol
    @url = config.url
  end

  Response = Struct.new(:body, :code)

  # Return a response object that responds to #body and #code
  def get(path)
    response = open("#{@protocol}://#{@url}#{path}")

    Response.new(response.read, response.status.first)
  rescue OpenURI::HTTPError
    Response.new(nil, '500')
  end
end

This custom request handler can be configured for Google or Geonames. For example, to configure with Geonames you would do the following:

Timezone::Lookup.config(:geonames) do |c|
  c.username = 'foobar'
  c.request_handler = MyRequestHandler
end

Testing Timezone Lookups

You can provide your own lookup stubs using the built in ::Timezone::Lookup::Test class.

::Timezone::Lookup.config(:test)
=> #<Timezone::Lookup::Test:... @stubs={}>

::Timezone::Lookup.lookup.stub(-10, 10, 'America/Los_Angeles')
=> "America/Los_Angeles"

::Timezone.lookup(-10, 10).name
=> 'America/Los_Angeles'

::Timezone.lookup(-11, 11)
=> Timezone::Error::Test: missing stub

You can also provide a fallback lookup, which will be returned if you query an un-stubbed lookup value.

::Timezone::Lookup.lookup.default('America/Los_Angeles')
=> "America/Los_Angeles"