Updating the time zone database

Noda Time comes with a version of the tz database (also known as the IANA Time Zone database, or zoneinfo or Olson database), which is now hosted by IANA. This database changes over time, as countries decide to change their time zone rules. As new versions of Noda Time are released, the version of tzdb will be updated. However, you may wish to use a new version of tzdb without changing which version of Noda Time you're using. This documentation tells you how to do so.

Noda Time's main library doesn't read tzdb text files directly - it uses a binary form which is the output of NodaTime.TzdbCompiler - another part of the Noda Time project. This saves both space (the 2013h version takes about 125K when compiled) and time, as the binary form contains various precomputed transitions. The file also contains a mapping from Windows time zone names to tzdb time zone IDs, primarily so that Noda Time can map the local time zone reported by TimeZoneInfo to a tzdb time zone, and (from Noda Time 1.1 onwards) TZDB location data.

In Noda Time 1.0, the data was stored in .NET resources. This became awkward in a number of ways, not least because of the lack of full resource support in Portable Class Libraries. In 1.1, a new file format was introduced, along with methods to read this format from any stream. Support for the resource format has been removed from Noda Time 2.0.

For more details on the exact formats, please see the documentation in the developer guide.

Obtaining and using a "NodaZoneData" file

Fetching a NodaZoneData file from nodatime.org

NodaZoneData files are available from nodatime.org and contain compiled versions of TZDB from 2013h onwards.

These can be downloaded and used with any Noda Time 1.1+ binary, so you don't need to update to the latest version of Noda Time in order to get the latest version of TZDB, and you don't have to build the file yourself either.

The URL http://nodatime.org/tzdb/latest.txt returns a plaintext response containing the URL of the latest NZD file. This may be used for automation.

Building a NodaZoneData file

  1. Find the link to the latest tzdb release, e.g. http://www.iana.org/time-zones/repository/releases/tzdata2015e.tar.gz
  2. Determine the Windows mapping file you want to use, or let NodaTime.TzdbCompiler do it for you with the versions supplied with the Noda Time source in the data\cldr directory. If these are out of date, you can download a new file from CLDR.
  3. Run NodaTime.TzdbCompiler. I'd suggest leaving it in its build directory and running it like this:
path\to\NodaTime.TzdbCompiler.exe -s tzdb-url -w windows-file-or-directory -o path\to\output.nzd

The -s argument can be an unpacked archive directory, a local archive, or a remote archive. The -w argument can be a path to a single file, or a directory containing multiple Windows Zones XML files, in which case the most appropriate one will be selected automatically.

Using a NodaZoneData file

Typically you'll want to use the newly-created resource file as the default time zone provider, across your whole application. While it's possible to have multiple time zone providers in play at a time, that's a very rare scenario. Using a resource file is relatively straightforward:

  • Open a stream to the file
  • Create a TzdbDateTimeZoneSource with the stream, using the static FromStream method
  • Create DateTimeZoneCache with the source
  • Use that cache (usually by way of dependency injection as an IDateTimeZoneProvider) wherever you need time zone information

Here's some sample code for the first three steps above:

using NodaTime;
using NodaTime.TimeZones;
using System;
using System.IO;

public class CustomTzdb
{
    static void Main()
    {
        IDateTimeZoneProvider provider;
        // Or use Assembly.GetManifestResourceStream for an embedded file
        using (var stream = File.OpenRead("tzdb-2013h.nzd"))
        {
            var source = TzdbDateTimeZoneSource.FromStream(stream);
            provider = new DateTimeZoneCache(source);
        }
        Console.WriteLine(provider.SourceVersionId);
    }
}

The stream is fully read in the call to TzdbDateTimeZoneSource.FromStream, so disposing of it afterwards (as shown above) doesn't affect the source you've created. The stream can come from anywhere - typically it would either be a standalone file in the file system, or an embedded resource file within one of your assemblies. You certainly could fetch it across a network, if you wanted. (It is read sequentially from start to end - no seeking is required.)