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. If you're not using 1.0, we strongly advise you to use the new format; support for the resource format will be removed in 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 (1.1+ format)

Update the NodaTime NuGet package

From March 2017 onwards, we aim to update NuGet packages with new TZDB data shortly after each TZDB release, each update counting as a patch release. This has the disadvantage that it's less clear when a patch release is really just TZDB data vs when it's a regular bug-fix, but makes it much simpler for users. Simply update the NuGet package version you're using, and you will get the new data.

All minor versions from 1.3 onwards are updated. Users still using versions older than 1.3 are encouraged to migrate, at least to 1.3.

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. Download the latest tzdb release
  2. Unpack the tar.gz file - you may need to download extra tools for this; 7-Zip can cope with .tar.gz files for example, and I'd expect other zip tools to do so too. You should end up with a directory containing files such as "america", "africa", "etcetera".
  3. Ideally, rename the directory to match the version number, e.g. "2013h". The directory name will be used in the version ID reported by the time zone provider later.
  4. Find the Windows mapping file you want to use. Currently, I'd recommend using the version supplied with the Noda Time source in the data\cldr directory in a file beginning "windowsZones". This file comes from CLDR.
  5. Run NodaTime.TzdbCompiler. I'd suggest leaving it in its build directory and running it like this:
path\to\NodaTime.TzdbCompiler.exe -s path\to\tzdb-files -w path\to\windowsMapping-file.xml -o path\to\output.nzd -t NodaZoneData

For example, rebuilding the 2013h data from Noda Time itself, starting in the project's root directory:

src\NodaTime.TzdbCompiler\bin\Release\NodaTime.TzdbCompiler -s data\tzdb\2013h -w data\cldr\windowsZones-24.xml -o tzdb-2013h.nzd -t NodaZoneData

The NodaZoneData format is the default output format, so you can omit the final -t NodaZoneData if you wish; you may prefer to be explicit for clarity.

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.)

Creating and using a resource file (legacy format)

Building the resource file

  1. Download the latest tzdb release
  2. Unpack the tar.gz file - you may need to download extra tools for this; 7-Zip can cope with .tar.gz files for example, and I'd expect other zip tools to do so too. You should end up with a directory containing files such as "america", "africa", "etcetera".
  3. Ideally, rename the directory to match the version number, e.g. "2013h". The directory name will be used in the version ID reported by the time zone provider later.
  4. Find the Windows mapping file you want to use. Currently, I'd recommend using the version supplied with the Noda Time source in the data\cldr directory, in a file beginning "windowsZones". This file comes from CLDR.
  5. Run NodaTime.TzdbCompiler. I'd suggest leaving it in its build directory and running it like this:
path\to\NodaTime.TzdbCompiler.exe -s path\to\tzdb-files -w path\to\windowsMapping-file.xml -o path\to\output.resources -t Resource

For example, rebuilding the 2013h data from Noda Time itself, starting in the project's root directory:

src\NodaTime.TzdbCompiler\bin\Release\NodaTime.TzdbCompiler -s data\tzdb\2013h -w data\cldr\windowsZones-24.xml -o tzdb-2013h.resource -t Resource

As an alternative, if there's enough demand, we may well provide pre-built resource files in the Noda Time project download section. It's worth knowing the above steps, however, in case you wish to use a cut-down set of time zones for resource-constrained environments.

Using a compiled resource 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:

  • Create a ResourceSet from the file
  • Create a TzdbDateTimeZoneSource with the ResourceSet
  • 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.Resources;

public class CustomTzdb
{
    static void Main()
    {
        var resourceSet = new ResourceSet("tzdb-2013h.resources");
        var source = new TzdbDateTimeZoneSource(resourceSet);
        IDateTimeZoneProvider provider = new DateTimeZoneCache(source);
        Console.WriteLine(provider.SourceVersionId);
    }
}

You may be surprised that TzdbDateTimeZoneSource doesn't implement IDisposable even though ResourceSet does. TzdbDateTimeZoneSource will never close or dispose the resource set it's given - it doesn't assume ownership of it. However, it will fail if you dispose the resource set and then ask for a time zone which hasn't yet been loaded. If you wish to have a completely disconnected time zone provider, I'd recommend loading the contents of the file into a MemoryStream and passing that to the ResourceSet constructor. Otherwise, in most cases it probably isn't a big deal to have the handle to the resource file open throughout the lifetime of the application.