Updating the time zone database in Noda Time

Noda Time comes with a version of the tzdb (aka zoneinfo) 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.

"Compiling" the database to a resource file

Noda Time's main library doesn't read tzdb text files directly - it uses a binary form which is the output of ZoneInfoCompiler - another part of the Noda Time project. This saves both space (the 2012c version takes about 189K when compiled, or about 598K in text form) and time, as the binary form contains various precomputed transitions. The resource 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.

ZoneInfoCompiler is not currently provided in binary form in Nuget packages (although this decision can easily be revisited if there's enough demand). You'll need to build it yourself - which should be as simple as getting hold of a Noda Time source distribution (the latest for your binary's major version number should be good enough; we won't change the format of the resource file without bumping the version number) and building the whole solution. You'll end up with binaries in ZoneInfoCompiler/bin/Debug (or Release).

Steps

  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. "2012c". 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 ZoneInfoCompiler\Data\winmap in a file beginning "windowsZones". This file comes from CLDR.
  5. Run ZoneInfoCompiler. I'd suggest leaving it in its build directory and running it like this:

    path\to\ZoneInfoCompiler.exe -s path\to\tzdb-files -w path\to\windowsMapping-file.xml -o path\to\output.resources -t Resource

    For example, rebuilding the 2012c data from Noda Time itself, starting in the ZoneInfoCompiler directory:

    bin\Release\ZoneInfoCompiler -s Data\2012c -w Data\winmap\windowsZones-21.xml -o tzdb-2012c.resources -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:

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-2012c.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.