Geo-coordinates might be sensitive information to share in any context, and I needed a self-hosted solution to ensure that coordinates were not leaked to 3rd party services. On another side, this feature is nicely self-contained and having one service to expose it spares the effort to bundle the TZ database everywhere.

API

the service exposes only one API:

GET /tz/${LATITUDE}/${LONGITUDE}

that returns a JSON reply (http/200), for example:

curl -s http://localhost:2004/tz/51.477811/0 | jq

{
  "coords": {
    "lat": 51.47781,
    "lon": 0
  },
  "tz": "Europe/London"
}

or in case of errors (http/4**), for example:

curl -v http://localhost:2004/tz/51.477811/1000 | jq
*   Trying 127.0.0.1:2004...
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
  0     0    0     0    0     0      0      0 --:--:-- --:--:-- --:--:--     0* Connected to localhost (127.0.0.1) port 2004 (#0)
> GET /tz/51.477811/1000 HTTP/1.1
> Host: localhost:2004
> User-Agent: curl/7.81.0
> Accept: */*
>
* Mark bundle as not supporting multiuse
< HTTP/1.1 400 Bad Request
< Content-Type: application/json; charset=UTF-8
< Vary: Origin
< Date: Fri, 23 Jun 2023 19:09:29 GMT
< Content-Length: 54
<
{ [54 bytes data]
100    54  100    54    0     0  89403      0 --:--:-- --:--:-- --:--:-- 54000
* Connection #0 to host localhost left intact

{
  "message": "lon value 1000 out of range (-180/+180)"
}

Authorization

Geo2Tz supports a basic token authorization mechanism, if the configuration value for web.auth_token_value is a non-empty string, geo2tz will check the query parameter value to authorize incoming requests.

For example, running the service with:

docker run -p 2004:2004 -e GEO2TZ_WEB_AUTH_TOKEN_VALUE=secret ghcr.io/noandrea/geo2tz:2.1.5

will enable authorization. With the authorization enabled, a query that does not specify the token will fail with an HTTP code 401:

> curl -sv http://localhost:2004/tz/41.902782/12.496365 | jq

*   Trying 127.0.0.1:2004...
* Connected to localhost (127.0.0.1) port 2004 (#0)
> GET /tz/41.902782/12.496365 HTTP/1.1
> Host: localhost:2004
> User-Agent: curl/7.81.0
> Accept: */*
>
* Mark bundle as not supporting multiuse
< HTTP/1.1 401 Unauthorized
< Content-Type: application/json; charset=UTF-8
< Vary: Origin
< Date: Sun, 31 Jul 2022 20:06:56 GMT
< Content-Length: 27
<
{ [27 bytes data]
* Connection #0 to host localhost left intact
{
  "message": "unauthorized"
}

Passing the token in the query parameters will succeed instead:

> curl -s http://localhost:2004/tz/41.902782/12.496365\?t\=secret | jq

{
  "coords": {
    "lat": 41.902782,
    "lon": 12.496365
  },
  "tz": "Europe/Rome"
}

Docker

Docker image is available at geo2tz

docker run -p 2004:2004 ghcr.io/noandrea/geo2tz:2.1.5

The image is built on scratch, the image size is ~92MB:

Docker compose

Docker compose YAML example

version: '3'
services:
  geo2tz:
    container_name: geo2tz
    image: ghcr.io/noandrea/geo2tz:2.1.5
    ports:
    - 2004:2004
    # uncomment to enable authorization via request token
    # environment:
    # - GEO2TZ_WEB_AUTH_TOKEN_VALUE=somerandomstringhere
    # - GEO2TZ_WEB_AUTH_TOKEN_PARAM_NAME=t
    # - GEO2TZ_WEB_LISTEN_ADDRESS=":2004"

K8s

Kubernetes configuration example:

---
# Deployment
apiVersion: extensions/v1beta1
kind: Deployment
metadata:
  labels:
    app: geo2tz
  name: geo2tz
spec:
  replicas: 1
  revisionHistoryLimit: 3
  selector:
    matchLabels:
      app: geo2tz
  template:
    metadata:
      labels:
        app: geo2tz
    spec:
      containers:
      - env:
        # if this var is not empty it will enabled token authorization for requests
        #- name: GEO2TZ_WEB_AUTH_TOKEN_VALUE
        #  value: "secretsmaybebetter" # default is empty
        #- name: GEO2TZ_WEB_AUTH_TOKEN_PARAM_NAME
        #  value: "t" # default value
        #- name: GEO2TZ_WEB_LISTEN_ADDRESS
        #  value: ":2004" # default value
        image: ghcr.io/noandrea/geo2tz:2.1.5
        imagePullPolicy: Always
        name: geo2tz
        ports:
        - name: http
          containerPort: 2004
---
# Service
# the service for the above deployment
apiVersion: v1
kind: Service
metadata:
  name: geo2tz-service
spec:
  type: ClusterIP
  ports:
  - name: http
    port: 80
    protocol: TCP
    targetPort: http
  selector:
    app: geo2tz

Development notes

To update the timezone database you have a few options:

update to the latest version

geo2tz update latest

update to a specific version

geo2tz update 2023b

the update command will download the timezone geojson zip and generate a version file in the tzdata directory, the version file is used to track the current version of the database.

Tests and known issues

Automated tests are executed for coordinates with a precision between 1.11m (4 decimals) and 11.1m (5 decimals), the test file is db/testdata/coordinates.json.

Some of the location are marked with err since they produce incorrect results, this is due to the fact that the timezone boundaries often overlaps. If you have additional test cases that you think are relevant, please open an issue or a PR.