ExNominatim

ExNominatim is a full-featured client for the OpenStreetMap Nominatim API V1, with extensive request validation, robust error-handling and reporting, and user guidance with helpful validation messages.

Goals

Prevent unnecessary calls to the Nominatim API server by validating intended requests and preventing them if the request parameters are invalid.
Solid error-handling for robustness in production.
Provide helpful validation messages to the user when a request is deemed invalid.

Features

Covers the /search, /reverse, /lookup, /status and /details endpoints.
Utilizes request parameter structs with the appropriate fields (except for json_callback) for each endpoint.
Configurable for your application with overridable defaults using Elixir’s Config module to set any default values, including the :base_url option for use with self-hosted Nominatim API instances.
Validates parameter values prior to the request (possible to override this with the force: true option).
Provides helpful return tuples {:ok, ...}, {:error, reason} and {:error, {specific_error, other_info}} across the board.
Collects all detected field validation errors in an :errors field, and provides a :valid? field in each request params struct.
Automatically sets the User-Agent header to “ExNominatim/{version}” to comply with the Nominatim Usage Policy.

Installation

The package can be installed from Hex by adding ex_nominatim to your list of dependencies in mix.exs:

def deps do
  [
    {:ex_nominatim, "~> 1.1.1"}
  ]
end

The code can be found on Github/waseigo/ex_nominatim.

Documentation has been published on HexDocs.

There is also a thread open on the Elixir Programming Language Forum: ExNominatim - A full-featured client for the OpenStreetMap Nominatim API V1.

Usage

By calling the endpoint functions of the ExNominatim module you will be hitting the public Nominatim API server with each endpoint’s default options as described in the API documentation; i.e., all requests use https://nominatim.openstreetmap.org as the value of :base_url in opts and the default parameters for each endpoint are handled by the API according to its documentation.

Please respect the Nominatim Usage Policy when using the public server.

Optional configuration and default parameters

In the more likely scenario where you use ExNominatim in your own application (e.g., in a Phoenix application) called MyApp, you can override all defaults across all endpoints and then even for each endpoint through your application’s configuration, e.g. in the config/config.exs file of a Phoenix app. For example:

config :my_app, MyApp.ExNominatim,
  all: [
    base_url: "http://localhost:8080",
    force: true,
    format: "json",
    process: true,
    atomize: true
  ],
  search: [format: "geocodejson", force: false],
  reverse: [namedetails: 1],
  lookup: [],
  details: [],
  status: [format: "json"]

The configuration above has the following effects:

Requests to all endpoints will use the self-hosted Nominatim API instance at port 8080 of localhost, accessible over HTTP.
Request parameter validation errors (valid?: false in the request parameters struct) will be ignored for requests to all endpoints, except for requests to the /search endpoint.
Unless requested otherwise in opts, requests to the /search endpoint will return data in GeocodeJSON format (instead of the default jsonv2).
Requests to the /reverse endpoint will set :namedetails to 1 (unless otherwise set in opts).
Requests to the /status endpoint will return JSON instead of the default text (HTTP status code 200 and text OK or HTTP status 500 and a detailed error mesage).
The responses from all endpoints will be processed automatically using ExNominatim.Report.process/1, and any maps and contents thereof (or map contents of structs’s keys) will be converted from bitstring keys to atom keys using ExNominatim.Report.atomize/1.

Refer to the documentation of the main ExNominatim module for more information.

Ideas and someday/maybe features

Build Cachex in (see Reactive Warming) and provide the option to automatically throttle requests to the public API to the “absolute maximum of 1 request per second” as requested by the Nominatim Usage Policy.
Implement a test suite.

Who made this?

Many thanks to all the volunteers and contributors of OpenStreetMap and Nominatim.