FHIR Package Loader

FHIR Package Loader is a utility that downloads published FHIR packages from the FHIR package registry.

Usage

This tool can be used directly through a command line interface (CLI) or it can be used as a dependency in another JavaScript/TypeScript project to download FHIR packages and load the contents into memory.

FHIR Package Loader requires Node.js to be installed on the user's system. Users should install Node.js 18, although other current LTS versions are also expected to work.

Once Node.js is installed, use either of the following methods to use the FHIR Package Loader.

Command Line

To download and unzip FHIR packages through the command line, you can run the following command directly:

npx fhir-package-loader install <package@version...> # downloads specified FHIR packages

Note: npx comes with npm 5.2+ and higher.

npx will ensure you are using the latest version and will allow you to run the CLI without needing to install and manage any dependency.

Alternatively, if you'd like to install the package, it can be installed globally and used as follows:

npm install -g fhir-package-loader # installs the package from npm

After installation, the fhir-package-loader command line will be available on your path:

fpl --help # outputs information about using the command line
fpl install --help

fpl install <package@version...> # downloads specified FHIR packages

With both approaches, the same commands are available. The install command allows you to specify the FHIR packages to download, along with a few additional options:

Usage: fpl install <fhirPackages...> [options]

download and unzip specified FHIR packages

Arguments:
  fhirPackages      list of FHIR packages to load using the format packageId@packageVersion...

Options:
  -c, --cachePath <dir>  where to save packages to and load definitions from (default is the local [FHIR cache](https://confluence.hl7.org/pages/viewpage.action?pageId=66928417#FHIRPackageCache-Location))
  -d, --debug       output extra debugging information
  -h, --help        display help for command

General information about any command can be found with fpl --help:

Usage: fpl [options] [command]

CLI for downloading FHIR packages

Options:
  -v, --version                        output the version number
  -h, --help                           display help for command

Commands:
  install [options] <fhirPackages...>  download and unzip specified FHIR packages
  help [command]                       display help for command

Examples:
  fpl install hl7.fhir.us.core@current
  fpl install [email protected] [email protected] --cachePath ./myProject

API

Additionally, FHIR Package Loader exposes functions that can be used to query and download packages.

fpl(fhirPackages[, options])

The fpl function can be used to download FHIR packages and load their definitions.

Parameters

fhirPackages - An array of strings (or a comma separated string) that specifies the FHIR packages and versions to load. These can be in the format of package#version or package@version.

• For example: '[email protected], [email protected]' or ['[email protected]', '[email protected]']

options - An object which can have the following attributes:

• cachePath - A string that specifies where to look for already downloaded packages and download them to if they are not found. The default is the the local FHIR cache.

• log - A function that is responsible for logging information. It takes in two strings, a level and a message, and does not return anything.

  • For example: log: console.log will pass in console.log as the logging function and the level and message will be logged as console.log(level, message)

Return Value

A Promise that resolves to an object with the following attributes:

• defs - A FHIRDefinitions class instances that contains any definitions loaded from the specified package(s).
• errors An array of strings containing any errors detected during package loading.
• warnings An array of strings containing any warnings detected during package loading.
• failedPackages An array of strings containing the package#version of any packages that encountered an error during download or load and were not properly loaded to defs.

getLatestVersion(packageName[, log])

The getLatestVersion function can be used to query the latest version of a FHIR package.

Parameters

packageName - A string that specifies the FHIR package to query.

log - A function that is responsible for logging information. It takes in two strings, a level and a message, and does not return anything.

Return Value

A Promise that resolves to a string containing the latest version of the FHIR package.

Usage

To use the API, FHIR Package Loader must be installed as a dependency of your project. To add it as a dependency, navigate to your project directory and use npm to install the package:

cd myProject
npm install fhir-package-loader

Once installed as a dependency, you can import and use the API for loading FHIR packages. This function provides the same functionality you get through the CLI, but you also have access to the in memory definitions from the packages. The following example shows two ways to use the function in a project:

import { fpl } from 'fhir-package-loader';

async function myApp() {
  // Downloads and unzips packages to FHIR cache or other specified location (if not already present)
  await fpl(['package@version, package2@version'])
    .then(results => {
      // handle results
    })
    .catch(err => {
      // handle thrown errors
    });

  // Similar to above, but uses options
  await fpl(['package@version'], {
    cachePath: '../myPackages',
    log: console.log
  })
    .then(results => {
      // handle results
    })
    .catch(err => {
      // handle thrown errors
    });
}

Mock Out in Unit Tests

If you use fhir-package-loader as a dependency in your project, you can choose to mock any function from the package. This may be helpful for writing unit tests that do not need to download packages from the FHIR registry. One way to do this is using the following snippet:

jest.mock('fhir-package-loader', () => {
  const original = jest.requireActual('fhir-package-loader');
  return {
    ...original,
    loadDependencies: jest.fn(), // can optionally include a mock implementation
    // any other functions to be mocked out
  }
}

For Developers

Installation

FHIR Package Loader is a TypeScript project. At a minimum, it requires Node.js to build, test, and run the CLI. Developers should install Node.js 18, although other current LTS versions are also expected to work.

Once Node.js is installed, run the following command from this project's root folder:

npm install

Exposed functions

While the CLI and API should be sufficient for the majority of use cases, FHIR Package Loader exposes a few additional functions and classes that can be used within JavaScript/TypeScript projects. Below are the key exports:

Export	Description
fpl	API function to download and load definitions for a provided list of packages.
getLatestVersion	API function to find the latest version of a package.
loadDependencies	Takes a list of FHIR packages, a path to a directory (optional, defaults to FHIR cache), a log function (optional) and returns FHIRDefinitions from the provided packages.
mergeDependency	Takes a package name, a package version, an instance of FHIRDefinitions, a path to a directory (optional, defaults to FHIR cache), a log function (optional) and returns FHIRDefinitions with definitions added directly from the package.
loadFromPath	Takes a path, a package and version (format: package#version), and an instance of FHIRDefinitions and loads the definitions from the provided package at the provided path into FHIRDefinitions.
FHIRDefinitions	A class for FHIRDefinitions for one or more packages. This could be extended if there are additional properties that are specific to your implementation.

License

Copyright 2022 The MITRE Corporation

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.