FHIR Package Cache

Package Cache

Each system has a global package cache that stores the packages known to that system. This cache is shared between tools for efficiency. Authors of tools that work with FHIR packages are encouraged to follow this specification for the convenience of users.

The package cache keeps the uncompressed content of all installed packages. Different versions of a package are installed side-by-side, and are individually resolvable. A Fhir package client should use the global package cache, but may keep a local cache in a working folder instead. The global package cache makes sure that each packages is installed only once on the computer

Location

The location differs per operating system.

Location of the global package cache:

• Windows: c:\users\<username>\.fhir\packages
• Unix/Linux: /~/.fhir/packages

For system services (daemons):

• Windows: c:\ProgramData\.fhir\packages
• Unix/Linux: /var/lib/.fhir/packages

The package cache root folder contains a folder per package where the folder name is the package name, a dash and the package version.

 hl7.fhir.us.core#0.1.1

In addition, the package cache root folder contains a file ".index.json".

Note: package names are not allowed to contain the character "#"

Packages .index.json

The packages .index.json file contains the following content:

 {
   "cache-version" : "1",
   "urls" : {
      "[package-id]" : "[canonical]" 
   }
 }

details:

• cache-version = 1 - indicates that the contents of the package cache conform to this specification. Applications using the package cache SHALL check this value and shall rebuild the cache from scratch if the value is != 1
• urls: a list of mappings between package ids and canonical URLs - shared between applications to save a user resolving the same canonical URL repeatedly - a map of package-id = canonical URL

Folder contents

In each package folder the package is unzipped as it is. The contents of the folder are the unpacked version of the GZipped tarball and SHALL otherwise conform to the requirements for the FHIR NPM Package Spec.

There is at least one folder called "package", in which all the content of the package is found, including the package manifest. Other folders with other uses may exist if found in the source package.

In addition, the folder contains a file ".index.json" - see below.

Recursion

A package client must resolve package dependencies recursively, but keep the package cache flat. An installed package should itself not contain any dependencies. All packages are installed on the same level.

Package .index.json

This is a file created by the tool that extracts the package. It contains:

{

 "date" : "[date]",
 "canonicals": {
   "http://hl7.org/fhir/StructureDefinition/actualgroup": "StructureDefinition-actualgroup.json",
   ...
 }

}

• [date] : the date of extraction in XML format. Sole purpose is to display to the user how long the package has been in the cache
• canonicals: a map from the canonical URL to the literal filename in the package (this makes access faster)