The main use of the local file system for the core library (other than the validator - see below) is for the NPM package cache. The default location and content is as specified in the FHIR specification, but you can choose where this goes if you want, or provide your own NPM package cache manager. However there are other uses of the local file system scattered throughout the code, particularly in the test cases.
All access to the local file system runs through the class ManagedFileAccess. You can set the static features of this class to completely cut the library off from the local filesystem, or provide your own file system accessor, or limit the files accessed to particular sub-directories. See ManagedFileAccess for details.
Note that libraries that this library depends on still access the filesystem directly. Review of the use of these libraries is ongoing.
Validator: The validator CLI also accesses local files as specified in the command line parameters, and runs in the user context. TODO: we are considering whether to support a command line parameter restricting path access to particular directories.
The library will access the web to download needed collateral, or to access terminology resources or servers. All access is by http(s) using base java http library, and is controlled by the class ManagedWebAccess. You can set the static features of this class to completely cut the library off from the web, or provide your own web accessor, or limit the web resources accessed to particular domains or sub-domains. See ManagedWebAccess for details.
Note that for legacy reasons, network access can also be prohibited using FhirSettings.setProhibitNetworkAccess(), but this is deprecated.
Note that libraries that this library depends on may still access the network directly. Review of the use of these libraries is ongoing.
Validator: The validator CLI accesses the web to download packages and make use of the terminology server, which defaults to https://tx.fhir.org.
todo
todo
Other than the https client, the library doesn't have any crypto functions in it.
TODO: Actually, it does, reading SHCs