Keeping service data between reloads

Services can keep data between reloads in several ways. Note than if a service is purged, its data is deleted (both from the data directory and the registry).

Keeping data in the node registry

Rust SDK has got built-in instruments to work the with the registry.

To connect to the registry, use “init_registry” method of the initial payload:

let registry = initial.init_registry();

Service registry methods automatically operate under a key path eva/svc_data/<SVC_ID> and it is not necessary to set key prefixes.

More info about “Registry” object and its methods can be found at https://docs.rs/eva-common/latest/eva_common/services/struct.Registry.html

Keeping data in files

The method “data_path” of the initial payload returns path to a directory where the service can store its data.

let data_path: Option<&str> = initial.data_path();

If the data path is None, it means that the service is started under “nobody” user and can not use the data path.

Note

To avoid permission problems, the service should always use its data path only after “initial.drop_privileges()” method is called.