Data Seeders

When a C19 agent first launches and joins a C19 cluster, it is expected from the connection layer to connect and exchange the state with other, already running agents. This allows a new C19 agent to sync with other peers as it launches.

Nonetheless there are cases where a user would want to initialize the agent with some data. For that we have data seeders.

Depending on the State layer implementation, when it first loads it is expected to initialize and load a data seeder. If you choose to implement a State layer, please consider supporting the DataSeeder API so users will have a consistent option to seed your state with data.

The File Data Seeder

The File data seeder will load data from a file. The data in the file must be compatible with the State layer and it's up to the user to make sure it does.

The Default state layer expects the following format:

{
  "cat": {
    "value": "garfield",
    "ttl": 3600000
  },
  "dog": {
    "value": "snoopy"
  }
}

When the Default state layer is being initialized it loads the data seeder, if one is configured:

#![allow(unused)]
fn main() {
fn init(&self) -> state::SafeState {
    ...

    // if we have a data seeder then use it to seed the data
    this.data_seeder.clone().and_then(|data_seeder| {
        if let Err(e) =  this.seed(data_seeder) {
            warn!("Failed to seed data; ({})", e);
        }

        Some(())
    });
    
    ...
}
}

The DataSeeder Trait

#![allow(unused)]
fn main() {
pub trait DataSeeder: std::fmt::Debug + Send + Sync {
    fn load(&self) -> Result<Box<dyn StateValue>, Box<dyn StdError>>;
}

}

A very simple trait with a load function that returns a StateValue.

We will explore the implementation of the File data seeder in detail when we walk through the Defaul layer implementations.