Config

Typed configuration is deserialized into user structs.

#[derive(serde::Deserialize)]
struct AppConfig {
    name: String,
    port: u16,
}

let config = Config::from_pairs([("name", "nidus"), ("port", "3000")]);
let typed = config.deserialize::<AppConfig>()?;

JSON object sources can be loaded explicitly:

let config = Config::from_json_str(
    r#"{
        "name": "nidus",
        "port": 3000
    }"#,
)?;

The same JSON object format can be loaded from a file:

let config = Config::from_json_file("config/defaults.json")?;

Environment variables can be loaded through an explicit prefix. Double underscores create nested objects. Prefix matching is case-sensitive, and keys are normalized to lowercase after the prefix is removed:

#[derive(serde::Deserialize)]
struct AppConfig {
    name: String,
    database: DatabaseConfig,
}

#[derive(serde::Deserialize)]
struct DatabaseConfig {
    url: String,
}

let config = Config::from_env_prefix("APP");
// APP_NAME=nidus
// APP_DATABASE__URL=postgres://localhost/nidus
let typed = config.deserialize::<AppConfig>()?;

Multiple sources can be layered with later values taking precedence:

let defaults = Config::from_pairs([("port", "3000")]);
let env = Config::from_env_prefix("APP");
let config = defaults.merge(env);

Raw values can be inspected before or after typed deserialization when tests or startup checks need targeted assertions. Path segments traverse objects by key and arrays by zero-based numeric index:

let database_url = config
    .get_path(["database", "url"])
    .and_then(serde_json::Value::as_str);

let first_server_port: Option<u16> = config.get_path_typed(["servers", "0", "port"])?;

Individual values can also be deserialized with path-aware errors:

let port = config.get_typed::<u16>("port")?;
let database_url: Option<String> = config.get_path_typed(["database", "url"])?;

Use required-value helpers for explicit startup checks:

let port = config.get_required_typed::<u16>("port")?;
let database_url: String = config.get_required_path_typed(["database", "url"])?;

Applications should keep configuration explicit and validate it during startup.