config

config (crates.io) is a library for building configuration structs from sources like env variables, yaml files and so on. You can combine it with validator to build a full configuration for your application.

Install

# Install config
cargo add config
cargo add serde --features derive

# Optional libraries I recommend
cargo add dotenv
cargo add validator --features derive

Example

In this example, I have created a struct, which holds base_url and port. base_url is mandatory while port has a default value. I can load it using a config file, or using environment variables.

I also included dotenv, so the environment variables are optionally read using an .env file.

use config::{Environment, File};
use dotenv::dotenv;
use serde::Deserialize;
use validator::Validate;

use crate::errors::AppError;

#[derive(Debug, Clone, Deserialize, Validate)]
pub struct Config {
    #[validate(length(min = 1))]
    pub base_url: String,
    #[validate(range(min = 1, max = 65535))]
    pub port: u16,
}

pub fn load() -> Result<Config, AppError> {
    dotenv().ok();

    let settings = config::Config::builder()
        .set_default("port", 8080)?
        .add_source(File::with_name("config").required(false))
        .add_source(Environment::default())
        .build()?;

    let config: Config = settings.try_deserialize()?;
    config
        .validate()
        .map_err(|err| AppError::ConfigValidation(err))?;

    Ok(config)
}