Env Settings

Env Settings is a Rust library that helps you to initialize structs using environment variables

This Rust library took inspiration from pydantic's BaseSettings Python class

Installation

cargo add env-settings env-settings-derive env-settings-utils

Usage

When you add the EnvSettings derive to a struct, two public methods are added to it

• fn from_env(...) -> env_settings_utils::EnvSettingsResult<Self>

  Create a new instance using just the environment variables. Skipped fields must be passed. If something fails, it returns an env_settings_utils::EnvSettingsError error

• fn new(...) -> env_settings_utils::EnvSettingsResult<Self>

  Create a new instance using a combination of environment variables and parameters. More in detail, every field that can be initialized by the environment variables can be passed as parameter wrapped in an Option object. Then if the parameter is Some, it is used, otherwise the value is recoved from the environment variables. Skipped fields must be passed. If something fails, it returns an env_settings_utils::EnvSettingsError error

Basic

export name=paolo
export favourite_number=42

use env_settings_derive::EnvSettings;

#[derive(EnvSettings)]
struct MyStruct {
    name: String,

    favourite_number: u8,
}

fn main() {
    let my_struct = MyStruct::from_env().unwrap();
    assert_eq!(my_struct.name, "paolo".to_string());
    assert_eq!(my_struct.favourite_number, 42);

    let name = "luca";
    let my_struct = MyStruct::new(Some(name.to_string()), None).unwrap();
    assert_eq!(my_struct.name, name);
    assert_eq!(my_struct.favourite_number, 42);
}

Advanced

echo "MY_STRUCT_FAVOURITE_NUMBER=42\n" > .env
export MY_BIRTH_DATE=01/01/1970

use env_settings_derive::EnvSettings;

#[derive(EnvSettings)]
#[env_settings(case_insensitive, file_path = ".env", prefix="MY_STRUCT_")]
struct MyStruct {
    #[env_settings(default = "paolo")]
    name: String,

    favourite_number: u8,

    #[env_settings(variable = "MY_BIRTH_DATE")]
    birth_date: String,

    birth_place: Option<String>,

    #[env_settings(skip)]
    friends: Vec<String>,
}

fn main() {
    let friends = vec!["luca".to_string()];
    let my_struct = MyStruct::from_env(friends.clone()).unwrap();
    assert_eq!(my_struct.name, "paolo".to_string());
    assert_eq!(my_struct.favourite_number, 42);
    assert_eq!(my_struct.birth_date, "01/01/1970");
    assert_eq!(my_struct.birth_place, None);
    assert_eq!(my_struct.friends, friends);

    let name = "luca";
    let my_struct = MyStruct::new(
        Some(name.to_string()),
        None,
        None,
        Some("london".to_string()),
        friends.clone(),
    ).unwrap();
    assert_eq!(my_struct.name, name);
    assert_eq!(my_struct.favourite_number, 42);
    assert_eq!(my_struct.birth_date, "01/01/1970");
    assert_eq!(my_struct.birth_place, Some("london".to_string()));
    assert_eq!(my_struct.friends, friends);
}

Parameters

Struct

The current supported parameters for the structs are:

• case_insensitive: whether the environment variables matching should be case insensitive. By default, matching is case sensitive.
• delay: whether to delay the lookup for environment variables from compilation time to run time. By default the lookup is performed at compilation time
• file_path: the file path to read to add some environment variables (e.g. .env). By default, it is not set
• prefix: the prefix to add to the name of the struct fields before matching the environment variables. By default, it is not set

Field

The current supported parameters for the fields are:

• default: the default value to use if the environment variable is not found. By default, it is not set
• skip: whether to skip the parsing of the environment variable. It is necessary if the type specified does not implement std::str::FromStr.
• variable: the environment variable to use for the lookup. By default, the name of the field

Variables resolution hierarchy

1. Arguments passed to the new method (if using new).
2. Environment variables
3. Variables loaded from a file (e.g. .env)
4. Default values

Contribute

Before starting to work on a contribution please read:

• Code of Conduct
• Contributing
• Goverance
• Security
• Support

Run tests

When testing run:

cargo test -- --test-threads=1

to prevent tests from competitively interacting with the same file

License

This project is licensed under the terms of the MIT or Apache 2.0 license.