Usage
Let's say you application relies on the following environment variables:
And you want to initialize Config
structure like this one:
struct Config {
host: String,
port: u16,
}
You can achieve this with the following code without boilerplate:
use envconfig::Envconfig;
#[derive(Envconfig)]
pub struct Config {
#[envconfig(from = "DB_HOST")]
pub db_host: String,
#[envconfig(from = "DB_PORT", default = "5432")]
pub db_port: u16,
}
fn main() {
std::env::set_var("DB_HOST", "127.0.0.1");
let config = Config::init_from_env().unwrap();
assert_eq!(config.db_host, "127.0.0.1");
assert_eq!(config.db_port, 5432);
}
Testing
When writing tests you should avoid using environment variables. Cargo runs Rust tests in parallel by default which means
you can end up with race conditions in your tests if two or more are fighting over an environment variable.
To solve this you can initialise your struct
from a HashMap<String, String>
in your tests. The HashMap
should
match what you expect the real environment variables to be; for example DB_HOST
environment variable becomes a
DB_HOST
key in your HashMap
.
use envconfig::Envconfig;
#[derive(Envconfig)]
pub struct Config {
#[envconfig(from = "DB_HOST")]
pub db_host: String,
#[envconfig(from = "DB_PORT", default = "5432")]
pub db_port: u16,
}
#[test]
fn test_config_can_be_loaded_from_hashmap() {
let mut hashmap = HashMap::new();
hashmap.insert("DB_HOST".to_string(), "127.0.0.1".to_string());
let config = Config::init_from_hashmap(&hashmap).unwrap();
assert_eq!(config.db_host, "127.0.0.1");
assert_eq!(config.db_port, 5432);
}
Contributing
Running tests
Tests do some manipulation with environment variables, so to
prevent flaky tests they have to be executed in a single thread:
cargo test -- --test-threads=1
License
MIT © Sergey Potapov
Contributors
- greyblake Potapov Sergey - creator, maintainer.
- allevo Tommaso Allevi - support nested structures
- hobofan Maximilian Goisser - update dependencies