Crate serviceconf 

Environment variable configuration with file-based secrets support

serviceconf provides a declarative API for loading configuration from environment variables with native support for file-based secrets (Kubernetes Secrets, Docker Secrets).

The primary feature that distinguishes this library from other environment variable configuration libraries is the #[conf(from_file)] attribute, which allows reading secrets from files while falling back to direct environment variables for local development.

Features

• File-based secrets: Read secrets from Kubernetes/Docker mounted files
• Declarative: Automatic implementation with #[derive(ServiceConf)]
• Type-safe: Compile-time type checking
• Default values: Support for Default trait and explicit values
• Custom deserializers: Support for JSON, TOML, or custom parsing functions

Value Parsing

Default (using FromStr):

• Strings: DATABASE_URL=postgres://localhost/db
• Numbers: MAX_CONNECTIONS=42
• Booleans: DEBUG=true

Custom deserializers - specify with #[conf(deserializer = "function")]:

• JSON: #[conf(deserializer = "serde_json::from_str")]
• TOML: #[conf(deserializer = "toml::from_str")]
• Custom: Define your own deserializer function

Example

use serviceconf::ServiceConf;

#[derive(Debug, ServiceConf)]
struct Config {
    // File-based secret: reads from API_KEY or API_KEY_FILE
    #[conf(from_file)]
    pub api_key: String,

    // Default value if not set
    #[conf(default = 8080)]
    pub port: u16,
}

Attributes

#[conf(from_file)] - File-based Secrets

Load from {VAR_NAME}_FILE in addition to the environment variable. This is the primary feature of serviceconf for handling file-based secrets in Kubernetes and Docker environments.

Loading priority:

1. Direct env var (API_KEY) - for local development
2. File path from env var (API_KEY_FILE) - for production

#[derive(ServiceConf)]
pub struct Config {
    // Reads from API_KEY or API_KEY_FILE
    #[conf(from_file)]
    pub api_key: String,
}

#[conf(default = "value")]

Specify a default value when the environment variable is not set.

#[derive(ServiceConf)]
struct Config {
    #[conf(default = "127.0.0.1:8080".to_string())]
    pub server_addr: String,

    #[conf(default = 10)]
    pub max_connections: u32,

    #[conf(default = false)]
    pub enable_tls: bool,
}

#[conf(name = "CUSTOM_NAME")]

Specify an environment variable name different from the field name.

#[derive(ServiceConf)]
pub struct Config {
    // Load from REDIS_URL environment variable
    #[conf(name = "REDIS_URL")]
    pub redis_connection_string: String,
}

Enums

EnvError

Environment variable loading error

Derive Macros

ServiceConf

ServiceConf derive macro