MoosicBox Environment Utils

A utility library for parsing and handling environment variables with type-safe conversions and compile-time macros.

Features

Type-Safe Parsing: Parse environment variables to specific numeric types (usize, u64, u32, u16, i64, i32, i16, i8, f32)
Compile-Time Macros: Extract environment variables at compile time with default values
Const-Compatible Parsing: Const-friendly integer parsing functions for compile-time evaluation
Optional Values: Handle missing environment variables gracefully with Option types
Error Handling: Proper error types for parsing failures and missing variables

Installation

Add this to your Cargo.toml:

[dependencies]
moosicbox_env_utils = "0.1.1"

Usage

Basic Environment Variable Parsing

use moosicbox_env_utils::{env_usize, default_env_usize, option_env_usize};

fn main() -> Result<(), Box<dyn std::error::Error>> {
    // Parse required environment variable
    let port = env_usize("PORT")?;
    println!("Server port: {}", port);

    // Parse with default value
    let timeout = default_env_usize("TIMEOUT", 30)?;
    println!("Timeout: {} seconds", timeout);

    // Parse optional environment variable
    match option_env_usize("MAX_CONNECTIONS")? {
        Some(max_conn) => println!("Max connections: {}", max_conn),
        None => println!("No connection limit set"),
    }

    Ok(())
}

Compile-Time Environment Variable Macros

use moosicbox_env_utils::{env_usize, default_env_usize, default_env_u64, default_env_u32};

// Extract environment variables at compile time
const SERVER_PORT: usize = env_usize!("PORT");
const MAX_BUFFER_SIZE: usize = default_env_usize!("BUFFER_SIZE", 8192);
const CACHE_TTL: u64 = default_env_u64!("CACHE_TTL", 3600);
const WORKER_THREADS: u32 = default_env_u32!("WORKERS", 4);

fn main() {
    println!("Server will run on port: {}", SERVER_PORT);
    println!("Buffer size: {} bytes", MAX_BUFFER_SIZE);
    println!("Cache TTL: {} seconds", CACHE_TTL);
    println!("Worker threads: {}", WORKER_THREADS);
}

Different Numeric Types

use moosicbox_env_utils::{
    option_env_u64, option_env_u32, option_env_u16,
    option_env_i64, option_env_i32, option_env_i16, option_env_i8,
    option_env_f32
};

async fn configure_application() -> Result<(), Box<dyn std::error::Error>> {
    // Unsigned integers
    let memory_limit: Option<u64> = option_env_u64("MEMORY_LIMIT_MB")?;
    let max_requests: Option<u32> = option_env_u32("MAX_REQUESTS")?;
    let port: Option<u16> = option_env_u16("PORT")?;

    // Signed integers
    let timezone_offset: Option<i64> = option_env_i64("TIMEZONE_OFFSET")?;
    let priority: Option<i32> = option_env_i32("PROCESS_PRIORITY")?;
    let thread_priority: Option<i16> = option_env_i16("THREAD_PRIORITY")?;
    let log_level: Option<i8> = option_env_i8("LOG_LEVEL")?;

    // Floating point
    let cpu_threshold: Option<f32> = option_env_f32("CPU_THRESHOLD")?;

    println!("Configuration loaded:");
    if let Some(mem) = memory_limit {
        println!("  Memory limit: {} MB", mem);
    }
    if let Some(reqs) = max_requests {
        println!("  Max requests: {}", reqs);
    }
    if let Some(threshold) = cpu_threshold {
        println!("  CPU threshold: {:.2}%", threshold * 100.0);
    }

    Ok(())
}

String Environment Variables

use moosicbox_env_utils::default_env;

fn main() {
    // Get string environment variable with default
    let app_name = default_env("APP_NAME", "MoosicBox");
    let environment = default_env("ENVIRONMENT", "development");

    println!("Application: {} ({})", app_name, environment);
}

Const Integer Parsing

use moosicbox_env_utils::{parse_usize, parse_isize};

const fn compile_time_parsing() -> usize {
    // These functions work at compile time
    match parse_usize("12345") {
        Ok(value) => value,
        Err(_) => 0,
    }
}

const PARSED_VALUE: usize = compile_time_parsing();

fn main() {
    println!("Parsed at compile time: {}", PARSED_VALUE);

    // Also works at runtime
    let runtime_value = parse_isize("-42").unwrap();
    println!("Parsed at runtime: {}", runtime_value);
}

API Reference

Runtime Functions

env_usize(name) - Parse required usize environment variable
default_env_usize(name, default) - Parse usize with fallback default
option_env_* functions - Parse optional values for various types
default_env(name, default) - Get string environment variable with default

Compile-Time Macros

env_usize!(name) - Extract required usize at compile time
default_env_usize!(name, default) - Extract usize with default at compile time
default_env_u64!(name, default) - Extract u64 with default at compile time
default_env_u32!(name, default) - Extract u32 with default at compile time
option_env_*! macros - Extract optional values at compile time

Const Functions

parse_usize(s) - Parse string to usize (const-compatible)
parse_isize(s) - Parse string to isize with sign support (const-compatible)

Error Handling

The library provides specific error types for different failure scenarios:

EnvUsizeError - Environment variable missing or parsing failed
DefaultEnvUsizeError - Parsing failed (missing variables return default)
OptionEnvUsizeError - Parsing failed for numeric types
OptionEnvF32Error - Parsing failed for floating point
ParseIntError - Invalid digit encountered during const parsing

Performance

Const functions enable compile-time evaluation
Macro-based extraction has zero runtime cost
Runtime parsing uses standard library implementations for reliability

moosicbox_env_utils 0.1.4