App JSON Settings

Typed application settings storage for Rust.

app-json-settings persists a Rust struct as your application configuration. You do not manipulate JSON manually and you do not manage config file paths yourself.

The library focuses on safe, minimal, cross-platform configuration handling.

Quick start

# Cargo.toml
[dependencies]
serde = { version = "1", features = ["derive"] }
app-json-settings = "2"

use app_json_settings::ConfigManager;

#[derive(serde::Serialize, serde::Deserialize, Default)]
struct Settings {
    volume: u32,
}

fn save() -> app_json_settings::Result<()> {
    ConfigManager::new().save(&Settings { volume: 100 })?;
    Ok(())
}

fn load() -> app_json_settings::Result<()> {
    let settings = ConfigManager::<Settings>::new().load_or_default()?;
    println!("{}", settings.volume);
    Ok(())
}

Why this library

Writing config handling code repeatedly leads to:

• fragile first-run initialization
• manual path handling per OS
• read → modify → write mistakes
• string-key based settings

This crate removes those concerns and lets the struct be the configuration.

Design goals

• Minimal API surface
• Predictable behavior
• No runtime dependencies beyond Serde
• Works for CLI, GUI, mobile, and server applications

This crate is not a general database or dynamic settings system. It is a typed persistent configuration layer.

Features

Safe configuration I/O

• Load and save settings with minimal code
• load_or_default() prevents first-run crashes
• update() provides safe read-modify-write

Typed serialization

• Uses your own struct as the configuration model
• No string keys
• Compile-time refactor safety
• Serde Serialize / Deserialize supported

JSON focused

• JSON only (intentionally)

• Selectable output:

  • compact
  • pretty

• Suitable for mobile I/O constraints while still human-readable

Cross-platform support

The library internally resolves platform-specific config directories:

• Windows → %APPDATA%
• macOS → ~/Library/Application Support
• Linux / Unix → $XDG_CONFIG_HOME or ~/.config

No platform conditional code is required in your application.

Customization

let config = ConfigManager::<Settings>::new()
    .with_filename("user.json")
    .disable_pretty_json();

Options:

• custom directory
• custom file name
• compact or pretty JSON output

Partial update

You usually do not need to manually load and save.

config.update(|s| {
    s.volume = 200;
})?;

update() guarantees a safe read-modify-write cycle.

Choosing the right API

Open-source, with care

This project is lovingly built and maintained by volunteers. We hope it helps streamline your work. Please understand that the project has its own direction — while we welcome feedback, it might not fit every edge case 🌱

Acknowledgements

Depends on the crates of serde, serde_json .