Skip to main content

Toml formatted CAC configuration file in a simple rust application

This document shows how to use a TOML formatted CAC configuration file in your Rust application.

Add dependencies to your Cargo.toml​

[dependencies]
cac_toml = { git = "https://github.com/juspay/superposition.git", branch = "main" }
toml = { version = "0.8.8", features = ["preserve_order"] }

Include a simple context-aware-configuration file​

Create a configuration file called example.cac.toml with the following content.

[default-config]
per_km_rate = { "value" = 20.0, "schema" = { "type" = "number" } }
surge_factor = { "value" = 0.0, "schema" = { "type" = "number" } }

[dimensions]
city = { schema = { "type" = "string", "enum" = ["Bangalore", "Delhi"] } }
vehicle_type = { schema = { "type" = "string", "enum" = [ "auto", "cab", "bike", ] } }
hour_of_day = { schema = { "type" = "integer", "minimum" = 0, "maximum" = 23 }}

[context."$vehicle_type == 'cab'"]
per_km_rate = 25.0

[context."$vehicle_type == 'bike'"]
per_km_rate = 15.0

[context."$city == 'Bangalore' && $vehicle_type == 'cab'"]
per_km_rate = 22.0

[context."$city == 'Delhi' && $vehicle_type == 'cab' && $hour_of_day >= 18"]
surge_factor = 5.0

[context."$city == 'Delhi' && $vehicle_type == 'cab' && $hour_of_day <= 6"]
surge_factor = 5.0

Use it in your application with a sample context​

Use the above configuration file in a simple rust application (src/main.rs) to resolve the configuration for a given context i.e. one or dimensions. In this case - get configuration when vehicle_type is cab.

use cac_toml::ContextAwareConfig;
use std::collections::HashMap;
use std::process;
use toml::Value;

fn main() {
    let file: String = String::from("example.cac.toml");

    let mut dimensions: HashMap<String, Value> = HashMap::new();
    dimensions.insert(String::from("vehicle_type"), Value::String(String::from("cab")));

    let cac = ContextAwareConfig::parse(&file).unwrap_or_else(|_err| {
        eprintln!("Could not parse file at {}", file);
        process::exit(-1);
    });

    println!("{:#?}", cac.get_resolved_config(&dimensions));
    process::exit(0);
}

Build and run the application​

cargo run

You should see the following output:

{
    "per_km_rate": Float(
        25.0,
    ),
    "surge_factor": Float(
        0.0,
    ),
}