How to create a TOML file from Rust?

Question

I have collected all my data into a vector and I need to create a TOML file with that data. I have managed to create and open a file:

let mut file = try!(File::create("servers.toml"));

My vector<(string,(string, u32))> contains the following data, which should look like this in TOML.

[server.A]
Ipaddr="192.168.4.1"
Port no=4476

[server.B]
......

I have a lot of data which needs to be written in TOML and I know TOML is a text file. How is encoder used for?

Bennettbenni

Welcome to Stack Overflow! Please edit your question to show us what you have tried; it's expected that you show a good amount of effort when asking a question; this isn't a service where people will write code for you for free! – Pearliepearline

Also note that vector<(string,(string, u32))> is not a valid type, at least using the standard library. If you are using types not found in the standard library, you need to include that in your question. You should produce a minimal reproducible example that will allow people to better understand your problem and help you. – Pearliepearline

Answer 1

This uses the TOML crate for the structure and serialization. The main benefit is that values should be properly escaped.

use std::fs;
use toml::{map::Map, Value}; // 0.5.1

fn to_toml(v: Vec<(String, (String, u32))>) -> Value {
    let mut servers = Map::new();
    for (name, (ip_addr, port)) in v {
        let mut server = Map::new();
        server.insert("Ipaddr".into(), Value::String(ip_addr));
        server.insert("Port no".into(), Value::Integer(port as i64));
        servers.insert(name, Value::Table(server));
    }

    let mut map = Map::new();
    map.insert("server".into(), Value::Table(servers));
    Value::Table(map)
}

fn main() {
    let v = vec![
        ("A".into(), ("192.168.4.1".into(), 4476)),
        ("B".into(), ("192.168.4.8".into(), 1234)),
    ];

    let toml_string = toml::to_string(&to_toml(v)).expect("Could not encode TOML value");
    println!("{}", toml_string);

    fs::write("servers.toml", toml_string).expect("Could not write to file!");
}

You can also use this with Serde's automatic serialization and deserialization to avoid dealing with the low-level details:

use serde::Serialize; // 1.0.91
use std::{collections::BTreeMap, fs};
use toml; // 0.5.1

#[derive(Debug, Default, Serialize)]
struct Servers<'a> {
    servers: BTreeMap<&'a str, Server<'a>>,
}

#[derive(Debug, Serialize)]
struct Server<'a> {
    #[serde(rename = "Ipaddr")]
    ip_addr: &'a str,

    #[serde(rename = "Port no")]
    port_no: i64,
}

fn main() {
    let mut file = Servers::default();
    file.servers.insert(
        "A",
        Server {
            ip_addr: "192.168.4.1",
            port_no: 4476,
        },
    );
    file.servers.insert(
        "B",
        Server {
            ip_addr: "192.168.4.8",
            port_no: 1234,
        },
    );

    let toml_string = toml::to_string(&file).expect("Could not encode TOML value");
    println!("{}", toml_string);
    fs::write("servers.toml", toml_string).expect("Could not write to file!");
}

Pearliepearline