I would like to serialize and then deserialize distinct objects in distinct parts of the same file, in RON format. So, I wrote this sample code:

use std::error::Error;
use std::fs::File;
use std::io::{BufReader, BufWriter, Read, Seek, Write};

const PATH: &str = "data.ron";
const SEPARATOR: &[u8] = b" something ";

fn serialize() -> Result<(), Box<dyn Error>> {
    let file = File::create(PATH)?;
    let mut writer = BufWriter::new(file);
    ron::ser::to_writer(&mut writer, &"Hi")?;
    writer.write(SEPARATOR)?;
    ron::ser::to_writer(&mut writer, &12.30)?;
    println!("Wrote file: {}", PATH);
    Ok(())
}

fn deserialize() -> Result<(), Box<dyn Error>> {
    let file = File::open(PATH)?;
    let mut reader = BufReader::new(file);
    let word: String = ron::de::from_reader(&mut reader)?;
    reader.seek(std::io::SeekFrom::Current(SEPARATOR.len() as i64))?;
    let number: f64 = ron::de::from_reader(&mut reader)?;
    println!("Read back: {}, {}", word, number);
    Ok(())
}

fn main() -> Result<(), Box<dyn Error>> {
    serialize()?;
    deserialize()?;
    Ok(())
}

It can be compiled and run with these dependencies:

ron = "0.8"
serde = "1.0.219"

It prints this to the console:

Wrote file: data.ron
Error: SpannedError { code: TrailingCharacters, position: Position { line: 1, col: 6 } }

The generated file contains this:

"Hi" something 12.3

A first problem is that, if I set the dependency ron = "0.9" or ron = "0.10.1", the program cannot be compiled anymore, because the trait bound `BufWriter<File>: std::fmt::Write` is not satisfied..
However, the biggest problem is that SpannedError that I get after having deserialized the string "Hi".

2 posts - 2 participants

Read full topic