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Writing to a file seeks the internal cursor in Rust

Writing to a File seeks the internal cursor forward the length of the input. As such, file.read_to_string will only return data after the written input. To get back to the beginning, we can file.seek to a SeekFrom location. Here's a demo rust app

rust

use std::{
    fs::OpenOptions,
    io::{Read, Seek, SeekFrom, Write},
};

fn main() -> std::io::Result<()> {
    let mut file = OpenOptions::new()
        .create(true)
        .write(true)
        .read(true)
        .open("foo.txt")?;
    file.write_all(b"some offset")?;

    let mut contents_1 = String::new();
    file.read_to_string(&mut contents_1)?;
    dbg!(contents_1);

    file.seek(SeekFrom::Start(0))?;

    let mut contents_2 = String::new();
    file.read_to_string(&mut contents_2)?;
    dbg!(contents_2);

    Ok(())
}