Writing to file with Append(false) doesn't work as expected - rust

Question

I am learning to program with Rust and decided to build a CLI to manage my personal library. I'm still working on a quick proof of concept before going further so I have the barebones of what I need to work.
I am saving data to a file called "books.json" using std::fs and serde_json. The program works great the first time I run it, but on the second run, instead of overwriting the file, it is appending the data (for test purposes, it would add the same book twice).
Here's the code I have written so far. By using OpenOptions.append(false), shouldn't the file be overwritten when I write to it?
use serde::{Deserialize, Serialize};
use serde_json::Error;
use std::fs;
use std::fs::File;
use std::io::Read;
use std::io::Write;
#[derive(Serialize, Deserialize)]
struct Book {
title: String,
author: String,
isbn: String,
pub_year: usize,
}
fn main() -> Result<(), serde_json::Error> {
let mut file = fs::OpenOptions::new()
.read(true)
.write(true)
.append(false)
.create(true)
.open("books.json")
.expect("Unable to open");
let mut data = String::new();
file.read_to_string(&mut data);
let mut bookshelf: Vec<Book> = Vec::new();
if file.metadata().unwrap().len() != 0 {
bookshelf = serde_json::from_str(&data)?;
}
let book = Book {
title: "The Institute".to_string(),
author: "Stephen King".to_string(),
isbn: "9781982110567".to_string(),
pub_year: 2019,
};
bookshelf.push(book);
let j: String = serde_json::to_string(&bookshelf)?;
file.write_all(j.as_bytes()).expect("Unable to write data");
Ok(())
}
books.json after running the program twice:
[{"title":"The Institute","author":"Stephen King","isbn":"9781982110567","pub_year":2019}]
[{"title":"The Institute","author":"Stephen King","isbn":"9781982110567","pub_year":2019},
{"title":"The Institute","author":"Stephen King","isbn":"9781982110567","pub_year":2019}]%

Answer 1

Members of the Rust Discord community pointed out that by using OpenOptions, the file pointer was ending up at the end of the file when I wrote to it. They suggested I use fs::read and fs::write, and that worked. I then added some code to handle cases where the file did not already exist.
The main() function would then need to look something like this:
fn main() -> std::io::Result<()> {
let f = File::open("books.json");
let _ = match f {
Ok(file) => file,
Err(error) => match error.kind() {
ErrorKind::NotFound => match File::create("books.json") {
Ok(fc) => fc,
Err(e) => panic!("Problem creating the file: {:?}", e),
},
},
};
let data = fs::read_to_string("books.json").expect("Unable to read file");
let mut bookshelf: Vec<Book> = Vec::new();
if fs::metadata("books.json").unwrap().len() != 0 {
bookshelf = serde_json::from_str(&data)?;
}
let book = Book {
title: "The Institute".to_string(),
author: "Stephen King".to_string(),
isbn: "9781982110567".to_string(),
pub_year: 2019,
};
bookshelf.push(book);
let json: String = serde_json::to_string(&bookshelf)?;
fs::write("books.json", &json).expect("Unable to write file");
println!("{}", &json);
Ok(())
}