在文件具有更多数据之前，如何在rust中阻止

use std::fs::File;
use std::io::Write;

fn main() {
    let mut file = File::create("example.txt").expect("Failed to create file");
    file.write_all(b"Hello, World!").expect("Failed to write to file");
    
    // 截断文件，只保留前面的数据
    file.set_len(file.seek(std::io::SeekFrom::Current(0)).expect("Failed to get current position"))
        .expect("Failed to truncate file");
}

use std::fs::File;
use std::io::Write;

fn main() {
    let mut file = File::create("example.txt").expect("Failed to create file");
    file.write_all(b"Hello, World!").expect("Failed to write to file");
    
    let metadata = file.metadata().expect("Failed to get file metadata");
    let current_size = metadata.len();
    let expected_size = 10; // 期望的文件大小
    
    if current_size > expected_size {
        // 截断文件，只保留前面的数据
        file.set_len(expected_size).expect("Failed to truncate file");
    }
}

use std::fs::File;
use std::io::{Write, BufWriter};

fn main() {
    let file = File::create("example.txt").expect("Failed to create file");
    let mut writer = BufWriter::new(file);
    
    writer.write_all(b"Hello, World!").expect("Failed to write to file");
    writer.flush().expect("Failed to flush buffer");
}