src/lib.rs


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use sha2::{Digest, Sha256};
use std::fs::File;
use std::io::{BufReader, Read};
use std::path::{Path, PathBuf};

const BUF_SIZE: usize = 4096;

#[derive(Debug)]
pub struct FileChecksum {
    pub filename: PathBuf,
    pub checksum: String,
}

impl FileChecksum {
    pub fn new(filename: &Path, checksum: String) -> Self {
        Self {
            filename: filename.to_path_buf(),
            checksum,
        }
    }

    pub fn print(&self) {
        println!("{} {}", self.checksum, self.filename.display());
    }
}

pub fn checksum(filename: &Path) -> Result<FileChecksum, std::io::Error> {
    let mut checksum = Sha256::new();

    let file = File::open(filename)?;
    let mut reader = BufReader::new(file);
    loop {
        let mut buf = vec![0; BUF_SIZE];
        let n = reader.read(&mut buf)?;
        if n == 0 {
            break;
        }
        checksum.update(&buf[..n]);
    }

    let checksum = checksum.finalize();
    let checksum = format!("{checksum:x}");
    Ok(FileChecksum::new(filename, checksum))
}