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|
//! File manifests.
//!
//! This crate defines the [`ManifestEntry`] struct to represent an
//! entry in a file manifest. The entry contains data about each file.
//! A manifest can be produced of some data, and later, a new manifest
//! can be produced and compared with the original. If the manifests
//! have changed, the data has changed. If they haven't changed, the
//! data has probably not changed.
//!
//! Such manifests can be used, for example, to verify that data that
//! has been restored from a backup is the same as what was backed up.
//!
//! This crate uses Linux metadata of files.
//!
//! ~~~
//! let m = std::fs::metadata(".").unwrap();
//! let e = summain::ManifestEntry(m);
//! println!("{}", serde_yaml::to_string(e).unwrap());
//! ~~~
//!
//! The output is something like:
//!
//! ~~~yaml
//! path: "."
//! mode: drwxrwxr-x
//! mtime: 1606565867
//! mtime_nsec: 500355545
//! nlink: 6
//! size: ~
//! ~~~
use serde::Serialize;
use sha2::{Digest, Sha256};
use std::fs::File;
use std::fs::{read_link, symlink_metadata};
use std::io::{BufReader, Read};
use std::os::linux::fs::MetadataExt;
use std::path::{Path, PathBuf};
const BUF_SIZE: usize = 1024 * 1024;
/// An entry in a file manifest.
#[derive(Serialize, Debug)]
pub struct ManifestEntry {
#[serde(skip)]
is_regular: bool,
// Store the original name in a hidden field, for compute_checksum.
#[serde(skip)]
filename: PathBuf,
// We store pathname as a string so that we can handle non-UTF8 names.
path: String,
#[serde(with = "mode")]
mode: u32,
mtime: i64,
mtime_nsec: i64,
nlink: u64,
size: Option<u64>,
sha256: Option<String>,
target: Option<PathBuf>,
}
impl ManifestEntry {
/// Create a new manifest entry.
///
/// The pathname of the file and the metadata are passed in by the
/// caller. This function doesn't query the system for it.
///
/// The structure can be serialized using serde.
pub async fn new(path: &Path) -> std::io::Result<Self> {
let m = symlink_metadata(path)?;
let target = if m.file_type().is_symlink() {
Some(read_link(path)?)
} else {
None
};
Ok(Self {
is_regular: m.is_file(),
filename: path.to_path_buf(),
path: path.to_string_lossy().into_owned(),
mode: m.st_mode(),
mtime: m.st_mtime(),
mtime_nsec: m.st_mtime_nsec(),
nlink: m.st_nlink(),
size: if m.is_dir() { None } else { Some(m.st_size()) },
sha256: None,
target,
})
}
pub fn compute_checksum(&mut self) -> std::io::Result<()> {
if self.is_regular {
self.sha256 = Some(file_checksum(&self.filename)?);
}
Ok(())
}
}
fn file_checksum(path: &Path) -> std::io::Result<String> {
let mut hasher = Sha256::new();
let file = File::open(path)?;
let mut reader = BufReader::new(file);
loop {
let mut buf = vec![0; BUF_SIZE];
let n = reader.read(&mut buf)?;
if n == 0 {
break;
}
hasher.update(&buf[..n]);
}
let hash = hasher.finalize();
Ok(format!("{:x}", hash))
}
mod mode {
use serde::{self, Serializer};
pub fn serialize<S>(mode: &u32, serializer: S) -> Result<S::Ok, S::Error>
where
S: Serializer,
{
let s = unix_mode::to_string(*mode);
serializer.serialize_str(&s)
}
}
|
