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use std::fmt::{Display, Write};
use serde::{Deserialize, Serialize};
use sha2::{Digest, Sha256};
/// Information about a `Document`'s revision history.
#[derive(Debug, Clone, Copy, Eq, PartialEq, Serialize, Deserialize)]
pub struct Revision {
/// The current revision id of the document. This value is sequentially incremented on each document update.
pub id: u32,
/// The SHA256 digest of the bytes contained within the `Document`.
pub sha256: [u8; 32],
}
impl Revision {
/// Creates the first revision for a document with the SHA256 digest of the passed bytes.
#[must_use]
pub fn new(contents: &[u8]) -> Self {
Self::with_id(0, contents)
/// Creates a revision with `id` for a document with the SHA256 digest of the passed bytes.
pub fn with_id(id: u32, contents: &[u8]) -> Self {
Self {
id,
sha256: digest(contents),
/// Creates the next revision in sequence with an updated digest. If the digest doesn't change, None is returned.
///
/// # Panics
/// Panics if `id` overflows.
pub fn next_revision(&self, new_contents: &[u8]) -> Option<Self> {
let sha256 = digest(new_contents);
if sha256 == self.sha256 {
None
} else {
Some(Self {
id: self
.id
.checked_add(1)
.expect("need to implement revision id wrapping or increase revision id size"),
sha256,
})
impl Display for Revision {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
self.id.fmt(f)?;
f.write_char('-')?;
for byte in self.sha256 {
f.write_fmt(format_args!("{:02x}", byte))?;
Ok(())
fn digest(payload: &[u8]) -> [u8; 32] {
let mut hasher = Sha256::default();
hasher.update(payload);
hasher.finalize().into()
#[test]
fn revision_tests() {
let original_contents = b"one";
let first_revision = Revision::new(original_contents);
let original_digest =
hex_literal::hex!("7692c3ad3540bb803c020b3aee66cd8887123234ea0c6e7143c0add73ff431ed");
assert_eq!(
first_revision,
Revision {
id: 0,
sha256: original_digest
);
assert!(first_revision.next_revision(original_contents).is_none());
let updated_contents = b"two";
let next_revision = first_revision
.next_revision(updated_contents)
.expect("new contents should create a new revision");
next_revision,
id: 1,
sha256: hex_literal::hex!(
"3fc4ccfe745870e2c0d99f71f30ff0656c8dedd41cc1d7d3d376b0dbe685e2f3"
)
assert!(next_revision.next_revision(updated_contents).is_none());
next_revision.next_revision(original_contents),
Some(Revision {
id: 2,
fn revision_display_test() {
first_revision.to_string(),
"0-7692c3ad3540bb803c020b3aee66cd8887123234ea0c6e7143c0add73ff431ed"