76 lines
2.0 KiB
Rust
76 lines
2.0 KiB
Rust
|
use serde::{Deserialize, Serialize};
|
||
|
|
|
||
|
|
pub trait Migrate: Serialize + for<'de> Deserialize<'de> + 'static {
|
||
|
|
/// A sequence of bytes to add at the beginning of the serialized
|
||
|
|
/// string, to identify that the data is of this version.
|
||
|
|
const MARKER: &'static [u8] = b"";
|
||
|
|
|
||
|
|
/// The previous version of this data type, from which items of this version
|
||
|
|
/// can be migrated. Set `type Previous = NoPrevious` to indicate that this datatype
|
||
|
|
/// is the initial schema and cannot be migrated.
|
||
|
|
type Previous: Migrate;
|
||
|
|
|
||
|
|
/// This function must be filled in by implementors to migrate from a previons iteration
|
||
|
|
/// of the data format.
|
||
|
|
fn migrate(previous: Self::Previous) -> Self;
|
||
|
|
|
||
|
|
fn decode(bytes: &[u8]) -> Option<Self> {
|
||
|
|
if bytes.len() >= Self::MARKER.len() && &bytes[..Self::MARKER.len()] == Self::MARKER {
|
||
|
|
if let Ok(value) =
|
||
|
|
rmp_serde::decode::from_read_ref::<_, Self>(&bytes[Self::MARKER.len()..])
|
||
|
|
{
|
||
|
|
return Some(value);
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
Self::Previous::decode(bytes).map(Self::migrate)
|
||
|
|
}
|
||
|
|
|
||
|
|
fn encode(&self) -> Result<Vec<u8>, rmp_serde::encode::Error> {
|
||
|
|
let mut wr = Vec::with_capacity(128);
|
||
|
|
wr.extend_from_slice(Self::MARKER);
|
||
|
|
let mut se = rmp_serde::Serializer::new(&mut wr)
|
||
|
|
.with_struct_map()
|
||
|
|
.with_string_variants();
|
||
|
|
self.serialize(&mut se)?;
|
||
|
|
Ok(wr)
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
pub trait InitialFormat: Serialize + for<'de> Deserialize<'de> + 'static {
|
||
|
|
/// A sequence of bytes to add at the beginning of the serialized
|
||
|
|
/// string, to identify that the data is of this version.
|
||
|
|
const MARKER: &'static [u8] = b"";
|
||
|
|
}
|
||
|
|
|
||
|
|
// ----
|
||
|
|
|
||
|
|
impl<T: InitialFormat> Migrate for T {
|
||
|
|
const MARKER: &'static [u8] = <T as InitialFormat>::MARKER;
|
||
|
|
|
||
|
|
type Previous = NoPrevious;
|
||
|
|
|
||
|
|
fn migrate(_previous: Self::Previous) -> Self {
|
||
|
|
unreachable!();
|
||
|
|
}
|
||
|
|
}
|
||
|
|
|
||
|
|
#[derive(Serialize, Deserialize)]
|
||
|
|
pub struct NoPrevious;
|
||
|
|
|
||
|
|
impl Migrate for NoPrevious {
|
||
|
|
type Previous = NoPrevious;
|
||
|
|
|
||
|
|
fn migrate(_previous: Self::Previous) -> Self {
|
||
|
|
unreachable!();
|
||
|
|
}
|
||
|
|
|
||
|
|
fn decode(_bytes: &[u8]) -> Option<Self> {
|
||
|
|
None
|
||
|
|
}
|
||
|
|
|
||
|
|
fn encode(&self) -> Result<Vec<u8>, rmp_serde::encode::Error> {
|
||
|
|
unreachable!()
|
||
|
|
}
|
||
|
|
}
|