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switching-serializers.rs
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switching-serializers.rs
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//! Demonstrates using dataversion to migrate from unversioned data in one
//! format to versioned data in another format.
use std::{
fmt::Debug,
io::{BufReader, Read},
};
use dataversion::Versioned;
use serde::{Deserialize, Serialize};
#[derive(Copy, Clone, Debug)]
enum Versions {
Legacy = 0,
Current = 1,
}
impl Versioned for Versions {
fn version(&self) -> u64 {
*self as u64
}
}
impl TryFrom<u64> for Versions {
type Error = dataversion::UnknownVersion;
fn try_from(value: u64) -> Result<Self, Self::Error> {
match value {
0 => Ok(Self::Legacy),
1 => Ok(Self::Current),
other => Err(dataversion::UnknownVersion(other)),
}
}
}
#[derive(Serialize, Deserialize, Default, Eq, PartialEq, Debug)]
pub struct User {
id: u32,
name: String,
}
impl User {
/// Converts the user to bytes suitable for storage.
pub fn to_vec(&self) -> Result<Vec<u8>, pot::Error> {
let mut serialized = Vec::new();
// This example uses Write to build the payload without extra data
// copying, but it's a little more verbose. To see a simpler API, refer
// to `wrap()` and see its usage in `versioned-serde.rs`.
dataversion::write_header(&Versions::Current, &mut serialized)?;
pot::to_writer(self, &mut serialized)?;
Ok(serialized)
}
fn deserialize_versioned<R: Read>(
version: u64,
data: BufReader<R>,
) -> Result<Self, dataversion::Error<SerializerErrors>> {
match Versions::try_from(version)? {
Versions::Legacy => bincode::deserialize_from(data).map_err(SerializerErrors::Bincode),
Versions::Current => pot::from_reader(data).map_err(SerializerErrors::Pot),
}
.map_err(dataversion::Error::Other)
}
}
fn main() -> anyhow::Result<()> {
let original_user = User {
id: 42,
name: String::from("ecton"),
};
// To simulate loading a file that was previously stored in some arbitrary
// format, we're starting with a plain-encoded bincode user record.
let originally_stored_data = bincode::serialize(&original_user)?;
// If we pass the bincode-encoded file into
let deserialized_user =
dataversion::decode(&originally_stored_data[..], User::deserialize_versioned)?;
assert_eq!(original_user, deserialized_user);
// And, when we write out our new version, it will be wrapped by
// `dataversion` with the current version information.
let new_data = deserialized_user.to_vec()?;
let deserialized_user = dataversion::decode(&new_data[..], User::deserialize_versioned)?;
assert_eq!(original_user, deserialized_user);
Ok(())
}
#[derive(thiserror::Error, Debug)]
pub enum SerializerErrors {
#[error("pot error: {0}")]
Pot(#[from] pot::Error),
#[error("bincode error: {0}")]
Bincode(#[from] bincode::Error),
}
#[test]
fn runs() {
main().unwrap();
}