diff options
| -rw-r--r-- | src/util/migrate.rs | 97 |
1 files changed, 91 insertions, 6 deletions
diff --git a/src/util/migrate.rs b/src/util/migrate.rs index f6028bf4..b7d6edc1 100644 --- a/src/util/migrate.rs +++ b/src/util/migrate.rs @@ -1,19 +1,21 @@ use serde::{Deserialize, Serialize}; +/// Indicates that this type has an encoding that can be migrated from +/// a previous version upon upgrades of Garage. 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 VERSION_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. + /// can be migrated. type Previous: Migrate; - /// This function must be filled in by implementors to migrate from a previons iteration - /// of the data format. + /// The migration function that transforms a value decoded in the old format + /// to an up-to-date value. fn migrate(previous: Self::Previous) -> Self; + /// Decode an encoded version of this type, going through a migration if necessary. fn decode(bytes: &[u8]) -> Option<Self> { let marker_len = Self::VERSION_MARKER.len(); if bytes.len() >= marker_len && &bytes[..marker_len] == Self::VERSION_MARKER { @@ -25,6 +27,7 @@ pub trait Migrate: Serialize + for<'de> Deserialize<'de> + 'static { Self::Previous::decode(bytes).map(Self::migrate) } + /// Encode this type with optionnal version marker fn encode(&self) -> Result<Vec<u8>, rmp_serde::encode::Error> { let mut wr = Vec::with_capacity(128); wr.extend_from_slice(Self::VERSION_MARKER); @@ -36,14 +39,13 @@ pub trait Migrate: Serialize + for<'de> Deserialize<'de> + 'static { } } +/// Indicates that this type has no previous encoding version to be migrated from. 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 VERSION_MARKER: &'static [u8] = b""; } -// ---- - impl<T: InitialFormat> Migrate for T { const VERSION_MARKER: &'static [u8] = <T as InitialFormat>::VERSION_MARKER; @@ -54,6 +56,7 @@ impl<T: InitialFormat> Migrate for T { } } +/// Internal type used by InitialFormat, not meant for general use. #[derive(Serialize, Deserialize)] pub struct NoPrevious; @@ -72,3 +75,85 @@ impl Migrate for NoPrevious { unreachable!() } } + +#[cfg(test)] +mod test { + use super::*; + + #[derive(Serialize, Deserialize, PartialEq, Eq, Debug)] + struct V1 { + a: usize, + b: String, + } + impl InitialFormat for V1 {} + + #[derive(Serialize, Deserialize, PartialEq, Eq, Debug)] + struct V2 { + a: usize, + b: Vec<String>, + c: String, + } + impl Migrate for V2 { + const VERSION_MARKER: &'static [u8] = b"GtestV2"; + type Previous = V1; + fn migrate(prev: V1) -> V2 { + V2 { + a: prev.a, + b: vec![prev.b], + c: String::new(), + } + } + } + + #[test] + fn test_v1() { + let x = V1 { + a: 12, + b: "hello".into(), + }; + let x_enc = x.encode().unwrap(); + let y = V1::decode(&x_enc).unwrap(); + assert_eq!(x, y); + } + + #[test] + fn test_v2() { + let x = V2 { + a: 12, + b: vec!["hello".into(), "world".into()], + c: "plop".into(), + }; + let x_enc = x.encode().unwrap(); + assert_eq!(&x_enc[..V2::VERSION_MARKER.len()], V2::VERSION_MARKER); + let y = V2::decode(&x_enc).unwrap(); + assert_eq!(x, y); + } + + #[test] + fn test_migrate() { + let x = V1 { + a: 12, + b: "hello".into(), + }; + let x_enc = x.encode().unwrap(); + + let xx = V1::decode(&x_enc).unwrap(); + assert_eq!(x, xx); + + let y = V2::decode(&x_enc).unwrap(); + assert_eq!( + y, + V2 { + a: 12, + b: vec!["hello".into()], + c: "".into(), + } + ); + + let y_enc = y.encode().unwrap(); + assert_eq!(&y_enc[..V2::VERSION_MARKER.len()], V2::VERSION_MARKER); + + let z = V2::decode(&y_enc).unwrap(); + assert_eq!(y, z); + } +} |