Refactor how things are migrated

Cargo.lock

@@ -1277,6 +1277,7 @@ dependencies = [
  "garage_db",
  "git-version",
  "hex",
+ "hexdump",
  "http",
  "hyper",
  "lazy_static",

src/block/repair.rs

@@ -178,6 +178,7 @@ struct ScrubWorkerPersisted {
 	time_last_complete_scrub: u64,
 	corruptions_detected: u64,
 }
+impl garage_util::migrate::InitialFormat for ScrubWorkerPersisted {}
 
 enum ScrubWorkerState {
 	Running(BlockStoreIterator),

src/block/resync.rs

@@ -63,6 +63,7 @@ struct ResyncPersistedConfig {
 	n_workers: usize,
 	tranquility: u32,
 }
+impl garage_util::migrate::InitialFormat for ResyncPersistedConfig {}
 
 enum ResyncIterResult {
 	BusyDidSomething,

src/garage/Cargo.toml

@@ -74,7 +74,7 @@ base64 = "0.13"
 
 
 [features]
-default = [ "bundled-libs", "metrics", "sled" ]
+default = [ "bundled-libs", "metrics", "sled", "k2v" ]
 
 k2v = [ "garage_util/k2v", "garage_api/k2v" ]
 

src/model/bucket_alias_table.rs

@@ -5,14 +5,22 @@ use garage_util::data::*;
 use garage_table::crdt::*;
 use garage_table::*;
 
+mod v08 {
+	use super::*;
+
 	/// The bucket alias table holds the names given to buckets
 	/// in the global namespace.
 	#[derive(PartialEq, Eq, Clone, Debug, Serialize, Deserialize)]
 	pub struct BucketAlias {
-	name: String,
+		pub(super) name: String,
 		pub state: crdt::Lww<Option<Uuid>>,
 	}
 
+	impl garage_util::migrate::InitialFormat for BucketAlias {}
+}
+
+pub use v08::*;
+
 impl BucketAlias {
 	pub fn new(name: String, ts: u64, bucket_id: Option<Uuid>) -> Option<Self> {
 		if !is_valid_bucket_name(&name) {

src/model/bucket_table.rs

@@ -7,6 +7,9 @@ use garage_util::time::*;
 
 use crate::permission::BucketKeyPerm;
 
+mod v08 {
+	use super::*;
+
 	/// A bucket is a collection of objects
 	///
 	/// Its parameters are not directly accessible as:
@@ -73,6 +76,11 @@ pub struct BucketQuotas {
 		pub max_objects: Option<u64>,
 	}
 
+	impl garage_util::migrate::InitialFormat for Bucket {}
+}
+
+pub use v08::*;
+
 impl AutoCrdt for BucketQuotas {
 	const WARN_IF_DIFFERENT: bool = true;
 }

src/model/index_counter.rs

@@ -12,6 +12,7 @@ use garage_rpc::system::System;
 use garage_util::background::BackgroundRunner;
 use garage_util::data::*;
 use garage_util::error::*;
+use garage_util::migrate::Migrate;
 use garage_util::time::*;
 
 use garage_table::crdt::*;
@@ -29,6 +30,9 @@ pub trait CountedItem: Clone + PartialEq + Send + Sync + 'static {
 	fn counts(&self) -> Vec<(&'static str, i64)>;
 }
 
+mod v08 {
+	use super::*;
+
 	/// A counter entry in the global table
 	#[derive(Clone, PartialEq, Debug, Serialize, Deserialize)]
 	pub struct CounterEntry<T: CountedItem> {
@@ -37,6 +41,17 @@ pub struct CounterEntry<T: CountedItem> {
 		pub values: BTreeMap<String, CounterValue>,
 	}
 
+	/// A counter entry in the global table
+	#[derive(PartialEq, Eq, Clone, Debug, Serialize, Deserialize)]
+	pub struct CounterValue {
+		pub node_values: BTreeMap<Uuid, (u64, i64)>,
+	}
+
+	impl<T: CountedItem> garage_util::migrate::InitialFormat for CounterEntry<T> {}
+}
+
+pub use v08::*;
+
 impl<T: CountedItem> Entry<T::CP, T::CS> for CounterEntry<T> {
 	fn partition_key(&self) -> &T::CP {
 		&self.pk
@@ -78,12 +93,6 @@ impl<T: CountedItem> CounterEntry<T> {
 	}
 }
 
-/// A counter entry in the global table
-#[derive(PartialEq, Eq, Clone, Debug, Serialize, Deserialize)]
-pub struct CounterValue {
-	pub node_values: BTreeMap<Uuid, (u64, i64)>,
-}
-
 impl<T: CountedItem> Crdt for CounterEntry<T> {
 	fn merge(&mut self, other: &Self) {
 		for (name, e2) in other.values.iter() {
@@ -195,11 +204,9 @@ impl<T: CountedItem> IndexCounter<T> {
 		let tree_key = self.table.data.tree_key(pk, sk);
 
 		let mut entry = match tx.get(&self.local_counter, &tree_key[..])? {
-			Some(old_bytes) => {
+			Some(old_bytes) => LocalCounterEntry::<T>::decode(&old_bytes)
-				rmp_serde::decode::from_read_ref::<_, LocalCounterEntry<T>>(&old_bytes)
+				.ok_or_message("Cannot decode local counter entry")
-					.map_err(Error::RmpDecode)
+				.map_err(db::TxError::Abort)?,
-					.map_err(db::TxError::Abort)?
-			}
 			None => LocalCounterEntry {
 				pk: pk.clone(),
 				sk: sk.clone(),
@@ -214,7 +221,8 @@ impl<T: CountedItem> IndexCounter<T> {
 			ent.1 += *inc;
 		}
 
-		let new_entry_bytes = rmp_to_vec_all_named(&entry)
+		let new_entry_bytes = entry
+			.encode()
 			.map_err(Error::RmpEncode)
 			.map_err(db::TxError::Abort)?;
 		tx.insert(&self.local_counter, &tree_key[..], new_entry_bytes)?;
@@ -263,7 +271,7 @@ impl<T: CountedItem> IndexCounter<T> {
 					tv.1 = 0;
 				}
 
-				let local_counter_bytes = rmp_to_vec_all_named(&local_counter)?;
+				let local_counter_bytes = local_counter.encode()?;
 				self.local_counter
 					.insert(&local_counter_k, &local_counter_bytes)?;
 
@@ -330,7 +338,7 @@ impl<T: CountedItem> IndexCounter<T> {
 					tv.1 += v;
 				}
 
-				let local_counter_bytes = rmp_to_vec_all_named(&local_counter)?;
+				let local_counter_bytes = local_counter.encode()?;
 				self.local_counter
 					.insert(&local_counter_key, local_counter_bytes)?;
 
@@ -357,6 +365,8 @@ struct LocalCounterEntry<T: CountedItem> {
 	values: BTreeMap<String, (u64, i64)>,
 }
 
+impl<T: CountedItem> garage_util::migrate::InitialFormat for LocalCounterEntry<T> {}
+
 impl<T: CountedItem> LocalCounterEntry<T> {
 	fn into_counter_entry(self, this_node: Uuid) -> CounterEntry<T> {
 		CounterEntry {

src/model/k2v/item_table.rs

@@ -1,7 +1,8 @@
-use serde::{Deserialize, Serialize};
 use std::collections::BTreeMap;
 use std::sync::Arc;
 
+use serde::{Deserialize, Serialize};
+
 use garage_db as db;
 use garage_util::data::*;
 
@@ -17,12 +18,18 @@ pub const CONFLICTS: &str = "conflicts";
 pub const VALUES: &str = "values";
 pub const BYTES: &str = "bytes";
 
+mod v08 {
+	use crate::k2v::causality::K2VNodeId;
+	use garage_util::data::Uuid;
+	use serde::{Deserialize, Serialize};
+	use std::collections::BTreeMap;
+
 	#[derive(PartialEq, Eq, Clone, Debug, Serialize, Deserialize)]
 	pub struct K2VItem {
 		pub partition: K2VItemPartition,
 		pub sort_key: String,
 
-	items: BTreeMap<K2VNodeId, DvvsEntry>,
+		pub(super) items: BTreeMap<K2VNodeId, DvvsEntry>,
 	}
 
 	#[derive(PartialEq, Eq, Clone, Debug, Serialize, Deserialize, Hash)]
@@ -32,9 +39,9 @@ pub struct K2VItemPartition {
 	}
 
 	#[derive(PartialEq, Eq, Clone, Debug, Serialize, Deserialize)]
-struct DvvsEntry {
+	pub struct DvvsEntry {
-	t_discard: u64,
+		pub(super) t_discard: u64,
-	values: Vec<(u64, DvvsValue)>,
+		pub(super) values: Vec<(u64, DvvsValue)>,
 	}
 
 	#[derive(PartialEq, Eq, Clone, Debug, Serialize, Deserialize)]
@@ -43,6 +50,11 @@ pub enum DvvsValue {
 		Deleted,
 	}
 
+	impl garage_util::migrate::InitialFormat for K2VItem {}
+}
+
+pub use v08::*;
+
 impl K2VItem {
 	/// Creates a new K2VItem when no previous entry existed in the db
 	pub fn new(bucket_id: Uuid, partition_key: String, sort_key: String) -> Self {

src/model/key_table.rs

@@ -1,12 +1,58 @@
 use serde::{Deserialize, Serialize};
 
-use garage_table::crdt::*;
+use garage_util::crdt::{self, Crdt};
-use garage_table::*;
 use garage_util::data::*;
 
+use garage_table::{DeletedFilter, EmptyKey, Entry, TableSchema};
+
 use crate::permission::BucketKeyPerm;
 
-use crate::prev::v051::key_table as old;
+pub(crate) mod v05 {
+	use garage_util::crdt;
+	use serde::{Deserialize, Serialize};
+
+	/// An api key
+	#[derive(PartialEq, Eq, Clone, Debug, Serialize, Deserialize)]
+	pub struct Key {
+		/// The id of the key (immutable), used as partition key
+		pub key_id: String,
+
+		/// The secret_key associated
+		pub secret_key: String,
+
+		/// Name for the key
+		pub name: crdt::Lww<String>,
+
+		/// Is the key deleted
+		pub deleted: crdt::Bool,
+
+		/// Buckets in which the key is authorized. Empty if `Key` is deleted
+		// CRDT interaction: deleted implies authorized_buckets is empty
+		pub authorized_buckets: crdt::LwwMap<String, PermissionSet>,
+	}
+
+	/// Permission given to a key in a bucket
+	#[derive(PartialOrd, Ord, PartialEq, Eq, Clone, Debug, Serialize, Deserialize)]
+	pub struct PermissionSet {
+		/// The key can be used to read the bucket
+		pub allow_read: bool,
+		/// The key can be used to write in the bucket
+		pub allow_write: bool,
+	}
+
+	impl crdt::AutoCrdt for PermissionSet {
+		const WARN_IF_DIFFERENT: bool = true;
+	}
+
+	impl garage_util::migrate::InitialFormat for Key {}
+}
+
+mod v08 {
+	use super::v05;
+	use crate::permission::BucketKeyPerm;
+	use garage_util::crdt;
+	use garage_util::data::Uuid;
+	use serde::{Deserialize, Serialize};
 
 	/// An api key
 	#[derive(PartialEq, Eq, Clone, Debug, Serialize, Deserialize)]
@@ -40,6 +86,36 @@ pub struct KeyParams {
 		pub local_aliases: crdt::LwwMap<String, Option<Uuid>>,
 	}
 
+	impl garage_util::migrate::Migrate for Key {
+		type Previous = v05::Key;
+
+		fn migrate(old_k: v05::Key) -> Key {
+			let name = crdt::Lww::raw(old_k.name.timestamp(), old_k.name.get().clone());
+
+			let state = if old_k.deleted.get() {
+				crdt::Deletable::Deleted
+			} else {
+				// Authorized buckets is ignored here,
+				// migration is performed in specific migration code in
+				// garage/migrate.rs
+				crdt::Deletable::Present(KeyParams {
+					secret_key: old_k.secret_key,
+					name,
+					allow_create_bucket: crdt::Lww::new(false),
+					authorized_buckets: crdt::Map::new(),
+					local_aliases: crdt::LwwMap::new(),
+				})
+			};
+			Key {
+				key_id: old_k.key_id,
+				state,
+			}
+		}
+	}
+}
+
+pub use v08::*;
+
 impl KeyParams {
 	fn new(secret_key: &str, name: &str) -> Self {
 		KeyParams {
@@ -173,28 +249,4 @@ impl TableSchema for KeyTable {
 			}
 		}
 	}
-
-	fn try_migrate(bytes: &[u8]) -> Option<Self::E> {
-		let old_k = rmp_serde::decode::from_read_ref::<_, old::Key>(bytes).ok()?;
-		let name = crdt::Lww::raw(old_k.name.timestamp(), old_k.name.get().clone());
-
-		let state = if old_k.deleted.get() {
-			crdt::Deletable::Deleted
-		} else {
-			// Authorized buckets is ignored here,
-			// migration is performed in specific migration code in
-			// garage/migrate.rs
-			crdt::Deletable::Present(KeyParams {
-				secret_key: old_k.secret_key,
-				name,
-				allow_create_bucket: crdt::Lww::new(false),
-				authorized_buckets: crdt::Map::new(),
-				local_aliases: crdt::LwwMap::new(),
-			})
-		};
-		Some(Key {
-			key_id: old_k.key_id,
-			state,
-		})
-	}
 }

src/model/prev/v051/bucket_table.rs

@@ -3,7 +3,7 @@ use serde::{Deserialize, Serialize};
 use garage_table::crdt::Crdt;
 use garage_table::*;
 
-use super::key_table::PermissionSet;
+use crate::key_table::v05::PermissionSet;
 
 /// A bucket is a collection of objects
 ///

src/model/prev/v051/key_table.rs

@@ -1,50 +0,0 @@
-use serde::{Deserialize, Serialize};
-
-use garage_table::crdt::*;
-use garage_table::*;
-
-/// An api key
-#[derive(PartialEq, Eq, Clone, Debug, Serialize, Deserialize)]
-pub struct Key {
-	/// The id of the key (immutable), used as partition key
-	pub key_id: String,
-
-	/// The secret_key associated
-	pub secret_key: String,
-
-	/// Name for the key
-	pub name: crdt::Lww<String>,
-
-	/// Is the key deleted
-	pub deleted: crdt::Bool,
-
-	/// Buckets in which the key is authorized. Empty if `Key` is deleted
-	// CRDT interaction: deleted implies authorized_buckets is empty
-	pub authorized_buckets: crdt::LwwMap<String, PermissionSet>,
-}
-
-/// Permission given to a key in a bucket
-#[derive(PartialOrd, Ord, PartialEq, Eq, Clone, Debug, Serialize, Deserialize)]
-pub struct PermissionSet {
-	/// The key can be used to read the bucket
-	pub allow_read: bool,
-	/// The key can be used to write in the bucket
-	pub allow_write: bool,
-}
-
-impl AutoCrdt for PermissionSet {
-	const WARN_IF_DIFFERENT: bool = true;
-}
-
-impl Crdt for Key {
-	fn merge(&mut self, other: &Self) {
-		self.name.merge(&other.name);
-		self.deleted.merge(&other.deleted);
-
-		if self.deleted.get() {
-			self.authorized_buckets.clear();
-		} else {
-			self.authorized_buckets.merge(&other.authorized_buckets);
-		}
-	}
-}

src/model/prev/v051/mod.rs

@@ -1,4 +1 @@
 pub(crate) mod bucket_table;
-pub(crate) mod key_table;
-pub(crate) mod object_table;
-pub(crate) mod version_table;

src/model/prev/v051/object_table.rs

@@ -1,149 +0,0 @@
-use serde::{Deserialize, Serialize};
-use std::collections::BTreeMap;
-
-use garage_util::data::*;
-
-use garage_table::crdt::*;
-
-/// An object
-#[derive(PartialEq, Eq, Clone, Debug, Serialize, Deserialize)]
-pub struct Object {
-	/// The bucket in which the object is stored, used as partition key
-	pub bucket: String,
-
-	/// The key at which the object is stored in its bucket, used as sorting key
-	pub key: String,
-
-	/// The list of currenty stored versions of the object
-	versions: Vec<ObjectVersion>,
-}
-
-impl Object {
-	/// Get a list of currently stored versions of `Object`
-	pub fn versions(&self) -> &[ObjectVersion] {
-		&self.versions[..]
-	}
-}
-
-/// Informations about a version of an object
-#[derive(PartialEq, Eq, Clone, Debug, Serialize, Deserialize)]
-pub struct ObjectVersion {
-	/// Id of the version
-	pub uuid: Uuid,
-	/// Timestamp of when the object was created
-	pub timestamp: u64,
-	/// State of the version
-	pub state: ObjectVersionState,
-}
-
-/// State of an object version
-#[derive(PartialEq, Eq, Clone, Debug, Serialize, Deserialize)]
-pub enum ObjectVersionState {
-	/// The version is being received
-	Uploading(ObjectVersionHeaders),
-	/// The version is fully received
-	Complete(ObjectVersionData),
-	/// The version uploaded containded errors or the upload was explicitly aborted
-	Aborted,
-}
-
-impl Crdt for ObjectVersionState {
-	fn merge(&mut self, other: &Self) {
-		use ObjectVersionState::*;
-		match other {
-			Aborted => {
-				*self = Aborted;
-			}
-			Complete(b) => match self {
-				Aborted => {}
-				Complete(a) => {
-					a.merge(b);
-				}
-				Uploading(_) => {
-					*self = Complete(b.clone());
-				}
-			},
-			Uploading(_) => {}
-		}
-	}
-}
-
-/// Data stored in object version
-#[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Debug, Serialize, Deserialize)]
-pub enum ObjectVersionData {
-	/// The object was deleted, this Version is a tombstone to mark it as such
-	DeleteMarker,
-	/// The object is short, it's stored inlined
-	Inline(ObjectVersionMeta, #[serde(with = "serde_bytes")] Vec<u8>),
-	/// The object is not short, Hash of first block is stored here, next segments hashes are
-	/// stored in the version table
-	FirstBlock(ObjectVersionMeta, Hash),
-}
-
-impl AutoCrdt for ObjectVersionData {
-	const WARN_IF_DIFFERENT: bool = true;
-}
-
-/// Metadata about the object version
-#[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Debug, Serialize, Deserialize)]
-pub struct ObjectVersionMeta {
-	/// Headers to send to the client
-	pub headers: ObjectVersionHeaders,
-	/// Size of the object
-	pub size: u64,
-	/// etag of the object
-	pub etag: String,
-}
-
-/// Additional headers for an object
-#[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Debug, Serialize, Deserialize)]
-pub struct ObjectVersionHeaders {
-	/// Content type of the object
-	pub content_type: String,
-	/// Any other http headers to send
-	pub other: BTreeMap<String, String>,
-}
-
-impl ObjectVersion {
-	fn cmp_key(&self) -> (u64, Uuid) {
-		(self.timestamp, self.uuid)
-	}
-
-	/// Is the object version completely received
-	pub fn is_complete(&self) -> bool {
-		matches!(self.state, ObjectVersionState::Complete(_))
-	}
-}
-
-impl Crdt for Object {
-	fn merge(&mut self, other: &Self) {
-		// Merge versions from other into here
-		for other_v in other.versions.iter() {
-			match self
-				.versions
-				.binary_search_by(|v| v.cmp_key().cmp(&other_v.cmp_key()))
-			{
-				Ok(i) => {
-					self.versions[i].state.merge(&other_v.state);
-				}
-				Err(i) => {
-					self.versions.insert(i, other_v.clone());
-				}
-			}
-		}
-
-		// Remove versions which are obsolete, i.e. those that come
-		// before the last version which .is_complete().
-		let last_complete = self
-			.versions
-			.iter()
-			.enumerate()
-			.rev()
-			.find(|(_, v)| v.is_complete())
-			.map(|(vi, _)| vi);
-
-		if let Some(last_vi) = last_complete {
-			self.versions = self.versions.drain(last_vi..).collect::<Vec<_>>();
-		}
-	}
-}

src/model/prev/v051/version_table.rs

@@ -1,79 +0,0 @@
-use serde::{Deserialize, Serialize};
-
-use garage_util::data::*;
-
-use garage_table::crdt::*;
-use garage_table::*;
-
-/// A version of an object
-#[derive(PartialEq, Eq, Clone, Debug, Serialize, Deserialize)]
-pub struct Version {
-	/// UUID of the version, used as partition key
-	pub uuid: Uuid,
-
-	// Actual data: the blocks for this version
-	// In the case of a multipart upload, also store the etags
-	// of individual parts and check them when doing CompleteMultipartUpload
-	/// Is this version deleted
-	pub deleted: crdt::Bool,
-	/// list of blocks of data composing the version
-	pub blocks: crdt::Map<VersionBlockKey, VersionBlock>,
-	/// Etag of each part in case of a multipart upload, empty otherwise
-	pub parts_etags: crdt::Map<u64, String>,
-
-	// Back link to bucket+key so that we can figure if
-	// this was deleted later on
-	/// Bucket in which the related object is stored
-	pub bucket: String,
-	/// Key in which the related object is stored
-	pub key: String,
-}
-
-#[derive(PartialEq, Eq, Clone, Copy, Debug, Serialize, Deserialize)]
-pub struct VersionBlockKey {
-	/// Number of the part
-	pub part_number: u64,
-	/// Offset of this sub-segment in its part
-	pub offset: u64,
-}
-
-impl Ord for VersionBlockKey {
-	fn cmp(&self, other: &Self) -> std::cmp::Ordering {
-		self.part_number
-			.cmp(&other.part_number)
-			.then(self.offset.cmp(&other.offset))
-	}
-}
-
-impl PartialOrd for VersionBlockKey {
-	fn partial_cmp(&self, other: &Self) -> Option<std::cmp::Ordering> {
-		Some(self.cmp(other))
-	}
-}
-
-/// Informations about a single block
-#[derive(PartialEq, Eq, Ord, PartialOrd, Clone, Copy, Debug, Serialize, Deserialize)]
-pub struct VersionBlock {
-	/// Blake2 sum of the block
-	pub hash: Hash,
-	/// Size of the block
-	pub size: u64,
-}
-
-impl AutoCrdt for VersionBlock {
-	const WARN_IF_DIFFERENT: bool = true;
-}
-
-impl Crdt for Version {
-	fn merge(&mut self, other: &Self) {
-		self.deleted.merge(&other.deleted);
-
-		if self.deleted.get() {
-			self.blocks.clear();
-			self.parts_etags.clear();
-		} else {
-			self.blocks.merge(&other.blocks);
-			self.parts_etags.merge(&other.parts_etags);
-		}
-	}
-}

src/model/s3/block_ref_table.rs

@@ -1,4 +1,3 @@
-use serde::{Deserialize, Serialize};
 use std::sync::Arc;
 
 use garage_db as db;
@@ -10,6 +9,11 @@ use garage_table::*;
 
 use garage_block::manager::*;
 
+mod v08 {
+	use garage_util::crdt;
+	use garage_util::data::{Hash, Uuid};
+	use serde::{Deserialize, Serialize};
+
 	#[derive(PartialEq, Eq, Clone, Debug, Serialize, Deserialize)]
 	pub struct BlockRef {
 		/// Hash (blake2 sum) of the block, used as partition key
@@ -23,6 +27,11 @@ pub struct BlockRef {
 		pub deleted: crdt::Bool,
 	}
 
+	impl garage_util::migrate::InitialFormat for BlockRef {}
+}
+
+pub use v08::*;
+
 impl Entry<Hash, Uuid> for BlockRef {
 	fn partition_key(&self) -> &Hash {
 		&self.block

src/model/s3/object_table.rs

@@ -1,5 +1,4 @@
 use serde::{Deserialize, Serialize};
-use std::collections::BTreeMap;
 use std::sync::Arc;
 
 use garage_db as db;
@@ -13,12 +12,96 @@ use garage_table::*;
 use crate::index_counter::*;
 use crate::s3::version_table::*;
 
-use crate::prev::v051::object_table as old;
-
 pub const OBJECTS: &str = "objects";
 pub const UNFINISHED_UPLOADS: &str = "unfinished_uploads";
 pub const BYTES: &str = "bytes";
 
+mod v05 {
+	use garage_util::data::{Hash, Uuid};
+	use serde::{Deserialize, Serialize};
+	use std::collections::BTreeMap;
+
+	/// An object
+	#[derive(PartialEq, Eq, Clone, Debug, Serialize, Deserialize)]
+	pub struct Object {
+		/// The bucket in which the object is stored, used as partition key
+		pub bucket: String,
+
+		/// The key at which the object is stored in its bucket, used as sorting key
+		pub key: String,
+
+		/// The list of currenty stored versions of the object
+		pub(super) versions: Vec<ObjectVersion>,
+	}
+
+	/// Informations about a version of an object
+	#[derive(PartialEq, Eq, Clone, Debug, Serialize, Deserialize)]
+	pub struct ObjectVersion {
+		/// Id of the version
+		pub uuid: Uuid,
+		/// Timestamp of when the object was created
+		pub timestamp: u64,
+		/// State of the version
+		pub state: ObjectVersionState,
+	}
+
+	/// State of an object version
+	#[derive(PartialEq, Eq, Clone, Debug, Serialize, Deserialize)]
+	pub enum ObjectVersionState {
+		/// The version is being received
+		Uploading(ObjectVersionHeaders),
+		/// The version is fully received
+		Complete(ObjectVersionData),
+		/// The version uploaded containded errors or the upload was explicitly aborted
+		Aborted,
+	}
+
+	/// Data stored in object version
+	#[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Debug, Serialize, Deserialize)]
+	pub enum ObjectVersionData {
+		/// The object was deleted, this Version is a tombstone to mark it as such
+		DeleteMarker,
+		/// The object is short, it's stored inlined
+		Inline(ObjectVersionMeta, #[serde(with = "serde_bytes")] Vec<u8>),
+		/// The object is not short, Hash of first block is stored here, next segments hashes are
+		/// stored in the version table
+		FirstBlock(ObjectVersionMeta, Hash),
+	}
+
+	/// Metadata about the object version
+	#[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Debug, Serialize, Deserialize)]
+	pub struct ObjectVersionMeta {
+		/// Headers to send to the client
+		pub headers: ObjectVersionHeaders,
+		/// Size of the object
+		pub size: u64,
+		/// etag of the object
+		pub etag: String,
+	}
+
+	/// Additional headers for an object
+	#[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Debug, Serialize, Deserialize)]
+	pub struct ObjectVersionHeaders {
+		/// Content type of the object
+		pub content_type: String,
+		/// Any other http headers to send
+		pub other: BTreeMap<String, String>,
+	}
+
+	impl garage_util::migrate::InitialFormat for Object {}
+}
+
+mod v08 {
+	use garage_util::data::Uuid;
+	use serde::{Deserialize, Serialize};
+
+	use super::v05;
+
+	pub use v05::{
+		ObjectVersion, ObjectVersionData, ObjectVersionHeaders, ObjectVersionMeta,
+		ObjectVersionState,
+	};
+
 	/// An object
 	#[derive(PartialEq, Eq, Clone, Debug, Serialize, Deserialize)]
 	pub struct Object {
@@ -29,9 +112,26 @@ pub struct Object {
 		pub key: String,
 
 		/// The list of currenty stored versions of the object
-	versions: Vec<ObjectVersion>,
+		pub(super) versions: Vec<ObjectVersion>,
 	}
 
+	impl garage_util::migrate::Migrate for Object {
+		type Previous = v05::Object;
+
+		fn migrate(old: v05::Object) -> Object {
+			use garage_util::data::blake2sum;
+
+			Object {
+				bucket_id: blake2sum(old.bucket.as_bytes()),
+				key: old.key,
+				versions: old.versions,
+			}
+		}
+	}
+}
+
+pub use v08::*;
+
 impl Object {
 	/// Initialize an Object struct from parts
 	pub fn new(bucket_id: Uuid, key: String, versions: Vec<ObjectVersion>) -> Self {
@@ -68,28 +168,6 @@ impl Object {
 	}
 }
 
-/// Informations about a version of an object
-#[derive(PartialEq, Eq, Clone, Debug, Serialize, Deserialize)]
-pub struct ObjectVersion {
-	/// Id of the version
-	pub uuid: Uuid,
-	/// Timestamp of when the object was created
-	pub timestamp: u64,
-	/// State of the version
-	pub state: ObjectVersionState,
-}
-
-/// State of an object version
-#[derive(PartialEq, Eq, Clone, Debug, Serialize, Deserialize)]
-pub enum ObjectVersionState {
-	/// The version is being received
-	Uploading(ObjectVersionHeaders),
-	/// The version is fully received
-	Complete(ObjectVersionData),
-	/// The version uploaded containded errors or the upload was explicitly aborted
-	Aborted,
-}
-
 impl Crdt for ObjectVersionState {
 	fn merge(&mut self, other: &Self) {
 		use ObjectVersionState::*;
@@ -111,42 +189,10 @@ impl Crdt for ObjectVersionState {
 	}
 }
 
-/// Data stored in object version
-#[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Debug, Serialize, Deserialize)]
-pub enum ObjectVersionData {
-	/// The object was deleted, this Version is a tombstone to mark it as such
-	DeleteMarker,
-	/// The object is short, it's stored inlined
-	Inline(ObjectVersionMeta, #[serde(with = "serde_bytes")] Vec<u8>),
-	/// The object is not short, Hash of first block is stored here, next segments hashes are
-	/// stored in the version table
-	FirstBlock(ObjectVersionMeta, Hash),
-}
-
 impl AutoCrdt for ObjectVersionData {
 	const WARN_IF_DIFFERENT: bool = true;
 }
 
-/// Metadata about the object version
-#[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Debug, Serialize, Deserialize)]
-pub struct ObjectVersionMeta {
-	/// Headers to send to the client
-	pub headers: ObjectVersionHeaders,
-	/// Size of the object
-	pub size: u64,
-	/// etag of the object
-	pub etag: String,
-}
-
-/// Additional headers for an object
-#[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Debug, Serialize, Deserialize)]
-pub struct ObjectVersionHeaders {
-	/// Content type of the object
-	pub content_type: String,
-	/// Any other http headers to send
-	pub other: BTreeMap<String, String>,
-}
-
 impl ObjectVersion {
 	fn cmp_key(&self) -> (u64, Uuid) {
 		(self.timestamp, self.uuid)
@@ -290,11 +336,6 @@ impl TableSchema for ObjectTable {
 			ObjectFilter::IsUploading => entry.versions.iter().any(|v| v.is_uploading()),
 		}
 	}
-
-	fn try_migrate(bytes: &[u8]) -> Option<Self::E> {
-		let old_obj = rmp_serde::decode::from_read_ref::<_, old::Object>(bytes).ok()?;
-		Some(migrate_object(old_obj))
-	}
 }
 
 impl CountedItem for Object {
@@ -342,61 +383,3 @@ impl CountedItem for Object {
 
 // vvvvvvvv migration code, stupid stuff vvvvvvvvvvvv
 // (we just want to change bucket into bucket_id by hashing it)
-
-fn migrate_object(o: old::Object) -> Object {
-	let versions = o
-		.versions()
-		.iter()
-		.cloned()
-		.map(migrate_object_version)
-		.collect();
-	Object {
-		bucket_id: blake2sum(o.bucket.as_bytes()),
-		key: o.key,
-		versions,
-	}
-}
-
-fn migrate_object_version(v: old::ObjectVersion) -> ObjectVersion {
-	ObjectVersion {
-		uuid: Uuid::try_from(v.uuid.as_slice()).unwrap(),
-		timestamp: v.timestamp,
-		state: match v.state {
-			old::ObjectVersionState::Uploading(h) => {
-				ObjectVersionState::Uploading(migrate_object_version_headers(h))
-			}
-			old::ObjectVersionState::Complete(d) => {
-				ObjectVersionState::Complete(migrate_object_version_data(d))
-			}
-			old::ObjectVersionState::Aborted => ObjectVersionState::Aborted,
-		},
-	}
-}
-
-fn migrate_object_version_headers(h: old::ObjectVersionHeaders) -> ObjectVersionHeaders {
-	ObjectVersionHeaders {
-		content_type: h.content_type,
-		other: h.other,
-	}
-}
-
-fn migrate_object_version_data(d: old::ObjectVersionData) -> ObjectVersionData {
-	match d {
-		old::ObjectVersionData::DeleteMarker => ObjectVersionData::DeleteMarker,
-		old::ObjectVersionData::Inline(m, b) => {
-			ObjectVersionData::Inline(migrate_object_version_meta(m), b)
-		}
-		old::ObjectVersionData::FirstBlock(m, h) => ObjectVersionData::FirstBlock(
-			migrate_object_version_meta(m),
-			Hash::try_from(h.as_slice()).unwrap(),
-		),
-	}
-}
-
-fn migrate_object_version_meta(m: old::ObjectVersionMeta) -> ObjectVersionMeta {
-	ObjectVersionMeta {
-		headers: migrate_object_version_headers(m.headers),
-		size: m.size,
-		etag: m.etag,
-	}
-}

src/model/s3/version_table.rs

@@ -1,4 +1,3 @@
-use serde::{Deserialize, Serialize};
 use std::sync::Arc;
 
 use garage_db as db;
@@ -11,7 +10,61 @@ use garage_table::*;
 
 use crate::s3::block_ref_table::*;
 
-use crate::prev::v051::version_table as old;
+mod v05 {
+	use garage_util::crdt;
+	use garage_util::data::{Hash, Uuid};
+	use serde::{Deserialize, Serialize};
+
+	/// A version of an object
+	#[derive(PartialEq, Eq, Clone, Debug, Serialize, Deserialize)]
+	pub struct Version {
+		/// UUID of the version, used as partition key
+		pub uuid: Uuid,
+
+		// Actual data: the blocks for this version
+		// In the case of a multipart upload, also store the etags
+		// of individual parts and check them when doing CompleteMultipartUpload
+		/// Is this version deleted
+		pub deleted: crdt::Bool,
+		/// list of blocks of data composing the version
+		pub blocks: crdt::Map<VersionBlockKey, VersionBlock>,
+		/// Etag of each part in case of a multipart upload, empty otherwise
+		pub parts_etags: crdt::Map<u64, String>,
+
+		// Back link to bucket+key so that we can figure if
+		// this was deleted later on
+		/// Bucket in which the related object is stored
+		pub bucket: String,
+		/// Key in which the related object is stored
+		pub key: String,
+	}
+
+	#[derive(PartialEq, Eq, Clone, Copy, Debug, Serialize, Deserialize)]
+	pub struct VersionBlockKey {
+		/// Number of the part
+		pub part_number: u64,
+		/// Offset of this sub-segment in its part
+		pub offset: u64,
+	}
+
+	/// Informations about a single block
+	#[derive(PartialEq, Eq, Ord, PartialOrd, Clone, Copy, Debug, Serialize, Deserialize)]
+	pub struct VersionBlock {
+		/// Blake2 sum of the block
+		pub hash: Hash,
+		/// Size of the block
+		pub size: u64,
+	}
+
+	impl garage_util::migrate::InitialFormat for Version {}
+}
+
+mod v08 {
+	use garage_util::crdt;
+	use garage_util::data::Uuid;
+	use serde::{Deserialize, Serialize};
+
+	use super::v05;
 
 	/// A version of an object
 	#[derive(PartialEq, Eq, Clone, Debug, Serialize, Deserialize)]
@@ -37,6 +90,28 @@ pub struct Version {
 		pub key: String,
 	}
 
+	pub use v05::{VersionBlock, VersionBlockKey};
+
+	impl garage_util::migrate::Migrate for Version {
+		type Previous = v05::Version;
+
+		fn migrate(old: v05::Version) -> Version {
+			use garage_util::data::blake2sum;
+
+			Version {
+				uuid: old.uuid,
+				deleted: old.deleted,
+				blocks: old.blocks,
+				parts_etags: old.parts_etags,
+				bucket_id: blake2sum(old.bucket.as_bytes()),
+				key: old.key,
+			}
+		}
+	}
+}
+
+pub use v08::*;
+
 impl Version {
 	pub fn new(uuid: Uuid, bucket_id: Uuid, key: String, deleted: bool) -> Self {
 		Self {
@@ -64,14 +139,6 @@ impl Version {
 	}
 }
 
-#[derive(PartialEq, Eq, Clone, Copy, Debug, Serialize, Deserialize)]
-pub struct VersionBlockKey {
-	/// Number of the part
-	pub part_number: u64,
-	/// Offset of this sub-segment in its part
-	pub offset: u64,
-}
-
 impl Ord for VersionBlockKey {
 	fn cmp(&self, other: &Self) -> std::cmp::Ordering {
 		self.part_number
@@ -86,15 +153,6 @@ impl PartialOrd for VersionBlockKey {
 	}
 }
 
-/// Informations about a single block
-#[derive(PartialEq, Eq, Ord, PartialOrd, Clone, Copy, Debug, Serialize, Deserialize)]
-pub struct VersionBlock {
-	/// Blake2 sum of the block
-	pub hash: Hash,
-	/// Size of the block
-	pub size: u64,
-}
-
 impl AutoCrdt for VersionBlock {
 	const WARN_IF_DIFFERENT: bool = true;
 }
@@ -166,42 +224,4 @@ impl TableSchema for VersionTable {
 	fn matches_filter(entry: &Self::E, filter: &Self::Filter) -> bool {
 		filter.apply(entry.deleted.get())
 	}
-
-	fn try_migrate(bytes: &[u8]) -> Option<Self::E> {
-		let old = rmp_serde::decode::from_read_ref::<_, old::Version>(bytes).ok()?;
-
-		let blocks = old
-			.blocks
-			.items()
-			.iter()
-			.map(|(k, v)| {
-				(
-					VersionBlockKey {
-						part_number: k.part_number,
-						offset: k.offset,
-					},
-					VersionBlock {
-						hash: Hash::try_from(v.hash.as_slice()).unwrap(),
-						size: v.size,
-					},
-				)
-			})
-			.collect::<crdt::Map<_, _>>();
-
-		let parts_etags = old
-			.parts_etags
-			.items()
-			.iter()
-			.map(|(k, v)| (*k, v.clone()))
-			.collect::<crdt::Map<_, _>>();
-
-		Some(Version {
-			uuid: Hash::try_from(old.uuid.as_slice()).unwrap(),
-			deleted: crdt::Bool::new(old.deleted.get()),
-			blocks,
-			parts_etags,
-			bucket_id: blake2sum(old.bucket.as_bytes()),
-			key: old.key,
-		})
-	}
 }

src/rpc/layout.rs

@@ -35,6 +35,8 @@ pub struct ClusterLayout {
 	pub staging_hash: Hash,
 }
 
+impl garage_util::migrate::InitialFormat for ClusterLayout {}
+
 #[derive(PartialEq, Eq, PartialOrd, Ord, Clone, Debug, Serialize, Deserialize)]
 pub struct NodeRoleV(pub Option<NodeRole>);
 

src/rpc/system.rs

@@ -73,13 +73,17 @@ impl Rpc for SystemRpc {
 	type Response = Result<SystemRpc, Error>;
 }
 
+#[derive(Serialize, Deserialize)]
+pub struct PeerList(Vec<(Uuid, SocketAddr)>);
+impl garage_util::migrate::InitialFormat for PeerList {}
+
 /// This node's membership manager
 pub struct System {
 	/// The id of this node
 	pub id: Uuid,
 
 	persist_cluster_layout: Persister<ClusterLayout>,
-	persist_peer_list: Persister<Vec<(Uuid, SocketAddr)>>,
+	persist_peer_list: Persister<PeerList>,
 
 	local_status: ArcSwap<NodeStatus>,
 	node_status: RwLock<HashMap<Uuid, (u64, NodeStatus)>>,
@@ -721,7 +725,7 @@ impl System {
 
 				// Add peer list from list stored on disk
 				if let Ok(peers) = self.persist_peer_list.load_async().await {
-					ping_list.extend(peers.iter().map(|(id, addr)| ((*id).into(), *addr)))
+					ping_list.extend(peers.0.iter().map(|(id, addr)| ((*id).into(), *addr)))
 				}
 
 				// Fetch peer list from Consul
@@ -801,12 +805,16 @@ impl System {
 		// and append it to the list we are about to save,
 		// so that no peer ID gets lost in the process.
 		if let Ok(mut prev_peer_list) = self.persist_peer_list.load_async().await {
-			prev_peer_list.retain(|(id, _ip)| peer_list.iter().all(|(id2, _ip2)| id2 != id));
+			prev_peer_list
-			peer_list.extend(prev_peer_list);
+				.0
+				.retain(|(id, _ip)| peer_list.iter().all(|(id2, _ip2)| id2 != id));
+			peer_list.extend(prev_peer_list.0);
 		}
 
 		// Save new peer list to file
-		self.persist_peer_list.save_async(&peer_list).await
+		self.persist_peer_list
+			.save_async(&PeerList(peer_list))
+			.await
 	}
 
 	async fn pull_cluster_layout(self: Arc<Self>, peer: Uuid) {

src/table/data.rs

@@ -10,6 +10,7 @@ use garage_db::counted_tree_hack::CountedTree;
 
 use garage_util::data::*;
 use garage_util::error::*;
+use garage_util::migrate::Migrate;
 
 use garage_rpc::system::System;
 
@@ -219,7 +220,8 @@ where
 			//   data format, the messagepack encoding changed. In this case,
 			//   we also have to write the migrated value in the table and update
 			//   the associated Merkle tree entry.
-			let new_bytes = rmp_to_vec_all_named(&new_entry)
+			let new_bytes = new_entry
+				.encode()
 				.map_err(Error::RmpEncode)
 				.map_err(db::TxError::Abort)?;
 			let changed = Some(&new_bytes[..]) != old_bytes.as_deref();
@@ -329,9 +331,9 @@ where
 			Some(old_v) => {
 				let mut entry = self.decode_entry(&old_v).map_err(db::TxError::Abort)?;
 				entry.merge(ins);
-				rmp_to_vec_all_named(&entry)
+				entry.encode()
 			}
-			None => rmp_to_vec_all_named(ins),
+			None => ins.encode(),
 		};
 		let new_entry = new_entry
 			.map_err(Error::RmpEncode)
@@ -351,18 +353,18 @@ where
 	}
 
 	pub fn decode_entry(&self, bytes: &[u8]) -> Result<F::E, Error> {
-		match rmp_serde::decode::from_read_ref::<_, F::E>(bytes) {
+		match F::E::decode(bytes) {
-			Ok(x) => Ok(x),
-			Err(e) => match F::try_migrate(bytes) {
 			Some(x) => Ok(x),
 			None => {
-					warn!("Unable to decode entry of {}: {}", F::TABLE_NAME, e);
+				error!("Unable to decode entry of {}", F::TABLE_NAME);
 				for line in hexdump::hexdump_iter(bytes) {
 					debug!("{}", line);
 				}
-					Err(e.into())
+				Err(Error::Message(format!(
+					"Unable to decode entry of {}",
+					F::TABLE_NAME
+				)))
 			}
-			},
 		}
 	}
 

src/table/schema.rs

@@ -2,6 +2,7 @@ use serde::{Deserialize, Serialize};
 
 use garage_db as db;
 use garage_util::data::*;
+use garage_util::migrate::Migrate;
 
 use crate::crdt::Crdt;
 
@@ -46,7 +47,7 @@ impl SortKey for FixedBytes32 {
 
 /// Trait for an entry in a table. It must be sortable and partitionnable.
 pub trait Entry<P: PartitionKey, S: SortKey>:
-	Crdt + PartialEq + Clone + Serialize + for<'de> Deserialize<'de> + Send + Sync
+	Crdt + PartialEq + Clone + Migrate + Send + Sync + 'static
 {
 	/// Get the key used to partition
 	fn partition_key(&self) -> &P;
@@ -65,23 +66,23 @@ pub trait TableSchema: Send + Sync + 'static {
 	const TABLE_NAME: &'static str;
 
 	/// The partition key used in that table
-	type P: PartitionKey + Clone + PartialEq + Serialize + for<'de> Deserialize<'de> + Send + Sync;
+	type P: PartitionKey
+		+ Clone
+		+ PartialEq
+		+ Serialize
+		+ for<'de> Deserialize<'de>
+		+ Send
+		+ Sync
+		+ 'static;
 	/// The sort key used int that table
-	type S: SortKey + Clone + Serialize + for<'de> Deserialize<'de> + Send + Sync;
+	type S: SortKey + Clone + Serialize + for<'de> Deserialize<'de> + Send + Sync + 'static;
 
 	/// They type for an entry in that table
 	type E: Entry<Self::P, Self::S>;
 
 	/// The type for a filter that can be applied to select entries
 	/// (e.g. filter out deleted entries)
-	type Filter: Clone + Serialize + for<'de> Deserialize<'de> + Send + Sync;
+	type Filter: Clone + Serialize + for<'de> Deserialize<'de> + Send + Sync + 'static;
-
-	// Action to take if not able to decode current version:
-	// try loading from an older version
-	/// Try migrating an entry from an older version
-	fn try_migrate(_bytes: &[u8]) -> Option<Self::E> {
-		None
-	}
 
 	/// Actions triggered by data changing in a table. If such actions
 	/// include updates to the local database that should be applied

src/table/sync.rs

@@ -302,7 +302,7 @@ where
 			);
 			return Ok(());
 		}
-		let root_ck_hash = hash_of::<MerkleNode>(&root_ck)?;
+		let root_ck_hash = hash_of_merkle_node(&root_ck)?;
 
 		// Check if they have the same root checksum
 		// If so, do nothing.
@@ -468,7 +468,7 @@ where
 		match message {
 			SyncRpc::RootCkHash(range, h) => {
 				let (_root_ck_key, root_ck) = self.get_root_ck(*range)?;
-				let hash = hash_of::<MerkleNode>(&root_ck)?;
+				let hash = hash_of_merkle_node(&root_ck)?;
 				Ok(SyncRpc::RootCkDifferent(hash != *h))
 			}
 			SyncRpc::GetNode(k) => {
@@ -622,7 +622,7 @@ impl<F: TableSchema + 'static, R: TableReplication + 'static> Worker for SyncWor
 
 // ---- UTIL ----
 
-fn hash_of<T: Serialize>(x: &T) -> Result<Hash, Error> {
+fn hash_of_merkle_node(x: &MerkleNode) -> Result<Hash, Error> {
 	Ok(blake2sum(&rmp_to_vec_all_named(x)?[..]))
 }
 

src/table/table.rs

@@ -18,6 +18,7 @@ use garage_util::background::BackgroundRunner;
 use garage_util::data::*;
 use garage_util::error::Error;
 use garage_util::metrics::RecordDuration;
+use garage_util::migrate::Migrate;
 
 use garage_rpc::system::System;
 use garage_rpc::*;
@@ -122,7 +123,7 @@ where
 		let hash = e.partition_key().hash();
 		let who = self.data.replication.write_nodes(&hash);
 
-		let e_enc = Arc::new(ByteBuf::from(rmp_to_vec_all_named(e)?));
+		let e_enc = Arc::new(ByteBuf::from(e.encode()?));
 		let rpc = TableRpc::<F>::Update(vec![e_enc]);
 
 		self.system
@@ -173,7 +174,7 @@ where
 			let entry = entry.borrow();
 			let hash = entry.partition_key().hash();
 			let who = self.data.replication.write_nodes(&hash);
-			let e_enc = Arc::new(ByteBuf::from(rmp_to_vec_all_named(entry)?));
+			let e_enc = Arc::new(ByteBuf::from(entry.encode()?));
 			for node in who {
 				call_list.entry(node).or_default().push(e_enc.clone());
 			}
@@ -412,7 +413,7 @@ where
 	// =============== UTILITY FUNCTION FOR CLIENT OPERATIONS ===============
 
 	async fn repair_on_read(&self, who: &[Uuid], what: F::E) -> Result<(), Error> {
-		let what_enc = Arc::new(ByteBuf::from(rmp_to_vec_all_named(&what)?));
+		let what_enc = Arc::new(ByteBuf::from(what.encode()?));
 		self.system
 			.rpc
 			.try_call_many(

src/util/Cargo.toml

@@ -23,6 +23,7 @@ bytes = "1.0"
 digest = "0.10"
 err-derive = "0.3"
 git-version = "0.3.4"
+hexdump = "0.1"
 xxhash-rust = { version = "0.8", default-features = false, features = ["xxh3"] }
 hex = "0.4"
 lazy_static = "1.4"

src/util/lib.rs

@@ -11,6 +11,7 @@ pub mod data;
 pub mod error;
 pub mod formater;
 pub mod metrics;
+pub mod migrate;
 pub mod persister;
 pub mod time;
 pub mod token_bucket;

src/util/migrate.rs

@@ -0,0 +1,75 @@
+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!()
+	}
+}

src/util/persister.rs

@@ -3,21 +3,16 @@ use std::path::{Path, PathBuf};
 
 use tokio::io::{AsyncReadExt, AsyncWriteExt};
 
-use serde::{Deserialize, Serialize};
-
-use crate::data::*;
 use crate::error::Error;
+use crate::migrate::Migrate;
 
-pub struct Persister<T: Serialize + for<'de> Deserialize<'de>> {
+pub struct Persister<T: Migrate> {
 	path: PathBuf,
 
 	_marker: std::marker::PhantomData<T>,
 }
 
-impl<T> Persister<T>
+impl<T: Migrate> Persister<T> {
-where
-	T: Serialize + for<'de> Deserialize<'de>,
-{
 	pub fn new(base_dir: &Path, file_name: &str) -> Self {
 		let mut path = base_dir.to_path_buf();
 		path.push(file_name);
@@ -27,18 +22,37 @@ where
 		}
 	}
 
+	fn decode(&self, bytes: &[u8]) -> Result<T, Error> {
+		match T::decode(bytes) {
+			Some(v) => Ok(v),
+			None => {
+				error!(
+					"Unable to decode persisted data file {}",
+					self.path.display()
+				);
+				for line in hexdump::hexdump_iter(bytes) {
+					debug!("{}", line);
+				}
+				Err(Error::Message(format!(
+					"Unable to decode persisted data file {}",
+					self.path.display()
+				)))
+			}
+		}
+	}
+
 	pub fn load(&self) -> Result<T, Error> {
 		let mut file = std::fs::OpenOptions::new().read(true).open(&self.path)?;
 
 		let mut bytes = vec![];
 		file.read_to_end(&mut bytes)?;
 
-		let value = rmp_serde::decode::from_read_ref(&bytes[..])?;
+		let value = self.decode(&bytes[..])?;
 		Ok(value)
 	}
 
 	pub fn save(&self, t: &T) -> Result<(), Error> {
-		let bytes = rmp_to_vec_all_named(t)?;
+		let bytes = t.encode()?;
 
 		let mut file = std::fs::OpenOptions::new()
 			.write(true)
@@ -57,12 +71,12 @@ where
 		let mut bytes = vec![];
 		file.read_to_end(&mut bytes).await?;
 
-		let value = rmp_serde::decode::from_read_ref(&bytes[..])?;
+		let value = self.decode(&bytes[..])?;
 		Ok(value)
 	}
 
 	pub async fn save_async(&self, t: &T) -> Result<(), Error> {
-		let bytes = rmp_to_vec_all_named(t)?;
+		let bytes = t.encode()?;
 
 		let mut file = tokio::fs::File::create(&self.path).await?;
 		file.write_all(&bytes[..]).await?;