Add support for model migrations

8 files changed, 220 insertions, 91 deletions

diff --git a/Cargo.lock b/Cargo.lock
index 4f82dbea..53ae6fbc 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -340,15 +340,15 @@ dependencies = [
 
 [[package]]
 name = "garage"
-version = "0.1.0"
+version = "0.1.1"
 dependencies = [
  "bytes 0.4.12 (registry+https://github.com/rust-lang/crates.io-index)",
  "futures 0.3.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "futures-util 0.3.5 (registry+https://github.com/rust-lang/crates.io-index)",
- "garage_api 0.1.0",
- "garage_model 0.1.0",
+ "garage_api 0.1.1",
+ "garage_model 0.1.1",
  "garage_rpc 0.1.0",
- "garage_table 0.1.0",
+ "garage_table 0.1.1",
  "garage_util 0.1.0",
  "hex 0.3.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.4.8 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -365,15 +365,15 @@ dependencies = [
 
 [[package]]
 name = "garage_api"
-version = "0.1.0"
+version = "0.1.1"
 dependencies = [
  "bytes 0.4.12 (registry+https://github.com/rust-lang/crates.io-index)",
  "chrono 0.4.13 (registry+https://github.com/rust-lang/crates.io-index)",
  "crypto-mac 0.7.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "futures 0.3.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "futures-util 0.3.5 (registry+https://github.com/rust-lang/crates.io-index)",
- "garage_model 0.1.0",
- "garage_table 0.1.0",
+ "garage_model 0.1.1",
+ "garage_table 0.1.1",
  "garage_util 0.1.0",
  "hex 0.3.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "hmac 0.7.1 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -392,14 +392,39 @@ dependencies = [
 [[package]]
 name = "garage_model"
 version = "0.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "arc-swap 0.4.7 (registry+https://github.com/rust-lang/crates.io-index)",
+ "async-trait 0.1.36 (registry+https://github.com/rust-lang/crates.io-index)",
+ "bytes 0.4.12 (registry+https://github.com/rust-lang/crates.io-index)",
+ "futures 0.3.5 (registry+https://github.com/rust-lang/crates.io-index)",
+ "futures-util 0.3.5 (registry+https://github.com/rust-lang/crates.io-index)",
+ "garage_rpc 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "garage_table 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "garage_util 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "hex 0.3.2 (registry+https://github.com/rust-lang/crates.io-index)",
+ "log 0.4.8 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rand 0.7.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rmp-serde 0.14.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.114 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde_bytes 0.11.5 (registry+https://github.com/rust-lang/crates.io-index)",
+ "sha2 0.8.2 (registry+https://github.com/rust-lang/crates.io-index)",
+ "sled 0.31.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "tokio 0.2.21 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "garage_model"
+version = "0.1.1"
 dependencies = [
  "arc-swap 0.4.7 (registry+https://github.com/rust-lang/crates.io-index)",
  "async-trait 0.1.36 (registry+https://github.com/rust-lang/crates.io-index)",
  "bytes 0.4.12 (registry+https://github.com/rust-lang/crates.io-index)",
  "futures 0.3.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "futures-util 0.3.5 (registry+https://github.com/rust-lang/crates.io-index)",
+ "garage_model 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "garage_rpc 0.1.0",
- "garage_table 0.1.0",
+ "garage_table 0.1.1",
  "garage_util 0.1.0",
  "hex 0.3.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.4.8 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -439,8 +464,57 @@ dependencies = [
 ]
 
 [[package]]
+name = "garage_rpc"
+version = "0.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "arc-swap 0.4.7 (registry+https://github.com/rust-lang/crates.io-index)",
+ "bytes 0.4.12 (registry+https://github.com/rust-lang/crates.io-index)",
+ "futures 0.3.5 (registry+https://github.com/rust-lang/crates.io-index)",
+ "futures-util 0.3.5 (registry+https://github.com/rust-lang/crates.io-index)",
+ "garage_util 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "gethostname 0.2.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "hex 0.3.2 (registry+https://github.com/rust-lang/crates.io-index)",
+ "http 0.2.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "hyper 0.13.6 (registry+https://github.com/rust-lang/crates.io-index)",
+ "hyper-rustls 0.20.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "log 0.4.8 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rand 0.7.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rmp-serde 0.14.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rustls 0.17.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.114 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde_json 1.0.56 (registry+https://github.com/rust-lang/crates.io-index)",
+ "sha2 0.8.2 (registry+https://github.com/rust-lang/crates.io-index)",
+ "tokio 0.2.21 (registry+https://github.com/rust-lang/crates.io-index)",
+ "tokio-rustls 0.13.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "webpki 0.21.3 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
 name = "garage_table"
 version = "0.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "arc-swap 0.4.7 (registry+https://github.com/rust-lang/crates.io-index)",
+ "async-trait 0.1.36 (registry+https://github.com/rust-lang/crates.io-index)",
+ "bytes 0.4.12 (registry+https://github.com/rust-lang/crates.io-index)",
+ "futures 0.3.5 (registry+https://github.com/rust-lang/crates.io-index)",
+ "futures-util 0.3.5 (registry+https://github.com/rust-lang/crates.io-index)",
+ "garage_rpc 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "garage_util 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "hex 0.3.2 (registry+https://github.com/rust-lang/crates.io-index)",
+ "log 0.4.8 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rand 0.7.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rmp-serde 0.14.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.114 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde_bytes 0.11.5 (registry+https://github.com/rust-lang/crates.io-index)",
+ "sled 0.31.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "tokio 0.2.21 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
+name = "garage_table"
+version = "0.1.1"
 dependencies = [
  "arc-swap 0.4.7 (registry+https://github.com/rust-lang/crates.io-index)",
  "async-trait 0.1.36 (registry+https://github.com/rust-lang/crates.io-index)",
@@ -484,6 +558,31 @@ dependencies = [
 ]
 
 [[package]]
+name = "garage_util"
+version = "0.1.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+dependencies = [
+ "err-derive 0.2.4 (registry+https://github.com/rust-lang/crates.io-index)",
+ "futures 0.3.5 (registry+https://github.com/rust-lang/crates.io-index)",
+ "futures-util 0.3.5 (registry+https://github.com/rust-lang/crates.io-index)",
+ "hex 0.3.2 (registry+https://github.com/rust-lang/crates.io-index)",
+ "http 0.2.1 (registry+https://github.com/rust-lang/crates.io-index)",
+ "hyper 0.13.6 (registry+https://github.com/rust-lang/crates.io-index)",
+ "log 0.4.8 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rand 0.7.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rmp-serde 0.14.3 (registry+https://github.com/rust-lang/crates.io-index)",
+ "roxmltree 0.11.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "rustls 0.17.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde 1.0.114 (registry+https://github.com/rust-lang/crates.io-index)",
+ "serde_json 1.0.56 (registry+https://github.com/rust-lang/crates.io-index)",
+ "sha2 0.8.2 (registry+https://github.com/rust-lang/crates.io-index)",
+ "sled 0.31.0 (registry+https://github.com/rust-lang/crates.io-index)",
+ "tokio 0.2.21 (registry+https://github.com/rust-lang/crates.io-index)",
+ "toml 0.5.6 (registry+https://github.com/rust-lang/crates.io-index)",
+ "webpki 0.21.3 (registry+https://github.com/rust-lang/crates.io-index)",
+]
+
+[[package]]
 name = "generator"
 version = "0.6.21"
 source = "registry+https://github.com/rust-lang/crates.io-index"
@@ -1629,6 +1728,10 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 "checksum futures-task 0.3.5 (registry+https://github.com/rust-lang/crates.io-index)" = "bdb66b5f09e22019b1ab0830f7785bcea8e7a42148683f99214f73f8ec21a626"
 "checksum futures-util 0.3.5 (registry+https://github.com/rust-lang/crates.io-index)" = "8764574ff08b701a084482c3c7031349104b07ac897393010494beaa18ce32c6"
 "checksum fxhash 0.2.1 (registry+https://github.com/rust-lang/crates.io-index)" = "c31b6d751ae2c7f11320402d34e41349dd1016f8d5d45e48c4312bc8625af50c"
+"checksum garage_model 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "b6403312b28077fd585e5f96184d2d56142f10eb42709d2893294d70a892d73f"
+"checksum garage_rpc 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "0ef794407808c89f300f73457bdc567c953b323d7fe30534aba686a28ebb4a0d"
+"checksum garage_table 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "567d7e9f791a1d65d26e36840aa0570b3a2144302c32f62b5e63a39f147cbf57"
+"checksum garage_util 0.1.0 (registry+https://github.com/rust-lang/crates.io-index)" = "77de76a4167c041094f3f3415c6d3d773373e0326668fbce70dfd3b024788800"
 "checksum generator 0.6.21 (registry+https://github.com/rust-lang/crates.io-index)" = "add72f17bb81521258fcc8a7a3245b1e184e916bfbe34f0ea89558f440df5c68"
 "checksum generic-array 0.12.3 (registry+https://github.com/rust-lang/crates.io-index)" = "c68f0274ae0e023facc3c97b2e00f076be70e254bc851d972503b328db79b2ec"
 "checksum gethostname 0.2.1 (registry+https://github.com/rust-lang/crates.io-index)" = "e692e296bfac1d2533ef168d0b60ff5897b8b70a4009276834014dd8924cc028"
diff --git a/src/api/Cargo.toml b/src/api/Cargo.toml
index f9cd32b2..c8c5bf22 100644
--- a/src/api/Cargo.toml
+++ b/src/api/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "garage_api"
-version = "0.1.0"
+version = "0.1.1"
 authors = ["Alex Auvolat <alex@adnab.me>"]
 edition = "2018"
 license = "GPL-3.0"
@@ -14,8 +14,8 @@ path = "lib.rs"
 
 [dependencies]
 garage_util = { version = "0.1", path = "../util" }
-garage_table = { version = "0.1", path = "../table" }
-garage_model = { version = "0.1", path = "../model" }
+garage_table = { version = "0.1.1", path = "../table" }
+garage_model = { version = "0.1.1", path = "../model" }
 
 bytes = "0.4"
 hex = "0.3"
diff --git a/src/garage/Cargo.toml b/src/garage/Cargo.toml
index 8e64cf34..cb16bcd4 100644
--- a/src/garage/Cargo.toml
+++ b/src/garage/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "garage"
-version = "0.1.0"
+version = "0.1.1"
 authors = ["Alex Auvolat <alex@adnab.me>"]
 edition = "2018"
 license = "GPL-3.0"
@@ -16,9 +16,9 @@ path = "main.rs"
 [dependencies]
 garage_util = { version = "0.1", path = "../util" }
 garage_rpc = { version = "0.1", path = "../rpc" }
-garage_table = { version = "0.1", path = "../table" }
-garage_model = { version = "0.1", path = "../model" }
-garage_api = { version = "0.1", path = "../api" }
+garage_table = { version = "0.1.1", path = "../table" }
+garage_model = { version = "0.1.1", path = "../model" }
+garage_api = { version = "0.1.1", path = "../api" }
 
 bytes = "0.4"
 rand = "0.7"
diff --git a/src/model/Cargo.toml b/src/model/Cargo.toml
index 76d759fd..a138691d 100644
--- a/src/model/Cargo.toml
+++ b/src/model/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "garage_model"
-version = "0.1.0"
+version = "0.1.1"
 authors = ["Alex Auvolat <alex@adnab.me>"]
 edition = "2018"
 license = "GPL-3.0"
@@ -15,7 +15,8 @@ path = "lib.rs"
 [dependencies]
 garage_util = { version = "0.1", path = "../util" }
 garage_rpc = { version = "0.1", path = "../rpc" }
-garage_table = { version = "0.1", path = "../table" }
+garage_table = { version = "0.1.1", path = "../table" }
+model010 = { package = "garage_model", version = "0.1.0" }
 
 bytes = "0.4"
 rand = "0.7"
diff --git a/src/table/Cargo.toml b/src/table/Cargo.toml
index 7efdbb08..1963f3da 100644
--- a/src/table/Cargo.toml
+++ b/src/table/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "garage_table"
-version = "0.1.0"
+version = "0.1.1"
 authors = ["Alex Auvolat <alex@adnab.me>"]
 edition = "2018"
 license = "GPL-3.0"
diff --git a/src/table/lib.rs b/src/table/lib.rs
index f490b491..e30a6665 100644
--- a/src/table/lib.rs
+++ b/src/table/lib.rs
@@ -3,9 +3,11 @@
 #[macro_use]
 extern crate log;
 
+pub mod schema;
 pub mod table;
 pub mod table_fullcopy;
 pub mod table_sharded;
 pub mod table_sync;
 
 pub use table::*;
+pub use schema::*;
diff --git a/src/table/schema.rs b/src/table/schema.rs
new file mode 100644
index 00000000..cedaacac
--- /dev/null
+++ b/src/table/schema.rs
@@ -0,0 +1,77 @@
+use async_trait::async_trait;
+use serde::{Deserialize, Serialize};
+
+use garage_util::data::*;
+use garage_util::error::Error;
+
+
+pub trait PartitionKey {
+	fn hash(&self) -> Hash;
+}
+
+pub trait SortKey {
+	fn sort_key(&self) -> &[u8];
+}
+
+pub trait Entry<P: PartitionKey, S: SortKey>:
+	PartialEq + Clone + Serialize + for<'de> Deserialize<'de> + Send + Sync
+{
+	fn partition_key(&self) -> &P;
+	fn sort_key(&self) -> &S;
+
+	fn merge(&mut self, other: &Self);
+}
+
+#[derive(Clone, PartialEq, Eq, Serialize, Deserialize)]
+pub struct EmptyKey;
+impl SortKey for EmptyKey {
+	fn sort_key(&self) -> &[u8] {
+		&[]
+	}
+}
+impl PartitionKey for EmptyKey {
+	fn hash(&self) -> Hash {
+		[0u8; 32].into()
+	}
+}
+
+impl PartitionKey for String {
+	fn hash(&self) -> Hash {
+		hash(self.as_bytes())
+	}
+}
+impl SortKey for String {
+	fn sort_key(&self) -> &[u8] {
+		self.as_bytes()
+	}
+}
+
+impl PartitionKey for Hash {
+	fn hash(&self) -> Hash {
+		self.clone()
+	}
+}
+impl SortKey for Hash {
+	fn sort_key(&self) -> &[u8] {
+		self.as_slice()
+	}
+}
+
+#[async_trait]
+pub trait TableSchema: Send + Sync {
+	type P: PartitionKey + Clone + PartialEq + Serialize + for<'de> Deserialize<'de> + Send + Sync;
+	type S: SortKey + Clone + Serialize + for<'de> Deserialize<'de> + Send + Sync;
+	type E: Entry<Self::P, Self::S>;
+	type Filter: Clone + Serialize + for<'de> Deserialize<'de> + Send + Sync;
+
+    // Action to take if not able to decode current version:
+    // try loading from an older version
+    fn try_migrate(_bytes: &[u8]) -> Option<Self::E> {
+        None
+    }
+
+	async fn updated(&self, old: Option<Self::E>, new: Option<Self::E>) -> Result<(), Error>;
+	fn matches_filter(_entry: &Self::E, _filter: &Self::Filter) -> bool {
+		true
+	}
+}
diff --git a/src/table/table.rs b/src/table/table.rs
index 94bacc60..7a5caf4f 100644
--- a/src/table/table.rs
+++ b/src/table/table.rs
@@ -3,7 +3,6 @@ use std::sync::Arc;
 use std::time::Duration;
 
 use arc_swap::ArcSwapOption;
-use async_trait::async_trait;
 use futures::stream::*;
 use serde::{Deserialize, Serialize};
 use serde_bytes::ByteBuf;
@@ -16,6 +15,7 @@ use garage_rpc::rpc_client::*;
 use garage_rpc::rpc_server::*;
 
 use crate::table_sync::*;
+use crate::schema::*;
 
 const TABLE_RPC_TIMEOUT: Duration = Duration::from_secs(10);
 
@@ -48,70 +48,6 @@ pub enum TableRPC<F: TableSchema> {
 
 impl<F: TableSchema> RpcMessage for TableRPC<F> {}
 
-pub trait PartitionKey {
-	fn hash(&self) -> Hash;
-}
-
-pub trait SortKey {
-	fn sort_key(&self) -> &[u8];
-}
-
-pub trait Entry<P: PartitionKey, S: SortKey>:
-	PartialEq + Clone + Serialize + for<'de> Deserialize<'de> + Send + Sync
-{
-	fn partition_key(&self) -> &P;
-	fn sort_key(&self) -> &S;
-
-	fn merge(&mut self, other: &Self);
-}
-
-#[derive(Clone, PartialEq, Eq, Serialize, Deserialize)]
-pub struct EmptyKey;
-impl SortKey for EmptyKey {
-	fn sort_key(&self) -> &[u8] {
-		&[]
-	}
-}
-impl PartitionKey for EmptyKey {
-	fn hash(&self) -> Hash {
-		[0u8; 32].into()
-	}
-}
-
-impl PartitionKey for String {
-	fn hash(&self) -> Hash {
-		hash(self.as_bytes())
-	}
-}
-impl SortKey for String {
-	fn sort_key(&self) -> &[u8] {
-		self.as_bytes()
-	}
-}
-
-impl PartitionKey for Hash {
-	fn hash(&self) -> Hash {
-		self.clone()
-	}
-}
-impl SortKey for Hash {
-	fn sort_key(&self) -> &[u8] {
-		self.as_slice()
-	}
-}
-
-#[async_trait]
-pub trait TableSchema: Send + Sync {
-	type P: PartitionKey + Clone + PartialEq + Serialize + for<'de> Deserialize<'de> + Send + Sync;
-	type S: SortKey + Clone + Serialize + for<'de> Deserialize<'de> + Send + Sync;
-	type E: Entry<Self::P, Self::S>;
-	type Filter: Clone + Serialize + for<'de> Deserialize<'de> + Send + Sync;
-
-	async fn updated(&self, old: Option<Self::E>, new: Option<Self::E>) -> Result<(), Error>;
-	fn matches_filter(_entry: &Self::E, _filter: &Self::Filter) -> bool {
-		true
-	}
-}
 
 pub trait TableReplication: Send + Sync {
 	// See examples in table_sharded.rs and table_fullcopy.rs
@@ -250,7 +186,7 @@ where
 		for resp in resps {
 			if let TableRPC::ReadEntryResponse(value) = resp {
 				if let Some(v_bytes) = value {
-					let v = rmp_serde::decode::from_read_ref::<_, F::E>(v_bytes.as_slice())?;
+					let v = Self::decode_entry(v_bytes.as_slice())?;
 					ret = match ret {
 						None => Some(v),
 						Some(mut x) => {
@@ -306,8 +242,7 @@ where
 		for resp in resps {
 			if let TableRPC::Update(entries) = resp {
 				for entry_bytes in entries.iter() {
-					let entry =
-						rmp_serde::decode::from_read_ref::<_, F::E>(entry_bytes.as_slice())?;
+					let entry = Self::decode_entry(entry_bytes.as_slice())?;
 					let entry_key = self.tree_key(entry.partition_key(), entry.sort_key());
 					match ret.remove(&entry_key) {
 						None => {
@@ -429,7 +364,7 @@ where
 			let keep = match filter {
 				None => true,
 				Some(f) => {
-					let entry = rmp_serde::decode::from_read_ref::<_, F::E>(value.as_ref())?;
+					let entry = Self::decode_entry(value.as_ref())?;
 					F::matches_filter(&entry, f)
 				}
 			};
@@ -448,15 +383,14 @@ where
 		let mut epidemic_propagate = vec![];
 
 		for update_bytes in entries.iter() {
-			let update = rmp_serde::decode::from_read_ref::<_, F::E>(update_bytes.as_slice())?;
+			let update = Self::decode_entry(update_bytes.as_slice())?;
 
 			let tree_key = self.tree_key(update.partition_key(), update.sort_key());
 
 			let (old_entry, new_entry) = self.store.transaction(|db| {
 				let (old_entry, new_entry) = match db.get(&tree_key)? {
 					Some(prev_bytes) => {
-						let old_entry = rmp_serde::decode::from_read_ref::<_, F::E>(&prev_bytes)
-							.map_err(Error::RMPDecode)
+						let old_entry = Self::decode_entry(&prev_bytes)
 							.map_err(sled::ConflictableTransactionError::Abort)?;
 						let mut new_entry = old_entry.clone();
 						new_entry.merge(&update);
@@ -504,7 +438,7 @@ where
 				break;
 			}
 			if let Some(old_val) = self.store.remove(&key)? {
-				let old_entry = rmp_serde::decode::from_read_ref::<_, F::E>(&old_val)?;
+				let old_entry = Self::decode_entry(&old_val)?;
 				self.instance.updated(Some(old_entry), None).await?;
 				self.system
 					.background
@@ -521,4 +455,16 @@ where
 		ret.extend(s.sort_key());
 		ret
 	}
+
+    fn decode_entry(bytes: &[u8]) -> Result<F::E, Error> {
+         match rmp_serde::decode::from_read_ref::<_, F::E>(bytes) {
+             Ok(x) => Ok(x),
+             Err(e) => {
+                 match F::try_migrate(bytes) {
+                     Some(x) => Ok(x),
+                     None => Err(e.into()),
+                 }   
+             }
+         }
+    }
 }