Introduce a recovery strategy as a replacement for set_discard_if_cor…

…rupted

The user can now choose between discarding corrupted data, moving it out
of the way (into another file) and starting with an empty database or
bubbling up the error.

Fixes #234

src/backend/common.rs

@@ -42,3 +42,16 @@ pub enum WriteFlags {
     APPEND,
     APPEND_DUP,
 }
+
+/// Strategy to use when corrupted data is detected while opening a database.
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum RecoveryStrategy {
+    /// Bubble up the error on detecting a corrupted data file. The default.
+    Error,
+
+    /// Discard the corrupted data and start with an empty database.
+    Discard,
+
+    /// Move the corrupted data file to `$file.corrupt` and start with an empty database.
+    Rename,
+}

src/backend/impl_lmdb/environment.rs

@@ -19,6 +19,7 @@ use super::{
     DatabaseFlagsImpl, DatabaseImpl, EnvironmentFlagsImpl, ErrorImpl, InfoImpl, RoTransactionImpl,
     RwTransactionImpl, StatImpl,
 };
+use crate::backend::common::RecoveryStrategy;
 use crate::backend::traits::{
     BackendEnvironment, BackendEnvironmentBuilder, BackendInfo, BackendIter, BackendRoCursor,
     BackendRoCursorTransaction, BackendStat,
@@ -86,7 +87,8 @@ impl<'b> BackendEnvironmentBuilder<'b> for EnvironmentBuilderImpl {
         self
     }
 
-    fn set_discard_if_corrupted(&mut self, _discard_if_corrupted: bool) -> &mut Self {
+    /// **UNIMPLEMENTED.** Will panic at runtime.
+    fn set_corruption_recovery_strategy(&mut self, _strategy: RecoveryStrategy) -> &mut Self {
         // Unfortunately, when opening a database, LMDB doesn't handle all the ways it could have
         // been corrupted. Prefer using the `SafeMode` backend if this is important.
         unimplemented!();

src/backend/impl_safe/environment.rs

@@ -24,9 +24,11 @@ use super::{
     database::Database, DatabaseFlagsImpl, DatabaseImpl, EnvironmentFlagsImpl, ErrorImpl, InfoImpl,
     RoTransactionImpl, RwTransactionImpl, StatImpl,
 };
+use crate::backend::common::RecoveryStrategy;
 use crate::backend::traits::{BackendEnvironment, BackendEnvironmentBuilder};
 
 const DEFAULT_DB_FILENAME: &str = "data.safe.bin";
+const DEFAULT_CORRUPT_DB_EXTENSION: &str = "bin.corrupt";
 
 type DatabaseArena = Arena<Database>;
 type DatabaseNameMap = HashMap<Option<String>, DatabaseImpl>;
@@ -38,7 +40,7 @@ pub struct EnvironmentBuilderImpl {
     max_dbs: Option<usize>,
     map_size: Option<usize>,
     make_dir_if_needed: bool,
-    discard_if_corrupted: bool,
+    corruption_recovery_strategy: RecoveryStrategy,
 }
 
 impl<'b> BackendEnvironmentBuilder<'b> for EnvironmentBuilderImpl {
@@ -53,7 +55,7 @@ impl<'b> BackendEnvironmentBuilder<'b> for EnvironmentBuilderImpl {
             max_dbs: None,
             map_size: None,
             make_dir_if_needed: false,
-            discard_if_corrupted: false,
+            corruption_recovery_strategy: RecoveryStrategy::Error,
         }
     }
 
@@ -85,8 +87,8 @@ impl<'b> BackendEnvironmentBuilder<'b> for EnvironmentBuilderImpl {
         self
     }
 
-    fn set_discard_if_corrupted(&mut self, discard_if_corrupted: bool) -> &mut Self {
-        self.discard_if_corrupted = discard_if_corrupted;
+    fn set_corruption_recovery_strategy(&mut self, strategy: RecoveryStrategy) -> &mut Self {
+        self.corruption_recovery_strategy = strategy;
         self
     }
 
@@ -106,7 +108,7 @@ impl<'b> BackendEnvironmentBuilder<'b> for EnvironmentBuilderImpl {
             self.max_dbs,
             self.map_size,
         )?;
-        env.read_from_disk(self.discard_if_corrupted)?;
+        env.read_from_disk(self.corruption_recovery_strategy)?;
         Ok(env)
     }
 }
@@ -152,16 +154,32 @@ impl EnvironmentImpl {
         Ok(bincode::serialize(&data)?)
     }
 
-    fn deserialize(
-        bytes: &[u8],
-        discard_if_corrupted: bool,
+    fn load(
+        path: &Path,
+        strategy: RecoveryStrategy,
     ) -> Result<(DatabaseArena, DatabaseNameMap), ErrorImpl> {
+        let bytes = fs::read(path)?;
+
+        match Self::deserialize(&bytes) {
+            Ok((arena, name_map)) => Ok((arena, name_map)),
+            Err(err) => match strategy {
+                RecoveryStrategy::Error => Err(err),
+                RecoveryStrategy::Discard => Ok((DatabaseArena::new(), HashMap::new())),
+                RecoveryStrategy::Rename => {
+                    let corrupted_path = path.with_extension(DEFAULT_CORRUPT_DB_EXTENSION);
+                    fs::rename(path, corrupted_path)?;
+
+                    Ok((DatabaseArena::new(), HashMap::new()))
+                }
+            },
+        }
+    }
+
+    fn deserialize(bytes: &[u8]) -> Result<(DatabaseArena, DatabaseNameMap), ErrorImpl> {
         let mut arena = DatabaseArena::new();
         let mut name_map = HashMap::new();
-        let data: HashMap<_, _> = match bincode::deserialize(bytes) {
-            Err(_) if discard_if_corrupted => Ok(HashMap::new()),
-            result => result,
-        }?;
+        let data: HashMap<_, _> = bincode::deserialize(bytes)?;
+
         for (name, db) in data {
             name_map.insert(name, DatabaseImpl(arena.alloc(db)));
         }
@@ -199,15 +217,15 @@ impl EnvironmentImpl {
         })
     }
 
-    pub(crate) fn read_from_disk(&mut self, discard_if_corrupted: bool) -> Result<(), ErrorImpl> {
+    pub(crate) fn read_from_disk(&mut self, strategy: RecoveryStrategy) -> Result<(), ErrorImpl> {
         let mut path = Cow::from(&self.path);
         if fs::metadata(&path)?.is_dir() {
             path.to_mut().push(DEFAULT_DB_FILENAME);
         };
         if fs::metadata(&path).is_err() {
             return Ok(());
         };
-        let (arena, name_map) = Self::deserialize(&fs::read(&path)?, discard_if_corrupted)?;
+        let (arena, name_map) = Self::load(&path, strategy)?;
         self.dbs = RwLock::new(EnvironmentDbs { arena, name_map });
         Ok(())
     }

src/backend/traits.rs

@@ -14,7 +14,7 @@ use std::{
 };
 
 use crate::{
-    backend::common::{DatabaseFlags, EnvironmentFlags, WriteFlags},
+    backend::common::{DatabaseFlags, EnvironmentFlags, RecoveryStrategy, WriteFlags},
     error::StoreError,
 };
 
@@ -83,7 +83,8 @@ pub trait BackendEnvironmentBuilder<'b>: Debug + Eq + PartialEq + Copy + Clone {
 
     fn set_make_dir_if_needed(&mut self, make_dir_if_needed: bool) -> &mut Self;
 
-    fn set_discard_if_corrupted(&mut self, discard_if_corrupted: bool) -> &mut Self;
+    /// Set the corruption recovery strategy. See [`RecoveryStrategy`] for details.
+    fn set_corruption_recovery_strategy(&mut self, strategy: RecoveryStrategy) -> &mut Self;
 
     fn open(&self, path: &Path) -> Result<Self::Environment, Self::Error>;
 }

tests/manager.rs

@@ -15,7 +15,7 @@ use tempfile::Builder;
 #[cfg(feature = "lmdb")]
 use rkv::backend::{Lmdb, LmdbEnvironment};
 use rkv::{
-    backend::{BackendEnvironmentBuilder, SafeMode, SafeModeEnvironment},
+    backend::{BackendEnvironmentBuilder, RecoveryStrategy, SafeMode, SafeModeEnvironment},
     CloseOptions, Rkv, StoreOptions, Value,
 };
 
@@ -247,7 +247,7 @@ fn test_safe_mode_corrupt_while_open_1() {
 
     // But we can use a builder and pass `discard_if_corrupted` to deal with it.
     let mut builder = Rkv::environment_builder::<SafeMode>();
-    builder.set_discard_if_corrupted(true);
+    builder.set_corruption_recovery_strategy(RecoveryStrategy::Discard);
     manager
         .get_or_create_from_builder(root.path(), builder, Rkv::from_builder::<SafeMode>)
         .expect("created");
@@ -378,3 +378,94 @@ fn test_safe_mode_corrupt_while_open_2() {
         Some(Value::Str("byé, yöu"))
     );
 }
+
+/// Test how the manager can discard corrupted databases, while moving the corrupted one aside for
+/// later inspection.
+#[test]
+fn test_safe_mode_corrupt_while_open_3() {
+    type Manager = rkv::Manager<SafeModeEnvironment>;
+
+    let root = Builder::new()
+        .prefix("test_safe_mode_corrupt_while_open_3")
+        .tempdir()
+        .expect("tempdir");
+    fs::create_dir_all(root.path()).expect("dir created");
+
+    let mut safebin = root.path().to_path_buf();
+    safebin.push("data.safe.bin");
+
+    // Oops, corruption.
+    fs::write(&safebin, "bogus").expect("dbfile corrupted");
+    assert!(safebin.exists(), "Corrupted database file was written to");
+
+    // Create environment.
+    let mut manager = Manager::singleton().write().unwrap();
+
+    // Recreating environment fails.
+    manager
+        .get_or_create(root.path(), Rkv::new::<SafeMode>)
+        .expect_err("not created");
+    assert!(manager.get(root.path()).expect("success").is_none());
+
+    // But we can use a builder and pass `RecoveryStrategy::Rename` to deal with it.
+    let mut builder = Rkv::environment_builder::<SafeMode>();
+    builder.set_corruption_recovery_strategy(RecoveryStrategy::Rename);
+    manager
+        .get_or_create_from_builder(root.path(), builder, Rkv::from_builder::<SafeMode>)
+        .expect("created");
+    assert!(manager.get(root.path()).expect("success").is_some());
+
+    assert!(!safebin.exists(), "Database file was moved out of the way");
+
+    let mut corruptbin = root.path().to_path_buf();
+    corruptbin.push("data.safe.bin.corrupt");
+    assert!(corruptbin.exists(), "Corrupted database file exists");
+
+    let shared_env = manager
+        .get_or_create(root.path(), Rkv::new::<SafeMode>)
+        .expect("created");
+    let env = shared_env.read().unwrap();
+
+    // Writing still works.
+    let store = env
+        .open_single("store", StoreOptions::create())
+        .expect("opened");
+
+    let reader = env.read().expect("reader");
+    assert_eq!(store.get(&reader, "foo").expect("read"), None, "Nothing to be read");
+
+    // We can write.
+    let mut writer = env.write().expect("writer");
+    store
+        .put(&mut writer, "foo", &Value::I64(5678))
+        .expect("wrote");
+    writer.commit().expect("committed");
+    env.sync(true).expect("synced");
+
+    assert!(safebin.exists(), "Database file exists");
+
+    // Close everything.
+    drop(env);
+    drop(shared_env);
+    manager
+        .try_close(root.path(), CloseOptions::default())
+        .expect("closed without deleting");
+    assert!(manager.get(root.path()).expect("success").is_none());
+
+    // Recreate environment.
+    let shared_env = manager
+        .get_or_create(root.path(), Rkv::new::<SafeMode>)
+        .expect("created");
+    let env = shared_env.read().unwrap();
+
+    // Verify that the dbfile is not corrupted.
+    let store = env
+        .open_single("store", StoreOptions::default())
+        .expect("opened");
+    let reader = env.read().expect("reader");
+    assert_eq!(
+        store.get(&reader, "foo").expect("read"),
+        Some(Value::I64(5678)),
+        "Database contains expected value"
+    );
+}