Migrate existing delineators to delimiter 0xfe.

src/config.rs

@@ -6,7 +6,7 @@ use thiserror::Error;
 
 /// Shortcut to defining db migration versions. Will probably
 /// eventually be moved to a config file.
-const MIGRATION_VERSION: u32 = 3;
+const MIGRATION_VERSION: u32 = 4;
 
 #[derive(Error, Debug)]
 pub enum ConfigError {

src/db/data_migrations.rs

@@ -6,9 +6,10 @@ use phf::phf_map;
 pub(super) type DataMigration = (fn(&Database) -> Result<(), DataError>, &'static str);
 
 static MIGRATIONS: phf::Map<u32, DataMigration> = phf_map! {
-    1u32 => (add_room_user_variable_count, "add_room_user_variable_count"),
+    1u32 => (add_room_user_variable_count::migrate, "add_room_user_variable_count"),
     2u32 => (delete_v0_schema, "delete_v0_schema"),
     3u32 => (delete_variable_count, "delete_variable_count"),
+    4u32 => (change_delineator_delimiter::migrate, "change_delineator_delimiter")
 };
 
 pub fn get_migrations(versions: &[u32]) -> Result<Vec<DataMigration>, MigrationError> {

src/db/variables.rs

@@ -62,7 +62,7 @@ impl<'a> From<RoomAndUser<'a>> for Vec<u8> {
     fn from(value: RoomAndUser<'a>) -> Vec<u8> {
         let mut bytes = vec![];
         bytes.extend_from_slice(value.0.as_bytes());
-        bytes.push(0xff);
+        bytes.push(0xfe);
         bytes.extend_from_slice(value.1.as_bytes());
         bytes
     }

src/db/variables/migrations.rs

@@ -8,6 +8,8 @@ use sled::{Batch, IVec};
 use zerocopy::byteorder::U32;
 use zerocopy::AsBytes;
 
+pub(in crate::db) mod add_room_user_variable_count {
+    use super::*;
     //Not to be confused with the super::RoomAndUser delineator.
     #[derive(PartialEq, Eq, std::hash::Hash)]
     struct RoomAndUser {
@@ -50,7 +52,7 @@ fn map_value_to_room_and_user(
         }
     }
 
-pub(in crate::db) fn add_room_user_variable_count(db: &Database) -> Result<(), DataError> {
+    pub(in crate::db) fn migrate(db: &Database) -> Result<(), DataError> {
         let tree = &db.variables.0;
         let prefix = variables_space_prefix("");
 
@@ -70,7 +72,8 @@ pub(in crate::db) fn add_room_user_variable_count(db: &Database) -> Result<(), D
                 });
 
         //Start a transaction on the variables tree.
-    let tx_result: Result<_, TransactionError<DataError>> = db.variables.0.transaction(|tx_vars| {
+        let tx_result: Result<_, TransactionError<DataError>> =
+            db.variables.0.transaction(|tx_vars| {
                 let batch = counts.iter().fold(Batch::default(), |mut batch, entry| {
                     let (info, count) = entry;
 
@@ -93,6 +96,7 @@ pub(in crate::db) fn add_room_user_variable_count(db: &Database) -> Result<(), D
         tx_result?; //For some reason, it cannot infer the type
         Ok(())
     }
+}
 
 pub(in crate::db) fn delete_v0_schema(db: &Database) -> Result<(), DataError> {
     let mut vars = db.variables.0.scan_prefix("");
@@ -132,3 +136,92 @@ pub(in crate::db) fn delete_variable_count(db: &Database) -> Result<(), DataErro
     db.variables.0.apply_batch(batch)?;
     Ok(())
 }
+
+pub(in crate::db) mod change_delineator_delimiter {
+    use super::*;
+
+    /// An entry in the room user variables keyspace.
+    struct UserVariableEntry {
+        room_id: String,
+        username: String,
+        variable_name: String,
+        value: IVec,
+    }
+
+    /// Extract keys and values from the variables keyspace according
+    /// to the v1 schema.
+    fn extract_v1_entries(
+        entry: sled::Result<(IVec, IVec)>,
+    ) -> Result<UserVariableEntry, MigrationError> {
+        if let Ok((key, value)) = entry {
+            let keys: Vec<Result<&str, _>> = key
+                .split(|&b| b == 0xff)
+                .map(|b| str::from_utf8(b))
+                .collect();
+
+            if let &[_, Ok(room_id), Ok(username), Ok(variable)] = keys.as_slice() {
+                Ok(UserVariableEntry {
+                    room_id: room_id.to_owned(),
+                    username: username.to_owned(),
+                    variable_name: variable.to_owned(),
+                    value: value,
+                })
+            } else {
+                Err(MigrationError::MigrationFailed(
+                    "a key violates utf8 schema".to_string(),
+                ))
+            }
+        } else {
+            Err(MigrationError::MigrationFailed(
+                "encountered unexpected key".to_string(),
+            ))
+        }
+    }
+
+    /// Create an old key, where delineator is separated by 0xff.
+    fn create_old_key(prefix: &[u8], insert: &UserVariableEntry) -> Vec<u8> {
+        let mut key = vec![];
+        key.extend_from_slice(&prefix); //prefix already has 0xff.
+        key.extend_from_slice(&insert.room_id.as_bytes());
+        key.push(0xff);
+        key.extend_from_slice(&insert.username.as_bytes());
+        key.push(0xff);
+        key.extend_from_slice(&insert.variable_name.as_bytes());
+        key
+    }
+
+    /// Create an old key, where delineator is separated by 0xfe.
+    fn create_new_key(prefix: &[u8], insert: &UserVariableEntry) -> Vec<u8> {
+        let mut key = vec![];
+        key.extend_from_slice(&prefix); //prefix already has 0xff.
+        key.extend_from_slice(&insert.room_id.as_bytes());
+        key.push(0xfe);
+        key.extend_from_slice(&insert.username.as_bytes());
+        key.push(0xff);
+        key.extend_from_slice(&insert.variable_name.as_bytes());
+        key
+    }
+
+    pub fn migrate(db: &Database) -> Result<(), DataError> {
+        let tree = &db.variables.0;
+        let prefix = variables_space_prefix("");
+
+        let results: Vec<UserVariableEntry> = tree
+            .scan_prefix(&prefix)
+            .map(extract_v1_entries)
+            .collect::<Result<Vec<_>, MigrationError>>()?;
+
+        let mut batch = Batch::default();
+
+        for insert in results {
+            let old = create_old_key(&prefix, &insert);
+            let new = create_new_key(&prefix, &insert);
+
+            batch.remove(old);
+            batch.insert(new, insert.value);
+        }
+
+        tree.apply_batch(batch)?;
+        Ok(())
+    }
+}