Count user variables on a per-room basis.

src/db.rs

@@ -1,5 +1,7 @@
 use byteorder::LittleEndian;
-use sled::{Db, IVec, Tree};
+use sled::transaction::abort;
+use sled::transaction::{TransactionError, TransactionalTree, UnabortableTransactionError};
+use sled::{Db, Tree};
 use std::collections::HashMap;
 use thiserror::Error;
 use zerocopy::byteorder::I32;
@@ -10,6 +12,8 @@ use zerocopy::{AsBytes, LayoutVerified};
 /// read.
 type LittleEndianI32Layout<'a> = LayoutVerified<&'a [u8], I32<LittleEndian>>;
 
+const VARIABLE_COUNT_KEY: &'static str = "variable_count";
+
 #[derive(Clone)]
 pub struct Database {
     db: Db,
@@ -32,6 +36,23 @@ pub enum DataError {
 
     #[error("internal database error: {0}")]
     InternalError(#[from] sled::Error),
+
+    #[error("transaction error: {0}")]
+    TransactionError(#[from] sled::transaction::TransactionError),
+
+    #[error("unabortable transaction error: {0}")]
+    UnabortableTransactionError(#[from] UnabortableTransactionError),
+}
+
+impl From<TransactionError<DataError>> for DataError {
+    fn from(error: TransactionError<DataError>) -> Self {
+        match error {
+            TransactionError::Abort(data_err) => data_err,
+            TransactionError::Storage(storage_err) => {
+                DataError::TransactionError(TransactionError::Storage(storage_err))
+            }
+        }
+    }
 }
 
 fn to_key(room_id: &str, username: &str, variable_name: &str) -> Vec<u8> {
@@ -42,6 +63,10 @@ fn to_key(room_id: &str, username: &str, variable_name: &str) -> Vec<u8> {
     key
 }
 
+fn room_variable_count_key(room_id: &str, username: &str) -> Vec<u8> {
+    to_key(room_id, username, VARIABLE_COUNT_KEY)
+}
+
 fn to_prefix(room_id: &str, username: &str) -> Vec<u8> {
     let mut prefix = vec![];
     prefix.extend_from_slice(room_id.as_bytes());
@@ -49,7 +74,9 @@ fn to_prefix(room_id: &str, username: &str) -> Vec<u8> {
     prefix
 }
 
-fn convert(raw_value: &[u8]) -> Result<i32, DataError> {
+/// Convert bytes to an i32 with zero-copy deserialization. An error
+/// is returned if the bytes do not represent an i32.
+fn convert_i32(raw_value: &[u8]) -> Result<i32, DataError> {
     let layout = LittleEndianI32Layout::new_unaligned(raw_value.as_ref());
 
     if let Some(layout) = layout {
@@ -60,6 +87,29 @@ fn convert(raw_value: &[u8]) -> Result<i32, DataError> {
     }
 }
 
+/// Atomically alter the count of variables in the database, by the
+/// given amount. Count cannot go below 0.
+fn alter_room_variable_count(
+    variables: &TransactionalTree,
+    room_id: &str,
+    username: &str,
+    amount: i32,
+) -> Result<i32, DataError> {
+    let key = room_variable_count_key(room_id, username);
+    let mut new_count = match variables.get(&key)? {
+        Some(bytes) => convert_i32(&bytes)? + amount,
+        None => amount,
+    };
+
+    if new_count < 0 {
+        new_count = 0;
+    }
+
+    let db_value: I32<LittleEndian> = I32::new(new_count);
+    variables.insert(key, db_value.as_bytes())?;
+    Ok(new_count)
+}
+
 impl Database {
     pub fn new<P: AsRef<std::path::Path>>(path: P) -> Result<Database, DataError> {
         let db = sled::open(path)?;
@@ -89,17 +139,30 @@ impl Database {
                     //Strips room and username from key, leaving
                     //behind name.
                     let variable_name = std::str::from_utf8(&key[prefix_len..])?;
-                    Ok((variable_name.to_owned(), convert(&raw_value)?))
+                    Ok((variable_name.to_owned(), convert_i32(&raw_value)?))
                 }
                 Err(e) => Err(e.into()),
             })
             .collect();
 
-        //Convert to hash map. Can we do this in the first mapping
-        //step instead?
+        //Convert_I32 to hash map. Can we do this in the first mapping
+        //step instead? For some reason this is faster.
         variables.map(|entries| entries.into_iter().collect())
     }
 
+    pub async fn get_variable_count(
+        &self,
+        room_id: &str,
+        username: &str,
+    ) -> Result<i32, DataError> {
+        let key = room_variable_count_key(room_id, username);
+        if let Some(raw_value) = self.variables.get(&key)? {
+            convert_i32(&raw_value)
+        } else {
+            Ok(0)
+        }
+    }
+
     pub async fn get_user_variable(
         &self,
         room_id: &str,
@@ -109,7 +172,7 @@ impl Database {
         let key = to_key(room_id, username, variable_name);
 
         if let Some(raw_value) = self.variables.get(&key)? {
-            convert(&raw_value)
+            convert_i32(&raw_value)
         } else {
             Err(DataError::KeyDoesNotExist(String::from_utf8(key).unwrap()))
         }
@@ -122,12 +185,24 @@ impl Database {
         variable_name: &str,
         value: i32,
     ) -> Result<(), DataError> {
+        self.variables
+            .transaction(|tx| {
                 let key = to_key(room_id, username, variable_name);
                 let db_value: I32<LittleEndian> = I32::new(value);
-        self.variables
-            .insert(&key, IVec::from(db_value.as_bytes()))?;
+                let old_value = tx.insert(key, db_value.as_bytes())?;
+
+                //Only increment variable count on new keys.
+                if let None = old_value {
+                    match alter_room_variable_count(&tx, room_id, username, 1) {
+                        Err(e) => abort(e),
+                        _ => Ok(()),
+                    }
+                } else {
                     Ok(())
                 }
+            })
+            .map_err(|e| e.into())
+    }
 
     pub async fn delete_user_variable(
         &self,
@@ -135,11 +210,176 @@ impl Database {
         username: &str,
         variable_name: &str,
     ) -> Result<(), DataError> {
+        self.variables
+            .transaction(|tx| {
                 let key = to_key(room_id, username, variable_name);
-        if let Some(_) = self.variables.remove(&key)? {
-            Ok(())
-        } else {
-            Err(DataError::KeyDoesNotExist(String::from_utf8(key).unwrap()))
+                if let Some(_) = tx.remove(key.clone())? {
+                    match alter_room_variable_count(&tx, room_id, username, -1) {
+                        Err(e) => abort(e),
+                        _ => Ok(()),
                     }
+                } else {
+                    abort(DataError::KeyDoesNotExist(String::from_utf8(key).unwrap()))
+                }
+            })
+            .map_err(|e| e.into())
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use tempfile::tempdir;
+
+    //Room Variable count tests
+
+    #[tokio::test]
+    async fn alter_room_variable_count_test() {
+        let db = Database::new(&tempdir().unwrap()).unwrap();
+
+        let alter_count = |amount: i32| {
+            db.variables
+                .transaction(|tx| {
+                    match alter_room_variable_count(&tx, "room", "username", amount) {
+                        Err(e) => abort(e),
+                        _ => Ok(()),
+                    }
+                })
+                .expect("got transaction failure");
+        };
+
+        async fn get_count(db: &Database) -> i32 {
+            db.get_variable_count("room", "username")
+                .await
+                .expect("could not get variable count")
+        }
+
+        //addition
+        alter_count(5);
+        assert_eq!(5, get_count(&db).await);
+
+        //subtraction
+        alter_count(-3);
+        assert_eq!(2, get_count(&db).await);
+    }
+
+    #[tokio::test]
+    async fn alter_room_variable_count_cannot_go_below_0_test() {
+        let db = Database::new(&tempdir().unwrap()).unwrap();
+        db.variables
+            .transaction(
+                |tx| match alter_room_variable_count(&tx, "room", "username", -1000) {
+                    Err(e) => abort(e),
+                    _ => Ok(()),
+                },
+            )
+            .expect("got transaction failure");
+
+        let count = db
+            .get_variable_count("room", "username")
+            .await
+            .expect("could not get variable count");
+
+        assert_eq!(0, count);
+    }
+
+    #[tokio::test]
+    async fn empty_db_reports_0_room_variable_count_test() {
+        let db = Database::new(&tempdir().unwrap()).unwrap();
+
+        let count = db
+            .get_variable_count("room", "username")
+            .await
+            .expect("could not get variable count");
+
+        assert_eq!(0, count);
+    }
+
+    #[tokio::test]
+    async fn set_user_variable_increments_count() {
+        let db = Database::new(&tempdir().unwrap()).unwrap();
+        db.set_user_variable("room", "username", "myvariable", 5)
+            .await
+            .expect("could not insert variable");
+
+        let count = db
+            .get_variable_count("room", "username")
+            .await
+            .expect("could not get variable count");
+
+        assert_eq!(1, count);
+    }
+
+    #[tokio::test]
+    async fn update_user_variable_does_not_increment_count() {
+        let db = Database::new(&tempdir().unwrap()).unwrap();
+        db.set_user_variable("room", "username", "myvariable", 5)
+            .await
+            .expect("could not insert variable");
+
+        db.set_user_variable("room", "username", "myvariable", 10)
+            .await
+            .expect("could not update variable");
+
+        let count = db
+            .get_variable_count("room", "username")
+            .await
+            .expect("could not get variable count");
+
+        assert_eq!(1, count);
+    }
+
+    // Set/get/delete variable tests
+
+    #[tokio::test]
+    async fn set_and_get_variable_test() {
+        let db = Database::new(&tempdir().unwrap()).unwrap();
+        db.set_user_variable("room", "username", "myvariable", 5)
+            .await
+            .expect("could not insert variable");
+
+        let value = db
+            .get_user_variable("room", "username", "myvariable")
+            .await
+            .expect("could not get value");
+
+        assert_eq!(5, value);
+    }
+
+    #[tokio::test]
+    async fn delete_variable_test() {
+        let db = Database::new(&tempdir().unwrap()).unwrap();
+        db.set_user_variable("room", "username", "myvariable", 5)
+            .await
+            .expect("could not insert variable");
+
+        db.delete_user_variable("room", "username", "myvariable")
+            .await
+            .expect("could not delete value");
+
+        let result = db.get_user_variable("room", "username", "myvariable").await;
+
+        assert!(result.is_err());
+        assert!(matches!(result, Err(DataError::KeyDoesNotExist(_))));
+    }
+
+    #[tokio::test]
+    async fn get_missing_variable_returns_key_does_not_exist() {
+        let db = Database::new(&tempdir().unwrap()).unwrap();
+        let result = db.get_user_variable("room", "username", "myvariable").await;
+
+        assert!(result.is_err());
+        assert!(matches!(result, Err(DataError::KeyDoesNotExist(_))));
+    }
+
+    #[tokio::test]
+    async fn remove_missing_variable_returns_key_does_not_exist() {
+        let db = Database::new(&tempdir().unwrap()).unwrap();
+        let result = db
+            .delete_user_variable("room", "username", "myvariable")
+            .await;
+
+        assert!(result.is_err());
+        assert!(matches!(result, Err(DataError::KeyDoesNotExist(_))));
     }
 }