use mapped mutex guard (#177)

tower-sessions-core/src/session.rs

@@ -15,7 +15,7 @@ use base64::{engine::general_purpose::URL_SAFE_NO_PAD, DecodeError, Engine as _}
 use serde::{de::DeserializeOwned, Deserialize, Serialize};
 use serde_json::Value;
 use time::{Duration, OffsetDateTime};
-use tokio::sync::{Mutex, MutexGuard};
+use tokio::sync::{MappedMutexGuard, Mutex, MutexGuard};
 
 use crate::{session_store, SessionStore};
 
@@ -97,21 +97,21 @@ impl Session {
     }
 
     #[tracing::instrument(skip(self), err)]
-    async fn get_record(&self) -> Result<MutexGuard<Option<Record>>> {
+    async fn get_record(&self) -> Result<MappedMutexGuard<Record>> {
         let mut record_guard = self.record.lock().await;
-        let session_id = *self.session_id.lock();
 
-        // Lazily load the record.
+        // Lazily load the record since `None` here indicates we have no yet loaded it.
         if record_guard.is_none() {
             tracing::trace!("record not loaded from store; loading");
 
-            *record_guard = if let Some(session_id) = session_id {
-                match self.store.load(&session_id).await.map_err(Error::Store)? {
-                    Some(mut loaded_record) => {
+            let session_id = *self.session_id.lock();
+            *record_guard = Some(if let Some(session_id) = session_id {
+                match self.store.load(&session_id).await? {
+                    Some(loaded_record) => {
                         tracing::trace!("record found in store");
-                        loaded_record.expiry_date = self.expiry_date();
-                        Some(loaded_record)
+                        loaded_record
                     }
+
                     None => {
                         // A well-behaved user agent should not send session cookies after
                         // expiration. Even so it's possible for an expired session to be removed
@@ -120,16 +120,19 @@ impl Session {
                         // malicious behavior.
                         tracing::warn!("possibly suspicious activity: record not found in store");
                         *self.session_id.lock() = None;
-                        Some(self.create_record())
+                        self.create_record()
                     }
                 }
             } else {
                 tracing::trace!("session id not found");
-                Some(self.create_record())
-            }
+                self.create_record()
+            })
         }
 
-        Ok(record_guard)
+        Ok(MutexGuard::map(record_guard, |opt| {
+            opt.as_mut()
+                .expect("Record should always be `Option::Some` at this point")
+        }))
     }
 
     /// Inserts a `impl Serialize` value into the session.
@@ -207,14 +210,13 @@ impl Session {
     /// - If the session has not been hydrated and loading from the store fails,
     ///   we fail with [`Error::Store`].
     pub async fn insert_value(&self, key: &str, value: Value) -> Result<Option<Value>> {
-        Ok(self.get_record().await?.as_mut().and_then(|record| {
-            if record.data.get(key) != Some(&value) {
-                self.is_modified.store(true, atomic::Ordering::Release);
-                record.data.insert(key.to_string(), value)
-            } else {
-                None
-            }
-        }))
+        let mut record_guard = self.get_record().await?;
+        Ok(if record_guard.data.get(key) != Some(&value) {
+            self.is_modified.store(true, atomic::Ordering::Release);
+            record_guard.data.insert(key.to_string(), value)
+        } else {
+            None
+        })
     }
 
     /// Gets a value from the store.
@@ -275,11 +277,8 @@ impl Session {
     /// - If the session has not been hydrated and loading from the store fails,
     ///   we fail with [`Error::Store`].
     pub async fn get_value(&self, key: &str) -> Result<Option<Value>> {
-        Ok(self
-            .get_record()
-            .await?
-            .as_ref()
-            .and_then(|record| record.data.get(key).cloned()))
+        let record_guard = self.get_record().await?;
+        Ok(record_guard.data.get(key).cloned())
     }
 
     /// Removes a value from the store, retuning the value of the key if it was
@@ -346,10 +345,9 @@ impl Session {
     /// - If the session has not been hydrated and loading from the store fails,
     ///   we fail with [`Error::Store`].
     pub async fn remove_value(&self, key: &str) -> Result<Option<Value>> {
-        Ok(self.get_record().await?.as_mut().and_then(|record| {
-            self.is_modified.store(true, atomic::Ordering::Release);
-            record.data.remove(key)
-        }))
+        let mut record_guard = self.get_record().await?;
+        self.is_modified.store(true, atomic::Ordering::Release);
+        Ok(record_guard.data.remove(key))
     }
 
     /// Clears the session of all data but does not delete it from the store.
@@ -649,24 +647,21 @@ impl Session {
     /// - If saving to the store fails, we fail with [`Error::Store`].
     #[tracing::instrument(skip(self), err)]
     pub async fn save(&self) -> Result<()> {
-        // N.B.: `get_record` will create a new record if one isn't found in the store.
-        if let Some(record) = self.get_record().await?.as_mut() {
-            record.expiry_date = self.expiry_date();
-
-            {
-                let mut session_id_guard = self.session_id.lock();
-                if session_id_guard.is_none() {
-                    // Generate a new ID here since e.g. flush may have been called, which will
-                    // not directly update the record ID.
-                    let id = Id::default();
-                    *session_id_guard = Some(id);
-                    record.id = id;
-                }
+        let mut record_guard = self.get_record().await?;
+        record_guard.expiry_date = self.expiry_date();
+        {
+            let mut session_id_guard = self.session_id.lock();
+            if session_id_guard.is_none() {
+                // Generate a new ID here since e.g. flush may have been called, which will
+                // not directly update the record ID.
+                let id = Id::default();
+                *session_id_guard = Some(id);
+                record_guard.id = id;
             }
-
-            self.store.save(record).await.map_err(Error::Store)?;
         }
 
+        self.store.save(&record_guard).await.map_err(Error::Store)?;
+
         Ok(())
     }
 
@@ -829,13 +824,10 @@ impl Session {
     ///   with [`Error::Store`].
     pub async fn cycle_id(&self) -> Result<()> {
         let mut record_guard = self.get_record().await?;
-        let Some(record) = record_guard.as_mut() else {
-            return Ok(());
-        };
 
-        let old_session_id = record.id;
-        record.id = Id::default();
-        *self.session_id.lock() = Some(record.id);
+        let old_session_id = record_guard.id;
+        record_guard.id = Id::default();
+        *self.session_id.lock() = Some(record_guard.id);
 
         self.store
             .delete(&old_session_id)