Add GETSET command

src/cmd/string.rs

@@ -16,3 +16,7 @@ pub fn get(db: &Db, args: &[Bytes]) -> Result<Value, Error> {
 pub fn set(db: &Db, args: &[Bytes]) -> Result<Value, Error> {
     db.set(&args[1], &Value::Blob(args[2].to_owned()))
 }
+
+pub fn getset(db: &Db, args: &[Bytes]) -> Result<Value, Error> {
+    db.getset(&args[1], &Value::Blob(args[2].to_owned()))
+}

src/db/mod.rs

@@ -59,6 +59,13 @@ impl Db {
         Ok(entries.get(key).cloned().unwrap_or(Value::Null))
     }
 
+    pub fn getset(&self, key: &Bytes, value: &Value) -> Result<Value, Error> {
+        let mut entries = self.entries[self.get_slot(key)].write().unwrap();
+        let prev = entries.get(key).cloned().unwrap_or(Value::Null);
+        entries.insert(key.clone(), value.clone());
+        Ok(prev)
+    }
+
     pub fn set(&self, key: &Bytes, value: &Value) -> Result<Value, Error> {
         let mut entries = self.entries[self.get_slot(key)].write().unwrap();
         entries.insert(key.clone(), value.clone());

src/dispatcher.rs

@@ -47,6 +47,11 @@ dispatcher! {
         ["random" "loading" "stale"],
         -3,
     },
+    getset {
+        cmd::string::getset,
+        ["random" "loading" "stale"],
+        -3,
+    },
     time {
         do_time,
         ["random" "loading" "stale"],