diff --git a/src/lib.rs b/src/lib.rs
index 4f5d33e..a3d7a57 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -89,9 +89,7 @@ pub trait KVMapHandle {
     fn delete(&mut self, key: &[u8]);
 
     /// Querying a range starting from the first key greater than or equal to the given key.
-    ///
-    /// Note: For simplicity, it returns only the values.
-    fn scan(&mut self, key: &[u8], n: usize) -> Vec<Box<[u8]>>;
+    fn scan(&mut self, key: &[u8], n: usize) -> Vec<(Box<[u8]>, Box<[u8]>)>;
 }
 
 /// A single operation that is applied to the key-value store.
@@ -129,7 +127,12 @@ pub struct Response {
     pub id: usize,
 
     /// The real payload that contains the potential returned value.
-    pub data: Option<Box<[u8]>>,
+    ///
+    /// - For a `SET` or `DELETE` request, this should be `None`.
+    /// - For a `GET` request, this should contain the value of the key (single element).
+    /// - For a `SCAN` request, this should contain the sequence of the range query results, ordered
+    ///   like `key0, value0, key1, value1 ...`.
+    pub data: Option<Vec<Box<[u8]>>>,
 }
 
 /// A non-blocking, thread-safe key-value map.
diff --git a/src/server.rs b/src/server.rs
index d78bb43..2f5ede1 100644
--- a/src/server.rs
+++ b/src/server.rs
@@ -37,45 +37,40 @@ fn read_requests(reader: &mut impl Read) -> Result<Vec<Request>, bincode::Error>
 #[derive(Serialize, Deserialize)]
 struct ResponseHeader {
     id: usize,
-    len: usize,
+    has_data: bool,
 }
 
 fn write_response(
     writer: &mut impl Write,
     id: usize,
-    data: Option<&[u8]>,
+    data: Option<&[&[u8]]>,
 ) -> Result<(), bincode::Error> {
-    let len = match data {
-        Some(data) => data.len(),
-        None => 0,
+    let has_data = match data {
+        Some(_) => true,
+        None => false,
     };
-    let header = ResponseHeader { id, len };
+    let header = ResponseHeader { id, has_data };
     if let Err(e) = bincode::serialize_into(&mut *writer, &header) {
         return Err(e);
     }
     // has payload
-    if len != 0 {
-        if let Err(e) = writer.write_all(data.unwrap()) {
-            return Err(bincode::Error::from(e));
+    if has_data {
+        if let Err(e) = bincode::serialize_into(&mut *writer, data.unwrap()) {
+            return Err(e);
         }
     }
     Ok(())
 }
 
 fn read_response(reader: &mut impl Read) -> Result<Response, bincode::Error> {
-    let header = bincode::deserialize_from::<_, ResponseHeader>(&mut *reader)?;
-    let id = header.id;
-    let len = header.len;
-    if len != 0 {
-        let mut data = vec![0u8; len].into_boxed_slice();
-        if let Err(e) = reader.read_exact(&mut data[..]) {
-            Err(bincode::Error::from(e))
-        } else {
-            Ok(Response {
-                id,
-                data: Some(data),
-            })
-        }
+    let ResponseHeader { id, has_data } =
+        bincode::deserialize_from::<_, ResponseHeader>(&mut *reader)?;
+    if has_data {
+        let data = bincode::deserialize_from::<_, Vec<Box<[u8]>>>(&mut *reader)?;
+        Ok(Response {
+            id,
+            data: Some(data),
+        })
     } else {
         Ok(Response { id, data: None })
     }
@@ -102,7 +97,8 @@ fn serve_requests_regular(
             }
             Operation::Get { ref key } => match handle.get(key) {
                 Some(v) => {
-                    assert!(write_response(&mut *writer, id, Some(&v[..]),).is_ok());
+                    let data = &vec![&v[..]];
+                    assert!(write_response(&mut *writer, id, Some(data)).is_ok());
                 }
                 None => {
                     assert!(write_response(&mut *writer, id, None).is_ok());
@@ -113,9 +109,15 @@ fn serve_requests_regular(
                 assert!(write_response(&mut *writer, id, None).is_ok());
             }
             Operation::Scan { ref key, n } => {
-                for v in handle.scan(key, *n) {
-                    assert!(write_response(&mut *writer, id, Some(&v[..])).is_ok());
-                }
+                let kv = handle.scan(key, *n);
+                let data = kv
+                    .iter()
+                    .fold(Vec::with_capacity(kv.len() * 2), |mut vec, kv| {
+                        vec.push(&kv.0[..]);
+                        vec.push(&kv.1[..]);
+                        vec
+                    });
+                assert!(write_response(&mut *writer, id, Some(&data[..])).is_ok());
             }
         }
     }
@@ -230,12 +232,20 @@ type StreamMap = HashMap<Token, Connection>;
 
 impl AsyncResponder for ResponseWriter {
     fn callback(&self, response: Response) {
-        assert!(write_response(
-            &mut *self.0.borrow_mut(),
-            response.id,
-            response.data.as_deref()
-        )
-        .is_ok());
+        let Response { id, data } = response;
+        match data {
+            Some(data) => {
+                assert!(write_response(
+                    &mut *self.0.borrow_mut(),
+                    id,
+                    Some(&data.iter().map(|d| &d[..]).collect::<Vec<&[u8]>>()[..])
+                )
+                .is_ok());
+            }
+            None => {
+                assert!(write_response(&mut *self.0.borrow_mut(), id, None).is_ok());
+            }
+        }
     }
 }
 
@@ -680,7 +690,10 @@ impl KVClient {
         let response = responses.pop().unwrap();
         assert_eq!(response.id, 0);
         match response.data {
-            Some(v) => Some(v),
+            Some(mut v) => {
+                assert_eq!(v.len(), 1);
+                v.pop()
+            }
             None => None,
         }
     }
@@ -906,7 +919,7 @@ mod tests {
                             // set
                             assert_eq!(r.data, None);
                         } else {
-                            assert_eq!(r.data, Some([170u8; 16].into()));
+                            assert_eq!(r.data, Some(vec![[170u8; 16].into()]));
                         }
                         pending -= 1;
                     }
@@ -927,7 +940,7 @@ mod tests {
                         // set
                         assert_eq!(r.data, None);
                     } else {
-                        assert_eq!(r.data, Some([170u8; 16].into()));
+                        assert_eq!(r.data, Some(vec![[170u8; 16].into()]));
                     }
                     pending -= 1;
                 }
diff --git a/src/stores.rs b/src/stores.rs
index 81dc798..3ba7d02 100644
--- a/src/stores.rs
+++ b/src/stores.rs
@@ -155,7 +155,8 @@ mod tests {
         assert_eq!(v.len(), 10000);
         for i in 10000..20000usize {
             let bytes = i.clone().to_be_bytes();
-            assert_eq!(*v[i - 10000], bytes);
+            assert_eq!(*v[i - 10000].0, bytes);
+            assert_eq!(*v[i - 10000].1, bytes);
         }
 
         // query 10000 next 20000, should have 10000
@@ -163,7 +164,8 @@ mod tests {
         assert_eq!(v.len(), 10000);
         for i in 10000..20000usize {
             let bytes = i.clone().to_be_bytes();
-            assert_eq!(*v[i - 10000], bytes);
+            assert_eq!(*v[i - 10000].0, bytes);
+            assert_eq!(*v[i - 10000].1, bytes);
         }
 
         // query 10000 next 5, should have 5
@@ -171,7 +173,8 @@ mod tests {
         assert_eq!(v.len(), 5);
         for i in 10000..10005usize {
             let bytes = i.clone().to_be_bytes();
-            assert_eq!(*v[i - 10000], bytes);
+            assert_eq!(*v[i - 10000].0, bytes);
+            assert_eq!(*v[i - 10000].1, bytes);
         }
 
         // query 13333 next 444, should have 444
@@ -179,7 +182,8 @@ mod tests {
         assert_eq!(v.len(), 444);
         for i in 13333..13777usize {
             let bytes = i.clone().to_be_bytes();
-            assert_eq!(*v[i - 13333], bytes);
+            assert_eq!(*v[i - 13333].0, bytes);
+            assert_eq!(*v[i - 13333].1, bytes);
         }
 
         // query 13333 next 0, should have 0
@@ -195,7 +199,8 @@ mod tests {
         assert_eq!(v.len(), 5000);
         for i in 10000..15000usize {
             let bytes = i.clone().to_be_bytes();
-            assert_eq!(*v[i - 10000], bytes);
+            assert_eq!(*v[i - 10000].0, bytes);
+            assert_eq!(*v[i - 10000].1, bytes);
         }
 
         // query 8000 next 5000, should have 5000
@@ -203,7 +208,8 @@ mod tests {
         assert_eq!(v.len(), 5000);
         for i in 10000..15000usize {
             let bytes = i.clone().to_be_bytes();
-            assert_eq!(*v[i - 10000], bytes);
+            assert_eq!(*v[i - 10000].0, bytes);
+            assert_eq!(*v[i - 10000].1, bytes);
         }
     }
 
diff --git a/src/stores/btreemap.rs b/src/stores/btreemap.rs
index bd3c6f1..828c5e1 100644
--- a/src/stores/btreemap.rs
+++ b/src/stores/btreemap.rs
@@ -61,7 +61,7 @@ impl KVMapHandle for MutexBTreeMap {
         self.0.lock().remove(key);
     }
 
-    fn scan(&mut self, _key: &[u8], _n: usize) -> Vec<Box<[u8]>> {
+    fn scan(&mut self, _key: &[u8], _n: usize) -> Vec<(Box<[u8]>, Box<[u8]>)> {
         // technically iteration is supported but querying a specific range is not a stable feature
         unimplemented!("Range query is not supported");
     }
@@ -108,7 +108,7 @@ impl KVMapHandle for RwLockBTreeMap {
         self.0.write().remove(key);
     }
 
-    fn scan(&mut self, _key: &[u8], _n: usize) -> Vec<Box<[u8]>> {
+    fn scan(&mut self, _key: &[u8], _n: usize) -> Vec<(Box<[u8]>, Box<[u8]>)> {
         // technically iteration is supported but querying a specific range is not a stable feature
         unimplemented!("Range query is not supported");
     }
diff --git a/src/stores/chashmap.rs b/src/stores/chashmap.rs
index 1db689e..fbebac5 100644
--- a/src/stores/chashmap.rs
+++ b/src/stores/chashmap.rs
@@ -46,7 +46,7 @@ impl KVMapHandle for CHashMap {
         self.0.remove(key);
     }
 
-    fn scan(&mut self, _key: &[u8], _n: usize) -> Vec<Box<[u8]>> {
+    fn scan(&mut self, _key: &[u8], _n: usize) -> Vec<(Box<[u8]>, Box<[u8]>)> {
         unimplemented!("Range query is not supported");
     }
 }
diff --git a/src/stores/contrie.rs b/src/stores/contrie.rs
index 45bdc3e..c783e1b 100644
--- a/src/stores/contrie.rs
+++ b/src/stores/contrie.rs
@@ -47,7 +47,7 @@ impl KVMapHandle for Contrie {
         self.0.remove(key);
     }
 
-    fn scan(&mut self, _key: &[u8], _n: usize) -> Vec<Box<[u8]>> {
+    fn scan(&mut self, _key: &[u8], _n: usize) -> Vec<(Box<[u8]>, Box<[u8]>)> {
         unimplemented!("Range query is not supported");
     }
 }
diff --git a/src/stores/dashmap.rs b/src/stores/dashmap.rs
index 7ed0e6c..a05cddc 100644
--- a/src/stores/dashmap.rs
+++ b/src/stores/dashmap.rs
@@ -47,7 +47,7 @@ impl KVMapHandle for DashMap {
         self.0.remove(key);
     }
 
-    fn scan(&mut self, _key: &[u8], _n: usize) -> Vec<Box<[u8]>> {
+    fn scan(&mut self, _key: &[u8], _n: usize) -> Vec<(Box<[u8]>, Box<[u8]>)> {
         unimplemented!("Range query is not supported");
     }
 }
diff --git a/src/stores/flurry.rs b/src/stores/flurry.rs
index 9a4efdb..6a591ba 100644
--- a/src/stores/flurry.rs
+++ b/src/stores/flurry.rs
@@ -47,7 +47,7 @@ impl KVMapHandle for Flurry {
         self.0.pin().remove(key);
     }
 
-    fn scan(&mut self, _key: &[u8], _n: usize) -> Vec<Box<[u8]>> {
+    fn scan(&mut self, _key: &[u8], _n: usize) -> Vec<(Box<[u8]>, Box<[u8]>)> {
         unimplemented!("Range query is not supported");
     }
 }
diff --git a/src/stores/hashmap.rs b/src/stores/hashmap.rs
index cfd4c30..9f52e70 100644
--- a/src/stores/hashmap.rs
+++ b/src/stores/hashmap.rs
@@ -100,7 +100,7 @@ impl KVMapHandle for MutexHashMap {
         self.shards[sid].lock().remove(key);
     }
 
-    fn scan(&mut self, _key: &[u8], _n: usize) -> Vec<Box<[u8]>> {
+    fn scan(&mut self, _key: &[u8], _n: usize) -> Vec<(Box<[u8]>, Box<[u8]>)> {
         unimplemented!("Range query is not supported");
     }
 }
@@ -166,7 +166,7 @@ impl KVMapHandle for RwLockHashMap {
         self.shards[sid].write().remove(key);
     }
 
-    fn scan(&mut self, _key: &[u8], _n: usize) -> Vec<Box<[u8]>> {
+    fn scan(&mut self, _key: &[u8], _n: usize) -> Vec<(Box<[u8]>, Box<[u8]>)> {
         unimplemented!("Range query is not supported");
     }
 }
diff --git a/src/stores/null.rs b/src/stores/null.rs
index a6deec2..95dba3e 100644
--- a/src/stores/null.rs
+++ b/src/stores/null.rs
@@ -55,7 +55,7 @@ impl KVMapHandle for NullMap {
 
     fn delete(&mut self, _key: &[u8]) {}
 
-    fn scan(&mut self, _key: &[u8], _n: usize) -> Vec<Box<[u8]>> {
+    fn scan(&mut self, _key: &[u8], _n: usize) -> Vec<(Box<[u8]>, Box<[u8]>)> {
         Vec::new()
     }
 }
diff --git a/src/stores/papaya.rs b/src/stores/papaya.rs
index fe3e0e5..f99d227 100644
--- a/src/stores/papaya.rs
+++ b/src/stores/papaya.rs
@@ -47,7 +47,7 @@ impl KVMapHandle for Papaya {
         self.0.pin().remove(key);
     }
 
-    fn scan(&mut self, _key: &[u8], _n: usize) -> Vec<Box<[u8]>> {
+    fn scan(&mut self, _key: &[u8], _n: usize) -> Vec<(Box<[u8]>, Box<[u8]>)> {
         unimplemented!("Range query is not supported");
     }
 }
diff --git a/src/stores/rocksdb.rs b/src/stores/rocksdb.rs
index 81f7eab..531038b 100644
--- a/src/stores/rocksdb.rs
+++ b/src/stores/rocksdb.rs
@@ -60,7 +60,7 @@ impl KVMapHandle for RocksDB {
         assert!(self.db.delete(key).is_ok());
     }
 
-    fn scan(&mut self, key: &[u8], n: usize) -> Vec<Box<[u8]>> {
+    fn scan(&mut self, key: &[u8], n: usize) -> Vec<(Box<[u8]>, Box<[u8]>)> {
         let mut kv = Vec::with_capacity(n);
         let iter = self
             .db
@@ -70,7 +70,7 @@ impl KVMapHandle for RocksDB {
             if i == n {
                 break;
             }
-            kv.push(item.unwrap().1);
+            kv.push(item.unwrap());
             i += 1;
         }
         kv
diff --git a/src/stores/scc.rs b/src/stores/scc.rs
index 1ba0a3e..484bebe 100644
--- a/src/stores/scc.rs
+++ b/src/stores/scc.rs
@@ -50,7 +50,7 @@ impl KVMapHandle for SccHashMap {
         self.0.remove(key);
     }
 
-    fn scan(&mut self, _key: &[u8], _n: usize) -> Vec<Box<[u8]>> {
+    fn scan(&mut self, _key: &[u8], _n: usize) -> Vec<(Box<[u8]>, Box<[u8]>)> {
         unimplemented!("Range query is not supported");
     }
 }