diff --git a/src/chat.rs b/src/chat.rs
index 367447f..b0ea538 100644
--- a/src/chat.rs
+++ b/src/chat.rs
@@ -15,6 +15,7 @@
  */
 use crate::client::*;
 
+#[derive(Debug)]
 pub struct Message {
     username: String,
     content: String,
@@ -31,6 +32,7 @@ impl Message {
     }
 }
 
+#[derive(Debug)]
 pub struct Chat {
     messages: Vec<Message>, // messages in this file
 }
diff --git a/src/file.rs b/src/file.rs
index b938f9a..a782768 100644
--- a/src/file.rs
+++ b/src/file.rs
@@ -15,12 +15,14 @@
  */
 use crate::chat::*;
 use crate::user::*;
+use crate::util::*;
 use std::collections::HashMap;
 
+#[derive(Debug)]
 pub struct File {
-    path: String, // absolute path
-    chat: Chat,   // messages in this file
-    view: String, // the file view
+    path: String,         // absolute path
+    chat: Chat,           // messages in this file
+    view: Option<String>, // the file view
 }
 
 impl File {
@@ -28,7 +30,7 @@ impl File {
         Self {
             path: _path,
             chat: Chat::new(),
-            view: String::default(),
+            view: None,
         }
     }
 
@@ -42,8 +44,29 @@ impl File {
         &mut self.chat
     }
 
+    fn load_file(&mut self) {
+        if !self.view.is_none() {
+            return;
+        }
+        self.view = Some(read_to_string(&self.path));
+    }
+
+    pub fn update(&mut self, add_or_delete: &String, beg: u64, end: u64, content: &String) {
+        self.load_file(); // ensure read
+
+        match add_or_delete.clone().as_str() {
+            "add" => {
+                //self.view.insert(content, beg);
+            }
+            "delete" => {}
+            _ => {
+                unreachable!()
+            }
+        }
+    }
+
     /// Write the content to file.
-    pub async fn save(&self) {
-        // TODO: ..
+    pub fn save(&self) {
+        let _ = std::fs::write(&self.path, &self.view.clone().unwrap());
     }
 }
diff --git a/src/handler/file.rs b/src/handler/file.rs
index 8adbfc1..2aad2ea 100644
--- a/src/handler/file.rs
+++ b/src/handler/file.rs
@@ -14,9 +14,10 @@
  * limitations under the License.
  */
 
-/// Return a list of users in the file.
-pub mod users {
+// Addition and Deletion to the file.
+pub mod update {
     use crate::channel::*;
+    use crate::handler::file::*;
     use crate::handler::room::*;
     use crate::room::*;
     use crate::util::*;
@@ -24,63 +25,70 @@ pub mod users {
     use std::sync::Arc;
     use tokio::sync::Mutex;
 
-    const METHOD: &str = "file::users";
+    const METHOD: &str = "file::update";
 
     pub async fn handle(channel: &mut Channel, room: &Arc<Mutex<Room>>, json: &Value) {
         let addr = &channel.get_connection().addr;
-        let room = room.lock().await;
-        let client = room.get_client(addr).unwrap();
+        let mut room = room.lock().await;
 
-        if !check_entered(channel, &client, METHOD).await {
-            return;
-        }
+        let path = data_str(json, "path").unwrap();
+        let add_or_delete = data_str(json, "add_or_delete").unwrap();
+        let beg = data_u64(json, "beg").unwrap();
+        let end = data_u64(json, "end").unwrap();
+        let content = data_str(json, "content").unwrap();
 
-        let this_user = client.user().unwrap();
+        let path = to_room_path(&addr, &room, &path);
+        let file = room.get_file_mut(&path);
 
-        // If user is not in the file, ignore it.
-        if this_user.path.is_none() {
+        if file.is_none() {
+            tracing::debug!("Updating an non-existence file: {}", path);
+            // TODO: Create one?
             return;
         }
 
-        // Prepare data to send.
-        let mut users = Vec::new();
+        let file = file.unwrap();
 
-        for _client in room.get_clients().iter() {
-            let user = _client.user();
+        file.update(&add_or_delete, beg, end, &content);
+    }
+}
 
-            if user.is_none() {
-                continue;
-            }
+/// Save file.
+pub mod save {
+    use crate::channel::*;
+    use crate::handler::file::*;
+    use crate::handler::room::*;
+    use crate::room::*;
+    use crate::util::*;
+    use serde_json::Value;
+    use std::sync::Arc;
+    use tokio::sync::Mutex;
 
-            let user = user.unwrap();
+    const METHOD: &str = "file::save";
 
-            // Ignore the sender client.
-            if this_user == user {
-                continue;
-            }
-
-            // Ignore when user not visiting any project files.
-            if user.path.is_none() {
-                continue;
-            }
+    pub async fn handle(channel: &mut Channel, room: &Arc<Mutex<Room>>, json: &Value) {
+        let addr = &channel.get_connection().addr;
+        let mut room = room.lock().await;
 
-            // Ignore if not in the same file.
-            if client.user_relative_path() != _client.user_relative_path() {
-                continue;
-            }
+        let path = data_str(json, "path").unwrap();
+        let path = to_room_path(&addr, &room, &path);
+        let file = room.get_file_mut(&path);
 
-            users.push(user.clone());
+        if file.is_none() {
+            tracing::debug!("Updating an non-existence file: {}", path);
+            // TODO: Create one?
+            return;
         }
 
-        let users = serde_json::to_string(&users).unwrap();
+        let file = file.unwrap();
+        file.save();
 
-        channel
-            .send_json(&serde_json::json!({
-                "method": METHOD,
-                "clients": users,
-                "status": "success",
-            }))
-            .await;
+        let relative_path = no_room_path(&room, &path);
+
+        room.broadcast_json(&serde_json::json!({
+            "method": METHOD,
+            "file": relative_path,
+            "status": "success",
+        }));
     }
 }
 
@@ -125,6 +133,76 @@ pub mod sync {
     }
 }
 
+/// Return a list of users in the file.
+pub mod users {
+    use crate::channel::*;
+    use crate::handler::room::*;
+    use crate::room::*;
+    use crate::util::*;
+    use serde_json::Value;
+    use std::sync::Arc;
+    use tokio::sync::Mutex;
+
+    const METHOD: &str = "file::users";
+
+    pub async fn handle(channel: &mut Channel, room: &Arc<Mutex<Room>>, json: &Value) {
+        let addr = &channel.get_connection().addr;
+        let room = room.lock().await;
+        let client = room.get_client(addr).unwrap();
+
+        if !check_entered(channel, &client, METHOD).await {
+            return;
+        }
+
+        let this_user = client.user().unwrap();
+
+        // If user is not in the file, ignore it.
+        if this_user.path.is_none() {
+            return;
+        }
+
+        // Prepare data to send.
+        let mut users = Vec::new();
+
+        for _client in room.get_clients().iter() {
+            let user = _client.user();
+
+            if user.is_none() {
+                continue;
+            }
+
+            let user = user.unwrap();
+
+            // Ignore the sender client.
+            if this_user == user {
+                continue;
+            }
+
+            // Ignore when user not visiting any project files.
+            if user.path.is_none() {
+                continue;
+            }
+
+            // Ignore if not in the same file.
+            if client.user_relative_path() != _client.user_relative_path() {
+                continue;
+            }
+
+            users.push(user.clone());
+        }
+
+        let users = serde_json::to_string(&users).unwrap();
+
+        channel
+            .send_json(&serde_json::json!({
+                "method": METHOD,
+                "clients": users,
+                "status": "success",
+            }))
+            .await;
+    }
+}
+
 /// Say
 pub mod say {
     use crate::channel::*;
diff --git a/src/handler/mod.rs b/src/handler/mod.rs
index 314fa8d..70404dc 100644
--- a/src/handler/mod.rs
+++ b/src/handler/mod.rs
@@ -23,7 +23,6 @@ use crate::room::*;
 use serde_json::Value;
 use std::sync::Arc;
 use tokio::sync::Mutex;
-
 pub async fn handle(channel: &mut Channel, room: &Arc<Mutex<Room>>, json: &str) {
     let v = serde_json::from_str(json);
     let val: Value = v.unwrap();
@@ -40,9 +39,11 @@ pub async fn handle(channel: &mut Channel, room: &Arc<Mutex<Room>>, json: &str)
         "room::users" => room::users::handle(channel, room, &val).await,
         "room::sync" => room::sync::handle(channel, room, &val).await,
         "room::update_client" => room::update_client::handle(channel, room, &val).await,
+        "file::update" => file::update::handle(channel, room, &val).await,
+        "file::save" => file::save::handle(channel, room, &val).await,
+        "file::sync" => file::sync::handle(channel, room, &val).await,
         "file::users" => file::users::handle(channel, room, &val).await,
         "file::say" => file::say::handle(channel, room, &val).await,
-        "file::sync" => file::sync::handle(channel, room, &val).await,
         _ => {
             tracing::error!("Unkown method request: {:?}", method);
         }
diff --git a/src/handler/room.rs b/src/handler/room.rs
index b9a2d99..020ea74 100644
--- a/src/handler/room.rs
+++ b/src/handler/room.rs
@@ -16,9 +16,6 @@
 use crate::channel::*;
 use crate::client::*;
 use crate::room::*;
-use serde_json::Value;
-use std::fs;
-use std::net::SocketAddr;
 use std::sync::Arc;
 use tokio::sync::Mutex;
 
@@ -87,20 +84,6 @@ pub async fn check_admin(channel: &mut Channel, client: &Client, method: &str) -
     return false;
 }
 
-/// Convert path's absolute project path to this room path.
-///
-/// # Arguments
-///
-/// * `addr` - Socket address used to get the client's project path.
-/// * `room` - Used to get client and room path.
-/// * `path` - Path we want to convert.
-pub fn to_room_path(addr: &SocketAddr, room: &Room, path: &str) -> String {
-    let server_path = room.get_path().clone();
-    let client = room.get_client(addr).unwrap();
-    let project_path = client.get_path();
-    path.replace(project_path, &server_path)
-}
-
 /// Enter room
 pub mod enter {
     use crate::channel::*;
@@ -202,10 +185,9 @@ pub mod exit {
 pub mod kick {
     use crate::channel::*;
     use crate::handler::room::*;
-    use crate::room::*;
     use crate::util::*;
     use serde_json::Value;
-    use std::sync::{Arc, MutexGuard};
+    use std::sync::Arc;
     use tokio::sync::Mutex;
 
     const METHOD: &str = "room::kick";
@@ -259,10 +241,9 @@ pub mod kick {
 pub mod broadcast {
     use crate::channel::*;
     use crate::handler::room::*;
-    use crate::room::*;
     use crate::util::*;
     use serde_json::Value;
-    use std::sync::{Arc, MutexGuard};
+    use std::sync::Arc;
     use tokio::sync::Mutex;
 
     const METHOD: &str = "room::broadcast";
@@ -293,7 +274,6 @@ pub mod broadcast {
 pub mod update_client {
     use crate::channel::*;
     use crate::handler::room::*;
-    use crate::room::*;
     use crate::util::*;
     use serde_json::Value;
     use std::sync::Arc;
@@ -329,7 +309,6 @@ pub mod update_client {
 pub mod users {
     use crate::channel::*;
     use crate::handler::room::*;
-    use crate::room::*;
     use serde_json::Value;
     use std::sync::Arc;
     use tokio::sync::Mutex;
@@ -369,7 +348,6 @@ pub mod users {
 pub mod sync {
     use crate::channel::*;
     use crate::handler::room::*;
-    use crate::room::*;
     use crate::util::*;
     use serde_json::Value;
     use std::sync::Arc;
@@ -389,7 +367,7 @@ pub mod sync {
         let project_path = data_str(json, "path").unwrap();
 
         let room_path = room.get_path().clone();
-        let files = room.get_files();
+        let files = room.get_path_files();
 
         for file in files.into_iter() {
             let abs_path = file;
diff --git a/src/room.rs b/src/room.rs
index 58f844b..655203f 100644
--- a/src/room.rs
+++ b/src/room.rs
@@ -127,12 +127,12 @@ impl Room {
     /// # Arguments
     ///
     /// * `path` - The file path.
-    pub fn get_file(&mut self, path: &String) -> Option<&mut File> {
+    pub fn get_file_mut(&mut self, path: &String) -> Option<&mut File> {
         self.files.get_mut(path)
     }
 
     /// Return a list of files need to be sync.
-    pub fn get_files(&self) -> Vec<&String> {
+    pub fn get_path_files(&self) -> Vec<&String> {
         self.files.keys().clone().collect::<Vec<&String>>()
     }
 
diff --git a/src/util.rs b/src/util.rs
index 5585f23..e0225a0 100644
--- a/src/util.rs
+++ b/src/util.rs
@@ -13,9 +13,11 @@
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */
+use crate::room::*;
 use crate::user::*;
 use path_slash::PathBufExt as _;
 use serde_json::Value;
+use std::net::SocketAddr;
 use std::path::PathBuf;
 
 /// Get data as string.
@@ -81,6 +83,31 @@ pub fn read_to_string(path: &String) -> String {
     std::fs::read_to_string(path).expect(format!("Unable to read file: {}", path).as_str())
 }
 
+/// Convert path's absolute project path to this room path.
+///
+/// # Arguments
+///
+/// * `addr` - Socket address used to get the client's project path.
+/// * `room` - Used to get client and room path.
+/// * `path` - Path we want to convert.
+pub fn to_room_path(addr: &SocketAddr, room: &Room, path: &str) -> String {
+    let room_path = room.get_path().clone();
+    let client = room.get_client(addr).unwrap();
+    let project_path = client.get_path();
+    path.replace(project_path, &room_path)
+}
+
+/// Remove room path.
+///
+/// # Arguments
+///
+/// * `room` - Room object.
+/// * `path` - Path we want to remove room path.
+pub fn no_room_path(room: &Room, path: &str) -> String {
+    let room_path = room.get_path().clone();
+    path.replace(&room_path, "")
+}
+
 /// Convert backslash to slash.
 ///
 /// # Arguments