How to send a message to a particular client with socket io

Question

I m starting with socket io   node js  I know how to send a message locally and to broadcast socket broadcast emit   function - all the connected clients receive the same message   Now  I would like to know how to send a private message to a particular client  I mean one socket for a private chat between 2 person  Client-To-Client stream   Thanks

User · Answer

In a project of our company we are using "rooms" approach and it's name is a combination of user ids of all users in a conversation as a unique identifier (our implementation is more like facebook messenger), example:

|id | name |1 | Scott |2 | Susan

"room" name will be "1-2" (ids are ordered Asc.) and on disconnect socket.io automatically cleans up the room

this way you send messages just to that room and only to online (connected) users (less packages sent throughout the server).

User · Answer

You can refer to socket io rooms   When you handshaked socket - you can join him to named room  for instance  user   userid      After that  you can send private message to any client by convenient name  for instance      io sockets in  user 125   emit  new message    text   Hello world       In operation above we send  new message  to user  125    thanks

User · Answer

As the az7ar answer is beautifully said but Let me make it simpler with socket io rooms  request a server with a unique identifier to join a server  here we are using an email as a unique identifier  Client Socket io socket on  connect   function        socket emit  join    email  user example com         When the user joined a server  create a room for that user Server Socket io io on  connection   function  socket       socket on  join   function  data            socket join data email              Now we are all set with joining  let emit something to from the server to room  so that user can listen  Server Socket io io to  user example com   emit  message    msg   hello world       Let finalize the topic with listening to message event to the client side socket on  quot message quot   function data      alert data msg        The reference from  Socket io rooms

User · Answer

When a user connects  it should send a message to the server with a username which has to be unique  like an email    A pair of username and socket should be stored in an object like this   var users          userA example com    socket object        userB example com    socket object        userC example com    socket object      On the client  emit an object to the server with the following data         to  the other receiver s username as a string       from  the person who sent the message as string       message  the message to be sent as string      On the server  listen for messages  When a message is received  emit the data to the receiver   users data to  emit  receivedMessage   data    On the client  listen for emits from the server called  receivedMessage   and by reading the data you can handle who it came from and the message that was sent

User · Answer

You can use socket io rooms  From the client side emit an event   join  in this case  can be anything  with any unique identifier  email  id    Client Side   var socket   io connect  http   localhost    socket emit  join    email  user1 example com      Now  from the server side use that information to create an unique room for that user  Server Side   var io   require  socket io   listen 80    io sockets on  connection   function  socket      socket on  join   function  data        socket join data email      We are using room of socket io             So  now every user has joined a room named after user s email  So if you want to send a specific user a message you just have to  Server Side   io sockets in  user1 example com   emit  new msg    msg   hello       The last thing left to do on the client side is listen to the  new msg  event   Client Side   socket on  new msg   function data        alert data msg       I hope you get the idea

User · Answer

SURE  Simply   This is what you need    io to socket id  emit  event   data     whenever a user joined to the server  socket details will be generated including ID  This is the ID really helps to send a message to particular people   first we need to store all the socket ids in array   var people      people name     socket id    here name is the receiver name  Example   people  ccccc   2387423cjhgfwerwer23    So  now we can get that socket id with the receiver name whenever we are sending message   for this we need to know the receivername  You need to emit receiver name to the server   final thing is    socket on  chat message   function data   io to people data receiver   emit  chat message   data msg         Hope this works well for you   Good Luck

User · Answer

Here is the full solution for Android Client   Socket IO Server   Lot of code but works    There seems to be lack of support  for Android and IOS when it comes to socket io which is a tragedy of sorts  Basically creating a room name by joining user unique id from mysql or mongo then sorting it  done in Android Client and sent to server    So each pair has a unique but common amongst the pair room name   Then just go about chatting in that room  For quick refernce how room is created in Android     Build The Chat Room         if  Integer parseInt mySqlUserId   lt  Integer parseInt toMySqlUserId                 room    quot ic quot    mySqlUserId   toMySqlUserId            else               room    quot ic quot    toMySqlUserId   mySqlUserId             The Full Works Package Json  quot dependencies quot          quot express quot    quot  4 17 1 quot        quot socket io quot    quot  2 3 0 quot          quot devDependencies quot          quot nodemon quot    quot  2 0 6 quot       Socket IO Server app   require  express     http   require  http   createServer app  io   require  socket io   http   app get       req  res    gt         res send  Chat server is running on port 5000       io on  connection    socket    gt            console log  one user connected     socket id           Join Chat Room     socket on  join   function data             console log        Joined Room                       console log data               Json Parse String To Access Child Elements         var messageJson   JSON parse data           const room   messageJson room          console log room            socket join room                    On Receiving Individual Chat Message  ic message      socket on  ic message   function data            console log        IC Message                       console log data               Json Parse String To Access Child Elements         var messageJson   JSON parse data           const room   messageJson room          const message   messageJson message           console log room           console log message               Sending to all clients in room except sender         socket broadcast to room  emit  new msg                 msg  message                           socket on  disconnect   function             console log  one user disconnected     socket id                 http listen 5000       gt         console log  Node app is running on port 5000       Android Socket IO Class public class SocketIOClient        public Socket mSocket                 try               mSocket   IO socket  quot http   192 168 1 5 5000 quot              catch  URISyntaxException e                throw new RuntimeException e                        public Socket getSocket             return mSocket           Android Activity public class IndividualChatSocketIOActivity extends AppCompatActivity           Activity Number For Bottom Navigation Menu     private final Context mContext   IndividualChatSocketIOActivity this          Strings     private String mySqlUserId      private String toMySqlUserId          Widgets     private EditText etTextMessage      private ImageView ivSendMessage          Socket IO     SocketIOClient socketIOClient   new SocketIOClient        private String room        Override     protected void onCreate  Nullable Bundle savedInstanceState            super onCreate savedInstanceState           setContentView R layout activity chat               Widgets         etTextMessage   findViewById R id a chat et text message           ivSendMessage   findViewById R id a chat iv send message               Get The MySql UserId from Shared Preference         mySqlUserId   StartupMethods getFromSharedPreferences  quot shared quot                                                                  quot id quot                                                                 mContext               Variables From Individual List Adapter         Intent intent   getIntent             if  intent hasExtra  quot to id quot                   toMySqlUserId   Objects requireNonNull Objects requireNonNull getIntent   getExtras                                                               get  quot to id quot                                        toString                          Build The Chat Room         if  Integer parseInt mySqlUserId   lt  Integer parseInt toMySqlUserId                 room    quot ic quot    mySqlUserId   toMySqlUserId            else               room    quot ic quot    toMySqlUserId   mySqlUserId                     connectToSocketIO             joinChat             leaveChat             getChatMessages             sendChatMessages                 Override     protected void onPause             super onPause                private void connectToSocketIO              socketIOClient mSocket   socketIOClient getSocket            socketIOClient mSocket on Socket EVENT CONNECT ERROR                                    onConnectError           socketIOClient mSocket on Socket EVENT CONNECT TIMEOUT                                    onConnectError           socketIOClient mSocket on Socket EVENT CONNECT                                    onConnect           socketIOClient mSocket on Socket EVENT DISCONNECT                                    onDisconnect           socketIOClient mSocket connect               private void joinChat                 Prepare To Send Data Through WebSockets         JSONObject jsonObject   new JSONObject                Header Fields         try                jsonObject put  quot room quot                              room                socketIOClient mSocket emit  quot join quot                                           String valueOf jsonObject               catch  JSONException e                e printStackTrace                          private void leaveChat                private void getChatMessages              socketIOClient mSocket on  quot new msg quot                                     new Emitter Listener                                            Override                                       public void call Object    args                                              try                                                 JSONObject messageJson   new JSONObject args 0  toString                                                   String message   String valueOf messageJson                                                  runOnUiThread new Runnable                                                        Override                                                   public void run                                                           Toast makeText IndividualChatSocketIOActivity this                                                                       message                                                                       Toast LENGTH SHORT                                                              show                                                                                                                                                      catch  JSONException e                                                  e printStackTrace                                                                                                                                         private void sendChatMessages              ivSendMessage setOnClickListener new View OnClickListener                  Override             public void onClick View v                     String message   etTextMessage getText                                                  toString                                                  trim                        Prepare To Send Data Thru WebSockets                 JSONObject jsonObject   new JSONObject                        Header Fields                 try                       jsonObject put  quot room quot                                      room                        jsonObject put  quot message quot                                      message                        socketIOClient mSocket emit  quot ic message quot                                                   String valueOf jsonObject                       catch  JSONException e                        e printStackTrace                                                            public Emitter Listener onConnect   new Emitter Listener              Override         public void call Object    args                 runOnUiThread new Runnable                      Override                 public void run                         Toast makeText IndividualChatSocketIOActivity this                                      quot Connected To Socket Server quot                                      Toast LENGTH SHORT                            show                                                    Log d  quot TAG quot                      quot Socket Connected  quot                          private Emitter Listener onConnectError   new Emitter Listener              Override         public void call Object    args                 runOnUiThread new Runnable                      Override                 public void run                                                             private Emitter Listener onDisconnect   new Emitter Listener              Override         public void call Object    args                 runOnUiThread new Runnable                      Override                 public void run                                                             Android Gradle    SocketIO implementation   io socket socket io-client 1 0 0            excluding org json which is provided by Android     exclude group   org json   module   json

[javascript] How to send a message to a particular client with socket.io

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