Multiple clients and send messages to all clients

[DowranRowshenow]

By doing as strangerattractor said, in this issue Add Function to send messages to clients, the server can send a message to the client. But this will only send to the last connected client. As a rough solution, we can do it like this:

1. Add new List<TcpClient> variable to the WebSocketServer class like this:

    private List<TcpClient> connectedTcpClients;
   

2. Also add this line to the ListenForTcpConnection() function like this:

    connectedTcpClient = tcpListener.AcceptTcpClient();
    connectedTcpClients.Add(connectedTcpClient);
   

3. Change the SendMessageToClient() function in the Add Function to send messages to clients to this:

    public virtual void SendMessageToClient(string msg)
    {
        foreach (var client in connectedTcpClients)
        {
            NetworkStream stream = client.GetStream();
            Queue<string> que = new Queue<string>(msg.SplitInGroups(125));
            int len = que.Count;
   
            while (que.Count > 0)
            {
                var header = GetHeader(
                    que.Count > 1 ? false : true,
                    que.Count == len ? false : true
                );
   
                byte[] list = Encoding.UTF8.GetBytes(que.Dequeue());
                header = (header << 7) + list.Length;
                stream.Write(IntToByteArray((ushort)header), 0, 2);
                stream.Write(list, 0, list.Length);
            }   
        }
    }
   

This should work with multiple clients.

[wouterswim]

Updated to also remove clients from the List when they are no longer connected...

public virtual void SendMessageToClient(string msg)
        {
            foreach (var client in connectedTcpClients)
            { 
                if (!client.Connected)
                {
                    connectedTcpClients.Remove(client);
                }
                NetworkStream stream = client.GetStream();
                Queue<string> que = new Queue<string>(msg.SplitInGroups(125));
                int len = que.Count;

                while (que.Count > 0)
                {
                    var header = GetHeader(
                        que.Count > 1 ? false : true,
                        que.Count == len ? false : true
                    );

                    byte[] list = Encoding.UTF8.GetBytes(que.Dequeue());
                    header = (header << 7) + list.Length;
                    stream.Write(IntToByteArray((ushort)header), 0, 2);
                    stream.Write(list, 0, list.Length);
                }
            }
        }

[zaxaco]

Change the following line:

private List<TcpClient> connectedTcpClients;

to this:

private List<TcpClient> connectedTcpClients = new();

[MrDChristop]

The removal of an item inside a foreach loop throws a Collection was modified; enumeration operation may not execute. exception.
Remove this if statement block inside the loop

 if (!client.Connected)
 {
      connectedTcpClients.Remove(client);
  }

Place this elegant alternative before the loop

connectedTcpClients.RemoveAll(item => !item.Connected);

Here it is all together

public virtual void SendMessageToClients(string msg)
        {
            connectedTcpClients.RemoveAll(item => !item.Connected);

            foreach (var client in connectedTcpClients)
            {
                    NetworkStream stream = client.GetStream();
                    Queue<string> que = new Queue<string>(msg.SplitInGroups(125));
                    int len = que.Count;

                    while (que.Count > 0)
                    {
                        var header = GetHeader(
                            que.Count > 1 ? false : true,
                            que.Count == len ? false : true
                        );

                        byte[] list = Encoding.UTF8.GetBytes(que.Dequeue());
                        header = (header << 7) + list.Length;
                        stream.Write(IntToByteArray((ushort)header), 0, 2);
                        stream.Write(list, 0, list.Length);
                    }
                }
            }

Updated to also remove clients from the List when they are no longer connected...

public virtual void SendMessageToClient(string msg)
        {
            foreach (var client in connectedTcpClients)
            { 
                if (!client.Connected)
                {
                    connectedTcpClients.Remove(client);
                }
                NetworkStream stream = client.GetStream();
                Queue<string> que = new Queue<string>(msg.SplitInGroups(125));
                int len = que.Count;

                while (que.Count > 0)
                {
                    var header = GetHeader(
                        que.Count > 1 ? false : true,
                        que.Count == len ? false : true
                    );

                    byte[] list = Encoding.UTF8.GetBytes(que.Dequeue());
                    header = (header << 7) + list.Length;
                    stream.Write(IntToByteArray((ushort)header), 0, 2);
                    stream.Write(list, 0, list.Length);
                }
            }
        }

[Bian-Sh]

The removal of an item inside a foreach loop throws a Collection was modified; enumeration operation may not execute. exception. Remove this if statement block inside the loop

 if (!client.Connected)
 {
      connectedTcpClients.Remove(client);
  }

Place this elegant alternative before the loop

connectedTcpClients.RemoveAll(item => !item.Connected);

Here it is all together

public virtual void SendMessageToClients(string msg)
        {
            connectedTcpClients.RemoveAll(item => !item.Connected);

            foreach (var client in connectedTcpClients)
            {
                    NetworkStream stream = client.GetStream();
                    Queue<string> que = new Queue<string>(msg.SplitInGroups(125));
                    int len = que.Count;

                    while (que.Count > 0)
                    {
                        var header = GetHeader(
                            que.Count > 1 ? false : true,
                            que.Count == len ? false : true
                        );

                        byte[] list = Encoding.UTF8.GetBytes(que.Dequeue());
                        header = (header << 7) + list.Length;
                        stream.Write(IntToByteArray((ushort)header), 0, 2);
                        stream.Write(list, 0, list.Length);
                    }
                }
            }

Updated to also remove clients from the List when they are no longer connected...

public virtual void SendMessageToClient(string msg)
        {
            foreach (var client in connectedTcpClients)
            { 
                if (!client.Connected)
                {
                    connectedTcpClients.Remove(client);
                }
                NetworkStream stream = client.GetStream();
                Queue<string> que = new Queue<string>(msg.SplitInGroups(125));
                int len = que.Count;

                while (que.Count > 0)
                {
                    var header = GetHeader(
                        que.Count > 1 ? false : true,
                        que.Count == len ? false : true
                    );

                    byte[] list = Encoding.UTF8.GetBytes(que.Dequeue());
                    header = (header << 7) + list.Length;
                    stream.Write(IntToByteArray((ushort)header), 0, 2);
                    stream.Write(list, 0, list.Length);
                }
            }
        }

In the provided code, attempting to remove elements from the connectedTcpClients collection while iterating over it using a foreach loop will result in an InvalidOperationException with the message:

System.InvalidOperationException: Collection was modified; enumeration operation may not execute.

This exception occurs because modifying a collection during iteration invalidates the enumerator, leading to runtime errors.