UDP Server send consecutive back to client

[Tuan Nguyen]

Hi everybody
I'm try to setup a simple UDP server-client, so far, i can send msg and get response from server.
However, i want to server to keep track of client and send data whenever it wants. Since UDP is connection-less, so i keep the Socketaddress from datagrampacket.

@Override
protected void channelRead0(ChannelHandlerContext ctx, DatagramPacket packet) throws Exception {
    System.out.println(packet.sender().toString());
}

But from here, how can i setup an system to send data to client through socketaddress?
Thanks

[Alexander Gehret]

As I understand it you just want to send Data? :) Then you can just use
ctx.writeandflush()

Or did I get anything wrong and udp is handled different from tcp?

[Alexander Gehret]

Otherwise I guess you could just send something like this

channel.write(new NettyElementInfo(), 
                new InetSocketAddress("255.255.255.255", 9555));

(and replace the broadcast adress of course with your correct destination address)

[Tuan Nguyen]

Thank for your reply Alexander
The ChannelContextHandler only available when server receive msg from client, and i can use it to write msg back to client, ofc.
However, when want to tell client about some update information, i don't know how to do it.

What you suggest here is create a new Channel to send data? Can you give me some snippet code please?  Thanks

[THUFIR HAWAT]

you have:

@Override
protected void channelRead0(ChannelHandlerContext ctx, DatagramPacket packet) throws Exception {
System.out.println(packet.sender().toString());
}

in your handler.

why don't you create new datagram as described in a previous post?

private DatagramPacket getNext(String host, int port) {
DatagramPacket packet = new DatagramPacket(
Unpooled.copiedBuffer("QOTM?", CharsetUtil.UTF_8),
new InetSocketAddress(host, port));
return packet;
}

and then your handler can just write it to wherever you like. This is adapted from the handler for the QOTM (Quote of the Moment):

https://github.com/netty/netty/tree/master/example/src/main/java/io/netty/example

while it's from the client handler, it could just as easily go in your server handler.

-Thufir

[Tuan Nguyen]

THUFIR, Thank for your reply
Yes, i can create a new DatagramPacket with the InetAddress i got, however, i confuse with the way to send it back to client WITHOUT ChannelHandlerContext. Since i want to send data back to client whenever i want, not when i get a msg.

Btw, is this group take too much to get approve post?

[Alexander Gehret]

You could as well just save the ctx in something like an array or
hashmap, like "connected clients" and then use all ctx to write back to
each client.

[THUFIR HAWAT]

The QOTM server sends a datagram, outside of the handler. HTH