REBOL [ title: "UDP IP Broadcast/Receive for TCP Client/Server" date: 26-jan-2014 file: %udp-ip-for-tcp-client-server.r author: Nick Antonaccio purpose: { This script demonstrates a solution to a typical problem encountered with TCP network apps. A TCP server needs to be found at a known IP address. One solution is to configure your server machine with a static IP address in the router. This setup step is different for every router manufacturer, is often beyond the technical ability of the app user, the router may not be accessible due do to security concerns in an enterprise environment, etc. Another solution is to upload the server's current IP address to a server at a known URL (web server, FTP, etc. managed off site), but this just extends the problem to another network server, requires an Internet connection, etc. Another solution could potentially be to save the server IP address to a file on a mapped network drive, but this stills requires some configuration which may be out of the user's capability (mapping network drives to a folder on the server machine, on each client computer). A crude solution for simple applications could be to manually enter the IP address of the server (i.e., Joe yells to John down the hall "the server IP address is 192.168.1.10"). This example demonstrates a consistently usable solution for all TCP apps. It creates two separate scripts which run on the client and server, to manage all server IP address updates. The %send-ip.r script runs on the server machine and continuously broadcasts the IP address over UDP. The %receive-ip.r script runs on the client, receives the current IP and writes it to a file. Because UDP is a broadcast protocol, no known IP addresses are required for this to work. Once the server script is running, the clients can all simply start and receive the current IP address being broadcast. This example includes a separate TCP chat app which simply reads the saved IP address and connects to the server. No other network configuration is required. To implement this routine in any TCP application, just run the %send-ip.r script on any server, run the %receive-ip.r script on any client(s), and you can read the %local-ip.r file in your client apps to connect to the current IP address of the server. } ] write %receive-ip.r {rebol [] net-in: open udp://:9905 print "waiting..." forever [ received: wait [net-in] probe join "Received: " trim/lines ip: copy received write %local-ip.r ip wait 2 ]} launch %receive-ip.r write %send-ip.r {rebol [] net-out: open/lines udp://255.255.255.255:9905 set-modes net-out [broadcast: on] print "Sending..." forever [ insert net-out form read join dns:// read dns:// wait 2 ]} launch %send-ip.r write %tcp-chat.r {rebol [title: "TCP-Chat"] view layout [ across q: btn "Serve"[focus g p: first wait open/lines tcp://:8 z: 1]text"OR" k: btn "Connect"[focus g p: open/lines rejoin[tcp:// i/text ":8"]z: 1] i: field form read %local-ip.r return ; read join dns:// read dns:// r: area rate 4 feel [engage: func [f a e][if a = 'time and value? 'z [ if error? try [x: first wait p] [quit] r/text: rejoin [x newline r/text] show r ]]] return g: field "Type message here [ENTER]" [insert p value focus face] ]} wait 2 launch %tcp-chat.r launch %tcp-chat.r