new udp

Author: hnasr

19-udp/190-UDP-Server.js

@@ -1,15 +1,23 @@
 const dgram = require('dgram')
 const server = dgram.createSocket('udp4');
-
+ 
 server.on('message', (msg, rinfo) => {
   console.log(`server got: ${msg} from ${rinfo.address}:${rinfo.port}`); 
-  //we can send something back.
+  //we can send something back to the destination
+  //we write a udp datagram and set the destination ip/ port 
+  //notice it is called send and not write, because it is a whole message
+  server.send("hello client!", rinfo.port,  rinfo.address);
+  
 });
 
 server.on('listening', () => {
   const address = server.address();
   console.log(`server listening ${address.address}:${address.port}`);
 });
 
-server.bind(3333);
+
+server.bind(3333); 
+//use this to send a sample udp message
+echo "Hello UDP" | nc -u 127.0.0.1 3333
+
 // Prints: server listening 0.0.0.0:3333

19-udp/191-UDP-Client.js

@@ -1,20 +1,22 @@
-const dgram = require('dgram')
+const dgram = require('dgram');
+const { isTypedArray } = require('util/types');
 const client = dgram.createSocket('udp4');
 
 client.on('message', (msg, rinfo) => {
   console.log(`client got: ${msg} from ${rinfo.address}:${rinfo.port}`);
 });
+//this automatically binds to a random port, (can't send anything otherwise)
+client.send("hello server", 3333, "127.0.0.1")
 
-//optional but we can bind to a random port of our choice
-client.bind(55555);
-
-client.connect( 3333,"127.0.0.1", () => {
-  console.log ("server exists .. send something.. ")
-  //notice that its called send and not write 
-  //because it is not a stream of bytes ..but an actual unit (message) we send 
-  client.send("a whole message");
-});
+//optionally bind to a source port of your choosing
+//if you don't do that, kernel will pick one for you
+//client.bind(55555) 
 
+//technically if you know the clients bind source port anyone can send stuff to it ! 
+//try it
+////echo "Hello UDP" | nc -u 127.0.0.1 randomport
+client.on("error", (err) => console.log(err) )
+//a bind was successful! 
 client.on('listening', () => {
   const address = client.address();
   //this will keep reading

19-udp/192-UDP-Client-Persisted.js

@@ -0,0 +1,24 @@
+const dgram = require('dgram')
+const client = dgram.createSocket('udp4');
+
+client.on('message', (msg, rinfo) => {
+  console.log(`client got: ${msg} from ${rinfo.address}:${rinfo.port}`);
+});
+
+//optional but we can bind to a random port of our choice
+//client.bind(55555);
+
+client.connect( 3333,"127.0.0.1", () => {
+  console.log ("server exists .. send something.. ")
+  //notice that its called send and not write 
+  //because it is not a stream of bytes ..but an actual unit (message) we send 
+  client.send("a whole message");
+});
+
+client.on("error", (err) => console.log(err) )
+client.on('listening', () => {
+  const address = client.address();
+  //this will keep reading
+  console.log(`client listening ${address.address}:${address.port}`);
+});
+