UDP Dgram ERR_SOCKET_CANNOT_SEND #2484

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1. bnoordhuis commented on Feb 25, 2020

   

   bnoordhuis

   on Feb 25, 2020

   Member

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   You're trying to send data before the socket has been bound. Node tries to do that implicitly for you but the operation fails, presumably because either the address is already in use or because the bind address is wrong.

   Either way, you should get a more legible error when you move the server.send(...) call inside your server.on("listening", ...) event listener. Right now, that ERR_SOCKET_CANNOT_SEND is masquerading the real error.

   cc @cjihrig I see you added that in nodejs/node@5587ff1ccd9. It might be better to forward the original listen error?
2. cjihrig commented on Feb 25, 2020

   

   cjihrig

   on Feb 25, 2020

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   cc @cjihrig I see you added that in nodejs/node@5587ff1. It might be better to forward the original listen error?

   That commit is over three years old, so I don't recall if I had any reason for implementing it that way, but it makes sense now to forward the original error.
3. Luuccc commented on Feb 25, 2020

   

   Luuccc

   on Feb 25, 2020

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   You're trying to send data before the socket has been bound. Node tries to do that implicitly for you but the operation fails, presumably because either the address is already in use or because the bind address is wrong.

   Either way, you should get a more legible error when you move the server.send(...) call inside your server.on("listening", ...) event listener. Right now, that ERR_SOCKET_CANNOT_SEND is masquerading the real error.

   Thanks, I've tried nesting the event calls, and adding the connect event, which no-longer throws an error. When a successful connection occurs, the correct address is given, but it doesn't listen to the same ip/port.

   As well as throwing an error on sending a message, which I couldn't find a reference to.

   const dgram = require('dgram');
   const buffer = require("buffer");
   const server = dgram.createSocket('udp4');
   
   var item = "Message";
   var hostIP = "127.0.0.1";
   var hostPort = 45239;
   
   server.connect(hostPort,hostIP,function(){
       var info = server.address();
       console.log("Connected to " + info.address + ":" + info.port);
   });
   
   server.on("message", function(message, info){
       console.log(info.address + ':' + info.port +' - ' + message);
   });
   
   server.on("listening", function(){
       var info = server.address();
       console.log("Server listening to "  + info.address + ":" + info.port);
       server.send(Buffer.from(item),hostPort,hostIP,function(error){
           if (error){
               console.log(error);
               server.close();
           }else{
               console.log("Data sent");
           }
       });
   });
   

   Output

   Server listening to 0.0.0.0:52870
   Connected to 127.0.0.1:52870
   Error: send EISCONN 127.0.0.1:45239
       at doSend (dgram.js:697:16)
       at defaultTriggerAsyncIdScope (internal/async_hooks.js:311:12)
       at afterDns (dgram.js:643:5)
       at processTicksAndRejections (internal/process/task_queues.js:85:21) {
     errno: 'EISCONN',
     code: 'EISCONN',
     syscall: 'send',
     address: '127.0.0.1',
     port: 45239
   }
   
4. Luuccc commented on Feb 27, 2020

   

   Luuccc

   on Feb 27, 2020

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   After trial and error, I ended up with this working script, sending a piece of data to a destination, and listening for its response. Where LOCAL_IP would normally be 192.168.X.Y , and HOST_IP being the destination IP.

   var LOCAL_IP = "XXX.XXX.XX.XX"
   var HOST_IP = "XX.XXX.XX.XXX";
   var PORT = 45239;
   
   var dgram = require("dgram");
   var client = dgram.createSocket("udp4");
   
   //Listen for repsonse locally
   client.on("listening", function(){
       var adrInfo = client.address();
       console.log("Client listening on "  + adrInfo.address + ":" + adrInfo.port);
       var text = Buffer.from("Message");
       client.send(text,PORT,HOST_IP,function(error){
           if (error){
               console.log(error);
           }else{
               console.log("Sent " + text);
           }
       });
       client.on("message", function(message, remote){
           console.log("Recieved response as: " + message + " from " + remote.address + ":" + remote.port);
       });
   });
   //On error event display error
   client.on('error',function(error){
       console.log('Error: ' + error);
       client.close();
   });
   
   //Binding to given location
   client.bind(PORT, LOCAL_IP);
   //Close socket after x ms
   setTimeout(function(){client.close();},8000);
5. Luuccc

   closed this as completedon Feb 27, 2020
6. cjihrig

   added 2 commits that reference this issue on Feb 28, 2020

   dgram: don't hide implicit bind errors

   ...

   1b2e294

   errors: remove unused ERR_SOCKET_CANNOT_SEND error

   ...

   331d636