Registering socket connection with Node.js tcp server

Question

Say I have a Node.js tcp server:

const map = new Map();

const s = net.createServer(function(socket){

     socket.pipe(jsonParser()).on('data', function(v){
        v && v.pid && map.set(v.pid, socket);
     }):
});

I connect to it using Bash like so:

exec 3<>/dev/tcp/localhost/9091  # persistent file descriptor

exit_code=$?

if [[ ${exit_code} -ne 0 ]]; then
   echo "could not connect to daemon";
   exit;
fi

echo "{\"pid\":${BASH_PID},\"args\":[${ARGS}],\"cwd\":\"$(pwd)\"}"  >&3

my question is - do I have to wait for the first message from the socket to know more information about the socket? Or is there some way to get the information upon first connection, without having to listen to data being written to/from the socket?

"information about the socket"? What is that? What information are you trying to get? — jfriend00
– jfriend00, Commented Apr 20, 2018 at 19:05
the information that's in the bash echo statement, the pid that it's connecting from, pwd, etc. — Alexander Mills
– Alexander Mills, Commented Apr 20, 2018 at 19:05
@jfriend00 the nature of the original question is as follows: is the fastest way to register information with the server, is for the client to do: 1. try to make connection. 2. receive a message from the server that you are connected. 3. Then send the server a message with some data (such as username/password). — Alexander Mills
– Alexander Mills, Commented May 9, 2018 at 21:11
My question is simply if there is a faster way (single request) to "register/authenticate" with the server, something faster than steps 1,2,3 above. — Alexander Mills
– Alexander Mills, Commented May 9, 2018 at 21:12

jfriend00 · Accepted Answer · 2018-05-09 22:36:19Z

1

It appears your question is this: "What is the fastest way to register/authenticate with the TCP server if you're making up your own protocol"?

Establish TCP connection
Send authentication credentials
Receive response that indicates success or failure to authenticate

You do not have to wait for the server to send you something back after establishing the TCP connection (that's already been done internally at the TCP level - you don't have to have an application-level message after connection).

edited May 9, 2018 at 22:36

answered May 9, 2018 at 22:30

jfriend00

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4 Comments

Alexander Mills Over a year ago

Yeah I guess you can't include the creds with the connection request? (The first request).

jfriend00 Over a year ago

@AlexanderMills - With TCP you have to establish the transport before you can send application level data.

jfriend00 Over a year ago

@AlexanderMills - You could use UDP instead of TCP for your client and server and basically skip step 1. Of course, you accept some other compromises with UDP (such as delivery reliability, packet ordering, etc...).

Alexander Mills Over a year ago

thanks since you know about this, do you have thoughts on this related question? stackoverflow.com/questions/50262882/…

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