Given a TCP server, how to get the connection domain address - go

Question

I have a simple TCP server and, when a client connects, I want to get the domain address used to connect:
package main
import (
"fmt"
"net"
"os"
)
const (
CONN_HOST = "localhost"
CONN_PORT = "3333"
CONN_TYPE = "tcp"
)
func main() {
// Listen for incoming connections.
l, err := net.Listen(CONN_TYPE, CONN_HOST+":"+CONN_PORT)
if err != nil {
fmt.Println("Error listening:", err.Error())
os.Exit(1)
}
// Close the listener when the application closes.
defer l.Close()
fmt.Println("Listening on " + CONN_HOST + ":" + CONN_PORT)
for {
// Listen for an incoming connection.
conn, err := l.Accept()
if err != nil {
fmt.Println("Error accepting: ", err.Error())
os.Exit(1)
}
// Handle connections in a new goroutine.
go handleRequest(conn)
}
}
// Handles incoming requests.
func handleRequest(conn net.Conn) {
// Make a buffer to hold incoming data.
buf := make([]byte, 1024)
// Read the incoming connection into the buffer.
_, err := conn.Read(buf)
if err != nil {
fmt.Println("Error reading:", err.Error())
}
// Send a response back to person contacting us.
conn.Write([]byte("Message received."))
// Close the connection when you're done with it.
conn.Close()
}
I tried debugging the conn net.Conn param but I can't find any reference to the domain address. Tried with http://test.127.0.0.1.xip.io:3333/ and I'm interested in getting test.127.0.0.1.xip.io somehow. Any ideas?

Answer 1

What you are trying to do is not possible with plain TCP. TCP works on plain IP-Addresses without domains.
To explain what is going on:
When you are establishing a connection to, e.g. example.com, first of all a DNS Lookup for example.com is done. In this case, the DNS Lookup would result in 93.184.216.34. You can read more about DNS here.
A TCP Connection with 93.184.216.34 is established after that, the original domain name is not sent with the request.
Because you sometimes need the original name the user was trying to connect to, some protocols send the domain name after connecting. HTTP for example does this via the Host header.
Maybe you can do something like that and require to send the original host first through your TCP Connection!