Go net.DialUDP auto-selecting loopback interface - go

Question

I have a need to send some UDP packets from eth0 on a host to itself, also on eth0.
I have some working Go code, but it appears to be using the loopback interface instead of eth0 as expected.
package main
import (
"net"
)
func main() {
ip := net.ParseIP("192.168.1.158")
src := net.UDPAddr{IP: ip, Port: 8888,}
dest := net.UDPAddr{IP: ip, Port: 88}
conn, _ := net.DialUDP("udp", &src, &dest)
conn.Write([]byte("hi"))
}
192.168.1.158 is the primary and only IP address for the interface on my machine.
Running the following command shows me the traffic:
sudo tcpdump udp -v -i lo
However, I would expect the traffic be to/from the system interface with the IP address I've defined.
Am I missing a step here?
I have also tried this slightly different approach, but with the same results:
src, _ := net.ResolveUDPAddr("udp", "192.168.1.158:8888")
dest, _ := net.ResolveUDPAddr("udp", "192.168.1.158:88")

Answer 1

However, I would expect the traffic be to/from the system interface with the IP address I've defined.
This is simply the wrong expectation and unrelated to Go.
Just try ping 192.168.1.158 and check with tcpdump -i lo -n icmp vs. tcpdump -i eth0 -n icmp where the data actually gets transferred. You will see that the packets are transferred on the lo interface. Similar a ip route get 192.168.1.158 will show you that the route to your local address goes through the lo interface.