To use a random available port in Golang, you can use :0. I believe the port 0 would works for another language as well as I tried in python.
$ python -m SimpleHTTPServer 0
Serving HTTP on 0.0.0.0 port 43481 ...
According to lifewire, port 0 is a non-ephemeral port that works as a wildcard that tells the system to find any available ports particularly in the Unix OS.
The Go Code
package main
import (
"log"
"net"
"net/http"
)
func createListener() (l net.Listener, close func()) {
l, err := net.Listen("tcp", ":0")
if err != nil {
panic(err)
}
return l, func() {
_ = l.Close()
}
}
func main() {
l, close := createListener()
defer close()
http.Handle("/", http.HandlerFunc(func(rw http.ResponseWriter, r *http.Request) {
// handle like normal
}))
log.Println("listening at", l.Addr().(*net.TCPAddr).Port)
http.Serve(l, nil)
}
Execute it:
$ go run main.go
2022/01/04 17:40:16 listening at 33845
Thank you for reading!
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