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Clavin June
Clavin June

Posted on • Originally published at clavinjune.dev on

Listening to Random Available Port in Go

#go #network #beginners

Photo by @mbaumi on Unsplash

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 ...
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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) }
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Execute it:

$ go run main.go 2022/01/04 17:40:16 listening at 33845
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Thank you for reading!

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