How can I start the browser AFTER the server started listening?

Question

In Go, how can I start the browser AFTER the server started listening?

Preferably the simplest way possible.

My code so far, super dumbed down to the point:

package main

import (  
    // Standard library packages
    "fmt"
    "net/http"
    "github.com/skratchdot/open-golang/open"
    // Third party packages
    "github.com/julienschmidt/httprouter"
)


// go get github.com/toqueteos/webbrowser

func main() {  
    // Instantiate a new router
    r := httprouter.New()

    // Add a handler on /test
    r.GET("/test", func(w http.ResponseWriter, r *http.Request, _ httprouter.Params) {
        // Simply write some test data for now
        fmt.Fprint(w, "Welcome!\n")
    })
    
    //open.Run("https://google.com/")
     
    // open.Start("https://google.com")

    // http://127.0.0.1:3000/test
    // Fire up the server
    http.ListenAndServe("localhost:3000", r)
    fmt.Println("ListenAndServe is blocking")  
    open.RunWith("http://localhost:3000/test", "firefox")  
    fmt.Println("Done")
}

Answer 1

Open the listener, start the browser and then enter the server loop:

l, err := net.Listen("tcp", "localhost:3000")
if err != nil {
    log.Fatal(err)
}

// The browser can connect now because the listening socket is open.

err := open.Start("http://localhost:3000/test")
if err != nil {
     log.Println(err)
}

// Start the blocking server loop.

log.Fatal(http.Serve(l, r)) 

There's no need to poll as shown in another answer. The browser will connect if the listening socket is open before the browser is started.

ListenAndServe is a convenience function that opens a socket and calls Serve. The code in this answer splits out these steps so the browser can be opened after listening starts but before the blocking call to Serve.