main.go

package main

import (
	"fmt"
	"log"
	"net/http"
	"os"
	"time"
)

func main() {
	addr := ":" + os.Getenv("PORT")
	http.HandleFunc("/", handle)
	log.Fatal(http.ListenAndServe(addr, nil))
}

func handle(w http.ResponseWriter, r *http.Request) {
	if err := r.ParseForm(); err != nil {
		http.Error(w, "Error parsing form.", http.StatusBadRequest)
		return
	}

	url := r.Form.Get("text")

	start := time.Now()
	_, err := http.Get(url)
	if err != nil {
		http.Error(w, "Error requesting URL.", http.StatusInternalServerError)
		return
	}

	w.Header().Set("Content-Type", "application/json")
	text := fmt.Sprintf("%s took %s", url, time.Since(start))
	jsonString := fmt.Sprintf(`
		{
			"response_type": "in_channel",
			"text": "%s"
		}
	`, text)
	fmt.Fprintf(w, jsonString)
}