Google Cloud: Get Cloud Run URL in Go

main.go

// $ gcloud run deploy --source .
package main

import (
	"context"
	"fmt"
	"log"
	"net/http"
	"os"
	"strings"
	"errors"

	"cloud.google.com/go/compute/metadata"
	"google.golang.org/api/option"
	"google.golang.org/api/run/v1"
)

func main() {
	log.Print("starting server...")
	http.HandleFunc("/", handler)

	// Determine port for HTTP service.
	port := os.Getenv("PORT")
	if port == "" {
		port = "8080"
		log.Printf("defaulting to port %s", port)
	}

	// Start HTTP server.
	log.Printf("listening on port %s", port)
	if err := http.ListenAndServe(":"+port, nil); err != nil {
		log.Fatal(err)
	}
}

func getCloudRunUrl(ctx context.Context) (string, error) {
	c := metadata.NewClient(nil)
	r, err := c.Get("instance/region")
	if err != nil {
		return "", err
	}
	// projects/{project_number}/regions/us-central1
	rs := strings.Split(r, "/")
	projectNumber := rs[1]
	region := rs[3]
	service := os.Getenv("K_SERVICE")
	if service == "" {
		return "", errors.New("K_SERVICE not set")
	}
	runService, err := run.NewService(ctx,
		option.WithEndpoint(fmt.Sprintf("https://%s-run.googleapis.com", region)))
	if err != nil {
		return "", err
	}
	name := fmt.Sprintf("namespaces/%s/services/%s", projectNumber, service)
	p, err := runService.Namespaces.Services.Get(name).Do()
	if err != nil {
		return "", err
	}
	return p.Status.Url, nil
}

func handler(w http.ResponseWriter, r *http.Request) {
	url, err := getCloudRunUrl(r.Context())
	if err != nil {
		http.Error(w, err.Error(), http.StatusInternalServerError)
		return
	}
	fmt.Fprintf(w, "Cloud Run URL: %s\n", url)
}