gceProject() golang function that implements multiple methods of determining the GCP project it is being run within

gceproject.go

package main

import (
	"context"
	"errors"
	"log"
	"os"
	"time"

	"golang.org/x/oauth2/google"
)

func main() {
	project, err := gceProject()
	if err != nil {
		log.Fatal(err)
	}
	log.Println(project)
}

// gceProject attempts to determine the GCE Project that it is running within.
// The controller needs this information because it is not available on any of the
// objects monitored by the controller (PV, PVC, nor PD).
//
// It looks for the project in the following order:
//   1. env var GOOGLE_PROJECT
//   2. APPLICATION_DEFAULT_CREDENTIALS - https://github.com/golang/oauth2/blob/HEAD/google/default.go#L61-L75
//     a. A JSON file whose path is specified by the GOOGLE_APPLICATION_CREDENTIALS environment variable.
//     b. A JSON file in a location known to the gcloud command-line tool.
//        On Windows, this is %APPDATA%/gcloud/application_default_credentials.json.
//        On other systems, $HOME/.config/gcloud/application_default_credentials.json.
//     c. On Google App Engine standard first generation runtimes (<= Go 1.9) it uses
//        the appengine.AccessToken function.
//     d. On Google Compute Engine, Google App Engine standard second generation runtimes
//        (>= Go 1.11), and Google App Engine flexible environment, it fetches
//        credentials from the metadata server.
func gceProject() (string, error) {
	// 1 - environment GOOGLE_PROJECT
	if project := os.Getenv("GOOGLE_PROJECT"); project != "" {
		log.Println("DEBUG: found project via environment") // you can remove this, or replace with your own logger
		return project, nil
	}

	// 2 - ADC: https://github.com/golang/oauth2/blob/HEAD/google/default.go#L61-L75
	ctx, cancel := context.WithTimeout(context.Background(), 3*time.Second)
	defer cancel()
	credentials, err := google.FindDefaultCredentials(ctx)
	if err == nil {
		if credentials.ProjectID != "" {
			log.Println("DEBUG: found project via APPLICATION_DEFAULT_CREDENTIALS") // you can remove this, or replace with your own logger
			return credentials.ProjectID, nil
		}
	}
	return "", errors.New("Unable to automatically determine Google Cloud Project. You must set the env var 'GOOGLE_PROJECT'")
}