Go service that reads Google Cloud Storage objects

function.go

package goportable

import (
	"encoding/json" //encoding the response
	"log"           //writing logs
	"net/http"
	"strings" //flattening an array

	"cloud.google.com/go/storage"                                     //talking to cloud storage
	"github.com/GoogleCloudPlatform/functions-framework-go/functions" //go middleware
	"google.golang.org/api/iterator"                                  //looping through objects
)

func init() {
	functions.HTTP("ReadFiles", readFiles)
}

// readFiles is an HTTP Cloud Function with a request parameter.
func readFiles(w http.ResponseWriter, r *http.Request) {

	log.Printf("called the API!")

	//grab querystring param, if empty, set to default value
	bucketname := r.URL.Query().Get("bucketname")
	if bucketname == "" {
		bucketname = "seroter-app-files"
	}

	//grab context
	ctx := r.Context()
	//instantiate storage client
	client, err := storage.NewClient(ctx)
	if err != nil {
		log.Printf("error happened!")
	}

	defer client.Close()

	//reference a specific bucket
	bkt := client.Bucket(bucketname)

	//query for all files in the selected bucket
	query := &storage.Query{Prefix: ""}
	var names []string
	it := bkt.Objects(ctx, query)
	for {
		attrs, err := it.Next()
		if err == iterator.Done {
			break
		}
		if err != nil {
			log.Fatal(err)
		}
		names = append(names, attrs.Name)
	}

	//log the names of retrieved files
	log.Printf("Files returned: %s", names)

	//create a response map that'll convert to a flat JSON payload
	response := make(map[string]string)
	response["files"] = strings.Join(names, " , ")
	jsonResponse, _ := json.Marshal(response)

	w.Write(jsonResponse)
}