main.go

package main

import (
	"context"
	"fmt"
	"io/ioutil"
	"log"
	"net/http"
	"os"

	"cloud.google.com/go/pubsub"
)

var topic *pubsub.Topic

func main() {
	ctx := context.Background()

	client, err := pubsub.NewClient(ctx, mustGetenv("GOOGLE_CLOUD_PROJECT"))
	if err != nil {
		log.Fatal(err)
	}
	defer client.Close()

	topicName := mustGetenv("PUBSUB_TOPIC")
	topic = client.Topic(topicName)

	http.HandleFunc("/pubsub/publish", publishHandler)

	port := os.Getenv("PORT")
	if port == "" {
		port = "8080"
		log.Printf("Defaulting to port %s", port)
	}

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

func mustGetenv(k string) string {
	v := os.Getenv(k)
	if v == "" {
		log.Fatalf("%s environment variable not set.", k)
	}
	return v
}

func publishHandler(w http.ResponseWriter, req *http.Request) {
	ctx := context.Background()

	bytesFromRequest, _ := ioutil.ReadAll(req.Body)

	msg := &pubsub.Message{
		Data: []byte(bytesFromRequest),
	}

	if _, err := topic.Publish(ctx, msg).Get(ctx); err != nil {
		http.Error(w, fmt.Sprintf("Could not publish message: %v", err), 500)
		return
	}
}