// Package contexttip is an example of how to use Pub/Sub and context.Context in
// a Cloud Function.
package contexttip
import (
"context"
"encoding/json"
"fmt"
"log"
"net/http"
"os"
"cloud.google.com/go/pubsub"
)
// GOOGLE_CLOUD_PROJECT is a user-set environment variable.
var projectID = os.Getenv("GOOGLE_CLOUD_PROJECT")
// client is a global Pub/Sub client, initialized once per instance.
var client *pubsub.Client
func init() {
// err is pre-declared to avoid shadowing client.
var err error
// client is initialized with context.Background() because it should
// persist between function invocations.
client, err = pubsub.NewClient(context.Background(), projectID)
if err != nil {
log.Fatalf("pubsub.NewClient: %v", err)
}
}
type publishRequest struct {
Topic string `json:"topic"`
Message string `json:"message"`
}
// PublishMessage publishes a message to Pub/Sub. PublishMessage only works
// with topics that already exist.
func PublishMessage(w http.ResponseWriter, r *http.Request) {
// Parse the request body to get the topic name and message.
p := publishRequest{}
if err := json.NewDecoder(r.Body).Decode(&p); err != nil {
log.Printf("json.NewDecoder: %v", err)
http.Error(w, "Error parsing request", http.StatusBadRequest)
return
}
if p.Topic == "" || p.Message == "" {
s := "missing 'topic' or 'message' parameter"
log.Println(s)
http.Error(w, s, http.StatusBadRequest)
return
}
m := &pubsub.Message{
Data: []byte(p.Message),
}
// Publish and Get use r.Context() because they are only needed for this
// function invocation. If this were a background function, they would use
// the ctx passed as an argument.
id, err := client.Topic(p.Topic).Publish(r.Context(), m).Get(r.Context())
if err != nil {
log.Printf("topic(%s).Publish.Get: %v", p.Topic, err)
http.Error(w, "Error publishing message", http.StatusInternalServerError)
return
}
fmt.Fprintf(w, "Message published: %v", id)
}
