Add test342: PubSub Go - Not works on GAE standard

The pubsub library is unsupported on GAE standard:

googleapis/google-cloud-go#702

Maybe I should try Python...

test342-gae_cron_pubsub/app.yaml

@@ -0,0 +1,12 @@
+runtime: go
+api_version: go1
+
+handlers:
+  - url: /topics
+    script: _go_app
+    secure: always
+
+  - url: /publish/.*
+    script: _go_app
+    login: admin
+    secure: always

test342-gae_cron_pubsub/cron.yaml

@@ -0,0 +1,4 @@
+cron:
+  - description: periodic event
+    url: /publish/periodic-1min
+    schedule: every 1 minutes

test342-gae_cron_pubsub/main.go

@@ -0,0 +1,85 @@
+package main
+
+import (
+	"fmt"
+	"net/http"
+	"time"
+
+	"cloud.google.com/go/pubsub"
+	"github.com/go-chi/chi"
+	"google.golang.org/api/iterator"
+	"google.golang.org/appengine"
+	"google.golang.org/appengine/log"
+)
+
+// The pubsub library does not work!
+// https://github.com/GoogleCloudPlatform/google-cloud-go/issues/702
+
+func main() {
+	r := chi.NewRouter()
+	r.Get("/topics", handleTopics)
+	r.Get("/publish/{topic}", handlePublish)
+	http.Handle("/", r)
+	appengine.Main()
+}
+
+func handleTopics(w http.ResponseWriter, r *http.Request) {
+	ctx := appengine.NewContext(r)
+
+	client, err := pubsub.NewClient(ctx, appengine.AppID(ctx))
+	if err != nil {
+		log.Errorf(ctx, "Failed to create client: %s", err)
+		http.Error(w, "", http.StatusInternalServerError)
+		return
+	}
+	defer client.Close()
+
+	w.WriteHeader(http.StatusOK)
+
+	it := client.Topics(ctx)
+	for {
+		t, err := it.Next()
+		if err == iterator.Done {
+			break
+		}
+		if err != nil {
+			log.Errorf(ctx, "Failed to list topics: %s", err)
+			return
+		}
+		fmt.Fprintln(w, t)
+	}
+}
+
+func handlePublish(w http.ResponseWriter, r *http.Request) {
+	ctx := appengine.NewContext(r)
+
+	client, err := pubsub.NewClient(ctx, appengine.AppID(ctx))
+	if err != nil {
+		log.Errorf(ctx, "Failed to create client: %s", err)
+		http.Error(w, "", http.StatusInternalServerError)
+		return
+	}
+	defer client.Close()
+
+	name := chi.URLParam(r, "topic")
+	topic := client.Topic(name)
+
+	topic.PublishSettings = pubsub.PublishSettings{
+		DelayThreshold: 100 * time.Millisecond,
+		CountThreshold: 1,
+		ByteThreshold:  1e6,
+		NumGoroutines:  1,
+		Timeout:        1 * time.Second,
+	}
+
+	msg := pubsub.Message{
+		Data: []byte(name),
+	}
+	if _, err := topic.Publish(ctx, &msg).Get(ctx); err != nil {
+		log.Errorf(ctx, "Failed to publish message: %s", err)
+		http.Error(w, "", http.StatusInternalServerError)
+		return
+	}
+
+	w.WriteHeader(http.StatusOK)
+}