code: func PubSubHandler(ctx *router.Context) {
  	err := pubSubHandlerImpl(ctx.Context, ctx.Request)
  	if err != nil {
  		logging.Errorf(ctx.Context, "error while handling pubsub event")
  		errors.Log(ctx.Context, err)
  	}
  	if transient.Tag.In(err) {
  		// Transient errors are 500 so that PubSub retries them.
  		ctx.Writer.WriteHeader(http.StatusInternalServerError)
  		return
  	}
  	// No errors or non-transient errors are 200s so that PubSub does not retry
  	// them.
  	ctx.Writer.WriteHeader(http.StatusOK)
  }
docs: // PubSubHandler is a webhook that stores the builds coming in from pubsub.