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Backend Development

Backend Development

Overview

In a Zenthyr app, your backend runs on the JVM and owns the application lifecycle. The frontend sends JSON messages to the backend, and your backend replies with JSON responses.

Project Structure

src/
└── <app-namespace>/
    └── main.clj      # Application entry point (`-main`)

Key Features

Handler-Based IPC

Your backend provides a :handler function to zenthyr/start-app!. Zenthyr calls it with the parsed JSON message (as a Clojure map with keyword keys). The handler returns a Clojure map that will be encoded back to JSON and delivered to the frontend.

(ns my-app.main
  (:gen-class)
  (:require [zenthyr.core :as zenthyr]))


(defonce state (atom {:count 0}))


(defn handler [{:keys [type] :as message}]
  (case type
    "counter/increment"
    (let [new-state (swap! state update :count inc)]
      {:count (:count new-state)})


    "counter/get"
    {:count (:count @state)}


    {:error (str "Unknown message type: " type)
     :message message}))


(defn -main [& _args]
  (zenthyr/start-app! {:handler handler}))

Development Workflow

Run the app from the project root:

Terminal window
lein run

Best Practices

  1. State Management
  2. Keep the handler total and explicit (return a clear error map for unknown messages)
  3. Keep messages JSON-friendly (strings, numbers, booleans, arrays, objects)
  4. Keep long-running work out of the UI thread (spawn work and respond when ready)

Next Steps