This repository contains two small Express applications that were built during the second software training to explore how to move from a conventional HTTP REST style API to a JSON-RPC workflow and to review the surrounding technology stack.

• HTTP/: baseline Express API that exposes a simple greeting endpoint and a calculator over REST routes.
• JSONRPC/: follow-up implementation that accepts JSON-RPC 2.0 requests and returns JSON-RPC responses using lightweight request/response DTO classes.

├── HTTP
│   ├── controllers/v1/indexcontroller.js   # "hello" style POST endpoint: multiplies two numbers
│   ├── controllers/v1/calculatorcontroller.js   # add/sub/mul/div REST calculator
│   └── index.js   # Express bootstrap (port 3000)
├── JSONRPC
│   ├── controllers/jsonrpc-controller.js   # Single JSON-RPC entry point
│   ├── dto/jsonrpc-request.js              # JSON-RPC request DTO
│   ├── dto/jsonrpc-response.js             # JSON-RPC response DTO
│   └── index.js                            # Express bootstrap (port 3000)
└── README.md

Each folder keeps its own package.json and node_modules. Run one server at a time because both default to port 3000.

• Node.js 20+ (LTS is recommended)
• npm (ships with Node.js)

cd HTTP
npm install
node index.js

Example requests:

curl -X POST http://localhost:3000/v1 \
  -H "Content-Type: application/json" \
  -d '{"x": 2, "y": 3}'

curl -X POST http://localhost:3000/v1/calc/add \
  -H "Content-Type: application/json" \
  -d '{"a": 10, "b": 4}'

curl -X POST http://localhost:3000/v1/calc/div \
  -H "Content-Type: application/json" \
  -d '{"a": 10, "b": 0}'    # returns validation error

Key points:

• Standard Express routers map to resource-style paths.
• Request bodies use native JSON and are validated inline.
• Responses are classic REST JSON payloads ({ result, message }).

cd JSONRPC
npm install
node index.js

Send JSON-RPC 2.0 payloads to POST http://localhost:3000/jsonrpc:

curl -X POST http://localhost:3000/jsonrpc \
  -H "Content-Type: application/json" \
  -d '{
    "jsonrpc": "2.0",
    "method": "calc.add",
    "params": {"a": 10, "b": 4},
    "id": 1
  }'

Expected response shape:

{
  "jsonrpc": "2.0",
  "id": 1,
  "result": "calc.add has been called",
  "error": null
}

This controller simply echoes the method name and illustrates how to structure JSON-RPC requests and responses. Extend jsonrpc-controller.js to dispatch on method and apply your own domain logic.

• Express 5: HTTP transport layer. Even in JSON-RPC mode we still receive HTTP POST requests; Express handles routing and JSON body parsing.
• Manual DTOs (dto/jsonrpc-request.js, dto/jsonrpc-response.js): Keep the JSON-RPC 2.0 envelope consistent and decouple transport-specific logic from business handlers.
• JSON-RPC 2.0 Specification: Defines jsonrpc, method, params, id, result, and error fields. Requests and responses are plain JSON objects sent over HTTP.
• Transition Considerations: When migrating from REST to JSON-RPC, design a dispatcher that maps method strings to handlers, reuse validation from the REST version, and ensure clients can handle both success and error envelopes.

• Implement actual calculator logic inside the JSON-RPC controller, mirroring what exists in the REST example.
• Add automated tests (e.g., Jest or supertest) to confirm both REST and JSON-RPC endpoints behave as expected.
• Introduce a small client or Postman collection to demonstrate the request formats used in the exercise.

Happy experimenting!