Implementing the Service

In this step you will generate code and implement the calculator service.

1. Generate code

go install goa.design/goa/v3/cmd/goa@latest
goa gen jsonrpccalc/design

This generates server and client code for JSON‑RPC over HTTP (and SSE if your methods use streaming results). For WebSocket streaming, see the JSON‑RPC concepts section.

2. Implement service logic

Create cmd/server/main.go and implement the Add method in the generated service package. The implementation mirrors the REST/gRPC tutorials.

Example minimal server wiring:

// cmd/server/main.go
package main

// Import generated packages for your service and the generated JSON‑RPC HTTP server.
// The exact import paths depend on your module name and service name.

type calcSvc struct{}

// Implement the generated interface method.
// func (calcSvc) Add(ctx context.Context, p *calc.AddPayload) (*calc.AddResult, error) {
//     return &calc.AddResult{Sum: p.A + p.B}, nil
// }

func main() {
    // 1) Create the service implementation
    // 2) Build endpoints with the generated helper
    // 3) Mount the generated JSON‑RPC HTTP server on your mux
    // 4) Start the HTTP server on :8080
}

Notes on IDs and streaming (authoritative):

• Non‑streaming: If you don’t declare an ID() field, the framework still correlates responses using the request envelope id. Add ID("request_id", String) in the payload only if your handler needs to read the id value.
• SSE: SendAndClose sets the response envelope id to the result ID if set, otherwise to the original request id.
• WebSocket: bidirectional streaming uses a single connection per service; use StreamingPayload/StreamingResult and include ID() in both when you need typed correlation.

3. Run the server

Proceed to Running to start the server and call it over HTTP and SSE.