bible/kit/patterns/go-code-style/contract.md

Contract: Go Code Style and Project Conventions

Logging

See kit/patterns/go-logging/contract.md for full rules.

Summary: use slog, log to stdout/stderr (binary console), never to browser console.

Error Handling

Always wrap errors with context. Use fmt.Errorf("...: %w", err).

// CORRECT
if err := db.Save(&record).Error; err != nil {
    return fmt.Errorf("save component %s: %w", record.ID, err)
}

// WRONG — loses context
return err

• Never silently discard errors with _ in production paths.
• Return errors up the call stack; log at the handler/task boundary, not deep in service code.

Code Formatting

• Always run gofmt before committing. No exceptions.
• No manual alignment of struct fields or variable assignments.

HTTP Handler Structure

Handlers are thin. Business logic belongs in a service layer.

Handler   → validates input, calls service, writes response
Service   → business logic, calls repository
Repository → SQL queries only, returns domain types

• Handlers must not contain SQL queries.
• Services must not write HTTP responses.
• Repositories must not contain business rules.

Startup Sequence (Go web app)

1. Parse flags / load config
2. Connect to DB — fail fast if unavailable (see go-database contract)
3. Run migrations
4. Initialize services and background workers
5. Register routes
6. Start HTTP server

Never reverse steps 2 and 5. Never start serving before migrations complete.

Configuration

• Config lives in a single config.yaml file, not scattered env vars.
• Env vars may override config values but must be documented.
• Never hardcode ports, DSNs, or file paths in application code.
• Provide a config.example.yaml committed to the repo.
• The actual config.yaml is gitignored.

Template / UI Rendering

• Server-rendered HTML via Go templates is the default.
• htmx for partial updates — no full SPA framework unless explicitly decided.
• Template errors must return 500 and log the error server-side.
• Never expose raw Go error messages to the end user in rendered HTML.

Business Logic Placement

• Threshold computation, status derivation, and scoring live on the server.
• The UI only reflects what the server returns — it does not recompute status client-side.
• Example: "critical / warning / ok" badge color is determined by the handler, not by JS.

Dependency Rules

• Prefer standard library. Add a dependency only when the stdlib alternative is significantly worse.
• Document the reason for each non-stdlib dependency in a comment or ADL entry.