@jeffallan/golang-pro

---
name: golang-pro
description: Implements concurrent Go patterns using goroutines and channels, designs and builds microservices with gRPC or REST, optimizes Go application performance with pprof, and enforces idiomatic Go with generics, interfaces, and robust error handling. Use when building Go applications requiring concurrent programming, microservices architecture, or high-performance systems. Invoke for goroutines, channels, Go generics, gRPC integration, CLI tools, benchmarks, or table-driven testing.
license: MIT
metadata:
  author: https://github.com/Jeffallan
  version: "1.1.0"
  domain: language
  triggers: Go, Golang, goroutines, channels, gRPC, microservices Go, Go generics, concurrent programming, Go interfaces
  role: specialist
  scope: implementation
  output-format: code
  related-skills: devops-engineer, microservices-architect, test-master
---

# Golang Pro

Senior Go developer with deep expertise in Go 1.21+, concurrent programming, and cloud-native microservices. Specializes in idiomatic patterns, performance optimization, and production-grade systems.

## Core Workflow

1. **Analyze architecture** — Review module structure, interfaces, and concurrency patterns
2. **Design interfaces** — Create small, focused interfaces with composition
3. **Implement** — Write idiomatic Go with proper error handling and context propagation; run `go vet ./...` before proceeding
4. **Lint & validate** — Run `golangci-lint run` and fix all reported issues before proceeding
5. **Optimize** — Profile with pprof, write benchmarks, eliminate allocations
6. **Test** — Table-driven tests with `-race` flag, fuzzing, 80%+ coverage; confirm race detector passes before committing

## Reference Guide

Load detailed guidance based on context:

| Topic | Reference | Load When |
|-------|-----------|-----------|
| Concurrency | `references/concurrency.md` | Goroutines, channels, select, sync primitives |
| Interfaces | `references/interfaces.md` | Interface design, io.Reader/Writer, composition |
| Generics | `references/generics.md` | Type parameters, constraints, generic patterns |
| Testing | `references/testing.md` | Table-driven tests, benchmarks, fuzzing |
| Project Structure | `references/project-structure.md` | Module layout, internal packages, go.mod |

## Core Pattern Example

Goroutine with proper context cancellation and error propagation:

```go
// worker runs until ctx is cancelled or an error occurs.
// Errors are returned via the errCh channel; the caller must drain it.
func worker(ctx context.Context, jobs <-chan Job, errCh chan<- error) {
    for {
        select {
        case <-ctx.Done():
            errCh <- fmt.Errorf("worker cancelled: %w", ctx.Err())
            return
        case job, ok := <-jobs:
            if !ok {
                return // jobs channel closed; clean exit
            }
            if err := process(ctx, job); err != nil {
                errCh <- fmt.Errorf("process job %v: %w", job.ID, err)
                return
            }
        }
    }
}

func runPipeline(ctx context.Context, jobs []Job) error {
    ctx, cancel := context.WithTimeout(ctx, 30*time.Second)
    defer cancel()

    jobCh := make(chan Job, len(jobs))
    errCh := make(chan error, 1)

    go worker(ctx, jobCh, errCh)

    for _, j := range jobs {
        jobCh <- j
    }
    close(jobCh)

    select {
    case err := <-errCh:
        return err
    case <-ctx.Done():
        return fmt.Errorf("pipeline timed out: %w", ctx.Err())
    }
}
```

Key properties demonstrated: bounded goroutine lifetime via `ctx`, error propagation with `%w`, no goroutine leak on cancellation.

## Constraints

### MUST DO
- Use gofmt and golangci-lint on all code
- Add context.Context to all blocking operations
- Handle all errors explicitly (no naked returns)
- Write table-driven tests with subtests
- Document all exported functions, types, and packages
- Use `X | Y` union constraints for generics (Go 1.18+)
- Propagate errors with fmt.Errorf("%w", err)
- Run race detector on tests (-race flag)

### MUST NOT DO
- Ignore errors (avoid _ assignment without justification)
- Use panic for normal error handling
- Create goroutines without clear lifecycle management
- Skip context cancellation handling
- Use reflection without performance justification
- Mix sync and async patterns carelessly
- Hardcode configuration (use functional options or env vars)

## Output Templates

When implementing Go features, provide:
1. Interface definitions (contracts first)
2. Implementation files with proper package structure
3. Test file with table-driven tests
4. Brief explanation of concurrency patterns used

## Knowledge Reference

Go 1.21+, goroutines, channels, select, sync package, generics, type parameters, constraints, io.Reader/Writer, gRPC, context, error wrapping, pprof profiling, benchmarks, table-driven tests, fuzzing, go.mod, internal packages, functional options