name: golang-master
description: Golang language expert specializing in concurrency, performance optimization, standard library, and testing. Use when writing Go code, debugging concurrency issues, or optimizing performance.

Golang Language Expert

Expert assistant for Go language mastery including concurrency patterns, performance optimization, standard library usage, and testing strategies.

Thinking Process

When activated, follow this structured thinking approach to solve Go-related problems:

Step 1: Problem Classification

Goal: Understand what type of Go challenge this is.

Key Questions to Ask:
- Is this a concurrency problem? (goroutines, channels, race conditions)
- Is this a performance problem? (memory, CPU, allocations)
- Is this a design problem? (interfaces, struct composition, packages)
- Is this a debugging problem? (error tracing, unexpected behavior)
- Is this a testing problem? (unit tests, benchmarks, mocks)

Decision Point: Classify the problem to select appropriate patterns:
- Concurrency → Check for race conditions, proper synchronization
- Performance → Profile first, then optimize
- Design → Apply interface segregation, composition over inheritance
- Debugging → Trace error chain, check nil handling
- Testing → Table-driven tests, dependency injection

Step 2: Context Analysis

Goal: Understand the existing codebase context and constraints.

Key Questions to Ask:
- What Go version is being used? (generics require 1.18+)
- What is the module structure? (standard layout vs flat)
- What dependencies exist? (standard library vs third-party)
- Are there existing patterns to follow? (error handling style, logging approach)

Actions:
1. Check go.mod for Go version and dependencies
2. Scan existing code for established patterns
3. Identify any project-specific conventions

Step 3: Solution Design (Idiomatic Go)

Goal: Design a solution that follows Go best practices.

Thinking Framework - Apply These Principles:

1. Simplicity First
2. "Is there a simpler way to achieve this?"

3. Avoid over-engineering; Go favors explicitness

4. Error Handling

5. "What can fail here? How should failures propagate?"
6. Use fmt.Errorf("context: %w", err) for wrapping

7. Define custom error types for domain-specific errors

8. Concurrency Safety

9. "Is this data accessed from multiple goroutines?"
10. "Do I need a mutex, channel, or atomic operation?"

11. Prefer channels for coordination, mutexes for state protection

12. Interface Design

13. "What behavior is needed, not what data?"
14. Keep interfaces small (1-3 methods)

15. Accept interfaces, return concrete types

16. Resource Management

17. "What needs to be closed/cleaned up?"
18. Use defer for cleanup
19. Propagate context for cancellation

Step 4: Implementation with Patterns

Goal: Apply well-known Go patterns appropriately.

Pattern Selection Guide:

Decision Point: For each pattern, ask:
- "Why is this pattern appropriate for this problem?"
- "What are the edge cases I need to handle?"

Step 5: Testing Strategy

Goal: Ensure code correctness and maintainability.

Thinking Framework:
- "What are the happy paths to test?"
- "What edge cases could break this?"
- "Is this code testable? If not, how should I refactor?"

Testing Checklist:
1. Table-driven tests for functions with multiple input scenarios
2. Race detection for concurrent code (go test -race)
3. Benchmarks for performance-critical code
4. Mock interfaces for external dependencies

Step 6: Review and Refine

Goal: Ensure the solution is production-ready.

Final Checks:
- [ ] All errors are handled or explicitly ignored with comment
- [ ] Context is propagated through the call chain
- [ ] Resources are properly closed (defer, Close())
- [ ] No goroutine leaks (channels closed, contexts cancelled)
- [ ] Code is testable (dependencies injected)
- [ ] Documentation for exported symbols

Usage

Run Linters

bash /mnt/skills/user/golang-master/scripts/lint.sh [project-dir] [fix-mode]

Arguments:
- project-dir - Project directory (default: current directory)
- fix-mode - Set to true to auto-fix issues (default: false)

Examples:

bash /mnt/skills/user/golang-master/scripts/lint.sh
bash /mnt/skills/user/golang-master/scripts/lint.sh ./my-project true

Runs: go vet, gofmt, staticcheck, golangci-lint, go mod tidy

Run Benchmarks

bash /mnt/skills/user/golang-master/scripts/benchmark.sh [project-dir] [pattern] [profile-type]

Arguments:
- project-dir - Project directory (default: current directory)
- pattern - Benchmark pattern to match (default: .)
- profile-type - Profiling: none, cpu, mem, all (default: none)

Examples:

bash /mnt/skills/user/golang-master/scripts/benchmark.sh
bash /mnt/skills/user/golang-master/scripts/benchmark.sh . BenchmarkProcess cpu
bash /mnt/skills/user/golang-master/scripts/benchmark.sh ./myproject . all

Documentation Resources

Official Documentation:
- Go Docs: https://go.dev/doc/
- Effective Go: https://go.dev/doc/effective_go
- Go by Example: https://gobyexample.com/
- uber-go/guide: https://github.com/uber-go/guide

Concurrency Patterns

Worker Pool

func workerPool(jobs <-chan Job, numWorkers int) <-chan Result {
    results := make(chan Result, len(jobs))
    var wg sync.WaitGroup

    for i := 0; i < numWorkers; i++ {
        wg.Add(1)
        go func() {
            defer wg.Done()
            for job := range jobs {
                results <- process(job)
            }
        }()
    }

    go func() {
        wg.Wait()
        close(results)
    }()

    return results
}

Context with Timeout

func fetchWithTimeout(url string) ([]byte, error) {
    ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
    defer cancel()

    req, err := http.NewRequestWithContext(ctx, "GET", url, nil)
    if err != nil {
        return nil, err
    }

    resp, err := http.DefaultClient.Do(req)
    if err != nil {
        return nil, err
    }
    defer resp.Body.Close()

    return io.ReadAll(resp.Body)
}

Semaphore Pattern

type Semaphore struct {
    sem chan struct{}
}

func NewSemaphore(n int) *Semaphore {
    return &Semaphore{sem: make(chan struct{}, n)}
}

func (s *Semaphore) Acquire() { s.sem <- struct{}{} }
func (s *Semaphore) Release() { <-s.sem }

Error Handling

Wrapping Errors

func processUser(id int) error {
    user, err := fetchUser(id)
    if err != nil {
        return fmt.Errorf("failed to fetch user %d: %w", id, err)
    }

    if err := validateUser(user); err != nil {
        return fmt.Errorf("validation failed for user %d: %w", id, err)
    }

    return nil
}

Custom Error Types

type NotFoundError struct {
    Resource string
    ID       string
}

func (e *NotFoundError) Error() string {
    return fmt.Sprintf("%s not found: %s", e.Resource, e.ID)
}

// Usage
if errors.Is(err, &NotFoundError{}) {
    // Handle not found
}

Error Checking

// Use errors.Is for sentinel errors
if errors.Is(err, sql.ErrNoRows) {
    return nil, &NotFoundError{Resource: "user", ID: id}
}

// Use errors.As for error types
var netErr *net.OpError
if errors.As(err, &netErr) {
    // Handle network error
}

Performance Profiling

CPU Profiling

# Run benchmark with CPU profile
go test -cpuprofile=cpu.prof -bench=.
go tool pprof cpu.prof

# Interactive commands
(pprof) top10
(pprof) web
(pprof) list FunctionName

Memory Profiling

# Run benchmark with memory profile
go test -memprofile=mem.prof -bench=.
go tool pprof -alloc_space mem.prof

# Check for allocations
go build -gcflags='-m' ./...

Benchmark Example

func BenchmarkProcess(b *testing.B) {
    data := setupTestData()
    b.ResetTimer()

    for i := 0; i < b.N; i++ {
        process(data)
    }
}

func BenchmarkProcessParallel(b *testing.B) {
    data := setupTestData()
    b.ResetTimer()

    b.RunParallel(func(pb *testing.PB) {
        for pb.Next() {
            process(data)
        }
    })
}

Testing Patterns

Table-Driven Tests

func TestAdd(t *testing.T) {
    tests := []struct {
        name     string
        a, b     int
        expected int
    }{
        {"positive", 2, 3, 5},
        {"negative", -1, -2, -3},
        {"zero", 0, 0, 0},
    }

    for _, tt := range tests {
        t.Run(tt.name, func(t *testing.T) {
            result := Add(tt.a, tt.b)
            if result != tt.expected {
                t.Errorf("Add(%d, %d) = %d; want %d",
                    tt.a, tt.b, result, tt.expected)
            }
        })
    }
}

Present Results to User

When providing Go solutions:
- Use idiomatic Go patterns
- Always handle errors explicitly
- Include context propagation
- Provide test examples
- Note Go version requirements (generics: 1.18+)

Troubleshooting

"Data race detected"
- Use go test -race to find races
- Protect shared state with mutex
- Consider channels for communication

"Goroutine leak"
- Ensure channels are closed
- Use context for cancellation
- Check for blocking operations

"High memory usage"
- Profile with pprof
- Check for slice capacity issues
- Look for map accumulation