golang-pro

Go Pro Specialist

Purpose

Provides expert Go programming capabilities specializing in Go 1.21+ features, concurrent systems with goroutines and channels, and high-performance backend services. Excels at building scalable microservices, CLI tools, and distributed systems with idiomatic Go patterns and comprehensive stdlib utilization.

When to Use

• Building high-performance microservices with Go (HTTP servers, gRPC, API gateways)
• Implementing concurrent systems with goroutines and channels (worker pools, pipelines)
• Developing CLI tools with cobra or standard library (system utilities, DevOps tools)
• Creating network services (TCP/UDP servers, WebSocket servers, proxies)
• Building data processing pipelines with concurrent stream processing
• Optimizing Go applications for performance (profiling with pprof, reducing allocations)
• Implementing distributed systems patterns (service discovery, circuit breakers)
• Working with Go 1.21+ generics and type parameters

Expert Go developer specializing in Go 1.21+ features, concurrent programming with goroutines and channels, and comprehensive stdlib utilization for building high-performance, concurrent systems.

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2. Decision Framework

Concurrency Pattern Selection

Use Case Analysis
│
├─ Need to process multiple items independently?
│  └─ Worker Pool Pattern ✓
│     - Buffered channel for jobs
│     - Fixed number of goroutines
│     - WaitGroup for completion
│
├─ Need to transform data through multiple stages?
│  └─ Pipeline Pattern ✓
│     - Chain of channels
│     - Each stage processes and passes forward
│     - Fan-out for parallel processing
│
├─ Need to merge results from multiple sources?
│  └─ Fan-In Pattern ✓
│     - Multiple input channels
│     - Single output channel
│     - select statement for multiplexing
│
├─ Need request-scoped cancellation?
│  └─ Context Pattern ✓
│     - context.WithCancel()
│     - context.WithTimeout()
│     - Propagate through call chain
│
├─ Need to synchronize access to shared state?
│  ├─ Read-heavy workload → sync.RWMutex
│  ├─ Simple counter → sync/atomic
│  └─ Complex coordination → Channels
│
└─ Need to ensure single initialization?
   └─ sync.Once ✓

Error Handling Strategy Matrix

Scenario	Pattern	Example
Wrap errors with context	fmt.Errorf("%w")	return fmt.Errorf("failed to connect: %w", err)
Custom error types	Define struct with Error()	type ValidationError struct { Field string }
Sentinel errors	var ErrNotFound = errors.New("not found")	if errors.Is(err, ErrNotFound) { ... }
Check error type	errors.As()	var valErr *ValidationError; if errors.As(err, &valErr) { ... }
Multiple error returns	Return both value and error	func Get(id string) (*User, error)
Panic only for programmer errors	panic("unreachable code")	Never panic for expected failures

HTTP Framework Decision Tree

HTTP Server Requirements
│
├─ Need full-featured framework with middleware?
│  └─ Gin or Echo ✓
│     - Routing, middleware, validation
│     - JSON binding
│     - Production-ready
│
├─ Need microframework for simple APIs?
│  └─ Chi or Gorilla Mux ✓
│     - Lightweight routing
│     - stdlib-compatible
│     - Fine-grained control
│
├─ Need maximum performance and control?
│  └─ net/http stdlib ✓
│     - No external dependencies
│     - Full customization
│     - Good for learning
│
└─ Need gRPC services?
   └─ google.golang.org/grpc ✓
      - Protocol Buffers
      - Streaming support
      - Cross-language

Red Flags → Escalate to Oracle

Observation	Why Escalate	Example
Goroutine leak causing memory growth	Complex lifecycle management	"Memory grows indefinitely, suspect goroutines not terminating"
Race condition despite mutexes	Subtle synchronization bug	"go test -race shows data race in production code"
Context cancellation not propagating	Distributed system coordination	"Canceled requests still running after client disconnect"
Generics causing compile-time explosion	Type system complexity	"Generic function with constraints causing 10+ min compile time"
CGO memory corruption	Unsafe code interaction	"Segfaults when calling C library from Go"

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Workflow 2: HTTP Server with Graceful Shutdown

Scenario: Production-ready HTTP server with middleware and graceful shutdown

Step 1: Define server structure

package main

import (
    "context"
    "errors"
    "log"
    "net/http"
    "os"
    "os/signal"
    "syscall"
    "time"
)

type Server struct {
    httpServer *http.Server
    logger     *log.Logger
}

func NewServer(addr string, handler http.Handler) *Server {
    return &Server{
        httpServer: &http.Server{
            Addr:         addr,
            Handler:      handler,
            ReadTimeout:  15 * time.Second,
            WriteTimeout: 15 * time.Second,
            IdleTimeout:  60 * time.Second,
        },
        logger: log.New(os.Stdout, "[SERVER] ", log.LstdFlags|log.Lmicroseconds),
    }
}

func (s *Server) Start() error {
    s.logger.Printf("Starting server on %s", s.httpServer.Addr)
    
    if err := s.httpServer.ListenAndServe(); err != nil && !errors.Is(err, http.ErrServerClosed) {
        return err
    }
    
    return nil
}

func (s *Server) Shutdown(ctx context.Context) error {
    s.logger.Println("Shutting down server...")
    return s.httpServer.Shutdown(ctx)
}

Step 2: Implement middleware

// Middleware for logging
func LoggingMiddleware(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        start := time.Now()
        
        // Wrap response writer to capture status code
        wrapped := &responseWriter{ResponseWriter: w, statusCode: http.StatusOK}
        
        next.ServeHTTP(wrapped, r)
        
        log.Printf("%s %s %d %s", r.Method, r.URL.Path, wrapped.statusCode, time.Since(start))
    })
}

type responseWriter struct {
    http.ResponseWriter
    statusCode int
}

func (rw *responseWriter) WriteHeader(code int) {
    rw.statusCode = code
    rw.ResponseWriter.WriteHeader(code)
}

// Middleware for panic recovery
func RecoveryMiddleware(next http.Handler) http.Handler {
    return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        defer func() {
            if err := recover(); err != nil {
                log.Printf("Panic recovered: %v", err)
                http.Error(w, "Internal Server Error", http.StatusInternalServerError)
            }
        }()
        
        next.ServeHTTP(w, r)
    })
}

// Middleware for request timeout
func TimeoutMiddleware(timeout time.Duration) func(http.Handler) http.Handler {
    return func(next http.Handler) http.Handler {
        return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
            ctx, cancel := context.WithTimeout(r.Context(), timeout)
            defer cancel()
            
            r = r.WithContext(ctx)
            
            done := make(chan struct{})
            go func() {
                next.ServeHTTP(w, r)
                close(done)
            }()
            
            select {
            case <-done:
                return
            case <-ctx.Done():
                http.Error(w, "Request Timeout", http.StatusRequestTimeout)
            }
        })
    }
}

Step 3: Setup routes and graceful shutdown

func main() {
    // Setup routes
    mux := http.NewServeMux()
    
    mux.HandleFunc("/health", func(w http.ResponseWriter, r *http.Request) {
        w.WriteHeader(http.StatusOK)
        w.Write([]byte("OK"))
    })
    
    mux.HandleFunc("/api/users", func(w http.ResponseWriter, r *http.Request) {
        // Simulate slow endpoint
        time.Sleep(2 * time.Second)
        w.Header().Set("Content-Type", "application/json")
        w.Write([]byte(`{"users": []}`))
    })
    
    // Apply middleware chain
    handler := RecoveryMiddleware(LoggingMiddleware(TimeoutMiddleware(5 * time.Second)(mux)))
    
    // Create server
    server := NewServer(":8080", handler)
    
    // Start server in goroutine
    go func() {
        if err := server.Start(); err != nil {
            log.Fatalf("Server failed: %v", err)
        }
    }()
    
    // Wait for interrupt signal
    quit := make(chan os.Signal, 1)
    signal.Notify(quit, syscall.SIGINT, syscall.SIGTERM)
    <-quit
    
    // Graceful shutdown with 30s timeout
    ctx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
    defer cancel()
    
    if err := server.Shutdown(ctx); err != nil {
        log.Printf("Server shutdown error: %v", err)
    }
    
    log.Println("Server stopped")
}

Expected outcome:

• Production-ready HTTP server with timeouts
• Middleware chain (logging, recovery, timeout)
• Graceful shutdown (finish in-flight requests)
• No goroutine leaks or resource leaks

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4. Patterns & Templates

Pattern 1: Context Propagation for Cancellation

Use case: Cancel all downstream operations when client disconnects

// Template: Context-aware HTTP handler
func HandleRequest(w http.ResponseWriter, r *http.Request) {
    ctx := r.Context()
    
    // Pass context to all downstream calls
    result, err := fetchData(ctx)
    if err != nil {
        if errors.Is(err, context.Canceled) {
            // Client disconnected
            return
        }
        http.Error(w, err.Error(), http.StatusInternalServerError)
        return
    }
    
    json.NewEncoder(w).Encode(result)
}

func fetchData(ctx context.Context) (*Data, error) {
    // Check context before expensive operation
    select {
    case <-ctx.Done():
        return nil, ctx.Err()
    default:
    }
    
    // Simulate database call with timeout
    resultChan := make(chan *Data, 1)
    errChan := make(chan error, 1)
    
    go func() {
        // Actual database query
        time.Sleep(2 * time.Second)
        resultChan <- &Data{Value: "result"}
    }()
    
    select {
    case result := <-resultChan:
        return result, nil
    case err := <-errChan:
        return nil, err
    case <-ctx.Done():
        return nil, ctx.Err() // Canceled or timed out
    }
}

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Pattern 3: Table-Driven Tests

Use case: Comprehensive test coverage with minimal code

func TestAdd(t *testing.T) {
    tests := []struct {
        name     string
        a, b     int
        expected int
    }{
        {"positive numbers", 2, 3, 5},
        {"negative numbers", -2, -3, -5},
        {"mixed signs", -2, 3, 1},
        {"zero values", 0, 0, 0},
        {"large numbers", 1000000, 2000000, 3000000},
    }
    
    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)
            }
        })
    }
}

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❌ Anti-Pattern: Range Loop Variable Capture

What it looks like:

// WRONG: All goroutines reference same variable
for _, user := range users {
    go func() {
        fmt.Println(user.Name) // Captures loop variable by reference!
    }()
}
// Prints last user's name multiple times!

Why it fails:

• Variable reuse: Loop variable reused across iterations
• All goroutines see final value: By the time goroutine runs, loop finished
• Data race: Multiple goroutines access same variable

Correct approach:

// CORRECT: Pass variable as argument (Go 1.21 and earlier)
for _, user := range users {
    go func(u User) {
        fmt.Println(u.Name) // Each goroutine has own copy
    }(user)
}

// CORRECT: Use local variable (Go 1.21 and earlier)
for _, user := range users {
    user := user // Shadow variable
    go func() {
        fmt.Println(user.Name)
    }()
}

// Go 1.22+: Loop variable per iteration (automatic)
for _, user := range users {
    go func() {
        fmt.Println(user.Name) // Now safe in Go 1.22+
    }()
}

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6. Integration Patterns

backend-developer:

• Handoff: Backend-developer defines business logic → golang-pro implements with idiomatic Go patterns
• Collaboration: REST API design, database integration, authentication/authorization
• Tools: Chi/Gin frameworks, GORM/sqlx, JWT libraries
• Example: Backend defines order service → golang-pro implements with goroutines for concurrent inventory checks

database-optimizer:

• Handoff: Golang-pro identifies slow database queries → database-optimizer creates indexes
• Collaboration: Query optimization, connection pooling (pgx, database/sql)
• Tools: database/sql, pgx driver, sqlx for PostgreSQL
• Example: Golang-pro uses database/sql prepared statements → database-optimizer tunes PostgreSQL for connection pooling

devops-engineer:

• Handoff: Golang-pro builds service → devops-engineer containerizes and deploys
• Collaboration: Dockerfile optimization, health checks, metrics endpoints
• Tools: Docker multi-stage builds, Kubernetes probes, Prometheus metrics
• Example: Golang-pro exposes /metrics endpoint → devops-engineer configures Prometheus scraping

kubernetes-specialist:

• Handoff: Golang-pro builds cloud-native app → kubernetes-specialist deploys to K8s
• Collaboration: Graceful shutdown (SIGTERM), health/readiness probes, resource limits
• Tools: Kubernetes client-go, operator patterns, CRDs
• Example: Golang-pro implements graceful shutdown → kubernetes-specialist sets terminationGracePeriodSeconds

frontend-developer:

• Handoff: Frontend needs API → golang-pro provides RESTful/gRPC endpoints
• Collaboration: API contract design, CORS configuration, WebSocket connections
• Tools: OpenAPI/Swagger, gRPC-web, WebSocket (gorilla/websocket)
• Example: Frontend uses GraphQL → golang-pro implements gqlgen resolvers with DataLoader

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