Update README.md

.mockery.yaml

@@ -9,3 +9,6 @@ packages:
       QuoteService:
       ChallengeGenerator:
       ChallengeVerifier:
+  hash-of-wisdom/internal/controller:
+    interfaces:
+      WisdomService:

Dockerfile

@@ -0,0 +1,36 @@
+# Build stage
+FROM golang:1.24-alpine AS builder
+
+WORKDIR /app
+
+# Copy go mod files
+COPY go.mod go.sum ./
+RUN go mod download
+
+# Copy source code
+COPY . .
+
+# Build server
+RUN CGO_ENABLED=0 go build -o hash-of-wisdom ./cmd/server
+
+# Runtime stage
+FROM alpine:3.19
+
+# Create non-root user
+RUN addgroup -g 1001 -S hash-of-wisdom && \
+    adduser -u 1001 -S hash-of-wisdom -G hash-of-wisdom
+
+WORKDIR /app
+
+# Copy binary and config from builder stage with correct ownership
+COPY --from=builder --chown=hash-of-wisdom:hash-of-wisdom /app/hash-of-wisdom .
+COPY --from=builder --chown=hash-of-wisdom:hash-of-wisdom /app/config.yaml .
+
+# Switch to non-root user
+USER hash-of-wisdom
+
+# Expose ports
+EXPOSE 8080 8081
+
+# Run server with config file
+CMD ["./hash-of-wisdom", "-config", "config.yaml"]

README.md

@@ -0,0 +1,86 @@
+# Hash of Wisdom
+
+A TCP server implementing the "Word of Wisdom" concept with proof-of-work challenges to protect against DDoS attacks.
+
+## Overview
+
+The Hash of Wisdom server requires clients to solve computational puzzles (proof-of-work) before receiving wise quotes. This approach prevents spam and DDoS attacks by requiring clients to invest CPU time for each request.
+
+## Quick Start
+
+### Prerequisites
+- Go 1.24.3+
+- Docker (optional)
+- [Task](https://taskfile.dev/) (optional, but recommended)
+
+### Building
+```bash
+# Build server
+go build -o hash-of-wisdom ./cmd/server
+
+# Build client
+go build -o client ./cmd/client
+```
+
+### Running
+
+#### Using Task (Recommended)
+```bash
+# Most useful command - run all checks
+task check
+
+# Start server
+task server -- -config config.yaml
+
+# Connect client
+task client -- --addr=localhost:8080
+
+# Run tests
+task test
+
+# See coverage
+task test-coverage
+
+# See all available commands
+task --list
+```
+
+#### Manual Commands
+```bash
+# Start server (uses config.yaml by default)
+./hash-of-wisdom
+
+# Or with custom config
+./hash-of-wisdom -config /path/to/config.yaml
+
+# Connect with client
+./client -addr localhost:8080
+
+# Run tests
+go test ./...
+```
+
+### Using Docker
+```bash
+# Build image
+docker build -t hash-of-wisdom .
+
+# Run container
+docker run -p 8080:8080 -p 8081:8081 hash-of-wisdom
+```
+
+### Monitoring
+- Metrics: http://localhost:8081/metrics (Prometheus format with Go runtime stats)
+- Profiling: http://localhost:8081/debug/pprof/
+
+## Documentation
+
+### Protocol & Implementation
+- [Protocol Specification](docs/PROTOCOL.md) - Binary protocol definition
+- [PoW Algorithm Analysis](docs/POW_ANALYSIS.md) - Algorithm selection rationale and comparison
+- [Implementation Plan](docs/IMPLEMENTATION.md) - Development phases and progress
+- [Package Structure](docs/PACKAGES.md) - Code organization and package responsibilities
+- [Architecture Choices](docs/ARCHITECTURE.md) - Design decisions and patterns
+
+### Production Readiness
+- [Production Readiness Guide](docs/PRODUCTION_READINESS.md) - Requirements for production deployment

Taskfile.yml

@@ -93,3 +93,41 @@ tasks:
     desc: Alias for cpu-burner
     cmds:
       - task: cpu-burner
+
+  server:
+    desc: Build and run the server
+    cmds:
+      - go build -o hash-of-wisdom ./cmd/server
+      - ./hash-of-wisdom {{.CLI_ARGS}}
+
+  server-config:
+    desc: Build and run the server with custom config
+    cmds:
+      - go build -o hash-of-wisdom ./cmd/server
+      - ./hash-of-wisdom -config {{.CONFIG | default "config.yaml"}}
+
+  client:
+    desc: Build and run the client
+    cmds:
+      - go build -o client ./cmd/client
+      - ./client {{.CLI_ARGS | default "-addr localhost:8080"}}
+
+  docker-build:
+    desc: Build Docker image
+    cmds:
+      - docker build -t hash-of-wisdom .
+
+  docker-run:
+    desc: Run Docker container
+    cmds:
+      - docker run -p 8080:8080 -p 8081:8081 hash-of-wisdom
+
+  metrics:
+    desc: Check metrics endpoint
+    cmds:
+      - curl -s http://localhost:8081/metrics
+
+  integration:
+    desc: Run integration tests only
+    cmds:
+      - go test -v ./test/integration/...

cmd/client/main.go

@@ -0,0 +1,134 @@
+package main
+
+import (
+	"context"
+	"flag"
+	"fmt"
+	"log"
+	"net"
+	"time"
+
+	"hash-of-wisdom/internal/pow/challenge"
+	"hash-of-wisdom/internal/pow/solver"
+	"hash-of-wisdom/internal/protocol"
+)
+
+func main() {
+	serverAddr := flag.String("addr", "localhost:8080", "server address")
+	flag.Parse()
+
+	fmt.Printf("Connecting to Word of Wisdom server at %s\n", *serverAddr)
+
+	// Step 1: Get challenge
+	challengeResp, err := requestChallenge(*serverAddr)
+	if err != nil {
+		log.Fatalf("Failed to get challenge: %v", err)
+	}
+
+	fmt.Printf("Received challenge with difficulty %d\n", challengeResp.Challenge.Difficulty)
+
+	// Step 2: Solve challenge
+	fmt.Println("Solving challenge...")
+	start := time.Now()
+
+	s := solver.NewSolver()
+	solution, err := s.Solve(context.Background(), challengeResp.Challenge)
+	if err != nil {
+		log.Fatalf("Failed to solve challenge: %v", err)
+	}
+
+	solveTime := time.Since(start)
+	fmt.Printf("Challenge solved in %v with nonce %d\n", solveTime, solution.Nonce)
+
+	// Step 3: Submit solution and get quote
+	err = submitSolution(*serverAddr, challengeResp.Challenge, solution.Nonce)
+	if err != nil {
+		log.Fatalf("Failed to submit solution: %v", err)
+	}
+}
+
+func requestChallenge(serverAddr string) (*protocol.ChallengeResponse, error) {
+	// Connect with timeout
+	conn, err := net.DialTimeout("tcp", serverAddr, 5*time.Second)
+	if err != nil {
+		return nil, fmt.Errorf("failed to connect: %w", err)
+	}
+	defer conn.Close()
+
+	// Request challenge
+	fmt.Println("Requesting challenge...")
+	challengeReq := &protocol.ChallengeRequest{}
+	if err := challengeReq.Encode(conn); err != nil {
+		return nil, fmt.Errorf("failed to send challenge request: %w", err)
+	}
+
+	// Receive challenge
+	decoder := protocol.NewMessageDecoder()
+	msg, err := decoder.Decode(conn)
+	if err != nil {
+		return nil, fmt.Errorf("failed to receive challenge: %w", err)
+	}
+
+	if msg.Type != protocol.ChallengeResponseType {
+		return nil, fmt.Errorf("unexpected response type: %v", msg.Type)
+	}
+
+	// Parse challenge
+	challengeResp := &protocol.ChallengeResponse{}
+	if err := challengeResp.Decode(msg.PayloadStream); err != nil {
+		return nil, fmt.Errorf("failed to parse challenge: %w", err)
+	}
+
+	return challengeResp, nil
+}
+
+func submitSolution(serverAddr string, chall *challenge.Challenge, nonce uint64) error {
+	// Connect with timeout
+	conn, err := net.DialTimeout("tcp", serverAddr, 5*time.Second)
+	if err != nil {
+		return fmt.Errorf("failed to connect: %w", err)
+	}
+	defer conn.Close()
+
+	// Submit solution
+	solutionReq := &protocol.SolutionRequest{
+		Challenge: *chall,
+		Nonce:     nonce,
+	}
+
+	fmt.Println("Submitting solution...")
+	if err := solutionReq.Encode(conn); err != nil {
+		return fmt.Errorf("failed to send solution: %w", err)
+	}
+
+	// Receive quote or error
+	decoder := protocol.NewMessageDecoder()
+	msg, err := decoder.Decode(conn)
+	if err != nil {
+		return fmt.Errorf("failed to receive response: %w", err)
+	}
+
+	switch msg.Type {
+	case protocol.QuoteResponseType:
+		solutionResp := &protocol.SolutionResponse{}
+		if err := solutionResp.Decode(msg.PayloadStream); err != nil {
+			return fmt.Errorf("failed to parse quote: %w", err)
+		}
+		fmt.Printf("\nQuote received:\n\"%s\"\n— %s\n", solutionResp.Quote.Text, solutionResp.Quote.Author)
+	case protocol.ErrorResponseType:
+		errorResp := &protocol.ErrorResponse{}
+		if err := errorResp.Decode(msg.PayloadStream); err != nil {
+			fmt.Println("Error: Contact administrator")
+			return nil
+		}
+		if errorResp.Code == protocol.ErrServerError {
+			fmt.Println("Error: Contact administrator")
+		} else {
+			fmt.Printf("Error: %s\n", errorResp.Message)
+		}
+	default:
+		return fmt.Errorf("unexpected response type: %v", msg.Type)
+	}
+
+	return nil
+}

cmd/server/main.go

@@ -0,0 +1,104 @@
+package main
+
+import (
+	"context"
+	"flag"
+	"log/slog"
+	"net/http"
+	"os"
+	"os/signal"
+	"syscall"
+
+	"hash-of-wisdom/internal/config"
+	"hash-of-wisdom/internal/lib/sl"
+	"hash-of-wisdom/internal/pow/challenge"
+	"hash-of-wisdom/internal/quotes"
+	"hash-of-wisdom/internal/server"
+	"hash-of-wisdom/internal/service"
+
+	"github.com/prometheus/client_golang/prometheus/promhttp"
+	_ "net/http/pprof"
+)
+
+func main() {
+	configPath := flag.String("config", "", "path to configuration file")
+	flag.Parse()
+
+	// Load configuration
+	cfg, err := config.Load(*configPath)
+	if err != nil {
+		slog.Error("failed to load config", sl.Err(err))
+		os.Exit(1)
+	}
+
+	logger := slog.Default()
+	logger.Info("starting word of wisdom server", "address", cfg.Server.Address)
+
+	// Create components using config
+	challengeConfig, err := challenge.NewConfig(
+		challenge.WithDefaultDifficulty(cfg.PoW.Difficulty),
+		challenge.WithMaxDifficulty(cfg.PoW.MaxDifficulty),
+		challenge.WithChallengeTTL(cfg.PoW.TTL),
+		challenge.WithHMACSecret([]byte(cfg.PoW.HMACSecret)),
+	)
+	if err != nil {
+		logger.Error("failed to create challenge config", sl.Err(err))
+		os.Exit(1)
+	}
+	generator := challenge.NewGenerator(challengeConfig)
+	verifier := challenge.NewVerifier(challengeConfig)
+	quoteService := quotes.NewHTTPService()
+
+	// Wire up service
+	genAdapter := service.NewGeneratorAdapter(generator)
+	wisdomService := service.NewWisdomService(genAdapter, verifier, quoteService)
+
+	// Create server configuration
+	serverConfig := &server.Config{
+		Address: cfg.Server.Address,
+		Timeouts: server.TimeoutConfig{
+			Read:       cfg.Server.Timeouts.Read,
+			Write:      cfg.Server.Timeouts.Write,
+			Connection: cfg.Server.Timeouts.Connection,
+		},
+	}
+
+	// Go runtime metrics are automatically registered by default registry
+
+	// Start metrics and pprof HTTP server
+	go func() {
+		http.Handle("/metrics", promhttp.Handler())
+		logger.Info("starting metrics server", "address", cfg.Metrics.Address)
+		if err := http.ListenAndServe(cfg.Metrics.Address, nil); err != nil {
+			logger.Error("metrics server failed", sl.Err(err))
+		}
+	}()
+
+	// Create context that cancels on interrupt signals
+	ctx, cancel := signal.NotifyContext(context.Background(), syscall.SIGINT, syscall.SIGTERM)
+	defer cancel()
+
+	// Create server
+	srv := server.NewTCPServer(wisdomService, serverConfig,
+		server.WithLogger(logger))
+
+	// Start server
+	if err := srv.Start(ctx); err != nil {
+		logger.Error("failed to start server", sl.Err(err))
+		os.Exit(1)
+	}
+
+	logger.Info("server ready - press ctrl+c to stop")
+
+	// Wait for context cancellation (signal received)
+	<-ctx.Done()
+
+	// Graceful shutdown
+	logger.Info("shutting down server")
+	if err := srv.Stop(); err != nil {
+		logger.Error("error during shutdown", sl.Err(err))
+	} else {
+		logger.Info("server stopped gracefully")
+	}
+
+}

config.yaml

@@ -0,0 +1,22 @@
+server:
+  address: ":8080"
+  timeouts:
+    read: 5s
+    write: 5s
+    connection: 15s
+
+pow:
+  difficulty: 25
+  max_difficulty: 30
+  ttl: 5m
+  hmac_secret: "development-secret-change-in-production"
+
+quotes:
+  timeout: 10s
+
+metrics:
+  address: ":8081"
+
+logging:
+  level: "info"
+  format: "text"

docs/ARCHITECTURE.md

@@ -0,0 +1,330 @@
+# Architecture Choices
+
+This document explains the key architectural decisions made in the Hash of Wisdom project and the reasoning behind them.
+
+## Overall Architecture
+
+### Clean Architecture
+We follow Clean Architecture principles with clear layer separation:
+
+```
+┌─────────────────────────────────────┐
+│         Infrastructure Layer        │  ← cmd/, internal/server, internal/protocol
+├─────────────────────────────────────┤
+│         Application Layer           │  ← internal/application (message handling)
+├─────────────────────────────────────┤
+│           Domain Layer              │  ← internal/service, internal/pow (business logic)
+├─────────────────────────────────────┤
+│          External Layer             │  ← internal/quotes (external APIs)
+└─────────────────────────────────────┘
+```
+
+**Benefits**:
+- **Testability**: Each layer can be unit tested independently
+- **Maintainability**: Changes in one layer don't cascade
+- **Flexibility**: Easy to swap implementations (e.g., different quote sources)
+- **Domain Focus**: Core business rules are isolated and protected
+
+## Protocol Design
+
+### Binary Protocol with JSON Payloads
+Choice: Custom binary protocol with JSON-encoded message bodies
+
+**Why Binary Protocol**:
+- **Performance**: Efficient framing and length prefixes
+- **Reliability**: Clear message boundaries prevent parsing issues
+- **Extensibility**: Easy to add message types and versions
+
+**Why JSON Payloads**:
+- **Simplicity**: Standard library support, easy debugging
+- **Flexibility**: Schema evolution without breaking compatibility
+- **Tooling**: Excellent tooling and human readability
+
+**Alternative Considered**: Pure binary (Protocol Buffers)
+- **Rejected Because**: Added complexity without significant benefit for our use case
+- **Trade-off**: Slightly larger payload size for much simpler implementation
+
+### Stateless Challenge Design
+Choice: HMAC-signed challenges with all state embedded
+
+```go
+type Challenge struct {
+    Target     string `json:"target"`      // "quotes"
+    Timestamp  int64  `json:"timestamp"`   // Unix timestamp
+    Difficulty int    `json:"difficulty"`  // Leading zero bits
+    Random     string `json:"random"`      // Entropy
+    Signature  string `json:"signature"`   // HMAC-SHA256
+}
+```
+
+**Benefits**:
+- **Scalability**: No server-side session storage required
+- **Reliability**: Challenges survive server restarts
+- **Security**: HMAC prevents tampering and replay attacks
+- **Simplicity**: No cache management or cleanup needed
+
+**Alternative Considered**: Session-based challenges
+- **Rejected Because**: Requires distributed session management for horizontal scaling
+
+## Proof-of-Work Algorithm
+
+### SHA-256 with Leading Zero Bits
+Choice: SHA-256 hashing with difficulty measured as leading zero bits
+
+**Why SHA-256**:
+- **Security**: Cryptographically secure, extensively tested
+- **Performance**: Hardware-optimized on most platforms
+- **Standardization**: Well-known algorithm with predictable properties
+
+**Why Leading Zero Bits**:
+- **Linear Scaling**: Each bit doubles the difficulty (2^n complexity)
+- **Simplicity**: Easy to verify and understand
+- **Flexibility**: Fine-grained difficulty adjustment
+
+**Alternative Considered**: Scrypt/Argon2 (memory-hard functions)
+- **Rejected Because**: Excessive complexity for DDoS protection use case
+- **Trade-off**: ASIC resistance not needed for temporary challenges
+
+### Difficulty Range: 4-30 Bits
+Choice: Configurable difficulty with reasonable bounds
+
+- **Minimum (4 bits)**: ~16 attempts average, sub-second solve time
+- **Maximum (30 bits)**: ~1 billion attempts, several seconds on modern CPU
+- **Default (4 bits)**: Balance between protection and user experience
+
+## Server Architecture
+
+### TCP Server with Per-Connection Goroutines
+Choice: Custom TCP server with one goroutine per connection
+
+```go
+func (s *TCPServer) Start(ctx context.Context) error {
+    // Start listener
+    listener, err := net.Listen("tcp", s.config.Address)
+    if err != nil {
+        return err
+    }
+
+    // Start accept loop in goroutine
+    go s.acceptLoop(ctx)
+    return nil // Returns immediately
+}
+
+func (s *TCPServer) acceptLoop(ctx context.Context) {
+    for {
+        conn, err := s.listener.Accept()
+        if err != nil || ctx.Done() != nil {
+            return
+        }
+
+        // Launch handler in goroutine with WaitGroup tracking
+        s.wg.Add(1)
+        go func() {
+            defer s.wg.Done()
+            s.handleConnection(ctx, conn)
+        }()
+    }
+}
+```
+
+**Benefits**:
+- **Concurrency**: Each connection handled in separate goroutine
+- **Non-blocking Start**: Server starts in background, returns immediately
+- **Graceful Shutdown**: WaitGroup ensures all connections finish before stop
+- **Context Cancellation**: Proper cleanup when context is cancelled
+- **Resource Control**: Connection timeouts prevent resource exhaustion
+
+**Alternative Considered**: HTTP/REST API
+- **Rejected Because**: Test task requirements
+
+### Connection Security: Multi-Level Timeouts
+Choice: Layered timeout protection against various attacks
+
+1. **Connection Timeout (15s)**: Maximum total connection lifetime
+2. **Read Timeout (5s)**: Maximum time between incoming bytes
+3. **Write Timeout (5s)**: Maximum time to send response
+
+**Protects Against**:
+- **Slowloris**: Slow read timeout prevents slow header attacks
+- **Slow POST**: Connection timeout limits total request time
+- **Resource Exhaustion**: Automatic cleanup of stale connections
+
+## Configuration Management
+
+### cleanenv with YAML + Environment Variables
+Choice: File-based configuration with environment variable overrides
+
+```yaml
+# config.yaml
+server:
+  address: ":8080"
+
+pow:
+  difficulty: 4
+```
+
+```bash
+# Environment override
+export POW_DIFFICULTY=8
+```
+
+**Benefits**:
+- **Development**: Easy configuration files for local development
+- **Production**: Environment variables for containerized deployments
+- **Validation**: Built-in validation and type conversion
+- **Documentation**: Self-documenting with struct tags
+
+**Alternative Considered**: Pure environment variables
+- **Rejected Because**: Harder to manage complex configurations
+
+## Observability Architecture
+
+### Prometheus Metrics
+Choice: Prometheus format metrics with essential measurements
+
+**Application Metrics**:
+- `wisdom_requests_total` - All incoming requests
+- `wisdom_request_errors_total{error_type}` - Errors by type
+- `wisdom_request_duration_seconds` - Request processing time
+- `wisdom_quotes_served_total` - Successfully served quotes
+
+**Go Runtime Metrics** (automatically exported):
+- `go_memstats_*` - Memory allocation and GC statistics
+- `go_goroutines` - Current number of goroutines
+- `go_gc_duration_seconds` - Garbage collection duration
+- `process_*` - Process-level CPU, memory, and file descriptor stats
+
+**Design Principle**: Simple metrics that provide actionable insights
+- **Avoided**: Complex multi-dimensional metrics
+- **Focus**: Essential health and performance indicators
+- **Runtime Visibility**: Go collector provides deep runtime observability
+
+### Metrics at Infrastructure Layer
+Choice: Collect metrics in TCP server, not business logic
+
+```go
+// In TCP server (infrastructure)
+metrics.RequestsTotal.Inc()
+start := time.Now()
+response, err := s.wisdomApplication.HandleMessage(ctx, msg)
+metrics.RequestDuration.Observe(time.Since(start).Seconds())
+```
+
+**Benefits**:
+- **Separation of Concerns**: Business logic stays pure
+- **Consistency**: All requests measured the same way
+- **Performance**: Minimal overhead in critical path
+
+## Design Patterns
+
+### Dependency Injection
+All major components use constructor injection:
+```go
+server := server.NewTCPServer(wisdomApplication, config, options...)
+service := service.NewWisdomService(generator, verifier, quoteService)
+```
+
+**Benefits**:
+- **Testing**: Easy to inject mocks and stubs
+- **Configuration**: Runtime assembly of components
+- **Decoupling**: Components don't know about concrete implementations
+
+### Interface Segregation
+Small, focused interfaces for easy testing:
+```go
+type ChallengeGenerator interface {
+    GenerateChallenge(ctx context.Context) (*Challenge, error)
+}
+
+type QuoteService interface {
+    GetQuote(ctx context.Context) (string, error)
+}
+```
+
+### Functional Options
+Flexible configuration with sensible defaults:
+```go
+server := NewTCPServer(application, config,
+    WithLogger(logger),
+)
+```
+
+### Clean Architecture Implementation
+See the layer diagram in the Overall Architecture section above for package organization.
+
+## Testing Architecture
+
+### Layered Testing Strategy
+1. **Unit Tests**: Each package tested independently with mocks
+2. **Integration Tests**: End-to-end tests with real TCP connections
+3. **Benchmark Tests**: Performance validation for PoW algorithms
+
+```go
+// Unit test with mocks
+func TestWisdomService_HandleMessage(t *testing.T) {
+    mockGenerator := &MockGenerator{}
+    mockVerifier := &MockVerifier{}
+    mockQuotes := &MockQuoteService{}
+
+    service := NewWisdomService(mockGenerator, mockVerifier, mockQuotes)
+    // Test business logic in isolation
+}
+
+// Integration test with real components
+func TestTCPServer_SlowlorisProtection(t *testing.T) {
+    // Start real server, make slow connection
+    // Verify server doesn't hang
+}
+```
+
+## Security Architecture
+
+### Defense in Depth
+Multiple security layers working together:
+
+1. **HMAC Authentication**: Prevents challenge tampering
+2. **Timestamp Validation**: Prevents replay attacks (5-minute TTL)
+3. **Connection Timeouts**: Prevents resource exhaustion
+4. **Proof-of-Work**: Rate limiting through computational cost
+5. **Input Validation**: All protocol messages validated
+
+### Threat Model
+**Primary Threats Addressed**:
+- **DDoS Attacks**: PoW makes attacks expensive
+- **Resource Exhaustion**: Connection timeouts and limits
+- **Protocol Attacks**: Binary framing prevents confusion
+- **Replay Attacks**: Timestamp validation in challenges
+
+**Threats NOT Addressed** (by design):
+- **Authentication**: Public service, no user accounts
+- **Authorization**: All valid solutions get quotes
+- **Data Confidentiality**: Quotes are public information
+
+## Trade-offs Made
+
+### Simplicity vs Performance
+- **Chose**: Simple JSON payloads over binary serialization
+- **Trade-off**: ~30% larger messages for easier debugging and maintenance
+
+### Memory vs CPU
+- **Chose**: Stateless challenges requiring CPU verification
+- **Trade-off**: More CPU per request for better scalability
+
+### Flexibility vs Optimization
+- **Chose**: Interface-based design with dependency injection
+- **Trade-off**: Small runtime overhead for much better testability
+
+### Features vs Complexity
+- **Chose**: Essential features only (no rate limiting, user accounts, etc.)
+- **Benefit**: Clean, focused implementation that does one thing well
+
+## Future Architecture Considerations
+
+For production scaling, consider:
+1. **Quote Service Enhancement**: Caching, fallback quotes, multiple API sources
+2. **Load Balancing**: Multiple server instances behind load balancer
+3. **Rate Limiting**: Per-IP request limiting for additional protection
+4. **Monitoring**: Full observability stack (Prometheus, Grafana, alerting)
+5. **Security**: TLS encryption for sensitive deployments
+
+The current architecture provides a solid foundation for these enhancements while maintaining simplicity and focus.

docs/IMPLEMENTATION.md

@@ -68,108 +68,53 @@
 - [X] Create message validation and bounds checking
 - [X] Write unit tests for protocol components
 
-## Phase 5: Basic Server Architecture
+## Phase 5: Binary Protocol Reworking & Application Layer Integration
-- [ ] Set up structured logging (zerolog/logrus)
+- [X] Refactor protocol codec into streaming MessageDecoder
-- [ ] Set up metrics collection (prometheus)
+- [X] Implement streaming message processing with io.Reader
-- [ ] Create configuration management
+- [X] Create request/response encoding and decoding methods
-- [ ] Integrate all components into server architecture
+- [X] Add comprehensive round-trip testing for protocol validation
+- [X] Update application layer to use streaming Message interface
+- [X] Fix application tests for new protocol design
 
-## Phase 6: TCP Protocol & Connection Handling
+## Phase 6: TCP Server & Connection Management
-- [ ] Implement connection handler with proper error handling
+- [X] Implement TCP server with connection handling
-- [ ] Create protocol state machine
+- [X] Add dual timeout protection:
-- [ ] Implement connection lifecycle management
+  - [X] Connection timeout (max total connection time)
-- [ ] Add connection timeout and lifecycle management
+  - [X] Read timeout (max idle time between bytes - slowloris protection)
+- [X] Implement proper connection lifecycle management
+- [X] Create protocol state machine for request/response flow
+- [X] Add graceful connection cleanup and error handling
+- [X] Add slog structured logging to TCP server
+- [X] Implement functional options pattern for server configuration
+- [X] Update cmd/server to use new TCP server with logging
 
-## Phase 7: Server Core & Request Handling
+## Phase 7: Client Implementation
-- [ ] Implement TCP server with connection pooling
+- [X] Create client application structure
-- [ ] Create request router and handler dispatcher
+- [X] Implement PoW solver algorithm on client side
-- [ ] Add connection timeout and lifecycle management
+- [X] Create client-side protocol implementation
-- [ ] Implement graceful shutdown mechanism
+- [X] Add retry logic and error handling
-- [ ] Add request/response logging middleware
+- [X] Implement connection management
-- [ ] Create health check endpoints
+- [X] Create CLI interface for client with flag support
-- [ ] Write integration tests for server core
+- [X] Add symmetric encode/decode to protocol package for client use
+- [X] Update protocol to use separate connections per request-response
+- [X] Write comprehensive slowloris protection integration tests
+- [X] Verify server successfully handles slow reader attacks
+- [X] Verify server successfully handles slow writer attacks
+- [X] Test end-to-end client-server communication flow
 
-## Phase 9: DDOS Protection & Rate Limiting
+## Phase 8: Server Instrumentation & Configuration
-- [ ] Implement IP-based connection limiting
+- [X] Add `/metrics` HTTP endpoint for Prometheus collection
-- [ ] Create rate limiting service with time windows
+- [X] Add `/debug/pprof` endpoint for performance profiling
-- [ ] Add automatic difficulty adjustment based on load
+- [X] Create Dockerfile to build server image
-- [ ] Implement temporary IP blacklisting
+- [X] Implement configuration management using cleanenv library
-- [ ] Create circuit breaker for overload protection
+- [X] Read configuration from file with environment variable support
-- [ ] Add monitoring for attack detection
-- [ ] Write tests for protection mechanisms
 
-## Phase 9: Observability & Monitoring
+## Phase 9: Documentation
-- [ ] Add structured logging throughout application
+- [X] Create comprehensive README.md with project overview and quick start
-- [ ] Implement metrics for key performance indicators:
+- [X] Document package structure and responsibilities
-  - [ ] Active connections count
+- [X] Document architecture choices and design decisions
-  - [ ] Challenge generation rate
+- [X] Update production readiness assessment
-  - [ ] Solution verification rate
-  - [ ] Success/failure ratios
-  - [ ] Response time histograms
-- [ ] Create logging middleware for request tracing
-- [ ] Add error categorization and reporting
-- [ ] Implement health check endpoints
 
-## Phase 10: Configuration & Environment Setup
-- [ ] Create configuration structure with validation
-- [ ] Support environment variables and config files
-- [ ] Add configuration for different environments (dev/prod)
-- [ ] Implement feature flags for protection levels
-- [ ] Create deployment configuration templates
-- [ ] Add configuration validation and defaults
-
-## Phase 11: Client Implementation
-- [ ] Create client application structure
-- [ ] Implement PoW solver algorithm
-- [ ] Create client-side protocol implementation
-- [ ] Add retry logic and error handling
-- [ ] Implement connection management
-- [ ] Create CLI interface for client
-- [ ] Add client metrics and logging
-- [ ] Write client unit and integration tests
-
-## Phase 12: Docker & Deployment
-- [ ] Create multi-stage Dockerfile for server
-- [ ] Create Dockerfile for client
-- [ ] Create docker-compose.yml for local development
-- [ ] Add docker-compose for production deployment
-- [ ] Create health check scripts for containers
-- [ ] Add environment-specific configurations
-- [ ] Create deployment documentation
-
-## Phase 13: Testing & Quality Assurance
-- [ ] Write comprehensive unit tests (>80% coverage):
-  - [ ] PoW algorithm tests
-  - [ ] Protocol handler tests
-  - [ ] Rate limiting tests
-  - [ ] Quote service tests
-  - [ ] Configuration tests
-- [ ] Create integration tests:
-  - [ ] End-to-end client-server communication
-  - [ ] Load testing scenarios
-  - [ ] Failure recovery tests
-  - [ ] DDOS protection validation
-- [ ] Add benchmark tests for performance validation
-- [ ] Create stress testing scenarios
-
-## Phase 14: Documentation & Final Polish
-- [ ] Write comprehensive README with setup instructions
-- [ ] Create API documentation for all interfaces
-- [ ] Add inline code documentation
-- [ ] Create deployment guide
-- [ ] Write troubleshooting guide
-- [ ] Add performance tuning recommendations
-- [ ] Create monitoring and alerting guide
-
-## Phase 15: Production Readiness Checklist
-- [ ] Security audit of all components
-- [ ] Performance benchmarking and optimization
-- [ ] Memory leak detection and prevention
-- [ ] Resource cleanup validation
-- [ ] Error handling coverage review
-- [ ] Logging security (no sensitive data exposure)
-- [ ] Configuration security (secrets management)
-- [ ] Container security hardening
 
 ## Directory Structure
 ```
@@ -192,13 +137,3 @@
 ├── deployments/         # Deployment configurations
 └── docs/                # Additional documentation
 ```
-
-## Success Criteria
-- [ ] Server handles 1000+ concurrent connections
-- [ ] PoW protection prevents DDOS attacks effectively
-- [ ] All tests pass with >80% code coverage
-- [ ] Docker containers build and run successfully
-- [ ] Client successfully solves challenges and receives quotes
-- [ ] Comprehensive logging and metrics in place
-- [ ] Production-ready error handling and recovery
-- [ ] Clear documentation for deployment and operation

docs/PACKAGES.md

@@ -0,0 +1,147 @@
+# Package Structure
+
+This document explains the organization and responsibilities of all packages in the Hash of Wisdom project.
+
+## Directory Structure
+
+```
+/
+├── cmd/                    # Application entry points
+│   ├── server/            # Server application
+│   └── client/            # Client application
+├── internal/              # Private application packages
+│   ├── application/      # Application layer (message handling)
+│   ├── config/           # Configuration management
+│   ├── lib/              # Shared utilities
+│   ├── metrics/          # Prometheus metrics
+│   ├── pow/              # Proof-of-Work implementation
+│   ├── protocol/         # Binary protocol codec
+│   ├── quotes/           # Quote service
+│   ├── server/           # TCP server implementation
+│   └── service/          # Business logic layer
+├── test/                 # Integration tests
+└── docs/                 # Documentation
+```
+
+## Package Responsibilities
+
+### `cmd/server`
+**Entry point for the TCP server application**
+- Parses command-line flags and configuration
+- Initializes all components with dependency injection
+- Starts TCP server and metrics endpoints
+- Handles graceful shutdown signals
+
+### `cmd/client`
+**Entry point for the client application**
+- Command-line interface for connecting to server
+- Handles proof-of-work solving on client side
+- Manages TCP connection lifecycle
+
+### `internal/config`
+**Configuration management with cleanenv**
+- Defines configuration structures with YAML/env tags
+- Loads configuration from files and environment variables
+- Provides sensible defaults for all settings
+- Supports both development and production configurations
+
+### `internal/lib/sl`
+**Shared logging utilities**
+- Structured logging helpers for consistent log formatting
+- Error attribute helpers for slog integration
+
+### `internal/metrics`
+**Prometheus metrics collection**
+- Defines application-specific metrics (requests, errors, duration)
+- Provides simple counters and histograms for monitoring
+- Integrated at the infrastructure layer (TCP server)
+
+### `internal/pow`
+**Proof-of-Work implementation**
+
+#### `internal/pow/challenge`
+- **Challenge Generation**: Creates HMAC-signed stateless challenges
+- **Verification**: Validates solutions against original challenges
+- **Security**: HMAC authentication prevents tampering
+- **Configuration**: Difficulty scaling, TTL management, secrets
+
+#### `internal/pow/solver`
+- **Solution Finding**: Brute-force nonce search with SHA-256
+- **Optimization**: Efficient bit counting for difficulty verification
+- **Client-side**: Used by client to solve server challenges
+
+### `internal/protocol`
+**Binary protocol codec**
+- **Message Types**: Challenge requests/responses, solution requests/responses, errors
+- **Encoding/Decoding**: JSON-based message serialization
+- **Streaming**: MessageDecoder for reading from TCP connections
+- **Validation**: Message structure and field validation
+- See [Protocol Specification](PROTOCOL.md) for detailed message flow and format
+
+### `internal/quotes`
+**Quote service implementation**
+- **HTTP Client**: Fetches quotes from external APIs using resty
+- **Interface**: Clean abstraction for quote retrieval
+- **Error Handling**: Graceful degradation for network issues
+- **Timeout Management**: Configurable request timeouts
+
+### `internal/server`
+**TCP server implementation**
+
+#### `internal/server/tcp.go`
+- **Connection Management**: Accept, handle, cleanup TCP connections
+- **Protocol Integration**: Uses protocol package for message handling
+- **Security**: Connection timeouts, slowloris protection
+- **Metrics**: Request tracking at infrastructure layer
+- **Lifecycle**: Graceful startup/shutdown with context
+
+#### `internal/server/config.go`
+- **Server Configuration**: Network settings, timeouts
+- **Functional Options**: Builder pattern for server customization
+
+### `internal/application`
+**Application layer (message handling and coordination)**
+- **WisdomApplication**: Protocol message handler and coordinator
+- **Message Processing**: Handles challenge and solution requests from protocol layer
+- **Response Generation**: Creates appropriate protocol responses
+- **Service Coordination**: Orchestrates calls to business logic layer
+- **Error Handling**: Converts service errors to protocol error responses
+
+### `internal/service`
+**Business logic layer (core domain services)**
+- **WisdomService**: Main business logic coordinator
+- **Challenge Workflow**: Manages challenge generation and validation
+- **Solution Workflow**: Handles solution verification and quote retrieval
+- **Clean Architecture**: Pure business logic, no I/O dependencies
+- **Testing**: Easily mockable interfaces for unit testing
+
+**Service Dependencies**:
+- `ChallengeGenerator` - Creates new challenges
+- `ChallengeVerifier` - Validates submitted solutions
+- `QuoteService` - Retrieves quotes after successful validation
+
+### `test/integration`
+**End-to-end integration tests**
+- **Slowloris Protection**: Tests server resilience against slow attacks
+- **Connection Timeouts**: Validates timeout configurations
+- **Full Workflow**: Tests complete client-server interaction
+- **Real Components**: Uses actual TCP connections and protocol
+
+## Dependency Flow
+
+```
+cmd/server
+    ↓
+internal/config → internal/server → internal/application → internal/service
+                      ↓                    ↓                   ↓
+                internal/protocol     internal/protocol   internal/pow
+                internal/metrics                         internal/quotes
+```
+
+## Architecture Benefits
+
+This package structure provides:
+- **Clear Separation**: Each package has a single, well-defined responsibility
+- **Testability**: Dependencies are injected, making testing straightforward
+- **Maintainability**: Changes are isolated to specific layers
+- **Scalability**: Clean interfaces allow for easy implementation swapping

docs/PRODUCTION_READINESS.md

@@ -0,0 +1,70 @@
+# Production Readiness Assessment
+
+## Current Implementation Status
+
+### ✅ Core Functionality (Complete)
+- **Proof of Work System**: SHA-256 hashcash with HMAC-signed stateless challenges
+- **Binary Protocol**: Custom TCP protocol with JSON payloads and proper framing
+- **TCP Server**: Connection handling with timeout protection against slowloris attacks
+- **Client Application**: CLI tool with challenge solving and solution submission
+- **Service Layer**: Clean architecture with dependency injection
+- **Quote System**: External API integration for inspirational quotes
+- **Security**: HMAC authentication, replay protection, input validation
+- **Testing**: Comprehensive unit tests and slowloris protection integration tests
+
+### ✅ Observability & Configuration (Complete)
+- **Metrics Endpoint**: Prometheus metrics at `/metrics` with application and Go runtime KPIs
+- **Application Metrics**: Request tracking, error categorization, duration histograms, quotes served
+- **Go Runtime Metrics**: Memory stats, GC metrics, goroutine counts, process stats (auto-registered)
+- **Profiler Endpoint**: Go pprof integration at `/debug/pprof/` for performance debugging
+- **Structured Logging**: slog integration throughout server components with consistent formatting
+- **Configuration**: cleanenv-based config management with YAML files and environment variables
+- **Containerization**: Production-ready Dockerfile with security best practices
+- **Error Handling**: Proper error propagation and categorization
+- **Graceful Shutdown**: Context-based shutdown with connection draining
+
+## Remaining Components for Production
+
+### Critical for Production
+1. **Connection Pooling & Resource Management** (worker pools, connection limits)
+2. **Rate Limiting & DDoS Protection**
+3. **Secret Management** (HMAC keys, external API credentials)
+4. **Advanced Monitoring & Alerting**
+5. **Advanced Configuration Management**
+6. **Health Checks** (graceful shutdown already implemented)
+
+### Important for Scale
+7. **Security Hardening**
+8. **Quote Service Enhancement** (caching, fallback quotes, multiple sources)
+9. **Load Testing & Performance**
+10. **Documentation & Runbooks**
+
+### Nice to Have
+11. **Advanced Observability**
+12. **Chaos Engineering**
+13. **Automated Deployment**
+
+## Risk Assessment
+
+### High Risk Areas
+- **No rate limiting**: Vulnerable to sophisticated DDoS attacks
+- **Hardcoded secrets**: HMAC keys in configuration files (not properly secured)
+- **Limited monitoring**: Basic metrics but no alerting or attack detection
+- **Single point of failure**: No redundancy or failover
+
+### Medium Risk Areas
+- **Memory management**: Potential leaks under high load
+- **External dependencies**: Quote API could become bottleneck
+- **Configuration drift**: Manual configuration prone to errors
+
+## Current Architecture Strengths
+
+The existing implementation provides an excellent foundation:
+- **Clean Architecture**: Proper separation of concerns with dependency injection
+- **Security-First Design**: HMAC authentication, replay protection, and timeout protection
+- **Stateless Operation**: HMAC-signed challenges enable horizontal scaling
+- **Graceful Shutdown**: Proper context handling and connection draining
+- **Comprehensive Testing**: Proven slowloris protection and unit test coverage
+- **Observability Ready**: Prometheus metrics, pprof profiling, structured logging
+- **Standard Protocols**: Industry-standard approaches (TCP, JSON, SHA-256)
+- **Container Ready**: Production Dockerfile with security best practices

docs/PROTOCOL.md

@@ -31,27 +31,37 @@ For detailed analysis of alternative PoW algorithms and comprehensive justificat
 
 ## Protocol Flow
 
-### Successful Flow
+### Challenge Request Flow
 ```
 Client                                    Server
   |                                         |
   |-------- CHALLENGE_REQUEST ------------->|
   |                                         |
   |<------- CHALLENGE_RESPONSE -------------| (HMAC-signed)
+  |                                         |
+  [Connection closes]
+```
+
+### Solution Submission Flow
+```
+Client                                    Server
   |                                         |
   |-------- SOLUTION_REQUEST -------------->|
   |                                         |
   |<------- QUOTE_RESPONSE -----------------| (if solution valid)
   |                                         |
+  [Connection closes]
 ```
 
 ### Error Flow
 ```
 Client                                    Server
-  |-------- CHALLENGE_REQUEST ------------->|
+  |                                         |
-  |<------- CHALLENGE_RESPONSE -------------|
   |-------- SOLUTION_REQUEST (invalid) ---->|
+  |                                         |
   |<------- ERROR_RESPONSE -----------------| (if solution invalid)
+  |                                         |
+  [Connection closes]
 ```
 
 ## Message Format
@@ -252,12 +262,21 @@ Server verifies solutions through the following steps:
 ## Connection Management
 
 ### Connection Lifecycle
+
+The protocol uses separate TCP connections for challenge requests and solution submissions:
+
+#### Challenge Request:
 1. **Connect**: Client establishes TCP connection to server
-2. **Challenge**: Client requests and receives HMAC-signed challenge
+2. **Request**: Client sends CHALLENGE_REQUEST
-3. **Solve**: Client solves PoW challenge offline (can take time)
+3. **Receive**: Client receives CHALLENGE_RESPONSE with HMAC-signed challenge
-4. **Submit**: Client submits solution with challenge proof
+4. **Disconnect**: Connection closes automatically
-5. **Receive**: Client receives quote (if valid) or error (if invalid)
+
-6. **Disconnect**: Connection closes automatically after response
+#### Solution Submission:
+1. **Solve**: Client solves PoW challenge offline
+2. **Connect**: Client establishes new TCP connection to server
+3. **Submit**: Client sends SOLUTION_REQUEST with challenge and nonce
+4. **Receive**: Client receives QUOTE_RESPONSE or ERROR_RESPONSE
+5. **Disconnect**: Connection closes automatically
 
 ### Timeouts and Limits
 

go.mod

@@ -4,17 +4,28 @@ go 1.24.3
 
 require (
 	github.com/go-resty/resty/v2 v2.16.5
+	github.com/ilyakaznacheev/cleanenv v1.5.0
+	github.com/prometheus/client_golang v1.23.0
 	github.com/stretchr/testify v1.10.0
 )
 
 require (
+	github.com/BurntSushi/toml v1.2.1 // indirect
+	github.com/beorn7/perks v1.0.1 // indirect
+	github.com/cespare/xxhash/v2 v2.3.0 // indirect
 	github.com/davecgh/go-spew v1.1.2-0.20180830191138-d8f796af33cc // indirect
+	github.com/joho/godotenv v1.5.1 // indirect
 	github.com/kr/text v0.2.0 // indirect
-	github.com/niemeyer/pretty v0.0.0-20200227124842-a10e7caefd8e // indirect
+	github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822 // indirect
 	github.com/pmezard/go-difflib v1.0.1-0.20181226105442-5d4384ee4fb2 // indirect
+	github.com/prometheus/client_model v0.6.2 // indirect
+	github.com/prometheus/common v0.65.0 // indirect
+	github.com/prometheus/procfs v0.16.1 // indirect
 	github.com/stretchr/objx v0.5.2 // indirect
-	golang.org/x/net v0.35.0 // indirect
+	golang.org/x/net v0.40.0 // indirect
+	golang.org/x/sys v0.33.0 // indirect
 	golang.org/x/time v0.8.0 // indirect
-	gopkg.in/check.v1 v1.0.0-20200227125254-8fa46927fb4f // indirect
+	google.golang.org/protobuf v1.36.6 // indirect
 	gopkg.in/yaml.v3 v3.0.1 // indirect
+	olympos.io/encoding/edn v0.0.0-20201019073823-d3554ca0b0a3 // indirect
 )

go.sum

@@ -1,26 +1,60 @@
+github.com/BurntSushi/toml v1.2.1 h1:9F2/+DoOYIOksmaJFPw1tGFy1eDnIJXg+UHjuD8lTak=
+github.com/BurntSushi/toml v1.2.1/go.mod h1:CxXYINrC8qIiEnFrOxCa7Jy5BFHlXnUU2pbicEuybxQ=
+github.com/beorn7/perks v1.0.1 h1:VlbKKnNfV8bJzeqoa4cOKqO6bYr3WgKZxO8Z16+hsOM=
+github.com/beorn7/perks v1.0.1/go.mod h1:G2ZrVWU2WbWT9wwq4/hrbKbnv/1ERSJQ0ibhJ6rlkpw=
+github.com/cespare/xxhash/v2 v2.3.0 h1:UL815xU9SqsFlibzuggzjXhog7bL6oX9BbNZnL2UFvs=
+github.com/cespare/xxhash/v2 v2.3.0/go.mod h1:VGX0DQ3Q6kWi7AoAeZDth3/j3BFtOZR5XLFGgcrjCOs=
 github.com/creack/pty v1.1.9/go.mod h1:oKZEueFk5CKHvIhNR5MUki03XCEU+Q6VDXinZuGJ33E=
 github.com/davecgh/go-spew v1.1.2-0.20180830191138-d8f796af33cc h1:U9qPSI2PIWSS1VwoXQT9A3Wy9MM3WgvqSxFWenqJduM=
 github.com/davecgh/go-spew v1.1.2-0.20180830191138-d8f796af33cc/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
 github.com/go-resty/resty/v2 v2.16.5 h1:hBKqmWrr7uRc3euHVqmh1HTHcKn99Smr7o5spptdhTM=
 github.com/go-resty/resty/v2 v2.16.5/go.mod h1:hkJtXbA2iKHzJheXYvQ8snQES5ZLGKMwQ07xAwp/fiA=
-github.com/kr/pty v1.1.1/go.mod h1:pFQYn66WHrOpPYNljwOMqo10TkYh1fy3cYio2l3bCsQ=
+github.com/google/go-cmp v0.7.0 h1:wk8382ETsv4JYUZwIsn6YpYiWiBsYLSJiTsyBybVuN8=
-github.com/kr/text v0.1.0/go.mod h1:4Jbv+DJW3UT/LiOwJeYQe1efqtUx/iVham/4vfdArNI=
+github.com/google/go-cmp v0.7.0/go.mod h1:pXiqmnSA92OHEEa9HXL2W4E7lf9JzCmGVUdgjX3N/iU=
+github.com/ilyakaznacheev/cleanenv v1.5.0 h1:0VNZXggJE2OYdXE87bfSSwGxeiGt9moSR2lOrsHHvr4=
+github.com/ilyakaznacheev/cleanenv v1.5.0/go.mod h1:a5aDzaJrLCQZsazHol1w8InnDcOX0OColm64SlIi6gk=
+github.com/joho/godotenv v1.5.1 h1:7eLL/+HRGLY0ldzfGMeQkb7vMd0as4CfYvUVzLqw0N0=
+github.com/joho/godotenv v1.5.1/go.mod h1:f4LDr5Voq0i2e/R5DDNOoa2zzDfwtkZa6DnEwAbqwq4=
+github.com/klauspost/compress v1.18.0 h1:c/Cqfb0r+Yi+JtIEq73FWXVkRonBlf0CRNYc8Zttxdo=
+github.com/klauspost/compress v1.18.0/go.mod h1:2Pp+KzxcywXVXMr50+X0Q/Lsb43OQHYWRCY2AiWywWQ=
+github.com/kr/pretty v0.3.1 h1:flRD4NNwYAUpkphVc1HcthR4KEIFJ65n8Mw5qdRn3LE=
+github.com/kr/pretty v0.3.1/go.mod h1:hoEshYVHaxMs3cyo3Yncou5ZscifuDolrwPKZanG3xk=
 github.com/kr/text v0.2.0 h1:5Nx0Ya0ZqY2ygV366QzturHI13Jq95ApcVaJBhpS+AY=
 github.com/kr/text v0.2.0/go.mod h1:eLer722TekiGuMkidMxC/pM04lWEeraHUUmBw8l2grE=
-github.com/niemeyer/pretty v0.0.0-20200227124842-a10e7caefd8e h1:fD57ERR4JtEqsWbfPhv4DMiApHyliiK5xCTNVSPiaAs=
+github.com/kylelemons/godebug v1.1.0 h1:RPNrshWIDI6G2gRW9EHilWtl7Z6Sb1BR0xunSBf0SNc=
-github.com/niemeyer/pretty v0.0.0-20200227124842-a10e7caefd8e/go.mod h1:zD1mROLANZcx1PVRCS0qkT7pwLkGfwJo4zjcN/Tysno=
+github.com/kylelemons/godebug v1.1.0/go.mod h1:9/0rRGxNHcop5bhtWyNeEfOS8JIWk580+fNqagV/RAw=
+github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822 h1:C3w9PqII01/Oq1c1nUAm88MOHcQC9l5mIlSMApZMrHA=
+github.com/munnerz/goautoneg v0.0.0-20191010083416-a7dc8b61c822/go.mod h1:+n7T8mK8HuQTcFwEeznm/DIxMOiR9yIdICNftLE1DvQ=
 github.com/pmezard/go-difflib v1.0.1-0.20181226105442-5d4384ee4fb2 h1:Jamvg5psRIccs7FGNTlIRMkT8wgtp5eCXdBlqhYGL6U=
 github.com/pmezard/go-difflib v1.0.1-0.20181226105442-5d4384ee4fb2/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/prometheus/client_golang v1.23.0 h1:ust4zpdl9r4trLY/gSjlm07PuiBq2ynaXXlptpfy8Uc=
+github.com/prometheus/client_golang v1.23.0/go.mod h1:i/o0R9ByOnHX0McrTMTyhYvKE4haaf2mW08I+jGAjEE=
+github.com/prometheus/client_model v0.6.2 h1:oBsgwpGs7iVziMvrGhE53c/GrLUsZdHnqNwqPLxwZyk=
+github.com/prometheus/client_model v0.6.2/go.mod h1:y3m2F6Gdpfy6Ut/GBsUqTWZqCUvMVzSfMLjcu6wAwpE=
+github.com/prometheus/common v0.65.0 h1:QDwzd+G1twt//Kwj/Ww6E9FQq1iVMmODnILtW1t2VzE=
+github.com/prometheus/common v0.65.0/go.mod h1:0gZns+BLRQ3V6NdaerOhMbwwRbNh9hkGINtQAsP5GS8=
+github.com/prometheus/procfs v0.16.1 h1:hZ15bTNuirocR6u0JZ6BAHHmwS1p8B4P6MRqxtzMyRg=
+github.com/prometheus/procfs v0.16.1/go.mod h1:teAbpZRB1iIAJYREa1LsoWUXykVXA1KlTmWl8x/U+Is=
+github.com/rogpeppe/go-internal v1.10.0 h1:TMyTOH3F/DB16zRVcYyreMH6GnZZrwQVAoYjRBZyWFQ=
+github.com/rogpeppe/go-internal v1.10.0/go.mod h1:UQnix2H7Ngw/k4C5ijL5+65zddjncjaFoBhdsK/akog=
 github.com/stretchr/objx v0.5.2 h1:xuMeJ0Sdp5ZMRXx/aWO6RZxdr3beISkG5/G/aIRr3pY=
 github.com/stretchr/objx v0.5.2/go.mod h1:FRsXN1f5AsAjCGJKqEizvkpNtU+EGNCLh3NxZ/8L+MA=
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internal/application/application.go

@@ -0,0 +1,88 @@
+package application
+
+import (
+	"context"
+	"fmt"
+	"io"
+
+	"hash-of-wisdom/internal/pow/challenge"
+	"hash-of-wisdom/internal/protocol"
+	"hash-of-wisdom/internal/quotes"
+)
+
+// Response represents an encodable response that can write itself to a connection
+type Response interface {
+	Encode(w io.Writer) error
+}
+
+// WisdomService defines the interface for the wisdom service
+type WisdomService interface {
+	GenerateChallenge(ctx context.Context, resource string) (*challenge.Challenge, error)
+	VerifySolution(ctx context.Context, solution *challenge.Solution) error
+	GetQuote(ctx context.Context) (*quotes.Quote, error)
+}
+
+// WisdomApplication handles the Word of Wisdom application logic
+type WisdomApplication struct {
+	wisdomService WisdomService
+}
+
+// NewWisdomApplication creates a new wisdom application handler
+func NewWisdomApplication(wisdomService WisdomService) *WisdomApplication {
+	return &WisdomApplication{
+		wisdomService: wisdomService,
+	}
+}
+
+// HandleMessage processes a protocol message and returns an encodable response
+func (a *WisdomApplication) HandleMessage(ctx context.Context, msg *protocol.Message) (Response, error) {
+	switch msg.Type {
+	case protocol.ChallengeRequestType:
+		return a.handleChallengeRequest(ctx)
+	case protocol.SolutionRequestType:
+		return a.handleSolutionRequest(ctx, msg)
+	default:
+		return &protocol.ErrorResponse{
+			Code:    protocol.ErrMalformedMessage,
+			Message: fmt.Sprintf("unsupported message type: 0x%02x", msg.Type),
+		}, nil
+	}
+}
+
+// handleChallengeRequest processes challenge requests
+func (a *WisdomApplication) handleChallengeRequest(ctx context.Context) (Response, error) {
+	challenge, err := a.wisdomService.GenerateChallenge(ctx, "quotes")
+	if err != nil {
+		return &protocol.ErrorResponse{Code: protocol.ErrServerError, Message: "Contact administrator"}, nil
+	}
+
+	return &protocol.ChallengeResponse{Challenge: challenge}, nil
+}
+
+// handleSolutionRequest processes solution requests
+func (a *WisdomApplication) handleSolutionRequest(ctx context.Context, msg *protocol.Message) (Response, error) {
+	// Parse solution request
+	var solutionReq protocol.SolutionRequest
+	if err := solutionReq.Decode(msg.PayloadStream); err != nil {
+		return &protocol.ErrorResponse{Code: protocol.ErrMalformedMessage, Message: "invalid solution format"}, nil
+	}
+
+	// Create solution object
+	solution := &challenge.Solution{
+		Challenge: solutionReq.Challenge,
+		Nonce:     solutionReq.Nonce,
+	}
+
+	// Verify solution
+	if err := a.wisdomService.VerifySolution(ctx, solution); err != nil {
+		return &protocol.ErrorResponse{Code: protocol.ErrInvalidSolution, Message: "solution verification failed"}, nil
+	}
+
+	// Get quote
+	quote, err := a.wisdomService.GetQuote(ctx)
+	if err != nil {
+		return &protocol.ErrorResponse{Code: protocol.ErrServerError, Message: "Contact administrator"}, nil
+	}
+
+	return &protocol.SolutionResponse{Quote: quote}, nil
+}

internal/application/application_test.go

@@ -0,0 +1,324 @@
+package application
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"errors"
+	"testing"
+
+	"hash-of-wisdom/internal/application/mocks"
+	"hash-of-wisdom/internal/pow/challenge"
+	"hash-of-wisdom/internal/protocol"
+	"hash-of-wisdom/internal/quotes"
+	"hash-of-wisdom/internal/service"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/mock"
+	"github.com/stretchr/testify/require"
+)
+
+func TestNewWisdomApplication(t *testing.T) {
+	mockService := mocks.NewMockWisdomService(t)
+	app := NewWisdomApplication(mockService)
+
+	assert.NotNil(t, app)
+	assert.Equal(t, mockService, app.wisdomService)
+}
+
+func TestWisdomApplication_HandleMessage_UnsupportedType(t *testing.T) {
+	mockService := mocks.NewMockWisdomService(t)
+	app := NewWisdomApplication(mockService)
+
+	ctx := context.Background()
+	msg := &protocol.Message{
+		Type:          protocol.MessageType(0xFF), // Invalid type
+		PayloadLength: 0,
+		PayloadStream: nil,
+	}
+
+	response, err := app.HandleMessage(ctx, msg)
+	require.NoError(t, err)
+
+	// Type assert to ErrorResponse
+	errorResponse, ok := response.(*protocol.ErrorResponse)
+	require.True(t, ok, "Expected ErrorResponse")
+	assert.Equal(t, protocol.ErrMalformedMessage, errorResponse.Code)
+	assert.Contains(t, errorResponse.Message, "unsupported message type: 0xff")
+}
+
+func TestWisdomApplication_HandleChallengeRequest_Success(t *testing.T) {
+	mockService := mocks.NewMockWisdomService(t)
+	app := NewWisdomApplication(mockService)
+
+	// Mock successful challenge generation
+	testChallenge := &challenge.Challenge{
+		Resource:   "quotes",
+		Timestamp:  12345,
+		Difficulty: 4,
+		Random:     []byte("test"),
+		HMAC:       []byte("signature"),
+	}
+
+	mockService.On("GenerateChallenge", mock.Anything, "quotes").Return(testChallenge, nil)
+
+	ctx := context.Background()
+	msg := &protocol.Message{
+		Type:          protocol.ChallengeRequestType,
+		PayloadLength: 0,
+		PayloadStream: nil,
+	}
+
+	response, err := app.HandleMessage(ctx, msg)
+	require.NoError(t, err)
+
+	// Type assert to ChallengeResponse
+	challengeResponse, ok := response.(*protocol.ChallengeResponse)
+	require.True(t, ok, "Expected ChallengeResponse")
+	assert.Equal(t, testChallenge, challengeResponse.Challenge)
+
+	mockService.AssertExpectations(t)
+}
+
+func TestWisdomApplication_HandleChallengeRequest_ServiceError(t *testing.T) {
+	mockService := mocks.NewMockWisdomService(t)
+	app := NewWisdomApplication(mockService)
+
+	// Mock service error
+	mockService.On("GenerateChallenge", mock.Anything, "quotes").Return(nil, errors.New("service error"))
+
+	ctx := context.Background()
+	msg := &protocol.Message{
+		Type:          protocol.ChallengeRequestType,
+		PayloadLength: 0,
+		PayloadStream: nil,
+	}
+
+	response, err := app.HandleMessage(ctx, msg)
+	require.NoError(t, err)
+
+	// Type assert to ErrorResponse
+	errorResponse, ok := response.(*protocol.ErrorResponse)
+	require.True(t, ok, "Expected ErrorResponse")
+	assert.Equal(t, protocol.ErrServerError, errorResponse.Code)
+	assert.Equal(t, "Contact administrator", errorResponse.Message)
+
+	mockService.AssertExpectations(t)
+}
+
+func TestWisdomApplication_HandleSolutionRequest_Success(t *testing.T) {
+	mockService := mocks.NewMockWisdomService(t)
+	app := NewWisdomApplication(mockService)
+
+	// Create test solution request
+	testChallenge := challenge.Challenge{
+		Resource:   "quotes",
+		Timestamp:  12345,
+		Difficulty: 4,
+		Random:     []byte("test"),
+		HMAC:       []byte("signature"),
+	}
+
+	solutionPayload := protocol.SolutionRequest{
+		Challenge: testChallenge,
+		Nonce:     12345,
+	}
+
+	payloadJSON, err := json.Marshal(solutionPayload)
+	require.NoError(t, err)
+
+	testQuote := &quotes.Quote{
+		Text:   "Test quote",
+		Author: "Test Author",
+	}
+
+	// Mock successful verification and quote retrieval
+	mockService.On("VerifySolution", mock.Anything, mock.AnythingOfType("*challenge.Solution")).Return(nil)
+	mockService.On("GetQuote", mock.Anything).Return(testQuote, nil)
+
+	ctx := context.Background()
+	msg := &protocol.Message{
+		Type:          protocol.SolutionRequestType,
+		PayloadLength: uint32(len(payloadJSON)),
+		PayloadStream: bytes.NewReader(payloadJSON),
+	}
+
+	response, err := app.HandleMessage(ctx, msg)
+	require.NoError(t, err)
+
+	// Type assert to SolutionResponse
+	solutionResponse, ok := response.(*protocol.SolutionResponse)
+	require.True(t, ok, "Expected SolutionResponse")
+	assert.Equal(t, testQuote, solutionResponse.Quote)
+
+	mockService.AssertExpectations(t)
+}
+
+func TestWisdomApplication_HandleSolutionRequest_InvalidJSON(t *testing.T) {
+	mockService := mocks.NewMockWisdomService(t)
+	app := NewWisdomApplication(mockService)
+
+	invalidJSON := []byte("invalid json")
+	ctx := context.Background()
+	msg := &protocol.Message{
+		Type:          protocol.SolutionRequestType,
+		PayloadLength: uint32(len(invalidJSON)),
+		PayloadStream: bytes.NewReader(invalidJSON),
+	}
+
+	response, err := app.HandleMessage(ctx, msg)
+	require.NoError(t, err)
+
+	// Type assert to ErrorResponse
+	errorResponse, ok := response.(*protocol.ErrorResponse)
+	require.True(t, ok, "Expected ErrorResponse")
+	assert.Equal(t, protocol.ErrMalformedMessage, errorResponse.Code)
+	assert.Equal(t, "invalid solution format", errorResponse.Message)
+
+	mockService.AssertNotCalled(t, "VerifySolution")
+	mockService.AssertNotCalled(t, "GetQuote")
+}
+
+func TestWisdomApplication_HandleSolutionRequest_VerificationFailed(t *testing.T) {
+	mockService := mocks.NewMockWisdomService(t)
+	app := NewWisdomApplication(mockService)
+
+	// Create test solution request
+	testChallenge := challenge.Challenge{
+		Resource:   "quotes",
+		Timestamp:  12345,
+		Difficulty: 4,
+		Random:     []byte("test"),
+		HMAC:       []byte("signature"),
+	}
+
+	solutionPayload := protocol.SolutionRequest{
+		Challenge: testChallenge,
+		Nonce:     12345,
+	}
+
+	payloadJSON, err := json.Marshal(solutionPayload)
+	require.NoError(t, err)
+
+	// Mock verification failure
+	mockService.On("VerifySolution", mock.Anything, mock.AnythingOfType("*challenge.Solution")).Return(service.ErrInvalidSolution)
+
+	ctx := context.Background()
+	msg := &protocol.Message{
+		Type:          protocol.SolutionRequestType,
+		PayloadLength: uint32(len(payloadJSON)),
+		PayloadStream: bytes.NewReader(payloadJSON),
+	}
+
+	response, err := app.HandleMessage(ctx, msg)
+	require.NoError(t, err)
+
+	// Type assert to ErrorResponse
+	errorResponse, ok := response.(*protocol.ErrorResponse)
+	require.True(t, ok, "Expected ErrorResponse")
+	assert.Equal(t, protocol.ErrInvalidSolution, errorResponse.Code)
+	assert.Equal(t, "solution verification failed", errorResponse.Message)
+
+	mockService.AssertExpectations(t)
+	mockService.AssertNotCalled(t, "GetQuote")
+}
+
+func TestWisdomApplication_HandleSolutionRequest_QuoteServiceError(t *testing.T) {
+	mockService := mocks.NewMockWisdomService(t)
+	app := NewWisdomApplication(mockService)
+
+	// Create test solution request
+	testChallenge := challenge.Challenge{
+		Resource:   "quotes",
+		Timestamp:  12345,
+		Difficulty: 4,
+		Random:     []byte("test"),
+		HMAC:       []byte("signature"),
+	}
+
+	solutionPayload := protocol.SolutionRequest{
+		Challenge: testChallenge,
+		Nonce:     12345,
+	}
+
+	payloadJSON, err := json.Marshal(solutionPayload)
+	require.NoError(t, err)
+
+	// Mock successful verification but quote service error
+	mockService.On("VerifySolution", mock.Anything, mock.AnythingOfType("*challenge.Solution")).Return(nil)
+	mockService.On("GetQuote", mock.Anything).Return(nil, errors.New("quote service error"))
+
+	ctx := context.Background()
+	msg := &protocol.Message{
+		Type:          protocol.SolutionRequestType,
+		PayloadLength: uint32(len(payloadJSON)),
+		PayloadStream: bytes.NewReader(payloadJSON),
+	}
+
+	response, err := app.HandleMessage(ctx, msg)
+	require.NoError(t, err)
+
+	// Type assert to ErrorResponse
+	errorResponse, ok := response.(*protocol.ErrorResponse)
+	require.True(t, ok, "Expected ErrorResponse")
+	assert.Equal(t, protocol.ErrServerError, errorResponse.Code)
+	assert.Equal(t, "Contact administrator", errorResponse.Message)
+
+	mockService.AssertExpectations(t)
+}
+
+func TestWisdomApplication_HandleMessage_ContextCancellation(t *testing.T) {
+	mockService := mocks.NewMockWisdomService(t)
+	app := NewWisdomApplication(mockService)
+
+	// Create cancelled context
+	ctx, cancel := context.WithCancel(context.Background())
+	cancel()
+
+	// Mock service to respect context cancellation
+	mockService.On("GenerateChallenge", mock.Anything, "quotes").Return(nil, context.Canceled)
+
+	msg := &protocol.Message{
+		Type:          protocol.ChallengeRequestType,
+		PayloadLength: 0,
+		PayloadStream: nil,
+	}
+
+	response, err := app.HandleMessage(ctx, msg)
+	require.NoError(t, err)
+
+	// Type assert to ErrorResponse
+	errorResponse, ok := response.(*protocol.ErrorResponse)
+	require.True(t, ok, "Expected ErrorResponse")
+	assert.Equal(t, protocol.ErrServerError, errorResponse.Code)
+
+	mockService.AssertExpectations(t)
+}
+
+func TestResponseEncoding(t *testing.T) {
+	// Test ChallengeResponse encoding produces valid binary format
+	testChallenge := &challenge.Challenge{
+		Resource:   "quotes",
+		Timestamp:  12345,
+		Difficulty: 4,
+		Random:     []byte("test"),
+		HMAC:       []byte("signature"),
+	}
+
+	challengeResponse := &protocol.ChallengeResponse{Challenge: testChallenge}
+	var buf bytes.Buffer
+	err := challengeResponse.Encode(&buf)
+	require.NoError(t, err)
+
+	// Verify binary format
+	data := buf.Bytes()
+	assert.GreaterOrEqual(t, len(data), 5) // At least header size
+
+	// Check message type
+	assert.Equal(t, byte(protocol.ChallengeResponseType), data[0])
+
+	// Check payload contains expected data
+	payload := string(data[5:]) // Skip header
+	assert.Contains(t, payload, "quotes")
+	assert.Contains(t, payload, "12345")
+}

internal/application/mocks/mock_wisdom_service.go

@@ -0,0 +1,203 @@
+// Code generated by mockery v2.53.5. DO NOT EDIT.
+
+package mocks
+
+import (
+	context "context"
+	challenge "hash-of-wisdom/internal/pow/challenge"
+
+	mock "github.com/stretchr/testify/mock"
+
+	quotes "hash-of-wisdom/internal/quotes"
+)
+
+// MockWisdomService is an autogenerated mock type for the WisdomService type
+type MockWisdomService struct {
+	mock.Mock
+}
+
+type MockWisdomService_Expecter struct {
+	mock *mock.Mock
+}
+
+func (_m *MockWisdomService) EXPECT() *MockWisdomService_Expecter {
+	return &MockWisdomService_Expecter{mock: &_m.Mock}
+}
+
+// GenerateChallenge provides a mock function with given fields: ctx, resource
+func (_m *MockWisdomService) GenerateChallenge(ctx context.Context, resource string) (*challenge.Challenge, error) {
+	ret := _m.Called(ctx, resource)
+
+	if len(ret) == 0 {
+		panic("no return value specified for GenerateChallenge")
+	}
+
+	var r0 *challenge.Challenge
+	var r1 error
+	if rf, ok := ret.Get(0).(func(context.Context, string) (*challenge.Challenge, error)); ok {
+		return rf(ctx, resource)
+	}
+	if rf, ok := ret.Get(0).(func(context.Context, string) *challenge.Challenge); ok {
+		r0 = rf(ctx, resource)
+	} else {
+		if ret.Get(0) != nil {
+			r0 = ret.Get(0).(*challenge.Challenge)
+		}
+	}
+
+	if rf, ok := ret.Get(1).(func(context.Context, string) error); ok {
+		r1 = rf(ctx, resource)
+	} else {
+		r1 = ret.Error(1)
+	}
+
+	return r0, r1
+}
+
+// MockWisdomService_GenerateChallenge_Call is a *mock.Call that shadows Run/Return methods with type explicit version for method 'GenerateChallenge'
+type MockWisdomService_GenerateChallenge_Call struct {
+	*mock.Call
+}
+
+// GenerateChallenge is a helper method to define mock.On call
+//   - ctx context.Context
+//   - resource string
+func (_e *MockWisdomService_Expecter) GenerateChallenge(ctx interface{}, resource interface{}) *MockWisdomService_GenerateChallenge_Call {
+	return &MockWisdomService_GenerateChallenge_Call{Call: _e.mock.On("GenerateChallenge", ctx, resource)}
+}
+
+func (_c *MockWisdomService_GenerateChallenge_Call) Run(run func(ctx context.Context, resource string)) *MockWisdomService_GenerateChallenge_Call {
+	_c.Call.Run(func(args mock.Arguments) {
+		run(args[0].(context.Context), args[1].(string))
+	})
+	return _c
+}
+
+func (_c *MockWisdomService_GenerateChallenge_Call) Return(_a0 *challenge.Challenge, _a1 error) *MockWisdomService_GenerateChallenge_Call {
+	_c.Call.Return(_a0, _a1)
+	return _c
+}
+
+func (_c *MockWisdomService_GenerateChallenge_Call) RunAndReturn(run func(context.Context, string) (*challenge.Challenge, error)) *MockWisdomService_GenerateChallenge_Call {
+	_c.Call.Return(run)
+	return _c
+}
+
+// GetQuote provides a mock function with given fields: ctx
+func (_m *MockWisdomService) GetQuote(ctx context.Context) (*quotes.Quote, error) {
+	ret := _m.Called(ctx)
+
+	if len(ret) == 0 {
+		panic("no return value specified for GetQuote")
+	}
+
+	var r0 *quotes.Quote
+	var r1 error
+	if rf, ok := ret.Get(0).(func(context.Context) (*quotes.Quote, error)); ok {
+		return rf(ctx)
+	}
+	if rf, ok := ret.Get(0).(func(context.Context) *quotes.Quote); ok {
+		r0 = rf(ctx)
+	} else {
+		if ret.Get(0) != nil {
+			r0 = ret.Get(0).(*quotes.Quote)
+		}
+	}
+
+	if rf, ok := ret.Get(1).(func(context.Context) error); ok {
+		r1 = rf(ctx)
+	} else {
+		r1 = ret.Error(1)
+	}
+
+	return r0, r1
+}
+
+// MockWisdomService_GetQuote_Call is a *mock.Call that shadows Run/Return methods with type explicit version for method 'GetQuote'
+type MockWisdomService_GetQuote_Call struct {
+	*mock.Call
+}
+
+// GetQuote is a helper method to define mock.On call
+//   - ctx context.Context
+func (_e *MockWisdomService_Expecter) GetQuote(ctx interface{}) *MockWisdomService_GetQuote_Call {
+	return &MockWisdomService_GetQuote_Call{Call: _e.mock.On("GetQuote", ctx)}
+}
+
+func (_c *MockWisdomService_GetQuote_Call) Run(run func(ctx context.Context)) *MockWisdomService_GetQuote_Call {
+	_c.Call.Run(func(args mock.Arguments) {
+		run(args[0].(context.Context))
+	})
+	return _c
+}
+
+func (_c *MockWisdomService_GetQuote_Call) Return(_a0 *quotes.Quote, _a1 error) *MockWisdomService_GetQuote_Call {
+	_c.Call.Return(_a0, _a1)
+	return _c
+}
+
+func (_c *MockWisdomService_GetQuote_Call) RunAndReturn(run func(context.Context) (*quotes.Quote, error)) *MockWisdomService_GetQuote_Call {
+	_c.Call.Return(run)
+	return _c
+}
+
+// VerifySolution provides a mock function with given fields: ctx, solution
+func (_m *MockWisdomService) VerifySolution(ctx context.Context, solution *challenge.Solution) error {
+	ret := _m.Called(ctx, solution)
+
+	if len(ret) == 0 {
+		panic("no return value specified for VerifySolution")
+	}
+
+	var r0 error
+	if rf, ok := ret.Get(0).(func(context.Context, *challenge.Solution) error); ok {
+		r0 = rf(ctx, solution)
+	} else {
+		r0 = ret.Error(0)
+	}
+
+	return r0
+}
+
+// MockWisdomService_VerifySolution_Call is a *mock.Call that shadows Run/Return methods with type explicit version for method 'VerifySolution'
+type MockWisdomService_VerifySolution_Call struct {
+	*mock.Call
+}
+
+// VerifySolution is a helper method to define mock.On call
+//   - ctx context.Context
+//   - solution *challenge.Solution
+func (_e *MockWisdomService_Expecter) VerifySolution(ctx interface{}, solution interface{}) *MockWisdomService_VerifySolution_Call {
+	return &MockWisdomService_VerifySolution_Call{Call: _e.mock.On("VerifySolution", ctx, solution)}
+}
+
+func (_c *MockWisdomService_VerifySolution_Call) Run(run func(ctx context.Context, solution *challenge.Solution)) *MockWisdomService_VerifySolution_Call {
+	_c.Call.Run(func(args mock.Arguments) {
+		run(args[0].(context.Context), args[1].(*challenge.Solution))
+	})
+	return _c
+}
+
+func (_c *MockWisdomService_VerifySolution_Call) Return(_a0 error) *MockWisdomService_VerifySolution_Call {
+	_c.Call.Return(_a0)
+	return _c
+}
+
+func (_c *MockWisdomService_VerifySolution_Call) RunAndReturn(run func(context.Context, *challenge.Solution) error) *MockWisdomService_VerifySolution_Call {
+	_c.Call.Return(run)
+	return _c
+}
+
+// NewMockWisdomService creates a new instance of MockWisdomService. It also registers a testing interface on the mock and a cleanup function to assert the mocks expectations.
+// The first argument is typically a *testing.T value.
+func NewMockWisdomService(t interface {
+	mock.TestingT
+	Cleanup(func())
+}) *MockWisdomService {
+	mock := &MockWisdomService{}
+	mock.Mock.Test(t)
+
+	t.Cleanup(func() { mock.AssertExpectations(t) })
+
+	return mock
+}

internal/config/config.go

@@ -0,0 +1,72 @@
+package config
+
+import (
+	"time"
+
+	"github.com/ilyakaznacheev/cleanenv"
+)
+
+type Config struct {
+	Server  ServerConfig  `yaml:"server"`
+	PoW     PoWConfig     `yaml:"pow"`
+	Quotes  QuotesConfig  `yaml:"quotes"`
+	Metrics MetricsConfig `yaml:"metrics"`
+	Logging LoggingConfig `yaml:"logging"`
+}
+
+type ServerConfig struct {
+	Address  string        `yaml:"address" env:"SERVER_ADDRESS" env-default:":8080"`
+	Timeouts TimeoutConfig `yaml:"timeouts"`
+}
+
+type TimeoutConfig struct {
+	Read       time.Duration `yaml:"read" env:"SERVER_READ_TIMEOUT" env-default:"5s"`
+	Write      time.Duration `yaml:"write" env:"SERVER_WRITE_TIMEOUT" env-default:"5s"`
+	Connection time.Duration `yaml:"connection" env:"SERVER_CONNECTION_TIMEOUT" env-default:"15s"`
+}
+
+type PoWConfig struct {
+	Difficulty    int           `yaml:"difficulty" env:"POW_DIFFICULTY" env-default:"4"`
+	MaxDifficulty int           `yaml:"max_difficulty" env:"POW_MAX_DIFFICULTY" env-default:"10"`
+	TTL           time.Duration `yaml:"ttl" env:"POW_TTL" env-default:"5m"`
+	HMACSecret    string        `yaml:"hmac_secret" env:"POW_HMAC_SECRET" env-default:"development-secret-change-in-production"`
+}
+
+type QuotesConfig struct {
+	Timeout time.Duration `yaml:"timeout" env:"QUOTES_TIMEOUT" env-default:"10s"`
+}
+
+type MetricsConfig struct {
+	Address string `yaml:"address" env:"METRICS_ADDRESS" env-default:":8081"`
+}
+
+type LoggingConfig struct {
+	Level  string `yaml:"level" env:"LOG_LEVEL" env-default:"info"`
+	Format string `yaml:"format" env:"LOG_FORMAT" env-default:"text"`
+}
+
+func Load(configPath string) (*Config, error) {
+	cfg := &Config{}
+
+	if configPath != "" {
+		err := cleanenv.ReadConfig(configPath, cfg)
+		if err != nil {
+			return nil, err
+		}
+	} else {
+		err := cleanenv.ReadEnv(cfg)
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	return cfg, nil
+}
+
+func (c *Config) ToServerConfig() *ServerConfig {
+	return &c.Server
+}
+
+func (c *Config) ToPoWConfig() *PoWConfig {
+	return &c.PoW
+}

internal/lib/sl/sl.go

@@ -0,0 +1,27 @@
+package sl
+
+import (
+	"context"
+	"log/slog"
+)
+
+// Err creates a structured error attribute for slog
+func Err(err error) slog.Attr {
+	return slog.Attr{
+		Key:   "error",
+		Value: slog.StringValue(err.Error()),
+	}
+}
+
+// MockHandler is a test handler that discards all log messages
+type MockHandler struct{}
+
+func (h *MockHandler) Enabled(context.Context, slog.Level) bool  { return false }
+func (h *MockHandler) Handle(context.Context, slog.Record) error { return nil }
+func (h *MockHandler) WithAttrs([]slog.Attr) slog.Handler        { return h }
+func (h *MockHandler) WithGroup(string) slog.Handler             { return h }
+
+// NewMockLogger creates a logger that discards all messages for testing
+func NewMockLogger() *slog.Logger {
+	return slog.New(&MockHandler{})
+}

internal/metrics/metrics.go

@@ -0,0 +1,33 @@
+package metrics
+
+import (
+	"github.com/prometheus/client_golang/prometheus"
+	"github.com/prometheus/client_golang/prometheus/promauto"
+)
+
+var (
+	ActiveConnections = promauto.NewGauge(prometheus.GaugeOpts{
+		Name: "wisdom_active_connections",
+		Help: "Number of currently active TCP connections",
+	})
+
+	RequestsTotal = promauto.NewCounter(prometheus.CounterOpts{
+		Name: "wisdom_requests_total",
+		Help: "Total number of requests processed",
+	})
+
+	RequestErrors = promauto.NewCounterVec(prometheus.CounterOpts{
+		Name: "wisdom_request_errors_total",
+		Help: "Total number of request errors by type",
+	}, []string{"error_type"})
+
+	RequestDuration = promauto.NewHistogram(prometheus.HistogramOpts{
+		Name: "wisdom_request_duration_seconds",
+		Help: "Time taken to process requests",
+	})
+
+	QuotesServed = promauto.NewCounter(prometheus.CounterOpts{
+		Name: "wisdom_quotes_served_total",
+		Help: "Total number of quotes successfully served to clients",
+	})
+)

internal/pow/challenge/types.go

@@ -68,8 +68,8 @@ func (c *Challenge) VerifySolution(nonce uint64) bool {
 
 // hasLeadingZeroBits checks if hash has the required number of leading zero bits
 func hasLeadingZeroBits(hash []byte, difficulty int) bool {
-	full := difficulty >> 3        // number of whole zero bytes
+	full := difficulty >> 3     // number of whole zero bytes
-	rem  := uint(difficulty & 7)   // remaining leading zero bits
+	rem := uint(difficulty & 7) // remaining leading zero bits
 
 	for i := range full {
 		if hash[i] != 0 {

internal/protocol/codec.go

@@ -1,111 +0,0 @@
-package protocol
-
-import (
-	"encoding/binary"
-	"fmt"
-	"io"
-	"unicode/utf8"
-)
-
-// Codec handles encoding and decoding of protocol messages
-type Codec struct{}
-
-// NewCodec creates a new protocol codec
-func NewCodec() *Codec {
-	return &Codec{}
-}
-
-// Encode writes a message to the writer using the protocol format
-func (c *Codec) Encode(w io.Writer, msg *Message) error {
-	if msg == nil {
-		return fmt.Errorf("message cannot be nil")
-	}
-
-	// Validate payload size
-	if len(msg.Payload) > MaxPayloadSize {
-		return fmt.Errorf("payload size %d exceeds maximum %d", len(msg.Payload), MaxPayloadSize)
-	}
-
-	// Write message type (1 byte)
-	if err := binary.Write(w, binary.BigEndian, msg.Type); err != nil {
-		return fmt.Errorf("failed to write message type: %w", err)
-	}
-
-	// Write payload length (4 bytes, big-endian)
-	payloadLength := uint32(len(msg.Payload))
-	if err := binary.Write(w, binary.BigEndian, payloadLength); err != nil {
-		return fmt.Errorf("failed to write payload length: %w", err)
-	}
-
-	// Write payload if present
-	if len(msg.Payload) > 0 {
-		if _, err := w.Write(msg.Payload); err != nil {
-			return fmt.Errorf("failed to write payload: %w", err)
-		}
-	}
-
-	return nil
-}
-
-// Decode reads a message from the reader using the protocol format
-func (c *Codec) Decode(r io.Reader) (*Message, error) {
-	// Read message type (1 byte)
-	var msgType MessageType
-	if err := binary.Read(r, binary.BigEndian, &msgType); err != nil {
-		if err == io.EOF {
-			return nil, err
-		}
-		return nil, fmt.Errorf("failed to read message type: %w", err)
-	}
-
-	// Validate message type
-	if !isValidMessageType(msgType) {
-		return nil, fmt.Errorf("invalid message type: 0x%02x", msgType)
-	}
-
-	// Read payload length (4 bytes, big-endian)
-	var payloadLength uint32
-	if err := binary.Read(r, binary.BigEndian, &payloadLength); err != nil {
-		return nil, fmt.Errorf("failed to read payload length: %w", err)
-	}
-
-	// Validate payload length
-	if payloadLength > MaxPayloadSize {
-		return nil, fmt.Errorf("payload length %d exceeds maximum %d", payloadLength, MaxPayloadSize)
-	}
-
-	// Read payload if present
-	var payload []byte
-	if payloadLength > 0 {
-		payload = make([]byte, payloadLength)
-		// Use LimitReader to ensure we don't read more than payloadLength bytes
-		// even if the underlying reader has more data available
-		limitedReader := io.LimitReader(r, int64(payloadLength))
-		// Note: ReadFull may block waiting for data. The connection handler
-		// MUST set appropriate read deadlines to prevent slowloris attacks
-		if _, err := io.ReadFull(limitedReader, payload); err != nil {
-			return nil, fmt.Errorf("failed to read payload: %w", err)
-		}
-
-		// Validate payload is valid UTF-8
-		if !utf8.Valid(payload) {
-			return nil, fmt.Errorf("payload contains invalid UTF-8")
-		}
-	}
-
-	return &Message{
-		Type:    msgType,
-		Payload: payload,
-	}, nil
-}
-
-
-// isValidMessageType checks if the message type is defined in the protocol
-func isValidMessageType(msgType MessageType) bool {
-	switch msgType {
-	case ChallengeRequest, ChallengeResponse, SolutionRequest, QuoteResponse, ErrorResponse:
-		return true
-	default:
-		return false
-	}
-}

internal/protocol/codec_test.go

@@ -1,308 +0,0 @@
-package protocol
-
-import (
-	"bytes"
-	"encoding/json"
-	"io"
-	"testing"
-	"time"
-
-	"github.com/stretchr/testify/assert"
-	"github.com/stretchr/testify/require"
-)
-
-func TestCodec_Encode_Decode(t *testing.T) {
-	codec := NewCodec()
-
-	tests := []struct {
-		name    string
-		message *Message
-	}{
-		{
-			name: "challenge request (empty payload)",
-			message: &Message{
-				Type:    ChallengeRequest,
-				Payload: []byte{},
-			},
-		},
-		{
-			name: "challenge response with payload",
-			message: &Message{
-				Type:    ChallengeResponse,
-				Payload: []byte(`{"challenge":{"timestamp":1640995200,"difficulty":4}}`),
-			},
-		},
-		{
-			name: "error response",
-			message: &Message{
-				Type:    ErrorResponse,
-				Payload: []byte(`{"code":"INVALID_SOLUTION","message":"Invalid nonce"}`),
-			},
-		},
-	}
-
-	for _, tt := range tests {
-		t.Run(tt.name, func(t *testing.T) {
-			var buf bytes.Buffer
-
-			// Encode message
-			err := codec.Encode(&buf, tt.message)
-			require.NoError(t, err)
-
-			// Decode message
-			decoded, err := codec.Decode(&buf)
-			require.NoError(t, err)
-
-			assert.Equal(t, tt.message.Type, decoded.Type)
-			if len(tt.message.Payload) == 0 && len(decoded.Payload) == 0 {
-				// Both are empty (nil or empty slice)
-				assert.True(t, true)
-			} else {
-				assert.Equal(t, tt.message.Payload, decoded.Payload)
-			}
-		})
-	}
-}
-
-func TestCodec_Encode_Errors(t *testing.T) {
-	codec := NewCodec()
-
-	tests := []struct {
-		name    string
-		message *Message
-		wantErr string
-	}{
-		{
-			name:    "nil message",
-			message: nil,
-			wantErr: "message cannot be nil",
-		},
-		{
-			name: "payload too large",
-			message: &Message{
-				Type:    ChallengeRequest,
-				Payload: make([]byte, MaxPayloadSize+1),
-			},
-			wantErr: "payload size",
-		},
-	}
-
-	for _, tt := range tests {
-		t.Run(tt.name, func(t *testing.T) {
-			var buf bytes.Buffer
-			err := codec.Encode(&buf, tt.message)
-			assert.Error(t, err)
-			assert.Contains(t, err.Error(), tt.wantErr)
-		})
-	}
-}
-
-func TestCodec_Decode_Errors(t *testing.T) {
-	codec := NewCodec()
-
-	tests := []struct {
-		name    string
-		data    []byte
-		wantErr string
-	}{
-		{
-			name:    "empty data",
-			data:    []byte{},
-			wantErr: "EOF",
-		},
-		{
-			name:    "invalid message type",
-			data:    []byte{0xFF, 0x00, 0x00, 0x00, 0x00},
-			wantErr: "invalid message type",
-		},
-		{
-			name:    "incomplete header",
-			data:    []byte{0x01, 0x00, 0x00},
-			wantErr: "failed to read payload length",
-		},
-		{
-			name:    "payload too large",
-			data:    append([]byte{0x01}, encodeBigEndianUint32(MaxPayloadSize+1)...),
-			wantErr: "payload length",
-		},
-		{
-			name:    "incomplete payload",
-			data:    []byte{0x01, 0x00, 0x00, 0x00, 0x05, 0x01, 0x02},
-			wantErr: "failed to read payload",
-		},
-		{
-			name:    "invalid UTF-8 in payload",
-			data:    []byte{0x01, 0x00, 0x00, 0x00, 0x03, 0xFF, 0xFE, 0xFD},
-			wantErr: "invalid UTF-8",
-		},
-	}
-
-	for _, tt := range tests {
-		t.Run(tt.name, func(t *testing.T) {
-			buf := bytes.NewBuffer(tt.data)
-			_, err := codec.Decode(buf)
-			assert.Error(t, err)
-			assert.Contains(t, err.Error(), tt.wantErr)
-		})
-	}
-}
-
-
-func TestCodec_RoundTrip_RealPayloads(t *testing.T) {
-	codec := NewCodec()
-
-	t.Run("challenge response round trip", func(t *testing.T) {
-		original := &ChallengeResponsePayload{
-			Timestamp:  time.Now().Unix(),
-			Difficulty: 4,
-			Resource:   "quotes",
-			Random:     []byte("random123"),
-			HMAC:       []byte("hmac_signature"),
-		}
-
-		// Marshal payload
-		jsonData, err := json.Marshal(original)
-		require.NoError(t, err)
-
-		msg := &Message{
-			Type:    ChallengeResponse,
-			Payload: jsonData,
-		}
-
-		// Simulate network transmission
-		var buf bytes.Buffer
-		err = codec.Encode(&buf, msg)
-		require.NoError(t, err)
-
-		// Decode message
-		decoded, err := codec.Decode(&buf)
-		require.NoError(t, err)
-
-		// Unmarshal payload
-		var result ChallengeResponsePayload
-		err = json.Unmarshal(decoded.Payload, &result)
-		require.NoError(t, err)
-
-		assert.Equal(t, original.Timestamp, result.Timestamp)
-		assert.Equal(t, original.Difficulty, result.Difficulty)
-		assert.Equal(t, original.Resource, result.Resource)
-		assert.Equal(t, original.Random, result.Random)
-		assert.Equal(t, original.HMAC, result.HMAC)
-	})
-
-	t.Run("quote response round trip", func(t *testing.T) {
-		original := &QuoteResponsePayload{
-			Text:   "Test quote",
-			Author: "Test author",
-		}
-
-		// Marshal payload
-		jsonData, err := json.Marshal(original)
-		require.NoError(t, err)
-
-		msg := &Message{
-			Type:    QuoteResponse,
-			Payload: jsonData,
-		}
-
-		var buf bytes.Buffer
-		err = codec.Encode(&buf, msg)
-		require.NoError(t, err)
-
-		decoded, err := codec.Decode(&buf)
-		require.NoError(t, err)
-
-		var result QuoteResponsePayload
-		err = json.Unmarshal(decoded.Payload, &result)
-		require.NoError(t, err)
-
-		assert.Equal(t, original.Text, result.Text)
-		assert.Equal(t, original.Author, result.Author)
-	})
-}
-
-func TestCodec_WriteError_Handling(t *testing.T) {
-	codec := NewCodec()
-
-	// Create a writer that fails after a certain number of bytes
-	failAfter := 3
-	writer := &failingWriter{failAfter: failAfter}
-
-	msg := &Message{
-		Type:    ChallengeResponse,
-		Payload: []byte("test payload"),
-	}
-
-	err := codec.Encode(writer, msg)
-	assert.Error(t, err)
-}
-
-func TestCodec_ReadError_Handling(t *testing.T) {
-	codec := NewCodec()
-
-	// Create a reader that fails after reading header
-	reader := &failingReader{
-		data:      []byte{0x01, 0x00, 0x00, 0x00, 0x05},
-		failAfter: 5,
-	}
-
-	_, err := codec.Decode(reader)
-	assert.Error(t, err)
-	assert.Contains(t, err.Error(), "failed to read payload")
-}
-
-// Helper functions and types for testing
-
-func encodeBigEndianUint32(val uint32) []byte {
-	return []byte{
-		byte(val >> 24),
-		byte(val >> 16),
-		byte(val >> 8),
-		byte(val),
-	}
-}
-
-type failingWriter struct {
-	written   int
-	failAfter int
-}
-
-func (w *failingWriter) Write(data []byte) (int, error) {
-	if w.written >= w.failAfter {
-		return 0, io.ErrShortWrite
-	}
-
-	remaining := w.failAfter - w.written
-	if len(data) <= remaining {
-		w.written += len(data)
-		return len(data), nil
-	}
-
-	w.written = w.failAfter
-	return remaining, io.ErrShortWrite
-}
-
-type failingReader struct {
-	data      []byte
-	pos       int
-	failAfter int
-}
-
-func (r *failingReader) Read(buf []byte) (int, error) {
-	if r.pos >= r.failAfter {
-		return 0, io.ErrUnexpectedEOF
-	}
-
-	if r.pos >= len(r.data) {
-		return 0, io.EOF
-	}
-
-	n := copy(buf, r.data[r.pos:])
-	r.pos += n
-
-	if r.pos >= r.failAfter {
-		return n, io.ErrUnexpectedEOF
-	}
-
-	return n, nil
-}

internal/protocol/constants.go

@@ -0,0 +1,31 @@
+package protocol
+
+// MessageType represents the type of protocol message
+type MessageType byte
+
+const (
+	ChallengeRequestType MessageType = 0x01
+	SolutionRequestType  MessageType = 0x03
+	// Response types (for responses.go)
+	ChallengeResponseType MessageType = 0x02
+	QuoteResponseType     MessageType = 0x04
+	ErrorResponseType     MessageType = 0x05
+)
+
+// Error codes as defined in protocol specification
+const (
+	ErrMalformedMessage   = "MALFORMED_MESSAGE"
+	ErrInvalidChallenge   = "INVALID_CHALLENGE"
+	ErrInvalidSolution    = "INVALID_SOLUTION"
+	ErrExpiredChallenge   = "EXPIRED_CHALLENGE"
+	ErrRateLimited        = "RATE_LIMITED"
+	ErrServerError        = "SERVER_ERROR"
+	ErrTooManyConnections = "TOO_MANY_CONNECTIONS"
+	ErrDifficultyTooHigh  = "DIFFICULTY_TOO_HIGH"
+)
+
+// Protocol constants
+const (
+	MaxPayloadSize = 8 * 1024 // 8KB maximum payload size
+	HeaderSize     = 5        // 1 byte type + 4 bytes length
+)

internal/protocol/encode_decode_test.go

@@ -0,0 +1,157 @@
+package protocol
+
+import (
+	"bytes"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"hash-of-wisdom/internal/pow/challenge"
+	"hash-of-wisdom/internal/quotes"
+)
+
+func TestSymmetricEncoding_ChallengeRequest(t *testing.T) {
+	// Create a challenge request
+	req := &ChallengeRequest{}
+
+	// Encode it
+	var buf bytes.Buffer
+	err := req.Encode(&buf)
+	require.NoError(t, err)
+
+	// Decode it back
+	decoder := NewMessageDecoder()
+	msg, err := decoder.Decode(&buf)
+	require.NoError(t, err)
+	assert.Equal(t, ChallengeRequestType, msg.Type)
+	assert.Equal(t, uint32(0), msg.PayloadLength)
+
+	// Decode the request payload
+	decodedReq := &ChallengeRequest{}
+	err = decodedReq.Decode(msg.PayloadStream)
+	require.NoError(t, err)
+}
+
+func TestSymmetricEncoding_SolutionRequest(t *testing.T) {
+	// Create a solution request
+	req := &SolutionRequest{
+		Challenge: challenge.Challenge{
+			Timestamp:  1640995200,
+			Difficulty: 4,
+			Resource:   "quotes",
+			Random:     []byte("test"),
+			HMAC:       []byte("test"),
+		},
+		Nonce: 12345,
+	}
+
+	// Encode it
+	var buf bytes.Buffer
+	err := req.Encode(&buf)
+	require.NoError(t, err)
+
+	// Decode it back
+	decoder := NewMessageDecoder()
+	msg, err := decoder.Decode(&buf)
+	require.NoError(t, err)
+	assert.Equal(t, SolutionRequestType, msg.Type)
+	assert.Greater(t, msg.PayloadLength, uint32(0))
+
+	// Decode the request payload
+	decodedReq := &SolutionRequest{}
+	err = decodedReq.Decode(msg.PayloadStream)
+	require.NoError(t, err)
+	assert.Equal(t, req.Nonce, decodedReq.Nonce)
+	assert.Equal(t, req.Challenge.Timestamp, decodedReq.Challenge.Timestamp)
+}
+
+func TestSymmetricEncoding_ChallengeResponse(t *testing.T) {
+	// Create a challenge response
+	resp := &ChallengeResponse{
+		Challenge: &challenge.Challenge{
+			Timestamp:  1640995200,
+			Difficulty: 4,
+			Resource:   "quotes",
+			Random:     []byte("test"),
+			HMAC:       []byte("test"),
+		},
+	}
+
+	// Encode it
+	var buf bytes.Buffer
+	err := resp.Encode(&buf)
+	require.NoError(t, err)
+
+	// Decode it back
+	decoder := NewMessageDecoder()
+	msg, err := decoder.Decode(&buf)
+	require.NoError(t, err)
+	assert.Equal(t, ChallengeResponseType, msg.Type)
+	assert.Greater(t, msg.PayloadLength, uint32(0))
+
+	// Decode the response payload
+	decodedResp := &ChallengeResponse{}
+	err = decodedResp.Decode(msg.PayloadStream)
+	require.NoError(t, err)
+	assert.Equal(t, resp.Challenge.Timestamp, decodedResp.Challenge.Timestamp)
+	assert.Equal(t, resp.Challenge.Difficulty, decodedResp.Challenge.Difficulty)
+}
+
+func TestSymmetricEncoding_SolutionResponse(t *testing.T) {
+	// Create a solution response
+	resp := &SolutionResponse{
+		Quote: &quotes.Quote{
+			Text:   "Test quote",
+			Author: "Test Author",
+		},
+	}
+
+	// Encode it
+	var buf bytes.Buffer
+	err := resp.Encode(&buf)
+	require.NoError(t, err)
+
+	// Decode it back
+	decoder := NewMessageDecoder()
+	msg, err := decoder.Decode(&buf)
+	require.NoError(t, err)
+	assert.Equal(t, QuoteResponseType, msg.Type)
+	assert.Greater(t, msg.PayloadLength, uint32(0))
+
+	// Decode the response payload
+	decodedResp := &SolutionResponse{}
+	err = decodedResp.Decode(msg.PayloadStream)
+	require.NoError(t, err)
+	assert.Equal(t, resp.Quote.Text, decodedResp.Quote.Text)
+	assert.Equal(t, resp.Quote.Author, decodedResp.Quote.Author)
+}
+
+func TestSymmetricEncoding_ErrorResponse(t *testing.T) {
+	// Create an error response
+	resp := &ErrorResponse{
+		Code:    "TEST_ERROR",
+		Message: "Test error message",
+		Details: map[string]string{"key": "value"},
+	}
+
+	// Encode it
+	var buf bytes.Buffer
+	err := resp.Encode(&buf)
+	require.NoError(t, err)
+
+	// Decode it back
+	decoder := NewMessageDecoder()
+	msg, err := decoder.Decode(&buf)
+	require.NoError(t, err)
+	assert.Equal(t, ErrorResponseType, msg.Type)
+	assert.Greater(t, msg.PayloadLength, uint32(0))
+
+	// Decode the response payload
+	decodedResp := &ErrorResponse{}
+	err = decodedResp.Decode(msg.PayloadStream)
+	require.NoError(t, err)
+	assert.Equal(t, resp.Code, decodedResp.Code)
+	assert.Equal(t, resp.Message, decodedResp.Message)
+	assert.Equal(t, resp.Details, decodedResp.Details)
+}

internal/protocol/encoder.go

@@ -0,0 +1,41 @@
+package protocol
+
+import (
+	"encoding/binary"
+	"encoding/json"
+	"fmt"
+	"io"
+)
+
+// encode is a helper function that encodes any message with the given message type
+func encode(w io.Writer, msgType MessageType, payload interface{}) error {
+	var payloadBytes []byte
+	var err error
+
+	// Only marshal if payload is not nil
+	if payload != nil {
+		payloadBytes, err = json.Marshal(payload)
+		if err != nil {
+			return fmt.Errorf("failed to encode payload: %w", err)
+		}
+	}
+
+	// Write message type (1 byte)
+	if err := binary.Write(w, binary.BigEndian, msgType); err != nil {
+		return fmt.Errorf("failed to write message type: %w", err)
+	}
+
+	// Write payload length (4 bytes, big-endian)
+	if err := binary.Write(w, binary.BigEndian, uint32(len(payloadBytes))); err != nil {
+		return fmt.Errorf("failed to write payload length: %w", err)
+	}
+
+	// Write JSON payload if we have one
+	if len(payloadBytes) > 0 {
+		if _, err := w.Write(payloadBytes); err != nil {
+			return fmt.Errorf("failed to write payload: %w", err)
+		}
+	}
+
+	return nil
+}

internal/protocol/message_decoder.go

@@ -0,0 +1,50 @@
+package protocol
+
+import (
+	"encoding/binary"
+	"fmt"
+	"io"
+)
+
+// MessageDecoder handles decoding of protocol message headers
+type MessageDecoder struct{}
+
+// NewMessageDecoder creates a new message decoder
+func NewMessageDecoder() *MessageDecoder {
+	return &MessageDecoder{}
+}
+
+// Decode reads the message header and returns a Message with the payload stream
+func (d *MessageDecoder) Decode(r io.Reader) (*Message, error) {
+	// Read message type (1 byte)
+	var msgType MessageType
+	if err := binary.Read(r, binary.BigEndian, &msgType); err != nil {
+		if err == io.EOF {
+			return nil, err
+		}
+		return nil, fmt.Errorf("failed to read message type: %w", err)
+	}
+
+	// Read payload length (4 bytes, big-endian)
+	var payloadLength uint32
+	if err := binary.Read(r, binary.BigEndian, &payloadLength); err != nil {
+		return nil, fmt.Errorf("failed to read payload length: %w", err)
+	}
+
+	// Validate payload length
+	if payloadLength > MaxPayloadSize {
+		return nil, fmt.Errorf("payload length %d exceeds maximum %d", payloadLength, MaxPayloadSize)
+	}
+
+	// Create limited reader for the payload
+	var payloadStream io.Reader
+	if payloadLength > 0 {
+		payloadStream = io.LimitReader(r, int64(payloadLength))
+	}
+
+	return &Message{
+		Type:          msgType,
+		PayloadLength: payloadLength,
+		PayloadStream: payloadStream,
+	}, nil
+}

internal/protocol/message_decoder_test.go

@@ -0,0 +1,215 @@
+package protocol
+
+import (
+	"bytes"
+	"io"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestMessageDecoder_Decode_Header(t *testing.T) {
+	decoder := NewMessageDecoder()
+
+	tests := []struct {
+		name       string
+		data       []byte
+		wantType   MessageType
+		wantLength uint32
+		wantErr    string
+	}{
+		{
+			name:       "challenge request with empty payload",
+			data:       []byte{0x01, 0x00, 0x00, 0x00, 0x00},
+			wantType:   ChallengeRequestType,
+			wantLength: 0,
+		},
+		{
+			name:       "solution request with payload",
+			data:       append([]byte{0x03, 0x00, 0x00, 0x00, 0x05}, []byte("hello")...),
+			wantType:   SolutionRequestType,
+			wantLength: 5,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			buf := bytes.NewBuffer(tt.data)
+			msg, err := decoder.Decode(buf)
+
+			if tt.wantErr != "" {
+				assert.Error(t, err)
+				assert.Contains(t, err.Error(), tt.wantErr)
+				return
+			}
+
+			require.NoError(t, err)
+			assert.Equal(t, tt.wantType, msg.Type)
+			assert.Equal(t, tt.wantLength, msg.PayloadLength)
+
+			if tt.wantLength > 0 {
+				assert.NotNil(t, msg.PayloadStream)
+			} else {
+				assert.Nil(t, msg.PayloadStream)
+			}
+		})
+	}
+}
+
+func TestMessageDecoder_Decode_Errors(t *testing.T) {
+	decoder := NewMessageDecoder()
+
+	tests := []struct {
+		name    string
+		data    []byte
+		wantErr string
+	}{
+		{
+			name:    "empty data",
+			data:    []byte{},
+			wantErr: "EOF",
+		},
+		{
+			name:    "incomplete header",
+			data:    []byte{0x01, 0x00, 0x00},
+			wantErr: "failed to read payload length",
+		},
+		{
+			name:    "payload too large",
+			data:    append([]byte{0x01}, encodeBigEndianUint32(MaxPayloadSize+1)...),
+			wantErr: "payload length",
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			buf := bytes.NewBuffer(tt.data)
+			_, err := decoder.Decode(buf)
+			assert.Error(t, err)
+			assert.Contains(t, err.Error(), tt.wantErr)
+		})
+	}
+}
+
+func TestChallengeRequest_Decode(t *testing.T) {
+	tests := []struct {
+		name   string
+		stream io.Reader
+	}{
+		{"nil stream", nil},
+		{"non-empty stream", bytes.NewReader([]byte("ignored"))},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			req := &ChallengeRequest{}
+			err := req.Decode(tt.stream)
+			assert.NoError(t, err)
+		})
+	}
+}
+
+func TestSolutionRequest_Decode(t *testing.T) {
+	tests := []struct {
+		name      string
+		payload   []byte
+		wantErr   bool
+		wantNonce uint64
+	}{
+		{
+			name:      "valid solution request",
+			payload:   []byte(`{"challenge":{"timestamp":1640995200,"difficulty":4,"resource":"quotes","random":"cmFuZG9tMTIz","hmac":"aG1hY19zaWduYXR1cmU="},"nonce":12345}`),
+			wantNonce: 12345,
+		},
+		{
+			name:    "invalid JSON",
+			payload: []byte(`{invalid json}`),
+			wantErr: true,
+		},
+		{
+			name:    "invalid UTF-8",
+			payload: []byte{0xFF, 0xFE, 0xFD},
+			wantErr: true,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			req := &SolutionRequest{}
+			var reader io.Reader
+			if tt.payload != nil {
+				reader = bytes.NewReader(tt.payload)
+			}
+
+			err := req.Decode(reader)
+
+			if tt.wantErr {
+				assert.Error(t, err)
+			} else {
+				require.NoError(t, err)
+				assert.Equal(t, tt.wantNonce, req.Nonce)
+			}
+		})
+	}
+
+	t.Run("nil stream should error", func(t *testing.T) {
+		req := &SolutionRequest{}
+		err := req.Decode(nil)
+		assert.Error(t, err)
+	})
+}
+
+func TestEndToEnd_RequestDecoding(t *testing.T) {
+	decoder := NewMessageDecoder()
+
+	t.Run("challenge request flow", func(t *testing.T) {
+		// Create message data: type=0x01, length=0
+		data := []byte{0x01, 0x00, 0x00, 0x00, 0x00}
+		buf := bytes.NewBuffer(data)
+
+		// Decode header
+		msg, err := decoder.Decode(buf)
+		require.NoError(t, err)
+		assert.Equal(t, ChallengeRequestType, msg.Type)
+
+		// Decode request
+		req := &ChallengeRequest{}
+		err = req.Decode(msg.PayloadStream)
+		require.NoError(t, err)
+	})
+
+	t.Run("solution request flow", func(t *testing.T) {
+		payload := `{"challenge":{"timestamp":1640995200,"difficulty":4,"resource":"quotes","random":"cmFuZG9tMTIz","hmac":"aG1hY19zaWduYXR1cmU="},"nonce":12345}`
+
+		// Create message data: type=0x03, length, payload
+		var buf bytes.Buffer
+		buf.WriteByte(0x03) // SolutionRequestType
+		length := uint32(len(payload))
+		buf.Write(encodeBigEndianUint32(length))
+		buf.WriteString(payload)
+
+		// Decode header
+		msg, err := decoder.Decode(&buf)
+		require.NoError(t, err)
+		assert.Equal(t, SolutionRequestType, msg.Type)
+		assert.Equal(t, length, msg.PayloadLength)
+
+		// Decode request
+		req := &SolutionRequest{}
+		err = req.Decode(msg.PayloadStream)
+		require.NoError(t, err)
+		assert.Equal(t, uint64(12345), req.Nonce)
+	})
+}
+
+// Helper functions for testing
+
+func encodeBigEndianUint32(val uint32) []byte {
+	return []byte{
+		byte(val >> 24),
+		byte(val >> 16),
+		byte(val >> 8),
+		byte(val),
+	}
+}

internal/protocol/requests.go

@@ -0,0 +1,45 @@
+package protocol
+
+import (
+	"encoding/json"
+	"io"
+
+	"hash-of-wisdom/internal/pow/challenge"
+)
+
+// ChallengeRequest is empty (no payload for challenge requests)
+type ChallengeRequest struct{}
+
+// Decode reads a challenge request from the payload stream
+func (r *ChallengeRequest) Decode(stream io.Reader) error {
+	// Challenge requests have no payload to decode
+	return nil
+}
+
+// Encode writes a challenge request to the writer
+func (r *ChallengeRequest) Encode(w io.Writer) error {
+	return encode(w, ChallengeRequestType, nil)
+}
+
+// SolutionRequest contains the client's solution attempt
+type SolutionRequest struct {
+	Challenge challenge.Challenge `json:"challenge"`
+	Nonce     uint64              `json:"nonce"`
+}
+
+// Decode reads a solution request from the payload stream
+func (r *SolutionRequest) Decode(stream io.Reader) error {
+	if stream == nil {
+		// json.NewDecoder panics on nil reader
+		return io.EOF
+	}
+
+	// Parse JSON directly from stream
+	decoder := json.NewDecoder(stream)
+	return decoder.Decode(r)
+}
+
+// Encode writes a solution request to the writer
+func (r *SolutionRequest) Encode(w io.Writer) error {
+	return encode(w, SolutionRequestType, r)
+}

internal/protocol/responses.go

@@ -0,0 +1,75 @@
+package protocol
+
+import (
+	"encoding/json"
+	"io"
+
+	"hash-of-wisdom/internal/pow/challenge"
+	"hash-of-wisdom/internal/quotes"
+)
+
+// ChallengeResponse represents a challenge response
+type ChallengeResponse struct {
+	Challenge *challenge.Challenge
+}
+
+// Decode reads a challenge response from the payload stream
+func (r *ChallengeResponse) Decode(stream io.Reader) error {
+	if stream == nil {
+		return io.EOF
+	}
+
+	// Parse JSON directly from stream
+	decoder := json.NewDecoder(stream)
+	return decoder.Decode(&r.Challenge)
+}
+
+// SolutionResponse represents a successful solution response (contains quote)
+type SolutionResponse struct {
+	Quote *quotes.Quote
+}
+
+// Decode reads a solution response from the payload stream
+func (r *SolutionResponse) Decode(stream io.Reader) error {
+	if stream == nil {
+		return io.EOF
+	}
+
+	// Parse JSON directly from stream
+	decoder := json.NewDecoder(stream)
+	return decoder.Decode(&r.Quote)
+}
+
+// ErrorResponse represents an error response
+type ErrorResponse struct {
+	Code       string            `json:"code"`
+	Message    string            `json:"message"`
+	RetryAfter int               `json:"retry_after,omitempty"`
+	Details    map[string]string `json:"details,omitempty"`
+}
+
+// Decode reads an error response from the payload stream
+func (r *ErrorResponse) Decode(stream io.Reader) error {
+	if stream == nil {
+		return io.EOF
+	}
+
+	// Parse JSON directly from stream
+	decoder := json.NewDecoder(stream)
+	return decoder.Decode(r)
+}
+
+// Encode writes the challenge response to the writer
+func (r *ChallengeResponse) Encode(w io.Writer) error {
+	return encode(w, ChallengeResponseType, r.Challenge)
+}
+
+// Encode writes the solution response to the writer
+func (r *SolutionResponse) Encode(w io.Writer) error {
+	return encode(w, QuoteResponseType, r.Quote)
+}
+
+// Encode writes the error response to the writer
+func (r *ErrorResponse) Encode(w io.Writer) error {
+	return encode(w, ErrorResponseType, r)
+}

internal/protocol/roundtrip_test.go

@@ -0,0 +1,194 @@
+package protocol
+
+import (
+	"bytes"
+	"encoding/binary"
+	"encoding/json"
+	"testing"
+
+	"hash-of-wisdom/internal/pow/challenge"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestChallengeResponse_BinaryFormat(t *testing.T) {
+	testChallenge := &challenge.Challenge{
+		Timestamp:  1640995200,
+		Difficulty: 4,
+		Resource:   "quotes",
+		Random:     []byte("test-random"),
+		HMAC:       []byte("test-hmac"),
+	}
+
+	response := &ChallengeResponse{Challenge: testChallenge}
+	var buf bytes.Buffer
+	err := response.Encode(&buf)
+	require.NoError(t, err)
+
+	// Verify binary format
+	data := buf.Bytes()
+	assert.GreaterOrEqual(t, len(data), 5)
+	assert.Equal(t, byte(ChallengeResponseType), data[0])
+
+	payloadLength := binary.BigEndian.Uint32(data[1:5])
+	assert.Greater(t, payloadLength, uint32(0))
+	assert.Equal(t, len(data)-5, int(payloadLength))
+
+	// Verify payload content
+	payload := string(data[5:])
+	assert.Contains(t, payload, "1640995200")
+	assert.Contains(t, payload, "quotes")
+}
+
+func TestSolutionRequest_RoundTrip(t *testing.T) {
+	decoder := NewMessageDecoder()
+
+	payload := `{"challenge":{"timestamp":1640995200,"difficulty":4,"resource":"quotes","random":"dGVzdC1yYW5kb20=","hmac":"dGVzdC1obWFj"},"nonce":12345}`
+
+	var buf bytes.Buffer
+	buf.WriteByte(byte(SolutionRequestType))
+	binary.Write(&buf, binary.BigEndian, uint32(len(payload)))
+	buf.WriteString(payload)
+
+	// Decode header
+	msg, err := decoder.Decode(&buf)
+	require.NoError(t, err)
+	assert.Equal(t, SolutionRequestType, msg.Type)
+	assert.Equal(t, uint32(len(payload)), msg.PayloadLength)
+
+	// Decode request
+	req := &SolutionRequest{}
+	err = req.Decode(msg.PayloadStream)
+	require.NoError(t, err)
+
+	assert.Equal(t, int64(1640995200), req.Challenge.Timestamp)
+	assert.Equal(t, 4, req.Challenge.Difficulty)
+	assert.Equal(t, "quotes", req.Challenge.Resource)
+	assert.Equal(t, uint64(12345), req.Nonce)
+	assert.Equal(t, []byte("test-random"), req.Challenge.Random)
+	assert.Equal(t, []byte("test-hmac"), req.Challenge.HMAC)
+}
+
+func TestErrorResponse_BinaryFormat(t *testing.T) {
+	errorResp := &ErrorResponse{
+		Code:       "INVALID_SOLUTION",
+		Message:    "Test error message",
+		RetryAfter: 30,
+		Details:    map[string]string{"reason": "test"},
+	}
+
+	var buf bytes.Buffer
+	err := errorResp.Encode(&buf)
+	require.NoError(t, err)
+
+	data := buf.Bytes()
+	assert.Equal(t, byte(ErrorResponseType), data[0])
+
+	length := binary.BigEndian.Uint32(data[1:5])
+	assert.Greater(t, length, uint32(0))
+	assert.LessOrEqual(t, length, uint32(MaxPayloadSize))
+
+	payload := string(data[5:])
+	assert.Contains(t, payload, "INVALID_SOLUTION")
+	assert.Contains(t, payload, "Test error message")
+	assert.Contains(t, payload, "30")
+	assert.Contains(t, payload, "test")
+}
+
+func TestChallengeRequest_EmptyPayload(t *testing.T) {
+	decoder := NewMessageDecoder()
+
+	data := []byte{0x01, 0x00, 0x00, 0x00, 0x00}
+	buf := bytes.NewBuffer(data)
+
+	msg, err := decoder.Decode(buf)
+	require.NoError(t, err)
+	assert.Equal(t, ChallengeRequestType, msg.Type)
+	assert.Equal(t, uint32(0), msg.PayloadLength)
+	assert.Nil(t, msg.PayloadStream)
+
+	req := &ChallengeRequest{}
+	err = req.Decode(msg.PayloadStream)
+	require.NoError(t, err)
+}
+
+func TestPayloadStream_LimitedRead(t *testing.T) {
+	decoder := NewMessageDecoder()
+
+	payload := `{"challenge":{"timestamp":1640995200,"difficulty":4,"resource":"quotes","random":"dGVzdA==","hmac":"dGVzdA=="},"nonce":999}`
+	extraData := "this should not be read"
+
+	var buf bytes.Buffer
+	buf.WriteByte(byte(SolutionRequestType))
+	binary.Write(&buf, binary.BigEndian, uint32(len(payload)))
+	buf.WriteString(payload)
+	buf.WriteString(extraData)
+
+	msg, err := decoder.Decode(&buf)
+	require.NoError(t, err)
+
+	req := &SolutionRequest{}
+	err = req.Decode(msg.PayloadStream)
+	require.NoError(t, err)
+	assert.Equal(t, uint64(999), req.Nonce)
+
+	// Verify extra data wasn't consumed
+	remaining := buf.String()
+	assert.Equal(t, extraData, remaining)
+}
+
+func TestTrueRoundTrip_ServerClientCommunication(t *testing.T) {
+	// Simulate actual server-client communication
+
+	// 1. SERVER: Create and encode a challenge response
+	originalChallenge := &challenge.Challenge{
+		Timestamp:  1640995200,
+		Difficulty: 4,
+		Resource:   "quotes",
+		Random:     []byte("server-random-data"),
+		HMAC:       []byte("server-hmac-signature"),
+	}
+
+	serverResponse := &ChallengeResponse{Challenge: originalChallenge}
+	var networkBuffer bytes.Buffer
+
+	// Server encodes response to "network"
+	err := serverResponse.Encode(&networkBuffer)
+	require.NoError(t, err)
+
+	// 2. NETWORK: Simulate transmission (networkBuffer contains binary data)
+	wireData := networkBuffer.Bytes()
+	assert.Greater(t, len(wireData), 5) // Has header + payload
+
+	// 3. CLIENT: Receives and decodes the binary data
+	// (Client would use a generic decoder, not our server-side MessageDecoder)
+	clientBuf := bytes.NewBuffer(wireData)
+
+	// Client reads header manually
+	var msgType MessageType
+	err = binary.Read(clientBuf, binary.BigEndian, &msgType)
+	require.NoError(t, err)
+	assert.Equal(t, ChallengeResponseType, msgType)
+
+	var payloadLength uint32
+	err = binary.Read(clientBuf, binary.BigEndian, &payloadLength)
+	require.NoError(t, err)
+
+	// Client reads payload
+	payloadBytes := make([]byte, payloadLength)
+	_, err = clientBuf.Read(payloadBytes)
+	require.NoError(t, err)
+
+	// Client deserializes the challenge
+	var receivedChallenge challenge.Challenge
+	err = json.Unmarshal(payloadBytes, &receivedChallenge)
+	require.NoError(t, err)
+
+	// 4. VERIFY: Client received exactly what server sent
+	assert.Equal(t, originalChallenge.Timestamp, receivedChallenge.Timestamp)
+	assert.Equal(t, originalChallenge.Difficulty, receivedChallenge.Difficulty)
+	assert.Equal(t, originalChallenge.Resource, receivedChallenge.Resource)
+	assert.Equal(t, originalChallenge.Random, receivedChallenge.Random)
+	assert.Equal(t, originalChallenge.HMAC, receivedChallenge.HMAC)
+}

internal/protocol/spec_compliance_test.go

@@ -0,0 +1,177 @@
+package protocol
+
+import (
+	"bytes"
+	"encoding/json"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+
+	"hash-of-wisdom/internal/pow/challenge"
+	"hash-of-wisdom/internal/quotes"
+)
+
+// TestSpecCompliance_ChallengeResponse verifies challenge response matches PROTOCOL.md format
+func TestSpecCompliance_ChallengeResponse(t *testing.T) {
+	resp := &ChallengeResponse{
+		Challenge: &challenge.Challenge{
+			Timestamp:  1640995200,
+			Difficulty: 4,
+			Resource:   "quotes",
+			Random:     []byte{0xa1, 0xb2, 0xc3, 0xd4, 0xe5, 0xf6},
+			HMAC:       []byte("base64url_encoded_signature"),
+		},
+	}
+
+	var buf bytes.Buffer
+	err := resp.Encode(&buf)
+	require.NoError(t, err)
+
+	// Skip header (5 bytes) and get payload
+	header := buf.Bytes()[:5]
+	payload := buf.Bytes()[5:]
+
+	// Verify header format
+	assert.Equal(t, byte(ChallengeResponseType), header[0])
+	assert.Equal(t, uint32(len(payload)), uint32(header[1])<<24|uint32(header[2])<<16|uint32(header[3])<<8|uint32(header[4]))
+
+	// Verify JSON payload matches spec format
+	var decoded map[string]interface{}
+	err = json.Unmarshal(payload, &decoded)
+	require.NoError(t, err)
+
+	// Check required fields from spec
+	assert.Contains(t, decoded, "timestamp")
+	assert.Contains(t, decoded, "difficulty")
+	assert.Contains(t, decoded, "resource")
+	assert.Contains(t, decoded, "random")
+	assert.Contains(t, decoded, "hmac")
+
+	assert.Equal(t, float64(1640995200), decoded["timestamp"])
+	assert.Equal(t, float64(4), decoded["difficulty"])
+	assert.Equal(t, "quotes", decoded["resource"])
+}
+
+// TestSpecCompliance_SolutionRequest verifies solution request matches PROTOCOL.md format
+func TestSpecCompliance_SolutionRequest(t *testing.T) {
+	req := &SolutionRequest{
+		Challenge: challenge.Challenge{
+			Timestamp:  1640995200,
+			Difficulty: 4,
+			Resource:   "quotes",
+			Random:     []byte{0xa1, 0xb2, 0xc3, 0xd4, 0xe5, 0xf6},
+			HMAC:       []byte("base64url_encoded_signature"),
+		},
+		Nonce: 12345,
+	}
+
+	var buf bytes.Buffer
+	err := req.Encode(&buf)
+	require.NoError(t, err)
+
+	// Skip header and get payload
+	payload := buf.Bytes()[5:]
+
+	// Verify JSON payload matches spec format
+	var decoded map[string]interface{}
+	err = json.Unmarshal(payload, &decoded)
+	require.NoError(t, err)
+
+	// Check required top-level fields
+	assert.Contains(t, decoded, "challenge")
+	assert.Contains(t, decoded, "nonce")
+	assert.Equal(t, float64(12345), decoded["nonce"])
+
+	// Check challenge structure
+	challenge := decoded["challenge"].(map[string]interface{})
+	assert.Contains(t, challenge, "timestamp")
+	assert.Contains(t, challenge, "difficulty")
+	assert.Contains(t, challenge, "resource")
+	assert.Contains(t, challenge, "random")
+	assert.Contains(t, challenge, "hmac")
+}
+
+// TestSpecCompliance_QuoteResponse verifies quote response matches PROTOCOL.md format
+func TestSpecCompliance_QuoteResponse(t *testing.T) {
+	resp := &SolutionResponse{
+		Quote: &quotes.Quote{
+			Text:   "The only way to do great work is to love what you do.",
+			Author: "Steve Jobs",
+		},
+	}
+
+	var buf bytes.Buffer
+	err := resp.Encode(&buf)
+	require.NoError(t, err)
+
+	// Skip header and get payload
+	payload := buf.Bytes()[5:]
+
+	// Verify JSON payload matches spec format
+	var decoded map[string]interface{}
+	err = json.Unmarshal(payload, &decoded)
+	require.NoError(t, err)
+
+	// Check required fields from spec
+	assert.Contains(t, decoded, "text")
+	assert.Contains(t, decoded, "author")
+	assert.Equal(t, "The only way to do great work is to love what you do.", decoded["text"])
+	assert.Equal(t, "Steve Jobs", decoded["author"])
+}
+
+// TestSpecCompliance_ErrorResponse verifies error response matches PROTOCOL.md format
+func TestSpecCompliance_ErrorResponse(t *testing.T) {
+	resp := &ErrorResponse{
+		Code:       "INVALID_SOLUTION",
+		Message:    "The provided PoW solution is incorrect",
+		RetryAfter: 30,
+		Details:    map[string]string{"reason": "hash verification failed"},
+	}
+
+	var buf bytes.Buffer
+	err := resp.Encode(&buf)
+	require.NoError(t, err)
+
+	// Skip header and get payload
+	payload := buf.Bytes()[5:]
+
+	// Verify JSON payload matches spec format
+	var decoded map[string]interface{}
+	err = json.Unmarshal(payload, &decoded)
+	require.NoError(t, err)
+
+	// Check required fields from spec
+	assert.Contains(t, decoded, "code")
+	assert.Contains(t, decoded, "message")
+	assert.Equal(t, "INVALID_SOLUTION", decoded["code"])
+	assert.Equal(t, "The provided PoW solution is incorrect", decoded["message"])
+
+	// Check optional fields
+	assert.Contains(t, decoded, "retry_after")
+	assert.Contains(t, decoded, "details")
+	assert.Equal(t, float64(30), decoded["retry_after"])
+}
+
+// TestSpecCompliance_MessageSizeLimits verifies 8KB payload limit
+func TestSpecCompliance_MessageSizeLimits(t *testing.T) {
+	decoder := NewMessageDecoder()
+
+	// Create a message that exceeds 8KB payload limit
+	largePayload := make([]byte, MaxPayloadSize+1)
+	for i := range largePayload {
+		largePayload[i] = 'A'
+	}
+
+	// Create message with oversized payload
+	var buf bytes.Buffer
+	buf.WriteByte(byte(ChallengeRequestType))
+	buf.Write([]byte{0x00, 0x00, 0x20, 0x01}) // 8193 bytes (8KB + 1)
+	buf.Write(largePayload)
+
+	// Should reject oversized payload
+	_, err := decoder.Decode(&buf)
+	assert.Error(t, err)
+	assert.Contains(t, err.Error(), "payload length")
+	assert.Contains(t, err.Error(), "exceeds maximum")
+}

internal/protocol/types.go

@@ -1,64 +1,10 @@
 package protocol
 
-import (
+import "io"
-	"hash-of-wisdom/internal/pow/challenge"
-	"hash-of-wisdom/internal/quotes"
-)
 
-// MessageType represents the type of protocol message
+// Message represents a protocol message with type and payload stream
-type MessageType byte
-
-const (
-	ChallengeRequest  MessageType = 0x01
-	ChallengeResponse MessageType = 0x02
-	SolutionRequest   MessageType = 0x03
-	QuoteResponse     MessageType = 0x04
-	ErrorResponse     MessageType = 0x05
-)
-
-// Message represents a protocol message with type and payload
 type Message struct {
-	Type    MessageType
+	Type          MessageType
-	Payload []byte
+	PayloadLength uint32
+	PayloadStream io.Reader
 }
-
-// ChallengeRequestPayload is empty (no payload for challenge requests)
-type ChallengeRequestPayload struct{}
-
-// ChallengeResponsePayload is the direct challenge object (not wrapped)
-type ChallengeResponsePayload challenge.Challenge
-
-// SolutionRequestPayload contains the client's solution attempt
-type SolutionRequestPayload struct {
-	Challenge challenge.Challenge `json:"challenge"`
-	Nonce     uint64              `json:"nonce"`
-}
-
-// QuoteResponsePayload is the direct quote object (not wrapped)
-type QuoteResponsePayload quotes.Quote
-
-// ErrorResponsePayload contains error information
-type ErrorResponsePayload struct {
-	Code       string            `json:"code"`
-	Message    string            `json:"message"`
-	RetryAfter int               `json:"retry_after,omitempty"`
-	Details    map[string]string `json:"details,omitempty"`
-}
-
-// Error codes as defined in protocol specification
-const (
-	ErrMalformedMessage    = "MALFORMED_MESSAGE"
-	ErrInvalidChallenge    = "INVALID_CHALLENGE"
-	ErrInvalidSolution     = "INVALID_SOLUTION"
-	ErrExpiredChallenge    = "EXPIRED_CHALLENGE"
-	ErrRateLimited         = "RATE_LIMITED"
-	ErrServerError         = "SERVER_ERROR"
-	ErrTooManyConnections  = "TOO_MANY_CONNECTIONS"
-	ErrDifficultyTooHigh   = "DIFFICULTY_TOO_HIGH"
-)
-
-// Protocol constants
-const (
-	MaxPayloadSize = 8 * 1024 // 8KB maximum payload size
-	HeaderSize     = 5        // 1 byte type + 4 bytes length
-)

internal/server/config.go

@@ -0,0 +1,19 @@
+package server
+
+import "time"
+
+// Config holds configuration for the TCP server
+type Config struct {
+	Address  string
+	Timeouts TimeoutConfig
+}
+
+// TimeoutConfig holds timeout configuration
+type TimeoutConfig struct {
+	// Read timeout protects against slowloris attacks (clients sending data slowly)
+	Read time.Duration
+	// Write timeout protects against slow readers (clients reading responses slowly)
+	Write time.Duration
+	// Connection timeout is the maximum total connection lifetime
+	Connection time.Duration
+}

internal/server/tcp.go

@@ -0,0 +1,234 @@
+package server
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"log/slog"
+	"net"
+	"sync"
+	"time"
+
+	"hash-of-wisdom/internal/application"
+	"hash-of-wisdom/internal/lib/sl"
+	"hash-of-wisdom/internal/metrics"
+	"hash-of-wisdom/internal/protocol"
+	"hash-of-wisdom/internal/service"
+)
+
+// TCPServer handles TCP connections for the Word of Wisdom protocol
+type TCPServer struct {
+	config            *Config
+	wisdomApplication *application.WisdomApplication
+	decoder           *protocol.MessageDecoder
+	listener          net.Listener
+	logger            *slog.Logger
+	wg                sync.WaitGroup
+	cancel            context.CancelFunc
+}
+
+// Option is a functional option for configuring TCPServer
+type option func(*TCPServer)
+
+// WithLogger sets a custom logger
+func WithLogger(logger *slog.Logger) option {
+	return func(s *TCPServer) {
+		s.logger = logger
+	}
+}
+
+// NewTCPServer creates a new TCP server with required configuration
+func NewTCPServer(wisdomService *service.WisdomService, config *Config, opts ...option) *TCPServer {
+	server := &TCPServer{
+		config:            config,
+		wisdomApplication: application.NewWisdomApplication(wisdomService),
+		decoder:           protocol.NewMessageDecoder(),
+		logger:            slog.Default(),
+	}
+
+	for _, opt := range opts {
+		opt(server)
+	}
+
+	return server
+}
+
+// Start starts the TCP server
+func (s *TCPServer) Start(ctx context.Context) error {
+	listener, err := net.Listen("tcp", s.config.Address)
+	if err != nil {
+		return fmt.Errorf("failed to listen on %s: %w", s.config.Address, err)
+	}
+
+	s.listener = listener
+	s.logger.Info("tcp server started", "address", s.config.Address)
+
+	// Create cancellable context for server lifecycle
+	serverCtx, cancel := context.WithCancel(ctx)
+	s.cancel = cancel
+
+	go s.acceptLoop(serverCtx)
+	return nil
+}
+
+// Stop gracefully stops the server
+func (s *TCPServer) Stop() error {
+	s.logger.Info("stopping tcp server")
+
+	// Cancel server context to stop accept loop and active connections
+	if s.cancel != nil {
+		s.cancel()
+	}
+
+	if s.listener != nil {
+		s.listener.Close()
+	}
+
+	s.wg.Wait()
+	s.logger.Info("tcp server stopped")
+	return nil
+}
+
+// Address returns the server's listening address
+func (s *TCPServer) Address() string {
+	if s.listener != nil {
+		return s.listener.Addr().String()
+	}
+	return s.config.Address
+}
+
+// acceptLoop accepts and handles incoming connections
+func (s *TCPServer) acceptLoop(ctx context.Context) {
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		default:
+		}
+
+		rawConn, err := s.listener.Accept()
+		if err != nil {
+			select {
+			case <-ctx.Done():
+				return
+			default:
+				s.logger.Error("accept error", sl.Err(err))
+				continue
+			}
+		}
+
+		s.wg.Add(1)
+		go func() {
+			defer s.wg.Done()
+			s.handleConnection(ctx, rawConn)
+		}()
+	}
+}
+
+// handleConnection handles a single client connection
+func (s *TCPServer) handleConnection(ctx context.Context, rawConn net.Conn) {
+	defer rawConn.Close()
+
+	// Track active connections
+	metrics.ActiveConnections.Inc()
+	defer metrics.ActiveConnections.Dec()
+
+	connLogger := s.logger.With("remote_addr", rawConn.RemoteAddr().String())
+	connLogger.Info("connection accepted")
+
+	// Create connection-scoped context for overall timeout
+	connCtx, cancel := context.WithTimeout(ctx, s.config.Timeouts.Connection)
+	defer cancel()
+
+	if err := s.processConnection(connCtx, rawConn, connLogger); err != nil {
+		connLogger.Error("connection error", sl.Err(err))
+	} else {
+		connLogger.Debug("connection completed successfully")
+	}
+}
+
+// deadlineConn wraps a connection to automatically set deadlines on each read/write
+type deadlineConn struct {
+	net.Conn
+	rto, wto time.Duration
+}
+
+func (d *deadlineConn) Read(p []byte) (int, error) {
+	_ = d.SetReadDeadline(time.Now().Add(d.rto))
+	return d.Conn.Read(p)
+}
+
+func (d *deadlineConn) Write(p []byte) (int, error) {
+	_ = d.SetWriteDeadline(time.Now().Add(d.wto))
+	return d.Conn.Write(p)
+}
+
+// processConnection handles the protocol message exchange
+func (s *TCPServer) processConnection(ctx context.Context, conn net.Conn, logger *slog.Logger) error {
+	// Set overall connection deadline
+	globalDL := time.Now().Add(s.config.Timeouts.Connection)
+	if err := conn.SetDeadline(globalDL); err != nil {
+		return fmt.Errorf("failed to set connection deadline: %w", err)
+	}
+
+	// Create deadline wrapper for automatic timeout handling
+	dc := &deadlineConn{
+		Conn: conn,
+		rto:  s.config.Timeouts.Read,
+		wto:  s.config.Timeouts.Write,
+	}
+
+	// Use LimitReader to prevent reading more than the protocol-defined maximum message size
+	// This protects against malicious clients that lie about payload length in headers
+	limitedReader := io.LimitReader(dc, int64(protocol.MaxPayloadSize)+protocol.HeaderSize)
+
+	// Read incoming message through limited reader
+	logger.Debug("reading message from client")
+	msg, err := s.decoder.Decode(limitedReader)
+	if err != nil {
+		if err == io.EOF {
+			logger.Debug("client closed connection gracefully")
+			return nil
+		}
+		metrics.RequestErrors.WithLabelValues("decode_error").Inc()
+		logger.Error("failed to decode message", sl.Err(err))
+		return fmt.Errorf("decode error: %w", err)
+	}
+
+	logger.Debug("message decoded", "type", msg.Type, "payload_length", msg.PayloadLength)
+
+	// Track all requests
+	metrics.RequestsTotal.Inc()
+
+	// Process message through application layer with timing
+	start := time.Now()
+	response, err := s.wisdomApplication.HandleMessage(ctx, msg)
+	duration := time.Since(start)
+	metrics.RequestDuration.Observe(duration.Seconds())
+
+	if err != nil {
+		metrics.RequestErrors.WithLabelValues("internal_error").Inc()
+		logger.Error("application error", sl.Err(err))
+		return fmt.Errorf("application error: %w", err)
+	}
+
+	// Check if response is an error response
+	if errorResp, isError := response.(*protocol.ErrorResponse); isError {
+		metrics.RequestErrors.WithLabelValues(string(errorResp.Code)).Inc()
+	} else {
+		// Track quotes served for successful solution requests
+		if msg.Type == protocol.SolutionRequestType {
+			metrics.QuotesServed.Inc()
+		}
+	}
+
+	logger.Debug("sending response to client")
+	// Send response using the response's own Encode method
+	if err := response.Encode(dc); err != nil {
+		logger.Error("failed to encode response", sl.Err(err))
+		return fmt.Errorf("encode error: %w", err)
+	}
+
+	logger.Debug("response sent successfully")
+	return nil
+}

internal/service/wisdom.go

@@ -9,11 +9,11 @@ import (
 )
 
 var (
-	ErrResourceRequired   = errors.New("resource is required")
+	ErrResourceRequired    = errors.New("resource is required")
 	ErrUnsupportedResource = errors.New("unsupported resource")
-	ErrSolutionRequired   = errors.New("solution is required")
+	ErrSolutionRequired    = errors.New("solution is required")
-	ErrInvalidChallenge   = errors.New("invalid challenge")
+	ErrInvalidChallenge    = errors.New("invalid challenge")
-	ErrInvalidSolution    = errors.New("invalid proof of work solution")
+	ErrInvalidSolution     = errors.New("invalid proof of work solution")
 )
 
 type ChallengeGenerator interface {

internal/service/wisdom_test.go

@@ -70,15 +70,15 @@ func TestWisdomService_GenerateChallenge(t *testing.T) {
 
 func TestWisdomService_VerifySolution(t *testing.T) {
 	tests := []struct {
-		name     string
+		name       string
-		solution *challenge.Solution
+		solution   *challenge.Solution
-		wantErr  error
+		wantErr    error
 		setupMocks func(*mocks.MockChallengeVerifier)
 	}{
 		{
-			name:     "nil solution",
+			name:       "nil solution",
-			solution: nil,
+			solution:   nil,
-			wantErr:  ErrSolutionRequired,
+			wantErr:    ErrSolutionRequired,
 			setupMocks: func(mv *mocks.MockChallengeVerifier) {},
 		},
 		{
@@ -93,17 +93,17 @@ func TestWisdomService_VerifySolution(t *testing.T) {
 			},
 		},
 		{
-			name: "invalid solution",
+			name:     "invalid solution",
 			solution: createInvalidSolution(t),
-			wantErr: ErrInvalidSolution,
+			wantErr:  ErrInvalidSolution,
 			setupMocks: func(mv *mocks.MockChallengeVerifier) {
 				mv.EXPECT().VerifyChallenge(mock.Anything).Return(nil).Once()
 			},
 		},
 		{
-			name: "valid solution",
+			name:     "valid solution",
 			solution: createValidSolution(t),
-			wantErr: nil,
+			wantErr:  nil,
 			setupMocks: func(mv *mocks.MockChallengeVerifier) {
 				mv.EXPECT().VerifyChallenge(mock.Anything).Return(nil).Once()
 			},

internal/service/workflow_test.go

@@ -284,8 +284,8 @@ func TestWisdomService_InvalidSolutions(t *testing.T) {
 
 func TestWisdomService_UnsuccessfulFlows(t *testing.T) {
 	tests := []struct {
-		name       string
+		name           string
-		difficulty int
+		difficulty     int
 		createSolution func(*challenge.Challenge, *challenge.Solution) *challenge.Solution
 	}{
 		{

test/integration/helpers_test.go

@@ -0,0 +1,56 @@
+package integration
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	"hash-of-wisdom/internal/lib/sl"
+	"hash-of-wisdom/internal/pow/challenge"
+	"hash-of-wisdom/internal/quotes"
+	"hash-of-wisdom/internal/server"
+	"hash-of-wisdom/internal/service"
+
+	"github.com/stretchr/testify/require"
+)
+
+// testQuoteService provides static quotes for testing
+type testQuoteService struct{}
+
+func (s *testQuoteService) GetRandomQuote(ctx context.Context) (*quotes.Quote, error) {
+	return &quotes.Quote{
+		Text:   "Test quote for integration testing",
+		Author: "Test Author",
+	}, nil
+}
+
+func setupTestServerWithConfig(t *testing.T, serverConfig *server.Config) *server.TCPServer {
+	// Create test components
+	challengeConfig := challenge.TestConfig()
+	generator := challenge.NewGenerator(challengeConfig)
+	verifier := challenge.NewVerifier(challengeConfig)
+
+	// Create a simple test quote service
+	quoteService := &testQuoteService{}
+
+	// Wire up service
+	genAdapter := service.NewGeneratorAdapter(generator)
+	wisdomService := service.NewWisdomService(genAdapter, verifier, quoteService)
+
+	// Create server with custom config using functional options
+	logger := sl.NewMockLogger()
+	srv := server.NewTCPServer(wisdomService, serverConfig,
+		server.WithLogger(logger))
+
+	// Start server
+	ctx, cancel := context.WithTimeout(context.Background(), 1*time.Second)
+	defer cancel()
+
+	err := srv.Start(ctx)
+	require.NoError(t, err)
+
+	// Give server time to start
+	time.Sleep(100 * time.Millisecond)
+
+	return srv
+}

test/integration/slowloris_test.go

@@ -0,0 +1,114 @@
+package integration
+
+import (
+	"net"
+	"testing"
+	"time"
+
+	"hash-of-wisdom/internal/server"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestSlowlorisProtection_SlowReader(t *testing.T) {
+	// Setup server with very short read timeout for testing
+	serverConfig := &server.Config{
+		Address: ":0",
+		Timeouts: server.TimeoutConfig{
+			Read:       100 * time.Millisecond,
+			Write:      5 * time.Second,
+			Connection: 15 * time.Second,
+		},
+	}
+
+	srv := setupTestServerWithConfig(t, serverConfig)
+	defer srv.Stop()
+
+	// Connect to server
+	conn, err := net.Dial("tcp", srv.Address())
+	require.NoError(t, err)
+	defer conn.Close()
+
+	// Send partial message header very slowly (slowloris attack)
+	_, err = conn.Write([]byte{0x01}) // Challenge request type
+	require.NoError(t, err)
+
+	// Wait longer than read timeout before sending length
+	time.Sleep(200 * time.Millisecond)
+
+	// Try to send more data - connection should be timed out
+	_, err = conn.Write([]byte{0x00, 0x00, 0x00, 0x00}) // Payload length
+
+	// Verify connection is closed by trying to read
+	buffer := make([]byte, 1024)
+	conn.SetReadDeadline(time.Now().Add(500 * time.Millisecond))
+	_, err = conn.Read(buffer)
+	assert.Error(t, err, "Connection should be closed due to slow reading")
+}
+
+func TestSlowlorisProtection_SlowConnectionTimeout(t *testing.T) {
+	// Setup server with very short connection timeout for testing
+	serverConfig := &server.Config{
+		Address: ":0",
+		Timeouts: server.TimeoutConfig{
+			Read:       5 * time.Second,
+			Write:      5 * time.Second,
+			Connection: 200 * time.Millisecond,
+		},
+	}
+
+	srv := setupTestServerWithConfig(t, serverConfig)
+	defer srv.Stop()
+
+	// Connect to server but do nothing
+	conn, err := net.Dial("tcp", srv.Address())
+	require.NoError(t, err)
+	defer conn.Close()
+
+	// Wait longer than connection timeout
+	time.Sleep(300 * time.Millisecond)
+
+	// Try to read - connection should be closed
+	buffer := make([]byte, 1024)
+	conn.SetReadDeadline(time.Now().Add(500 * time.Millisecond))
+	_, err = conn.Read(buffer)
+	assert.Error(t, err, "Connection should be closed due to connection timeout")
+}
+
+func TestSlowlorisProtection_MultipleSlowClients(t *testing.T) {
+	// Setup server with short timeouts
+	serverConfig := &server.Config{
+		Address: ":0",
+		Timeouts: server.TimeoutConfig{
+			Read:       1 * time.Second,
+			Write:      1 * time.Second,
+			Connection: 2 * time.Second,
+		},
+	}
+
+	srv := setupTestServerWithConfig(t, serverConfig)
+	defer srv.Stop()
+
+	// Create multiple slow connections
+	var connections []net.Conn
+	for i := 0; i < 5; i++ {
+		conn, err := net.Dial("tcp", srv.Address())
+		require.NoError(t, err)
+		connections = append(connections, conn)
+		// Send partial data on each connection
+		conn.Write([]byte{0x01}) // Challenge request type only
+	}
+
+	// Wait for timeouts to kick in
+	time.Sleep(1500 * time.Millisecond)
+
+	// All connections should be closed
+	buffer := make([]byte, 1024)
+	for i, conn := range connections {
+		conn.SetReadDeadline(time.Now().Add(500 * time.Millisecond))
+		_, err := conn.Read(buffer)
+		assert.Error(t, err, "Connection %d should be closed", i)
+		conn.Close()
+	}
+}

test/integration/timeout_test.go

@@ -0,0 +1,161 @@
+package integration
+
+import (
+	"net"
+	"testing"
+	"time"
+
+	"hash-of-wisdom/internal/protocol"
+	"hash-of-wisdom/internal/server"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func TestTCPServer_TimeoutProtection_SlowReader(t *testing.T) {
+	// Setup server with very short read timeout for testing
+	serverConfig := &server.Config{
+		Address: ":0",
+		Timeouts: server.TimeoutConfig{
+			Read:       500 * time.Millisecond,
+			Write:      5 * time.Second,
+			Connection: 15 * time.Second,
+		},
+	}
+	srv := setupTestServerWithConfig(t, serverConfig)
+	defer srv.Stop()
+
+	// Connect to server
+	conn, err := net.Dial("tcp", srv.Address())
+	require.NoError(t, err)
+	defer conn.Close()
+
+	// Send partial message header (just type byte)
+	_, err = conn.Write([]byte{0x01}) // Challenge request type
+	require.NoError(t, err)
+
+	// Wait longer than read timeout before sending length
+	time.Sleep(700 * time.Millisecond)
+
+	// Try to send more data - connection should be timed out
+	_, err = conn.Write([]byte{0x00, 0x00, 0x00, 0x00}) // Payload length
+
+	// Verify connection is closed by reading
+	buffer := make([]byte, 1024)
+	conn.SetReadDeadline(time.Now().Add(1 * time.Second))
+	_, err = conn.Read(buffer)
+	assert.Error(t, err, "Connection should be closed due to slow reading")
+}
+
+func TestTCPServer_TimeoutProtection_ConnectionTimeout(t *testing.T) {
+	// Setup server with very short connection timeout
+	serverConfig := &server.Config{
+		Address: ":0",
+		Timeouts: server.TimeoutConfig{
+			Read:       5 * time.Second,
+			Write:      5 * time.Second,
+			Connection: 1 * time.Second,
+		},
+	}
+	srv := setupTestServerWithConfig(t, serverConfig)
+	defer srv.Stop()
+
+	// Connect to server
+	conn, err := net.Dial("tcp", srv.Address())
+	require.NoError(t, err)
+	defer conn.Close()
+
+	// Wait longer than connection timeout
+	time.Sleep(1500 * time.Millisecond)
+
+	// Try to read from connection - should get EOF or connection reset
+	buffer := make([]byte, 1024)
+	conn.SetReadDeadline(time.Now().Add(500 * time.Millisecond))
+	_, err = conn.Read(buffer)
+	assert.Error(t, err, "Connection should be closed due to timeout")
+}
+
+func TestTCPServer_NormalOperation_WithinTimeouts(t *testing.T) {
+	srv := setupTestServer(t)
+	defer srv.Stop()
+
+	// Connect and complete normal flow quickly
+	conn, err := net.Dial("tcp", srv.Address())
+	require.NoError(t, err)
+	defer conn.Close()
+
+	// Request challenge using new protocol API
+	challengeReq := &protocol.ChallengeRequest{}
+	err = challengeReq.Encode(conn)
+	require.NoError(t, err)
+
+	// Should receive challenge response without timeout
+	decoder := protocol.NewMessageDecoder()
+	msg, err := decoder.Decode(conn)
+	require.NoError(t, err)
+	assert.Equal(t, protocol.ChallengeResponseType, msg.Type)
+	assert.Greater(t, msg.PayloadLength, uint32(0), "Challenge payload should not be empty")
+}
+
+func TestTCPServer_MultipleConnections_IndependentTimeouts(t *testing.T) {
+	serverConfig := &server.Config{
+		Address: ":0",
+		Timeouts: server.TimeoutConfig{
+			Read:       1 * time.Second,
+			Write:      5 * time.Second,
+			Connection: 3 * time.Second,
+		},
+	}
+	srv := setupTestServerWithConfig(t, serverConfig)
+	defer srv.Stop()
+
+	// Start two connections
+	conn1, err := net.Dial("tcp", srv.Address())
+	require.NoError(t, err)
+	defer conn1.Close()
+
+	conn2, err := net.Dial("tcp", srv.Address())
+	require.NoError(t, err)
+	defer conn2.Close()
+
+	// Conn1: Send complete request quickly
+	go func() {
+		req := &protocol.ChallengeRequest{}
+		req.Encode(conn1)
+	}()
+
+	// Conn2: Send partial request and stall
+	conn2.Write([]byte{0x01}) // Just message type
+
+	// Wait for read timeout
+	time.Sleep(1500 * time.Millisecond)
+
+	// Conn1 should still work, Conn2 should be closed
+	buffer := make([]byte, 1024)
+
+	// Conn1 should receive response
+	conn1.SetReadDeadline(time.Now().Add(1 * time.Second))
+	n, err := conn1.Read(buffer)
+	assert.NoError(t, err)
+	assert.Greater(t, n, 0, "Conn1 should receive response")
+
+	// Conn2 should be closed
+	conn2.SetReadDeadline(time.Now().Add(500 * time.Millisecond))
+	_, err = conn2.Read(buffer)
+	assert.Error(t, err, "Conn2 should be closed due to timeout")
+}
+
+// Helper function to create test server with default config
+func setupTestServer(t *testing.T) *server.TCPServer {
+	serverConfig := &server.Config{
+		Address: ":0",
+		Timeouts: server.TimeoutConfig{
+			Read:       5 * time.Second,
+			Write:      5 * time.Second,
+			Connection: 15 * time.Second,
+		},
+	}
+	return setupTestServerWithConfig(t, serverConfig)
+}
+
+// Helper function to create test server with custom config