fix: dns resolution taking long and add caching options (#8)

internal/config/config.go

@@ -25,6 +25,7 @@ type DefaultConfig struct {
 	Units        string   `mapstructure:"units"`
 	Color        string   `mapstructure:"color"`
 	Resolve      bool     `mapstructure:"resolve"`
+	DNSCache     bool     `mapstructure:"dns_cache"`
 	IPv4         bool     `mapstructure:"ipv4"`
 	IPv6         bool     `mapstructure:"ipv6"`
 	NoHeaders    bool     `mapstructure:"no_headers"`
@@ -57,6 +58,7 @@ func Load() (*Config, error) {
 	// environment variable bindings for readme-documented variables
 	_ = v.BindEnv("config", "SNITCH_CONFIG")
 	_ = v.BindEnv("defaults.resolve", "SNITCH_RESOLVE")
+	_ = v.BindEnv("defaults.dns_cache", "SNITCH_DNS_CACHE")
 	_ = v.BindEnv("defaults.theme", "SNITCH_THEME")
 	_ = v.BindEnv("defaults.color", "SNITCH_NO_COLOR")
 	
@@ -90,7 +92,6 @@ func Load() (*Config, error) {
 }
 
 func setDefaults(v *viper.Viper) {
-	// Set default values matching the README specification
 	v.SetDefault("defaults.interval", "1s")
 	v.SetDefault("defaults.numeric", false)
 	v.SetDefault("defaults.fields", []string{"pid", "process", "user", "proto", "state", "laddr", "lport", "raddr", "rport"})
@@ -98,6 +99,7 @@ func setDefaults(v *viper.Viper) {
 	v.SetDefault("defaults.units", "auto")
 	v.SetDefault("defaults.color", "auto")
 	v.SetDefault("defaults.resolve", true)
+	v.SetDefault("defaults.dns_cache", true)
 	v.SetDefault("defaults.ipv4", false)
 	v.SetDefault("defaults.ipv6", false)
 	v.SetDefault("defaults.no_headers", false)
@@ -116,6 +118,11 @@ func handleSpecialEnvVars(v *viper.Viper) {
 		v.Set("defaults.resolve", false)
 		v.Set("defaults.numeric", true)
 	}
+
+	// Handle SNITCH_DNS_CACHE - if set to "0", disable dns caching
+	if os.Getenv("SNITCH_DNS_CACHE") == "0" {
+		v.Set("defaults.dns_cache", false)
+	}
 }
 
 // Get returns the global configuration, loading it if necessary
@@ -123,7 +130,6 @@ func Get() *Config {
 	if globalConfig == nil {
 		config, err := Load()
 		if err != nil {
-			// Return default config on error
 			return &Config{
 				Defaults: DefaultConfig{
 					Interval:     "1s",
@@ -133,6 +139,7 @@ func Get() *Config {
 					Units:        "auto",
 					Color:        "auto",
 					Resolve:      true,
+					DNSCache:     true,
 					IPv4:         false,
 					IPv6:         false,
 					NoHeaders:    false,

internal/resolver/resolver.go

@@ -14,9 +14,10 @@ var debugTiming = os.Getenv("SNITCH_DEBUG_TIMING") != ""
 
 // Resolver handles DNS and service name resolution with caching and timeouts
 type Resolver struct {
-	timeout time.Duration
-	cache   map[string]string
-	mutex   sync.RWMutex
+	timeout  time.Duration
+	cache    map[string]string
+	mutex    sync.RWMutex
+	noCache  bool
 }
 
 // New creates a new resolver with the specified timeout
@@ -24,37 +25,44 @@ func New(timeout time.Duration) *Resolver {
 	return &Resolver{
 		timeout: timeout,
 		cache:   make(map[string]string),
+		noCache: false,
 	}
 }
 
+// SetNoCache disables caching - each lookup will hit DNS directly
+func (r *Resolver) SetNoCache(noCache bool) {
+	r.noCache = noCache
+}
+
 // ResolveAddr resolves an IP address to a hostname, with caching
 func (r *Resolver) ResolveAddr(addr string) string {
-	// Check cache first
-	r.mutex.RLock()
-	if cached, exists := r.cache[addr]; exists {
+	// check cache first (unless caching is disabled)
+	if !r.noCache {
+		r.mutex.RLock()
+		if cached, exists := r.cache[addr]; exists {
+			r.mutex.RUnlock()
+			return cached
+		}
 		r.mutex.RUnlock()
-		return cached
 	}
-	r.mutex.RUnlock()
 
-	// Parse IP to validate it
+	// parse ip to validate it
 	ip := net.ParseIP(addr)
 	if ip == nil {
-		// Not a valid IP, return as-is
 		return addr
 	}
 
-	// Perform resolution with timeout
+	// perform resolution with timeout
 	start := time.Now()
 	ctx, cancel := context.WithTimeout(context.Background(), r.timeout)
 	defer cancel()
 
 	names, err := net.DefaultResolver.LookupAddr(ctx, addr)
 
-	resolved := addr // fallback to original address
+	resolved := addr
 	if err == nil && len(names) > 0 {
 		resolved = names[0]
-		// Remove trailing dot if present
+		// remove trailing dot if present
 		if len(resolved) > 0 && resolved[len(resolved)-1] == '.' {
 			resolved = resolved[:len(resolved)-1]
 		}
@@ -65,10 +73,12 @@ func (r *Resolver) ResolveAddr(addr string) string {
 		fmt.Fprintf(os.Stderr, "[timing] slow DNS lookup: %s -> %s (%v)\n", addr, resolved, elapsed)
 	}
 
-	// Cache the result
-	r.mutex.Lock()
-	r.cache[addr] = resolved
-	r.mutex.Unlock()
+	// cache the result (unless caching is disabled)
+	if !r.noCache {
+		r.mutex.Lock()
+		r.cache[addr] = resolved
+		r.mutex.Unlock()
+	}
 
 	return resolved
 }
@@ -81,15 +91,17 @@ func (r *Resolver) ResolvePort(port int, proto string) string {
 
 	cacheKey := strconv.Itoa(port) + "/" + proto
 
-	// Check cache first
-	r.mutex.RLock()
-	if cached, exists := r.cache[cacheKey]; exists {
+	// check cache first (unless caching is disabled)
+	if !r.noCache {
+		r.mutex.RLock()
+		if cached, exists := r.cache[cacheKey]; exists {
+			r.mutex.RUnlock()
+			return cached
+		}
 		r.mutex.RUnlock()
-		return cached
 	}
-	r.mutex.RUnlock()
 
-	// Perform resolution with timeout
+	// perform resolution with timeout
 	ctx, cancel := context.WithTimeout(context.Background(), r.timeout)
 	defer cancel()
 
@@ -97,16 +109,18 @@ func (r *Resolver) ResolvePort(port int, proto string) string {
 
 	resolved := strconv.Itoa(port) // fallback to port number
 	if err == nil && service != 0 {
-		// Try to get service name
+		// try to get service name
 		if serviceName := getServiceName(port, proto); serviceName != "" {
 			resolved = serviceName
 		}
 	}
 
-	// Cache the result
-	r.mutex.Lock()
-	r.cache[cacheKey] = resolved
-	r.mutex.Unlock()
+	// cache the result (unless caching is disabled)
+	if !r.noCache {
+		r.mutex.Lock()
+		r.cache[cacheKey] = resolved
+		r.mutex.Unlock()
+	}
 
 	return resolved
 }
@@ -169,22 +183,38 @@ func getServiceName(port int, proto string) string {
 	return ""
 }
 
-// Global resolver instance
+// global resolver instance
 var globalResolver *Resolver
 
-// SetGlobalResolver sets the global resolver instance
-func SetGlobalResolver(timeout time.Duration) {
+// ResolverOptions configures the global resolver
+type ResolverOptions struct {
+	Timeout time.Duration
+	NoCache bool
+}
+
+// SetGlobalResolver sets the global resolver instance with options
+func SetGlobalResolver(opts ResolverOptions) {
+	timeout := opts.Timeout
+	if timeout == 0 {
+		timeout = 200 * time.Millisecond
+	}
 	globalResolver = New(timeout)
+	globalResolver.SetNoCache(opts.NoCache)
 }
 
 // GetGlobalResolver returns the global resolver instance
 func GetGlobalResolver() *Resolver {
 	if globalResolver == nil {
-		globalResolver = New(200 * time.Millisecond) // Default timeout
+		globalResolver = New(200 * time.Millisecond)
 	}
 	return globalResolver
 }
 
+// SetNoCache configures whether the global resolver bypasses cache
+func SetNoCache(noCache bool) {
+	GetGlobalResolver().SetNoCache(noCache)
+}
+
 // ResolveAddr is a convenience function using the global resolver
 func ResolveAddr(addr string) string {
 	return GetGlobalResolver().ResolveAddr(addr)
@@ -199,3 +229,48 @@ func ResolvePort(port int, proto string) string {
 func ResolveAddrPort(addr string, port int, proto string) (string, string) {
 	return GetGlobalResolver().ResolveAddrPort(addr, port, proto)
 }
+
+// ResolveAddrsParallel resolves multiple addresses concurrently and caches results.
+// This should be called before rendering to pre-warm the cache.
+func (r *Resolver) ResolveAddrsParallel(addrs []string) {
+	// dedupe and filter addresses that need resolution
+	unique := make(map[string]struct{})
+	for _, addr := range addrs {
+		if addr == "" || addr == "*" {
+			continue
+		}
+		// skip if already cached
+		r.mutex.RLock()
+		_, exists := r.cache[addr]
+		r.mutex.RUnlock()
+		if exists {
+			continue
+		}
+		unique[addr] = struct{}{}
+	}
+
+	if len(unique) == 0 {
+		return
+	}
+
+	var wg sync.WaitGroup
+	// limit concurrency to avoid overwhelming dns
+	sem := make(chan struct{}, 32)
+
+	for addr := range unique {
+		wg.Add(1)
+		go func(a string) {
+			defer wg.Done()
+			sem <- struct{}{}
+			defer func() { <-sem }()
+			r.ResolveAddr(a)
+		}(addr)
+	}
+
+	wg.Wait()
+}
+
+// ResolveAddrsParallel is a convenience function using the global resolver
+func ResolveAddrsParallel(addrs []string) {
+	GetGlobalResolver().ResolveAddrsParallel(addrs)
+}

internal/resolver/resolver_bench_test.go

@@ -0,0 +1,159 @@
+package resolver
+
+import (
+	"fmt"
+	"testing"
+	"time"
+)
+
+func BenchmarkResolveAddr_CacheHit(b *testing.B) {
+	r := New(100 * time.Millisecond)
+	addr := "127.0.0.1"
+
+	// pre-populate cache
+	r.ResolveAddr(addr)
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		r.ResolveAddr(addr)
+	}
+}
+
+func BenchmarkResolveAddr_CacheMiss(b *testing.B) {
+	r := New(10 * time.Millisecond) // short timeout for faster benchmarks
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		// use different addresses to avoid cache hits
+		addr := fmt.Sprintf("127.0.0.%d", i%256)
+		r.ClearCache() // clear cache to force miss
+		r.ResolveAddr(addr)
+	}
+}
+
+func BenchmarkResolveAddr_NoCache(b *testing.B) {
+	r := New(10 * time.Millisecond)
+	r.SetNoCache(true)
+	addr := "127.0.0.1"
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		r.ResolveAddr(addr)
+	}
+}
+
+func BenchmarkResolvePort_CacheHit(b *testing.B) {
+	r := New(100 * time.Millisecond)
+
+	// pre-populate cache
+	r.ResolvePort(80, "tcp")
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		r.ResolvePort(80, "tcp")
+	}
+}
+
+func BenchmarkResolvePort_WellKnown(b *testing.B) {
+	r := New(100 * time.Millisecond)
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		r.ClearCache()
+		r.ResolvePort(443, "tcp")
+	}
+}
+
+func BenchmarkGetServiceName(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		getServiceName(80, "tcp")
+	}
+}
+
+func BenchmarkGetServiceName_NotFound(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		getServiceName(12345, "tcp")
+	}
+}
+
+func BenchmarkResolveAddrsParallel_10(b *testing.B) {
+	benchmarkResolveAddrsParallel(b, 10)
+}
+
+func BenchmarkResolveAddrsParallel_100(b *testing.B) {
+	benchmarkResolveAddrsParallel(b, 100)
+}
+
+func BenchmarkResolveAddrsParallel_1000(b *testing.B) {
+	benchmarkResolveAddrsParallel(b, 1000)
+}
+
+func benchmarkResolveAddrsParallel(b *testing.B, count int) {
+	addrs := make([]string, count)
+	for i := 0; i < count; i++ {
+		addrs[i] = fmt.Sprintf("127.0.%d.%d", i/256, i%256)
+	}
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		r := New(10 * time.Millisecond)
+		r.ResolveAddrsParallel(addrs)
+	}
+}
+
+func BenchmarkConcurrentResolveAddr(b *testing.B) {
+	r := New(100 * time.Millisecond)
+	addr := "127.0.0.1"
+
+	// pre-populate cache
+	r.ResolveAddr(addr)
+
+	b.ResetTimer()
+	b.RunParallel(func(pb *testing.PB) {
+		for pb.Next() {
+			r.ResolveAddr(addr)
+		}
+	})
+}
+
+func BenchmarkConcurrentResolvePort(b *testing.B) {
+	r := New(100 * time.Millisecond)
+
+	// pre-populate cache
+	r.ResolvePort(80, "tcp")
+
+	b.ResetTimer()
+	b.RunParallel(func(pb *testing.PB) {
+		for pb.Next() {
+			r.ResolvePort(80, "tcp")
+		}
+	})
+}
+
+func BenchmarkGetCacheSize(b *testing.B) {
+	r := New(100 * time.Millisecond)
+
+	// populate with some entries
+	for i := 0; i < 100; i++ {
+		r.ResolvePort(i+1, "tcp")
+	}
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		r.GetCacheSize()
+	}
+}
+
+func BenchmarkClearCache(b *testing.B) {
+	r := New(100 * time.Millisecond)
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		// populate and clear
+		for j := 0; j < 10; j++ {
+			r.ResolvePort(j+1, "tcp")
+		}
+		r.ClearCache()
+	}
+}
+

internal/resolver/resolver_test.go

@@ -0,0 +1,387 @@
+package resolver
+
+import (
+	"sync"
+	"testing"
+	"time"
+)
+
+func TestNew(t *testing.T) {
+	r := New(100 * time.Millisecond)
+	if r == nil {
+		t.Fatal("expected non-nil resolver")
+	}
+	if r.timeout != 100*time.Millisecond {
+		t.Errorf("expected timeout 100ms, got %v", r.timeout)
+	}
+	if r.cache == nil {
+		t.Error("expected cache to be initialized")
+	}
+	if r.noCache {
+		t.Error("expected noCache to be false by default")
+	}
+}
+
+func TestSetNoCache(t *testing.T) {
+	r := New(100 * time.Millisecond)
+
+	r.SetNoCache(true)
+	if !r.noCache {
+		t.Error("expected noCache to be true")
+	}
+
+	r.SetNoCache(false)
+	if r.noCache {
+		t.Error("expected noCache to be false")
+	}
+}
+
+func TestResolveAddr_InvalidIP(t *testing.T) {
+	r := New(100 * time.Millisecond)
+
+	// invalid ip should return as-is
+	result := r.ResolveAddr("not-an-ip")
+	if result != "not-an-ip" {
+		t.Errorf("expected 'not-an-ip', got %q", result)
+	}
+
+	// empty string should return as-is
+	result = r.ResolveAddr("")
+	if result != "" {
+		t.Errorf("expected empty string, got %q", result)
+	}
+}
+
+func TestResolveAddr_Caching(t *testing.T) {
+	r := New(100 * time.Millisecond)
+
+	// first call should cache
+	addr := "127.0.0.1"
+	result1 := r.ResolveAddr(addr)
+
+	// verify cache is populated
+	if r.GetCacheSize() != 1 {
+		t.Errorf("expected cache size 1, got %d", r.GetCacheSize())
+	}
+
+	// second call should use cache
+	result2 := r.ResolveAddr(addr)
+	if result1 != result2 {
+		t.Errorf("expected same result from cache, got %q and %q", result1, result2)
+	}
+}
+
+func TestResolveAddr_NoCacheMode(t *testing.T) {
+	r := New(100 * time.Millisecond)
+	r.SetNoCache(true)
+
+	addr := "127.0.0.1"
+	r.ResolveAddr(addr)
+
+	// cache should remain empty when noCache is enabled
+	if r.GetCacheSize() != 0 {
+		t.Errorf("expected cache size 0 with noCache, got %d", r.GetCacheSize())
+	}
+}
+
+func TestResolvePort_Zero(t *testing.T) {
+	r := New(100 * time.Millisecond)
+
+	result := r.ResolvePort(0, "tcp")
+	if result != "0" {
+		t.Errorf("expected '0' for port 0, got %q", result)
+	}
+}
+
+func TestResolvePort_WellKnown(t *testing.T) {
+	r := New(100 * time.Millisecond)
+
+	tests := []struct {
+		port     int
+		proto    string
+		expected string
+	}{
+		{80, "tcp", "http"},
+		{443, "tcp", "https"},
+		{22, "tcp", "ssh"},
+		{53, "udp", "domain"},
+		{5432, "tcp", "postgresql"},
+	}
+
+	for _, tt := range tests {
+		result := r.ResolvePort(tt.port, tt.proto)
+		if result != tt.expected {
+			t.Errorf("ResolvePort(%d, %q) = %q, want %q", tt.port, tt.proto, result, tt.expected)
+		}
+	}
+}
+
+func TestResolvePort_Caching(t *testing.T) {
+	r := New(100 * time.Millisecond)
+
+	r.ResolvePort(80, "tcp")
+	r.ResolvePort(443, "tcp")
+
+	if r.GetCacheSize() != 2 {
+		t.Errorf("expected cache size 2, got %d", r.GetCacheSize())
+	}
+
+	// same port/proto should not add new entry
+	r.ResolvePort(80, "tcp")
+	if r.GetCacheSize() != 2 {
+		t.Errorf("expected cache size still 2, got %d", r.GetCacheSize())
+	}
+}
+
+func TestResolveAddrPort(t *testing.T) {
+	r := New(100 * time.Millisecond)
+
+	addr, port := r.ResolveAddrPort("127.0.0.1", 80, "tcp")
+
+	if addr == "" {
+		t.Error("expected non-empty address")
+	}
+	if port != "http" {
+		t.Errorf("expected port 'http', got %q", port)
+	}
+}
+
+func TestClearCache(t *testing.T) {
+	r := New(100 * time.Millisecond)
+
+	r.ResolveAddr("127.0.0.1")
+	r.ResolvePort(80, "tcp")
+
+	if r.GetCacheSize() == 0 {
+		t.Error("expected non-empty cache before clear")
+	}
+
+	r.ClearCache()
+
+	if r.GetCacheSize() != 0 {
+		t.Errorf("expected empty cache after clear, got %d", r.GetCacheSize())
+	}
+}
+
+func TestGetCacheSize(t *testing.T) {
+	r := New(100 * time.Millisecond)
+
+	if r.GetCacheSize() != 0 {
+		t.Errorf("expected initial cache size 0, got %d", r.GetCacheSize())
+	}
+
+	r.ResolveAddr("127.0.0.1")
+	if r.GetCacheSize() != 1 {
+		t.Errorf("expected cache size 1, got %d", r.GetCacheSize())
+	}
+}
+
+func TestGetServiceName(t *testing.T) {
+	tests := []struct {
+		port     int
+		proto    string
+		expected string
+	}{
+		{80, "tcp", "http"},
+		{443, "tcp", "https"},
+		{22, "tcp", "ssh"},
+		{53, "tcp", "domain"},
+		{53, "udp", "domain"},
+		{12345, "tcp", ""},
+		{0, "tcp", ""},
+	}
+
+	for _, tt := range tests {
+		result := getServiceName(tt.port, tt.proto)
+		if result != tt.expected {
+			t.Errorf("getServiceName(%d, %q) = %q, want %q", tt.port, tt.proto, result, tt.expected)
+		}
+	}
+}
+
+func TestResolveAddrsParallel(t *testing.T) {
+	r := New(100 * time.Millisecond)
+
+	addrs := []string{
+		"127.0.0.1",
+		"127.0.0.2",
+		"127.0.0.3",
+		"", // should be skipped
+		"*", // should be skipped
+	}
+
+	r.ResolveAddrsParallel(addrs)
+
+	// should have cached 3 addresses (excluding empty and *)
+	if r.GetCacheSize() != 3 {
+		t.Errorf("expected cache size 3, got %d", r.GetCacheSize())
+	}
+}
+
+func TestResolveAddrsParallel_Dedupe(t *testing.T) {
+	r := New(100 * time.Millisecond)
+
+	addrs := []string{
+		"127.0.0.1",
+		"127.0.0.1",
+		"127.0.0.1",
+		"127.0.0.2",
+	}
+
+	r.ResolveAddrsParallel(addrs)
+
+	// should have cached 2 unique addresses
+	if r.GetCacheSize() != 2 {
+		t.Errorf("expected cache size 2, got %d", r.GetCacheSize())
+	}
+}
+
+func TestResolveAddrsParallel_SkipsCached(t *testing.T) {
+	r := New(100 * time.Millisecond)
+
+	// pre-cache one address
+	r.ResolveAddr("127.0.0.1")
+
+	addrs := []string{
+		"127.0.0.1", // already cached
+		"127.0.0.2", // not cached
+	}
+
+	initialSize := r.GetCacheSize()
+	r.ResolveAddrsParallel(addrs)
+
+	// should have added 1 more
+	if r.GetCacheSize() != initialSize+1 {
+		t.Errorf("expected cache size %d, got %d", initialSize+1, r.GetCacheSize())
+	}
+}
+
+func TestResolveAddrsParallel_Empty(t *testing.T) {
+	r := New(100 * time.Millisecond)
+
+	// should not panic with empty input
+	r.ResolveAddrsParallel([]string{})
+	r.ResolveAddrsParallel(nil)
+
+	if r.GetCacheSize() != 0 {
+		t.Errorf("expected cache size 0, got %d", r.GetCacheSize())
+	}
+}
+
+func TestGlobalResolver(t *testing.T) {
+	// reset global resolver
+	globalResolver = nil
+
+	r := GetGlobalResolver()
+	if r == nil {
+		t.Fatal("expected non-nil global resolver")
+	}
+
+	// should return same instance
+	r2 := GetGlobalResolver()
+	if r != r2 {
+		t.Error("expected same global resolver instance")
+	}
+}
+
+func TestSetGlobalResolver(t *testing.T) {
+	SetGlobalResolver(ResolverOptions{
+		Timeout: 500 * time.Millisecond,
+		NoCache: true,
+	})
+
+	r := GetGlobalResolver()
+	if r.timeout != 500*time.Millisecond {
+		t.Errorf("expected timeout 500ms, got %v", r.timeout)
+	}
+	if !r.noCache {
+		t.Error("expected noCache to be true")
+	}
+
+	// reset for other tests
+	globalResolver = nil
+}
+
+func TestSetGlobalResolver_DefaultTimeout(t *testing.T) {
+	SetGlobalResolver(ResolverOptions{
+		Timeout: 0, // should use default
+	})
+
+	r := GetGlobalResolver()
+	if r.timeout != 200*time.Millisecond {
+		t.Errorf("expected default timeout 200ms, got %v", r.timeout)
+	}
+
+	// reset for other tests
+	globalResolver = nil
+}
+
+func TestGlobalConvenienceFunctions(t *testing.T) {
+	globalResolver = nil
+
+	// test global ResolveAddr
+	result := ResolveAddr("127.0.0.1")
+	if result == "" {
+		t.Error("expected non-empty result from global ResolveAddr")
+	}
+
+	// test global ResolvePort
+	port := ResolvePort(80, "tcp")
+	if port != "http" {
+		t.Errorf("expected 'http', got %q", port)
+	}
+
+	// test global ResolveAddrPort
+	addr, portStr := ResolveAddrPort("127.0.0.1", 443, "tcp")
+	if addr == "" {
+		t.Error("expected non-empty address")
+	}
+	if portStr != "https" {
+		t.Errorf("expected 'https', got %q", portStr)
+	}
+
+	// test global SetNoCache
+	SetNoCache(true)
+	if !GetGlobalResolver().noCache {
+		t.Error("expected global noCache to be true")
+	}
+
+	// reset
+	globalResolver = nil
+}
+
+func TestConcurrentAccess(t *testing.T) {
+	r := New(100 * time.Millisecond)
+
+	var wg sync.WaitGroup
+	for i := 0; i < 100; i++ {
+		wg.Add(1)
+		go func(n int) {
+			defer wg.Done()
+			addr := "127.0.0.1"
+			r.ResolveAddr(addr)
+			r.ResolvePort(80+n%10, "tcp")
+			r.GetCacheSize()
+		}(i)
+	}
+
+	wg.Wait()
+
+	// should not panic and cache should have entries
+	if r.GetCacheSize() == 0 {
+		t.Error("expected non-empty cache after concurrent access")
+	}
+}
+
+func TestResolveAddr_TrailingDot(t *testing.T) {
+	// this test verifies the trailing dot removal logic
+	// by checking the internal logic works correctly
+	r := New(100 * time.Millisecond)
+
+	// localhost should resolve and have trailing dot removed
+	result := r.ResolveAddr("127.0.0.1")
+	if len(result) > 0 && result[len(result)-1] == '.' {
+		t.Error("expected trailing dot to be removed")
+	}
+}
+

internal/tui/messages.go

@@ -3,6 +3,7 @@ package tui
 import (
 	"fmt"
 	"github.com/karol-broda/snitch/internal/collector"
+	"github.com/karol-broda/snitch/internal/resolver"
 	"syscall"
 	"time"
 
@@ -35,11 +36,20 @@ func (m model) tick() tea.Cmd {
 }
 
 func (m model) fetchData() tea.Cmd {
+	resolveAddrs := m.resolveAddrs
 	return func() tea.Msg {
 		conns, err := collector.GetConnections()
 		if err != nil {
 			return errMsg{err}
 		}
+		// pre-warm dns cache in parallel if resolution is enabled
+		if resolveAddrs {
+			addrs := make([]string, 0, len(conns)*2)
+			for _, c := range conns {
+				addrs = append(addrs, c.Laddr, c.Raddr)
+			}
+			resolver.ResolveAddrsParallel(addrs)
+		}
 		return dataMsg{connections: conns}
 	}
 }

internal/tui/model.go

@@ -64,6 +64,7 @@ type Options struct {
 	FilterSet    bool // true if user specified any filter flags
 	ResolveAddrs bool // when true, resolve IP addresses to hostnames
 	ResolvePorts bool // when true, resolve port numbers to service names
+	NoCache      bool // when true, disable DNS caching
 }
 
 func New(opts Options) model {