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

Author: karol-broda

README.md

@@ -167,9 +167,20 @@ shortcut flags work on all commands:
 -e, --established   established connections
 -4, --ipv4          ipv4 only
 -6, --ipv6          ipv6 only
--n, --numeric       no dns resolution
 ```
 
+## resolution
+
+dns and service name resolution options:
+
+```
+--resolve-addrs     resolve ip addresses to hostnames (default: true)
+--resolve-ports     resolve port numbers to service names
+--no-cache          disable dns caching (force fresh lookups)
+```
+
+dns lookups are performed in parallel and cached for performance. use `--no-cache` to bypass the cache for debugging or when addresses change frequently.
+
 for more specific filtering, use `key=value` syntax with `ls`:
 
 ```bash
@@ -208,8 +219,19 @@ optional config file at `~/.config/snitch/snitch.toml`:
 
 ```toml
 [defaults]
-numeric = false
-theme = "auto"
+numeric = false      # disable name resolution
+dns_cache = true     # cache dns lookups (set to false to disable)
+theme = "auto"       # color theme: auto, dark, light, mono
+```
+
+### environment variables
+
+```bash
+SNITCH_THEME=dark          # set default theme
+SNITCH_RESOLVE=0           # disable dns resolution
+SNITCH_DNS_CACHE=0         # disable dns caching
+SNITCH_NO_COLOR=1          # disable color output
+SNITCH_CONFIG=/path/to     # custom config file path
 ```
 
 ## requirements

cmd/ls.go

@@ -30,8 +30,6 @@ var (
 	sortBy        string
 	fields        string
 	colorMode     string
-	resolveAddrs  bool
-	resolvePorts  bool
 	plainOutput   bool
 )
 
@@ -400,10 +398,9 @@ func init() {
 	lsCmd.Flags().StringVarP(&sortBy, "sort", "s", cfg.Defaults.SortBy, "Sort by column (e.g., pid:desc)")
 	lsCmd.Flags().StringVarP(&fields, "fields", "f", strings.Join(cfg.Defaults.Fields, ","), "Comma-separated list of fields to show")
 	lsCmd.Flags().StringVar(&colorMode, "color", cfg.Defaults.Color, "Color mode (auto, always, never)")
-	lsCmd.Flags().BoolVar(&resolveAddrs, "resolve-addrs", !cfg.Defaults.Numeric, "Resolve IP addresses to hostnames")
-	lsCmd.Flags().BoolVar(&resolvePorts, "resolve-ports", false, "Resolve port numbers to service names")
 	lsCmd.Flags().BoolVarP(&plainOutput, "plain", "p", false, "Plain output (parsable, no styling)")
 
-	// shared filter flags
+	// shared flags
 	addFilterFlags(lsCmd)
+	addResolutionFlags(lsCmd)
 }

cmd/root.go

@@ -45,9 +45,8 @@ func init() {
 	cfg := config.Get()
 	rootCmd.Flags().StringVar(&topTheme, "theme", cfg.Defaults.Theme, "Theme for TUI (see 'snitch themes')")
 	rootCmd.Flags().DurationVarP(&topInterval, "interval", "i", 0, "Refresh interval (default 1s)")
-	rootCmd.Flags().BoolVar(&topResolveAddrs, "resolve-addrs", !cfg.Defaults.Numeric, "Resolve IP addresses to hostnames")
-	rootCmd.Flags().BoolVar(&topResolvePorts, "resolve-ports", false, "Resolve port numbers to service names")
 
-	// shared filter flags for root command
+	// shared flags for root command
 	addFilterFlags(rootCmd)
+	addResolutionFlags(rootCmd)
 }

cmd/runtime.go

@@ -4,14 +4,16 @@ import (
 	"fmt"
 	"github.com/karol-broda/snitch/internal/collector"
 	"github.com/karol-broda/snitch/internal/color"
+	"github.com/karol-broda/snitch/internal/config"
+	"github.com/karol-broda/snitch/internal/resolver"
 	"strconv"
 	"strings"
 
 	"github.com/spf13/cobra"
 )
 
 // Runtime holds the shared state for all commands.
-// it handles common filter logic, fetching, and filtering connections.
+// it handles common filter logic, fetching, filtering, and resolution.
 type Runtime struct {
 	// filter options built from flags and args
 	Filters collector.FilterOptions
@@ -23,6 +25,7 @@ type Runtime struct {
 	ColorMode    string
 	ResolveAddrs bool
 	ResolvePorts bool
+	NoCache      bool
 }
 
 // shared filter flags - used by all commands
@@ -35,6 +38,13 @@ var (
 	filterIPv6   bool
 )
 
+// shared resolution flags - used by all commands
+var (
+	resolveAddrs bool
+	resolvePorts bool
+	noCache      bool
+)
+
 // BuildFilters constructs FilterOptions from command args and shortcut flags.
 func BuildFilters(args []string) (collector.FilterOptions, error) {
 	filters, err := ParseFilterArgs(args)
@@ -77,6 +87,12 @@ func FetchConnections(filters collector.FilterOptions) ([]collector.Connection,
 func NewRuntime(args []string, colorMode string) (*Runtime, error) {
 	color.Init(colorMode)
 
+	cfg := config.Get()
+	
+	// configure resolver with cache setting (flag overrides config)
+	effectiveNoCache := noCache || !cfg.Defaults.DNSCache
+	resolver.SetNoCache(effectiveNoCache)
+
 	filters, err := BuildFilters(args)
 	if err != nil {
 		return nil, fmt.Errorf("failed to parse filters: %w", err)
@@ -87,13 +103,30 @@ func NewRuntime(args []string, colorMode string) (*Runtime, error) {
 		return nil, fmt.Errorf("failed to fetch connections: %w", err)
 	}
 
-	return &Runtime{
+	rt := &Runtime{
 		Filters:      filters,
 		Connections:  connections,
 		ColorMode:    colorMode,
 		ResolveAddrs: resolveAddrs,
 		ResolvePorts: resolvePorts,
-	}, nil
+		NoCache:      effectiveNoCache,
+	}
+
+	// pre-warm dns cache by resolving all addresses in parallel
+	if resolveAddrs {
+		rt.PreWarmDNS()
+	}
+
+	return rt, nil
+}
+
+// PreWarmDNS resolves all connection addresses in parallel to warm the cache.
+func (r *Runtime) PreWarmDNS() {
+	addrs := make([]string, 0, len(r.Connections)*2)
+	for _, c := range r.Connections {
+		addrs = append(addrs, c.Laddr, c.Raddr)
+	}
+	resolver.ResolveAddrsParallel(addrs)
 }
 
 // SortConnections sorts the runtime's connections in place.
@@ -201,3 +234,11 @@ func addFilterFlags(cmd *cobra.Command) {
 	cmd.Flags().BoolVarP(&filterIPv6, "ipv6", "6", false, "Only show IPv6 connections")
 }
 
+// addResolutionFlags adds the common resolution flags to a command.
+func addResolutionFlags(cmd *cobra.Command) {
+	cfg := config.Get()
+	cmd.Flags().BoolVar(&resolveAddrs, "resolve-addrs", !cfg.Defaults.Numeric, "Resolve IP addresses to hostnames")
+	cmd.Flags().BoolVar(&resolvePorts, "resolve-ports", false, "Resolve port numbers to service names")
+	cmd.Flags().BoolVar(&noCache, "no-cache", !cfg.Defaults.DNSCache, "Disable DNS caching (force fresh lookups)")
+}
+