feat: introduce theme management and performance improvements (#7)

internal/collector/collector_linux.go

@@ -11,21 +11,76 @@ import (
 	"path/filepath"
 	"strconv"
 	"strings"
+	"sync"
+	"sync/atomic"
 	"time"
 )
 
+// set SNITCH_DEBUG_TIMING=1 to enable timing diagnostics
+var debugTiming = os.Getenv("SNITCH_DEBUG_TIMING") != ""
+
+func logTiming(label string, start time.Time, extra ...string) {
+	if !debugTiming {
+		return
+	}
+	elapsed := time.Since(start)
+	if len(extra) > 0 {
+		fmt.Fprintf(os.Stderr, "[timing] %s: %v (%s)\n", label, elapsed, extra[0])
+	} else {
+		fmt.Fprintf(os.Stderr, "[timing] %s: %v\n", label, elapsed)
+	}
+}
+
+// userCache caches uid to username mappings to avoid repeated lookups
+var userCache = struct {
+	sync.RWMutex
+	m map[int]string
+}{m: make(map[int]string)}
+
+func lookupUsername(uid int) string {
+	userCache.RLock()
+	if username, exists := userCache.m[uid]; exists {
+		userCache.RUnlock()
+		return username
+	}
+	userCache.RUnlock()
+
+	start := time.Now()
+	username := strconv.Itoa(uid)
+	u, err := user.LookupId(strconv.Itoa(uid))
+	if err == nil && u != nil {
+		username = u.Username
+	}
+	elapsed := time.Since(start)
+	if debugTiming && elapsed > 10*time.Millisecond {
+		fmt.Fprintf(os.Stderr, "[timing] user.LookupId(%d) slow: %v\n", uid, elapsed)
+	}
+
+	userCache.Lock()
+	userCache.m[uid] = username
+	userCache.Unlock()
+
+	return username
+}
+
 // DefaultCollector implements the Collector interface using /proc filesystem
 type DefaultCollector struct{}
 
 // GetConnections fetches all network connections by parsing /proc files
 func (dc *DefaultCollector) GetConnections() ([]Connection, error) {
+	totalStart := time.Now()
+	defer func() { logTiming("GetConnections total", totalStart) }()
+
+	inodeStart := time.Now()
 	inodeMap, err := buildInodeToProcessMap()
+	logTiming("buildInodeToProcessMap", inodeStart, fmt.Sprintf("%d inodes", len(inodeMap)))
 	if err != nil {
 		return nil, fmt.Errorf("failed to build inode map: %w", err)
 	}
 
 	var connections []Connection
 
+	parseStart := time.Now()
 	tcpConns, err := parseProcNet("/proc/net/tcp", "tcp", 4, inodeMap)
 	if err == nil {
 		connections = append(connections, tcpConns...)
@@ -45,6 +100,7 @@ func (dc *DefaultCollector) GetConnections() ([]Connection, error) {
 	if err == nil {
 		connections = append(connections, udpConns6...)
 	}
+	logTiming("parseProcNet (all)", parseStart, fmt.Sprintf("%d connections", len(connections)))
 
 	return connections, nil
 }
@@ -71,9 +127,13 @@ type processInfo struct {
 	user    string
 }
 
-func buildInodeToProcessMap() (map[int64]*processInfo, error) {
-	inodeMap := make(map[int64]*processInfo)
+type inodeEntry struct {
+	inode int64
+	info  *processInfo
+}
 
+func buildInodeToProcessMap() (map[int64]*processInfo, error) {
+	readDirStart := time.Now()
 	procDir, err := os.Open("/proc")
 	if err != nil {
 		return nil, err
@@ -85,47 +145,103 @@ func buildInodeToProcessMap() (map[int64]*processInfo, error) {
 		return nil, err
 	}
 
+	// collect pids first
+	pids := make([]int, 0, len(entries))
 	for _, entry := range entries {
 		if !entry.IsDir() {
 			continue
 		}
+		pid, err := strconv.Atoi(entry.Name())
+		if err != nil {
+			continue
+		}
+		pids = append(pids, pid)
+	}
+	logTiming("  readdir /proc", readDirStart, fmt.Sprintf("%d pids", len(pids)))
 
-		pidStr := entry.Name()
-		pid, err := strconv.Atoi(pidStr)
+	// process pids in parallel with limited concurrency
+	scanStart := time.Now()
+	const numWorkers = 8
+	pidChan := make(chan int, len(pids))
+	resultChan := make(chan []inodeEntry, len(pids))
+
+	var totalFDs atomic.Int64
+	var wg sync.WaitGroup
+	for i := 0; i < numWorkers; i++ {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			for pid := range pidChan {
+				entries := scanProcessSockets(pid)
+				if len(entries) > 0 {
+					totalFDs.Add(int64(len(entries)))
+					resultChan <- entries
+				}
+			}
+		}()
+	}
+
+	for _, pid := range pids {
+		pidChan <- pid
+	}
+	close(pidChan)
+
+	go func() {
+		wg.Wait()
+		close(resultChan)
+	}()
+
+	inodeMap := make(map[int64]*processInfo)
+	for entries := range resultChan {
+		for _, e := range entries {
+			inodeMap[e.inode] = e.info
+		}
+	}
+	logTiming("  scan all processes", scanStart, fmt.Sprintf("%d socket fds scanned", totalFDs.Load()))
+
+	return inodeMap, nil
+}
+
+func scanProcessSockets(pid int) []inodeEntry {
+	start := time.Now()
+
+	procInfo, err := getProcessInfo(pid)
+	if err != nil {
+		return nil
+	}
+
+	pidStr := strconv.Itoa(pid)
+	fdDir := filepath.Join("/proc", pidStr, "fd")
+	fdEntries, err := os.ReadDir(fdDir)
+	if err != nil {
+		return nil
+	}
+
+	var results []inodeEntry
+	for _, fdEntry := range fdEntries {
+		fdPath := filepath.Join(fdDir, fdEntry.Name())
+		link, err := os.Readlink(fdPath)
 		if err != nil {
 			continue
 		}
 
-		procInfo, err := getProcessInfo(pid)
-		if err != nil {
-			continue
-		}
-
-		fdDir := filepath.Join("/proc", pidStr, "fd")
-		fdEntries, err := os.ReadDir(fdDir)
-		if err != nil {
-			continue
-		}
-
-		for _, fdEntry := range fdEntries {
-			fdPath := filepath.Join(fdDir, fdEntry.Name())
-			link, err := os.Readlink(fdPath)
+		if strings.HasPrefix(link, "socket:[") && strings.HasSuffix(link, "]") {
+			inodeStr := link[8 : len(link)-1]
+			inode, err := strconv.ParseInt(inodeStr, 10, 64)
 			if err != nil {
 				continue
 			}
-
-			if strings.HasPrefix(link, "socket:[") && strings.HasSuffix(link, "]") {
-				inodeStr := link[8 : len(link)-1]
-				inode, err := strconv.ParseInt(inodeStr, 10, 64)
-				if err != nil {
-					continue
-				}
-				inodeMap[inode] = procInfo
-			}
+			results = append(results, inodeEntry{inode: inode, info: procInfo})
 		}
 	}
 
-	return inodeMap, nil
+	elapsed := time.Since(start)
+	if debugTiming && elapsed > 20*time.Millisecond {
+		fmt.Fprintf(os.Stderr, "[timing] slow process scan: pid=%d (%s) fds=%d time=%v\n",
+			pid, procInfo.command, len(fdEntries), elapsed)
+	}
+
+	return results
 }
 
 func getProcessInfo(pid int) (*processInfo, error) {
@@ -173,12 +289,7 @@ func getProcessInfo(pid int) (*processInfo, error) {
 				uid, err := strconv.Atoi(fields[1])
 				if err == nil {
 					info.uid = uid
-					u, err := user.LookupId(strconv.Itoa(uid))
-					if err == nil {
-						info.user = u.Username
-					} else {
-						info.user = strconv.Itoa(uid)
-					}
+					info.user = lookupUsername(uid)
 				}
 			}
 			break

internal/collector/collector_test.go

@@ -1,7 +1,10 @@
+//go:build linux
+
 package collector
 
 import (
 	"testing"
+	"time"
 )
 
 func TestGetConnections(t *testing.T) {
@@ -13,4 +16,102 @@ func TestGetConnections(t *testing.T) {
 
 	// connections are dynamic, so just verify function succeeded
 	t.Logf("Successfully got %d connections", len(conns))
+}
+
+func TestGetConnectionsPerformance(t *testing.T) {
+	// measures performance to catch regressions
+	// run with: go test -v -run TestGetConnectionsPerformance
+
+	const maxDuration = 500 * time.Millisecond
+	const iterations = 5
+
+	// warm up caches first
+	_, err := GetConnections()
+	if err != nil {
+		t.Fatalf("warmup failed: %v", err)
+	}
+
+	var total time.Duration
+	var maxSeen time.Duration
+
+	for i := 0; i < iterations; i++ {
+		start := time.Now()
+		conns, err := GetConnections()
+		elapsed := time.Since(start)
+
+		if err != nil {
+			t.Fatalf("iteration %d failed: %v", i, err)
+		}
+
+		total += elapsed
+		if elapsed > maxSeen {
+			maxSeen = elapsed
+		}
+
+		t.Logf("iteration %d: %v (%d connections)", i+1, elapsed, len(conns))
+	}
+
+	avg := total / time.Duration(iterations)
+	t.Logf("average: %v, max: %v", avg, maxSeen)
+
+	if maxSeen > maxDuration {
+		t.Errorf("slowest iteration took %v, expected < %v", maxSeen, maxDuration)
+	}
+}
+
+func TestGetConnectionsColdCache(t *testing.T) {
+	// tests performance with cold user cache
+	// this simulates first run or after cache invalidation
+
+	const maxDuration = 2 * time.Second
+
+	clearUserCache()
+
+	start := time.Now()
+	conns, err := GetConnections()
+	elapsed := time.Since(start)
+
+	if err != nil {
+		t.Fatalf("GetConnections() failed: %v", err)
+	}
+
+	t.Logf("cold cache: %v (%d connections, %d cached users after)",
+		elapsed, len(conns), userCacheSize())
+
+	if elapsed > maxDuration {
+		t.Errorf("cold cache took %v, expected < %v", elapsed, maxDuration)
+	}
+}
+
+func BenchmarkGetConnections(b *testing.B) {
+	// warm cache benchmark - measures typical runtime
+	// run with: go test -bench=BenchmarkGetConnections -benchtime=5s
+
+	// warm up
+	_, _ = GetConnections()
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_, _ = GetConnections()
+	}
+}
+
+func BenchmarkGetConnectionsColdCache(b *testing.B) {
+	// cold cache benchmark - measures worst-case with cache cleared each iteration
+	// run with: go test -bench=BenchmarkGetConnectionsColdCache -benchtime=10s
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		clearUserCache()
+		_, _ = GetConnections()
+	}
+}
+
+func BenchmarkBuildInodeMap(b *testing.B) {
+	// benchmarks just the inode map building (most expensive part)
+
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_, _ = buildInodeToProcessMap()
+	}
 }

internal/collector/collector_test_helpers_linux.go

@@ -0,0 +1,18 @@
+//go:build linux
+
+package collector
+
+// clearUserCache clears the user lookup cache for testing
+func clearUserCache() {
+	userCache.Lock()
+	userCache.m = make(map[int]string)
+	userCache.Unlock()
+}
+
+// userCacheSize returns the number of cached user entries
+func userCacheSize() int {
+	userCache.RLock()
+	defer userCache.RUnlock()
+	return len(userCache.m)
+}
+