fix(go): channels null arrays + hash size enrichment on nodes

- Fix #148: channels endpoint returned null for msgLengths when no
  decrypted messages exist. Initialize msgLengths as make([]int, 0)
  in store path and guard channels slice in DB fallback path.

- Fix #149: nodes endpoint always returned hash_size=null and
  hash_size_inconsistent=false. Add GetNodeHashSizeInfo() to
  PacketStore that scans advert packets to compute per-node hash
  size, flip-flop detection, and sizes_seen. Enrich nodes in both
  handleNodes and handleNodeDetail with computed hash data.

fixes #148, fixes #149

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

cmd/server/routes.go

@@ -678,6 +678,14 @@ func (s *Server) handleNodes(w http.ResponseWriter, r *http.Request) {
 		writeError(w, 500, err.Error())
 		return
 	}
+	if s.store != nil {
+		hashInfo := s.store.GetNodeHashSizeInfo()
+		for _, node := range nodes {
+			if pk, ok := node["public_key"].(string); ok {
+				EnrichNodeWithHashSize(node, hashInfo[pk])
+			}
+		}
+	}
 	writeJSON(w, map[string]interface{}{"nodes": nodes, "total": total, "counts": counts})
 }
 
@@ -703,6 +711,11 @@ func (s *Server) handleNodeDetail(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	if s.store != nil {
+		hashInfo := s.store.GetNodeHashSizeInfo()
+		EnrichNodeWithHashSize(node, hashInfo[pubkey])
+	}
+
 	name := ""
 	if n, ok := node["name"]; ok && n != nil {
 		name = fmt.Sprintf("%v", n)
@@ -1073,8 +1086,10 @@ func (s *Server) handleAnalyticsChannels(w http.ResponseWriter, r *http.Request)
 		writeJSON(w, s.store.GetAnalyticsChannels(region))
 		return
 	}
-	var channels []map[string]interface{}
-	channels, _ = s.db.GetChannels()
+	channels, _ := s.db.GetChannels()
+	if channels == nil {
+		channels = make([]map[string]interface{}, 0)
+	}
 	writeJSON(w, map[string]interface{}{
 		"activeChannels":  len(channels),
 		"decryptable":     len(channels),

cmd/server/routes_test.go

@@ -4,6 +4,7 @@ import (
 	"encoding/json"
 	"net/http"
 	"net/http/httptest"
+	"strconv"
 	"testing"
 
 	"github.com/gorilla/mux"
@@ -1742,6 +1743,197 @@ func TestHandlerErrorBulkHealth(t *testing.T) {
 	}
 }
 
+
+func TestAnalyticsChannelsNoNullArrays(t *testing.T) {
+_, router := setupTestServer(t)
+req := httptest.NewRequest("GET", "/api/analytics/channels", nil)
+w := httptest.NewRecorder()
+router.ServeHTTP(w, req)
+
+if w.Code != 200 {
+t.Fatalf("expected 200, got %d", w.Code)
+}
+
+raw := w.Body.String()
+var body map[string]interface{}
+if err := json.Unmarshal([]byte(raw), &body); err != nil {
+t.Fatalf("invalid JSON: %v", err)
+}
+
+arrayFields := []string{"channels", "topSenders", "channelTimeline", "msgLengths"}
+for _, field := range arrayFields {
+val, exists := body[field]
+if !exists {
+t.Errorf("missing field %q", field)
+continue
+}
+if val == nil {
+t.Errorf("field %q is null, expected empty array []", field)
+continue
+}
+if _, ok := val.([]interface{}); !ok {
+t.Errorf("field %q is not an array, got %T", field, val)
+}
+}
+}
+
+func TestAnalyticsChannelsNoStoreFallbackNoNulls(t *testing.T) {
+db := setupTestDB(t)
+seedTestData(t, db)
+cfg := &Config{Port: 3000}
+hub := NewHub()
+srv := NewServer(db, cfg, hub)
+router := mux.NewRouter()
+srv.RegisterRoutes(router)
+
+req := httptest.NewRequest("GET", "/api/analytics/channels", nil)
+w := httptest.NewRecorder()
+router.ServeHTTP(w, req)
+
+if w.Code != 200 {
+t.Fatalf("expected 200, got %d", w.Code)
+}
+
+var body map[string]interface{}
+json.Unmarshal(w.Body.Bytes(), &body)
+
+arrayFields := []string{"channels", "topSenders", "channelTimeline", "msgLengths"}
+for _, field := range arrayFields {
+if body[field] == nil {
+t.Errorf("field %q is null in DB fallback, expected []", field)
+}
+}
+}
+
+func TestNodeHashSizeEnrichment(t *testing.T) {
+t.Run("nil info leaves defaults", func(t *testing.T) {
+node := map[string]interface{}{
+"public_key":             "abc123",
+"hash_size":              nil,
+"hash_size_inconsistent": false,
+}
+EnrichNodeWithHashSize(node, nil)
+if node["hash_size"] != nil {
+t.Error("expected hash_size to remain nil with nil info")
+}
+})
+
+t.Run("enriches with computed data", func(t *testing.T) {
+node := map[string]interface{}{
+"public_key":             "abc123",
+"hash_size":              nil,
+"hash_size_inconsistent": false,
+}
+info := &hashSizeNodeInfo{
+HashSize:     2,
+AllSizes:     map[int]bool{1: true, 2: true},
+Seq:          []int{1, 2, 1, 2},
+Inconsistent: true,
+}
+EnrichNodeWithHashSize(node, info)
+if node["hash_size"] != 2 {
+t.Errorf("expected hash_size 2, got %v", node["hash_size"])
+}
+if node["hash_size_inconsistent"] != true {
+t.Error("expected hash_size_inconsistent true")
+}
+sizes, ok := node["hash_sizes_seen"].([]int)
+if !ok {
+t.Fatal("expected hash_sizes_seen to be []int")
+}
+if len(sizes) != 2 || sizes[0] != 1 || sizes[1] != 2 {
+t.Errorf("expected [1,2], got %v", sizes)
+}
+})
+
+t.Run("single size omits sizes_seen", func(t *testing.T) {
+node := map[string]interface{}{
+"public_key":             "abc123",
+"hash_size":              nil,
+"hash_size_inconsistent": false,
+}
+info := &hashSizeNodeInfo{
+HashSize: 3,
+AllSizes: map[int]bool{3: true},
+Seq:      []int{3, 3, 3},
+}
+EnrichNodeWithHashSize(node, info)
+if node["hash_size"] != 3 {
+t.Errorf("expected hash_size 3, got %v", node["hash_size"])
+}
+if node["hash_size_inconsistent"] != false {
+t.Error("expected hash_size_inconsistent false")
+}
+if _, exists := node["hash_sizes_seen"]; exists {
+t.Error("hash_sizes_seen should not be set for single size")
+}
+})
+}
+
+func TestGetNodeHashSizeInfoFlipFlop(t *testing.T) {
+db := setupTestDB(t)
+seedTestData(t, db)
+store := NewPacketStore(db)
+store.Load()
+
+pk := "abcdef1234567890abcdef1234567890abcdef1234567890abcdef1234567890"
+db.conn.Exec("INSERT OR IGNORE INTO nodes (public_key, name, role) VALUES (?, 'TestNode', 'repeater')", pk)
+
+decoded := `{"name":"TestNode","pubKey":"` + pk + `"}`
+raw1 := "04" + "00" + "aabb"
+raw2 := "04" + "40" + "aabb"
+
+payloadType := 4
+for i := 0; i < 3; i++ {
+rawHex := raw1
+if i%2 == 1 {
+rawHex = raw2
+}
+tx := &StoreTx{
+ID:          9000 + i,
+RawHex:      rawHex,
+Hash:        "testhash" + strconv.Itoa(i),
+FirstSeen:   "2024-01-01T00:00:00Z",
+PayloadType: &payloadType,
+DecodedJSON: decoded,
+}
+store.packets = append(store.packets, tx)
+store.byPayloadType[4] = append(store.byPayloadType[4], tx)
+}
+
+info := store.GetNodeHashSizeInfo()
+ni := info[pk]
+if ni == nil {
+t.Fatal("expected hash info for test node")
+}
+if len(ni.AllSizes) != 2 {
+t.Errorf("expected 2 unique sizes, got %d", len(ni.AllSizes))
+}
+if !ni.Inconsistent {
+t.Error("expected inconsistent flag to be true for flip-flop pattern")
+}
+}
+
+func TestAnalyticsHashSizesNoNullArrays(t *testing.T) {
+_, router := setupTestServer(t)
+req := httptest.NewRequest("GET", "/api/analytics/hash-sizes", nil)
+w := httptest.NewRecorder()
+router.ServeHTTP(w, req)
+
+if w.Code != 200 {
+t.Fatalf("expected 200, got %d", w.Code)
+}
+
+var body map[string]interface{}
+json.Unmarshal(w.Body.Bytes(), &body)
+
+arrayFields := []string{"hourly", "topHops", "multiByteNodes"}
+for _, field := range arrayFields {
+if body[field] == nil {
+t.Errorf("field %q is null, expected []", field)
+}
+}
+}
 func min(a, b int) int {
 	if a < b {
 		return a

cmd/server/store.go

@@ -1321,7 +1321,7 @@ func (s *PacketStore) GetAnalyticsChannels(region string) map[string]interface{}
 
 	channelMap := map[string]*chanInfo{}
 	senderCounts := map[string]int{}
-	var msgLengths []int
+	msgLengths := make([]int, 0)
 	timeline := map[string]int{} // hour|channelName → count
 
 	grpTxts := s.byPayloadType[5]
@@ -2946,6 +2946,95 @@ func (s *PacketStore) GetAnalyticsHashSizes(region string) map[string]interface{
 	}
 }
 
+
+// hashSizeNodeInfo holds per-node hash size tracking data.
+type hashSizeNodeInfo struct {
+	HashSize     int
+	AllSizes     map[int]bool
+	Seq          []int
+	Inconsistent bool
+}
+
+// GetNodeHashSizeInfo scans advert packets to compute per-node hash size data.
+func (s *PacketStore) GetNodeHashSizeInfo() map[string]*hashSizeNodeInfo {
+	s.mu.RLock()
+	defer s.mu.RUnlock()
+
+	info := make(map[string]*hashSizeNodeInfo)
+
+	adverts := s.byPayloadType[4]
+	for _, tx := range adverts {
+		if tx.RawHex == "" || tx.DecodedJSON == "" {
+			continue
+		}
+		if len(tx.RawHex) < 4 {
+			continue
+		}
+		pathByte, err := strconv.ParseUint(tx.RawHex[2:4], 16, 8)
+		if err != nil {
+			continue
+		}
+		hs := int((pathByte>>6)&0x3) + 1
+
+		var d map[string]interface{}
+		if json.Unmarshal([]byte(tx.DecodedJSON), &d) != nil {
+			continue
+		}
+		pk := ""
+		if v, ok := d["pubKey"].(string); ok {
+			pk = v
+		} else if v, ok := d["public_key"].(string); ok {
+			pk = v
+		}
+		if pk == "" {
+			continue
+		}
+
+		ni := info[pk]
+		if ni == nil {
+			ni = &hashSizeNodeInfo{AllSizes: make(map[int]bool)}
+			info[pk] = ni
+		}
+		ni.HashSize = hs
+		ni.AllSizes[hs] = true
+		ni.Seq = append(ni.Seq, hs)
+	}
+
+	// Compute flip-flop (inconsistent) flag: need >= 3 observations,
+	// >= 2 unique sizes, and >= 2 transitions in the sequence.
+	for _, ni := range info {
+		if len(ni.Seq) < 3 || len(ni.AllSizes) < 2 {
+			continue
+		}
+		transitions := 0
+		for i := 1; i < len(ni.Seq); i++ {
+			if ni.Seq[i] != ni.Seq[i-1] {
+				transitions++
+			}
+		}
+		ni.Inconsistent = transitions >= 2
+	}
+
+	return info
+}
+
+// EnrichNodeWithHashSize populates hash_size, hash_size_inconsistent, and
+// hash_sizes_seen on a node map using precomputed hash size info.
+func EnrichNodeWithHashSize(node map[string]interface{}, info *hashSizeNodeInfo) {
+	if info == nil {
+		return
+	}
+	node["hash_size"] = info.HashSize
+	node["hash_size_inconsistent"] = info.Inconsistent
+	if len(info.AllSizes) > 1 {
+		sizes := make([]int, 0, len(info.AllSizes))
+		for s := range info.AllSizes {
+			sizes = append(sizes, s)
+		}
+		sort.Ints(sizes)
+		node["hash_sizes_seen"] = sizes
+	}
+}
 // --- Bulk Health (in-memory) ---
 
 func (s *PacketStore) GetBulkHealth(limit int, region string) []map[string]interface{} {