feat: add runtime statistics to healthcheck endpoint

Add the following counters to the healthcheck JSON response:

- sessions: current active session count (from DB)
- clients: current connected client count (from DB)
- queuedLines: total entries in client output queues (from DB)
- channels: current channel count (from DB)
- connectionsSinceBoot: total client connections since server start
- sessionsSinceBoot: total sessions created since server start
- messagesSinceBoot: total PRIVMSG/NOTICE messages since server start

Implementation:
- New internal/stats package with atomic counters for boot-scoped metrics
- New DB queries GetClientCount and GetQueueEntryCount
- Healthcheck.Healthcheck() now accepts context for DB queries
- Counter increments in session creation, registration, login, and messaging
- Stats tracker wired via Uber fx dependency injection
- Unit tests for stats package (100% coverage) and integration tests
- README updated with full healthcheck response documentation

closes #74

internal/db/queries.go

@@ -1266,3 +1266,42 @@ func (database *Database) PruneOldMessages(
 
 	return deleted, nil
 }
+
+// GetClientCount returns the total number of clients.
+func (database *Database) GetClientCount(
+	ctx context.Context,
+) (int64, error) {
+	var count int64
+
+	err := database.conn.QueryRowContext(
+		ctx,
+		"SELECT COUNT(*) FROM clients",
+	).Scan(&count)
+	if err != nil {
+		return 0, fmt.Errorf(
+			"get client count: %w", err,
+		)
+	}
+
+	return count, nil
+}
+
+// GetQueueEntryCount returns the total number of entries
+// in the client output queues.
+func (database *Database) GetQueueEntryCount(
+	ctx context.Context,
+) (int64, error) {
+	var count int64
+
+	err := database.conn.QueryRowContext(
+		ctx,
+		"SELECT COUNT(*) FROM client_queues",
+	).Scan(&count)
+	if err != nil {
+		return 0, fmt.Errorf(
+			"get queue entry count: %w", err,
+		)
+	}
+
+	return count, nil
+}

internal/handlers/api.go

@@ -212,6 +212,9 @@ func (hdlr *Handlers) handleCreateSession(
 		return
 	}
 
+	hdlr.stats.IncrSessions()
+	hdlr.stats.IncrConnections()
+
 	hdlr.deliverMOTD(request, clientID, sessionID, payload.Nick)
 
 	hdlr.respondJSON(writer, request, map[string]any{
@@ -977,6 +980,8 @@ func (hdlr *Handlers) handlePrivmsg(
 		return
 	}
 
+	hdlr.stats.IncrMessages()
+
 	if strings.HasPrefix(target, "#") {
 		hdlr.handleChannelMsg(
 			writer, request,

internal/handlers/api_test.go

@@ -26,6 +26,7 @@ import (
 	"git.eeqj.de/sneak/neoirc/internal/logger"
 	"git.eeqj.de/sneak/neoirc/internal/middleware"
 	"git.eeqj.de/sneak/neoirc/internal/server"
+	"git.eeqj.de/sneak/neoirc/internal/stats"
 	"go.uber.org/fx"
 	"go.uber.org/fx/fxtest"
 )
@@ -90,6 +91,7 @@ func newTestServer(
 				return cfg, nil
 			},
 			newTestDB,
+			stats.New,
 			newTestHealthcheck,
 			newTestMiddleware,
 			newTestHandlers,
@@ -144,12 +146,14 @@ func newTestHealthcheck(
 	cfg *config.Config,
 	log *logger.Logger,
 	database *db.Database,
+	tracker *stats.Tracker,
 ) (*healthcheck.Healthcheck, error) {
 	hcheck, err := healthcheck.New(lifecycle, healthcheck.Params{ //nolint:exhaustruct
 		Globals:  globs,
 		Config:   cfg,
 		Logger:   log,
 		Database: database,
+		Stats:    tracker,
 	})
 	if err != nil {
 		return nil, fmt.Errorf("test healthcheck: %w", err)
@@ -183,6 +187,7 @@ func newTestHandlers(
 	cfg *config.Config,
 	database *db.Database,
 	hcheck *healthcheck.Healthcheck,
+	tracker *stats.Tracker,
 ) (*handlers.Handlers, error) {
 	hdlr, err := handlers.New(lifecycle, handlers.Params{ //nolint:exhaustruct
 		Logger:      log,
@@ -190,6 +195,7 @@ func newTestHandlers(
 		Config:      cfg,
 		Database:    database,
 		Healthcheck: hcheck,
+		Stats:       tracker,
 	})
 	if err != nil {
 		return nil, fmt.Errorf("test handlers: %w", err)
@@ -1657,6 +1663,133 @@ func TestHealthcheck(t *testing.T) {
 	}
 }
 
+func TestHealthcheckRuntimeStatsFields(t *testing.T) {
+	tserver := newTestServer(t)
+
+	resp, err := doRequest(
+		t,
+		http.MethodGet,
+		tserver.url("/.well-known/healthcheck.json"),
+		nil,
+	)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	defer func() { _ = resp.Body.Close() }()
+
+	if resp.StatusCode != http.StatusOK {
+		t.Fatalf(
+			"expected 200, got %d", resp.StatusCode,
+		)
+	}
+
+	var result map[string]any
+
+	decErr := json.NewDecoder(resp.Body).Decode(&result)
+	if decErr != nil {
+		t.Fatalf("decode healthcheck: %v", decErr)
+	}
+
+	requiredFields := []string{
+		"sessions", "clients", "queuedLines",
+		"channels", "connectionsSinceBoot",
+		"sessionsSinceBoot", "messagesSinceBoot",
+	}
+
+	for _, field := range requiredFields {
+		if _, ok := result[field]; !ok {
+			t.Errorf(
+				"missing field %q in healthcheck", field,
+			)
+		}
+	}
+}
+
+func TestHealthcheckRuntimeStatsValues(t *testing.T) {
+	tserver := newTestServer(t)
+
+	token := tserver.createSession("statsuser")
+
+	tserver.sendCommand(token, map[string]any{
+		commandKey: joinCmd, toKey: "#statschan",
+	})
+	tserver.sendCommand(token, map[string]any{
+		commandKey: privmsgCmd,
+		toKey:      "#statschan",
+		bodyKey:    []string{"hello stats"},
+	})
+
+	result := tserver.fetchHealthcheck(t)
+
+	assertFieldGTE(t, result, "sessions", 1)
+	assertFieldGTE(t, result, "clients", 1)
+	assertFieldGTE(t, result, "channels", 1)
+	assertFieldGTE(t, result, "queuedLines", 0)
+	assertFieldGTE(t, result, "sessionsSinceBoot", 1)
+	assertFieldGTE(t, result, "connectionsSinceBoot", 1)
+	assertFieldGTE(t, result, "messagesSinceBoot", 1)
+}
+
+func (tserver *testServer) fetchHealthcheck(
+	t *testing.T,
+) map[string]any {
+	t.Helper()
+
+	resp, err := doRequest(
+		t,
+		http.MethodGet,
+		tserver.url("/.well-known/healthcheck.json"),
+		nil,
+	)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	defer func() { _ = resp.Body.Close() }()
+
+	if resp.StatusCode != http.StatusOK {
+		t.Fatalf(
+			"expected 200, got %d", resp.StatusCode,
+		)
+	}
+
+	var result map[string]any
+
+	decErr := json.NewDecoder(resp.Body).Decode(&result)
+	if decErr != nil {
+		t.Fatalf("decode healthcheck: %v", decErr)
+	}
+
+	return result
+}
+
+func assertFieldGTE(
+	t *testing.T,
+	result map[string]any,
+	field string,
+	minimum float64,
+) {
+	t.Helper()
+
+	val, ok := result[field].(float64)
+	if !ok {
+		t.Errorf(
+			"field %q: not a number (got %T)",
+			field, result[field],
+		)
+
+		return
+	}
+
+	if val < minimum {
+		t.Errorf(
+			"expected %s >= %v, got %v",
+			field, minimum, val,
+		)
+	}
+}
+
 func TestRegisterValid(t *testing.T) {
 	tserver := newTestServer(t)
 

internal/handlers/auth.go

@@ -82,6 +82,9 @@ func (hdlr *Handlers) handleRegister(
 		return
 	}
 
+	hdlr.stats.IncrSessions()
+	hdlr.stats.IncrConnections()
+
 	hdlr.deliverMOTD(request, clientID, sessionID, payload.Nick)
 
 	hdlr.respondJSON(writer, request, map[string]any{
@@ -180,6 +183,8 @@ func (hdlr *Handlers) handleLogin(
 		return
 	}
 
+	hdlr.stats.IncrConnections()
+
 	hdlr.deliverMOTD(
 		request, clientID, sessionID, payload.Nick,
 	)

internal/handlers/handlers.go

@@ -16,6 +16,7 @@ import (
 	"git.eeqj.de/sneak/neoirc/internal/hashcash"
 	"git.eeqj.de/sneak/neoirc/internal/healthcheck"
 	"git.eeqj.de/sneak/neoirc/internal/logger"
+	"git.eeqj.de/sneak/neoirc/internal/stats"
 	"go.uber.org/fx"
 )
 
@@ -30,6 +31,7 @@ type Params struct {
 	Config      *config.Config
 	Database    *db.Database
 	Healthcheck *healthcheck.Healthcheck
+	Stats       *stats.Tracker
 }
 
 const defaultIdleTimeout = 30 * 24 * time.Hour
@@ -41,6 +43,7 @@ type Handlers struct {
 	hc            *healthcheck.Healthcheck
 	broker        *broker.Broker
 	hashcashVal   *hashcash.Validator
+	stats         *stats.Tracker
 	cancelCleanup context.CancelFunc
 }
 
@@ -60,6 +63,7 @@ func New(
 		hc:          params.Healthcheck,
 		broker:      broker.New(),
 		hashcashVal: hashcash.NewValidator(resource),
+		stats:       params.Stats,
 	}
 
 	lifecycle.Append(fx.Hook{

internal/handlers/healthcheck.go

@@ -12,7 +12,7 @@ func (hdlr *Handlers) HandleHealthCheck() http.HandlerFunc {
 		writer http.ResponseWriter,
 		request *http.Request,
 	) {
-		resp := hdlr.hc.Healthcheck()
+		resp := hdlr.hc.Healthcheck(request.Context())
 		hdlr.respondJSON(writer, request, resp, httpStatusOK)
 	}
 }

internal/healthcheck/healthcheck.go

@@ -10,6 +10,7 @@ import (
 	"git.eeqj.de/sneak/neoirc/internal/db"
 	"git.eeqj.de/sneak/neoirc/internal/globals"
 	"git.eeqj.de/sneak/neoirc/internal/logger"
+	"git.eeqj.de/sneak/neoirc/internal/stats"
 	"go.uber.org/fx"
 )
 
@@ -21,6 +22,7 @@ type Params struct {
 	Config   *config.Config
 	Logger   *logger.Logger
 	Database *db.Database
+	Stats    *stats.Tracker
 }
 
 // Healthcheck tracks server uptime and provides health status.
@@ -64,11 +66,22 @@ type Response struct {
 	Version       string `json:"version"`
 	Appname       string `json:"appname"`
 	Maintenance   bool   `json:"maintenanceMode"`
+
+	// Runtime statistics.
+	Sessions             int64 `json:"sessions"`
+	Clients              int64 `json:"clients"`
+	QueuedLines          int64 `json:"queuedLines"`
+	Channels             int64 `json:"channels"`
+	ConnectionsSinceBoot int64 `json:"connectionsSinceBoot"`
+	SessionsSinceBoot    int64 `json:"sessionsSinceBoot"`
+	MessagesSinceBoot    int64 `json:"messagesSinceBoot"`
 }
 
 // Healthcheck returns the current health status of the server.
-func (hcheck *Healthcheck) Healthcheck() *Response {
-	return &Response{
+func (hcheck *Healthcheck) Healthcheck(
+	ctx context.Context,
+) *Response {
+	resp := &Response{
 		Status:        "ok",
 		Now:           time.Now().UTC().Format(time.RFC3339Nano),
 		UptimeSeconds: int64(hcheck.uptime().Seconds()),
@@ -76,6 +89,64 @@ func (hcheck *Healthcheck) Healthcheck() *Response {
 		Appname:       hcheck.params.Globals.Appname,
 		Version:       hcheck.params.Globals.Version,
 		Maintenance:   hcheck.params.Config.MaintenanceMode,
+
+		Sessions:             0,
+		Clients:              0,
+		QueuedLines:          0,
+		Channels:             0,
+		ConnectionsSinceBoot: hcheck.params.Stats.ConnectionsSinceBoot(),
+		SessionsSinceBoot:    hcheck.params.Stats.SessionsSinceBoot(),
+		MessagesSinceBoot:    hcheck.params.Stats.MessagesSinceBoot(),
+	}
+
+	hcheck.populateDBStats(ctx, resp)
+
+	return resp
+}
+
+// populateDBStats fills in database-derived counters.
+func (hcheck *Healthcheck) populateDBStats(
+	ctx context.Context,
+	resp *Response,
+) {
+	sessions, err := hcheck.params.Database.GetUserCount(ctx)
+	if err != nil {
+		hcheck.log.Error(
+			"healthcheck: session count failed",
+			"error", err,
+		)
+	} else {
+		resp.Sessions = sessions
+	}
+
+	clients, err := hcheck.params.Database.GetClientCount(ctx)
+	if err != nil {
+		hcheck.log.Error(
+			"healthcheck: client count failed",
+			"error", err,
+		)
+	} else {
+		resp.Clients = clients
+	}
+
+	queued, err := hcheck.params.Database.GetQueueEntryCount(ctx)
+	if err != nil {
+		hcheck.log.Error(
+			"healthcheck: queue entry count failed",
+			"error", err,
+		)
+	} else {
+		resp.QueuedLines = queued
+	}
+
+	channels, err := hcheck.params.Database.GetChannelCount(ctx)
+	if err != nil {
+		hcheck.log.Error(
+			"healthcheck: channel count failed",
+			"error", err,
+		)
+	} else {
+		resp.Channels = channels
 	}
 }
 

internal/stats/stats.go

@@ -0,0 +1,52 @@
+// Package stats tracks runtime statistics since server boot.
+package stats
+
+import (
+	"sync/atomic"
+)
+
+// Tracker holds atomic counters for runtime statistics
+// that accumulate since the server started.
+type Tracker struct {
+	connectionsSinceBoot atomic.Int64
+	sessionsSinceBoot    atomic.Int64
+	messagesSinceBoot    atomic.Int64
+}
+
+// New creates a new Tracker with all counters at zero.
+func New() *Tracker {
+	return &Tracker{} //nolint:exhaustruct // atomic fields have zero-value defaults
+}
+
+// IncrConnections increments the total connection count.
+func (t *Tracker) IncrConnections() {
+	t.connectionsSinceBoot.Add(1)
+}
+
+// IncrSessions increments the total session count.
+func (t *Tracker) IncrSessions() {
+	t.sessionsSinceBoot.Add(1)
+}
+
+// IncrMessages increments the total PRIVMSG/NOTICE count.
+func (t *Tracker) IncrMessages() {
+	t.messagesSinceBoot.Add(1)
+}
+
+// ConnectionsSinceBoot returns the total number of
+// client connections since boot.
+func (t *Tracker) ConnectionsSinceBoot() int64 {
+	return t.connectionsSinceBoot.Load()
+}
+
+// SessionsSinceBoot returns the total number of sessions
+// created since boot.
+func (t *Tracker) SessionsSinceBoot() int64 {
+	return t.sessionsSinceBoot.Load()
+}
+
+// MessagesSinceBoot returns the total number of
+// PRIVMSG/NOTICE messages sent since boot.
+func (t *Tracker) MessagesSinceBoot() int64 {
+	return t.messagesSinceBoot.Load()
+}

internal/stats/stats_test.go

@@ -0,0 +1,117 @@
+package stats_test
+
+import (
+	"testing"
+
+	"git.eeqj.de/sneak/neoirc/internal/stats"
+)
+
+func TestNew(t *testing.T) {
+	t.Parallel()
+
+	tracker := stats.New()
+	if tracker == nil {
+		t.Fatal("expected non-nil tracker")
+	}
+
+	if tracker.ConnectionsSinceBoot() != 0 {
+		t.Errorf(
+			"expected 0 connections, got %d",
+			tracker.ConnectionsSinceBoot(),
+		)
+	}
+
+	if tracker.SessionsSinceBoot() != 0 {
+		t.Errorf(
+			"expected 0 sessions, got %d",
+			tracker.SessionsSinceBoot(),
+		)
+	}
+
+	if tracker.MessagesSinceBoot() != 0 {
+		t.Errorf(
+			"expected 0 messages, got %d",
+			tracker.MessagesSinceBoot(),
+		)
+	}
+}
+
+func TestIncrConnections(t *testing.T) {
+	t.Parallel()
+
+	tracker := stats.New()
+
+	tracker.IncrConnections()
+	tracker.IncrConnections()
+	tracker.IncrConnections()
+
+	got := tracker.ConnectionsSinceBoot()
+	if got != 3 {
+		t.Errorf(
+			"expected 3 connections, got %d", got,
+		)
+	}
+}
+
+func TestIncrSessions(t *testing.T) {
+	t.Parallel()
+
+	tracker := stats.New()
+
+	tracker.IncrSessions()
+	tracker.IncrSessions()
+
+	got := tracker.SessionsSinceBoot()
+	if got != 2 {
+		t.Errorf(
+			"expected 2 sessions, got %d", got,
+		)
+	}
+}
+
+func TestIncrMessages(t *testing.T) {
+	t.Parallel()
+
+	tracker := stats.New()
+
+	tracker.IncrMessages()
+
+	got := tracker.MessagesSinceBoot()
+	if got != 1 {
+		t.Errorf(
+			"expected 1 message, got %d", got,
+		)
+	}
+}
+
+func TestCountersAreIndependent(t *testing.T) {
+	t.Parallel()
+
+	tracker := stats.New()
+
+	tracker.IncrConnections()
+	tracker.IncrSessions()
+	tracker.IncrMessages()
+	tracker.IncrMessages()
+
+	if tracker.ConnectionsSinceBoot() != 1 {
+		t.Errorf(
+			"expected 1 connection, got %d",
+			tracker.ConnectionsSinceBoot(),
+		)
+	}
+
+	if tracker.SessionsSinceBoot() != 1 {
+		t.Errorf(
+			"expected 1 session, got %d",
+			tracker.SessionsSinceBoot(),
+		)
+	}
+
+	if tracker.MessagesSinceBoot() != 2 {
+		t.Errorf(
+			"expected 2 messages, got %d",
+			tracker.MessagesSinceBoot(),
+		)
+	}
+}