Add Spinner, a Minecraft hostname-routing reverse proxy

Routes Java Edition connections by the hostname in the handshake, with
wildcard domains, backend failover, PROXY protocol v2, cached server-list
status from health probes, hot-reloaded config, and an admin page and
metrics endpoint. Includes CI, tagged releases and a container image.

Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>

internal/proxy/stats.go

@@ -0,0 +1,75 @@
+package proxy
+
+import (
+	"sort"
+	"sync"
+	"sync/atomic"
+	"time"
+)
+
+type serverStats struct {
+	active   atomic.Int64
+	total    atomic.Int64
+	failures atomic.Int64
+	bytesIn  atomic.Int64 // client -> backend
+	bytesOut atomic.Int64 // backend -> client
+}
+
+type Stats struct {
+	Started  time.Time
+	active   atomic.Int64
+	total    atomic.Int64
+	rejected atomic.Int64
+	unknown  atomic.Int64
+	mu       sync.Mutex
+	servers  map[string]*serverStats
+}
+
+func newStats() *Stats {
+	return &Stats{Started: time.Now(), servers: map[string]*serverStats{}}
+}
+
+func (s *Stats) server(name string) *serverStats {
+	s.mu.Lock()
+	defer s.mu.Unlock()
+	ss := s.servers[name]
+	if ss == nil {
+		ss = &serverStats{}
+		s.servers[name] = ss
+	}
+	return ss
+}
+
+type ServerSnapshot struct {
+	Name     string `json:"name"`
+	Active   int64  `json:"active"`
+	Total    int64  `json:"total"`
+	Failures int64  `json:"failures"`
+	BytesIn  int64  `json:"bytes_in"`
+	BytesOut int64  `json:"bytes_out"`
+}
+
+type Snapshot struct {
+	UptimeSecs int64            `json:"uptime_secs"`
+	Active     int64            `json:"active"`
+	Total      int64            `json:"total"`
+	Rejected   int64            `json:"rejected"`
+	Unknown    int64            `json:"unknown_host"`
+	Servers    []ServerSnapshot `json:"servers"`
+}
+
+func (s *Stats) Snapshot() Snapshot {
+	out := Snapshot{
+		UptimeSecs: int64(time.Since(s.Started).Seconds()),
+		Active:     s.active.Load(), Total: s.total.Load(),
+		Rejected: s.rejected.Load(), Unknown: s.unknown.Load(),
+	}
+	s.mu.Lock()
+	for n, ss := range s.servers {
+		out.Servers = append(out.Servers, ServerSnapshot{n, ss.active.Load(), ss.total.Load(),
+			ss.failures.Load(), ss.bytesIn.Load(), ss.bytesOut.Load()})
+	}
+	s.mu.Unlock()
+	sort.Slice(out.Servers, func(i, j int) bool { return out.Servers[i].Name < out.Servers[j].Name })
+	return out
+}