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/protocol/protocol_test.go

@@ -0,0 +1,87 @@
+package protocol
+
+import (
+	"bytes"
+	"net"
+	"testing"
+	"time"
+)
+
+func TestHandshakeRoundTrip(t *testing.T) {
+	in := BuildHandshake(767, "mc.example.com", 25565, 2)
+	h, raw, err := ReadHandshake(bytes.NewReader(in))
+	if err != nil {
+		t.Fatal(err)
+	}
+	want := Handshake{Protocol: 767, Host: "mc.example.com", Port: 25565, NextState: 2}
+	if h != want {
+		t.Fatalf("got %+v want %+v", h, want)
+	}
+	if !bytes.Equal(raw, in) {
+		t.Fatal("raw bytes not preserved")
+	}
+}
+
+func TestReadHandshakeRejects(t *testing.T) {
+	cases := map[string][]byte{
+		"legacy":      {0xfe, 0x01, 0xfa},
+		"huge length": {0xff, 0xff, 0xff, 0xff, 0x07},
+		"zero length": {0x00},
+		"wrong id":    Frame([]byte{0x05, 0x00}),
+		"short host":  Frame([]byte{0x00, 0x01, 0x40, 'a'}),
+		"truncated":   {0x10, 0x00},
+	}
+	for name, b := range cases {
+		if _, _, err := ReadHandshake(bytes.NewReader(b)); err == nil {
+			t.Errorf("%s: expected error", name)
+		}
+	}
+	if _, _, err := ReadHandshake(bytes.NewReader([]byte{0xfe, 0x01})); err != ErrLegacy {
+		t.Errorf("want ErrLegacy, got %v", err)
+	}
+}
+
+func TestVarInt(t *testing.T) {
+	if got := AppendVarInt(nil, 300); !bytes.Equal(got, []byte{0xac, 0x02}) {
+		t.Fatalf("got %x", got)
+	}
+	if got := AppendVarInt(nil, -1); len(got) != 5 {
+		t.Fatalf("negative should take 5 bytes, got %x", got)
+	}
+}
+
+func TestStatusExchange(t *testing.T) {
+	c, s := net.Pipe()
+	defer c.Close()
+	go func() {
+		defer s.Close()
+		ServeStatus(s, `{"ok":true}`)
+	}()
+	c.SetDeadline(time.Now().Add(2 * time.Second))
+	c.Write(Frame([]byte{0}))
+	id, payload, err := ReadPacket(c, maxStatus)
+	if err != nil || id != 0 || !bytes.Contains(payload, []byte(`{"ok":true}`)) {
+		t.Fatalf("id=%d payload=%q err=%v", id, payload, err)
+	}
+	c.Write(Frame(append([]byte{1}, 0, 0, 0, 0, 0, 0, 0, 42)))
+	id, payload, err = ReadPacket(c, 32)
+	if err != nil || id != 1 || payload[7] != 42 {
+		t.Fatalf("pong id=%d payload=%x err=%v", id, payload, err)
+	}
+}
+
+func TestQueryStatus(t *testing.T) {
+	c, s := net.Pipe()
+	defer c.Close()
+	go func() {
+		defer s.Close()
+		if _, _, err := ReadHandshake(s); err != nil {
+			return
+		}
+		ServeStatus(s, `{"players":{"online":3}}`)
+	}()
+	got, err := QueryStatus(c, "x", 25565, 2*time.Second)
+	if err != nil || got != `{"players":{"online":3}}` {
+		t.Fatalf("got %q err=%v", got, err)
+	}
+}