Initial commit: RegionIO Minecraft server core (26.1.2/protocol 775)

Vanilla-faithful overworld generator (final_density + multi-noise biomes),
full connection lifecycle (status/login/configuration/play), chunk streaming,
creative block editing, and the protocol/nbt/registry infrastructure.

internal/server/profile.go

@@ -0,0 +1,21 @@
+package server
+
+import (
+	"crypto/md5"
+)
+
+// Profile is an authenticated (or, in offline mode, derived) player identity.
+type Profile struct {
+	UUID [16]byte
+	Name string
+}
+
+// OfflineUUID derives the stable offline-mode UUID for a username, matching
+// vanilla's java.util.UUID.nameUUIDFromBytes("OfflinePlayer:" + name): an
+// MD5-based (version 3) UUID with the IETF variant bits set.
+func OfflineUUID(name string) [16]byte {
+	sum := md5.Sum([]byte("OfflinePlayer:" + name))
+	sum[6] = (sum[6] & 0x0f) | 0x30 // version 3
+	sum[8] = (sum[8] & 0x3f) | 0x80 // IETF variant
+	return sum
+}

internal/server/server.go

@@ -0,0 +1,98 @@
+// Package server holds the RegionIO core: configuration, shared state, and the
+// data shown to clients (status, MOTD).
+package server
+
+import (
+	"encoding/json"
+
+	"regionio/internal/protocol"
+	"regionio/internal/world"
+)
+
+// Config holds operator-tunable settings for a RegionIO instance.
+type Config struct {
+	Host       string
+	Port       int
+	MOTD       string
+	MaxPlayers int
+	// CompressionThreshold is the minimum uncompressed packet size (bytes) that
+	// triggers zlib compression. Negative disables compression entirely.
+	CompressionThreshold int
+	// WorldSeed seeds terrain generation.
+	WorldSeed int64
+}
+
+// DefaultConfig returns sensible defaults matching vanilla expectations.
+func DefaultConfig() Config {
+	return Config{
+		Host:                 "0.0.0.0",
+		Port:                 25565,
+		MOTD:                 "RegionIO — a Minecraft server in Go",
+		MaxPlayers:           20,
+		CompressionThreshold: 256,
+		// WorldSeed defaults to 0 for backward compatibility; operators override
+		// it via the REGIONIO_SEED env var or the -seed flag.
+		WorldSeed: 0,
+	}
+}
+
+// Server is the top-level core shared across all connections.
+type Server struct {
+	cfg    Config
+	chunks *world.Cache
+}
+
+// New constructs a Server from cfg.
+func New(cfg Config) *Server {
+	return &Server{
+		cfg:    cfg,
+		chunks: world.NewCache(int32(cfg.CompressionThreshold), world.NewVanillaGenerator(cfg.WorldSeed)),
+	}
+}
+
+// Config returns the active configuration.
+func (s *Server) Config() Config { return s.cfg }
+
+// Chunks returns the shared chunk cache.
+func (s *Server) Chunks() *world.Cache { return s.chunks }
+
+// statusResponse mirrors the JSON shape the client expects for the server-list
+// ping. Field names and nesting are part of the protocol contract.
+type statusResponse struct {
+	Version     statusVersion `json:"version"`
+	Players     statusPlayers `json:"players"`
+	Description statusText    `json:"description"`
+	// EnforcesSecureChat is read by the client; false keeps unsigned chat working.
+	EnforcesSecureChat bool `json:"enforcesSecureChat"`
+}
+
+type statusVersion struct {
+	Name     string `json:"name"`
+	Protocol int    `json:"protocol"`
+}
+
+type statusPlayers struct {
+	Max    int `json:"max"`
+	Online int `json:"online"`
+}
+
+type statusText struct {
+	Text string `json:"text"`
+}
+
+// StatusJSON returns the marshaled status response for the server-list ping.
+func (s *Server) StatusJSON(onlinePlayers int) ([]byte, error) {
+	resp := statusResponse{
+		Version: statusVersion{
+			Name:     protocol.GameVersion,
+			Protocol: protocol.ProtocolVersion,
+		},
+		Players: statusPlayers{
+			Max:    s.cfg.MaxPlayers,
+			Online: onlinePlayers,
+		},
+		Description:        statusText{Text: s.cfg.MOTD},
+		EnforcesSecureChat: false,
+	}
+	return json.Marshal(resp)
+}