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/nbt/encode.go

@@ -0,0 +1,95 @@
+package nbt
+
+import (
+	"encoding/binary"
+	"fmt"
+	"math"
+)
+
+// Marshal encodes root in the network format: the root tag's type byte followed
+// by its payload, with no root name (Minecraft 1.20.2+).
+func Marshal(root Tag) []byte {
+	dst := []byte{root.ID()}
+	return appendPayload(dst, root)
+}
+
+// MarshalNamed encodes root in the classic named format: type byte, root name,
+// then payload. Used for files and legacy framing.
+func MarshalNamed(name string, root Tag) []byte {
+	dst := []byte{root.ID()}
+	dst = appendString(dst, name)
+	return appendPayload(dst, root)
+}
+
+// appendString writes a modified-UTF-8 string with an unsigned-short length.
+func appendString(dst []byte, s string) []byte {
+	start := len(dst)
+	dst = append(dst, 0, 0) // length placeholder
+	dst = encodeModifiedUTF8(dst, s)
+	binary.BigEndian.PutUint16(dst[start:], uint16(len(dst)-start-2))
+	return dst
+}
+
+// appendPayload writes a tag's payload (no type byte, no name).
+func appendPayload(dst []byte, t Tag) []byte {
+	switch v := t.(type) {
+	case Byte:
+		return append(dst, byte(v))
+	case Short:
+		return binary.BigEndian.AppendUint16(dst, uint16(v))
+	case Int:
+		return binary.BigEndian.AppendUint32(dst, uint32(v))
+	case Long:
+		return binary.BigEndian.AppendUint64(dst, uint64(v))
+	case Float:
+		return binary.BigEndian.AppendUint32(dst, math.Float32bits(float32(v)))
+	case Double:
+		return binary.BigEndian.AppendUint64(dst, math.Float64bits(float64(v)))
+	case ByteArray:
+		dst = binary.BigEndian.AppendUint32(dst, uint32(len(v)))
+		return append(dst, v...)
+	case String:
+		return appendString(dst, string(v))
+	case IntArray:
+		dst = binary.BigEndian.AppendUint32(dst, uint32(len(v)))
+		for _, n := range v {
+			dst = binary.BigEndian.AppendUint32(dst, uint32(n))
+		}
+		return dst
+	case LongArray:
+		dst = binary.BigEndian.AppendUint32(dst, uint32(len(v)))
+		for _, n := range v {
+			dst = binary.BigEndian.AppendUint64(dst, uint64(n))
+		}
+		return dst
+	case List:
+		return appendList(dst, v)
+	case *Compound:
+		return appendCompound(dst, v)
+	default:
+		panic(fmt.Sprintf("nbt: cannot encode %T", t))
+	}
+}
+
+func appendList(dst []byte, l List) []byte {
+	elemID := l.ElemID
+	if len(l.Elems) == 0 {
+		elemID = TagEnd // Java writes TagEnd for empty lists.
+	}
+	dst = append(dst, elemID)
+	dst = binary.BigEndian.AppendUint32(dst, uint32(len(l.Elems)))
+	for _, e := range l.Elems {
+		dst = appendPayload(dst, e)
+	}
+	return dst
+}
+
+func appendCompound(dst []byte, c *Compound) []byte {
+	for _, k := range c.keys {
+		t := c.m[k]
+		dst = append(dst, t.ID())
+		dst = appendString(dst, k)
+		dst = appendPayload(dst, t)
+	}
+	return append(dst, TagEnd)
+}