up3

server/world/network_block_hash.go

@@ -0,0 +1,93 @@
+package world
+
+import (
+	"encoding/binary"
+	"fmt"
+	"sort"
+
+	"github.com/segmentio/fasthash/fnv1a"
+)
+
+// networkBlockHash produces the canonical "network block hash" for a (name, properties) block state.
+// This hash is used for mapping network palette entries back to runtime IDs.
+//
+// The scratch slice is used to reduce allocations. The returned slice should be passed back in on subsequent calls to
+// reuse the same backing array.
+func networkBlockHash(name string, properties map[string]any, scratch []byte) (uint32, []byte) {
+	if name == "minecraft:unknown" {
+		return 0xfffffffe, scratch // -2
+	}
+
+	keys := make([]string, 0, len(properties))
+	for k := range properties {
+		keys = append(keys, k)
+	}
+	sort.Strings(keys)
+
+	data := scratch[:0]
+	writeString := func(str string) {
+		data = binary.LittleEndian.AppendUint16(data, uint16(len(str)))
+		data = append(data, []byte(str)...)
+	}
+
+	data = append(data, 10) // compound
+	data = append(data, 0)
+	data = append(data, 0)
+
+	data = append(data, 8) // string
+	writeString("name")
+	writeString(name)
+
+	data = append(data, 10) // compound
+	writeString("states")
+	for _, k := range keys {
+		v := properties[k]
+		switch v := v.(type) {
+		case string:
+			data = append(data, 8) // string
+			writeString(k)
+			writeString(v)
+
+		case uint8:
+			data = append(data, 1) // tagByte
+			writeString(k)
+			data = append(data, byte(v))
+		case int8:
+			data = append(data, 1) // tagByte
+			writeString(k)
+			data = append(data, byte(v))
+		case bool:
+			b := 0
+			if v {
+				b = 1
+			}
+			data = append(data, 1) // tagByte
+			writeString(k)
+			data = append(data, byte(b))
+
+		case uint16:
+			data = append(data, 2) // tagInt16
+			writeString(k)
+			data = binary.LittleEndian.AppendUint16(data, uint16(v))
+		case int16:
+			data = append(data, 2) // tagInt16
+			writeString(k)
+			data = binary.LittleEndian.AppendUint16(data, uint16(v))
+
+		case uint32:
+			data = append(data, 3) // tagInt32
+			writeString(k)
+			data = binary.LittleEndian.AppendUint32(data, uint32(v))
+		case int32:
+			data = append(data, 3) // tagInt32
+			writeString(k)
+			data = binary.LittleEndian.AppendUint32(data, uint32(v))
+		default:
+			panic(fmt.Sprintf("unhandled nbt type: %T", v))
+		}
+	}
+	data = append(data, 0) // end
+	data = append(data, 0) // end
+
+	return fnv1a.HashBytes32(data), data
+}