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modbison/scripts/chunk_data_decoder.gd
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class_name ChunkDataDecoder
extends RefCounted
## Decodes chunk binary payloads (and JSON) into logical chunk data.
##
## Implements the binary format spec from docs/architecture/world.md §3.6.
## Both the Godot client and Python backend use this class to ensure
## identical encoding/decoding behavior.
##
## ## Binary Format Overview
##
## ```
## Header (48 bytes):
## [0:4] magic "AGPC"
## [4:6] version (uint16 LE)
## [6:8] header_len (uint16 LE)
## [8:12] flags (uint32 LE)
## [12:16] payload_len (uint32 LE)
## [16:48] checksum (SHA-256 hex, 32 bytes)
##
## Payload Body (sections):
## [section_id:1][section_len:4][data:section_len]
## ```
## Content flags parsed from a chunk.
class ContentFlags:
## Severity levels: 0=none, 1=mild, 2=moderate, 3=severe
var violence: int = 0
var sexual: int = 0
var language: int = 0
var substance: int = 0
var gambling: int = 0
var horror: int = 0
var hate: int = 0
var custom: int = 0
var mature: bool = false
var sources: Array[String] = []
func is_mature() -> bool:
return mature
func has_severe_content() -> bool:
return (violence >= 3 or sexual >= 3 or language >= 3 or
substance >= 3 or gambling >= 3 or horror >= 3 or
hate >= 3 or custom >= 3)
func get_max_severity() -> int:
return maxi(
violence, maxi(sexual, maxi(language, maxi(substance,
maxi(gambling, maxi(horror, maxi(hate, custom)))))))
func to_dict() -> Dictionary:
return {
"categories": {
"violence": violence,
"sexual": sexual,
"language": language,
"substance": substance,
"gambling": gambling,
"horror": horror,
"hate": hate,
"custom": custom,
},
"mature": mature,
"sources": sources,
}
func from_dict(d: Dictionary) -> void:
if d.has("categories"):
violence = d["categories"].get("violence", 0)
sexual = d["categories"].get("sexual", 0)
language = d["categories"].get("language", 0)
substance = d["categories"].get("substance", 0)
gambling = d["categories"].get("gambling", 0)
horror = d["categories"].get("horror", 0)
hate = d["categories"].get("hate", 0)
custom = d["categories"].get("custom", 0)
mature = d.get("mature", false)
sources = d.get("sources", [])
## A tile layer definition (palette + dense tile indices).
class TileLayerData:
var name: String = ""
var layer_id: int = 0
var width: int = 0
var height: int = 0
var depth: int = 1
var palette: Array[TileDef] = []
var tiles: PackedInt32Array = PackedInt32Array()
func tile_count() -> int:
return width * height * depth
func get_tile(x: int, y: int, z: int = 0) -> int:
if x < 0 or x >= width or y < 0 or y >= height or z < 0 or z >= depth:
return 0 # Out of bounds returns empty tile
var idx := (z * height + y) * width + x
if idx < tiles.size():
return tiles[idx]
return 0
## Editor mutator: writes `tile_id` at (x, y, z). Silently no-ops out of
## bounds, mirroring get_tile's "out of bounds is empty" contract rather
## than erroring -- callers that need bounds feedback should check first
## (see ChunkEditorModel.is_tile_in_bounds in scripts/editor/).
func set_tile(x: int, y: int, z: int, tile_id: int) -> void:
if x < 0 or x >= width or y < 0 or y >= height or z < 0 or z >= depth:
return
var idx := (z * height + y) * width + x
if idx < tiles.size():
tiles[idx] = tile_id
func get_tile_def(tile_id: int) -> TileDef:
for def in palette:
if def.id == tile_id:
return def
return null
## A world object parsed from chunk data.
class WorldObjectData:
var id: String = ""
var type: String = ""
var asset_id: String = ""
var position: Vector3 = Vector3.ZERO
var rotation: Vector4 = Vector4(0, 0, 0, 1)
var scale: Vector3 = Vector3.ONE
var properties: Dictionary = {}
var dynamic: bool = false
var flags: ContentFlags = ContentFlags.new()
func get_parent_id() -> String:
return str(properties.get("parent_id", ""))
func set_parent_id(p_id: String) -> void:
if p_id != "":
properties["parent_id"] = p_id
else:
properties.erase("parent_id")
## The complete decoded chunk payload.
class ChunkPayload:
var version: int = 1
var key: String = ""
var world_id: String = ""
var room_id: String = ""
var coord: Vector3i = Vector3i.ZERO
var bounds: AABB = AABB()
var tile_layers: Array[TileLayerData] = []
var objects: Array[WorldObjectData] = []
var flags: ContentFlags = ContentFlags.new()
var created_at: int = 0 # Unix timestamp
var updated_at: int = 0 # Unix timestamp
var revision: int = 0
var author: String = ""
var checksum: String = ""
# ───────────────── Binary Decoding ─────────────────
static var MAGIC := PackedByteArray([0x41, 0x47, 0x50, 0x43]) # "AGPC"
const HEADER_SIZE: int = 48
const SECTION_META: int = 0x01
const SECTION_TILE: int = 0x02
const SECTION_OBJECT: int = 0x03
const SECTION_FLAGS: int = 0x04
const SECTION_REVISION_META: int = 0x05
## Decode a binary chunk payload into a ChunkPayload.
## Returns null if the data is invalid or version is unsupported.
static func decode_binary(data: PackedByteArray) -> ChunkPayload:
if data.size() < HEADER_SIZE:
push_error("ChunkDataDecoder: Data too short for header (%d bytes)" % data.size())
return null
# Verify magic
var magic := PackedByteArray(data.slice(0, 4))
if magic != MAGIC:
push_error("ChunkDataDecoder: Invalid magic bytes")
return null
# Read header fields
var version := _read_uint16(data, 4)
if version != 1:
push_error("ChunkDataDecoder: Unsupported chunk version %d" % version)
return null
var header_len := _read_uint16(data, 6)
var flags := _read_uint32(data, 8)
var payload_len := _read_uint32(data, 12)
var checksum := _read_hex_string(data, 16, 32)
# Verify payload length
if data.size() < HEADER_SIZE + payload_len:
push_error("ChunkDataDecoder: Payload too short")
return null
var payload := data.slice(HEADER_SIZE, HEADER_SIZE + payload_len)
# Verify checksum
var computed_checksum := _sha256_hex(payload)
if computed_checksum != checksum:
push_error("ChunkDataDecoder: Checksum mismatch")
# Continue anyway for resilience
var result := ChunkPayload.new()
result.version = version
result.checksum = checksum
# Parse sections
var offset := 0
while offset < payload.size():
if offset + 5 > payload.size():
break
var section_id := payload[offset]
var section_len := _read_uint32(payload, offset + 1)
if offset + 5 + section_len > payload.size():
break
var section_data := payload.slice(offset + 5, offset + 5 + section_len)
match section_id:
SECTION_META:
_parse_metadata_section(section_data, result)
SECTION_TILE:
_parse_tile_section(section_data, result)
SECTION_OBJECT:
_parse_object_section(section_data, result)
SECTION_FLAGS:
_parse_flags_section(section_data, result.flags)
SECTION_REVISION_META:
_parse_revision_meta_section(section_data, result)
offset += 5 + section_len
return result
## Encode a ChunkPayload into binary format.
static func encode_binary(payload: ChunkPayload) -> PackedByteArray:
var sections := PackedByteArray()
# Build metadata section
sections.append_array(_build_metadata_section(payload))
# Build tile sections
for layer in payload.tile_layers:
sections.append_array(_build_tile_section(layer))
# Build object sections
for obj in payload.objects:
sections.append_array(_build_object_section(obj))
# Build flags section
sections.append_array(_build_flags_section(payload.flags))
# Build revision meta section
sections.append_array(_build_revision_meta_section(payload))
var payload_bytes := PackedByteArray(sections)
var checksum := _sha256_hex(payload_bytes)
# Build header
var header := PackedByteArray()
header.append_array(MAGIC)
header.append_array(_write_uint16(1)) # version
header.append_array(_write_uint16(0)) # header_len (after this field)
header.append_array(_write_uint32(0)) # flags
header.append_array(_write_uint32(payload_bytes.size()))
header.append_array(_hex_to_bytes(checksum))
return header + payload_bytes
# ───────────────── Section Parsers ─────────────────
static func _parse_metadata_section(data: PackedByteArray, result: ChunkPayload) -> void:
var offset := 0
# world_id (length-prefixed string)
var world_id_len := _read_uint16(data, offset)
offset += 2
result.world_id = data.slice(offset, offset + world_id_len).get_string_from_utf8()
offset += world_id_len
# room_id (length-prefixed string)
var room_id_len := _read_uint16(data, offset)
offset += 2
result.room_id = data.slice(offset, offset + room_id_len).get_string_from_utf8()
offset += room_id_len
# coord (3 × int32)
result.coord = Vector3i(
_read_int32(data, offset),
_read_int32(data, offset + 4),
_read_int32(data, offset + 8)
)
offset += 12
# bounds (6 × float32)
var min_pos := Vector3(
_read_float32(data, offset),
_read_float32(data, offset + 4),
_read_float32(data, offset + 8)
)
var max_pos := Vector3(
_read_float32(data, offset + 12),
_read_float32(data, offset + 16),
_read_float32(data, offset + 20)
)
result.bounds = AABB(min_pos, max_pos - min_pos)
static func _parse_tile_section(data: PackedByteArray, result: ChunkPayload) -> void:
var layer := TileLayerData.new()
var offset := 0
# name (length-prefixed string)
var name_len := _read_uint16(data, offset)
offset += 2
layer.name = data.slice(offset, offset + name_len).get_string_from_utf8()
offset += name_len
# layer_id (uint16)
layer.layer_id = _read_uint16(data, offset)
offset += 2
# dimensions (3 × uint16)
layer.width = _read_uint16(data, offset)
offset += 2
layer.height = _read_uint16(data, offset)
offset += 2
layer.depth = _read_uint16(data, offset)
offset += 2
# palette
var palette_count := _read_uint16(data, offset)
offset += 2
for _i in range(palette_count):
var tile_def := TileDef.new()
tile_def.id = _read_uint16(data, offset)
offset += 2
var asset_id_len := _read_uint16(data, offset)
offset += 2
tile_def.asset_id = data.slice(offset, offset + asset_id_len).get_string_from_utf8()
offset += asset_id_len
tile_def.solid = data[offset] != 0
offset += 1
tile_def.flags = _read_uint32(data, offset)
offset += 4
tile_def.variants = data[offset]
offset += 1
layer.palette.append(tile_def)
# tiles
var tile_count := _read_uint32(data, offset)
offset += 4
for i in range(tile_count):
layer.tiles.append(_read_uint16(data, offset))
offset += 2
result.tile_layers.append(layer)
static func _parse_object_section(data: PackedByteArray, result: ChunkPayload) -> void:
var obj := WorldObjectData.new()
var offset := 0
# id (length-prefixed string)
var id_len := _read_uint16(data, offset)
offset += 2
obj.id = data.slice(offset, offset + id_len).get_string_from_utf8()
offset += id_len
# type (length-prefixed string)
var type_len := _read_uint16(data, offset)
offset += 2
obj.type = data.slice(offset, offset + type_len).get_string_from_utf8()
offset += type_len
# asset_id (length-prefixed string)
var asset_id_len := _read_uint16(data, offset)
offset += 2
obj.asset_id = data.slice(offset, offset + asset_id_len).get_string_from_utf8()
offset += asset_id_len
# position (3 × float32)
obj.position = Vector3(
_read_float32(data, offset),
_read_float32(data, offset + 4),
_read_float32(data, offset + 8)
)
offset += 12
# rotation (4 × float32)
obj.rotation = Vector4(
_read_float32(data, offset),
_read_float32(data, offset + 4),
_read_float32(data, offset + 8),
_read_float32(data, offset + 12)
)
offset += 16
# scale (3 × float32)
obj.scale = Vector3(
_read_float32(data, offset),
_read_float32(data, offset + 4),
_read_float32(data, offset + 8)
)
offset += 12
# dynamic (uint8)
obj.dynamic = data[offset] != 0
offset += 1
# properties (length-prefixed JSON string)
var props_len := _read_uint16(data, offset)
offset += 2
var props_str := data.slice(offset, offset + props_len).get_string_from_utf8()
offset += props_len
# `or` in GDScript is a boolean operator, not Python/JS-style
# short-circuit-return -- `parsed or {}` returns a bool (true for any
# non-empty Dictionary), not `parsed` itself. Assigning that bool to
# `properties` (typed Dictionary) crashes at runtime for any object
# with real property data -- verified: a real fixture with
# {"locked": false, ...} threw "Invalid assignment of property or key
# 'properties' with value of type 'bool'".
var parsed_props: Variant = JSON.parse_string(props_str)
obj.properties = parsed_props if parsed_props is Dictionary else {}
# flags (ContentFlags)
obj.flags.violence = data[offset]
offset += 1
obj.flags.sexual = data[offset]
offset += 1
obj.flags.language = data[offset]
offset += 1
obj.flags.substance = data[offset]
offset += 1
obj.flags.gambling = data[offset]
offset += 1
obj.flags.horror = data[offset]
offset += 1
obj.flags.hate = data[offset]
offset += 1
obj.flags.custom = data[offset]
offset += 1
obj.flags.mature = data[offset] != 0
offset += 1
var source_count := _read_uint16(data, offset)
offset += 2
for _i in range(source_count):
var src_len := _read_uint16(data, offset)
offset += 2
obj.flags.sources.append(data.slice(offset, offset + src_len).get_string_from_utf8())
offset += src_len
result.objects.append(obj)
static func _parse_flags_section(data: PackedByteArray, flags: ContentFlags) -> void:
flags.violence = data[0]
flags.sexual = data[1]
flags.language = data[2]
flags.substance = data[3]
flags.gambling = data[4]
flags.horror = data[5]
flags.hate = data[6]
flags.custom = data[7]
flags.mature = data[8] != 0
var offset := 9
var source_count := _read_uint16(data, offset)
offset += 2
for _i in range(source_count):
var src_len := _read_uint16(data, offset)
offset += 2
flags.sources.append(data.slice(offset, offset + src_len).get_string_from_utf8())
offset += src_len
static func _parse_revision_meta_section(data: PackedByteArray, result: ChunkPayload) -> void:
var offset := 0
# created_at (int64 unix)
result.created_at = _read_int64(data, offset)
offset += 8
# updated_at (int64 unix)
result.updated_at = _read_int64(data, offset)
offset += 8
# revision (uint32)
result.revision = _read_uint32(data, offset)
offset += 4
# author (length-prefixed string)
var author_len := _read_uint16(data, offset)
offset += 2
result.author = data.slice(offset, offset + author_len).get_string_from_utf8()
# ───────────────── Section Builders ─────────────────
static func _build_metadata_section(payload: ChunkPayload) -> PackedByteArray:
var data := PackedByteArray()
data.append_array(_write_string(payload.world_id))
data.append_array(_write_string(payload.room_id))
data.append_array(_write_int32(payload.coord.x))
data.append_array(_write_int32(payload.coord.y))
data.append_array(_write_int32(payload.coord.z))
# Wire format is min + max (world.md §3, and _parse_metadata_section
# below reads the 2nd triple as max_pos and computes size = max - min)
# -- writing raw `.size` here instead of `.position + .size` was a
# latent bug that only escaped every test because AABB(Vector3.ZERO, ...)
# happens to make size == max when position is exactly zero. Any chunk
# at a real, nonzero world position (i.e. every real chunk except the
# one at the origin) would round-trip through encode_binary/decode_binary
# with a corrupted size. Same bug class as the backend's min+size/
# min+max mismatch fixed in chunk_codec.py (commit eb39e43).
var bounds_max: Vector3 = payload.bounds.position + payload.bounds.size
data.append_array(_write_float32(payload.bounds.position.x))
data.append_array(_write_float32(payload.bounds.position.y))
data.append_array(_write_float32(payload.bounds.position.z))
data.append_array(_write_float32(bounds_max.x))
data.append_array(_write_float32(bounds_max.y))
data.append_array(_write_float32(bounds_max.z))
# Every other section builder wraps its body with `_wrap_section`
# (section_id + uint32 length prefix) -- this one didn't, so
# `encode_binary()` spliced the raw metadata bytes directly into the
# section stream with no header at all. The decoder then read the
# metadata's own first bytes (a string length prefix) as a bogus
# section_id/section_len pair, producing a garbage length that
# overran the buffer ("truncated section body") and silently found
# zero real sections. Never caught before because nothing in this
# codebase called encode_binary() until
# scripts/smoke_test_http_chunk_source.gd.
return _wrap_section(data, SECTION_META)
static func _build_tile_section(layer: TileLayerData) -> PackedByteArray:
var data := PackedByteArray()
data.append_array(_write_string(layer.name))
data.append_array(_write_uint16(layer.layer_id))
data.append_array(_write_uint16(layer.width))
data.append_array(_write_uint16(layer.height))
data.append_array(_write_uint16(layer.depth))
data.append_array(_write_uint16(layer.palette.size()))
for tile_def in layer.palette:
data.append_array(_write_uint16(tile_def.id))
data.append_array(_write_string(tile_def.asset_id))
data.append(tile_def.solid as int)
data.append_array(_write_uint32(tile_def.flags))
data.append(tile_def.variants)
data.append_array(_write_uint32(layer.tiles.size()))
for tile_id in layer.tiles:
data.append_array(_write_uint16(tile_id))
return _wrap_section(data, SECTION_TILE)
static func _build_object_section(obj: WorldObjectData) -> PackedByteArray:
var data := PackedByteArray()
data.append_array(_write_string(obj.id))
data.append_array(_write_string(obj.type))
data.append_array(_write_string(obj.asset_id))
data.append_array(_write_float32(obj.position.x))
data.append_array(_write_float32(obj.position.y))
data.append_array(_write_float32(obj.position.z))
data.append_array(_write_float32(obj.rotation.x))
data.append_array(_write_float32(obj.rotation.y))
data.append_array(_write_float32(obj.rotation.z))
data.append_array(_write_float32(obj.rotation.w))
data.append_array(_write_float32(obj.scale.x))
data.append_array(_write_float32(obj.scale.y))
data.append_array(_write_float32(obj.scale.z))
data.append(obj.dynamic as int)
var props_json := JSON.stringify(obj.properties, " ")
data.append_array(_write_string(props_json))
data.append(obj.flags.violence)
data.append(obj.flags.sexual)
data.append(obj.flags.language)
data.append(obj.flags.substance)
data.append(obj.flags.gambling)
data.append(obj.flags.horror)
data.append(obj.flags.hate)
data.append(obj.flags.custom)
data.append(obj.flags.mature as int)
data.append_array(_write_uint16(obj.flags.sources.size()))
for src in obj.flags.sources:
data.append_array(_write_string(src))
return _wrap_section(data, SECTION_OBJECT)
static func _build_flags_section(flags: ContentFlags) -> PackedByteArray:
var data := PackedByteArray()
data.append(flags.violence)
data.append(flags.sexual)
data.append(flags.language)
data.append(flags.substance)
data.append(flags.gambling)
data.append(flags.horror)
data.append(flags.hate)
data.append(flags.custom)
data.append(flags.mature as int)
data.append_array(_write_uint16(flags.sources.size()))
for src in flags.sources:
data.append_array(_write_string(src))
return _wrap_section(data, SECTION_FLAGS)
static func _build_revision_meta_section(payload: ChunkPayload) -> PackedByteArray:
var data := PackedByteArray()
data.append_array(_write_int64(payload.created_at))
data.append_array(_write_int64(payload.updated_at))
data.append_array(_write_uint32(payload.revision))
data.append_array(_write_string(payload.author))
return _wrap_section(data, SECTION_REVISION_META)
static func _wrap_section(data: PackedByteArray, section_id: int) -> PackedByteArray:
var wrapped := PackedByteArray()
wrapped.append(section_id)
wrapped.append_array(_write_uint32(data.size()))
wrapped.append_array(data)
return wrapped
# ───────────────── Binary Helpers ─────────────────
static func _read_uint16(data: PackedByteArray, offset: int) -> int:
return data[offset] | (data[offset + 1] << 8)
static func _read_uint32(data: PackedByteArray, offset: int) -> int:
return (data[offset] | (data[offset + 1] << 8) |
(data[offset + 2] << 16) | (data[offset + 3] << 24))
static func _read_int32(data: PackedByteArray, offset: int) -> int:
var val := _read_uint32(data, offset)
if val >= 0x80000000:
return val - 0x100000000
return val
static func _read_int64(data: PackedByteArray, offset: int) -> int:
var lo := _read_uint32(data, offset)
var hi := _read_uint32(data, offset + 4)
return hi * 0x100000000 + lo
static func _read_float32(data: PackedByteArray, offset: int) -> float:
# `int as float` is a NUMERIC cast, not an IEEE-754 bit reinterpretation --
# it was silently corrupting every non-integer value (verified: bits for
# 1.5f decoded as 1069547520.0). decode_float() does a real bitcast and
# matches this format's little-endian byte order (§3.6).
return data.decode_float(offset)
static func _read_hex_string(data: PackedByteArray, offset: int, length: int) -> String:
var hex_chars := "0123456789abcdef"
var result := ""
for i in range(length):
var byte_val := data[offset + i]
result += hex_chars[byte_val >> 4]
result += hex_chars[byte_val & 0x0F]
return result
static func _write_uint16(val: int) -> PackedByteArray:
return PackedByteArray([(val & 0xFF), (val >> 8) & 0xFF])
static func _write_uint32(val: int) -> PackedByteArray:
return PackedByteArray([
val & 0xFF, (val >> 8) & 0xFF, (val >> 16) & 0xFF, (val >> 24) & 0xFF
])
static func _write_int32(val: int) -> PackedByteArray:
return _write_uint32(val)
static func _write_int64(val: int) -> PackedByteArray:
var lo := val & 0xFFFFFFFF
var hi := (val >> 32) & 0xFFFFFFFF
return _write_uint32(lo) + _write_uint32(hi)
static func _write_float32(val: float) -> PackedByteArray:
var out := PackedByteArray()
out.resize(4)
out.encode_float(0, val)
return out
static func _write_string(s: String) -> PackedByteArray:
var bytes := s.to_utf8_buffer()
return _write_uint16(bytes.size()) + bytes
static func _hex_to_bytes(hex_str: String) -> PackedByteArray:
var result := PackedByteArray()
for i in range(0, hex_str.length(), 2):
var byte_val := ("0x" + hex_str.substr(i, 2)).hex_to_int()
result.append(byte_val)
return result
# ───────────────── SHA-256 ─────────────────
static func _sha256_hex(data: PackedByteArray) -> String:
var ctx := HashingContext.new()
ctx.start(HashingContext.HASH_SHA256)
ctx.update(data)
var hash := ctx.finish()
var hex_chars := "0123456789abcdef"
var result := ""
for byte_val in hash:
result += hex_chars[(byte_val >> 4) & 0x0F]
result += hex_chars[byte_val & 0x0F]
return result