diff --git a/scripts/generate_messages.py b/scripts/generate_messages.py
index daafc12..3010023 100755
--- a/scripts/generate_messages.py
+++ b/scripts/generate_messages.py
@@ -53,6 +53,9 @@ class NetMessageMemberTypeJson(TypedDict):
     count: int
     member_type: ArrayMemberTypeJson
 
+    # data
+    size: Literal['specified_before']
+
 class NetMessageMemberJson(TypedDict):
     name: list[str]
     type: NetMessageMemberTypeJson
@@ -172,9 +175,16 @@ def generate_msg(msg: NetMessageJson, game: Literal['game', 'system']) -> None:
                 ftype = 'str'
                 default = "'default'"
             elif member['type']['kind'] in \
-                ('raw', 'sha256', 'rest', 'data'): # TODO: data has a size field
+                ('raw', 'sha256', 'rest'): # TODO: rest sha256 and raw
                 ftype = 'bytes'
                 default = "b'\\x00'"
+            elif member['type']['kind'] == 'data':
+                ftype = 'bytes'
+                default = "b'\\x00'"
+                if member['type']['size'] == 'specified_before':
+                    args.append('            data_size: Optional[int] = None')
+                else:
+                    raise ValueError(f"Error: unknown data size {member['type']}")
             # {"name": ["mode"], "type": {"kind": "enum", "enum": ["chat"]}},
             elif member['type']['kind'] == 'enum':
                 ftype = 'int'
@@ -248,8 +258,15 @@ def generate_msg(msg: NetMessageJson, game: Literal['game', 'system']) -> None:
             if member['type']['kind'] == 'string':
                 ftype = 'str'
             elif member['type']['kind'] in \
-                ('raw', 'sha256', 'rest', 'data'): # TODO: data has a size field
+                    ('raw', 'sha256', 'rest'): # TODO: sha256 and raw
                 ftype = 'bytes'
+            elif member['type']['kind'] == 'data':
+                ftype = 'bytes'
+                if member['type']['size'] == 'specified_before':
+                    out_file.write("        " \
+                        "self.data_size: int = data_size if data_size else len(data)\n")
+                else:
+                    raise ValueError(f"Error: unknown data size {member['type']}")
             # {"name": ["mode"], "type": {"kind": "enum", "enum": ["chat"]}},
             elif member['type']['kind'] == 'enum':
                 ftype = 'int'
@@ -307,8 +324,14 @@ def gen_unpack_members(msg: NetMessageJson) -> str:
             else:
                 unpacker = 'str()'
         elif member['type']['kind'] in \
-            ('raw', 'sha256', 'rest', 'data'): # TODO: data has a size field
+            ('raw', 'sha256', 'rest'): # TODO: do we need to fix size for sha256?
             unpacker = 'raw()'
+        elif member['type']['kind'] == 'data':
+            if member['type']['size'] == 'specified_before':
+                res += '        self.data_size = unpacker.get_int()\n'
+                unpacker = 'raw(self.data_size)'
+            else:
+                raise ValueError(f"Error: unknown data size {member['type']}")
         # {"name": ["mode"], "type": {"kind": "enum", "enum": ["chat"]}},
         elif member['type']['kind'] == 'enum':
             unpacker = 'int() # TODO: this is a enum'
@@ -373,8 +396,13 @@ def get_dependencies(msg: NetMessageJson) -> str:
             if member['type']['disallow_cc']:
                 packer_deps.append('SANITIZE_CC')
         elif member['type']['kind'] in \
-            ('raw', 'sha256', 'rest', 'data'): # TODO: data has a size field
+            ('raw', 'sha256', 'rest'):
             pass
+        elif member['type']['kind'] == 'data':
+            if member['type']['size'] == 'specified_before':
+                typing_deps.append('Optional')
+            else:
+                raise ValueError(f"Error: unknown data size {member['type']}")
         # {"name": ["mode"], "type": {"kind": "enum", "enum": ["chat"]}},
         elif member['type']['kind'] == 'enum':
             packer_deps.append('pack_int')
@@ -430,8 +458,14 @@ def pack_field(member: NetMessageMemberJson) -> str:
     if member['type']['kind'] == 'string':
         packer = 'str'
     elif member['type']['kind'] in \
-        ('raw', 'sha256', 'rest', 'data'): # TODO: data has a size field
+        ('raw', 'sha256', 'rest'): # TODO: raw sha256 rest
         return f'self.{name}'
+    elif member['type']['kind'] == 'data':
+        if member['type']['size'] == 'specified_before':
+            return f'pack_int(self.data_size) + \\\n' \
+                f'            self.{name}'
+        else:
+            raise ValueError(f"Error: unknown data size {member['type']}")
     # {"name": ["mode"], "type": {"kind": "enum", "enum": ["chat"]}},
     elif member['type']['kind'] == 'enum':
         packer = 'int'
diff --git a/twnet_parser/messages7/system/snap.py b/twnet_parser/messages7/system/snap.py
index 29fbe60..4475617 100644
--- a/twnet_parser/messages7/system/snap.py
+++ b/twnet_parser/messages7/system/snap.py
@@ -4,6 +4,7 @@ from twnet_parser.pretty_print import PrettyPrint
 from twnet_parser.packer import Unpacker
 from twnet_parser.chunk_header import ChunkHeader
 from twnet_parser.packer import pack_int
+from typing import Optional
 
 class MsgSnap(PrettyPrint):
     def __init__(
@@ -13,6 +14,7 @@ class MsgSnap(PrettyPrint):
             num_parts: int = 0,
             part: int = 0,
             crc: int = 0,
+            data_size: Optional[int] = None,
             data: bytes = b'\x00'
     ) -> None:
         self.message_name = 'snap'
@@ -24,6 +26,7 @@ class MsgSnap(PrettyPrint):
         self.num_parts: int = num_parts
         self.part: int = part
         self.crc: int = crc
+        self.data_size: int = data_size if data_size else len(data)
         self.data: bytes = data
 
     # first byte of data
@@ -36,7 +39,8 @@ class MsgSnap(PrettyPrint):
         self.num_parts = unpacker.get_int()
         self.part = unpacker.get_int()
         self.crc = unpacker.get_int()
-        self.data = unpacker.get_raw()
+        self.data_size = unpacker.get_int()
+        self.data = unpacker.get_raw(self.data_size)
         return True
 
     def pack(self) -> bytes:
@@ -45,4 +49,5 @@ class MsgSnap(PrettyPrint):
             pack_int(self.num_parts) + \
             pack_int(self.part) + \
             pack_int(self.crc) + \
+            pack_int(self.data_size) + \
             self.data
\ No newline at end of file
diff --git a/twnet_parser/messages7/system/snap_single.py b/twnet_parser/messages7/system/snap_single.py
index cfa197a..196481e 100644
--- a/twnet_parser/messages7/system/snap_single.py
+++ b/twnet_parser/messages7/system/snap_single.py
@@ -4,6 +4,7 @@ from twnet_parser.pretty_print import PrettyPrint
 from twnet_parser.packer import Unpacker
 from twnet_parser.chunk_header import ChunkHeader
 from twnet_parser.packer import pack_int
+from typing import Optional
 
 class MsgSnapSingle(PrettyPrint):
     def __init__(
@@ -11,6 +12,7 @@ class MsgSnapSingle(PrettyPrint):
             tick: int = 0,
             delta_tick: int = 0,
             crc: int = 0,
+            data_size: Optional[int] = None,
             data: bytes = b'\x00'
     ) -> None:
         self.message_name = 'snap_single'
@@ -20,6 +22,7 @@ class MsgSnapSingle(PrettyPrint):
         self.tick: int = tick
         self.delta_tick: int = delta_tick
         self.crc: int = crc
+        self.data_size: int = data_size if data_size else len(data)
         self.data: bytes = data
 
     # first byte of data
@@ -30,11 +33,13 @@ class MsgSnapSingle(PrettyPrint):
         self.tick = unpacker.get_int()
         self.delta_tick = unpacker.get_int()
         self.crc = unpacker.get_int()
-        self.data = unpacker.get_raw()
+        self.data_size = unpacker.get_int()
+        self.data = unpacker.get_raw(self.data_size)
         return True
 
     def pack(self) -> bytes:
         return pack_int(self.tick) + \
             pack_int(self.delta_tick) + \
             pack_int(self.crc) + \
+            pack_int(self.data_size) + \
             self.data
\ No newline at end of file