feat: add item thumbnail support

at least in v347, tool thumbnails are fetched through `/Game/Tools/ThumbnailAsset.ashx`.
usually the asset ids are decals, but i chose to route them through roblox's main api out of ease

Author: michei69

Source/assets/__init__.py

@@ -10,7 +10,7 @@
 
 # Internal or local application imports
 import util.const
-from . import material, queue, returns, serialisers, extractor
+from . import material, queue, returns, serialisers, extractor, thumbnail
 
 
 @dataclasses.dataclass
@@ -144,6 +144,8 @@ def _load_asset_num(self, asset_id: int) -> bytes | None:
     def _load_asset_str(self, asset_id: str) -> bytes | None:
         if material.check(asset_id):
             return material.load_asset(asset_id)
+        if thumbnail.check(asset_id):
+            return thumbnail.load_asset(asset_id)
         return None
 
     def _load_redir_asset(self, asset_id: int | str, redirect: asset_redirect) -> returns.base_type:

Source/assets/const.py

@@ -1,4 +1,5 @@
 ID_PREFIX = 'rbxmtl-'
+THUMB_PREFIX = 'rbxthmb-'
 
 MATERIAL_DICT_2014 = {
     'aluminum-diffuse.dds': 153465459,

Source/assets/thumbnail.py

@@ -0,0 +1,34 @@
+from . import const, extractor
+import json
+
+def transform_to_id_num(asset_id: str) -> int:
+    asset_sub = asset_id[len(const.THUMB_PREFIX):-4] # strip .png
+
+    try:
+        return int(asset_sub)
+    except:
+        return 0
+
+def check(asset_id: str):
+    return asset_id.startswith(const.THUMB_PREFIX)
+
+def load_asset(asset_id: str) -> bytes | None:
+    id = transform_to_id_num(asset_id)
+    if id == 0:
+        return None
+
+    # technically we could also download the decal and parse its contents
+    # to extract the thumbnail, but that might be overkill
+    raw = extractor.download_item(
+        "https://thumbnails.roblox.com/v1/assets?assetids=%s&size=700x700&format=Png&isCircular=false" %
+        (id,)
+    )
+    if raw is None:
+        return None
+
+    parsed = json.loads(raw)
+
+    if "data" in parsed and len(parsed["data"]) != 1:
+        return None
+
+    return extractor.download_item(parsed["data"][0]['imageUrl'])

Source/web_server/endpoints/assets.py

@@ -1,6 +1,7 @@
 from web_server._logic import web_server_handler, server_path
 import assets.returns as returns
 import util.const
+import assets.const
 
 
 @server_path("/asset")
@@ -57,3 +58,27 @@ def _(self: web_server_handler) -> bool:
     '''
     self.send_json('true')
     return True
+
+@server_path('/Game/Tools/ThumbnailAsset.ashx')
+def _(self: web_server_handler) -> bool:
+    asset_cache = self.game_config.asset_cache
+    asset_id = self.query["aid"]
+    if asset_id is None:
+        self.send_error(404)
+        return True
+    
+    asset = asset_cache.get_asset(
+        f"{assets.const.THUMB_PREFIX}{asset_id}.png",
+        bypass_blocklist=self.is_privileged,
+    )
+
+    if isinstance(asset, returns.ret_data):
+        self.send_data(asset.data)
+        return True
+    elif isinstance(asset, returns.ret_none):
+        self.send_error(404)
+        return True
+    elif isinstance(asset, returns.ret_relocate):
+        self.send_redirect(asset.url)
+        return True
+    return False