Convert media repo's FileInfo to attrs. (#10785)

This is mostly an internal change, but improves type hints in the
media code.

synapse/rest/media/v1/_base.py

@@ -18,6 +18,8 @@ import os
 import urllib
 from typing import Awaitable, Dict, Generator, List, Optional, Tuple
 
+import attr
+
 from twisted.internet.interfaces import IConsumer
 from twisted.protocols.basic import FileSender
 from twisted.web.server import Request
@@ -287,44 +289,62 @@ class Responder:
         pass
 
 
+@attr.s(slots=True, frozen=True, auto_attribs=True)
+class ThumbnailInfo:
+    """Details about a generated thumbnail."""
+
+    width: int
+    height: int
+    method: str
+    # Content type of thumbnail, e.g. image/png
+    type: str
+    # The size of the media file, in bytes.
+    length: Optional[int] = None
+
+
+@attr.s(slots=True, frozen=True, auto_attribs=True)
 class FileInfo:
-    """Details about a requested/uploaded file.
+    """Details about a requested/uploaded file."""
 
-    Attributes:
-        server_name (str): The server name where the media originated from,
-            or None if local.
-        file_id (str): The local ID of the file. For local files this is the
-            same as the media_id
-        url_cache (bool): If the file is for the url preview cache
-        thumbnail (bool): Whether the file is a thumbnail or not.
-        thumbnail_width (int)
-        thumbnail_height (int)
-        thumbnail_method (str)
-        thumbnail_type (str): Content type of thumbnail, e.g. image/png
-        thumbnail_length (int): The size of the media file, in bytes.
-    """
+    # The server name where the media originated from, or None if local.
+    server_name: Optional[str]
+    # The local ID of the file. For local files this is the same as the media_id
+    file_id: str
+    # If the file is for the url preview cache
+    url_cache: bool = False
+    # Whether the file is a thumbnail or not.
+    thumbnail: Optional[ThumbnailInfo] = None
 
-    def __init__(
-        self,
-        server_name,
-        file_id,
-        url_cache=False,
-        thumbnail=False,
-        thumbnail_width=None,
-        thumbnail_height=None,
-        thumbnail_method=None,
-        thumbnail_type=None,
-        thumbnail_length=None,
-    ):
-        self.server_name = server_name
-        self.file_id = file_id
-        self.url_cache = url_cache
-        self.thumbnail = thumbnail
-        self.thumbnail_width = thumbnail_width
-        self.thumbnail_height = thumbnail_height
-        self.thumbnail_method = thumbnail_method
-        self.thumbnail_type = thumbnail_type
-        self.thumbnail_length = thumbnail_length
+    # The below properties exist to maintain compatibility with third-party modules.
+    @property
+    def thumbnail_width(self):
+        if not self.thumbnail:
+            return None
+        return self.thumbnail.width
+
+    @property
+    def thumbnail_height(self):
+        if not self.thumbnail:
+            return None
+        return self.thumbnail.height
+
+    @property
+    def thumbnail_method(self):
+        if not self.thumbnail:
+            return None
+        return self.thumbnail.method
+
+    @property
+    def thumbnail_type(self):
+        if not self.thumbnail:
+            return None
+        return self.thumbnail.type
+
+    @property
+    def thumbnail_length(self):
+        if not self.thumbnail:
+            return None
+        return self.thumbnail.length
 
 
 def get_filename_from_headers(headers: Dict[bytes, List[bytes]]) -> Optional[str]: