set_avatar_from_file: raise if file isn't an image

TODO.md

@@ -1,7 +1,7 @@
 - Media
   - Verify things work with chat.privacytools.io (subdomain weirdness)
   - Confirmation box after picking file to upload
-  - Handle upload errors: non existent path, path is a dir, file too big, etc
+  - Handle upload/set avatar errors: bad path, is a dir, file too big, etc
   - Show real progression for mxc thumbnail loadings, uploads and downloads
 
   - Show reason under broken thumbnail icons
@@ -52,11 +52,9 @@
   - Don't store states in delegates
   - [hr not working](https://bugreports.qt.io/browse/QTBUG-74342)
   - Terrible performance using `QT_QPA_PLATFORM=wayland-egl`, must use `xcb`
-  - Verify big avatars aren't downloaded uselessly
   - Quote links color in room subtitles (e.g. "> http://foo.orgA)" )
 
 - UI
-  - Show error if uploading avatar fails or file is corrupted
   - Way to open context menus without a right mouse button
   - `smartVerticalFlick()` gradual acceleration
 
@@ -166,7 +164,6 @@
       the message with `decrypt_event()`"  - poljar
 
   - [Soft logouts](https://github.com/poljar/matrix-nio/commit/aba10)
-  - `translated` arg for avatar upload and login errors
   - Check if username exists on login screen
   - `pyotherside.atexit()`
   - Logout previous session if adding an account that's already connected

src/python/errors.py

@@ -62,6 +62,13 @@ class InvalidUserInContext(Exception):
 class UneededThumbnail(Exception):
     pass
 
+
 @dataclass
 class UnthumbnailableError(Exception):
     exception: Optional[Exception] = None
+
+
+@dataclass
+class BadMimeType(Exception):
+    wanted: str = field()
+    got:    str = field()

src/python/matrix_client.py

@@ -25,8 +25,8 @@ import nio
 
 from . import __about__, utils
 from .errors import (
-    InvalidUserInContext, MatrixError, UneededThumbnail, UnthumbnailableError,
-    UserNotFound,
+    BadMimeType, InvalidUserInContext, MatrixError, UneededThumbnail,
+    UnthumbnailableError, UserNotFound,
 )
 from .html_filter import HTML_FILTER
 from .models.items import (
@@ -617,7 +617,11 @@ class MatrixClient(nio.AsyncClient):
 
 
     async def set_avatar_from_file(self, path: Union[Path, str]) -> None:
-        # TODO: check if mime is image
+        mime = utils.guess_mime(path)
+
+        if mime.split("/")[0] != "image":
+            raise BadMimeType(wanted="image/*", got=mime)
+
         await self.set_avatar((await self.upload_file(path))[0])