Support sending bytes/stream as photos (improved _get_extension)

Letting _get_extension work for photos even when the only information
available is a stream or a few bytes allows sending arbitrary bytes
as photos, if force_document was not set to True explicitly.

telethon/client/uploads.py

@@ -337,6 +337,12 @@ class UploadMethods(ButtonMethods, MessageParseMethods, UserMethods):
             else:
                 file_name = str(file_id)
 
+        # If the file name lacks extension, add it if possible.
+        # Else Telegram complains with `PHOTO_EXT_INVALID_ERROR`
+        # even if the uploaded image is indeed a photo.
+        if not os.path.splitext(file_name)[-1]:
+            file_name += utils._get_extension(file)
+
         # Determine whether the file is too big (over 10MB) or not
         # Telegram does make a distinction between smaller or larger files
         is_large = file_size > 10 * 1024 * 1024

telethon/utils.py

@@ -4,6 +4,9 @@ to convert between an entity like a User, Chat, etc. into its Input version)
 """
 import base64
 import binascii
+import imghdr
+import inspect
+import io
 import itertools
 import math
 import mimetypes
@@ -16,7 +19,6 @@ from types import GeneratorType
 from .extensions import markdown, html
 from .helpers import add_surrogate, del_surrogate
 from .tl import types
-import inspect
 
 try:
     import hachoir
@@ -632,6 +634,12 @@ def _get_extension(file):
     """
     if isinstance(file, str):
         return os.path.splitext(file)[-1]
+    elif isinstance(file, bytes):
+        kind = imghdr.what(io.BytesIO(file))
+        return ('.' + kind) if kind else ''
+    elif isinstance(file, io.IOBase) and file.seekable():
+        kind = imghdr.what(file) is not None
+        return ('.' + kind) if kind else ''
     elif getattr(file, 'name', None):
         return _get_extension(file.name)
     else: