Don't use the deprecated imghdr module

kitty/rc/set_background_image.py

@@ -1,12 +1,12 @@
 #!/usr/bin/env python
 # License: GPLv3 Copyright: 2020, Kovid Goyal <kovid at kovidgoyal.net>
 
-import imghdr
 import os
 from base64 import standard_b64decode, standard_b64encode
 from typing import TYPE_CHECKING, Optional
 
 from kitty.types import AsyncResponse
+from kitty.utils import is_png
 
 from .base import (
     MATCH_WINDOW_OPTION,
@@ -89,7 +89,7 @@ failed, the command will exit with a success code.
         if path.lower() == 'none':
             ret['data'] = '-'
             return ret
-        if imghdr.what(path) != 'png':
+        if not is_png(path):
             self.fatal(f'{path} is not a PNG image')
 
         def file_pipe(path: str) -> CmdGenerator:

kitty/rc/set_window_logo.py

@@ -1,13 +1,12 @@
 #!/usr/bin/env python
 # License: GPLv3 Copyright: 2020, Kovid Goyal <kovid at kovidgoyal.net>
 
-
-import imghdr
 import os
 from base64 import standard_b64decode, standard_b64encode
 from typing import TYPE_CHECKING, Optional
 
 from kitty.types import AsyncResponse
+from kitty.utils import is_png
 
 from .base import (
     MATCH_WINDOW_OPTION,
@@ -85,7 +84,7 @@ failed, the command will exit with a success code.
         if path.lower() == 'none':
             ret['data'] = '-'
             return ret
-        if imghdr.what(path) != 'png':
+        if not is_png(path):
             self.fatal(f'{path} is not a PNG image')
 
         def file_pipe(path: str) -> CmdGenerator:

kitty/utils.py

@@ -1137,3 +1137,11 @@ def extract_all_from_tarfile_safely(tf: 'tarfile.TarFile', dest: str) -> None:
         tar.extractall(path, tar.getmembers(), numeric_owner=numeric_owner)
 
     safe_extract(tf, dest)
+
+
+def is_png(path: str) -> bool:
+    if path:
+        with suppress(Exception), open(path, 'rb') as f:
+            header = f.read(8)
+            return header.startswith(b'\211PNG\r\n\032\n')
+    return False