db/message: use DEVNULL stdin when there is no input

Avoid the child grabbing our stdin.

1 files changed, 2 insertions, 1 deletions

diff --git a/alot/db/message.py b/alot/db/message.py
index e10e29a5..8ca8f2b3 100644
--- a/alot/db/message.py
+++ b/alot/db/message.py
@@ -43,7 +43,8 @@ def _render_part_external(payload, ctype, params, filename):
 
         try:
             result = subprocess.run(h.cmd, shell = True, check = True,
-                                    capture_output = True, input = h.stdin)
+                                    capture_output = True, input = h.stdin,
+                                    stdin = None if h.stdin else subprocess.DEVNULL)
         except subprocess.CalledProcessError as e:
             logging.error('Calling mailcap handler "%s" failed with code %d: %s',
                           h.cmd, e.returncode, decode(e.stderr))