Ensure it doesn't wait forever if invoked without data

sysadmin/letsencrypt_mail.py

@@ -6,6 +6,8 @@
 
 from enum import Enum
 import fileinput
+import sys
+import select
 
 import drymail  # Vendored
 
@@ -30,7 +32,13 @@ def main():
     state = State.unknown
     text = list()
 
+    # https://stackoverflow.com/questions/33871836/find-out-if-there-is-input-from-a-pipe-or-not-in-python
+    if not select.select([sys.stdin], [], [], 0.0)[0]:
+        print("No input processed.")
+        sys.exit(1)
+
     for line in fileinput.input():
+
         line = line.strip()
         text.append(line)
 
@@ -51,6 +59,8 @@ def main():
         text=text
     )
 
+
+
     client = drymail.SMTPMailer(
         host='localhost')