Allow stdin=subprocess.DEVNULL

The current default is to connect through the existing stdin to the
subprocess, and there is no way to explicitly close the subprocess
stdin. Allow stdin=subprocess.DEVNULL for this.

Author: Anthchirp

HISTORY.rst

@@ -16,6 +16,8 @@ History
   (previously deprecated in `#62 <https://github.com/DiamondLightSource/python-procrunner/pull/62>`_)
 * The run() function no longer accepts a 'debug' argument
   (previously deprecated in `#63 <https://github.com/DiamondLightSource/python-procrunner/pull/63>`_)
+* The run() function now understands stdin=subprocess.DEVNULL to close the subprocess stdin,
+  rather than to connect through the existing stdin, which is the current default
 
 2.3.1 (2021-10-25)
 ------------------

src/procrunner/__init__.py

@@ -13,7 +13,7 @@
 import warnings
 from multiprocessing import Pipe
 from threading import Thread
-from typing import Any, Callable, Optional
+from typing import Any, Callable, Optional, Union
 
 #
 #  run() - A function to synchronously run an external process, supporting
@@ -304,7 +304,7 @@ def run(
     command,
     *,
     timeout: Optional[float] = None,
-    stdin: Optional[bytes] = None,
+    stdin: Optional[Union[bytes, int]] = None,
     print_stdout: bool = True,
     print_stderr: bool = True,
     callback_stdout: Optional[Callable] = None,
@@ -323,7 +323,8 @@ def run(
 
     :param array command: Command line to be run, specified as array.
     :param timeout: Terminate program execution after this many seconds.
-    :param stdin: Optional bytestring that is passed to command stdin.
+    :param stdin: Optional bytestring that is passed to command stdin,
+                  or subprocess.DEVNULL to disable stdin.
     :param boolean print_stdout: Pass stdout through to sys.stdout.
     :param boolean print_stderr: Pass stderr through to sys.stderr.
     :param callback_stdout: Optional function which is called for each
@@ -348,6 +349,12 @@ def run(
 
     if stdin is None:
         stdin_pipe = None
+    elif isinstance(stdin, int):
+        assert (
+            stdin == subprocess.DEVNULL
+        ), "stdin argument only allows subprocess.DEVNULL as numeric argument"
+        stdin_pipe = subprocess.DEVNULL
+        stdin = None
     else:
         assert sys.platform != "win32", "stdin argument not supported on Windows"
         stdin_pipe = subprocess.PIPE

tests/test_procrunner_system.py

@@ -23,6 +23,19 @@ def test_simple_command_invocation():
     assert result.stderr == b""
 
 
+def test_simple_command_invocation_with_closed_stdin():
+    if os.name == "nt":
+        command = ["cmd.exe", "/c", "echo", "hello"]
+    else:
+        command = ["echo", "hello"]
+
+    result = procrunner.run(command, stdin=subprocess.DEVNULL)
+
+    assert result.returncode == 0
+    assert result.stdout == b"hello" + os.linesep.encode("utf-8")
+    assert result.stderr == b""
+
+
 def test_decode_invalid_utf8_input(capsys):
     test_string = b"test\xa0string\n"
     if os.name == "nt":