From 9e9e37bea3267e758a1561b9d14b3c1de21b3791 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Marek=20Marczykowski-G=C3=B3recki?=
 <marmarek@invisiblethingslab.com>
Date: Mon, 24 Feb 2020 23:18:41 +0100
Subject: [PATCH] bpo-39744: make asyncio.subprocess communicate similar to
 non-asyncio one

subprocess's communicate(None) closes stdin of the child process, after
sending no (extra) data. Make asyncio variant do the same.
This fixes issues with processes that waits for EOF on stdin before
continuing.
---
 Doc/library/asyncio-subprocess.rst             |  5 +++--
 Lib/asyncio/subprocess.py                      | 11 ++++++-----
 Lib/test/test_asyncio/test_subprocess.py       | 18 ++++++++++++++++++
 .../2020-02-25-00-43-22.bpo-39744.hgK689.rst   |  1 +
 4 files changed, 28 insertions(+), 7 deletions(-)
 create mode 100644 Misc/NEWS.d/next/Library/2020-02-25-00-43-22.bpo-39744.hgK689.rst

diff --git a/Doc/library/asyncio-subprocess.rst b/Doc/library/asyncio-subprocess.rst
index 4274638c5e8625..ee2c71efa70ea7 100644
--- a/Doc/library/asyncio-subprocess.rst
+++ b/Doc/library/asyncio-subprocess.rst
@@ -207,8 +207,9 @@ their completion.
       Interact with process:
 
       1. send data to *stdin* (if *input* is not ``None``);
-      2. read data from *stdout* and *stderr*, until EOF is reached;
-      3. wait for process to terminate.
+      2. closes *stdin*;
+      3. read data from *stdout* and *stderr*, until EOF is reached;
+      4. wait for process to terminate.
 
       The optional *input* argument is the data (:class:`bytes` object)
       that will be sent to the child process.
diff --git a/Lib/asyncio/subprocess.py b/Lib/asyncio/subprocess.py
index cd10231f710f11..50727ca300e63e 100644
--- a/Lib/asyncio/subprocess.py
+++ b/Lib/asyncio/subprocess.py
@@ -144,10 +144,11 @@ def kill(self):
 
     async def _feed_stdin(self, input):
         debug = self._loop.get_debug()
-        self.stdin.write(input)
-        if debug:
-            logger.debug(
-                '%r communicate: feed stdin (%s bytes)', self, len(input))
+        if input is not None:
+            self.stdin.write(input)
+            if debug:
+                logger.debug(
+                    '%r communicate: feed stdin (%s bytes)', self, len(input))
         try:
             await self.stdin.drain()
         except (BrokenPipeError, ConnectionResetError) as exc:
@@ -180,7 +181,7 @@ async def _read_stream(self, fd):
         return output
 
     async def communicate(self, input=None):
-        if input is not None:
+        if self.stdin is not None:
             stdin = self._feed_stdin(input)
         else:
             stdin = self._noop()
diff --git a/Lib/test/test_asyncio/test_subprocess.py b/Lib/test/test_asyncio/test_subprocess.py
index eba6e2d1f28f3e..eeeca40c15cd28 100644
--- a/Lib/test/test_asyncio/test_subprocess.py
+++ b/Lib/test/test_asyncio/test_subprocess.py
@@ -151,6 +151,24 @@ async def run(data):
         self.assertEqual(exitcode, 0)
         self.assertEqual(stdout, b'some data')
 
+    def test_communicate_none_input(self):
+        args = PROGRAM_CAT
+
+        async def run():
+            proc = await asyncio.create_subprocess_exec(
+                *args,
+                stdin=subprocess.PIPE,
+                stdout=subprocess.PIPE,
+            )
+            stdout, stderr = await proc.communicate()
+            return proc.returncode, stdout
+
+        task = run()
+        task = asyncio.wait_for(task, support.LONG_TIMEOUT)
+        exitcode, stdout = self.loop.run_until_complete(task)
+        self.assertEqual(exitcode, 0)
+        self.assertEqual(stdout, b'')
+
     def test_shell(self):
         proc = self.loop.run_until_complete(
             asyncio.create_subprocess_shell('exit 7')
diff --git a/Misc/NEWS.d/next/Library/2020-02-25-00-43-22.bpo-39744.hgK689.rst b/Misc/NEWS.d/next/Library/2020-02-25-00-43-22.bpo-39744.hgK689.rst
new file mode 100644
index 00000000000000..791cf04f8b795d
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2020-02-25-00-43-22.bpo-39744.hgK689.rst
@@ -0,0 +1 @@
+Make func:``asyncio.subprocess.Process.communicate`` close subprocess's stdin even when called with input=None