Issue #26848: Fix asyncio/subprocess.communicate() to handle empty input.

Lib/asyncio/subprocess.py

@@ -166,7 +166,7 @@ def _read_stream(self, fd):
 
     @coroutine
     def communicate(self, input=None):
-        if input:
+        if input is not None:
             stdin = self._feed_stdin(input)
         else:
             stdin = self._noop()

Lib/test/test_asyncio/test_subprocess.py

@@ -287,6 +287,25 @@ def len_message(message):
         self.assertEqual(output.rstrip(), b'3')
         self.assertEqual(exitcode, 0)
 
+    def test_empty_input(self):
+        @asyncio.coroutine
+        def empty_input():
+            code = 'import sys; data = sys.stdin.read(); print(len(data))'
+            proc = yield from asyncio.create_subprocess_exec(
+                                          sys.executable, '-c', code,
+                                          stdin=asyncio.subprocess.PIPE,
+                                          stdout=asyncio.subprocess.PIPE,
+                                          stderr=asyncio.subprocess.PIPE,
+                                          close_fds=False,
+                                          loop=self.loop)
+            stdout, stderr = yield from proc.communicate(b'')
+            exitcode = yield from proc.wait()
+            return (stdout, exitcode)
+
+        output, exitcode = self.loop.run_until_complete(empty_input())
+        self.assertEqual(output.rstrip(), b'0')
+        self.assertEqual(exitcode, 0)
+
     def test_cancel_process_wait(self):
         # Issue #23140: cancel Process.wait()
 

Misc/NEWS

@@ -436,6 +436,9 @@ Library
 - Issue #26406: Avoid unnecessary serialization of getaddrinfo(3) calls on
   current versions of OpenBSD and NetBSD.  Patch by A. Jesse Jiryu Davis.
 
+- Issue #26848: Fix asyncio/subprocess.communicate() to handle empty input.
+  Patch by Jack O'Connor.
+
 Documentation
 -------------