[stable-2.15] Only use the selectors code path when we are prompt matching (#79931) (#80400)

(cherry picked from commit 6d1e355)

3 files changed, 60 insertions, 50 deletions

diff --git a/changelogs/fragments/run-command-selectors-prompt-only.yml b/changelogs/fragments/run-command-selectors-prompt-only.yml
new file mode 100644
index 0000000000..c0855bccea
--- /dev/null
+++ b/changelogs/fragments/run-command-selectors-prompt-only.yml
@@ -0,0 +1,4 @@
+bugfixes:
+- AnsibleModule.run_command - Only use selectors when needed, and rely on Python
+  stdlib subprocess for the simple task of collecting stdout/stderr when prompt
+  matching is not required.
diff --git a/lib/ansible/module_utils/basic.py b/lib/ansible/module_utils/basic.py
index 742b5fc73e..98ce69f586 100644
--- a/lib/ansible/module_utils/basic.py
+++ b/lib/ansible/module_utils/basic.py
@@ -2043,53 +2043,59 @@ class AnsibleModule(object):
                 # Select PollSelector which is supported by major platforms
                 selector = selectors.PollSelector()
 
-            selector.register(cmd.stdout, selectors.EVENT_READ)
-            selector.register(cmd.stderr, selectors.EVENT_READ)
-            if os.name == 'posix':
-                fcntl.fcntl(cmd.stdout.fileno(), fcntl.F_SETFL, fcntl.fcntl(cmd.stdout.fileno(), fcntl.F_GETFL) | os.O_NONBLOCK)
-                fcntl.fcntl(cmd.stderr.fileno(), fcntl.F_SETFL, fcntl.fcntl(cmd.stderr.fileno(), fcntl.F_GETFL) | os.O_NONBLOCK)
-
             if data:
                 if not binary_data:
                     data += '\n'
                 if isinstance(data, text_type):
                     data = to_bytes(data)
-                cmd.stdin.write(data)
-                cmd.stdin.close()
-
-            while True:
-                events = selector.select(1)
-                for key, event in events:
-                    b_chunk = key.fileobj.read()
-                    if b_chunk == b(''):
-                        selector.unregister(key.fileobj)
-                    if key.fileobj == cmd.stdout:
-                        stdout += b_chunk
-                    elif key.fileobj == cmd.stderr:
-                        stderr += b_chunk
-                # if we're checking for prompts, do it now
-                if prompt_re:
-                    if prompt_re.search(stdout) and not data:
-                        if encoding:
-                            stdout = to_native(stdout, encoding=encoding, errors=errors)
-                        return (257, stdout, "A prompt was encountered while running a command, but no input data was specified")
-                # only break out if no pipes are left to read or
-                # the pipes are completely read and
-                # the process is terminated
-                if (not events or not selector.get_map()) and cmd.poll() is not None:
-                    break
-                # No pipes are left to read but process is not yet terminated
-                # Only then it is safe to wait for the process to be finished
-                # NOTE: Actually cmd.poll() is always None here if no selectors are left
-                elif not selector.get_map() and cmd.poll() is None:
-                    cmd.wait()
-                    # The process is terminated. Since no pipes to read from are
-                    # left, there is no need to call select() again.
-                    break
 
-            cmd.stdout.close()
-            cmd.stderr.close()
-            selector.close()
+            if not prompt_re:
+                stdout, stderr = cmd.communicate(input=data)
+            else:
+                # We only need this to look for a prompt, to abort instead of hanging
+                selector.register(cmd.stdout, selectors.EVENT_READ)
+                selector.register(cmd.stderr, selectors.EVENT_READ)
+                if os.name == 'posix':
+                    fcntl.fcntl(cmd.stdout.fileno(), fcntl.F_SETFL, fcntl.fcntl(cmd.stdout.fileno(), fcntl.F_GETFL) | os.O_NONBLOCK)
+                    fcntl.fcntl(cmd.stderr.fileno(), fcntl.F_SETFL, fcntl.fcntl(cmd.stderr.fileno(), fcntl.F_GETFL) | os.O_NONBLOCK)
+
+                if data:
+                    cmd.stdin.write(data)
+                    cmd.stdin.close()
+
+                while True:
+                    events = selector.select(1)
+                    for key, event in events:
+                        b_chunk = key.fileobj.read()
+                        if b_chunk == b(''):
+                            selector.unregister(key.fileobj)
+                        if key.fileobj == cmd.stdout:
+                            stdout += b_chunk
+                        elif key.fileobj == cmd.stderr:
+                            stderr += b_chunk
+                    # if we're checking for prompts, do it now
+                    if prompt_re:
+                        if prompt_re.search(stdout) and not data:
+                            if encoding:
+                                stdout = to_native(stdout, encoding=encoding, errors=errors)
+                            return (257, stdout, "A prompt was encountered while running a command, but no input data was specified")
+                    # only break out if no pipes are left to read or
+                    # the pipes are completely read and
+                    # the process is terminated
+                    if (not events or not selector.get_map()) and cmd.poll() is not None:
+                        break
+                    # No pipes are left to read but process is not yet terminated
+                    # Only then it is safe to wait for the process to be finished
+                    # NOTE: Actually cmd.poll() is always None here if no selectors are left
+                    elif not selector.get_map() and cmd.poll() is None:
+                        cmd.wait()
+                        # The process is terminated. Since no pipes to read from are
+                        # left, there is no need to call select() again.
+                        break
+
+                cmd.stdout.close()
+                cmd.stderr.close()
+                selector.close()
 
             rc = cmd.returncode
         except (OSError, IOError) as e:
diff --git a/test/units/module_utils/basic/test_run_command.py b/test/units/module_utils/basic/test_run_command.py
index 04211e2df2..3a4ea52265 100644
--- a/test/units/module_utils/basic/test_run_command.py
+++ b/test/units/module_utils/basic/test_run_command.py
@@ -147,7 +147,7 @@ class TestRunCommandArgs:
                               for (arg, cmd_lst, cmd_str), sh in product(ARGS_DATA, (True, False))),
                              indirect=['stdin'])
     def test_args(self, cmd, expected, shell, rc_am):
-        rc_am.run_command(cmd, use_unsafe_shell=shell)
+        rc_am.run_command(cmd, use_unsafe_shell=shell, prompt_regex='i_dont_exist')
         assert rc_am._subprocess.Popen.called
         args, kwargs = rc_am._subprocess.Popen.call_args
         assert args == (expected, )
@@ -163,17 +163,17 @@ class TestRunCommandArgs:
 class TestRunCommandCwd:
     @pytest.mark.parametrize('stdin', [{}], indirect=['stdin'])
     def test_cwd(self, mocker, rc_am):
-        rc_am.run_command('/bin/ls', cwd='/new')
+        rc_am.run_command('/bin/ls', cwd='/new', prompt_regex='i_dont_exist')
         assert rc_am._subprocess.Popen.mock_calls[0][2]['cwd'] == b'/new'
 
     @pytest.mark.parametrize('stdin', [{}], indirect=['stdin'])
     def test_cwd_relative_path(self, mocker, rc_am):
-        rc_am.run_command('/bin/ls', cwd='sub-dir')
+        rc_am.run_command('/bin/ls', cwd='sub-dir', prompt_regex='i_dont_exist')
         assert rc_am._subprocess.Popen.mock_calls[0][2]['cwd'] == b'/home/foo/sub-dir'
 
     @pytest.mark.parametrize('stdin', [{}], indirect=['stdin'])
     def test_cwd_not_a_dir(self, mocker, rc_am):
-        rc_am.run_command('/bin/ls', cwd='/not-a-dir')
+        rc_am.run_command('/bin/ls', cwd='/not-a-dir', prompt_regex='i_dont_exist')
         assert rc_am._subprocess.Popen.mock_calls[0][2]['cwd'] == b'/not-a-dir'
 
     @pytest.mark.parametrize('stdin', [{}], indirect=['stdin'])
@@ -212,14 +212,14 @@ class TestRunCommandRc:
     @pytest.mark.parametrize('stdin', [{}], indirect=['stdin'])
     def test_check_rc_false(self, rc_am):
         rc_am._subprocess.Popen.return_value.returncode = 1
-        (rc, _, _) = rc_am.run_command('/bin/false', check_rc=False)
+        (rc, _, _) = rc_am.run_command('/bin/false', check_rc=False, prompt_regex='i_dont_exist')
         assert rc == 1
 
     @pytest.mark.parametrize('stdin', [{}], indirect=['stdin'])
     def test_check_rc_true(self, rc_am):
         rc_am._subprocess.Popen.return_value.returncode = 1
         with pytest.raises(SystemExit):
-            rc_am.run_command('/bin/false', check_rc=True)
+            rc_am.run_command('/bin/false', check_rc=True, prompt_regex='i_dont_exist')
         assert rc_am.fail_json.called
         args, kwargs = rc_am.fail_json.call_args
         assert kwargs['rc'] == 1
@@ -228,7 +228,7 @@ class TestRunCommandRc:
 class TestRunCommandOutput:
     @pytest.mark.parametrize('stdin', [{}], indirect=['stdin'])
     def test_text_stdin(self, rc_am):
-        (rc, stdout, stderr) = rc_am.run_command('/bin/foo', data='hello world')
+        (rc, stdout, stderr) = rc_am.run_command('/bin/foo', data='hello world', prompt_regex='i_dont_exist')
         assert rc_am._subprocess.Popen.return_value.stdin.getvalue() == b'hello world\n'
 
     @pytest.mark.parametrize('stdin', [{}], indirect=['stdin'])
@@ -237,7 +237,7 @@ class TestRunCommandOutput:
                                      SpecialBytesIO(b'hello', fh=mocker.sentinel.stdout),
                                      mocker.sentinel.stderr:
                                      SpecialBytesIO(b'', fh=mocker.sentinel.stderr)}
-        (rc, stdout, stderr) = rc_am.run_command('/bin/cat hello.txt')
+        (rc, stdout, stderr) = rc_am.run_command('/bin/cat hello.txt', prompt_regex='i_dont_exist')
         assert rc == 0
         # module_utils function.  On py3 it returns text and py2 it returns
         # bytes because it's returning native strings
@@ -251,7 +251,7 @@ class TestRunCommandOutput:
                                      mocker.sentinel.stderr:
                                      SpecialBytesIO(u'لرئيسية'.encode('utf-8'),
                                                     fh=mocker.sentinel.stderr)}
-        (rc, stdout, stderr) = rc_am.run_command('/bin/something_ugly')
+        (rc, stdout, stderr) = rc_am.run_command('/bin/something_ugly', prompt_regex='i_dont_exist')
         assert rc == 0
         # module_utils function.  On py3 it returns text and py2 it returns
         # bytes because it's returning native strings