From ca5be9d848c002017a5b8de70ccd1c7bea7a69d1 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Krist=C3=B3f=20T=C3=B3th?= <kristof.toth@avatao.com>
Date: Sun, 12 May 2019 22:30:49 +0200
Subject: [PATCH] Detect errors in the subprocess of CommandEventHandler

---
 lib/tfw/components/pipe_io_event_handler.py | 33 +++++++++++++++++----
 1 file changed, 27 insertions(+), 6 deletions(-)

diff --git a/lib/tfw/components/pipe_io_event_handler.py b/lib/tfw/components/pipe_io_event_handler.py
index d60fedf..676a8e5 100644
--- a/lib/tfw/components/pipe_io_event_handler.py
+++ b/lib/tfw/components/pipe_io_event_handler.py
@@ -6,11 +6,14 @@ from os import getpgid, killpg
 from os.path import join
 from signal import SIGTERM
 from secrets import token_urlsafe
+from time import sleep
+from threading import Thread
+from contextlib import suppress
 
 from tfw import EventHandlerBase
 from tfw.config.logs import logging
 
-from .pipe_io_server import PipeIOServer
+from .pipe_io_server import PipeIOServer, terminate_process_on_failure
 
 LOG = logging.getLogger(__name__)
 DEFAULT_PERMISSIONS = 0o600
@@ -107,18 +110,36 @@ class CommandEventHandler(PipeIOEventHandler):
         self._proc_stdout = open(self.pipe_io.in_pipe, 'wb')
         self._proc = Popen(
             command, shell=True, executable='/bin/bash',
-            stdin=self._proc_stdin, stdout=self._proc_stdout,
+            stdin=self._proc_stdin, stdout=self._proc_stdout, stderr=PIPE,
             start_new_session=True
         )
+        self._poll_check_proc_thread = self._start_poll_check_proc()
 
     def _generate_tempfilename(self):
         # pylint: disable=no-self-use
         random_filename = partial(token_urlsafe, 10)
         return join('/tmp', f'{type(self).__name__}.{random_filename()}')
 
+    def _start_poll_check_proc(self):
+        thread = Thread(target=self._poll_check_proc, daemon=True)
+        thread.start()
+        return thread
+
+    @terminate_process_on_failure
+    def _poll_check_proc(self):
+        while True:
+            self.check_proc()
+            sleep(1)
+
+    def check_proc(self):
+        if self._proc.poll() is not None:
+            _, stderr = self._proc.communicate()
+            raise RuntimeError(f'Subprocess failed: {stderr.decode()}')
+
     def cleanup(self):
-        process_group_id = getpgid(self._proc.pid)
-        killpg(process_group_id, SIGTERM)
-        self._proc_stdin.close()
-        self._proc_stdout.close()
+        with suppress(ProcessLookupError):
+            process_group_id = getpgid(self._proc.pid)
+            killpg(process_group_id, SIGTERM)
+            self._proc_stdin.close()
+            self._proc_stdout.close()
         super().cleanup()