From ce88b52295881a3dd1bc0efec8e72b1d3a235e87 Mon Sep 17 00:00:00 2001
From: Ivan Alejandro <ivanalejandro0@gmail.com>
Date: Tue, 22 Jul 2014 11:33:09 -0300
Subject: Add frontend alive check to the backend.

Stop the backend if the frontend process does not exist any more and
backend is not a daemon.
---
 changes/add-frontend-alive-check        |  2 ++
 src/leap/bitmask/app.py                 |  3 ++-
 src/leap/bitmask/backend/backend.py     | 24 +++++++++++++++++++++++-
 src/leap/bitmask/backend/leapbackend.py |  4 ++--
 src/leap/bitmask/backend_app.py         |  5 +++--
 5 files changed, 32 insertions(+), 6 deletions(-)
 create mode 100644 changes/add-frontend-alive-check

diff --git a/changes/add-frontend-alive-check b/changes/add-frontend-alive-check
new file mode 100644
index 00000000..54f88798
--- /dev/null
+++ b/changes/add-frontend-alive-check
@@ -0,0 +1,2 @@
+- Stop the backend if the frontend process does not exist any more and backend
+  is not a daemon. Related to #5873.
diff --git a/src/leap/bitmask/app.py b/src/leap/bitmask/app.py
index ab49ee37..37ded92a 100644
--- a/src/leap/bitmask/app.py
+++ b/src/leap/bitmask/app.py
@@ -180,7 +180,8 @@ def start_app():
 
     flags_dict = flags_to_dict()
 
-    backend = lambda: run_backend(opts.danger, flags_dict)
+    frontend_pid = os.getpid()
+    backend = lambda: run_backend(opts.danger, flags_dict, frontend_pid)
     backend_process = multiprocessing.Process(target=backend, name='Backend')
     backend_process.daemon = True
     backend_process.start()
diff --git a/src/leap/bitmask/backend/backend.py b/src/leap/bitmask/backend/backend.py
index c895f8f5..67ffe35a 100644
--- a/src/leap/bitmask/backend/backend.py
+++ b/src/leap/bitmask/backend/backend.py
@@ -18,6 +18,8 @@ import json
 import threading
 import time
 
+import psutil
+
 from twisted.internet import defer, reactor, threads
 
 import zmq
@@ -39,12 +41,16 @@ class Backend(object):
     PORT = '5556'
     BIND_ADDR = "tcp://127.0.0.1:%s" % PORT
 
-    def __init__(self):
+    PING_INTERVAL = 2  # secs
+
+    def __init__(self, frontend_pid=None):
         """
         Backend constructor, create needed instances.
         """
         self._signaler = Signaler()
 
+        self._frontend_pid = frontend_pid
+
         self._do_work = threading.Event()  # used to stop the worker thread.
         self._zmq_socket = None
 
@@ -81,6 +87,8 @@ class Backend(object):
         Note: we use a simple while since is less resource consuming than a
         Twisted's LoopingCall.
         """
+        pid = self._frontend_pid
+        check_wait = 0
         while self._do_work.is_set():
             # Wait for next request from client
             try:
@@ -93,6 +101,20 @@ class Backend(object):
                     raise
             time.sleep(0.01)
 
+            check_wait += 0.01
+            if pid is not None and check_wait > self.PING_INTERVAL:
+                check_wait = 0
+                self._check_frontend_alive()
+
+    def _check_frontend_alive(self):
+        """
+        Check if the frontend is alive and stop the backend if it is not.
+        """
+        pid = self._frontend_pid
+        if pid is not None and not psutil.pid_exists(pid):
+            logger.critical("The frontend is down!")
+            self.stop()
+
     def _stop_reactor(self):
         """
         Stop the Twisted reactor, but first wait a little for some threads to
diff --git a/src/leap/bitmask/backend/leapbackend.py b/src/leap/bitmask/backend/leapbackend.py
index d3c4fcda..6b0328ca 100644
--- a/src/leap/bitmask/backend/leapbackend.py
+++ b/src/leap/bitmask/backend/leapbackend.py
@@ -36,11 +36,11 @@ class LeapBackend(Backend):
     """
     Backend server subclass, used to implement the API methods.
     """
-    def __init__(self, bypass_checks=False):
+    def __init__(self, bypass_checks=False, frontend_pid=None):
         """
         Constructor for the backend.
         """
-        Backend.__init__(self)
+        Backend.__init__(self, frontend_pid)
 
         self._settings = Settings()
 
diff --git a/src/leap/bitmask/backend_app.py b/src/leap/bitmask/backend_app.py
index 5c0e4803..716ae4a7 100644
--- a/src/leap/bitmask/backend_app.py
+++ b/src/leap/bitmask/backend_app.py
@@ -44,7 +44,7 @@ def signal_handler(signum, frame):
     logger.debug("{0}: SIGNAL #{1} catched.".format(pname, signum))
 
 
-def run_backend(bypass_checks, flags_dict):
+def run_backend(bypass_checks, flags_dict, frontend_pid=None):
     """
     Run the backend for the application.
 
@@ -59,5 +59,6 @@ def run_backend(bypass_checks, flags_dict):
 
     dict_to_flags(flags_dict)
 
-    backend = LeapBackend(bypass_checks=bypass_checks)
+    backend = LeapBackend(bypass_checks=bypass_checks,
+                          frontend_pid=frontend_pid)
     backend.run()
-- 
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