set_close_exec on intermediary server port for unix & windows

Using the win32 API it's possible to prevent the intermediary server
socket from inheriting itself to subprocesses. So let's use that here.

Another bit of the solution for #2090.

src/octoprint/server/__init__.py

@@ -221,14 +221,13 @@ class Server(object):
 
 		### IMPORTANT!
 		###
-		### Do not start any subprocesses until the intermediary server shuts down again or they WILL inherit the
-		### open port and prevent us from firing up Tornado later. Thanks to close_fds not being available on Popen
-		### on Windows if you also want to be able to redirect stdout/stderr/stdin and fnctl also not being available
-		### we don't have a good way around this issue besides being careful not to spawn processes here.
+		### Best do not start any subprocesses until the intermediary server shuts down again or they MIGHT inherit the
+		### open port and prevent us from firing up Tornado later.
 		###
-		### Which kinda sucks tbh.
+		### The intermediary server's socket should have the CLOSE_EXEC flag (or its equivalent) set where possible, but
+		### we can only do that if fcntl is availabel or we are on Windows, so better safe than sorry.
 		###
-		### See also issue #2035
+		### See also issues #2035 and #2090
 
 		# then initialize the plugin manager
 		pluginManager.reload_plugins(startup=True, initialize_implementations=False)
@@ -1382,10 +1381,11 @@ class Server(object):
 		                                                      bind_and_activate=False)
 
 		# if possible, make sure our socket's port descriptor isn't handed over to subprocesses
-		if fcntl is not None and hasattr(fcntl, "FD_CLOEXEC"):
-			flags = fcntl.fcntl(self._intermediary_server.socket, fcntl.F_GETFD)
-			flags |= fcntl.FD_CLOEXEC
-			fcntl.fcntl(self._intermediary_server.socket, fcntl.F_SETFD, flags)
+		from octoprint.util.platform import set_close_exec
+		try:
+			set_close_exec(self._intermediary_server.fileno())
+		except:
+			self._logger.exception("Error while attempting to set_close_exec on intermediary server socket")
 
 		# then bind the server and have it serve our handler until stopped
 		try:
@@ -1395,7 +1395,13 @@ class Server(object):
 			self._intermediary_server.server_close()
 			raise
 
-		thread = threading.Thread(target=self._intermediary_server.serve_forever)
+		def serve():
+			try:
+				self._intermediary_server.serve_forever()
+			except:
+				self._logger.exception("Error in intermediary server")
+
+		thread = threading.Thread(target=serve)
 		thread.daemon = True
 		thread.start()
 

src/octoprint/util/platform/__init__.py

@@ -0,0 +1,41 @@
+# coding=utf-8
+from __future__ import absolute_import, division, print_function
+
+__license__ = 'GNU Affero General Public License http://www.gnu.org/licenses/agpl.html'
+__copyright__ = "Copyright (C) 2017 The OctoPrint Project - Released under terms of the AGPLv3 License"
+
+import sys
+
+try:
+	import fcntl
+except ImportError:
+	fcntl = None
+
+# set_close_exec
+
+if fcntl is not None and hasattr(fcntl, "FD_CLOEXEC"):
+	def set_close_exec(handle):
+		flags = fcntl.fcntl(handle, fcntl.F_GETFD)
+		flags |= fcntl.FD_CLOEXEC
+		fcntl.fcntl(handle, fcntl.F_SETFD, flags)
+
+elif sys.platform == "win32":
+	def set_close_exec(handle):
+		import ctypes
+		import ctypes.wintypes
+
+		# see https://msdn.microsoft.com/en-us/library/ms724935(v=vs.85).aspx
+		SetHandleInformation = ctypes.windll.kernel32.SetHandleInformation
+		SetHandleInformation.argtypes = (ctypes.wintypes.HANDLE, ctypes.wintypes.DWORD, ctypes.wintypes.DWORD)
+		SetHandleInformation.restype = ctypes.c_bool
+
+		HANDLE_FLAG_INHERIT = 0x00000001
+
+		result = SetHandleInformation(handle, HANDLE_FLAG_INHERIT, 0)
+		if not result:
+			raise ctypes.GetLastError()
+
+else:
+	def set_close_exec(handle):
+		# no-op
+		pass