Feedback: add socket usage check on bind and test.

notebook/notebookapp.py

@@ -115,6 +115,7 @@ from .utils import (
     check_pid,
     pathname2url,
     run_sync,
+    unix_socket_in_use,
     url_escape,
     url_path_join,
     urldecode_unix_socket_path,
@@ -1638,12 +1639,16 @@ class NotebookApp(JupyterApp):
         return self._bind_http_server_unix() if self.sock else self._bind_http_server_tcp()
 
     def _bind_http_server_unix(self):
+        if unix_socket_in_use(self.sock):
+            self.log.warning(_('The socket %s is already in use.') % self.sock)
+            return False
+
         try:
             sock = bind_unix_socket(self.sock, mode=int(self.sock_mode.encode(), 8))
             self.http_server.add_socket(sock)
         except socket.error as e:
             if e.errno == errno.EADDRINUSE:
-                self.log.info(_('The socket %s is already in use.') % self.sock)
+                self.log.warning(_('The socket %s is already in use.') % self.sock)
                 return False
             elif e.errno in (errno.EACCES, getattr(errno, 'WSAEACCES', errno.EACCES)):
                 self.log.warning(_("Permission to listen on sock %s denied") % self.sock)

notebook/tests/test_notebookapp_integration.py

@@ -135,3 +135,32 @@ def test_stop_multi_integration():
     p1.wait()
     p2.wait()
     p3.wait()
+
+
+@skip_win32
+def test_launch_socket_collision():
+    """Tests UNIX socket in-use detection for lifecycle correctness."""
+    sock = UNIXSocketNotebookTestBase.sock
+    check_msg = 'socket %s is already in use' % sock
+
+    _ensure_stopped()
+
+    # Start a server.
+    cmd = ['jupyter-notebook', '--sock=%s' % sock]
+    p1 = subprocess.Popen(cmd)
+    time.sleep(3)
+
+    # Try to start a server bound to the same UNIX socket.
+    try:
+        subprocess.check_output(cmd, stderr=subprocess.STDOUT)
+    except subprocess.CalledProcessError as e:
+        assert check_msg in e.output.decode()
+    else:
+        raise AssertionError('expected error, instead got %s' % e.output.decode())
+
+    # Stop the background server, ensure it's stopped and wait on the process to exit.
+    subprocess.check_call(['jupyter-notebook', 'stop', sock])
+
+    _ensure_stopped()
+
+    p1.wait()

notebook/utils.py

@@ -11,6 +11,7 @@ import ctypes
 import errno
 import inspect
 import os
+import socket
 import stat
 import sys
 from distutils.version import LooseVersion
@@ -22,6 +23,7 @@ from urllib.request import pathname2url
 # in tornado >=5 with Python 3
 from tornado.concurrent import Future as TornadoFuture
 from tornado import gen
+import requests_unixsocket
 from ipython_genutils import py3compat
 
 # UF_HIDDEN is a stat flag not defined in the stat module.
@@ -382,3 +384,19 @@ def urldecode_unix_socket_path(socket_path):
 def urlencode_unix_socket(socket_path):
     """Encodes a UNIX socket URL from a socket path for the `http+unix` URI form."""
     return 'http+unix://%s' % urlencode_unix_socket_path(socket_path)
+
+
+def unix_socket_in_use(socket_path):
+    """Checks whether a UNIX socket path on disk is in use by attempting to connect to it."""
+    if not os.path.exists(socket_path):
+        return False
+
+    try:
+        sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
+        sock.connect(socket_path)
+    except socket.error:
+        return False
+    else:
+        return True
+    finally:
+        sock.close()