tests/.../ftp_server: be spawn friendly

Make SimpleFtpServer work when using the 'spawn' method of
multiprocessing.

Instead of trying to pickle the FTPServer and friends to the new
process, buffer any config calls and then start the server only in the
new process.

1 files changed, 59 insertions, 15 deletions

diff --git a/tests/testutils/ftp_server.py b/tests/testutils/ftp_server.py
index 52c05f8ba..dbe3468e7 100644
--- a/tests/testutils/ftp_server.py
+++ b/tests/testutils/ftp_server.py
@@ -5,28 +5,72 @@ from pyftpdlib.handlers import FTPHandler
 from pyftpdlib.servers import FTPServer
 
 
-class SimpleFtpServer(multiprocessing.Process):
+class SimpleFtpServer():
+    # pylint: disable=attribute-defined-outside-init
+
     def __init__(self):
-        super().__init__()
-        self.authorizer = DummyAuthorizer()
-        handler = FTPHandler
-        handler.authorizer = self.authorizer
-        self.server = FTPServer(('127.0.0.1', 0), handler)
+        self._reset()
+
+    def _reset(self):
+        self._process = None
+        self._port = None
+        self._anonymous_dirs = []
+        self._user_list = []
+
+    def start(self):
+        assert self._process is None, "Server already running."
+        queue = multiprocessing.SimpleQueue()
 
-    def run(self):
-        self.server.serve_forever()
+        self._process = multiprocessing.Process(
+            target=_run_server,
+            args=(queue, self._anonymous_dirs, self._user_list),
+        )
+
+        self._process.start()
+        self._port = queue.get()
 
     def stop(self):
-        self.server.close_all()
-        self.server.close()
-        self.terminate()
-        self.join()
+        assert self._process is not None, "Server not running."
+
+        # Note that when spawning, terminating in this way will cause us to
+        # leak semaphores. This will lead to a warning from Python's semaphore
+        # tracker, which will clean them up for us.
+        #
+        # We could prevent this warning by using alternative methods that would
+        # let the _run_server() function finish, the extra complication doesn't
+        # seem worth it for this test class.
+        #
+        self._process.terminate()
+
+        self._process.join()
+        self._reset()
 
     def allow_anonymous(self, cwd):
-        self.authorizer.add_anonymous(cwd)
+        assert self._process is None, "Can't modify server after start()."
+        self._anonymous_dirs.append(cwd)
 
     def add_user(self, user, password, cwd):
-        self.authorizer.add_user(user, password, cwd, perm='elradfmwMT')
+        assert self._process is None, "Can't modify server after start()."
+        self._user_list.append((user, password, cwd))
 
     def base_url(self):
-        return 'ftp://127.0.0.1:{}'.format(self.server.address[1])
+        assert self._port is not None
+        return 'ftp://127.0.0.1:{}'.format(self._port)
+
+
+def _run_server(queue, anonymous_dirs, user_list):
+    authorizer = DummyAuthorizer()
+    handler = FTPHandler
+    handler.authorizer = authorizer
+
+    for cwd in anonymous_dirs:
+        authorizer.add_anonymous(cwd)
+
+    for user, password, cwd in user_list:
+        authorizer.add_user(user, password, cwd, perm='elradfmwMT')
+
+    server = FTPServer(('127.0.0.1', 0), handler)
+
+    port = server.address[1]
+    queue.put(port)
+    server.serve_forever(handle_exit=True)