Enable Linux and BSD compatibility (#49)

Summary:
Hey guys, first of all, great work on the framework.

I need to use the framework on FreeBSD servers and it was quite a boomer when I saw it was depending on epoll, so I took some time and came up with this solution using `selectors` instead of `select`, that way things got OS agnostic and selectors should in theory use the most efficient method mechanism available.

I took the care of also adjusting the `poll_mock()` in the tests. Please double check the work there as I was slightly unsure if that was the right way to go.

Luiz

Pull Request resolved: #49

Test Plan:
Test logs for Linux and FreeBSD:
#49 (comment)

Reviewed By: pallotron

Differential Revision: D29100368

Pulled By: skozlov404

fbshipit-source-id: d5b25392a8891deda6903e65989eef0525be759b

Author: lamaral

.github/workflows/build.yml

@@ -3,8 +3,7 @@ name: build
 on: [push, pull_request]
 
 jobs:
-  build:
-
+  build-linux:
     runs-on: ubuntu-latest
     strategy:
       matrix:
@@ -26,3 +25,24 @@ jobs:
     - name: Test
       run: |
         make test
+
+  build-bsd:
+    runs-on: macos-latest
+    strategy:
+      matrix:
+        python-version: [ '3.5', '3.6', '3.7', '3.8', '3.9' ]
+
+    steps:
+      - uses: actions/checkout@v2
+      - name: Set up Python ${{ matrix.python-version }}
+        uses: actions/setup-python@v2
+        with:
+          python-version: ${{ matrix.python-version }}
+      - name: Install dependencies and prepare for test
+        run: |
+          python -m pip install --upgrade pip
+          python -m pip install setuptools --upgrade
+          python -m pip install flake8
+      - name: Test
+        run: |
+          make test

README.md

@@ -101,7 +101,8 @@ and you are good to go:
 # Requirements
 
 * Linux (or any system that supports [`epoll`](http://linux.die.net/man/4/epoll))
-* Python 3.x
+* BSD (or any system that supports [`kqueue`](https://www.freebsd.org/cgi/man.cgi?query=kqueue&sektion=2))
+* Python 3.4+
 
 # Installation
 

fbtftp/base_server.py

@@ -7,7 +7,7 @@
 import collections
 import ipaddress
 import logging
-import select
+import selectors
 import socket
 import struct
 import threading
@@ -205,8 +205,8 @@ def __init__(
         self._listener = socket.socket(self._family, socket.SOCK_DGRAM)
         self._listener.setblocking(0)  # non-blocking
         self._listener.bind((address, port))
-        self._epoll = select.epoll()
-        self._epoll.register(self._listener.fileno(), select.EPOLLIN)
+        self._selector = selectors.DefaultSelector()
+        self._selector.register(self._listener, selectors.EVENT_READ)
         self._should_stop = False
         self._server_stats = ServerStats(address, stats_interval_seconds)
         self._metrics_timer = None
@@ -226,7 +226,7 @@ def run(self, run_once=False):
             self.run_once()
             if run_once:
                 break
-        self._epoll.close()
+        self._selector.close()
         self._listener.close()
         if self._metrics_timer is not None:
             self._metrics_timer.cancel()
@@ -271,11 +271,11 @@ def run_once(self):
         facility to know when data is ready to be retrived from the listening
         socket. See http://linux.die.net/man/4/epoll .
         """
-        events = self._epoll.poll()
-        for fileno, eventmask in events:
-            if not eventmask & select.EPOLLIN:
+        events = self._selector.select()
+        for key, mask in events:
+            if not mask & selectors.EVENT_READ:
                 continue
-            if fileno == self._listener.fileno():
+            if key.fd == self._listener.fileno():
                 self.on_new_data()
                 continue
 

tests/base_server_test.py

@@ -10,7 +10,7 @@
 from fbtftp.base_server import BaseServer
 
 MOCK_SOCKET_FILENO = 100
-SELECT_EPOLLIN = 1
+SELECTORS_EVENT_READ = 1
 
 
 class MockSocketListener:
@@ -72,14 +72,16 @@ def setUp(self):
         self.interval = 1
         self.network_queue = []
 
-    def poll_mock(self):
+    def select_mock(self):
         """
         mock the select.epoll.poll() method, returns an iterable containing a
         list of (fileno, eventmask), the fileno constant matches the
         MockSocketListener.fileno() method, eventmask matches select.EPOLLIN
         """
         if len(self.network_queue) > 0:
-            return [(MOCK_SOCKET_FILENO, SELECT_EPOLLIN)]
+            obj = lambda: None
+            obj.fd = MOCK_SOCKET_FILENO
+            return [(obj, SELECTORS_EVENT_READ)]
         return []
 
     def prepare_and_run(self, network_queue):
@@ -104,10 +106,10 @@ def prepare_and_run(self, network_queue):
         server._server_stats.increment_counter.assert_called_with("process_count")
         return server._handler
 
-    @patch("select.epoll")
-    def testRRQ(self, epoll_mock):
+    @patch("selectors.DefaultSelector")
+    def testRRQ(self, selector_mock):
         # link the self.poll_mock() method with the select.epoll patched object
-        epoll_mock.return_value.poll.side_effect = self.poll_mock
+        selector_mock.return_value.select.side_effect = self.select_mock
         self.network_queue = [
             # RRQ + file name + mode + optname + optvalue
             b"\x00\x01some_file\x00binascii\x00opt1_key\x00opt1_val\x00"
@@ -171,10 +173,10 @@ def testCallbackException(self):
         stats_callback.side_effect = Exception("boom!")
         self.start_timer_and_wait_for_callback(stats_callback)
 
-    @patch("select.epoll")
-    def testUnexpectedOpsCode(self, epoll_mock):
+    @patch("selectors.DefaultSelector")
+    def testUnexpectedOpsCode(self, selector_mock):
         # link the self.poll_mock() emthod with the select.epoll patched object
-        epoll_mock.return_value.poll.side_effect = self.poll_mock
+        selector_mock.return_value.select.side_effect = self.select_mock
         self.network_queue = [
             # RRQ + file name + mode + optname + optvalue
             b"\x00\xffsome_file\x00binascii\x00opt1_key\x00opt1_val\x00"