Enabled TCP Keep Alive on httpcore (httpx)

Currently there is no way to enable TCP KeepAlive directly on httpx
module

ref. PR:#1172

packages/httpcore/backends/sync.py

@@ -11,6 +11,7 @@
     WriteTimeout,
     map_exceptions,
 )
+from .tcp_keep_alive import enable_tcp_keep_alive
 from .._utils import is_socket_readable
 from .base import NetworkBackend, NetworkStream
 
@@ -86,6 +87,8 @@ def connect_tcp(
             sock = socket.create_connection(
                 address, timeout, source_address=source_address
             )
+            # Enable TCP Keep-Alive
+            enable_tcp_keep_alive(sock)
         return SyncStream(sock)
 
     def connect_unix_socket(

packages/httpcore/backends/tcp_keep_alive.py

@@ -0,0 +1,38 @@
+# -*- coding: utf-8 -*-
+"""
+    Copyright (C) 2021 Stefano Gottardo - @CastagnaIT
+    Helper to enable TCP Keep Alive
+
+    SPDX-License-Identifier: MIT
+    See LICENSES/MIT.md for more information.
+"""
+import socket
+import sys
+
+TCP_KEEP_IDLE = 45
+TCP_KEEPALIVE_INTERVAL = 10
+TCP_KEEP_CNT = 6
+
+
+def enable_tcp_keep_alive(sock):
+    """Enable TCP Keep-Alive (by default disabled)"""
+    # More info on PR: https://github.com/CastagnaIT/plugin.video.netflix/pull/1065
+    sock.setsockopt(socket.SOL_SOCKET, socket.SO_KEEPALIVE, 1)
+    if sys.platform == 'linux':
+        # TCP Keep Alive Probes for Linux/Android
+        if hasattr(socket, 'TCP_KEEPIDLE'):
+            sock.setsockopt(socket.IPPROTO_TCP, socket.TCP_KEEPIDLE, TCP_KEEP_IDLE)
+        if hasattr(socket, 'TCP_KEEPINTVL'):
+            sock.setsockopt(socket.IPPROTO_TCP, socket.TCP_KEEPINTVL, TCP_KEEPALIVE_INTERVAL)
+        if hasattr(socket, 'TCP_KEEPCNT'):
+            sock.setsockopt(socket.IPPROTO_TCP, socket.TCP_KEEPCNT, TCP_KEEP_CNT)
+    elif sys.platform == 'darwin':
+        # TCP Keep Alive Probes for MacOS
+        # NOTE: The socket constants from MacOS netinet/tcp.h are not exported by python's socket module
+        # The MacOS TCP_KEEPALIVE(0x10) constant should be the same thing of the linux TCP_KEEPIDLE constant
+        sock.setsockopt(socket.IPPROTO_TCP, getattr(socket, 'TCP_KEEPIDLE', 0x10), TCP_KEEP_IDLE)
+        sock.setsockopt(socket.IPPROTO_TCP, getattr(socket, 'TCP_KEEPINTVL', 0x101), TCP_KEEPALIVE_INTERVAL)
+        sock.setsockopt(socket.IPPROTO_TCP, getattr(socket, 'TCP_KEEPCNT', 0x102), TCP_KEEP_CNT)
+    elif sys.platform == 'win32':
+        # TCP Keep Alive Probes for Windows
+        sock.ioctl(socket.SIO_KEEPALIVE_VALS, (1, TCP_KEEP_IDLE * 1000, TCP_KEEPALIVE_INTERVAL * 1000))