fix file descriptor leak by using own implementation of getPrimaryIPAddr

tcp_syni.nim

@@ -1,5 +1,5 @@
 import asyncfutures, asyncdispatch, asyncnet, strformat
-from net import IpAddress, Port, `$`, `==`, getPrimaryIPAddr, toSockAddr, parseIpAddress
+from net import IpAddress, Port, `$`, `==`, toSockAddr, parseIpAddress
 from nativesockets import SockAddr, Sockaddr_storage, SockLen, setSockOptInt
 from random import randomize, rand
 from sequtils import any
@@ -7,6 +7,7 @@ import asyncutils
 import ip_packet
 import network_interface
 import raw_socket
+import utils
 
 var IPPROTO_IP {.importc: "IPPROTO_IP", header: "<netinet/in.h>".}: cint
 var IP_TTL {.importc: "IP_TTL", header: "<netinet/in.h>".}: cint

utils.nim

@@ -0,0 +1,28 @@
+from net import
+  IpAddress, IpAddressFamily, Port, newSocket, connect, close, getLocalAddr,
+  parseIpAddress
+from nativesockets import
+  AF_INET, AF_INET6, SOCK_DGRAM, IPPROTO_UDP
+
+# FIXME: getPrimaryAddr is not needed anymore once
+# https://github.com/nim-lang/Nim/pull/15538 is released.
+proc getPrimaryIPAddr*(dest = parseIpAddress("8.8.8.8")): IpAddress =
+  ## Finds the local IP address, usually assigned to eth0 on LAN or wlan0 on WiFi,
+  ## used to reach an external address. Useful to run local services.
+  ##
+  ## No traffic is sent.
+  ##
+  ## Supports IPv4 and v6.
+  ## Raises OSError if external networking is not set up.
+  ##
+  ## .. code-block:: Nim
+  ##   echo $getPrimaryIPAddr()  # "192.168.1.2"
+
+  let socket =
+    if dest.family == IpAddressFamily.IPv4:
+      newSocket(AF_INET, SOCK_DGRAM, IPPROTO_UDP)
+    else:
+      newSocket(AF_INET6, SOCK_DGRAM, IPPROTO_UDP)
+  socket.connect($dest, 80.Port)
+  result = socket.getLocalAddr()[0].parseIpAddress()
+  socket.close()