implement setupTcpInjectingSocket

raw_socket.nim

@@ -1,5 +1,12 @@
 import asyncdispatch
-from nativesockets import SOCK_RAW, bindAddr, htons
+from nativesockets import
+  AF_INET,
+  IPPROTO_IP,
+  IPPROTO_TCP,
+  SOCK_RAW,
+  bindAddr,
+  htons,
+  setSockOptInt
 from posix import setsockopt, SockAddr, SockLen, SocketHandle
 import network_interface
 
@@ -27,6 +34,7 @@ var
   AF_PACKET {.importc: "AF_PACKET", header: "<sys/socket.h>".}: cushort
   SOL_PACKET {.importc: "SOL_PACKET", header: "<sys/socket.h>".}: cushort
   ETH_P_ALL {.importc: "ETH_P_ALL", header: "<linux/if_ether.h>".}: cushort
+  IP_HDRINCL {.importc: "IP_HDRINCL", header: "<netinet/in.h>".}: cint
   PACKET_ADD_MEMBERSHIP {.importc: "PACKET_ADD_MEMBERSHIP", header: "<linux/if_packet.h>".}: cushort
   PACKET_MR_PROMISC {.importc: "PACKET_MR_PROMISC", header: "<linux/if_packet.h>".}: cushort
 
@@ -57,4 +65,11 @@ proc setupEthernetCapturingSocket*(iface: NetworkInterface): AsyncFD =
                 sizeof(req).SockLen) != 0:
     raise newException(RawSocketError, "cannot enable promiscuous mode")
 
+proc setupTcpInjectingSocket*(): AsyncFD =
+  # FIXME: would bindAddr be beneficial?
+  result = createAsyncNativeSocket(AF_INET.cint, SOCK_RAW.cint,
+                                   IPPROTO_TCP.cint)
 
+  # Tell the kernel to not generate an IP header, as we generate it ourselves,
+  # see raw(7) man page.
+  setSockOptInt(result.SocketHandle, IPPROTO_IP.int, IP_HDRINCL, 1)