From 07716a3709259369d4c5410b50c9eeba5e4e066a Mon Sep 17 00:00:00 2001
From: Christian Ulrich <christian@ulrich.earth>
Date: Sat, 11 Jul 2020 14:46:37 +0200
Subject: [PATCH] implement SYNI accept logic

---
 tcp_syni.nim | 37 +++++++++++++++++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/tcp_syni.nim b/tcp_syni.nim
index 69cd156..9c06c2d 100644
--- a/tcp_syni.nim
+++ b/tcp_syni.nim
@@ -77,6 +77,18 @@ proc captureSeqNumbers(puncher: TcpSyniPuncher, rawFd: AsyncFD,
           break
   await cb(seqNums)
 
+proc injectSyns(rawFd: AsyncFD, srcIp: IpAddress, srcPort: Port,
+                dstIp: IpAddress, dstPort: Port,
+                seqNums: seq[uint32]) {.async.} =
+  for seqNum in seqNums:
+    let ipPacket = IpPacket(protocol: tcp,
+                            tcpIpSrc: srcIp,
+                            tcpIpDst: dstIp,
+                            tcpPortSrc: dstPort,
+                            tcpPortDst: srcPort,
+                            tcpSeqNumber: seqNum)
+    asyncCheck rawFd.send(serialize(ipPacket))
+
 proc initPuncher*(srcPort: Port, dstIp: IpAddress, dstPorts: array[3, Port],
                   seqNums: seq[uint32] = @[]): Future[TcpSyniPuncher] {.async.} =
   let localIp = getPrimaryIPAddr(dstIp)
@@ -107,6 +119,25 @@ proc doConnect(srcIp: IpAddress, srcPort: Port, dstIp: IpAddress,
     echo &"connection {srcIP}:{srcPort.int} -> {dstIp}:{dstPort.int} failed: ", e.msg
     discard
 
+proc doAccept(srcIp: IpAddress, srcPort: Port, dstIp: IpAddress, dstPort: Port,
+              future: Future[AsyncSocket]) {.async.} =
+  let sock = newAsyncSocket()
+  sock.setSockOpt(OptReuseAddr, true)
+  sock.getFd.setSockOptInt(IPPROTO_IP, IP_TTL, 2)
+  sock.bindAddr(srcPort, $srcIp)
+  try:
+    await sock.connect($dstIp, dstPort)
+    echo "connected during accept phase"
+    sock.close()
+  except OSError:
+    discard
+  try:
+    let connectedSock = await sock.accept()
+    future.complete(connectedSock)
+  except OSError as e:
+    echo &"connection {srcIP}:{srcPort.int} -> {dstIp}:{dstPort.int} failed: ", e.msg
+    discard
+
 proc connect*(puncher: TcpSyniPuncher,
               progressCb: PunchProgressCb): Future[AsyncSocket] =
   result = newFuture[AsyncSocket]("tcp_syni.connect")
@@ -119,3 +150,9 @@ proc connect*(puncher: TcpSyniPuncher,
 
 proc accept*(puncher: TcpSyniPuncher): Future[AsyncSocket] =
   result = newFuture[AsyncSocket]("tcp_syni.accept")
+  let rawFd = setupTcpInjectingSocket()
+  for dstPort in puncher.dstPorts:
+    asyncCheck doAccept(puncher.srcIp, puncher.srcPort, puncher.dstIp, dstPort,
+                        result)
+    asyncCheck injectSyns(rawFd, puncher.srcIp, puncher.srcPort, puncher.dstIp,
+                          dstPort, puncher.seqNums)