implement primitive probing of the rendezvous server's public IP and provide it to LAN clients

examples/rendezvous_server/rendezvous_server.nim

@@ -1,9 +1,9 @@
-import asyncdispatch, asyncnet, os, strformat, strutils, tables
-from net import IpAddress, Port, `$`
+import asyncdispatch, asyncnet, os, sequtils, strformat, strutils, tables
+from nativesockets import htonl
+from net import IpAddress, Port, getPrimaryIPAddr, parseIpAddress, `$`
+import ../../asyncutils
 import ../../message
-
-# TODO: we need to find out our own external IP and return it to clients who
-# connect from our LAN
+import ../../network_interface
 
 type
   Client = object
@@ -25,12 +25,49 @@ type
     recipient: string
     data: string
 
+proc isPrivateIp(ip: IpAddress): bool =
+  const ranges: array[5, tuple[first: IpAddress, last: IpAddress]] =
+    [(parseIpAddress("10.0.0.0"), parseIpAddress("10.255.255.255")),
+     (parseIpAddress("172.16.0.0"), parseIpAddress("172.31.255.255")),
+     (parseIpAddress("192.168.0.0"), parseIpAddress("192.168.255.255")),
+     (parseIpAddress("169.254.0.0"), parseIpAddress("169.254.255.255")),
+     (parseIpAddress("127.0.0.0"), parseIpAddress("127.255.255.255"))]
+  for r in ranges:
+    let ipScalar = htonl(cast[uint32](ip.address_v4))
+    if ipScalar > htonl(cast[uint32](r.first.address_v4)) and
+       ipScalar < htonl(cast[uint32](r.last.address_v4)):
+      return true
+  return false
+
+proc isInNetwork(ip: IpAddress, iface: NetworkInterface): bool =
+  let ipScalar = htonl(cast[uint32](ip.address_v4))
+  let ifaceIpScalar = htonl(cast[uint32](iface.ipAddress.address_v4))
+  let netmaskScalar = htonl(cast[uint32](iface.netmask.address_v4))
+  (ipScalar and netmaskScalar) == (ifaceIpScalar and netmaskScalar)
+
+proc probePublicIp(): Future[IpAddress] {.async.} =
+  let output = await asyncExecCmd("ping -R -c 1 -s 1 -n 193.0.14.129")
+  let ipLines = output.splitLines()
+    .filter(proc(l: string): bool = l.startsWith("\t") or l.startsWith("RR:"))
+    .map(proc(l: string): string = l.strip(true, false, {'R', ':', '\t', ' '}))
+  for line in ipLines:
+    let ipAddr = parseIpAddress(line)
+    if not isPrivateIp(ipAddr):
+      return ipAddr
+  block:
+    raise newException(OSError, "cannot probe public IP address")
+
 proc removeClient(clients: TableRef[string, Client], peerId: string) =
   if peerId.len > 0: clients.del(peerId)
 
-proc processClient(client: AsyncSocket, clients: TableRef[string, Client]) {.async.} =
-  let (address, port) = client.getPeerAddr
-  await client.send(&"notify-endpoint|{address}|{port.int}\n")
+proc processClient(client: AsyncSocket,
+                   clients: TableRef[string, Client]) {.async.} =
+  let (address, port) = client.getPeerAddr()
+  var ipAddr = parseIpAddress(address)
+  if ipAddr.isPrivateIp() and
+     ipAddr.isInNetwork(fromIpAddress(getPrimaryIPAddr(ipAddr))):
+    ipAddr = await probePublicIp()
+  await client.send(&"notify-endpoint|{ipAddr}|{port.int}\n")
   var id = ""
   var peerId = ""
   while true: