Add support for heuristic SCION traffic identification.

Made that default, since the dispacher removal makes port-based sorting
flaky.

tools/wireshark/scion.lua

@@ -129,6 +129,23 @@ scion_proto.experts = {
     e_nosup_proto,
 }
 
+-- This function heuristically identifies SCION packets. If the packet looks like it may be
+-- a SCION packet, it returns true, which causes the associated scion disector to be invoked.
+-- This doesn't have much data available to weed out non-SCION packets. False positives end-up being
+-- described as broken SCION packets and are not passed to the vanilla UDP parser.
+-- However, with the removal of the dispatcher, we have no narrow set of UDP ports to identify
+-- SCION traffic from. So, there's no choice.
+local function scion_proto_filter(tvbuf, pktinfo, root)
+    local version = bit.rshift(tvbuf(0,1):uint(), 4)
+    local path_type = tvbuf(8, 1):uint()
+    local rsv = tvbuf(10, 2):uint()
+    if version == 0 and path_type < 5 and rsv == 0 then
+	pktinfo.conversation = scion_proto
+       return true
+    end
+    return false
+end
+
 function scion_proto.dissector(tvbuf, pktinfo, root)
     local tree = root:add(scion_proto, tvbuf())
     local header_str = tree
@@ -280,9 +297,9 @@ end
 function addr_str(buf, addrTypeLen, with_svc)
     local addrType = addrTypes[addrTypeLen]
     if addrType == "IPv4" then
-        return string.format("%s", buf:ipv4())
+        return string.format("%s", tostring(buf:ipv4()))
     elseif addrType == "IPv6" then
-        return string.format("%s", buf:ipv6())
+        return string.format("%s", tostring(buf:ipv6()))
     elseif with_svc and addrType == "SVC" then
         local svcVal = buf(0, 2):uint()
         local svc = svcTypes[svcVal]
@@ -1152,21 +1169,28 @@ function scmp_proto_dissect(tvbuf, pktinfo, root)
 end
 
 
--- Below we configure Wireshark to identify SCION as the next protocol when using
--- the specified range of ports.
---
 -- SCION packet on UDP/IP overlay.
-table_udp = DissectorTable.get("udp.port")
--- intra-AS traffic
-for i = 30000, 32000, 1 do
-    table_udp:add(i, scion_proto)
-end
--- inter-AS BR traffic
-for i = 40000, 40050, 1 do
-    table_udp:add(i, scion_proto)
-end
--- FIXME remove once acceptance tests are updated to use ports above
--- acceptance tests
-for i = 50000, 50050, 1 do
-    table_udp:add(i, scion_proto)
-end
+-- Two options are available. Identify SCION traffic by port number, or heuristically, by
+-- looking for clues in the header. The heuristic is not extremely robust. It may mistake
+-- non-SCION packet for scion packets. If you know precisely which ports carry SCION
+-- traffic (which is made difficult by the removal of the dispatcher), you may prefer to
+-- identify them by port. Keep the unwanted option commented out.
+
+-- Heuristic selection
+scion_proto:register_heuristic("udp", scion_proto_filter)
+
+-- Port-based selection
+-- table_udp = DissectorTable.get("udp.port")
+-- -- intra-AS traffic
+-- for i = 31000, 32767, 1 do
+--    table_udp:add(i, scion_proto)
+-- end
+-- -- inter-AS BR traffic
+-- for i = 40000, 40050, 1 do
+--    table_udp:add(i, scion_proto)
+-- end
+-- -- FIXME remove once acceptance tests are updated to use ports above
+-- -- acceptance tests
+-- for i = 50000, 50050, 1 do
+--     table_udp:add(i, scion_proto)
+-- end