Lua: add DissectorTable.try_heuristics() function

Add DissectorTable.try_heuristics(name, tvb, pinfo, tree). Previously,
there was no way for a Lua plugin to run an existing heuristic
dissector.

Based on Gerrit change 18718. Closes #17220.

epan/wslua/wslua_dissector.c

@@ -286,6 +286,35 @@ WSLUA_CONSTRUCTOR DissectorTable_heuristic_list (lua_State *L) {
     WSLUA_RETURN(1); /* The array table of registered heuristic list names */
 }
 
+WSLUA_CONSTRUCTOR DissectorTable_try_heuristics (lua_State *L) {
+    /*
+     Try all the dissectors in a given heuristic dissector table.
+     */
+#define WSLUA_ARG_DissectorTable_try_heuristics_LISTNAME 1 /* The name of the heuristic dissector. */
+#define WSLUA_ARG_DissectorTable_try_heuristics_TVB 2 /* The buffer to dissect. */
+#define WSLUA_ARG_DissectorTable_try_heuristics_PINFO 3 /* The packet info. */
+#define WSLUA_ARG_DissectorTable_try_heuristics_TREE 4 /* The tree on which to add the protocol items. */
+
+    const gchar* name = luaL_checkstring(L,WSLUA_ARG_DissectorTable_try_heuristics_LISTNAME);
+    Tvb tvb = checkTvb(L,WSLUA_ARG_DissectorTable_try_heuristics_TVB);
+    Pinfo pinfo = checkPinfo(L,WSLUA_ARG_DissectorTable_try_heuristics_PINFO);
+    TreeItem tree = checkTreeItem(L,WSLUA_ARG_DissectorTable_try_heuristics_TREE);
+    heur_dissector_list_t list;
+    heur_dtbl_entry_t *entry;
+
+    if (!(name && tvb && pinfo && tree)) return 0;
+
+    list = find_heur_dissector_list(name);
+    if (!list) {
+        luaL_error(L, "Heuristic list '%s' does not exist", name);
+        return 0;
+    }
+
+    lua_pushboolean(L, dissector_try_heuristic(list, tvb->ws_tvb, pinfo->ws_pinfo, tree->tree, &entry, NULL));
+
+    WSLUA_RETURN(1); /* True if the packet was recognized by the sub-dissector (stop dissection here). */
+}
+
 WSLUA_CONSTRUCTOR DissectorTable_get (lua_State *L) {
     /*
      Obtain a reference to an existing dissector table.
@@ -688,6 +717,7 @@ WSLUA_METHODS DissectorTable_methods[] = {
     WSLUA_CLASS_FNREG(DissectorTable,get),
     WSLUA_CLASS_FNREG(DissectorTable,list),
     WSLUA_CLASS_FNREG(DissectorTable,heuristic_list),
+    WSLUA_CLASS_FNREG(DissectorTable,try_heuristics),
     WSLUA_CLASS_FNREG(DissectorTable,add),
     WSLUA_CLASS_FNREG(DissectorTable,set),
     WSLUA_CLASS_FNREG(DissectorTable,remove),

test/lua/try_heuristics.lua

@@ -0,0 +1,61 @@
+-- Define a new protocol that runs TCP heuristics and on failure runs UDP heuristics
+--
+-- This expects to be run against dns_port.pcap, so it should end up resolving all packets to DNS with the UDP heuristic
+local test_proto = Proto("test", "Test Protocol")
+
+-- Have all tests passed so far?
+-- Anything that fails should set this to false, which will suppress the "".
+all_ok = true
+
+-- The number of frames expected
+-- Final test status is output with last frame
+LAST_FRAME = 4
+
+function test_proto.dissector(buf, pinfo, root)
+    print("Dissector function run")
+
+    orig_proto_name = tostring(pinfo.cols.protocol)
+
+    -- Run TCP heuristic dissectors
+    -- Dissection should fail, and the protocol name should be unchanged
+    tcp_success = DissectorTable.try_heuristics("tcp", buf, pinfo, root)
+    curr_proto_name = tostring(pinfo.cols.protocol)
+
+    if tcp_success then
+        all_ok = false
+        print("tcp heuristics were not expected to report success, but did!")
+    end
+
+    if curr_proto_name ~= orig_proto_name then
+        all_ok = false
+        print("after tcp heuristics were run, protocol " .. orig_proto_name .. " was not expected to change, but became " .. curr_proto_name .. "!")
+    end
+
+    -- Run UDP heuristic dissectors
+    -- Dissection should succeed, and the protocol name should be changed to DNS
+    udp_success = DissectorTable.try_heuristics("udp", buf, pinfo, root)
+    curr_proto_name = tostring(pinfo.cols.protocol)
+
+    if not udp_success then
+        all_ok = false
+        print("udp heuristics were expected to report success, but did not!")
+    end
+
+    if curr_proto_name ~= "DNS" then
+        all_ok = false
+        print("after udp heuristics were run, protocol should be changed to DNS, but became " .. curr_proto_name .. "!")
+    end
+
+    -- If we're on the last frame, report success or failure
+    if pinfo.number == LAST_FRAME then
+        if all_ok then
+            print("All tests passed!")
+        else
+            print("Some tests failed!")
+        end
+    end
+end
+
+-- Invoke test_proto on the expected UDP traffic
+DissectorTable.get("udp.port"):add(65333, test_proto)
+DissectorTable.get("udp.port"):add(65346, test_proto)

test/suite_wslua.py

@@ -282,6 +282,10 @@ class case_wslua(subprocesstest.SubprocessTestCase):
         '''wslua tvb without a tree'''
         check_lua_script(self, 'tvb.lua', dns_port_pcap, True)
 
+    def test_wslua_try_heuristics(self, check_lua_script):
+        '''wslua try_heuristics'''
+        check_lua_script(self, 'try_heuristics.lua', dns_port_pcap, True)
+
 
 @fixtures.uses_fixtures
 class case_wslua_unicode(subprocesstest.SubprocessTestCase):