tpncp: load hf array in the handoff function

tpncp reads hf entries from a database. There's a boolean preference
defining if the database is actually read. We can't access this
preference until the preferences are initialized. The code as it is now
wil always default to false and never read the database.

Check the preference in the handoff function and initialize the hf
entries if they are not yet initialized.

Change-Id: I545a49a946b78e1a0bc23e9803eb671d8765bba4
Reviewed-on: https://code.wireshark.org/review/18386
Reviewed-by: Martin Kaiser <wireshark@kaiser.cx>
Petri-Dish: Martin Kaiser <wireshark@kaiser.cx>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Michael Mann <mmann78@netscape.net>

epan/dissectors/packet-tpncp.c

@@ -105,7 +105,7 @@ static guint global_tpncp_trunkpack_tcp_port = TCP_PORT_TPNCP_TRUNKPACK;
 static guint global_tpncp_trunkpack_udp_port = UDP_PORT_TPNCP_TRUNKPACK;
 static guint global_tpncp_host_tcp_port = TCP_PORT_TPNCP_HOST;
 static guint global_tpncp_host_udp_port = UDP_PORT_TPNCP_HOST;
-static guint global_tpncp_load_db = FALSE;
+static gboolean global_tpncp_load_db = FALSE;
 
 static dissector_handle_t tpncp_handle;
 
@@ -760,6 +760,7 @@ done:
 void proto_reg_handoff_tpncp(void) {
     static gint tpncp_prefs_initialized = FALSE;
     static dissector_handle_t tpncp_tcp_handle;
+    gint idx;
 
     /*  If we weren't able to load the database (and thus the hf_ entries)
      *  do not attach to any ports (if we did then we'd get a "dissector bug"
@@ -782,6 +783,34 @@ void proto_reg_handoff_tpncp(void) {
     }
 
     if(global_tpncp_load_db){
+        if (hf_allocated == 0) {
+            if (init_tpncp_db() == -1) {
+                report_failure("tpncp: Could not load tpncp.dat file, tpncp dissector will not work");
+                return;
+            }
+
+            /* Rather than duplicating large quantities of code from
+             * proto_register_field_array() and friends to sanitize the tpncp.dat file
+             * when we read it, just catch any exceptions we get while registering and
+             * take them as a hint that the file is corrupt. Then move on, so that at
+             * least the rest of the protocol dissectors will still work.
+             */
+            TRY {
+                /* The function proto_register_field_array does not work with dynamic
+                 * arrays, so pass dynamic array elements one-by-one in the loop.
+                 */
+                for(idx = 0; idx < hf_size; idx++) {
+                    proto_register_field_array(proto_tpncp, &hf[idx], 1);
+                }
+            }
+
+            CATCH_ALL {
+                report_failure("Corrupt tpncp.dat file, tpncp dissector will not work.");
+            }
+
+            ENDTRY;
+        }
+
         trunkpack_tcp_port = global_tpncp_trunkpack_tcp_port;
         trunkpack_udp_port = global_tpncp_trunkpack_udp_port;
 
@@ -796,50 +825,26 @@ void proto_reg_handoff_tpncp(void) {
 /*-------------------------------------------------------------------------------------------------------------------------------------------*/
 
 void proto_register_tpncp(void) {
-    gint idx;
     module_t *tpncp_module;
     static gint *ett[] = {
         &ett_tpncp,
         &ett_tpncp_body
     };
 
+    /* this dissector reads hf entries from a database
+       a boolean preference defines whether the database is loaded or not
+       we initialize the hf array in the handoff function when we have
+       access to the preference's value */
+
     proto_tpncp = proto_register_protocol("AudioCodes TPNCP (TrunkPack Network Control Protocol)",
                                           "TPNCP", "tpncp");
-    if(global_tpncp_load_db){
-        if (init_tpncp_db() == -1) {
-            report_failure("tpncp: Could not load tpncp.dat file, tpncp dissector will not work");
-            return;
-        }
-
-
-        /* Rather than duplicating large quantities of code from
-         * proto_register_field_array() and friends to sanitize the tpncp.dat file
-         * when we read it, just catch any exceptions we get while registering and
-         * take them as a hint that the file is corrupt. Then move on, so that at
-         * least the rest of the protocol dissectors will still work.
-         */
-        TRY {
-            /* The function proto_register_field_array does not work with dynamic
-             * arrays, so pass dynamic array elements one-by-one in the loop.
-             */
-            for(idx = 0; idx < hf_size; idx++) {
-                proto_register_field_array(proto_tpncp, &hf[idx], 1);
-            }
-        }
-
-        CATCH_ALL {
-            report_failure("Corrupt tpncp.dat file, tpncp dissector will not work.");
-        }
-
-        ENDTRY;
-
-        proto_register_subtree_array(ett, array_length(ett));
-    }
 
     tpncp_handle = register_dissector("tpncp", dissect_tpncp, proto_tpncp);
 
     tpncp_module = prefs_register_protocol(proto_tpncp, proto_reg_handoff_tpncp);
 
+    proto_register_subtree_array(ett, array_length(ett));
+
     /* See https://bugs.wireshark.org/bugzilla/show_bug.cgi?id=9569 for some discussion on this as well */
     prefs_register_bool_preference(tpncp_module, "load_db",
                                    "Whether to load DB or not; if DB not loaded dissector is passive",