Add Decode As capabilities to MoldUDP dissector

Per the Nasdaq TotalView-ITCH v2/3 protocol specifications the
NASDAQ-ITCH dissector needs be able to dissect a MoldUDP payload.

Change-Id: Id5194930025a9abdfb1663234233fd51e525a34b
Reviewed-on: https://code.wireshark.org/review/19847
Petri-Dish: Michael Mann <mmann78@netscape.net>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Michael Mann <mmann78@netscape.net>

1 files changed, 33 insertions, 2 deletions

diff --git a/epan/dissectors/packet-moldudp.c b/epan/dissectors/packet-moldudp.c
index 7d697ed8f1..9bcb6c4f79 100644
--- a/epan/dissectors/packet-moldudp.c
+++ b/epan/dissectors/packet-moldudp.c
@@ -27,6 +27,7 @@
 
 #include <epan/packet.h>
 #include <epan/expert.h>
+#include <epan/decode_as.h>
 
 void proto_register_moldudp(void);
 void proto_reg_handoff_moldudp(void);
@@ -55,6 +56,18 @@ static gint ett_moldudp_msgblk = -1;
 static expert_field ei_moldudp_msglen_invalid = EI_INIT;
 static expert_field ei_moldudp_count_invalid = EI_INIT;
 
+static dissector_table_t moldudp_payload_table;
+
+static void moldudp_prompt(packet_info *pinfo _U_, gchar* result)
+{
+    g_snprintf(result, MAX_DECODE_AS_PROMPT_LEN, "Payload as");
+}
+
+static gpointer moldudp_value(packet_info *pinfo _U_)
+{
+    return 0;
+}
+
 /* Code to dissect a message block */
 static guint
 dissect_moldudp_msgblk(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree,
@@ -64,6 +77,7 @@ dissect_moldudp_msgblk(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree,
     proto_tree *blk_tree;
     guint16     msglen, real_msglen, whole_len;
     guint       remaining;
+    tvbuff_t*   next_tvb;
 
     if (tvb_reported_length(tvb) - offset < MOLDUDP_MSGLEN_LEN)
         return 0;
@@ -105,8 +119,15 @@ dissect_moldudp_msgblk(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree,
 
     offset += MOLDUDP_MSGLEN_LEN;
 
-    proto_tree_add_item(blk_tree, hf_moldudp_msgdata,
-            tvb, offset, real_msglen, ENC_NA);
+
+    /* Functionality for choosing subdissector is controlled through Decode As as MoldUDP doesn't
+       have a unique identifier to determine subdissector */
+    next_tvb = tvb_new_subset_length(tvb, offset, real_msglen);
+    if (!dissector_try_uint_new(moldudp_payload_table, 0, next_tvb, pinfo, tree, FALSE, NULL))
+    {
+        proto_tree_add_item(blk_tree, hf_moldudp_msgdata,
+                tvb, offset, real_msglen, ENC_NA);
+    }
 
     return whole_len;
 }
@@ -228,14 +249,24 @@ proto_register_moldudp(void)
 
     expert_module_t* expert_moldudp;
 
+    /* Decode As handling */
+    static build_valid_func moldudp_da_build_value[1] = {moldudp_value};
+    static decode_as_value_t moldudp_da_values = {moldudp_prompt, 1, moldudp_da_build_value};
+    static decode_as_t moldudp_da = {"moldudp", "MoldUDP Payload", "moldudp.payload", 1, 0, &moldudp_da_values, NULL, NULL,
+                                      decode_as_default_populate_list, decode_as_default_reset, decode_as_default_change, NULL};
+
     /* Register the protocol name and description */
     proto_moldudp = proto_register_protocol("MoldUDP", "MoldUDP", "moldudp");
 
+    moldudp_payload_table = register_dissector_table("moldudp.payload", "MoldUDP Payload", proto_moldudp, FT_UINT32, BASE_DEC);
+
     /* Required function calls to register the header fields and subtrees used */
     proto_register_field_array(proto_moldudp, hf, array_length(hf));
     proto_register_subtree_array(ett, array_length(ett));
     expert_moldudp = expert_register_protocol(proto_moldudp);
     expert_register_field_array(expert_moldudp, ei, array_length(ei));
+
+    register_decode_as(&moldudp_da);
 }