couple of messages in one packet - wireshark

Question

I wrote a dissector,
I found one packet which contains couple of different/indifferent messages inside it,
Can someone point on the problem ?
Is this even a problem ?
I reassemble TCP packets...
This is the function of dissection:
(FRAME_HEADER_LEN = 8)
static void
dissect_PROTOC(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
{
//Reassembling TCP fragments
tcp_dissect_pdus(tvb, pinfo, tree, TRUE, FRAME_HEADER_LEN,
get_PROTOC_message_len, dissect_PROTOC_message);
}
static guint get_PROTOC_message_len(packet_info *pinfo, tvbuff_t *tvb, int offset)
{
/* the packet's size is "length" + 4bytes of TYPESIZE + 4bytes of LENGTHSIZE + 256bytes of CONTEXTIDSIZE */
return (guint)(tvb_get_ntohl(tvb, offset + 4) + CONTEXT_ID_SIZE + TYPE_SIZE + LENGTH_SIZE); /* e.g. length is at offset 4 */
}
static void dissect_PROTOC_message(tvbuff_t *tvb, packet_info *pinfo, proto_tree *tree)
{
/* my dissecting code */
guint32 packet_type = tvb_get_ntohl(tvb, 0);
col_set_str(pinfo->cinfo, COL_PROTOCOL, "PROTOC");
/* Clear out stuff in the info column */
col_clear(pinfo->cinfo,COL_INFO);
col_add_fstr(pinfo->cinfo, COL_INFO, "%d > %d [%s]",pinfo->srcport, pinfo->destport,
val_to_str(packet_type, packettypenames, "Unknown (0x%02x)"));
if (tree) { /* we are being asked for details */
proto_item *ti = NULL;
proto_tree *PROTOC_tree = NULL;
proto_item *PROTOC_data = NULL;
proto_tree *PROTOC_data_tree = NULL;
guint32 type = 0;
guint32 length = 0;
gint offset = 0;
ti = proto_tree_add_item(tree, proto_PROTOC, tvb, 0, -1, ENC_NA);
proto_item_append_text(ti, ", Type: %s",
val_to_str(packet_type, packettypenames, "Unknown (0x%02x)"));
PROTOC_tree = proto_item_add_subtree(ti, ett_PROTOC);
//getting type
type = tvb_get_ntohl(tvb, offset);
proto_tree_add_item(PROTOC_tree, hf_PROTOC_pdu_type, tvb, 0, TYPE_SIZE, ENC_BIG_ENDIAN);
offset += TYPE_SIZE;
//getting length for the data length
length = tvb_get_ntohl(tvb, offset);
proto_tree_add_item(PROTOC_tree, hf_PROTOC_len, tvb, offset, LENGTH_SIZE, ENC_BIG_ENDIAN);
offset += LENGTH_SIZE;
proto_tree_add_item(PROTOC_tree, hf_PROTOC_contextid, tvb, offset, CONTEXT_ID_SIZE, ENC_BIG_ENDIAN);
offset += CONTEXT_ID_SIZE;
PROTOC_data = proto_tree_add_item(PROTOC_tree, hf_PROTOC_data, tvb, offset, length, FALSE);
PROTOC_data_tree = proto_item_add_subtree(PROTOC_data, ett_PROTOC_data);
offset += length;
}
}

Answer 1

I found one packet which contains couple of different/indifferent messages inside it,
...
I reassemble TCP packets...
That's pretty common for protocols running over TCP; there is no guarantee that TCP segment boundaries will correspond to packet boundaries in protocols running on top of TCP. A TCP segment can contain parts of, or all of, more than one higher-level protocol packet, and a higher-level protocol packet can be composed of data from more than one TCP segment.