Decode length-prefixed TCP messages

[GoogleCodeExporter]

It would be great if this worked for TCP streams with messages prefixed by
message length.

Original issue reported on code.google.com by dan%[email protected] on 26 Jul 2009 at 9:33

[GoogleCodeExporter]

I need this too.

-- Ken Sedgwick <[email protected]>

Original comment by [email protected] on 6 Aug 2009 at 4:21

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How does this fit in with the protobuf framework ? Is there a way to define 
these kinds 
of messages in protobuf ? We can add TCP support if needed. 

Original comment by [email protected] on 23 Mar 2010 at 1:10

[GoogleCodeExporter]

I'm using protobuf to frame protobuf over TCP.
As long as you realize that the Message subtype contains the length, that's not 
even 
particularly hard.
The main problem, from a protobuf protocol point of view, is that the type of 
the 
message isn't specified -- there is no good way to specify it within the 
context of 
protobuf, really. Just assume it's a protobuf payload, and decode id:data.
In fact, if the decoder was just recursively applying itself on the protobuf 
TCP 
stream, it would work fine.

Some variants use a byte, short, long or varint prefixed binary-data encoding 
(big- 
and little-endian, too). You could have different flavors for these:

Protobuf-recursive
Protobuf-varintPrefix
Protobuf-shortPrefix-LE
Protobuf-intPrevis-BE
...

Original comment by [email protected] on 4 Jun 2010 at 7:17

[GoogleCodeExporter]

I dont think using message length is a good identifier of message by itself. If 
you are transporting multiple protobuf messages on the same TCP stream what you 
could do is to define a meta message which consists of all the constituent 
protobuf messages as optional fields. That way you can allow protobuf itself to 
do overall decoding instead of having a specific implementation of message 
type. 

Original comment by [email protected] on 22 Jul 2010 at 1:45

[GoogleCodeExporter]

I use the TCP proto as dear.chap described, works very nicely. Does not 
increase the packet size compared to wrapping the message in a special 
meta-packet.

Original comment by [email protected] on 2 Sep 2010 at 2:02

[GoogleCodeExporter]

are there any plans to add TCP support to your plug in?  Thank You

Original comment by [email protected] on 16 Jan 2013 at 3:16

[GoogleCodeExporter]

tcp fixed head len is 4 bytes eg：
#define FRAME_HEADER_LEN 4
1. add get_message_len function: wireshared tcp package include head an body;
/* determine PDU length of protocol protobuf */
static guint get_protobuf_message_len(packet_info *pinfo, tvbuff_t *tvb, int 
offset)
{
    /* TODO: change this to your needs */
    guint ntohl_len = (guint)tvb_get_ntohl(tvb, offset); 
    guint letohl_len = (guint)tvb_get_letohl(tvb,offset);
    guint len = ntohl_len;
    if ( letohl_len < len ){
        len = letohl_len;
        }
    return len+FRAME_HEADER_LEN; /* e.g. length is at offset 0, len is body, 4 is head len, wireshark need total len(head+body)*/
}

2. add .body dissect function 

/* This method dissects fully reassembled messages */
static void dissect_protobuf_message(tvbuff_t *tvb, packet_info *pinfo, 
proto_tree *tree)
{
    /* TODO: implement your dissecting code */\
        if (check_col(pinfo->cinfo, COL_PROTOCOL)) {
                col_set_str(pinfo->cinfo, COL_PROTOCOL, "protobuf-tcp");
            }

            /* Clear out stuff in the info column */
            if(check_col(pinfo->cinfo,COL_INFO)){
                col_clear(pinfo->cinfo,COL_INFO);
            }


            if (tree) { /* we are being asked for details */

              /* Always make sure that offset is LESS than maxOffset */
              gint data_len = tvb_length(tvb) - FRAME_HEADER_LEN;
              proto_item * ti = NULL;
              tvbuff_t * next_tvb = tvb_new_subset_remaining (tvb,FRAME_HEADER_LEN);
              //gint maxOffset = tvb_length(next_tvb);

              ti = proto_tree_add_item(tree,proto_protobuf,tvb,0,4,ENC_NA);
              proto_item_append_text(ti, ", Length %d",data_len);
                  wireshark_pb_process_protobuf((void *) tree, pinfo->srcport, pinfo->destport, hf_protobuf, 
                (void *)next_tvb,  (void *)tvb_get_ptr(tvb,FRAME_HEADER_LEN,data_len), data_len);
            }
}



3. modify dissect_protobuf function:

static void dissect_protobuf(tvbuff_t *tvb, packet_info *pinfo, proto_tree 
*tree)
{
    if( pinfo->tcp_tree == NULL)
    {
        dissect_protobuf_udp(tvb,pinfo,tree);

    }else
    {
        tcp_dissect_pdus(tvb, pinfo, tree, TRUE, FRAME_HEADER_LEN,
                         get_protobuf_message_len, dissect_protobuf_message);
    }
}

Original comment by [email protected] on 19 Apr 2014 at 2:05

[GoogleCodeExporter]

I'm also using TCP as dear.chap is suggesting.

Original comment by [email protected] on 28 Jan 2015 at 5:23