On Sep 27, 2007, at 6:43 PM, Zongjun wrote:
I am using asn1 BER encoding at the sending side.
So does LDAP, and its dissector uses tcp_dissect_pdus().
The LDAP dissector is a bit complicated, as the LDAP packets use SASL
and have an extra non-BER header; however, for non-SASL packets, what
the LDAP dissector does is:
/* check if it is a normal BER encoded LDAP packet
* i.e. first byte is 0x30 followed by a length that is
* <64k
* (no ldap PDUs are ever >64kb? )
*/
if(tvb_get_guint8(tvb, 0)!=0x30){
goto this_was_not_normal_ldap;
}
/* check that length makes sense */
offset=get_ber_length(tvb, 1, &ldap_len, &ind);
/* dont check ind since indefinite length is never used for
ldap (famous last words)*/
if(ldap_len<2){
goto this_was_not_normal_ldap;
}
tcp_dissect_pdus(tvb, pinfo, tree, ldap_desegment, 4,
get_normal_ldap_pdu_len, dissect_normal_ldap_pdu);
where get_normal_ldap_pdu_len() is
static guint
get_normal_ldap_pdu_len(packet_info *pinfo _U_, tvbuff_t *tvb, int
offset)
{
guint32 len;
gboolean ind;
int data_offset;
/* normal ldap is tag+len bytes plus the length
* offset is where the tag is
* offset+1 is where length starts
*/
data_offset=get_ber_length(tvb, offset+1, &len, &ind);
return len+data_offset-offset;
}
and dissect_normal_ldap_pdu() is
static void
dissect_normal_ldap_pdu(tvbuff_t *tvb, packet_info *pinfo, proto_tree
*tree)
{
dissect_ldap_pdu(tvb, pinfo, tree, FALSE);
return;
}
If your protocol uses ASN.1 in such a way that a message is something
that has a standard BER length, that should work for you.
