Wireshark mailing list archives
Re: New dissector: variable length of a fields
From: Guy Harris <guy () alum mit edu>
Date: Sun, 16 Feb 2014 12:14:51 -0800
On Feb 16, 2014, at 2:09 AM, Dmitrij K <kdiman () live ru> wrote:
I have corrected that by: // for sz tvb_memcpy(tvb, (guint8 *)&ldata, offset, 2);
That will either give you the wrong answer on a little-endian machine (such as a 32-bit x86 or x86-64 PC) or on a big-endian machine (such as a PowerPC/MIPS/SPARC-based box under most operating systems). Either the field is: defined as big-endian, in which case you should use tvb_get_ntohs(); defined as little-endian, in which case you should use tvb_get_letohs(); big-endian in some packets and little-endian in others, in which case you need to somehow figure out what the byte order is. It appears, from the other calls you're making, that the field is little-endian.
proto_tree_add_item(my_tree, hf_hdr_sz, tvb, offset, 2, TRUE); offset += 2;
You appear to be using Wireshark 1.10.x (based on the line number in the assertion failure in your earlier message); in 1.10.x, the last argument to proto_tree_add_item() isn't a Boolean, it's an ENC_ value, so that should be proto_tree_add_item(my_tree, hf_hdr_sz, tvb, offset, 2, ENC_LITTLE_ENDIAN); offset += 2;
// for e_flags: proto_tree_add_item(my_tree, hf_hdr_e_flags, tvb, offset, 2, TRUE); offset += 2;
The same applies there: proto_tree_add_item(my_tree, hf_hdr_e_flags, tvb, offset, 2, ENC_LITTLE_ENDIAN); offset += 2;
// for magic3: proto_tree_add_item(my_tree, hf_hdr_magic3, tvb, offset, 1, FALSE); offset += 1;
That's a one-byte numerical field; the ENC_ argument is currently ignored, but the convention is to say proto_tree_add_item(my_tree, hf_hdr_magic3, tvb, offset, 1, ENC_NA); offset += 1; The key fix was replacing "-1" as the length field in the above call with "1", as per my other mail. ___________________________________________________________________________ Sent via: Wireshark-users mailing list <wireshark-users () wireshark org> Archives: http://www.wireshark.org/lists/wireshark-users Unsubscribe: https://wireshark.org/mailman/options/wireshark-users mailto:wireshark-users-request () wireshark org?subject=unsubscribe
Current thread:
- New dissector: variable length of a fields Dmitrij K (Feb 15)
- Re: New dissector: variable length of a fields Guy Harris (Feb 15)
- <Possible follow-ups>
- Re: New dissector: variable length of a fields Dmitrij K (Feb 15)
- Re: New dissector: variable length of a fields Dmitrij K (Feb 16)
- Re: New dissector: variable length of a fields Guy Harris (Feb 16)
- Re: New dissector: variable length of a fields Dmitrij K (Feb 16)
- Re: New dissector: variable length of a fields Dmitrij K (Feb 16)
- Re: New dissector: variable length of a fields Guy Harris (Feb 16)