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Summary

In a CoAP request which specifies both Accept and Content-Format options, Wireshark confuses the two options.

Steps to reproduce

Send a CoAP packet with Accept and Content-Format options; set to different values.

What is the current bug behavior?

WireShark tries to dissect the packet as if Content-Format = Accept. It then complains when it can't understand the payload.

What is the expected correct behavior?

It should ignore Accept and use Content-Format to decode the payload.

Sample capture file

broken-coap-accept.pcap

Relevant logs and/or screenshots

Frame 1: 93 bytes on wire (744 bits), 93 bytes captured (744 bits)
Raw packet data
Internet Protocol Version 6, Src: fd33:5db7:a637:12:f44c:5240:ee08:4204, Dst: fd9e:e308:e14c:b877::fd
User Datagram Protocol, Src Port: 5683, Dst Port: 61616
Constrained Application Protocol, Confirmable, POST, MID:46922
    01.. .... = Version: 1
    ..00 .... = Type: Confirmable (0)
    .... 1000 = Token Length: 8
    Code: POST (2)
    Message ID: 46922
    Token: 5f962159705078ed
    Opt Name: #1: If-Match: 3b 50 63 53 71 27 24 6c
    Opt Name: #2: Uri-Path: c
    Opt Name: #3: Content-Format: text/plain; charset=utf-8
    Opt Name: #4: Uri-Query: t=cku24xdK
    Opt Name: #5: Accept: application/cbor
    End of options marker: 255
    Payload: Payload Content-Format: application/cbor, Length: 7
Concise Binary Object Representation
[Malformed Packet: CBOR]
    [Expert Info (Error/Malformed): Malformed Packet (Exception occurred)]

Note that:

• Content-Format is text/plain
• Accept is application/cbor

WireShark should not be trying to parse the payload as CBOR because it is plain text!

This has been reported on the mailing list, but to date, no fixes have been forthcoming.

Build information

3.4.7 (Git commit e42cbf6a415f)

Compiled (64-bit) with Qt 5.15.2, with libpcap, with POSIX capabilities (Linux),
with libnl 3, with GLib 2.68.3, with zlib 1.2.11, without SMI, with c-ares
1.17.1, with Lua 5.1.5, with GnuTLS 3.7.2, with Gcrypt 1.8.7, without Kerberos,
without MaxMind DB resolver, without nghttp2, without brotli, without LZ4, with
Zstandard, without Snappy, without libxml2, with QtMultimedia, without automatic
updates, with SpeexDSP (using system library), with Minizip.

Running on Linux 5.13.11-rikishi, with Intel(R) Core(TM) i5-3320M CPU @ 2.60GHz
(with SSE4.2), with 7822 MB of physical memory, with locale en_AU.UTF-8, with
light display mode, without HiDPI, with libpcap version 1.10.1 (with
TPACKET_V3), with GnuTLS 3.7.2, with Gcrypt 1.8.7, with zlib 1.2.11, binary
plugins supported (19 loaded).

Built using gcc 10.3.0.