Subject: [core] #287: Add a quick warning that bytewise scanning for a payload marker is not a good idea

From: "core issue tracker" <[email-masked]>
Date: Sun, 07 Apr 2013 12:13:54 -0000

#287: Add a quick warning that bytewise scanning for a payload marker is not a
good idea

 Michael Scharf (tsv-dir reviewer) notes (msg04191-tsvdir-7):

 Section 3

 * Section 3

 »Following the header, token, and options, if any, comes the optional
 payload.  If present and of non-zero length, it is prefixed by a fixed,
 one-byte Payload Marker (0xFF) which indicates the end of options and the
 start of the payload.  The payload data extends from after the marker to
 the end of the UDP datagram, i.e., the Payload Length is calculated from
 the datagram size.  The absence of the Payload Marker denotes a zero-
 length payload.  The presence of a marker followed by a zero-length
 payload MUST be processed as a message format error.«

 => I think that the term "payload marker" is kind of dangerous; it would
 be better to use a term like "end-of-option option". When I first read
 this section, I wondered whether a CoAP implementation could just scan
 through the packet to find the begin of the payload by the first occence
 of 0xFF after the default CoAP header. However, this would require 0xFF to
 be masked in all options. Masking is realized in Section 3.1, but
 apparently not in Sections 3.2 and Section 5.4.

 Carsten Bormann plans to reply:

 The payload marker is not by itself an option.  Also, it is only present
 if there is payload.  Instead of changing the name, maybe we should add a
 note that byte-wise scanning for 0xFF is not a viable technique for
 finding the payload.

-- 
-------------------------+-------------------------------------------------
 Reporter:               |      Owner:  [email-masked]
  [email-masked]           |     Status:  new
     Type:  editorial    |  Milestone:  post-IESG-1
 Priority:  minor        |    Version:  coap-14
Component:  coap         |   Keywords:
 Severity:  Submitted    |
  WG Document            |
-------------------------+-------------------------------------------------

Ticket URL: <http://trac.tools.ietf.org/wg/core/trac/ticket/287>
core <http://tools.ietf.org/core/>

---

From: "core issue tracker" <[email-masked]>
Date: Fri, 12 Apr 2013 16:26:43 -0000

Changes (by [email-masked]):

 * status:  new => closed
 * resolution:   => fixed

Comment:

 Fixed in [1284]:

 Fix #287

-- 
-------------------------+-------------------------------------------------
 Reporter:               |       Owner:  draft-ietf-core-
  [email-masked]           |  [email-masked]
     Type:  editorial    |      Status:  closed
 Priority:  minor        |   Milestone:  post-IESG-1
Component:  coap         |     Version:  coap-14
 Severity:  Submitted    |  Resolution:  fixed
  WG Document            |
 Keywords:               |
-------------------------+-------------------------------------------------

Ticket URL: </ticket/287#comment:1>
core <http://tools.ietf.org/core/>