CoRE Working Group P. van der Stok
Internet-Draft consultant
Intended status: Informational K. Hartke
Expires: August 31, 2017 Universitaet Bremen TZI
February 27, 2017
The 'Pending' Response Code for the Constrained Application Protocol
(CoAP)
draft-hartke-core-pending-00
Abstract
This document proposes a new CoAP response code, 2.06 Pending. A
CoAP server can use this response code to signal that it has accepted
the request but has not yet started processing it or that processing
the request will take longer than a client is typically willing to
wait for a response. A 2.06 response can include status information
and indicate a location where the result will become available.
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on August 31, 2017.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. 2.06 Pending . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Observing Resources . . . . . . . . . . . . . . . . . . . 4
3. Security Considerations . . . . . . . . . . . . . . . . . . . 4
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
5. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
5.1. Normative References . . . . . . . . . . . . . . . . . . 5
5.2. Informative References . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
The Constrained Application Protocol (CoAP) [RFC7252] is a request/
response protocol not unlike HTTP. CoAP defines no upper bound for
the time between a request and the resulting response. E.g., in CoAP
over UDP, a server is expected to return an empty Acknowledgement to
the client if it cannot provide a response right away, but there is
no limit on when the server should return the Separate Response.
In particular in the case of requests with long processing times, a
CoAP client faces the problem that it cannot easily determine how
long it should wait for the response and whether the CoAP server is
even still processing the request. Long processing times occur, for
example, when requests need manual intervention to authorize their
processing, or when they perform a long sequence of remote actions.
An example is provided by the "possibly long" authorization request
specified in EST-coaps [I-D.vanderstok-ace-coap-est].
This document proposes a new CoAP response code, 2.06 Pending. The
semantics of this response code are modelled after the HTTP [RFC7231]
202 (Accepted) status code:
The 202 (Accepted) status code indicates that the request has been
accepted for processing, but the processing has not been
completed. The request might or might not eventually be acted
upon, as it might be disallowed when processing actually takes
place. [...] The representation sent with this response ought to
describe the request's current status and point to (or embed) a
status monitor that can provide the user with an estimate of when
the request will be fulfilled.
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The 2.06 (Pending) response code is not meant for overload cases,
which are better handled by the 5.03 (Service Unavailable) response
code.
1.1. Terminology
Readers are expected to be familiar with the terms and concepts
described in [RFC7252] and [RFC7641].
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
[RFC2119].
2. 2.06 Pending
A 2.06 (Pending) response in reply to a GET request indicates that
the target resource exists but no representation of the resource is
available yet. The Max-Age Option indicates after what time a client
should retry its GET request to retrieve the representation. The
client MAY observe the resource (see Section 2.1) to be notified when
the representation becomes available.
A 2.06 (Pending) response in reply to a POST request indicates that
the result of processing the request is not available yet, for
example, because the server needs more time to process the request
than a client is typically willing to wait for a response. The
server MAY specify a location using the Location-* options where the
result will become available. If the server does not specify a
location, the result will become available at the target resource of
the POST request. To receive the result, the client MAY poll or
observe the resource at the specified location using a GET request.
The Max-Age Option indicates how long the client should wait before
making the GET request.
A 2.06 (Pending) response MAY contain a payload that represents the
progress of processing the original request or any other status
information. The content format of this representation is specified
by the Content-Format Option.
A 2.06 (Pending) response is cacheable, but cannot be validated. If
it contains Location-* options, it invalidates any cached response
for the resource at the specified location; otherwise, it invalidates
any cached response for the target resource of the request.
As a consequence of being cacheable, a 2.06 (Pending) response in
reply to a POST request makes the POST method temporarily idempotent:
until Max-Age expires, any POST request with the same cache-key -- be
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it from the same client or any another client -- can yield the same
2.06 (Pending) response. (This is the same behavior as for 4.xx and
5.xx error responses in reply to POST requests.)
2.1. Observing Resources
When a client registers to observe [RFC7641] a resource for which no
representation is available yet, the server MAY send one or more 2.06
(Pending) notifications before sending the first 2.05 (Content) or
2.03 (Valid) notification. The possible resulting sequence of
notifications is shown in Figure 1.
__________ __________ __________
| | | | | |
---->| 2.06 |---->| 2.05 / |---->| 4.xx / |
| Pending | | 2.03 | | 5.xx |
|__________| |__________| |__________|
^ \ \ ^ \ ^
\__/ \ \___/ /
\_______________________/
Figure 1: Sequence of Notifications
Unless the server is not willing to add the client to the list of
observers, each 2.06 (Pending) notification MUST include an Observe
Option with a sequence number as specified in [RFC7641]. Otherwise,
the registration request falls back to a normal GET request.
3. Security Considerations
This section analyses the possible threats related to 2.06 (Pending)
responses. It is meant to inform protocol and application developers
about the security limitations of the response code as described in
this document.
A 2.06 (Pending) response is subject to the same general security
considerations as all CoAP responses as described in Section 11 of
[RFC7252]. Specifically, the security considerations for the
response code are closest to those of the Observe Option as stated in
Section 7 of [RFC7641], because the server stores additional state
over an extended period.
2.06 (Pending) responses are secured following the recommendations
for the existing CoAP response codes as specified in Section 9 of
[RFC7252]. When additional security techniques are standardized for
CoAP (e.g., based on object security), these are then also available
for securing the responses.
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4. IANA Considerations
This document adds the 2.06 (Pending) response code to the "CoAP
Response Codes" registry.
+------+-------------+-----------+
| Code | Description | Reference |
+------+-------------+-----------+
| 2.06 | Pending | [RFCXXXX] |
+------+-------------+-----------+
Table 1: New CoAP Response Codes
5. References
5.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014,
<http://www.rfc-editor.org/info/rfc7252>.
[RFC7641] Hartke, K., "Observing Resources in the Constrained
Application Protocol (CoAP)", RFC 7641,
DOI 10.17487/RFC7641, September 2015,
<http://www.rfc-editor.org/info/rfc7641>.
5.2. Informative References
[I-D.vanderstok-ace-coap-est]
Kumar, S. and P. Stok, "EST based on DTLS secured CoAP
(EST-coaps)", draft-vanderstok-ace-coap-est-00 (work in
progress), December 2016.
[RFC7231] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Semantics and Content", RFC 7231,
DOI 10.17487/RFC7231, June 2014,
<http://www.rfc-editor.org/info/rfc7231>.
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Authors' Addresses
Peter van der Stok
consultant
Phone: +31-492474673 (Netherlands), +33-966015248 (France)
Email: consultancy@vanderstok.org
URI: www.vanderstok.org
Klaus Hartke
Universitaet Bremen TZI
Postfach 330440
Bremen D-28359
Germany
Phone: +49-421-218-63905
Email: hartke@tzi.org
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