Internet DRAFT - draft-hartke-core-pending
draft-hartke-core-pending
CoRE Working Group P. van der Stok
Internet-Draft consultant
Intended status: Informational K. Hartke
Expires: August 30, 2018 Universitaet Bremen TZI
February 26, 2018
"Pending" Responses for the Constrained Application Protocol (CoAP)
draft-hartke-core-pending-02
Abstract
This document proposes a new type of response for the Constrained
Application Protocol (CoAP) called a "Pending" response. A CoAP
server can use a Pending response to indicate that it has accepted a
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.
Status of This Memo
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This Internet-Draft will expire on August 30, 2018.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Pending Responses . . . . . . . . . . . . . . . . . . . . . . 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. For example,
a CoAP-over-UDP 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 the time 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
actually 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 for this is the "possibly long" authorization
request specified in EST-coaps [I-D.vanderstok-ace-coap-est].
This document proposes a new kind of response in CoAP, called a
"Pending" response. The semantics of this response are modelled
after the HTTP 202 (Accepted) status code [RFC7231]:
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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Pending responses are not intended 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. Pending Responses
A Pending response is denoted by a response code in the 2.xx range
and a Content-Format Option that is set to content-format ID TBD1.
A 2.01 (Creation 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 retrieve the result, the client MAY poll or
observe the resource at this location using the GET request method.
A 2.02 (Deletion Pending) response in reply to a DELETE request
indicates that the server has accepted the request but the target has
not been fully deleted yet.
A 2.04 (Change Pending) response in reply to a POST or PUT request
indicates that the server has accepted the request but the result of
processing the request is not available yet.
A 2.05 (Content Pending) response in reply to GET request indicates
that the target resource exists but a representation of the resource
is not 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 [RFC7641] to get notified when
the representation becomes available (see Section 2.1 for details).
The payload of a Pending response MAY be a brief human-readable
diagnostic message, explaining the situation, or MUST be absent.
The cacheability of Pending responses is as specified for the
respective response code.
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2.1. Observing Resources
When a client registers to observe a resource [RFC7641] for which no
representation is available yet, the server MAY send one or more 2.05
(Content Pending) notifications before sending the first actual 2.05
(Content) or 2.03 (Valid) notification. The possible resulting
sequence of notifications is shown in Figure 1.
__________ __________ __________
| | | | | |
---->| 2.05 |---->| 2.05 / |---->| 4.xx / |
| Pending | | 2.03 | | 5.xx |
|__________| |__________| |__________|
^ \ \ ^ \ ^
\__/ \ \___/ /
\_______________________/
Figure 1: Sequence of Notifications
Unless the server is unwilling to add the client to the list of
observers, each 2.05 (Content 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 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 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.
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 content-format used to signal Pending
responses to the "CoAP Content-Formats" registry.
+------------+----------------+------+-----------------+
| Media Type | Content Coding | ID | Reference |
+------------+----------------+------+-----------------+
| - | - | TBD1 | [This Document] |
+------------+----------------+------+-----------------+
New CoAP Content-Formats
TBD1 is taken from the "First Come First Served" range of the "CoAP
Content-Formats" registry.
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,
<https://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,
<https://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,
<https://www.rfc-editor.org/info/rfc7641>.
5.2. Informative References
[I-D.vanderstok-ace-coap-est]
Stok, P., Kampanakis, P., Kumar, S., Richardson, M.,
Furuhed, M., and S. Raza, "EST over secure CoAP (EST-
coaps)", draft-vanderstok-ace-coap-est-04 (work in
progress), January 2018.
[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,
<https://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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