Constrained Resource Identifiers
CoRE Working Group K. Hartke
Intended status: Standards Track 9 March 2020
Expires: 10 September 2020
Constrained Resource Identifiers
The Constrained Resource Identifier (CRI) is a complement to the
Uniform Resource Identifier (URI) that serializes the URI components
in Concise Binary Object Representation (CBOR) instead of a sequence
of characters. This simplifies parsing, comparison and reference
resolution in environments with severe limitations on processing
power, code size, and memory size.
Note to Readers
This note is to be removed before publishing as an RFC.
The issues list for this Internet-Draft can be found at
A reference implementation and a set of test vectors can be found at
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 10 September 2020.
Copyright (c) 2020 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info) in effect on the date of publication of this document.
Please review these documents carefully, as they describe your rights
and restrictions with respect to this document. Code Components
extracted from this document must include Simplified BSD License text
as described in Section 4.e of the Trust Legal Provisions and are
provided without warranty as described in the Simplified BSD License.
Table of Contents
1.1. Notational Conventions
3. Creation and Normalization
5. CRI References
5.1. CBOR Serialization
5.2. Reference Resolution
6. Relationship between CRIs, URIs and IRIs
6.1. Converting CRIs to URIs
7. Security Considerations
8. IANA Considerations
9.1. Normative References
9.2. Informative References
Appendix A. Change Log
The Uniform Resource Identifier (URI) [RFC3986] and its most common
usage, the URI reference, are the Internet standard for linking to
resources in hypertext formats such as HTML [W3C.REC-html52-20171214]
and the HTTP "Link" header field [RFC8288].
A URI reference is a sequence of characters chosen from the
repertoire of US-ASCII characters. The individual components of a
URI reference are delimited by a number of reserved characters, which
necessitates the use of an escape mechanism ("percent-encoding") when
these reserved characters are used in a non-delimiting function. The
resolution of URI references involves parsing a character sequence
into its components, combining those components with the components
of a base URI, merging path components, removing dot-segments, and
recomposing the result back into a character sequence.
Overall, the proper handling of URI references is relatively
intricate. This can be a problem, especially in constrained
environments [RFC7228] where nodes often have severe code size and
memory size limitations. As a result, many implementations in such
environments support only an ad-hoc, informally-specified, bug-
ridden, non-interoperable subset of half of RFC 3986.
This document defines the Constrained Resource Identifier (CRI) by
constraining URIs to a simplified subset and serializing their
components in Concise Binary Object Representation (CBOR)
[RFC7049bis] instead of a sequence of characters. This allows
typical operations on URI references such as parsing, comparison and
reference resolution to be implemented (including all corner cases)
in a comparatively small amount of code.
As a result of simplification, however, CRIs are not capable of
expressing all URIs permitted by the generic syntax of RFC 3986
(hence the "constrained" in "Constrained Resource Identifier"). The
supported subset includes all URIs of the Constrained Application
Show full document text