Constrained Resource Identifiers
CoRE Working Group K. Hartke
Intended status: Standards Track 8 January 2020
Expires: 11 July 2020
Constrained Resource Identifiers
Constrained Resource Identifiers (CoRIs) are an alternate
serialization of Uniform Resource Identifiers (URIs) that encodes the
URI components in Concise Binary Object Representation (CBOR) instead
of a string of characters. This simplifies parsing, reference
resolution, and comparison of URIs 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
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This Internet-Draft will expire on 11 July 2020.
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Table of Contents
1.1. Notational Conventions
2. Data Model
2.2. Option Sequences
4.1. Reference Resolution
4.2. URI Recomposition
4.3. CoAP Encoding
5. Security Considerations
6. IANA Considerations
7.1. Normative References
7.2. Informative References
Appendix A. Change Log
Uniform Resource Identifier (URI) references [RFC3986] are the
standard way to link to resources in hypertext formats such as HTML
[W3C.REC-html52-20171214] or the HTTP "Link" header field [RFC8288].
A URI reference is either a URI or a relative reference that must be
resolved against a base URI.
URI references are strings 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 percent-encoding when these reserved characters are used
in a non-delimiting function. One component can also contain special
dot-segments that affect how the component is to be interpreted. The
resolution of URI references involves parsing the character string
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 string.
Overall, the proper processing of URIs is quite complicated. This
can be a problem in particular in constrained environments [RFC7228],
where devices often have severe code size limitations. As a result,
many implementations in these environments choose to support only an
ad-hoc, informally-specified, bug-ridden, non-interoperable subset of
half of the URI standard.
This document introduces Constrained Resource Identifier (CoRI)
references, an alternate serialization of URI references that encodes
the URI components in Concise Binary Object Representation (CBOR)
[RFC7049] instead of a string of characters. Assuming an
implementation of CBOR is already present on a device, typical
operations on URI references such as parsing, reference resolution,
and comparison can be implemented more easily than for character
strings. A full implementation that covers all corner cases is
intended to be implementable in a relatively small amount of code.
As a result of the simplification, CoRI references are not capable of
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