Constrained Resource Identifiers

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Last updated 2020-01-08 (latest revision 2019-11-04)
Replaces draft-hartke-t2trg-ciri
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CoRE Working Group                                             K. Hartke
Internet-Draft                                                  Ericsson
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

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Table of Contents

   1.  Introduction
     1.1.  Notational Conventions
   2.  Data Model
     2.1.  Options
     2.2.  Option Sequences
   3.  CBOR
   4.  Python
     4.1.  Reference Resolution
     4.2.  URI Recomposition
     4.3.  CoAP Encoding
   5.  Security Considerations
   6.  IANA Considerations
   7.  References
     7.1.  Normative References
     7.2.  Informative References
   Appendix A.  Change Log
   Author's Address

1.  Introduction

   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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