Constrained Resource Identifiers

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Last updated 2020-03-09
Replaces draft-hartke-t2trg-ciri
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CoRE Working Group                                             K. Hartke
Internet-Draft                                                  Ericsson
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

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Table of Contents

   1.  Introduction
     1.1.  Notational Conventions
   2.  Constraints
   3.  Creation and Normalization
   4.  Comparison
   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.  References
     9.1.  Normative References
     9.2.  Informative References
   Appendix A.  Change Log
   Author's Address

1.  Introduction

   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
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