--- 1/draft-ietf-core-resource-directory-17.txt 2018-12-20 06:13:14.457935416 -0800 +++ 2/draft-ietf-core-resource-directory-18.txt 2018-12-20 06:13:14.589938598 -0800 @@ -1,54 +1,56 @@ CoRE Z. Shelby Internet-Draft ARM Intended status: Standards Track M. Koster -Expires: April 26, 2019 SmartThings +Expires: June 23, 2019 SmartThings C. Bormann Universitaet Bremen TZI P. van der Stok consultant C. Amsuess, Ed. - October 23, 2018 + December 20, 2018 CoRE Resource Directory - draft-ietf-core-resource-directory-17 + draft-ietf-core-resource-directory-18 Abstract In many M2M applications, direct discovery of resources is not practical due to sleeping nodes, disperse networks, or networks where multicast traffic is inefficient. These problems can be solved by - employing an entity called a Resource Directory (RD), which hosts - registrations of resources held on other servers, allowing lookups to - be performed for those resources. This document specifies the web + employing an entity called a Resource Directory (RD), which contains + information about resources held on other servers, allowing lookups + to be performed for those resources. The input to an RD is composed + of links and the output is composed of links constructed from the + information stored in the RD. This document specifies the web interfaces that a Resource Directory supports for web servers to - discover the RD and to register, maintain, lookup and remove resource - descriptions. Furthermore, new link attributes useful in conjunction - with an RD are defined. + discover the RD and to register, maintain, lookup and remove + information on resources. Furthermore, new target attributes useful + in conjunction with an RD are defined. 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 April 26, 2019. + This Internet-Draft will expire on June 23, 2019. Copyright Notice Copyright (c) 2018 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 @@ -59,128 +61,126 @@ described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Architecture and Use Cases . . . . . . . . . . . . . . . . . 6 3.1. Principles . . . . . . . . . . . . . . . . . . . . . . . 6 3.2. Architecture . . . . . . . . . . . . . . . . . . . . . . 7 3.3. RD Content Model . . . . . . . . . . . . . . . . . . . . 8 - 3.4. Use Case: Cellular M2M . . . . . . . . . . . . . . . . . 12 - 3.5. Use Case: Home and Building Automation . . . . . . . . . 13 - 3.6. Use Case: Link Catalogues . . . . . . . . . . . . . . . . 13 + 3.4. Link-local addresses . . . . . . . . . . . . . . . . . . 12 + 3.5. Use Case: Cellular M2M . . . . . . . . . . . . . . . . . 12 + 3.6. Use Case: Home and Building Automation . . . . . . . . . 13 + 3.7. Use Case: Link Catalogues . . . . . . . . . . . . . . . . 13 4. Finding a Resource Directory . . . . . . . . . . . . . . . . 14 - 4.1. Resource Directory Address Option (RDAO) . . . . . . . . 15 + 4.1. Resource Directory Address Option (RDAO) . . . . . . . . 16 5. Resource Directory . . . . . . . . . . . . . . . . . . . . . 17 - 5.1. Payload Content Formats . . . . . . . . . . . . . . . . . 17 - 5.2. URI Discovery . . . . . . . . . . . . . . . . . . . . . . 17 - 5.3. Registration . . . . . . . . . . . . . . . . . . . . . . 20 + 5.1. Payload Content Formats . . . . . . . . . . . . . . . . . 18 + 5.2. URI Discovery . . . . . . . . . . . . . . . . . . . . . . 18 + 5.3. Registration . . . . . . . . . . . . . . . . . . . . . . 21 5.3.1. Simple Registration . . . . . . . . . . . . . . . . . 25 - 5.3.2. Third-party registration . . . . . . . . . . . . . . 27 - 5.3.3. RD-Groups . . . . . . . . . . . . . . . . . . . . . . 28 - 6. RD Lookup . . . . . . . . . . . . . . . . . . . . . . . . . . 29 - 6.1. Resource lookup . . . . . . . . . . . . . . . . . . . . . 29 - 6.2. Lookup filtering . . . . . . . . . . . . . . . . . . . . 30 - 6.3. Resource lookup examples . . . . . . . . . . . . . . . . 32 - 7. Security policies . . . . . . . . . . . . . . . . . . . . . . 35 - 7.1. Secure RD discovery . . . . . . . . . . . . . . . . . . . 36 - 7.2. Secure RD filtering . . . . . . . . . . . . . . . . . . . 37 - 7.3. Secure endpoint Name assignment . . . . . . . . . . . . . 37 - 8. Security Considerations . . . . . . . . . . . . . . . . . . . 37 - 8.1. Endpoint Identification and Authentication . . . . . . . 38 - 8.2. Access Control . . . . . . . . . . . . . . . . . . . . . 38 - 8.3. Denial of Service Attacks . . . . . . . . . . . . . . . . 38 - 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 39 - 9.1. Resource Types . . . . . . . . . . . . . . . . . . . . . 39 - 9.2. IPv6 ND Resource Directory Address Option . . . . . . . . 39 - 9.3. RD Parameter Registry . . . . . . . . . . . . . . . . . . 39 + 5.3.2. Third-party registration . . . . . . . . . . . . . . 28 + 5.4. Operations on the Registration Resource . . . . . . . . . 28 + 5.4.1. Registration Update . . . . . . . . . . . . . . . . . 29 + 5.4.2. Registration Removal . . . . . . . . . . . . . . . . 32 + 5.4.3. Further operations . . . . . . . . . . . . . . . . . 33 + 6. RD Lookup . . . . . . . . . . . . . . . . . . . . . . . . . . 33 + 6.1. Resource lookup . . . . . . . . . . . . . . . . . . . . . 34 + 6.2. Lookup filtering . . . . . . . . . . . . . . . . . . . . 34 + 6.3. Resource lookup examples . . . . . . . . . . . . . . . . 36 + 6.4. Endpoint lookup . . . . . . . . . . . . . . . . . . . . . 39 + 7. Security policies . . . . . . . . . . . . . . . . . . . . . . 40 + 7.1. Secure RD discovery . . . . . . . . . . . . . . . . . . . 41 + 7.2. Secure RD filtering . . . . . . . . . . . . . . . . . . . 41 + 7.3. Secure endpoint Name assignment . . . . . . . . . . . . . 42 + + 8. Security Considerations . . . . . . . . . . . . . . . . . . . 42 + 8.1. Endpoint Identification and Authentication . . . . . . . 42 + 8.2. Access Control . . . . . . . . . . . . . . . . . . . . . 43 + 8.3. Denial of Service Attacks . . . . . . . . . . . . . . . . 43 + 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 43 + 9.1. Resource Types . . . . . . . . . . . . . . . . . . . . . 43 + 9.2. IPv6 ND Resource Directory Address Option . . . . . . . . 44 + 9.3. RD Parameter Registry . . . . . . . . . . . . . . . . . . 44 9.3.1. Full description of the "Endpoint Type" Registration - Parameter . . . . . . . . . . . . . . . . . . . . . . 42 - 9.4. "Endpoint Type" (et=) RD Parameter values . . . . . . . . 42 - 9.5. Multicast Address Registration . . . . . . . . . . . . . 43 - 10. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 43 - 10.1. Lighting Installation . . . . . . . . . . . . . . . . . 43 - 10.1.1. Installation Characteristics . . . . . . . . . . . . 43 - 10.1.2. RD entries . . . . . . . . . . . . . . . . . . . . . 44 - 10.2. OMA Lightweight M2M (LWM2M) Example . . . . . . . . . . 47 - 10.2.1. The LWM2M Object Model . . . . . . . . . . . . . . . 48 - 10.2.2. LWM2M Register Endpoint . . . . . . . . . . . . . . 49 - 10.2.3. LWM2M Update Endpoint Registration . . . . . . . . . 51 - 10.2.4. LWM2M De-Register Endpoint . . . . . . . . . . . . . 51 - 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 51 - 12. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 51 - 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 58 - 13.1. Normative References . . . . . . . . . . . . . . . . . . 58 - 13.2. Informative References . . . . . . . . . . . . . . . . . 59 - Appendix A. Registration Management . . . . . . . . . . . . . . 61 - A.1. Registration Update . . . . . . . . . . . . . . . . . . . 62 - A.2. Registration Removal . . . . . . . . . . . . . . . . . . 65 - A.3. Read Endpoint Links . . . . . . . . . . . . . . . . . . . 66 - A.4. Update Endpoint Links . . . . . . . . . . . . . . . . . . 67 - A.5. Endpoint lookup . . . . . . . . . . . . . . . . . . . . . 67 + Parameter . . . . . . . . . . . . . . . . . . . . . . 46 + 9.4. "Endpoint Type" (et=) RD Parameter values . . . . . . . . 46 + 9.5. Multicast Address Registration . . . . . . . . . . . . . 47 + 10. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 47 + 10.1. Lighting Installation . . . . . . . . . . . . . . . . . 47 + 10.1.1. Installation Characteristics . . . . . . . . . . . . 47 + 10.1.2. RD entries . . . . . . . . . . . . . . . . . . . . . 49 + 10.2. OMA Lightweight M2M (LWM2M) Example . . . . . . . . . . 51 + 10.2.1. The LWM2M Object Model . . . . . . . . . . . . . . . 52 + 10.2.2. LWM2M Register Endpoint . . . . . . . . . . . . . . 53 + 10.2.3. LWM2M Update Endpoint Registration . . . . . . . . . 55 + 10.2.4. LWM2M De-Register Endpoint . . . . . . . . . . . . . 55 + 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 55 + 12. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 55 + 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 63 + 13.1. Normative References . . . . . . . . . . . . . . . . . . 63 + 13.2. Informative References . . . . . . . . . . . . . . . . . 64 + Appendix A. Groups Registration and Lookup . . . . . . . . . . . 66 Appendix B. Web links and the Resource Directory . . . . . . . . 68 B.1. A simple example . . . . . . . . . . . . . . . . . . . . 68 - B.1.1. Resolving the URIs . . . . . . . . . . . . . . . . . 69 + B.1.1. Resolving the URIs . . . . . . . . . . . . . . . . . 68 B.1.2. Interpreting attributes and relations . . . . . . . . 69 B.2. A slightly more complex example . . . . . . . . . . . . . 69 B.3. Enter the Resource Directory . . . . . . . . . . . . . . 70 B.4. A note on differences between link-format and Link - headers . . . . . . . . . . . . . . . . . . . . . . . . . 72 - Appendix C. Syntax examples for Protocol Negotiation . . . . . . 73 - Appendix D. Modernized Link Format parsing . . . . . . . . . . . 74 - D.1. For endpoint developers . . . . . . . . . . . . . . . . . 74 - D.2. Examples of links with differing interpretations . . . . 75 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 75 + headers . . . . . . . . . . . . . . . . . . . . . . . . . 71 + Appendix C. Limited Link Format . . . . . . . . . . . . . . . . 72 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 73 1. Introduction The work on Constrained RESTful Environments (CoRE) aims at realizing the REST architecture in a suitable form for the most constrained nodes (e.g., 8-bit microcontrollers with limited RAM and ROM) and networks (e.g. 6LoWPAN). CoRE is aimed at machine-to-machine (M2M) applications such as smart energy and building automation. The discovery of resources offered by a constrained server is very important in machine-to-machine applications where there are no humans in the loop and static interfaces result in fragility. The discovery of resources provided by an HTTP Web Server is typically - called Web Linking [RFC5988]. The use of Web Linking for the + called Web Linking [RFC8288]. The use of Web Linking for the description and discovery of resources hosted by constrained web servers is specified by the CoRE Link Format [RFC6690]. However, [RFC6690] only describes how to discover resources from the web server that hosts them by querying "/.well-known/core". In many M2M scenarios, direct discovery of resources is not practical due to sleeping nodes, disperse networks, or networks where multicast traffic is inefficient. These problems can be solved by employing an - entity called a Resource Directory (RD), which hosts registrations of - resources held on other servers, allowing lookups to be performed for - those resources. + entity called a Resource Directory (RD), which contains information + about resources held on other servers, allowing lookups to be + performed for those resources. This document specifies the web interfaces that a Resource Directory supports for web servers to discover the RD and to register, - maintain, lookup and remove resource descriptions. Furthermore, new - link attributes useful in conjunction with a Resource Directory are - defined. Although the examples in this document show the use of + maintain, lookup and remove information on resources. Furthermore, + new target attributes useful in conjunction with a Resource Directory + are defined. Although the examples in this document show the use of these interfaces with CoAP [RFC7252], they can be applied in an equivalent manner to HTTP [RFC7230]. 2. Terminology 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]. The term "byte" is used in its now customary sense as a synonym for "octet". This specification requires readers to be familiar with all the terms - and concepts that are discussed in [RFC3986], [RFC5988] and + and concepts that are discussed in [RFC3986], [RFC8288] and [RFC6690]. Readers should also be familiar with the terms and concepts discussed in [RFC7252]. To describe the REST interfaces defined in this specification, the URI Template format is used [RFC6570]. This specification makes use of the following additional terminology: resolve against The expression "a URI-reference is _resolved against_ a base URI" is used to describe the process of [RFC3986] Section 5.2. @@ -249,127 +249,114 @@ needs of the applications. Registrant-ep Registrant-ep is the endpoint that is registered into the RD. The registrant-ep can register itself, or a CT registers the registrant-ep. RDAO Resource Directory Address Option. - For several operations, interface descriptions are given in list - form; those describe the operation participants, request codes, URIs, - content formats and outcomes. Those templates contain normative - content in their Interaction, Method, URI Template and URI Template - Variables sections as well as the details of the Success condition. + For several operations, interface templates are given in list form; + those describe the operation participants, request codes, URIs, + content formats and outcomes. Sections of those templates contain + normative content about Interaction, Method, URI Template and URI + Template Variables as well as the details of the Success condition. The additional sections on options like Content-Format and on Failure codes give typical cases that an implementation of the RD should deal with. Those serve to illustrate the typical responses to readers who are not yet familiar with all the details of CoAP based interfaces; they do not limit what a server may respond under atypical circumstances. 3. Architecture and Use Cases 3.1. Principles The Resource Directory is primarily a tool to make discovery operations more efficient than querying /.well-known/core on all connected devices, or across boundaries that would be limiting those operations. - It provides a cache (in the high-level sense, not as defined in - [RFC7252]/[RFC2616]) of data that could otherwise only be obtained by - directly querying the /.well-known/core resource on the target - device, or by accessing those resources with a multicast request. + It provides information about resources hosted by other devices that + could otherwise only be obtained by directly querying the /.well- + known/core resource on these other devices, either by a unicast + request or a multicast request. - Only information SHOULD be stored in the resource directory that is - discoverable from querying the described device's /.well-known/core + Only information SHOULD be stored in the resource directory that can + be obtained by querying the described device's /.well-known/core resource directly. Data in the resource directory can only be provided by the device which hosts those data or a dedicated Commissioning Tool (CT). These CTs are thought to act on behalf of endpoints too constrained, or generally unable, to present that information themselves. No other - client can modify data in the resource directory. Changes in the - Resource Directory do not propagate automatically back to the web - server from where the links originated. + client can modify data in the resource directory. Changes to the + information in the Resource Directory do not propagate automatically + back to the web servers from where the information originated. 3.2. Architecture The resource directory architecture is illustrated in Figure 1. A - Resource Directory (RD) is used as a repository for Web Links - [RFC5988] describing resources hosted on other web servers, also - called endpoints (EP). An endpoint is a web server associated with a + Resource Directory (RD) is used as a repository of registrations + describing resources hosted on other web servers, also called + endpoints (EP). An endpoint is a web server associated with a scheme, IP address and port. A physical node may host one or more endpoints. The RD implements a set of REST interfaces for endpoints - to register and maintain sets of Web Links (called resource directory - registration entries), and for endpoints to lookup resources from the - RD. An RD can be logically segmented by the use of Sectors. This - information hierarchy is shown in Figure 2. + to register and maintain resource directory registrations, and for + endpoints to lookup resources from the RD. An RD can be logically + segmented by the use of Sectors. A mechanism to discover an RD using CoRE Link Format [RFC6690] is defined. - Registration entries in the RD are soft state and need to be - periodically refreshed. + Registrations in the RD are soft state and need to be periodically + refreshed. An endpoint uses specific interfaces to register, update and remove a - resource directory registration entry. It is also possible for an RD - to fetch Web Links from endpoints and add them as resource directory - registration entries. + registration. It is also possible for an RD to fetch Web Links from + endpoints and add their contents to resource directory registrations. - At the first registration of a set of entries, a "registration - resource" is created, the location of which is returned to the - registering endpoint. The registering endpoint uses this - registration resource to manage the contents of registration entries. + At the first registration of an endpoint, a "registration resource" + is created, the location of which is returned to the registering + endpoint. The registering endpoint uses this registration resource + to manage the contents of registrations. - A lookup interface for discovering any of the Web Links held in the + A lookup interface for discovering any of the Web Links stored in the RD is provided using the CoRE Link Format. Registration Lookup Interface Interface +----+ | | | EP |---- | | +----+ ---- | | --|- +------+ | +----+ | ----| | | +--------+ | EP | ---------|-----| RD |----|-----| Client | +----+ | ----| | | +--------+ --|- +------+ | +----+ ---- | | | EP |---- | | +----+ Figure 1: The resource directory architecture. - +------------+ - | Endpoint | <-- Name, Scheme, IP, Port - +------------+ - | - | - +------------+ - | Resource | <-- Target, Parameters - +------------+ - - Figure 2: The resource directory information hierarchy. - A Registrant-EP MAY keep concurrent registrations to more than one RD at the same time if explicitly configured to do so, but that is not expected to be supported by typical EP implementations. Any such registrations are independent of each other. The usual expectation when multiple discovery mechanisms or addresses are configured is - that they constitute a fallback path for a single registration. + that they constitute a fall-back path for a single registration. 3.3. RD Content Model - The Entity-Relationship (ER) models shown in Figure 3 and Figure 4 + The Entity-Relationship (ER) models shown in Figure 2 and Figure 3 model the contents of /.well-known/core and the resource directory respectively, with entity-relationship diagrams [ER]. Entities (rectangles) are used for concepts that exist independently. Attributes (ovals) are used for concepts that exist only in connection with a related entity. Relations (diamonds) give a semantic meaning to the relation between entities. Numbers specify the cardinality of the relations. Some of the attribute values are URIs. Those values are always full URIs and never relative references in the information model. They @@ -402,34 +389,35 @@ oooooooooooo 0+ | o target o--------+ o attribute o | 0+ oooooo oooooooooooo +-----o rel o | oooooo | | 1 ooooooooo +-----o context o ooooooooo - Figure 3: E-R Model of the content of /.well-known/core + Figure 2: E-R Model of the content of /.well-known/core - The model shown in Figure 3 models the contents of /.well-known/core + The model shown in Figure 2 models the contents of /.well-known/core which contains: o a set of links belonging to the hosting web server + The web server is free to choose links it deems appropriate to be exposed in its ".well-known/core". Typically, the links describe resources that are served by the host, but the set can also contain links to resources on other servers (see examples in [RFC6690] page 14). The set does not necessarily contain links to all resources served by the host. - A link has the following attributes (see [RFC5988]): + A link has the following attributes (see [RFC8288]): o Zero or more link relations: They describe relations between the link context and the link target. In link-format serialization, they are expressed as space- separated values in the "rel" attribute, and default to "hosts". o A link context URI: It defines the source of the relation, e.g. _who_ "hosts" something. @@ -481,26 +469,26 @@ o lt o----+ ooooooooooo 0+ | oooooooo | o target o-----+ | o attribute o | 0+ oooooo ooooooooooo 0+ | ooooooooooo +-----o rel o o endpoint o----+ | oooooo o attribute o | ooooooooooo | 1 ooooooooo +----o context o ooooooooo - Figure 4: E-R Model of the content of the Resource Directory + Figure 3: E-R Model of the content of the Resource Directory - The model shown in Figure 4 models the contents of the resource + The model shown in Figure 3 models the contents of the resource directory which contains in addition to /.well-known/core: - o 0 to n Registration (entries) of endpoints, + o 0 to n Registrations of endpoints, A registration is associated with one endpoint. A registration defines a set of links as defined for /.well-known/core. A Registration has six types of attributes: o a unique endpoint name ("ep") within a sector o a Registration Base URI ("base", a URI typically describing the scheme://authority part) o a lifetime ("lt"), @@ -510,23 +498,35 @@ o optionally a sector ("d") o optional additional endpoint attributes (from Section 9.3) The cardinality of "base" is currently 1; future documents are invited to extend the RD specification to support multiple values (e.g. [I-D.silverajan-core-coap-protocol-negotiation]). Its value is used as a Base URI when resolving URIs in the links contained in the endpoint. - Links are modelled as they are in Figure 3. + Links are modelled as they are in Figure 2. -3.4. Use Case: Cellular M2M +3.4. Link-local addresses + + Registration requests to the RD may arrive from link-local IP + addresses. When building a Registration Base URI from that source IP + address (which would become part of the resolved URIs in resource + lookup), its link-local IP literal typically contains a zone + identifier of the RD, and is not usable across hosts (see [RFC6874] + Section 1). + + Therefore, RD servers SHOULD reject registrations which use of URIs + containing link-local IP addresses. + +3.5. Use Case: Cellular M2M Over the last few years, mobile operators around the world have focused on development of M2M solutions in order to expand the business to the new type of users: machines. The machines are connected directly to a mobile network using an appropriate embedded wireless interface (GSM/GPRS, WCDMA, LTE) or via a gateway providing short and wide range wireless interfaces. From the system design point of view, the ambition is to design horizontal solutions that can enable utilization of machines in different applications depending on their current availability and capabilities as well as @@ -550,32 +549,32 @@ access to the endpoints. Mobile apps or web applications for environment monitoring contact the RD, look up the endpoints capable of providing information about the environment using an appropriate set of link parameters, obtain information on how to contact them (URLs of the proxy server), and then initiate interaction to obtain information that is finally processed, displayed on the screen and usually stored in a database. Similarly, fleet management systems provide the appropriate link parameters to the RD to look up for EPs deployed on the vehicles the application is responsible for. -3.5. Use Case: Home and Building Automation +3.6. Use Case: Home and Building Automation Home and commercial building automation systems can benefit from the use of M2M web services. The discovery requirements of these applications are demanding. Home automation usually relies on run- time discovery to commission the system, whereas in building automation a combination of professional commissioning and run-time discovery is used. Both home and building automation involve peer- to-peer interactions between endpoints, and involve battery-powered sleeping devices. -3.6. Use Case: Link Catalogues +3.7. Use Case: Link Catalogues Resources may be shared through data brokers that have no knowledge beforehand of who is going to consume the data. Resource Directory can be used to hold links about resources and services hosted anywhere to make them discoverable by a general class of applications. For example, environmental and weather sensors that generate data for public consumption may provide data to an intermediary server, or broker. Sensor data are published to the intermediary upon changes @@ -654,20 +652,25 @@ resource directory (using the ABRO option to find that [RFC6775]). Confirmation can be obtained by sending a Unicast to "coap://[6LBR]/.well-known/core?rt=core.rd*". 2. In a network that supports multicast well, discovering the RD using a multicast query for /.well-known/core as specified in CoRE Link Format [RFC6690]: Sending a Multicast GET to "coap://[MCD1]/.well-known/core?rt=core.rd*". RDs within the multicast scope will answer the query. + When answering a link-local multicast request, the RD SHOULD NOT + respond with their link-local addresses but use a routable one; + otherwise the registrant-ep would later need to pick an explicit base + address to avoid the issue of Section 3.4. + As some of the RD addresses obtained by the methods listed here are just (more or less educated) guesses, endpoints MUST make use of any error messages to very strictly rate-limit requests to candidate IP addresses that don't work out. For example, an ICMP Destination Unreachable message (and, in particular, the port unreachable code for this message) may indicate the lack of a CoAP server on the candidate host, or a CoAP error response code such as 4.05 "Method Not Allowed" may indicate unwillingness of a CoAP server to act as a directory server. @@ -722,30 +725,31 @@ A value of all zero bits (0x0) indicates that this Resource Directory address is not valid anymore. Reserved: This field is unused. It MUST be initialized to zero by the sender and MUST be ignored by the receiver. RD Address: IPv6 address of the RD. - Figure 5: Resource Directory Address Option + Figure 4: Resource Directory Address Option 5. Resource Directory This section defines the required set of REST interfaces between a Resource Directory (RD) and endpoints. Although the examples throughout this section assume the use of CoAP [RFC7252], these REST interfaces can also be realized using HTTP [RFC7230]. In all definitions in this section, both CoAP response codes (with dot notation) and HTTP response codes (without dot notation) are shown. + An RD implementing this specification MUST support the discovery, registration, update, lookup, and removal interfaces defined in this section. All operations on the contents of the Resource Directory MUST be atomic and idempotent. A resource directory MAY make the information submitted to it available to further directories, if it can ensure that a loop does not form. The protocol used between directories to ensure loop-free @@ -753,46 +757,48 @@ 5.1. Payload Content Formats Resource Directory implementations using this specification MUST support the application/link-format content format (ct=40). Resource Directories implementing this specification MAY support additional content formats. Any additional content format supported by a Resource Directory - implementing this specification MUST have an equivalent serialization - in the application/link-format content format. + implementing this specification SHOULD be able to express all the + information expressible in link-format. It MAY be able to express + information that is inexpressible in link-format, but those + expressions SHOULD be avoided where possible. 5.2. URI Discovery Before an endpoint can make use of an RD, it must first know the RD's address and port, and the URI path information for its REST APIs. This section defines discovery of the RD and its URIs using the well- known interface of the CoRE Link Format [RFC6690]. A complete set of RD discovery methods is described in Section 4. Discovery of the RD registration URI path is performed by sending either a multicast or unicast GET request to "/.well-known/core" and including a Resource Type (rt) parameter [RFC6690] with the value "core.rd" in the query string. Likewise, a Resource Type parameter value of "core.rd-lookup*" is used to discover the URIs for RD Lookup operations, core.rd* is used to discover all URI paths for RD operations. Upon success, the response will contain a payload with a link format entry for each RD function discovered, indicating the URI of the RD function returned and the corresponding Resource Type. When performing multicast discovery, the multicast IP address used will depend on the scope required and the multicast capabilities of - the network (see Section 9.5. + the network (see Section 9.5). A Resource Directory MAY provide hints about the content-formats it - supports in the links it exposes or registers, using the "ct" link + supports in the links it exposes or registers, using the "ct" target attribute, as shown in the example below. Clients MAY use these hints to select alternate content-formats for interaction with the Resource Directory. HTTP does not support multicast and consequently only unicast discovery can be supported using HTTP. The well-known entry points SHOULD be provided to enable unicast discovery. An implementation of this resource directory specification MUST support query filtering for the rt parameter as defined in [RFC6690]. @@ -816,31 +822,28 @@ Method: GET URI Template: /.well-known/core{?rt} URI Template Variables: rt := Resource Type. SHOULD contain one of the values "core.rd", "core.rd-lookup*", "core.rd-lookup-res", "core.rd-lookup-ep", or "core.rd*" - Content-Format: application/link-format (if any) - - Content-Format: application/link-format+json (if any) - Content-Format: application/link-format+cbor (if any) + Accept: absent, application/link-format or any other media type + representing web links The following response codes are defined for this interface: - Success: 2.05 "Content" or 200 "OK" with an application/link-format, - application/link-format+json, or application/link-format+cbor - payload containing one or more matching entries for the RD - resource. + Success: 2.05 "Content" or 200 "OK" with an application/link-format + or other web link payload containing one or more matching entries + for the RD resource. Failure: 4.00 "Bad Request" or 400 "Bad Request" is returned in case of a malformed request for a unicast request. Failure: No error response to a multicast request. HTTP support : YES (Unicast only) The following example shows an endpoint discovering an RD using this interface, thus learning that the directory resource location, in @@ -848,39 +851,38 @@ server hosting the resource is application/link-format (ct=40). Note that it is up to the RD to choose its RD locations. Req: GET coap://[MCD1]/.well-known/core?rt=core.rd* Res: 2.05 Content ;rt="core.rd";ct=40, ;rt="core.rd-lookup-ep";ct=40, ;rt="core.rd-lookup-res";ct=40, - Figure 6: Example discovery exchange + Figure 5: Example discovery exchange The following example shows the way of indicating that a client may request alternate content-formats. The Content-Format code attribute "ct" MAY include a space-separated sequence of Content-Format codes as specified in Section 7.2.1 of [RFC7252], indicating that multiple content-formats are available. The example below shows the required - Content-Format 40 (application/link-format) indicated as well as the - CBOR and JSON representation of link format. The RD resource - locations /rd, and /rd-lookup are example values. The server in this - example also indicates that it is capable of providing observation on - resource lookups. + Content-Format 40 (application/link-format) indicated as well as a + CBOR and JSON representation from [I-D.ietf-core-links-json] (which + have no numeric values assigned yet, so they are shown as TBD64 and + TBD504 as in that draft). The RD resource locations /rd, and /rd- + lookup are example values. The server in this example also indicates + that it is capable of providing observation on resource lookups. + + [ The RFC editor is asked to replace this and later occurrences of + MCD1 with the assigned IPv6 site-local address for "all CoRE Resource + Directories". ] - [ The RFC editor is asked to replace these and later occurrences of - MCD1, TBD64 and TBD504 with the assigned IPv6 site-local address for - "all CoRE Resource Directories" and the numeric ID values assigned by - IANA to application/link-format+cbor and application/link- - format+json, respectively, as they are defined in I-D.ietf-core- - links-json. ] Req: GET coap://[MCD1]/.well-known/core?rt=core.rd* Res: 2.05 Content ;rt="core.rd";ct="40 65225", ;rt="core.rd-lookup-res";ct="40 TBD64 TBD504";obs, ;rt="core.rd-lookup-ep";ct="40 TBD64 TBD504", From a management and maintenance perspective, it is necessary to identify the components that constitute the RD server. The identification refers to information about for example client-server @@ -902,89 +904,81 @@ (as in this example) or at individual RD components. The latter is to be expected when different applications are run on the same server. 5.3. Registration After discovering the location of an RD, a registrant-ep or CT MAY register the resources of the registrant-ep using the registration interface. This interface accepts a POST from an endpoint containing the list of resources to be added to the directory as the message - payload in the CoRE Link Format [RFC6690], JSON CoRE Link Format - (application/link-format+json), or CBOR CoRE Link Format - (application/link-format+cbor) [I-D.ietf-core-links-json], along with - query parameters indicating the name of the endpoint, and optionally - the sector, lifetime and base URI of the registration. It is - expected that other specifications will define further parameters - (see Section 9.3). The RD then creates a new registration resource - in the RD and returns its location. The receiving endpoint MUST use - that location when refreshing registrations using this interface. - Registration resources in the RD are kept active for the period - indicated by the lifetime parameter. The creating endpoint is - responsible for refreshing the registration resource within this - period using either the registration or update interface. The - registration interface MUST be implemented to be idempotent, so that - registering twice with the same endpoint parameters ep and d (sector) - does not create multiple registration resources. - - The following rules apply for an update identified by a given (ep, d) - value pair: + payload in the CoRE Link Format [RFC6690] or other representations of + web links, along with query parameters indicating the name of the + endpoint, and optionally the sector, lifetime and base URI of the + registration. It is expected that other specifications will define + further parameters (see Section 9.3). The RD then creates a new + registration resource in the RD and returns its location. The + receiving endpoint MUST use that location when refreshing + registrations using this interface. Registration resources in the RD + are kept active for the period indicated by the lifetime parameter. + The creating endpoint is responsible for refreshing the registration + resource within this period using either the registration or update + interface. The registration interface MUST be implemented to be + idempotent, so that registering twice with the same endpoint + parameters ep and d (sector) does not create multiple registration + resources. - o when the parameter values of the Update generate the same - attribute values as already present, the location of the already - existing registration is returned. + The following rules apply for a registration request targeting a + given (ep, d) value pair: - o when for a given (ep, d) value pair the update generates attribute - values which are different from the existing one, the existing - registration is removed and a new registration with a new location - is created. + o When the (ep, d) value pair of the registration-request is + different from any existing registration, a new registration is + generated. - o when the (ep, d) value pair of the update is different from any - existing registration, a new registration is generated. + o When the (ep, d) value pair of the registration-request is equal + to an existing registration, the content and parameters of the + existing registration are replaced with the content of the + registration request. The posted link-format document can (and typically does) contain relative references both in its link targets and in its anchors, or contain empty anchors. The RD server needs to resolve these references in order to faithfully represent them in lookups. They are resolved against the base URI of the registration, which is provided either explicitly in the "base" parameter or constructed implicitly from the requester's URI as constructed from its network address and scheme. - Link format documents submitted to the resource directory are - interpreted as Modernized Link Format (see Appendix D) by the RD. A - registrant-ep SHOULD NOT submit documents whose interpretations - according to [RFC6690] and Appendix D differ to avoid the ambiguities - described in Appendix B.4. - - In practice, most links (precisely listed in Appendix D.1) can be - submitted without consideration for those details. + For media types to which Appendix C applies (i.e. documents in + application/link-format), the RD only needs to accept representations + in Limited Link Format as described there. Its behavior with + representations outside that subset is implementation defined. The registration request interface is specified as follows: Interaction: EP -> RD Method: POST URI Template: {+rd}{?ep,d,lt,base,extra-attrs*} URI Template Variables: rd := RD registration URI (mandatory). This is the location of the RD, as obtained from discovery. ep := Endpoint name (mostly mandatory). The endpoint name is an identifier that MUST be unique within a sector. The maximum length of this parameter is 63 bytes. If the RD is configured to recognize the endpoint (e.g. based on its security context), - the endpoint sets no endpoint name, and the RD assigns one - based on a set of configuration parameter values. + the RD assigns an endpoint name based on a set of configuration + parameter values. d := Sector (optional). The sector to which this endpoint belongs. The maximum length of this parameter is 63 bytes. When this parameter is not present, the RD MAY associate the endpoint with a configured default sector or leave it empty. The endpoint name and sector name are not set when one or both are set in an accompanying authorization token. lt := Lifetime (optional). Lifetime of the registration in seconds. Range of 60-4294967295. If no lifetime is included @@ -997,61 +991,61 @@ have a path component of its own, and MUST be suitable as a base URI to resolve any relative references given in the registration. The parameter is therefore usually of the shape "scheme://authority" for HTTP and CoAP URIs. The URI SHOULD NOT have a query or fragment component as any non-empty relative part in a reference would remove those parts from the resulting URI. In the absence of this parameter the scheme of the protocol, source address and source port of the registration request are - assumed. That Base URI is constructed by concatenating the - used protcol's scheme with the characters "://", the - requester's source address as an address literal and ":" - followed by its port (if it was not the protocol's default one) - in analogy to [RFC7252] Section 6.5. + assumed. The Base URI is consecutively constructed by + concatenating the used protocol's scheme with the characters + "://", the requester's source address as an address literal and + ":" followed by its port (if it was not the protocol's default + one) in analogy to [RFC7252] Section 6.5. This parameter is mandatory when the directory is filled by a third party such as an commissioning tool. If the registrant-ep uses an ephemeral port to register with, it MUST include the base parameter in the registration to provide a valid network path. If the registrant-ep, located behind a NAT gateway, is registering with a Resource Directory which is on the network service side of the NAT gateway, the endpoint MUST use a persistent port for the outgoing registration in order to provide the NAT gateway with a valid network address for replies and incoming requests. + If the registrant-ep uses a link-local address to register, it + MUST give an explicit routable base address unless configured + otherwise as per Section 3.4 (or just register from that + address in the first place). + Endpoints that register with a base that contains a path component can not meaningfully use [RFC6690] Link Format due to its prevalence of the Origin concept in relative reference - resolution; they can submit payloads for interpretation as - Modernized Link Format. Typically, links submitted by such an - endpoint are of the "path-noscheme" (starts with a path not - preceded by a slash, precisely defined in [RFC3986] - Section 3.3) form. + resolution. Those applications should use different + representations of links to which Appendix C is not applicable + (e.g. [I-D.hartke-t2trg-coral]). extra-attrs := Additional registration attributes (optional). The endpoint can pass any parameter registered at Section 9.3 to the directory. If the RD is aware of the parameter's specified semantics, it processes it accordingly. Otherwise, it MUST store the unknown key and its value(s) as an endpoint attribute for further lookup. - Content-Format: application/link-format - - Content-Format: application/link-format+json - - Content-Format: application/link-format+cbor + Content-Format: application/link-format or any other indicated media + type representing web links The following response codes are defined for this interface: Success: 2.01 "Created" or 201 "Created". The Location-Path option or Location header MUST be included in the response. This location MUST be a stable identifier generated by the RD as it is used for all subsequent operations on this registration resource. The registration resource location thus returned is for the purpose of updating the lifetime of the registration and for maintaining the content of the registered links, including @@ -1086,99 +1080,104 @@ "Finding a Resource Directory" step. Care has to be taken to consider the freshness of results obtained earlier, e.g. of the result of a "/.well-known/core" response, the lifetime of an RDAO option and of DNS responses. Any rate limits and persistent errors from the "Finding a Resource Directory" step must be considered for the whole registration time, not only for a single operation. The following example shows a registrant-ep with the name "node1" registering two resources to an RD using this interface. The location "/rd" is an example RD location discovered in a request - similar to Figure 6. + similar to Figure 5. Req: POST coap://rd.example.com/rd?ep=node1 Content-Format: 40 Payload: ;ct=41;rt="temperature-c";if="sensor"; anchor="coap://spurious.example.com:5683", ;ct=41;rt="light-lux";if="sensor" Res: 2.01 Created Location-Path: /rd/4521 - Figure 7: Example registration payload + Figure 6: Example registration payload A Resource Directory may optionally support HTTP. Here is an example - of almost the same registration operation above, when done using HTTP - and the JSON Link Format. + of almost the same registration operation above, when done using + HTTP. Req: POST /rd?ep=node1&base=http://[2001:db8:1::1] HTTP/1.1 Host: example.com - Content-Type: application/link-format+json + Content-Type: application/link-format Payload: - [ - {"href": "/sensors/temp", "ct": "41", "rt": "temperature-c", - "if": "sensor", "anchor": "coap://spurious.example.com:5683"}, - {"href": "/sensors/light", "ct": "41", "rt": "light-lux", - "if": "sensor"} - ] + ;ct=41;rt="temperature-c";if="sensor"; + anchor="coap://spurious.example.com:5683", + ;ct=41;rt="light-lux";if="sensor" Res: 201 Created Location: /rd/4521 5.3.1. Simple Registration Not all endpoints hosting resources are expected to know how to upload links to an RD as described in Section 5.3. Instead, simple endpoints can implement the Simple Registration approach described in this section. An RD implementing this specification MUST implement Simple Registration. However, there may be security reasons why this form of directory discovery would be disabled. This approach requires that the registrant-ep makes available the hosted resources that it wants to be discovered, as links on its "/.well-known/core" interface as specified in [RFC6690]. The links in that document are subject to the same limitations as the payload - of a registration (with respect to Appendix D). + of a registration (with respect to Appendix C). The registrant-ep finds one or more addresses of the directory server as described in Section 4. The registrant-ep asks the selected directory server to probe its /.well-known/core and publish the links as follows: The registrant-ep sends (and regularly refreshes with) a POST request to the "/.well-known/core" URI of the directory server of choice. The body of the POST request is empty, and triggers the resource directory server to perform GET requests at the requesting registrant-ep's /.well-known/core to obtain the link-format payload to register. The registrant-ep includes the same registration parameters in the POST request as it would per Section 5.3. The registration base URI - of the registration is taken from the requesting server's URI. + of the registration is taken from the registrant-ep's network address + (as is default with regular registrations). - The Resource Directory MUST NOT query the registrant-ep's data before - sending the response; this is to accommodate very limited endpoints. + The Resource Directory needs to query the registrant-ep's discovery + resource to determine the success of the operation. It SHOULD keep a + cache of the discovery resource and not query it again as long as it + is fresh. - The success condition only indicates that the request was valid (i.e. - the passed parameters are valid per se), not that the link data could - be obtained or parsed or was successfully registered into the RD. + (This is to accomodate constrained registrant devices that can not + process an incoming and outgoing request at the same time. + Registrants MUST be able to serve a GET request to "/.well-known/ + core" after having requested registration. Constrained devices MAY + regard the initial request as temporarily failed when they need RAM + occupied by their own request to serve the RD's GET, and retry later + when the RD already has a cached representation of their discovery + resources. Then, the RD can reply immediately and the registrant can + receive the response.) The simple registration request interface is specified as follows: Interaction: EP -> RD Method: POST URI Template: /.well-known/core{?ep,d,lt,extra-attrs*} - URI Template Variables are as they are for registration in Section 5.3. The base attribute is not accepted to keep the registration interface simple; that rules out registration over CoAP- over-TCP or HTTP that would need to specify one. The following response codes are defined for this interface: Success: 2.04 "Changed". Failure: 4.00 "Bad Request". Malformed request. @@ -1197,125 +1196,303 @@ Method: GET URI Template: /.well-known/core The following response codes are defined for this interface: Success: 2.05 "Content". Failure: 4.00 "Bad Request". Malformed request. - Failure: 4.04 "Not Found". /.well-known/core does not exist or is - empty. + Failure: 4.04 "Not Found". /.well-known/core does not exist. Failure: 5.03 "Service Unavailable". Service could not perform the operation. HTTP support: NO The registration resources MUST be deleted after the expiration of their lifetime. Additional operations on the registration resource cannot be executed because no registration location is returned. The following example shows a registrant-ep using Simple Registration, by simply sending an empty POST to a resource directory. Req:(to RD server from [2001:db8:2::1]) POST /.well-known/core?lt=6000&ep=node1 No payload - Res: 2.04 Changed - - (later) - Req: (from RD server to [2001:db8:2::1]) GET /.well-known/core Accept: 40 - Res: 2.05 Content + Res: (to the RD from [2001:db8:2::1] ) 2.05 Content Content-Format: 40 Payload: + Res: (from the RD to [2001:db8:2::1]) 2.04 Changed + 5.3.2. Third-party registration For some applications, even Simple Registration may be too taxing for some very constrained devices, in particular if the security requirements become too onerous. In a controlled environment (e.g. building control), the Resource Directory can be filled by a third party device, called a Commissioning Tool (CT). The commissioning tool can fill the Resource Directory from a database or other means. For that purpose scheme, IP address and port of the URI of the registered device is the value of the "base" parameter of the registration described in Section 5.3. It should be noted that the value of the "base" parameter applies to all the links of the registration and has consequences for the anchor value of the individual links as exemplified in Appendix B. An eventual (currently non-existing) "base" attribute of the link is not affected by the value of "base" parameter in the registration. -5.3.3. RD-Groups +5.4. Operations on the Registration Resource - The RD-Groups usage pattern allows announcing application groups - inside a Resource Directory. + This section describes how the registering endpoint can maintain the + registrations that it created. The registering endpoint can be the + registrant-ep or the CT. An endpoint SHOULD NOT use this interface + for registrations that it did not create. The registrations are + resources of the RD. - Groups are represented by endpoint registrations. Their base address - is a multicast address, and they SHOULD be entered with the endpoint - type "core.rd-group". The endpoint name can also be referred to as a - group name in this context. + After the initial registration, the registering endpoint retains the + returned location of the Registration Resource for further + operations, including refreshing the registration in order to extend + the lifetime and "keep-alive" the registration. When the lifetime of + the registration has expired, the RD SHOULD NOT respond to discovery + queries concerning this endpoint. The RD SHOULD continue to provide + access to the Registration Resource after a registration time-out + occurs in order to enable the registering endpoint to eventually + refresh the registration. The RD MAY eventually remove the + registration resource for the purpose of garbage collection. If the + Registration Resource is removed, the corresponding endpoint will + need to be re-registered. - The registration is inserted into the RD by a Commissioning Tool, - which might also be known as a group manager here. It performs third - party registration and registration updates. + The Registration Resource may also be used cancel the registration + using DELETE, and to perform further operations beyond the scope of + this specification. - The links it registers SHOULD be available on all members that join - the group. Depending on the application, members that lack some - resource MAY be permissible if requests to them fail gracefully. + These operations are described below. - The following example shows a CT registering a group with the name - "lights" which provides two resources. The directory resource path - /rd is an example RD location discovered in a request similar to - Figure 6. +5.4.1. Registration Update - Req: POST coap://rd.example.com/rd?ep=lights&et=core.rd-group - &base=coap://[ff35:30:2001:db8::1] - Content-Format: 40 + The update interface is used by the registering endpoint to refresh + or update its registration with an RD. To use the interface, the + registering endpoint sends a POST request to the registration + resource returned by the initial registration operation. + + An update MAY update the lifetime- or the context- registration + parameters "lt", "base" as in Section 5.3. Parameters that are not + being changed SHOULD NOT be included in an update. Adding parameters + that have not changed increases the size of the message but does not + have any other implications. Parameters MUST be included as query + parameters in an update operation as in Section 5.3. + + A registration update resets the timeout of the registration to the + (possibly updated) lifetime of the registration, independent of + whether a "lt" parameter was given. + + If the context of the registration is changed in an update, relative + references submitted in the original registration or later updates + are resolved anew against the new context. + + The registration update operation only describes the use of POST with + an empty payload. Future standards might describe the semantics of + using content formats and payloads with the POST method to update the + links of a registration (see Section 5.4.3). + + The update registration request interface is specified as follows: + + Interaction: EP -> RD + + Method: POST + + URI Template: {+location}{?lt,base,extra-attrs*} + URI Template Variables: + + location := This is the Location returned by the RD as a result + of a successful earlier registration. + + lt := Lifetime (optional). Lifetime of the registration in + seconds. Range of 60-4294967295. If no lifetime is included, + the previous last lifetime set on a previous update or the + original registration (falling back to 90000) SHOULD be used. + + base := Base URI (optional). This parameter updates the Base URI + established in the original registration to a new value. If + the parameter is set in an update, it is stored by the RD as + the new Base URI under which to interpret the relative links + present in the payload of the original registration, following + the same restrictions as in the registration. If the parameter + is not set in the request but was set before, the previous Base + URI value is kept unmodified. If the parameter is not set in + the request and was not set before either, the source address + and source port of the update request are stored as the Base + URI. + + extra-attrs := Additional registration attributes (optional). As + with the registration, the RD processes them if it knows their + semantics. Otherwise, unknown attributes are stored as + endpoint attributes, overriding any previously stored endpoint + attributes of the same key. + + Content-Format: none (no payload) + + The following response codes are defined for this interface: + + Success: 2.04 "Changed" or 204 "No Content" if the update was + successfully processed. + + Failure: 4.00 "Bad Request" or 400 "Bad Request". Malformed + request. + + Failure: 4.04 "Not Found" or 404 "Not Found". Registration does not + exist (e.g. may have been removed). + + Failure: 5.03 "Service Unavailable" or 503 "Service Unavailable". + Service could not perform the operation. + + HTTP support: YES + + If the registration update fails with a "Service Unavailable" + response and a Max-Age option or Retry-After header, the registering + endpoint SHOULD retry the operation after the time indicated. If the + registration fails in another way, including request timeouts, or if + the time indicated exceeds the remaining lifetime, the registering + endpoint SHOULD attempt registration again. + + The following example shows how the registering endpoint updates its + registration resource at an RD using this interface with the example + location value: /rd/4521. + + Req: POST /rd/4521 + + Res: 2.04 Changed + + The following example shows the registering endpoint updating its + registration resource at an RD using this interface with the example + location value: /rd/4521. The initial registration by the + registering endpoint set the following values: + + o endpoint name (ep)=endpoint1 + + o lifetime (lt)=500 + + o Base URI (base)=coap://local-proxy-old.example.com:5683 + + o payload of Figure 6 + + The initial state of the Resource Directory is reflected in the + following request: + + Req: GET /rd-lookup/res?ep=endpoint1 + + Res: 2.01 Content Payload: - ;rt="light";if="core.a", - ;if="core.p";u="K" + ;ct=41; + rt="temperature"; anchor="coap://spurious.example.com:5683", + ;ct=41; + rt="light-lux"; if="sensor"; + anchor="coap://local-proxy-old.example.com:5683" - Res: 2.01 Created - Location-Path: /rd/12 + The following example shows the registering endpoint changing the + Base URI to "coaps://new.example.com:5684": - In this example, the group manager can easily permit devices that - have no writable color-temperature to join, as they would still - respond to brightness changing commands. Had the group instead - contained a single resource that sets brightness and color - temperature atomically, endpoints would need to support both - properties. + Req: POST /rd/4521?base=coaps://new.example.com:5684 - The resources of a group can be looked up like any other resource, - and the group registrations (along with any additional registration - parameters) can be looked up using the endpoint lookup interface. + Res: 2.04 Changed + + The consecutive query returns: + + Req: GET /rd-lookup/res?ep=endpoint1 + + Res: 2.01 Content + Payload: + ;ct=41;rt="temperature"; + anchor="coap://spurious.example.com:5683", + ;ct=41;rt="light-lux"; + if="sensor"; anchor="coaps://new.example.com:5684", + +5.4.2. Registration Removal + + Although RD registrations have soft state and will eventually timeout + after their lifetime, the registering endpoint SHOULD explicitly + remove an entry from the RD if it knows it will no longer be + available (for example on shut-down). This is accomplished using a + removal interface on the RD by performing a DELETE on the endpoint + resource. + + The removal request interface is specified as follows: + + Interaction: EP -> RD + + Method: DELETE + + URI Template: {+location} + + URI Template Variables: + + location := This is the Location returned by the RD as a result + of a successful earlier registration. + + The following response codes are defined for this interface: + + Success: 2.02 "Deleted" or 204 "No Content" upon successful deletion + + Failure: 4.00 "Bad Request" or 400 "Bad Request". Malformed + request. + + Failure: 4.04 "Not Found" or 404 "Not Found". Registration does not + exist (e.g. may already have been removed). + + Failure: 5.03 "Service Unavailable" or 503 "Service Unavailable". + Service could not perform the operation. + + HTTP support: YES + + The following examples shows successful removal of the endpoint from + the RD with example location value /rd/4521. + + Req: DELETE /rd/4521 + + Res: 2.02 Deleted + +5.4.3. Further operations + + Additional operations on the registration can be specified in future + documents, for example: + + o Send iPATCH (or PATCH) updates ([RFC8132]) to add, remove or + change the links of a registration. + + o Use GET to read the currently stored set of links in a + registration resource. + + Those operations are out of scope of this document, and will require + media types suitable for modifying sets of links. 6. RD Lookup To discover the resources registered with the RD, a lookup interface must be provided. This lookup interface is defined as a default, and it is assumed that RDs may also support lookups to return resource - descriptions in alternative formats (e.g. Atom or HTML Link) or - using more advanced interfaces (e.g. supporting context or semantic - based lookup). + descriptions in alternative formats (e.g. JSON or CBOR link format + [I-D.ietf-core-links-json]) or using more advanced interfaces (e.g. + supporting context or semantic based lookup) on different resources + that are discovered independently. RD Lookup allows lookups for endpoints and resources using attributes defined in this document and for use with the CoRE Link Format. The result of a lookup request is the list of links (if any) corresponding to the type of lookup. Thus, an endpoint lookup MUST return a list of endpoints and a resource lookup MUST return a list of links to resources. The lookup type is selected by a URI endpoint, which is indicated by a Resource Type as per Table 1 below: @@ -1344,22 +1521,22 @@ Above rules allow the client to interpret the response as links without any further knowledge of the storage conventions of the RD. The Resource Directory MAY replace the registration base URIs with a configured intermediate proxy, e.g. in the case of an HTTP lookup interface for CoAP endpoints. 6.2. Lookup filtering Using the Accept Option, the requester can control whether the returned list is returned in CoRE Link Format ("application/link- - format", default) or its alternate content-formats ("application/ - link-format+json" or "application/link-format+cbor"). + format", default) or in alternate content-formats (e.g. from + [I-D.ietf-core-links-json]). The page and count parameters are used to obtain lookup results in specified increments using pagination, where count specifies how many links to return and page specifies which subset of links organized in sequential pages, each containing 'count' links, starting with link zero and page zero. Thus, specifying count of 10 and page of 0 will return the first 10 links in the result set (links 0-9). Count = 10 and page = 1 will return the next 'page' containing links 10-19, and so on. @@ -1423,80 +1600,56 @@ Page numbering starts with zero. count := Count (optional). Number of results is limited to this parameter value. If the page parameter is also present, the response MUST only include 'count' links starting with the (page * count) link in the result set from the query. If the count parameter is not present, then the response MUST return all matching links in the result set. Link numbering starts with zero. - Content-Format: application/link-format (optional) - - Content-Format: application/link-format+json (optional) - - Content-Format: application/link-format+cbor (optional) + Accept: absent, application/link-format or any other indicated + media type representing web links The following responses codes are defined for this interface: Success: 2.05 "Content" or 200 "OK" with an "application/link- - format", "application/link-format+cbor", or "application/link- - format+json" payload containing matching entries for the lookup. - The payload can contain zero links (which is an empty payload, - "80" (hex) or "[]" in the respective content format), indicating - that no entities matched the request. + format" or other web link payload containing matching entries for + the lookup. The payload can contain zero links (which is an empty + payload in [RFC6690] link format, but could also be "[]" in JSON + based formats), indicating that no entities matched the request. Failure: No error response to a multicast request. Failure: 4.00 "Bad Request" or 400 "Bad Request". Malformed request. Failure: 5.03 "Service Unavailable" or 503 "Service Unavailable". Service could not perform the operation. HTTP support: YES - The endpoint lookup returns registration resources which can only be - manipulated by the registering endpoint. Examples of endpoint lookup - belong to the management aspects of the RD and are shown in - Appendix A.5. The resource lookup examples are shown in this - section. - 6.3. Resource lookup examples The examples in this section assume the existence of CoAP hosts with a default CoAP port 61616. HTTP hosts are possible and do not change the nature of the examples. The following example shows a client performing a resource lookup - with the example resource look-up locations discovered in Figure 6: + with the example resource look-up locations discovered in Figure 5: Req: GET /rd-lookup/res?rt=temperature Res: 2.05 Content ;rt="temperature"; anchor="coap://[2001:db8:3::123]:61616" - The same lookup using the CBOR Link Format media type: - - Req: GET /rd-lookup/res?rt=temperature - Accept: TBD64 - - Res: 2.05 Content - Content-Format: TBD64 - Payload in Hex notation: - 81A3017823636F61703A2F2F5B323030313A6462383A333A3A3132335D3A363136313 - 62F74656D7003781E636F61703A2F2F5B323030313A6462383A333A3A3132335D3A36 - 31363136096B74656D7065726174757265 - Decoded payload: - [{1: "coap://[2001:db8:3::123]:61616/temp", 9: "temperature", - 3: "coap://[2001:db8:3::123]:61616"}] A client that wants to be notified of new resources as they show up can use observation: Req: GET /rd-lookup/res?rt=light Observe: 0 Res: 2.05 Content Observe: 23 Payload: empty @@ -1568,30 +1721,58 @@ anchor="coap://sensor2.example.com", ;rt="temperature-c"; if="sensor"; anchor="coap://sensor2.example.com", ;rt="light-lux"; if="sensor"; anchor="coap://sensor2.example.com", ;rel="describedby"; anchor="coap://sensor2.example.com/sensors/temp", ;rel="alternate"; anchor="coap://sensor2.example.com/sensors/temp" - The following example shows a client performing a lookup of all - resources of all endpoints (groups) with et=core.rd-group. +6.4. Endpoint lookup - Req: GET /rd-lookup/res?et=core.rd-group + The endpoint lookup returns registration resources which can only be + manipulated by the registering endpoint. - ;rt="light";if="core.a"; - et="core.rd-group";anchor="coap://[ff35:30:2001:db8::1]", - ;if="core.p";u="K"; - et="core.rd-group"; - anchor="coap://[ff35:30:2001:db8::1]" + Endpoint registration resources are annotated with their endpoint + names (ep), sectors (d, if present) and registration base URI (base; + reports the registrant-ep's address if no explicit base was given) as + well as a constant resource type (rt="core.rd-ep"); the lifetime (lt) + is not reported. Additional endpoint attributes are added as target + attributes to their endpoint link unless their specification says + otherwise. + + Links to endpoints SHOULD be presented in path-absolute form or, if + required, as absolute references. (This avoids the RFC6690 + ambiguities.) + + While Endpoint Lookup does expose the registration resources, the RD + does not need to make them accessible to clients. Clients SHOULD NOT + attempt to dereference or manipulate them. + + A Resource Directory can report endpoints in lookup that are not + hosted at the same address. Lookup clients MUST be prepared to see + arbitrary URIs as registration resources in the results and treat + them as opaque identifiers; the precise semantics of such links are + left to future specifications. + + The following example shows a client performing an endpoint type (et) + lookup with the value oic.d.sensor (which is currently a registered + rt value): + + Req: GET /rd-lookup/ep?et=oic.d.sensor + + Res: 2.05 Content + ;base="coap://[2001:db8:3::127]:61616";ep="node5"; + et="oic.d.sensor";ct="40";rt="core.rd-ep", + ;base="coap://[2001:db8:3::129]:61616";ep="node7"; + et="oic.d.sensor";ct="40";d="floor-3";rt="core.rd-ep" 7. Security policies The Resource Directory (RD) provides assistance to applications situated on a selection of nodes to discover endpoints on connected nodes. This section discusses different security aspects of accessing the RD. The contents of the RD are inserted in two ways: @@ -1619,31 +1801,35 @@ authorized to learn the contents of a given RD. Within a region, for a given RD, a more fine-grained security division is possible based on the values of the endpoint registration parameters. Authorization to discover endpoints with a given set of filter values is recommended for those cases. When a node registers its endpoints, criteria are needed to authorize the node to enter them. An important aspect is the uniqueness of the (endpoint name, and optional sector) pair within the RD. Consider the two cases separately: (1) CT registers endpoints, and (2) the - registering node registers its own endpoint(s). * A CT needs - authorization to register a set of endpoints. This authorization can - be based on the region, i.e. a given CT is authorized to register any - endpoint (endpoint name, sector) into a given RD, or to register an - endpoint with (endpoint name, sector) value pairs assigned by the AS, - or can be more fine-grained, including a subset of registration - parameter values. * A given endpoint that registers itself, needs to - proof its possession of its unique (endpoint name, sector) value - pair. Alternatively, the AS can authorize the endpoint to register - with an (endpoint name, sector) value pair assigned by the AS. * A - separate document needs to specify these aspects to ensure + registering node registers its own endpoint(s). + + o A CT needs authorization to register a set of endpoints. This + authorization can be based on the region, i.e. a given CT is + authorized to register any endpoint (endpoint name, sector) into a + given RD, or to register an endpoint with (endpoint name, sector) + value pairs assigned by the AS, or can be more fine-grained, + including a subset of registration parameter values. + + o A given endpoint that registers itself, needs to proof its + possession of its unique (endpoint name, sector) value pair. + Alternatively, the AS can authorize the endpoint to register with + an (endpoint name, sector) value pair assigned by the AS. + + A separate document needs to specify these aspects to ensure interoperability between registering nodes and RD. The subsections below give some hints how to handle a subset of the different aspects. 7.1. Secure RD discovery The Resource Server (RS) discussed in [I-D.ietf-ace-oauth-authz] is equated to the RD. The client (C) needs to discover the RD as discussed in Section 4. C can discover the related AS by sending a request to the RD. The RD denies the request by sending the address @@ -1679,30 +1865,30 @@ checked by encrypting the certificate identifier with the private key of the registering endpoint, which the RD can decrypt with the public key stored in the certificate. Even simpler, the authorized registering endpoint can generate a random number (or string) that identifies the endpoint. The RD can check for the improbable replication of the random value. The RD MUST check that registering endpoint uses only one random value for each authorized endpoint. 8. Security Considerations - The security considerations as described in Section 7 of [RFC5988] + The security considerations as described in Section 5 of [RFC8288] and Section 6 of [RFC6690] apply. The "/.well-known/core" resource may be protected e.g. using DTLS when hosted on a CoAP server as described in [RFC7252]. DTLS or TLS based security SHOULD be used on all resource directory interfaces defined in this document. 8.1. Endpoint Identification and Authentication An Endpoint (name, sector) pair is unique within the et of endpoints - regsitered by the RD. An Endpoint MUST NOT be identified by its + registered by the RD. An Endpoint MUST NOT be identified by its protocol, port or IP address as these may change over the lifetime of an Endpoint. Every operation performed by an Endpoint on a resource directory SHOULD be mutually authenticated using Pre-Shared Key, Raw Public Key or Certificate based security. Consider the following threat: two devices A and B are registered at a single server. Both devices have unique, per-device credentials for use with DTLS to make sure that only parties with authorization @@ -1780,34 +1966,35 @@ 9.3. RD Parameter Registry This specification defines a new sub-registry for registration and lookup parameters called "RD Parameters" under "CoRE Parameters". Although this specification defines a basic set of parameters, it is expected that other standards that make use of this interface will define new ones. Each entry in the registry must include + o the human readable name of the parameter, - o the short name as used in query parameters or link attributes, + o the short name as used in query parameters or target attributes, o indication of whether it can be passed as a query parameter at registration of endpoints, as a query parameter in lookups, or be - expressed as a link attribute, + expressed as a target attribute, o validity requirements if any, and o a description. The query parameter MUST be both a valid URI query key [RFC3986] and - a parmname as used in [RFC5988]. + a token as used in [RFC8288]. The description must give details on whether the parameter can be updated, and how it is to be processed in lookups. The mechanisms around new RD parameters should be designed in such a way that they tolerate RD implementations that are unaware of the parameter and expose any parameter passed at registration or updates on in endpoint lookups. (For example, if a parameter used at registration were to be confidential, the registering endpoint should be instructed to only set that parameter if the RD advertises support @@ -1832,41 +2019,41 @@ | | | | | available | | Page | page | Integer | L | Used for pagination | | Count | count | Integer | L | Used for pagination | | Endpoint | et | | RLA | Semantic name of the | | Type | | | | endpoint (see | | | | | | Section 9.4) | +--------------+-------+---------------+-----+----------------------+ Table 2: RD Parameters - (Short: Short name used in query parameters or link attributes. Use: - R = used at registration, L = used at lookup, A = expressed in link - attribute + (Short: Short name used in query parameters or target attributes. + Use: R = used at registration, L = used at lookup, A = expressed in + target attribute The descriptions for the options defined in this document are only summarized here. To which registrations they apply and when they are to be shown is described in the respective sections of this document. The IANA policy for future additions to the sub-registry is "Expert Review" as described in [RFC8126]. The evaluation should consider formal criteria, duplication of functionality (Is the new entry redundant with an existing one?), topical suitability (E.g. is the described property actually a property of the endpoint and not a property of a particular resource, in which case it should go into the payload of the registration and need not be registered?), and the - potential for conflict with commonly used link attributes (For + potential for conflict with commonly used target attributes (For example, "if" could be used as a parameter for conditional registration if it were not to be used in lookup or attributes, but would make a bad parameter for lookup, because a resource lookup with an "if" query parameter could ambiguously filter by the registered - endpoint property or the [RFC6690] link attribute). It is expected + endpoint property or the [RFC6690] target attribute). It is expected that the registry will receive between 5 and 50 registrations in total over the next years. 9.3.1. Full description of the "Endpoint Type" Registration Parameter An endpoint registering at an RD can describe itself with endpoint types, similar to how resources are described with Resource Types in [RFC6690]. An endpoint type is expressed as a string, which can be either a URI or one of the values defined in the Endpoint Type sub- registry. Endpoint types can be passed in the "et" query parameter @@ -1899,22 +2086,21 @@ Section 9.3.1. o The registered values MUST conform to the ABNF reg-rel-type definition of [RFC6690] and MUST NOT be a URI. o It is recommended to use the period "." character for segmentation. The registry initially contains one value: - o "core.rd-group": An application group as described in - Section 5.3.3. + o "core.rd-group": An application group as described in Appendix A. 9.5. Multicast Address Registration IANA has assigned the following multicast addresses for use by CoAP nodes: IPv4 - "all CoRE resource directories" address, from the "IPv4 Multicast Address Space Registry" equal to "All CoAP Nodes", 224.0.1.187. As the address is used for discovery that may span beyond a single network, it has come from the Internetwork Control @@ -1929,24 +2115,24 @@ 10. Examples Two examples are presented: a Lighting Installation example in Section 10.1 and a LWM2M example in Section 10.2. 10.1. Lighting Installation This example shows a simplified lighting installation which makes use of the Resource Directory (RD) with a CoAP interface to facilitate - the installation and start up of the application code in the lights + the installation and start-up of the application code in the lights and sensors. In particular, the example leads to the definition of a group and the enabling of the corresponding multicast address as - described in Section 5.3.3. No conclusions must be drawn on the + described in Appendix A. No conclusions must be drawn on the realization of actual installation or naming procedures, because the example only "emphasizes" some of the issues that may influence the use of the RD and does not pretend to be normative. 10.1.1. Installation Characteristics The example assumes that the installation is managed. That means that a Commissioning Tool (CT) is used to authorize the addition of nodes, name them, and name their services. The CT can be connected to the installation in many ways: the CT can be part of the @@ -2088,21 +2274,21 @@ The luminary, knowing its sector and being configured to join any group containing lights, searches for candidate groups and joins them: Req: GET coap://[2001:db8:4::ff]/rd-lookup/ep ?d=R2-4-015&et=core.rd-group&rt=light Res: 2.05 Content ;ep="grp_R2-4-015";et="core.rd-group"; - base="coap://[ff05::1]" + base="coap://[ff05::1]";rt="core.rd-ep" From the returned base parameter value, the luminary learns the multicast address of the multicast group. Alternatively, the CT can communicate the multicast address directly to the luminaries by using the "coap-group" resource specified in [RFC7390]. Req: POST coap://[2001:db8:4::1]/coap-group Content-Format: application/coap-group+json @@ -2266,74 +2453,124 @@ et - Endpoint Type base - Registration Base URI The endpoint registration must include a payload containing links to all supported objects and existing object instances, optionally including the appropriate link-format relations. Here is an example LWM2M registration payload: ,,, - This link format payload indicates that object ID 1 (LWM2M Server Object) is supported, with a single instance 0 existing, object ID 3 (LWM2M Device object) is supported, with a single instance 0 existing, and object 5 (LWM2M Firmware Object) is supported, with no existing instances. 10.2.3. LWM2M Update Endpoint Registration The LwM2M update is really very similar to the registration update as - described in Appendix A.1, with the only difference that there are + described in Section 5.4.1, with the only difference that there are more parameters defined and available. All the parameters listed in that section are also available with the initial registration but are all optional: lt - Registration Lifetime b - Protocol Binding sms - MSISDN link payload - new or modified links A Registration update is also specified to be used to update the LWM2M server whenever the endpoint's UDP port or IP address are changed. 10.2.4. LWM2M De-Register Endpoint LWM2M allows for de-registration using the delete method on the returned location from the initial registration operation. LWM2M de- - registration proceeds as described in Appendix A.2. + registration proceeds as described in Section 5.4.2. 11. Acknowledgments Oscar Novo, Srdjan Krco, Szymon Sasin, Kerry Lynn, Esko Dijk, Anders Brandt, Matthieu Vial, Jim Schaad, Mohit Sethi, Hauke Petersen, Hannes Tschofenig, Sampo Ukkola, Linyi Tian, and Jan Newmarch have provided helpful comments, discussions and ideas to improve and shape this document. Zach would also like to thank his colleagues from the EU FP7 SENSEI project, where many of the resource directory concepts were originally developed. 12. Changelog + changes from -17 to -18 + + o Rather than re-specifying link format (Modernized Link Format), + describe a Limited Link Format that's the uncontested subset of + Link Format + + o Acknowledging the -17 version as part of the draft + o Move "Read endpoint links" operation to future specification like + PATCH + + o Demote links-json to an informative reference, and removed them + from exchange examples + + o Add note on unusability of link-local IP addresses, and describe + mitigation. + + o Reshuffling of sections: Move additional operations and endpoint + lookup back from appendix, and groups into one + + o Lookup interface tightened to not imply applicability for non + link-format lookups (as those can have vastly different views on + link cardinality) + + o Simple registration: Change sequence of GET and POST-response, + ensuring unsuccessful registrations are reported as such, and + suggest how devices that would have required the inverse behavior + can still cope with it. + + o Abstract and introduction reworded to avoid the impression that + resources are stored in full in the RD + + o Simplify the rules governing when a registration resource can or + must be changed. + + o Drop a figure that has become useless due to the changes of and + -13 and -17 + + o Wording consistency fixes: Use "Registrations" and "target + attributes" + + o Fix incorrect use of content negotiation in discovery interface + description (Content-Format -> Accept) + + o State that the base attribute value is part of endpoint lookup + even when implicit in the registration + + o Update references from RFC5988 to its update RFC8288 + + o Remove appendix on protocol-negotiation (which had a note to be + removed before publication) + changes from -16 to -17 (Note that -17 is published as a direct follow-up to -16, containing a single change to be discussed at IETF103) - o Removed groups that are enumerations of registrations and have dedicated mechanism o Add groups that are enumerations of shared resources and are a special case of endpoint registrations changes from -15 to -16 + o Recommend a common set of resources for members of a group o Clarified use of multicast group in lighting example o Add note on concurrent registrations from one EP being possible but not expected o Refresh web examples appendix to reflect current use of Modernized Link Format @@ -2639,40 +2877,30 @@ stable, allowing for endpoint and Domain information to be changed during updates. o Changed the lookup interface to accept endpoint and Domain as query string parameters to control the scope of a lookup. 13. References 13.1. Normative References - [I-D.ietf-core-links-json] - Li, K., Rahman, A., and C. Bormann, "Representing - Constrained RESTful Environments (CoRE) Link Format in - JSON and CBOR", draft-ietf-core-links-json-10 (work in - progress), February 2018. - [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform Resource Identifier (URI): Generic Syntax", STD 66, RFC 3986, DOI 10.17487/RFC3986, January 2005, . - [RFC5988] Nottingham, M., "Web Linking", RFC 5988, - DOI 10.17487/RFC5988, October 2010, - . - [RFC6570] Gregorio, J., Fielding, R., Hadley, M., Nottingham, M., and D. Orchard, "URI Template", RFC 6570, DOI 10.17487/RFC6570, March 2012, . [RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link Format", RFC 6690, DOI 10.17487/RFC6690, August 2012, . [RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service @@ -2694,50 +2922,60 @@ [I-D.arkko-core-dev-urn] Arkko, J., Jennings, C., and Z. Shelby, "Uniform Resource Names for Device Identifiers", draft-arkko-core-dev-urn-05 (work in progress), October 2017. [I-D.bormann-t2trg-rel-impl] Bormann, C., "impl-info: A link relation type for disclosing implementation information", draft-bormann- t2trg-rel-impl-00 (work in progress), January 2018. + [I-D.hartke-t2trg-coral] + Hartke, K., "The Constrained RESTful Application Language + (CoRAL)", draft-hartke-t2trg-coral-06 (work in progress), + October 2018. + [I-D.ietf-ace-oauth-authz] Seitz, L., Selander, G., Wahlstroem, E., Erdtman, S., and H. Tschofenig, "Authentication and Authorization for Constrained Environments (ACE) using the OAuth 2.0 - Framework (ACE-OAuth)", draft-ietf-ace-oauth-authz-16 - (work in progress), October 2018. + Framework (ACE-OAuth)", draft-ietf-ace-oauth-authz-17 + (work in progress), November 2018. [I-D.ietf-anima-bootstrapping-keyinfra] Pritikin, M., Richardson, M., Behringer, M., Bjarnason, S., and K. Watsen, "Bootstrapping Remote Secure Key Infrastructures (BRSKI)", draft-ietf-anima-bootstrapping- - keyinfra-16 (work in progress), June 2018. + keyinfra-17 (work in progress), November 2018. + + [I-D.ietf-core-links-json] + Li, K., Rahman, A., and C. Bormann, "Representing + Constrained RESTful Environments (CoRE) Link Format in + JSON and CBOR", draft-ietf-core-links-json-10 (work in + progress), February 2018. [I-D.silverajan-core-coap-protocol-negotiation] Silverajan, B. and M. Ocak, "CoAP Protocol Negotiation", draft-silverajan-core-coap-protocol-negotiation-09 (work in progress), July 2018. - [RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H., - Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext - Transfer Protocol -- HTTP/1.1", RFC 2616, - DOI 10.17487/RFC2616, June 1999, - . - [RFC6775] Shelby, Z., Ed., Chakrabarti, S., Nordmark, E., and C. Bormann, "Neighbor Discovery Optimization for IPv6 over Low-Power Wireless Personal Area Networks (6LoWPANs)", RFC 6775, DOI 10.17487/RFC6775, November 2012, . + [RFC6874] Carpenter, B., Cheshire, S., and R. Hinden, "Representing + IPv6 Zone Identifiers in Address Literals and Uniform + Resource Identifiers", RFC 6874, DOI 10.17487/RFC6874, + February 2013, . + [RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing", RFC 7230, DOI 10.17487/RFC7230, June 2014, . [RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained Application Protocol (CoAP)", RFC 7252, DOI 10.17487/RFC7252, June 2014, . @@ -2757,361 +2995,103 @@ . [RFC8288] Nottingham, M., "Web Linking", RFC 8288, DOI 10.17487/RFC8288, October 2017, . [RFC8392] Jones, M., Wahlstroem, E., Erdtman, S., and H. Tschofenig, "CBOR Web Token (CWT)", RFC 8392, DOI 10.17487/RFC8392, May 2018, . -Appendix A. Registration Management - - This section describes how the registering endpoint can maintain the - registries that it created. The registering endpoint can be the - registrant-ep or the CT. An endpoint SHOULD NOT use this interface - for registries that it did not create. The registries are resources - of the RD. - - After the initial registration, the registering endpoint retains the - returned location of the Registration Resource for further - operations, including refreshing the registration in order to extend - the lifetime and "keep-alive" the registration. When the lifetime of - the registration has expired, the RD SHOULD NOT respond to discovery - queries concerning this endpoint. The RD SHOULD continue to provide - access to the Registration Resource after a registration time-out - occurs in order to enable the registering endpoint to eventually - refresh the registration. The RD MAY eventually remove the - registration resource for the purpose of garbage collection. If the - Registration Resource is removed, the corresponding endpoint will - need to be re-registered. - - The Registration Resource may also be used to inspect the - registration resource using GET, update the registration, cancel the - registration using DELETE, or do an endpoint lookup. - - These operations are described below. - -A.1. Registration Update - - The update interface is used by the registering endpoint to refresh - or update its registration with an RD. To use the interface, the - registering endpoint sends a POST request to the registration - resource returned by the initial registration operation. - - An update MAY update the lifetime- or the context- registration - parameters "lt", "base" as in Section 5.3. Parameters that are not - being changed SHOULD NOT be included in an update. Adding parameters - that have not changed increases the size of the message but does not - have any other implications. Parameters MUST be included as query - parameters in an update operation as in Section 5.3. - - A registration update resets the timeout of the registration to the - (possibly updated) lifetime of the registration, independent of - whether a "lt" parameter was given. - - If the context of the registration is changed in an update, relative - references submitted in the original registration or later updates - are resolved anew against the new context. - - The registration update operation only describes the use of POST with - an empty payload. Future standards might describe the semantics of - using content formats and payloads with the POST method to update the - links of a registration (see Appendix A.4). - - The update registration request interface is specified as follows: - - Interaction: EP -> RD - - Method: POST - - URI Template: {+location}{?lt,con,extra-attrs*} - - URI Template Variables: - - location := This is the Location returned by the RD as a result - of a successful earlier registration. - - lt := Lifetime (optional). Lifetime of the registration in - seconds. Range of 60-4294967295. If no lifetime is included, - the previous last lifetime set on a previous update or the - original registration (falling back to 90000) SHOULD be used. - - base := Base URI (optional). This parameter updates the Base URI - established in the original registration to a new value. If - the parameter is set in an update, it is stored by the RD as - the new Base URI under which to interpret the relative links - present in the payload of the original registration, following - the same restrictions as in the registration. If the parameter - is not set in the request but was set before, the previous Base - URI value is kept unmodified. If the parameter is not set in - the request and was not set before either, the source address - and source port of the update request are stored as the Base - URI. - - extra-attrs := Additional registration attributes (optional). As - with the registration, the RD processes them if it knows their - semantics. Otherwise, unknown attributes are stored as - endpoint attributes, overriding any previously stored endpoint - attributes of the same key. - - Content-Format: none (no payload) - - The following response codes are defined for this interface: - - Success: 2.04 "Changed" or 204 "No Content" if the update was - successfully processed. - - Failure: 4.00 "Bad Request" or 400 "Bad Request". Malformed - request. - - Failure: 4.04 "Not Found" or 404 "Not Found". Registration does not - exist (e.g. may have expired). - - Failure: 5.03 "Service Unavailable" or 503 "Service Unavailable". - Service could not perform the operation. - - HTTP support: YES - - If the registration update fails with a "Service Unavailable" - response and a Max-Age option or Retry-After header, the registering - endpoint SHOULD retry the operation after the time indicated. If the - registration fails in another way, including request timeouts, or if - the time indicated exceeds the remaining lifetime, the registering - endpoint SHOULD attempt registration again. - - The following example shows how the registering endpoint updates its - registration resource at an RD using this interface with the example - location value: /rd/4521. - - Req: POST /rd/4521 - - Res: 2.04 Changed - The following example shows the registering endpoint updating its - registration resource at an RD using this interface with the example - location value: /rd/4521. The initial registration by the - registering endpoint set the following values: - - o endpoint name (ep)=endpoint1 +Appendix A. Groups Registration and Lookup - o lifetime (lt)=500 + The RD-Groups usage pattern allows announcing application groups + inside a Resource Directory. - o Base URI (base)=coap://local-proxy-old.example.com:5683 + Groups are represented by endpoint registrations. Their base address + is a multicast address, and they SHOULD be entered with the endpoint + type "core.rd-group". The endpoint name can also be referred to as a + group name in this context. - o payload of Figure 7 + The registration is inserted into the RD by a Commissioning Tool, + which might also be known as a group manager here. It performs third + party registration and registration updates. - The initial state of the Resource Directory is reflected in the - following request: + The links it registers SHOULD be available on all members that join + the group. Depending on the application, members that lack some + resource MAY be permissible if requests to them fail gracefully. - Req: GET /rd-lookup/res?ep=endpoint1 + The following example shows a CT registering a group with the name + "lights" which provides two resources. The directory resource path + /rd is an example RD location discovered in a request similar to + Figure 5. - Res: 2.01 Content + Req: POST coap://rd.example.com/rd?ep=lights&et=core.rd-group + &base=coap://[ff35:30:2001:db8::1] + Content-Format: 40 Payload: - ;ct=41; - rt="temperature"; anchor="coap://spurious.example.com:5683", - ;ct=41; - rt="light-lux"; if="sensor"; - anchor="coap://local-proxy-old.example.com:5683" - - The following example shows the registering endpoint changing the - Base URI to "coaps://new.example.com:5684": - - Req: POST /rd/4521?base=coaps://new.example.com:5684 - - Res: 2.04 Changed + ;rt="light";if="core.a", + ;if="core.p";u="K" - The consecutive query returns: + Res: 2.01 Created + Location-Path: /rd/12 - Req: GET /rd-lookup/res?ep=endpoint1 + In this example, the group manager can easily permit devices that + have no writable color-temperature to join, as they would still + respond to brightness changing commands. Had the group instead + contained a single resource that sets brightness and color + temperature atomically, endpoints would need to support both + properties. - Res: 2.01 Content - Payload: - ;ct=41;rt="temperature"; - anchor="coap://spurious.example.com:5683", - ;ct=41;rt="light-lux"; - if="sensor"; anchor="coaps://new.example.com:5684", + The resources of a group can be looked up like any other resource, + and the group registrations (along with any additional registration + parameters) can be looked up using the endpoint lookup interface. - The following example shows a client performing and enpoint lookup + The following example shows a client performing and endpoint lookup for all groups. Req: GET /rd-lookup/ep?et=core.rd-group Res: 2.01 Content Payload: ;ep="GRP_R2-4-015";et="core.rd-group"; - base="coap://[ff05:;1]", - ;ep=lights&et=core.rd-group; - base="coap://[ff35:30:2001:db8::1]" - -A.2. Registration Removal - - Although RD entries have soft state and will eventually timeout after - their lifetime, the registering endpoint SHOULD explicitly remove an - entry from the RD if it knows it will no longer be available (for - example on shut-down). This is accomplished using a removal - interface on the RD by performing a DELETE on the endpoint resource. - - The removal request interface is specified as follows: - - Interaction: EP -> RD - - Method: DELETE - - URI Template: {+location} - - URI Template Variables: - - location := This is the Location returned by the RD as a result - of a successful earlier registration. - - The following response codes are defined for this interface: - - Success: 2.02 "Deleted" or 204 "No Content" upon successful deletion - - Failure: 4.00 "Bad Request" or 400 "Bad Request". Malformed - request. - - Failure: 4.04 "Not Found" or 404 "Not Found". Registration does not - exist (e.g. may have expired). - - Failure: 5.03 "Service Unavailable" or 503 "Service Unavailable". - Service could not perform the operation. - - HTTP support: YES - - The following examples shows successful removal of the endpoint from - the RD with example location value /rd/4521. - - Req: DELETE /rd/4521 - - Res: 2.02 Deleted - -A.3. Read Endpoint Links - - Some registering endpoints may wish to manage their links as a - collection, and may need to read the current set of links stored in - the registration resource, in order to determine link maintenance - operations. - - One or more links MAY be selected by using query filtering as - specified in [RFC6690] Section 4.1 - - If no links are selected, the Resource Directory SHOULD return an - empty payload. - - The read request interface is specified as follows: - - Interaction: EP -> RD - - Method: GET - - URI Template: {+location}{?href,rel,rt,if,ct} - - URI Template Variables: - - location := This is the Location returned by the RD as a result - of a successful earlier registration. - - href,rel,rt,if,ct := link relations and attributes specified in - the query in order to select particular links based on their - relations and attributes. "href" denotes the URI target of the - link. See [RFC6690] Sec. 4.1 - - The following response codes are defined for this interface: - - Success: 2.05 "Content" or 200 "OK" upon success with an - "application/link-format", "application/link-format+cbor", or - "application/link-format+json" payload. - - Failure: 4.00 "Bad Request" or 400 "Bad Request". Malformed - request. - - Failure: 4.04 "Not Found" or 404 "Not Found". Registration does not - exist (e.g. may have expired). - - Failure: 5.03 "Service Unavailable" or 503 "Service Unavailable". - Service could not perform the operation. - - HTTP support: YES - - The following examples show successful read of the endpoint links - from the RD, with example location value /rd/4521 and example - registration payload of Figure 7. - - Req: GET /rd/4521 - - Res: 2.01 Content - Payload: - ;ct=41;rt="temperature-c";if="sensor"; - anchor="coap://spurious.example.com:5683", - ;ct=41;rt="light-lux";if="sensor" - -A.4. Update Endpoint Links - - An iPATCH (or PATCH) update ([RFC8132]) can add, remove or change the - links of a registration. - - Those operations are out of scope of this document, and will require - media types suitable for modifying sets of links. - -A.5. Endpoint lookup - - Endpoint lookups result in links to registration resources. Endpoint - registration resources are annotated with their endpoint names (ep), - sectors (d, if present) and registration base URI (base) as well as a - constant resource type (rt="core.rd-ep"); the lifetime (lt) is not - reported. Additional endpoint attributes are added as link - attributes to their endpoint link unless their specification says - otherwise. - - Serializations derived from Link Format, SHOULD present links to - endpoints in path-absolute form or, if required, as absolute - references. (This approach avoids the RFC6690 ambiguities.) - - While Endpoint Lookup does expose the registration resources, the RD - does not need to make them accessible to clients. Clients SHOULD NOT - attempt to dereference or manipulate them. - - A Resource Directory can report endpoints in lookup that are not - hosted at the same address. Lookup clients MUST be prepared to see - arbitrary URIs as registration resources in the results and treat - them as opaque identifiers; the precise semantics of such links are - left to future specifications. + base="coap://[ff05::1]", + ;ep=lights&et=core.rd-group; + base="coap://[ff35:30:2001:db8::1]";rt="core.rd-ep" - The following example shows a client performing an endpoint type (et) - lookup with the value oic.d.sensor (which is currently a registered - rt value): + The following example shows a client performing a lookup of all + resources of all endpoints (groups) with et=core.rd-group. - Req: GET /rd-lookup/ep?et=oic.d.sensor + Req: GET /rd-lookup/res?et=core.rd-group - Res: 2.05 Content - ;base="coap://[2001:db8:3::127]:61616";ep="node5"; - et="oic.d.sensor";ct="40", - ;base="coap://[2001:db8:3::129]:61616";ep="node7"; - et="oic.d.sensor";ct="40";d="floor-3" + ;rt="light";if="core.a"; + et="core.rd-group";anchor="coap://[ff35:30:2001:db8::1]", + ;if="core.p";u="K"; + et="core.rd-group"; + anchor="coap://[ff35:30:2001:db8::1]" Appendix B. Web links and the Resource Directory Understanding the semantics of a link-format document and its URI references is a journey through different documents ([RFC3986] defining URIs, [RFC6690] defining link-format documents based on [RFC8288] which defines link headers, and [RFC7252] providing the transport). This appendix summarizes the mechanisms and semantics at play from an entry in ".well-known/core" to a resource lookup. This text is primarily aimed at people entering the field of Constrained Restful Environments from applications that previously did not use web mechanisms. - At all examples in this section give compatible results for both - Modernized and RFC6690 Link Format; the explanation of the steps - follow Modernized Link Format. + The explanation of the steps makes some shortcuts in the more + confusing details of [RFC6690], which are justified as all examples + being in Limited Link Format. B.1. A simple example Let's start this example with a very simple host, "2001:db8:f0::1". A client that follows classical CoAP Discovery ([RFC7252] Section 7), sends the following multicast request to learn about neighbours supporting resources with resource-type "temperature". The client sends a link-local multicast: @@ -3146,23 +3127,22 @@ B.1.2. Interpreting attributes and relations Some more information but the record's target can be obtained from the payload: the resource type of the target is "temperature", and its content type is text/plain (ct=0). A relation in a web link is a three-part statement that specifies a named relation between the so-called "context resource" and the target resource, like "_This page_ has _its table of contents_ at _/ - toc.html_". In [RFC6690] and modernized link-format documents, there - is an implicit "host relation" specified with default parameter: - rel="hosts". + toc.html_". In link format documents, there is an implicit "host + relation" specified with default parameter: rel="hosts". In our example, the context resource of the link is the URI specified in the GET request "coap:://[2001:db8:f0::1]/.well-known/core". A full English expression of the "host relation" is: '"coap://[2001:db8:f0::1]/.well-known/core" is hosting the resource "coap://[2001:db8:f0::1]/temp", which is of the resource type "temperature" and can be accessed using the text/plain content format.' @@ -3226,25 +3206,25 @@ ;rt=temperature;ct=0; anchor="coap://[2001:db8:f0::1]" This is not _literally_ the same response that it would have received from a multicast request, but it contains the equivalent statement: '"coap://[2001:db8:f0::1]" is hosting the resource "coap://[2001:db8:f0::1]/temp", which is of the resource type "temperature" and can be accessed using the text/plain content format.' - (The difference is whether "/" or "/.well-known/core" hosts the - resources, which is one of the often misunderstood subtleties - Modernized Link Format addresses. Actually, /.well-known/core does - NOT host the resource but stores a URI reference to the resource.) + resources, which does not matter in this application; if it did, the + endpoint would have been more explicit. Actually, /.well-known/core + does NOT host the resource but stores a URI reference to the + resource.) To complete the examples, the client could also query all resources hosted at the endpoint with the known endpoint name "simple-host1". A request to "coap://[2001:db8:f0::ff]/rd-lookup/res?ep=simple-host1" would return ;rt=temperature;ct=0; anchor="coap://[2001:db8:f0::1]", ;rt=light-lux;ct=0; anchor="coap://[2001:db8:f0::1]", @@ -3263,44 +3243,39 @@ ;rt=temperature;ct=0; anchor="coap+tcp://simple-host1.example.com" and analogous records. B.4. A note on differences between link-format and Link headers While link-format and Link headers look very similar and are based on the same model of typed links, there are some differences between - [RFC6690] and [RFC5988], which are dealt with differently: + [RFC6690] and [RFC8288], which are dealt with differently: o "Resolving the target against the anchor": [RFC6690] Section 2.1 states that the anchor of a link is used as the Base URI against which the term inside the angle brackets (the target) is resolved, falling back to the resource's URI with paths stripped off (its "Origin"). In contrast to that, [RFC8288] Section B.2 describes that the anchor is immaterial to the resolution of the target reference. RFC6690, in the same section, also states that absent anchors set the context of the link to the target's URI with its path stripped off, while according to [RFC8288] Section 3.2, the context is the resource's base URI. - In the context of a Resource Directory, the authors decided to not - let this become an issue by recommending that links in the - Resource Directory be _deserializable_ by either rule set to give - the same results. Note that all examples of [RFC6690], [RFC8288] - and this document comply with that rule. - - The Modernized Link Format is introduced in Appendix D to - formalize what it means to apply the ruleset of RFC8288 to Link - Format documents. + The rules introduced in Appendix C ensure that an RD does not need + to deal with those differences when processing input data. Lookup + results are required to be absolute references for the same + reason. o There is no percent encoding in link-format documents. A link-format document is a UTF-8 encoded string of Unicode characters and does not have percent encoding, while Link headers are practically ASCII strings that use percent encoding for non- ASCII characters, stating the encoding explicitly when required. For example, while a Link header in a page about a Swedish city might read @@ -3308,159 +3283,54 @@ "Link: ;rel="live-environment-data"" a link-format document from the same source might describe the link as ";rel="live-environment-data"" Parsers and producers of link-format and header data need to be aware of this difference. -Appendix C. Syntax examples for Protocol Negotiation - - [ This appendix should not show up in a published version of this - document. ] - - The protocol negotiation that is being worked on in - [I-D.silverajan-core-coap-protocol-negotiation] makes use of the - Resource Directory. - - Until that document is update to use the latest resource-directory - specification, here are some examples of protocol negotiation with - the current Resource Directory: - - An endpoint could register as follows from its address - [2001:db8:f1::2]:5683: - - Req: POST coap://rd.example.com/rd?ep=node1 - &at=coap+tcp://[2001:db8:f1::2] - Content-Format: 40 - Payload: - ;ct=0;rt="temperature";if="core.s" - - Res: 2.01 Created - Location-Path: /rd/1234 - - An endpoint lookup would just reflect the registered attributes: - - Req: GET /rd-lookup/ep - - Res: 2.05 Content - ;ep="node1";base="coap://[2001:db8:f1::2]:5683"; - at="coap+tcp://[2001:db8:f1::2]" - - A UDP client would then see the following in a resource lookup: - - Req: GET /rd-lookup/res?rt=temperature - - Res: 2.05 Content - ;ct=0;rt="temperature"; - if="core.s"; anchor="coap://[2001:db8:f1::2]" - - while a TCP capable client could say: - - Req: GET /rd-lookup/res?rt=temperature&tt=tcp - - Res: 2.05 Content - ;ct=0;rt="temperature"; - if="core.s";anchor="coap+tcp://[2001:db8:f1::2]" - -Appendix D. Modernized Link Format parsing - - The CoRE Link Format as described in [RFC6690] is unsuitable for some - use cases of the Resource Directory, and their resolution scheme is - often misunderstood by developers familiar with [RFC8288]. - - For the correct application of base URIs, we describe the - interpretation of a Link Format document as a Modernized Link Format. - In Modernized Link Format, the document is processed as in Link - Format, with the exception of Section 2.1 of [RFC6690]: - - o The URI-reference inside angle brackets ("<>") describes the - target URI of the link. - - o The context of the link is expressed by the "anchor" parameter. - If the anchor attribute is absent, it defaults to the empty - reference (""). - - o Both these references are resolved according to Section 5 of - [RFC3986]. - - Content formats derived from [RFC6690] which inherit its resolution - rules, like JSON and CBOR link format of [I-D.ietf-core-links-json], - can be interpreted in analogy to that. - - For where the Resource Directory is concerned, all common forms of - links (e.g. all the examples of RFC6690) yield identical results. - When interpreting data read from ".well-known/core", differences in - interpretation only affect links where the absent anchor attribute - means "coap://host/" according to RFC6690 and "coap://host/.well- - known/core" according to Modernized Link format; those typically only - occur in conjunction with the vaguely defined implicit "hosts" - relationship. - -D.1. For endpoint developers - - When developing endpoints, i.e. when generating documents that will - be submitted to a Resource Directory, the differences between - Modernized Link Format and RFC6690 can be ignored as long as - - o all relative references start with a slash, - - and any of the following applies: - - o There is no anchor attribute, and the context of the link does not - matter to the application. - - Example: ";ct=40" - - o The anchor is a relative reference. - - Example: ";anchor="/sensors/temp";rel="alternate"" - - o The target is an absolute reference. - - Example: ";anchor="/sensors/ - temp";rel="describedby"" - -D.2. Examples of links with differing interpretations +Appendix C. Limited Link Format - Examples of links with different interpretations from either applying - RFC6690 or Modernized Link Format are shown here. The example is - assumed to be obtained from a document. + The CoRE Link Format as described in [RFC6690] has been interpreted + differently by implementers, and a strict implementation rules out + some use cases of a Resource Directory (e.g. base values with path + components). - o "": The target is "/sensors" in RFC6690 and "/device/ - sensors" in Modernized Link Format (whereas "" would be - unambiguous). + This appendix describes a subset of link format documents called + Limited Link Format. The rules herein are not very limiting in + practice - all examples in RFC6690, and all deployments the authors + are aware of already stick to them - but ease the implementation of + resource directory servers. - o "": The target is "/?which=these" in RFC6690 and - "/device/index?which=these" in Modernized Link Format. + It is applicable to representations in the application/link-format + media type, and any other media types that inherit [RFC6690] + Section 2.1. - o ";anchor="http://example.com/calib- - proto/1234";rel="topic"" is about "http://example.com/sensors" in - RFC6690 and about "/device/sensors" in Modernized Link Format. + A link format representation is in Limited Link format if, for each + link in it, the following applies: - This link can not be expressed in RFC6690 link format without the - server explicitly expressing most of its own URI (which is - problematic in reverse proxy scenarios or when the Uri-Host option - is not sent). + o All URI references either follow the URI or the path-absolute ABNF + rule of RFC3986 (i.e. target and anchor each either start with a + scheme or with a single slash), - o ";rel="alternate";anchor=""": According to RFC6690, this - states that the "/" resource has an alternative representation at - "/i", whereas Modernized Link Format says that "/devices/index" - has an alternative representation at "/i". + o if the anchor reference starts with a scheme, the target reference + starts with a scheme as well (i.e. relative references in target + cannot be used when the anchor is a full URI), and - The "anchor" attribute is usually left out; the link - ";rel="alternate"" is equivalent to the above and results in - the same interpretations. + o the application does not care whether links without an explicitly + given anchor have the origin's "/" or "/.well-known/core" resource + as their link context. Authors' Addresses + Zach Shelby ARM 150 Rose Orchard San Jose 95134 USA Phone: +1-408-203-9434 Email: zach.shelby@arm.com Michael Koster