--- 1/draft-ietf-core-resource-directory-11.txt 2017-10-30 12:14:06.535004749 -0700 +++ 2/draft-ietf-core-resource-directory-12.txt 2017-10-30 12:14:06.647007428 -0700 @@ -1,25 +1,25 @@ CoRE Z. Shelby Internet-Draft ARM Intended status: Standards Track M. Koster -Expires: January 4, 2018 SmartThings +Expires: May 3, 2018 SmartThings C. Bormann Universitaet Bremen TZI P. van der Stok consultant C. Amsuess, Ed. Energy Harvesting Solutions - July 03, 2017 + October 30, 2017 CoRE Resource Directory - draft-ietf-core-resource-directory-11 + draft-ietf-core-resource-directory-12 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 descriptions of resources held on other servers, allowing lookups to be performed for those resources. This document specifies the web interfaces that a Resource Directory supports in order for web @@ -35,21 +35,21 @@ 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 http://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 January 4, 2018. + This Internet-Draft will expire on May 3, 2018. Copyright Notice Copyright (c) 2017 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 (http://trustee.ietf.org/license-info) in effect on the date of publication of this document. Please review these documents @@ -58,86 +58,100 @@ include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 3. Architecture and Use Cases . . . . . . . . . . . . . . . . . 5 3.1. Principles . . . . . . . . . . . . . . . . . . . . . . . 5 - 3.2. Architecture . . . . . . . . . . . . . . . . . . . . . . 5 - 3.3. Use Case: Cellular M2M . . . . . . . . . . . . . . . . . 7 - 3.4. Use Case: Home and Building Automation . . . . . . . . . 8 - 3.5. Use Case: Link Catalogues . . . . . . . . . . . . . . . . 8 - 4. Finding a Resource Directory . . . . . . . . . . . . . . . . 9 - 4.1. Resource Directory Address Option (RDAO) . . . . . . . . 10 - 5. Resource Directory . . . . . . . . . . . . . . . . . . . . . 11 - 5.1. Content Formats . . . . . . . . . . . . . . . . . . . . . 12 - 5.2. URI Discovery . . . . . . . . . . . . . . . . . . . . . . 12 - 5.3. Registration . . . . . . . . . . . . . . . . . . . . . . 14 - 5.3.1. Simple Registration . . . . . . . . . . . . . . . . . 17 - 5.3.2. Simple publishing to Resource Directory Server . . . 18 - 5.3.3. Third-party registration . . . . . . . . . . . . . . 18 - 5.3.4. Plurality of link references in a Registration . . . 19 - 5.4. Operations on the Registration Resource . . . . . . . . . 19 - 5.4.1. Registration Update . . . . . . . . . . . . . . . . . 20 - 5.4.2. Registration Removal . . . . . . . . . . . . . . . . 22 - 5.4.3. Read Endpoint Links . . . . . . . . . . . . . . . . . 23 - 5.4.4. Update Endpoint Links . . . . . . . . . . . . . . . . 24 - 6. RD Groups . . . . . . . . . . . . . . . . . . . . . . . . . . 28 - 6.1. Register a Group . . . . . . . . . . . . . . . . . . . . 28 - 6.2. Group Removal . . . . . . . . . . . . . . . . . . . . . . 30 + 3.2. Architecture . . . . . . . . . . . . . . . . . . . . . . 6 + 3.3. Content model . . . . . . . . . . . . . . . . . . . . . . 7 + 3.4. Use Case: Cellular M2M . . . . . . . . . . . . . . . . . 11 + 3.5. Use Case: Home and Building Automation . . . . . . . . . 12 + 3.6. Use Case: Link Catalogues . . . . . . . . . . . . . . . . 12 + 4. Finding a Resource Directory . . . . . . . . . . . . . . . . 13 + 4.1. Resource Directory Address Option (RDAO) . . . . . . . . 14 + 5. Resource Directory . . . . . . . . . . . . . . . . . . . . . 15 + 5.1. Content Formats . . . . . . . . . . . . . . . . . . . . . 16 + 5.2. URI Discovery . . . . . . . . . . . . . . . . . . . . . . 16 + 5.3. Registration . . . . . . . . . . . . . . . . . . . . . . 18 + 5.3.1. Simple Registration . . . . . . . . . . . . . . . . . 22 + 5.3.2. Third-party registration . . . . . . . . . . . . . . 23 + 5.4. Operations on the Registration Resource . . . . . . . . . 23 + 5.4.1. Registration Update . . . . . . . . . . . . . . . . . 24 + 5.4.2. Registration Removal . . . . . . . . . . . . . . . . 26 + 5.4.3. Read Endpoint Links . . . . . . . . . . . . . . . . . 27 + 5.4.4. Update Endpoint Links . . . . . . . . . . . . . . . . 28 + 6. RD Groups . . . . . . . . . . . . . . . . . . . . . . . . . . 29 + 6.1. Register a Group . . . . . . . . . . . . . . . . . . . . 29 + 6.2. Group Removal . . . . . . . . . . . . . . . . . . . . . . 31 7. RD Lookup . . . . . . . . . . . . . . . . . . . . . . . . . . 31 - 8. Security Considerations . . . . . . . . . . . . . . . . . . . 36 - 8.1. Endpoint Identification and Authentication . . . . . . . 36 - 8.2. Access Control . . . . . . . . . . . . . . . . . . . . . 36 - 8.3. Denial of Service Attacks . . . . . . . . . . . . . . . . 37 - - 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 37 - 9.1. Resource Types . . . . . . . . . . . . . . . . . . . . . 37 - 9.2. IPv6 ND Resource Directory Address Option . . . . . . . . 37 - 9.3. RD Parameter Registry . . . . . . . . . . . . . . . . . . 37 - 10. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 38 - 10.1. Lighting Installation . . . . . . . . . . . . . . . . . 38 - 10.1.1. Installation Characteristics . . . . . . . . . . . . 39 - 10.1.2. RD entries . . . . . . . . . . . . . . . . . . . . . 40 - 10.2. OMA Lightweight M2M (LWM2M) Example . . . . . . . . . . 43 - 10.2.1. The LWM2M Object Model . . . . . . . . . . . . . . . 43 - 10.2.2. LWM2M Register Endpoint . . . . . . . . . . . . . . 45 - 10.2.3. LWM2M Update Endpoint Registration . . . . . . . . . 46 - 10.2.4. LWM2M De-Register Endpoint . . . . . . . . . . . . . 47 - 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 47 - 12. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 47 - 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 51 - 13.1. Normative References . . . . . . . . . . . . . . . . . . 51 - 13.2. Informative References . . . . . . . . . . . . . . . . . 52 - Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 53 + 7.1. Resource lookup . . . . . . . . . . . . . . . . . . . . . 32 + 7.2. Endpoint and group lookup . . . . . . . . . . . . . . . . 33 + 7.3. Lookup filtering . . . . . . . . . . . . . . . . . . . . 33 + 7.4. Lookup examples . . . . . . . . . . . . . . . . . . . . . 35 + 8. Security Considerations . . . . . . . . . . . . . . . . . . . 38 + 8.1. Endpoint Identification and Authentication . . . . . . . 38 + 8.2. Access Control . . . . . . . . . . . . . . . . . . . . . 39 + 8.3. Denial of Service Attacks . . . . . . . . . . . . . . . . 39 + 9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 39 + 9.1. Resource Types . . . . . . . . . . . . . . . . . . . . . 40 + 9.2. IPv6 ND Resource Directory Address Option . . . . . . . . 40 + 9.3. RD Parameter Registry . . . . . . . . . . . . . . . . . . 40 + 9.3.1. Full description of the "Endpoint Type" Registration + Parameter . . . . . . . . . . . . . . . . . . . . . . 42 + 9.4. "Endpoint Type" (et=) RD Parameter values . . . . . . . . 42 + 10. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 42 + 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 . . . . . . . . . . . . . . . 47 + 10.2.2. LWM2M Register Endpoint . . . . . . . . . . . . . . 49 + 10.2.3. LWM2M Update Endpoint Registration . . . . . . . . . 50 + 10.2.4. LWM2M De-Register Endpoint . . . . . . . . . . . . . 51 + 11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 51 + 12. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 51 + 13. References . . . . . . . . . . . . . . . . . . . . . . . . . 56 + 13.1. Normative References . . . . . . . . . . . . . . . . . . 56 + 13.2. Informative References . . . . . . . . . . . . . . . . . 57 + Appendix A. Web links and the Resource Directory . . . . . . . . 58 + A.1. A simple example . . . . . . . . . . . . . . . . . . . . 58 + A.1.1. Resolving the URIs . . . . . . . . . . . . . . . . . 59 + A.1.2. Interpreting attributes and relations . . . . . . . . 59 + A.2. A slightly more complex example . . . . . . . . . . . . . 59 + A.3. Enter the Resource Directory . . . . . . . . . . . . . . 60 + A.4. A note on differences between link-format and Link + headers . . . . . . . . . . . . . . . . . . . . . . . . . 62 + Appendix B. Syntax examples for Protocol Negotiation . . . . . . 62 + Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 63 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 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 requesting "/.well-known/core". In many - M2M scenarios, direct discovery of resources is not practical due to + 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 descriptions of resources held on other servers, allowing lookups to be performed for those resources. This document specifies the web interfaces that a Resource Directory supports in order 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 @@ -161,46 +175,53 @@ This specification makes use of the following additional terminology: Resource Directory A web entity that stores information about web resources and implements the REST interfaces defined in this specification for registration and lookup of those resources. Domain In the context of a Resource Directory, a domain is a logical - grouping of endpoints. This specification assumes that the list - of Domains supported by an RD is pre-configured by that RD. When - a domain is exported to DNS, the domain value equates to the DNS - domain name. + grouping of endpoints. Group In the context of a Resource Directory, a group is a logical grouping of endpoints for the purpose of group communications. - All groups within a domain are unique. + All groups within a domain have unique names. Endpoint Endpoint (EP) is a term used to describe a web server or client in [RFC7252]. In the context of this specification an endpoint is used to describe a web server that registers resources to the Resource Directory. An endpoint is identified by its endpoint - name, which is included during registration, and is unique within - the associated domain of the registration. + name, which is included during registration, and has a unique name + within the associated domain of the registration. Context - When registering links to a Resource Directory, the Context refers - to the scheme, address, port, and base path for all the links - registered on behalf of an endpoint, of the general form - scheme://host:port/path/ where the client may explicitly set the - scheme and host, and may supply the port and path as optional - parameters. When the context of a registration is explicitly set, - the URI resolution rules in [RFC3986] MUST be applied. + A Context is a base URL that gives scheme and (typically) + authority information about an Endpoint. The Context of an + Endpoint is provided at registration time, and is used by the + Resource Directory to resolve relative references inside the + registration into absolute URIs. + + Directory Resource + A resource in the Resource Directory (RD) containing registration + resources. + + Group Resource + A resource in the RD containing registration resources of the + Endpoints that form a group. + + Registration Resource + A resource in the RD that contains information about an Endpoint + and its links. Commissioning Tool Commissioning Tool (CT) is a device that assists during the installation of the network by assigning values to parameters, naming endpoints and groups, or adapting the installation to the needs of the applications. RDAO Resource Directory Address Option. @@ -229,41 +250,41 @@ information themselves. No other client can modify data in the resource directory or even expect those changes to propagate back to its source. 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] about resources hosted on other web servers, which are called endpoints (EP). An endpoint is a web server associated with a - scheme, IP address and port (called Context), thus 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 clients to - lookup resources from the RD or maintain groups. Endpoints - themselves can also act as clients. An RD can be logically segmented - by the use of Domains. The domain an endpoint is associated with can - be defined by the RD or configured by an outside entity. This - information hierarchy is shown in Figure 2. + scheme, IP address and port, thus 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 clients to lookup resources + from the RD or maintain groups. Endpoints themselves can also act as + clients. An RD can be logically segmented by the use of Domains. + The domain an endpoint is associated with can be defined by the RD or + configured by an outside entity. This information hierarchy is shown + in Figure 2. A mechanism to discover an RD using CoRE Link Format [RFC6690] is defined. Endpoints proactively register and maintain resource directory registration entries on the RD, which are soft state and need to be periodically refreshed. An endpoint is provided with 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 entries. + directory registration entries. 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 the registration entry. A lookup interface for discovering any of the Web Links held in the RD is provided using the CoRE Link Format. @@ -295,69 +316,236 @@ | Endpoint | <-- Name, Scheme, IP, Port +------------+ | | +------------+ | Resource | <-- Target, Parameters +------------+ Figure 2: The resource directory information hierarchy. -3.3. Use Case: Cellular M2M +3.3. Content model + + The Entity-Relationship (ER) models shown in Figure 3 and Figure 4 + 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 + can, however, be expressed as relative references in serializations, + and often are. + + These models provide an abstract view of the information expressed in + link-format documents and a Resource Directory. They cover the + concepts, but not necessarily all details of an RD's operation; they + are meant to give an overview, and not be a template for + implementations. + + +----------------------+ + | /.well-known/core | + +----------------------+ + | + | 1 + ////////\\\\\\\ + < contains > + \\\\\\\\/////// + | + | 0+ + +--------------------+ + | link | + +--------------------+ + | + | 1 oooooooo + +-----o target o + 0+ | oooooooo + oooooooooooo | + 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 + + The model shown in Figure 3 models the contents of /.well-known/core + which contains: + + o a set of links belonging to the host + + The host 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: + + o Zero or more link relations: They describe a 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, eg. + _who_ "hosts" something. + + In link-format serialization, it is expressed in the "anchor" + attribute. There, it can be a relative reference, in which case + it gets resolved against the URI of the ".well-known/core" + document it was obtained from . It defaults to that document's + URI. + + In the serialization, the context also serves as the Base URI for + resolving the target reference. + + o A link target URI: It defines the destination of the relation (eg. + _what_ is hosted), and is the topic of all target attributes. + + In link-format serialization, it is expressed between angular + brackets, and sometimes called the "href". If it is a relative URI, + it gets resolved against the link context URI. + + o Other target attributes (eg. resource type (rt), interface (if), + cor content-type (ct)). These provide additional information + about the target URI. + + +----------------------+ + | resource-directory | + +----------------------+ + | + | oooooooooooo 0-1 + | o MC address o---+ + | oooooooooooo | + | | + //////\\\\ 0+ +--------+ + < contains >----------------| group | + \\\\\///// +--------+ + | | + 0-n | | 1+ + ooooooo 1 +---------------+ ///////\\\\\\ + o con o-------| registration |---------< composed of > + ooooooo +---------------+ \\\\\\\////// + | | + | +--------------+ + oooooooo 1 | | + o loc o----+ /////\\\\ + oooooooo | < contains > + | \\\\\///// + oooooooo 1 | | + o ep o----+ | 0+ + oooooooo | +------------------+ + | | link | + oooooooo 0-1 | +------------------+ + o d o----+ | + oooooooo | | 1 oooooooo + | +-----o target o + oooooooo 0-1 | | oooooooo + 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 + + The model shown in Figure 4 models the contents of the resource + directory which contains in addition to /.well-known/core: + + o 0 to n Registration (entries), + o 0 or more Groups + + A Group has no or one Multicast address attribute and is composed of + 0 or more endpoints. A registration is associated with one endpoint + (ep). An endpoint can be part of 0 or more Groups . A registration + defines a set of links as defined for /.well-known/core. A + Registration has six attributes: + + o one ep (endpoint with a unique name) + + o one con (a string describing the scheme://authority part) + + o one lt (lifetime), + + o one loc (location in the RD) + + o optional one d (domain for query filtering), + + o optional additional endpoint attributes (from Section 9.3) + + The cardinality of con is currently 1. 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. + +3.4. 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 - air 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 application - requirements, thus avoiding silo like solutions. One of the crucial - enablers of such design is the ability to discover resources - (machines -- endpoints) capable of providing required information at - a given time or acting on instructions from the end users. + 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 + application requirements, thus avoiding silo like solutions. One of + the crucial enablers of such design is the ability to discover + resources (machines -- endpoints) capable of providing required + information at a given time or acting on instructions from the end + users. - In a typical scenario, during a boot-up procedure (and periodically - afterwards), the machines (endpoints) register with a Resource - Directory (for example EPs installed on vehicles enabling tracking of - their position for fleet management purposes and monitoring - environment parameters) hosted by the mobile operator or somewhere - else in the network, periodically a description of its own - capabilities. Due to the usual network configuration of mobile - networks, the EPs attached to the mobile network may not always be - efficiently reachable. Therefore, a remote server is usually used to - provide proxy access to the EPs. The address of each (proxy) - endpoint on this server is included in the resource description - stored in the RD. The users, for example mobile applications for - environment monitoring, contact the RD, look up the endpoints capable + Imagine a scenario where endpoints installed on vehicles enable + tracking of the position of these vehicles for fleet management + purposes and allow monitoring of environment parameters. During the + boot-up process endpoints register with a Resource Directory, which + is hosted by the mobile operator or somewhere in the cloud. + + Periodically, these endpoints update their registration and may + modify resources they offer. + + When endpoints are not always connected, for example because they + enter a sleep mode, a remote server is usually used to provide proxy + 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 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. -3.4. Use Case: Home and Building Automation +3.5. 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. -3.5. Use Case: Link Catalogues +3.6. 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 the data to an intermediary server, or broker. Sensor data are published to the intermediary upon changes @@ -379,60 +567,84 @@ be sufficient to store external metadata in Resource Directories. The additional features of Resource Directory allow domains to be defined to enable access to a particular set of resources from particular applications. This provides isolation and protection of sensitive data when needed. Resource groups may defined to allow batched reads from multiple resources. 4. Finding a Resource Directory - Several mechanisms can be employed for discovering the RD, including - assuming a default location (e.g. on an Edge Router in a LoWPAN), - assigning an anycast address to the RD, using DHCP, or discovering - the RD using .well-known/core and hyperlinks as specified in CoRE - Link Format [RFC6690]. Endpoints that want to contact a Resource - Directory can obtain candidate IP addresses for such servers in a - number of ways. + A device coming up may want to find one or more resource directories + to make itself known with. - In a 6LoWPAN, good candidates can be taken from: + The device may be pre-configured to exercise specific mechanisms for + finding the resource directory: - o specific static configuration (e.g., anycast addresses), if any, + o It may be configured with a specific IP address for the RD. That + IP address may also be an anycast address, allowing the network to + forward RD requests to an RD that is topologically close; each + target network environment in which some of these preconfigured + nodes are to be brought up is then configured with a route for + this anycast address that leads to an appropriate RD. (Instead of + using an anycast address, a multicast address can also be + preconfigured. The RD directory servers then need to configure + one of their interfaces with this multicast address.) - o the ABRO option of 6LoWPAN-ND [RFC6775], + o It may be configured with a DNS name for the RD and a resource- + record type to look up under this name; it can find a DNS server + to perform the lookup using the usual mechanisms for finding DNS + servers. - o other ND options that happen to point to servers (such as RDNSS), + o It may be configured to use a service discovery mechanism such as + DNS-SD [RFC6763]. The present specification suggests configuring + the service with name rd._sub._coap._udp, preferably within the + domain of the querying nodes. - o DHCPv6 options that might be defined later. + For cases where the device is not specifically configured with a way + to find a resource directory, the network may want to provide a + suitable default. - o The IPv6 Neighbor Discovery Resource Directory Address Option - described in Section 4.1 + o If the address configuration of the network is performed via + SLAAC, this is provided by the RDAO option Section 4.1. - In networks with more inexpensive use of multicast, the candidate IP - address may be a well-known multicast address, i.e. directory servers - are found by simply sending GET requests to that well-known multicast - address (see Section 5.2). + o If the address configuration of the network is performed via DHCP, + this could be provided via a DHCP option (no such option is + defined at the time of writing). - Constrained nodes configured in large batches may be configured for - an anycast address for the RD. Each target network environment in - which some of these preconfigured nodes are to be brought up is then - configured with a route for this anycast address that leads to an RD - that is appropriate for the environment. + Finally, if neither the device nor the network offer any specific + configuration, the device may want to employ heuristics to find a + suitable resource directory. - As some of these sources 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. + The present specification does not fully define these heuristics, but + suggests a number of candidates: + + o In a 6LoWPAN, just assume the Edge Router (6LBR) can act as a + 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*". + + o 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://[ff02::1]/.well-known/core?rt=core.rd*". RDs within the + multicast scope will answer the query. + + 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. 4.1. Resource Directory Address Option (RDAO) The Resource Directory Option (RDAO) using IPv6 neighbor Discovery (ND) carries information about the address of the Resource Directory (RD). This information is needed when endpoints cannot discover the Resource Directory with link-local multicast address because the endpoint and the RD are separated by a border Router (6LBR). In many circumstances the availability of DHCP cannot be guaranteed either during commissioning of the network. The presence and the use of the @@ -477,68 +689,74 @@ 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 3: Resource Directory Address Option + Figure 5: 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 + operation is outside the scope of this document. + 5.1. 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. 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]. It is however - expected that RDs will also be discoverable via other methods - depending on the deployment. + 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, and "core.gp" is used to discover the URI path for RD - Group operations. Upon success, the response will contain a payload - with a link format entry for each RD function discovered, indicating - the URI path 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. + operations, and "core.rd-group" is used to discover the URI path for + RD Group operations. Upon success, the response will contain a + payload with a link format entry for each RD function discovered, + indicating the URI path 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. A Resource Directory MAY provide hints about the content-formats it supports in the links it exposes or registers, using the "ct" link 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. Links to Resource Directories MAY be registered in other Resource Directories, and well-known entry @@ -552,214 +770,234 @@ Interaction: EP -> RD Method: GET URI Template: /.well-known/core{?rt} URI Template Variables: rt := Resource Type (optional). MAY contain one of the values - "core.rd", "core.rd-lookup*", "core.rd-lookup-d", "core.rd- - lookup-res", "core.rd-lookup-ep", "core.rd-lookup-gp", - "core.rd-group" or "core.rd*" + "core.rd", "core.rd-lookup*", "core.rd-lookup-res", "core.rd- + lookup-ep", "core.rd-lookup-gp", "core.rd-group" 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) 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. - Failure: 4.04 "Not Found" or 404 "Not Found" is returned in case no - matching entry is found for a unicast request. - 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 RD registration resource is, in - this example, at /rd, and that the content-format delivered by the - server hosting the resource is application/link-format (ct=40). Note - that it is up to the RD to choose its RD resource paths. + interface, thus learning that the directory resource is, in this + example, at /rd, and that the content-format delivered by the server + hosting the resource is application/link-format (ct=40). Note that + it is up to the RD to choose its RD resource paths. Req: GET coap://[ff02::1]/.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, ;rt="core.rd-lookup-gp";ct=40, - ;rt="core.rd-lookup-d";ct=40, ;rt="core.rd-group";ct=40 - Figure 4: Example discovery exchange + Figure 6: 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 a - more application-specific content format (picked as 65225 in this - example; this is in the experimental space, not an assigned value). - The RD resource paths /rd, /rd-lookup, and /rd-group are example - values. This server only implements some of the interfaces described - in this document. + Content-Format 40 (application/link-format) indicated as well as the + the CBOR and JSON representation of link format. The RD resource + paths /rd, /rd-lookup, and /rd-group are example values. + + [ The RFC editor is asked to replace these and later occurrences of + TBD64 and TBD504 with 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://[ff02::1]/.well-known/core?rt=core.rd* Res: 2.05 Content ;rt="core.rd";ct="40 65225", - ;rt="core.rd-lookup-res";ct="40 65225", - ;rt="core.rd-lookup-ep";ct="40 65225", - ;rt="core.rd-group";ct="40 65225" + ;rt="core.rd-lookup-res";ct="40 TBD64 TBD504", + ;rt="core.rd-lookup-ep";ct="40 TBD64 TBD504", + ;rt="core.rd-lookup-gp";ct=40 TBD64 TBD504", + ;rt="core.rd-group";ct="40 TBD64 TBD504" 5.3. Registration After discovering the location of an RD, an endpoint MAY register its resources 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 its domain and the lifetime 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. An endpoint MUST use that location when refreshing registrations using - this interface. Endpoint resources in the RD are kept active for the - period indicated by the lifetime parameter. The endpoint is - responsible for refreshing the entry 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 does not create multiple RD - entries. A new registration may be created at any time to supersede - an existing registration, replacing the registration parameters and - links. + this interface. Registration resources in the RD are kept active for + the period indicated by the lifetime parameter. The 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 does not + create multiple registration resources. A new registration resource + may be created at any time to supersede an existing registration, + replacing the registration parameters and links. + + An empty payload is considered a malformed 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. The + Base URI against which they are resolved is the context of the + registration, which is provided either explicitly in the "con" + parameter or constructed implicitly from the requester's network + address. When resolving relative target references, the server first + resolves the context of that link, and then interprets the target as + a reference relative to that context (see Appendix A.4). The registration request interface is specified as follows: Interaction: EP -> RD Method: POST - URI Template: {+rd}{?ep,d,et,lt,con} + URI Template: {+rd}{?ep,d,lt,con,extra-attrs*} URI Template Variables: rd := RD registration URI (mandatory). This is the location of the RD, as obtained from discovery. - ep := Endpoint name (mandatory). The endpoint name is an + ep := Endpoint name (mostly mandatory). The endpoint name is an identifier that MUST be unique within a domain. The maximum - length of this parameter is 63 bytes. + length of this parameter is 63 bytes. If the RD is configured + to recognize the endpoint (eg. based on its security context), + the endpoint can elide the endpoint name, and assign one based + on the configuration. d := Domain (optional). The domain to which this endpoint belongs. The maximum length of this parameter is 63 bytes. When this parameter is elided, the RD MAY associate the endpoint with a configured default domain. - et := Endpoint Type (optional). The semantic type of the - endpoint. This parameter SHOULD be less than 63 bytes. - lt := Lifetime (optional). Lifetime of the registration in seconds. Range of 60-4294967295. If no lifetime is included in the initial registration, a default value of 86400 (24 - hours) SHOULD be assumed. If the lt parameter is not included - in a registration refresh or update operation, the most - recently supplied value SHALL be re-used. + hours) SHOULD be assumed. - con := Context (optional). This parameter sets the scheme, - address, port and path at which this server is available in the - form scheme://host:port/path. In the absence of this parameter - the scheme of the protocol, source address and source port of - the register request are assumed. This parameter is mandatory - when the directory is filled by a third party such as an - commissioning tool. When con is used, scheme and host are - mandatory and port and path parameters are optional. If the - endpoint uses an ephemeral port to register with, it MUST - include the con: parameter in the registration to provide a - valid network path. If the endpoint which is 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. + con := Context (optional). This parameter sets the Default Base + URI under which the request's links are to be interpreted. The + URI MUST NOT have a path component of its own, but MUST be + suitable as a base URI to resolve any relative references given + in the registration. The parameter is therefore of the shape + "scheme://authority" for HTTP and CoAP URIs. In the absence of + this parameter the scheme of the protocol, source address and + source port of the registration request are assumed. This + parameter is mandatory when the directory is filled by a third + party such as an commissioning tool. If the endpoint uses an + ephemeral port to register with, it MUST include the con + parameter in the registration to provide a valid network path. + If the endpoint which is 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. + + 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 The following response codes are defined for this interface: Success: 2.01 "Created" or 201 "Created". The Location header option MUST be included in the response when a new registration resource is created. 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 updating and deleting links. + links, including updating and deleting links. A registration with + an already registered ep and d value pair responds with the same + success code and Location as the original registration; the set of + links registered with the endpoint is replaced with the links from + the payload. Failure: 4.00 "Bad Request" or 400 "Bad Request". Malformed request. - Failure: 4.09 "Conflict" or 409 "Conflict". Attempt to update the - registration content with links resulting in plurality of - references; see Section 5.3.4. - Failure: 5.03 "Service Unavailable" or 503 "Service Unavailable". Service could not perform the operation. HTTP support: YES The following example shows an endpoint 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 4. + similar to Figure 6. Req: POST coap://rd.example.com/rd?ep=node1 Content-Format: 40 Payload: ;ct=41;rt="temperature-c";if="sensor", ;ct=41;rt="light-lux";if="sensor" Res: 2.01 Created Location: /rd/4521 A Resource Directory may optionally support HTTP. Here is an example - of the same registration operation above, when done using HTTP. + of almost the same registration operation above, when done using HTTP + and the JSON Link Format. - Req: POST /rd?ep=node1&con=http://[2001:db8::1:1] HTTP/1.1 +Req: POST /rd?ep=node1&con=http://[2001:db8:1::1] HTTP/1.1 Host : example.com - Content-Type: application/link-format +Content-Type: application/link-format+json Payload: - ;ct=41;rt="temperature-c";if="sensor", - ;ct=41;rt="light-lux";if="sensor" +[ +{"href": "/sensors/temp", "ct": "41", "rt": "temperature-c", "if": "sensor"}, +{"href": "/sensors/light", "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 a 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 endpoint makes available the hosted @@ -762,254 +1000,230 @@ Simple Registration. However, there may be security reasons why this form of directory discovery would be disabled. This approach requires that the endpoint makes available the hosted resources that it wants to be discovered, as links on its "/.well- known/core" interface as specified in [RFC6690]. The endpoint then finds one or more addresses of the directory server as described in Section 4. - An endpoint can send (a selection of) hosted resources to a directory - server for publication as described in Section 5.3.2. - - The directory server integrates the information it received this way - into its resource directory. It MAY make the information available - to further directories, if it can ensure that a loop does not form. - The protocol used between directories to ensure loop-free operation - is outside the scope of this document. + An endpoint finally asks the directory server to probe it for + resources and publish them as follows: -5.3.2. Simple publishing to Resource Directory Server + It 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, which triggers the resource directory + server to perform GET requests at the requesting server's default + discovery URI to obtain the link-format payload to register. - An endpoint that wants to make itself discoverable occasionally sends - a POST request to the "/.well-known/core" URI of any candidate - directory server that it finds. The body of the POST request is - empty, which triggers the resource directory server to perform GET - requests at the requesting server's default discovery URI to obtain - the link-format payload to register. + The endpoint includes the same registration parameters in the POST + request as it would per Section 5.3. The context of the registration + is taken from the requesting server's URI. - The endpoint MUST include the endpoint name and MAY include the - registration parameters d, lt, and et, in the POST request as per - Section 5.3. + The endpoints MUST be deleted after the expiration of their lifetime. + Additional operations cannot be executed because no registration + location is returned. - The following example shows an endpoint using simple publishing, by + The following example shows an endpoint using Simple Registration, by simply sending an empty POST to a resource directory. - Req:(to RD server from [ff02::1]) - POST coap://rd.example.com/.well-known/core?lt=6000;ep=node1 - + Req:(to RD server from [2001:db8:2::1]) + POST /.well-known/core?lt=6000&ep=node1 Content-Format: 40 - - payload: - - (empty payload) + No payload Res: 2.04 Changed (later) - Req: (from RD server to [ff02::1]) - GET coap://[ff02::1]/.well-known/core - + Req: (from RD server to [2001:db8:2::1]) + GET /.well-known/core Accept: 40 Res: 2.05 Content - - payload: - + Payload: -5.3.3. Third-party registration +5.3.2. Third-party registration For some applications, even Simple Registration may be too taxing for certain 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 device, called a commissioning tool. The commissioning tool can fill the Resource Directory from a database or other means. For that purpose the scheme, IP address and port of the registered device is indicated in the Context parameter of the registration described in Section 5.3. -5.3.4. Plurality of link references in a Registration - - Plurality of link references within a Registration (registration - resource) is an indication of some error condition and should not be - allowed. - - Plurality of link references exists if, and only if, two or more - links in a Registration contain identical context, target, and - relation values. This condition would be likely to arise if there - were multiple co-ordinators or configuration tools, each with a - different set of configuration values for the same resource. - - A Resource Directory SHOULD reject a registration, or an operation on - a registration, which would result in a plurality of link references - within the the context of the registration. There is no requirement - in this document for a resource directory to check for plurality of - reference between different registrations. Resource Directory - operations which are rejected due to reference plurality SHOULD be - returned the "Conflict" code, indicating that there is someting wrong - with the request. - 5.4. Operations on the Registration Resource After the initial registration, an endpoint should retain 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. If the lifetime of - the registration expires, the RD SHOULD NOT respond to discovery - queries with information from the 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 resource recovery and + 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 resource recovery and garbage collection. If the Registration Resource is removed, the endpoint will need to re-register. The Registration Resource may also be used to inspect the registration resource using GET, update the registration link - contents using PATCH (as introduced in [RFC8132]), or cancel the - registration using DELETE. + contents, or cancel the registration using DELETE. These operations are described in this section. - In accordance with Section 5.3.4, operations which would result in - plural link references within the context of a registration resource - SHOULD be rejected using the "Conflict" result code. - 5.4.1. Registration Update The update interface is used by an endpoint to refresh or update its registration with an RD. To use the interface, the endpoint sends a POST request to the registration resource returned in the Location - header option in the response returned from the intial registration + header option in the response returned from the initial registration operation. - An update MAY update the lifetime or context registration parameters - "lt", "con" as in Section 5.3 ) if the previous settings are to be - retained. Parameters that are not being changed 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. - - Upon receiving an update request, an RD MUST reset the timeout for - that endpoint and update the scheme, IP address and port of the - endpoint, using the source address of the update, or the context - ("con") parameter if present. If the lifetime parameter "lt" is - included in the received update request, the RD MUST update the - lifetime of the registration and set the timeout equal to the new - lifetime. If the lifetime parameter is not included in the - registration update, the most recent setting is re-used for the next - registration time-out period. + An update MAY update the lifetime- or the context- registration + parameters "lt", "con" 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. - An update MAY optionally add or replace links for the endpoint by - including those links in the payload of the update as a CoRE Link - Format document. A link is replaced only if all of the target URI - and relation type (if present) and anchor value (if present) match. + 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 link payload is included, it SHOULD be checked for reference - plurality as described in Section 5.3.4 and rejected with a - "Conflict" result if there are plural link references detected. + If the context of the registration is changed in an update explicitly + or implicitly, relative references submitted in the original + registration or later updates are resolved anew against the new + context (like in the original registration). - In addition to the use of POST, as described in this section, there - is an alternate way to add, replace, and delete links using PATCH as - described in Section 5.4.4. + This operation only describes the use of POST with an empty payload. + As with modification of individual using iPATCH or PATCH as proposed + in Section 5.4.4, future standards might describe the semantics of + using content formats and payloads with the POST method to update the + links of a registration. The update registration request interface is specified as follows: Interaction: EP -> RD Method: POST - URI Template: {+location}{?lt,con} + + 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 86400) SHOULD be used. - con := Context (optional). This parameter sets the scheme, - address and port at which this server is available in the form - scheme://host:port/path. In the absence of this parameter the - scheme of the protocol, source address and source port of the - register request are assumed. This parameter is mandatory when - the directory is filled by a third party such as an - commissioning tool. When con is used, scheme and host are - mandatory and port and path parameters are optional. - - Content-Format: application/link-format (mandatory) + con := Context (optional). This parameter updates the context + 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 links of the + registration, following the same restrictions as in the + registration. If the parameter is not set and was set + explicitly before, the previous context value is kept + unmodified. If the parameter is not set and was not set + explicitly before either, the source address and source port of + the update request are stored as the context. - Content-Format: application/link-format+json (optional) + 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: application/link-format+cbor (optional) + 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: 4.09 "Conflict" or 409 "Conflict". Attempt to update the - registration content with links resulting in plurality of - references; see Section 5.3.4. - Failure: 5.03 "Service Unavailable" or 503 "Service Unavailable". Service could not perform the operation. HTTP support: YES - The following example shows an endpoint updating its registration at - an RD using this interface with the example location value: /rd/4521. + + The following example shows an endpoint updating 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 an endpoint updating its registration - with a new lifetime and context, changing an existing link, and - adding a new link using this interface with the example location - value /rd/4521. With the initial registration the client set the + resource at an RD using this interface with the example location + value: /rd/4521. The initial registration by the client set the following values: + o endpoint name (ep)=endpoint1 + o lifetime (lt)=500 o context (con)=coap://local-proxy-old.example.com:5683 - o resource= ;ct=41;rt="foobar";if="sensor" + The initial state of the Resource Directory is reflected in the + following request: - Req: POST /rd/4521?lt=600&con="coap://local-proxy.example.com:5683" - Content-Format: 40 +Req: GET /rd-lookup/res?ep=endpoint1 + +Res: 2.01 Content Payload: - ;ct=41;rt="temperature-f";if="sensor", - ;ct=41;rt="door";if="sensor" +;ct=41;rt="temperature";anchor="coap://local-proxy-old.example.com:5683", +;ct=41;rt="light-lux";if="sensor";anchor="coap://local-proxy-old.example.com:5683" + + The following example shows an EP changing the context to + "coaps://new.example.com:5684": + + Req: POST /rd/4521?con=coaps://new.example.com:5684 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="coaps://new.example.com:5684", +;ct=41;rt="light-lux";if="sensor";anchor="coaps://new.example.com:5684", + 5.4.2. Registration Removal Although RD entries have soft state and will eventually timeout after their lifetime, an endpoint SHOULD explicitly remove its 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. + Removed endpoints are implicitly removed from the groups to which + they belong. + The removal request interface is specified as follows: Interaction: EP -> RD Method: DELETE URI Template: {+location} URI Template Variables: @@ -1090,203 +1303,46 @@ Req: GET /rd/4521 Res: 2.01 Content Payload: ;ct=41;rt="temperature-c";if="sensor", ;ct=41;rt="light-lux";if="sensor" 5.4.4. Update Endpoint Links - A PATCH update adds, removes or changes links for the endpoint by - including link update information in the payload of the update as a - merge-patch+json format [RFC7396] document. - - Other PATCH document formats may be used as appropriate for patching - the array of objects format of a Registration Resource. In - particular, a select-merge patch document format could combine the - function of link selection query and link attribute replacement - values. - - One or more links are selected for update by using query filtering as - specified in [RFC6690] Section 4.1 - The query filter selects the links to be modified or deleted, by - matching the query parameter values to the values of the link - attributes. - - When the query parameters are not present in the request, the payload - specifies links to be added to the target document. When the query - parameters are present, the attribute names and values in the query - parameters select one or more links on which to apply the PATCH - operation. - - If no links are selected by the query parameters, the PATCH operation - SHOULD NOT update the state of any resource, and SHOULD return a - reply of "Changed". - - If an attribute name specified in the PATCH document exists in any - the set of selected links, all occurrences of the attribute value in - the target document MUST be updated using the value from the PATCH - payload. If the attribute name is not present in any selected links, - the attribute MUST be added to the links. - - If the PATCH payload contains plural link references, or processing - the PATCH payload would result in plural link references, the request - SHOULD be rejected with a "Conflict" result. - - If the PATCH payload results in the modification of link target, - context, or relation values, that is "href", "rel", or "anchor", the - request SHOULD be rejected with a "Conflict" result code. - - The update request interface is specified as follows: - - Interaction: EP -> RD - - Method: PATCH - - 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 - - Content-Format: application/merge-patch+json (mandatory) - The following response codes are defined for this interface: - - Success: 2.04 "Changed" 0r 204 "No Content" in 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 resource - does not exist (e.g. may have expired). - - Failure: 4.09 "Conflict" or 409 "Conflict". Attempt to update the - registration content with links resulting in plurality of - references; see Section 5.3.4. - - Failure: 5.03 "Service Unavailable" or 503 "Service Unavailable". - Service could not perform the operation. - - HTTP support: YES - - The following examples show an endpoint adding , - modifying , and removing links in RD - using the Update Endpoint Links function with the example location - value /rd/4521. - - The Registration Resource initial state is: - - Req: GET /rd/4521 - - Res: 2.01 Content - Payload: - ;ct=41;rt="temperature", - ;ct=41;rt="light-lux";if="sensor" - - The following example shows an EP adding the link ;ct=41;rt="humid-s";if="sensor" to the collection of links at - the location /rd/4521. - - Req: PATCH /rd/4521 - - Payload: - [{"href":"/sensors/humid","ct": 41, "rt": "humid-s", "if": "sensor"}] - - Content-Format: - application/merge-patch+json - - Res: 2.04 Changed - Req: GET /rd/4521 - - Res: 2.01 Content - Payload: - ;ct=41;rt="temperature", - ;ct=41;rt="light-lux";if="sensor", - ;ct=41;rt="humid-s";if="sensor" - - The following example shows an EP modifying all links at the example - location /rd/4521 which are identified by href="/sensors/temp", from - the initial link-value of ;rt="temperature" to the new - link-value ;rt="temperature-c";if="sensor" by changing - the value of the link attribute "rt" and adding the link attribute - if="sensor" using the PATCH operation with the supplied merge- - patch+json document payload. - - Req: PATCH /rd/4521?href=/sensors/temp - - Payload: - {"rt": "temperature-c", "if": "sensor"}, - - Content-Format: - application/merge-patch+json - - Res: 2.04 Changed - - Req: GET /rd/4521 - - Res: 2.01 Content - Payload: - ;ct=41;rt="temperature-c";if="sensor", - ;ct=41;rt="light-lux";if="sensor", - ;ct=41;rt="humid-s";if="sensor" - - This example shows an EP removing all links at the example location - /rd/4521 which are identified by href="/sensors/light". - - Req: PATCH /rd/4521?href=/sensors/light - - Payload: - {} - - Content-Format: - application/merge-patch+json - - Res: 2.04 Changed - Req: GET /rd/4521 - - Res: 2.01 Content - Payload: - ;ct=41;rt="temperature-c";if="sensor", - ;ct=41;rt="humid-s";if="sensor" + An iPATCH (or PATCH) update [RFC8132] adds, removes or changes links + of a registration by including link update information in the payload + of the update with a media type that still needs to be defined. 6. RD Groups This section defines the REST API for the creation, management, and lookup of endpoints for group operations. Similar to endpoint registration entries in the RD, groups may be created or removed. However unlike an endpoint entry, a group entry consists of a list of endpoints and does not have a lifetime associated with it. In order to make use of multicast requests with CoAP, a group MAY have a multicast address associated with it. 6.1. Register a Group In order to create a group, a commissioning tool (CT) used to configure groups, makes a request to the RD indicating the name of the group to create (or update), optionally the domain the group belongs to, and optionally the multicast address of the group. The - registration message includes the list of endpoints that belong to - that group. + registration message is a list of links to registration resources of + the endpoints that belong to that group. - All the endpoints in the group MUST be registered with the RD before - registering a group. If an endpoint is not yet registered to the RD - before registering the group, the registration message returns an - error. The RD sends a blank target URI for every endpoint link when - registering the group. + The commissioning tool SHOULD not send any target attributes with the + links to the registration resources, and the resource directory + SHOULD ignore any attributes that are set. Configuration of the endpoints themselves is out of scope of this specification. Such an interface for managing the group membership of an endpoint has been defined in [RFC7390]. The registration request interface is specified as follows: Interaction: CT -> RD Method: POST @@ -1301,86 +1357,84 @@ gp := Group Name (mandatory). The name of the group to be created or replaced, unique within that domain. The maximum length of this parameter is 63 bytes. d := Domain (optional). The domain to which this group belongs. The maximum length of this parameter is 63 bytes. Optional. When this parameter is elided, the RD MAY associate the endpoint with a configured default domain. con := Context (optional). This parameter sets the scheme, - address and port at which this server is available in the form - scheme://host:port/path. In the absence of this parameter the - scheme of the protocol, source address and source port of the - register request are assumed. This parameter is mandatory when - the directory is filled by a third party such as an - commissioning tool. When con is used, scheme and host are - mandatory and port and path parameters are optional. + address and port of the multicast address associated with the + group. When con is used, scheme and host are mandatory and + port parameter is optional. Content-Format: application/link-format Content-Format: application/link-format+json Content-Format: application/link-format+cbor The following response codes are defined for this interface: Success: 2.01 "Created" or 201 "Created". The Location header option MUST be returned in response to a successful group CREATE operation. This Location MUST be a stable identifier generated by - the RD as it is used for delete operations of the group - registration resource. + the RD as it is used for delete operations of the group resource. Failure: 4.00 "Bad Request" or 400 "Bad Request". Malformed request. Failure: 4.04 "Not Found" or 404 "Not Found". An Endpoint is not registered in the RD (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 example shows an EP registering a group with the name - "lights" which has two endpoints to an RD using this interface. The - RD group path /rd-group is an example RD location discovered in a - request similar to Figure 4. + "lights" which has two endpoints. The RD group path /rd-group is an + example RD location discovered in a request similar to Figure 6. Req: POST coap://rd.example.com/rd-group?gp=lights + &con=coap://[ff35:30:2001:db8::1] Content-Format: 40 Payload: - <>;ep="node1", - <>;ep="node2" + , + Res: 2.01 Created Location: /rd-group/12 + The href value is the path to the registration resource of the + Endpoint. + 6.2. Group Removal A group can be removed simply by sending a removal message to the location of the group registration resource which was returned when - intially registering the group. Removing a group MUST NOT remove the - endpoints of the group from the RD. + initially registering the group. Removing a group MUST NOT remove + the endpoints of the group from the RD. The removal request interface is specified as follows: Interaction: CT -> RD Method: DELETE URI Template: {+location} URI Template Variables: - location := This is the Location returned by the RD as a result - of a successful group registration. + location := This is the path of the group resource returned by + the RD as a result of a successful group registration. The following responses 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". Group does not exist. @@ -1391,275 +1445,356 @@ The following examples shows successful removal of the group from the RD with the example location value /rd-group/12. Req: DELETE /rd-group/12 Res: 2.02 Deleted 7. RD Lookup - In order for an RD to be used for discovering resources registered - with it, an optional lookup interface may 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). - - RD Lookup allows lookups for domains, groups, 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, a domain lookup MUST - return a list of domains, a group lookup MUST return a list of - groups, an endpoint lookup MUST return a list of endpoints and a - resource lookup MUST return a list of links to resources. + 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). - RD Lookup does not expose registration resources directly, but - returns link content from registration resource entries which satisfy - RD Lookup queries. + RD Lookup allows lookups for groups, 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, a group lookup MUST + return a list of groups, 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: +-------------+--------------------+-----------+ | Lookup Type | Resource Type | Mandatory | +-------------+--------------------+-----------+ | Resource | core.rd-lookup-res | Mandatory | | Endpoint | core.rd-lookup-ep | Mandatory | - | Domain | core.rd-lookup-d | Optional | | Group | core.rd-lookup-gp | Optional | +-------------+--------------------+-----------+ Table 1: Lookup Types - Each endpoint and resource lookup result returns respectively the - scheme (IP address and port) followed by the path part of the URI of - every endpoint and resource inside angle brackets ("<>") and followed - by the other parameters. +7.1. Resource lookup - The target of these links SHOULD be the actual location of the - domain, endpoint or resource, but MAY be an intermediate proxy e.g. - in the case of an HTTP lookup interface for CoAP endpoints. + Resource lookup results in links that are semantically equivalent to + the links submitted to the RD if they were accessed on the endpoint + itself. The links and link parameters returned are equal to the + submitted ones except for anchor, which was resolved by the server + against the endpoint's context. - The domain lookup returns every lookup domain with a base RD resource - value (e.g. "/rd") encapsulated within angle brackets. + Links that did not have an anchor attribute are therefore returned + with the (explicitly or implicitly set) context URI of the + registration as the anchor. Links whose anchor was submitted as an + absolute URI are returned as they were registered. The hrefs of + links can always be served as they were submitted; the server MAY + return relative references in absolute form in to resource lookups, + but that results in needlessly verbose responses. - In case that a group does not implement any multicast address, the - group lookup returns every group lookup with a group base resource - value encapsulated within angle brackets (e.g. "/rd/look-up"). - Otherwise, the group lookup returns the multicast address of the - group inside angle brackets. + Above rules allow the client to interpret the response as links + without any further knowledge of what the RD does. The Resource + Directory MAY replace the contexts with a configured intermediate + proxy, e.g. in the case of an HTTP lookup interface for CoAP + endpoints. + +7.2. Endpoint and group lookup + + Endpoint and group lookups result in links to registration resources + and group resources, respectively. Endpoint registration resources + are annotated with their endpoint names (ep), domains (d, if + present), context (con) and lifetime (lt, if present). Additional + endpoint attributes are added as link attributes to their endpoint + link unless their specification says otherwise. Group resources are + annotated with their group names (gp), domain (d, if present) and + multicast address (con, if present). + + 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. + +7.3. Lookup filtering Using the Accept Option, the requester can control whether this 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"). 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. - Multiple query parameters MAY be included in a lookup, all included - parameters MUST match for a resource to be returned. The - character'*' MAY be included at the end of a parameter value as a - wildcard operator. + Multiple search criteria MAY be included in a lookup. All included + criteria MUST match for a link to be returned. - RD Lookup requests MAY use any set of query parameters to match the - registered attributes and relations. In addition, this interface MAY - be used with queries that specify domains, endpoints, and groups. - For example, a domain lookup filtering on groups would return a list - of domains that contain the specified groups. An endpoint lookup - filtering on groups would return a list of endpoints that are in the - specified groups. + A link matches a search criterion if it has an attribute of the same + name and the same value, allowing for a trailing "*" wildcard + operator as in Section 4.1 of [RFC6690]. Attributes that are defined + as "link-type" match if the search value matches any of their values + (see Section 4.1 of [RFC6690]; eg. "?if=core.s" matches ";if="abc + core.s";"). A link also matches a search criterion if the link that + would be produced for any of its containing entities would match the + criterion: A search criterion matches an endpoint if it matches the + endpoint itself or any of the groups it is contained in, and one on a + resource if it matches the resource, the resource's endpoint, or any + of the endpoint's groups. + + Note that "href" is also a valid search criterion and matches target + references. Like all search criteria, on a resource lookup it can + match the target reference of the resource link itself, but also the + registration resource of the endpoint that registered it, or any + group resource that endpoint is contained in. Clients that are interested in a lookup result repeatedly or continuously can use mechanisms like ETag caching, resource observation ([RFC7641]), or any future mechanism that might allow more efficient observations of collections. These are advertised, detected and used according to their own specifications and can be used with the lookup interface as with any other resource. The lookup interface is specified as follows: Interaction: Client -> RD Method: GET - URI Template: {+type-lookup- - location}{?d,res,ep,gp,et,rt,page,count,resource-param} + + URI Template: {+type-lookup-location}{?page,count,search*} URI Template Variables: type-lookup-location := RD Lookup URI for a given lookup type (mandatory). The address is discovered as described in Section 5.2. - ep := Endpoint name (optional). Used for endpoint, group and - resource lookups. - - d := Domain (optional). Used for domain, group, endpoint and - resource lookups. - - res := resource (optional). Used for domain, group, endpoint and - resource lookups. - - gp := Group name (optional). Used for endpoint, group and - resource lookups. + search := Search criteria for limiting the number of results + (optional). page := Page (optional). Parameter can not be used without the count parameter. Results are returned from result set in pages that contain 'count' links starting from index (page * count). 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. - rt := Resource type (optional). Used for group, endpoint and - resource lookups. - - et := Endpoint type (optional). Used for group, endpoint and - resource lookups. - - resource-param := Link attribute parameters (optional). Any link - target attribute as defined in Section 4.1 of [RFC6690], used - for resource lookups. - Content-Format: application/link-format (optional) Content-Format: application/link-format+json (optional) + Content-Format: application/link-format+cbor (optional) 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. - - Failure: 4.04 "Not Found" or 404 "Not Found" in case no matching - entry is found for a unicast request. + 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. 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 +7.4. Lookup examples + The examples in this section assume 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 4: + with the example resource look-up locations discovered in Figure 6: Req: GET /rd-lookup/res?rt=temperature Res: 2.05 Content - ;rt="temperature" + ;rt="temperature";anchor="coap://[2001:db8:3::123]:61616" - The following example shows a client performing an endpoint type - lookup: + The same lookup using the CBOR Link Format media type: - Req: GET /rd-lookup/ep?et=power-node +Req: GET /rd-lookup/res?rt=temperature +Accept: TBD64 Res: 2.05 Content - ;ep="node5", - ;ep="node7" +Content-Format: TBD64 +Payload in Hex notation: +81A301652F74656D70096B74656D706572617475726503781E636F61703A2F2F5B323030 +313A6462383A333A3A3132335D3A3631363136 +Decoded payload: +[{1: "/temp", 9: "temperature", 3: "coap://[2001:db8:3::123]:61616"}] - The following example shows a client performing a domain lookup: + A client that wants to be notified of new resources as they show up + can use observation: - Req: GET /rd-lookup/d + Req: GET /rd-lookup/res?rt=light + Observe: 0 Res: 2.05 Content - <>;d="domain1", - <>;d="domain2" + Observe: 23 + Payload: empty + + (at a later point in time) + + Res: 2.05 Content + Observe: 24 + Payload: + ;rt="light";anchor="coap://[2001:db8:3::124]", + ;rt="light";anchor="coap://[2001:db8:3::124]", + ;rt="light";anchor="coap://[2001:db8:3::124]" + + The following example shows a client performing an endpoint type + lookup: + + Req: GET /rd-lookup/ep?et=power-node + + Res: 2.05 Content + ;con="coap://[2001:db8:3::127]:61616";ep="node5"; + et="power-node";ct="40";lt="600", + ;con="coap://[2001:db8:3::129]:61616";ep="node7"; + et="power-node";ct="40";lt="600";d="floor-3" The following example shows a client performing a group lookup for all groups: Req: GET /rd-lookup/gp Res: 2.05 Content - <>;gp="lights1";d="example.com" - <>;gp="lights2";d="ecample.com" +;gp="lights1";d="example.com";con="coap://[ff35:30:2001:db8::1]", +;gp="lights2";d="example.com";con="coap://[ff35:30:2001:db8::2]" The following example shows a client performing a lookup for all endpoints in a particular group: Req: GET /rd-lookup/ep?gp=lights1 Res: 2.05 Content - ;ep="node1", - ;ep="node2" +;con="coap://[2001:db8:3::123]:61616";ep="node1";et="power-node";ct="40";lt="600", +;con="coap://[2001:db8:3::124]:61616";ep="node2";et="power-node";ct="40";lt="600" The following example shows a client performing a lookup for all - groups an endpoint belongs to: + groups the endpoint "node1" belongs to: Req: GET /rd-lookup/gp?ep=node1 Res: 2.05 Content - <>;gp="lights1" + ;gp="lights1" + + The following example shows a client performing a paginated resource + lookup - The following example shows a client performing a paginated lookup Req: GET /rd-lookup/res?page=0&count=5 Res: 2.05 Content - ;rt=sensor;ct=60 - ;rt=sensor;ct=60 - ;rt=sensor;ct=60 - ;rt=sensor;ct=60 - ;rt=sensor;ct=60 + ;rt=sensor;ct=60;anchor="coap://[2001:db8:3::123]:61616", + ;rt=sensor;ct=60;anchor="coap://[2001:db8:3::123]:61616", + ;rt=sensor;ct=60;anchor="coap://[2001:db8:3::123]:61616", + ;rt=sensor;ct=60;anchor="coap://[2001:db8:3::123]:61616", + ;rt=sensor;ct=60;anchor="coap://[2001:db8:3::123]:61616" Req: GET /rd-lookup/res?page=1&count=5 Res: 2.05 Content - ;rt=sensor;ct=60 - ;rt=sensor;ct=60 - ;rt=sensor;ct=60 - ;rt=sensor;ct=60 - ;rt=sensor;ct=60 + ;rt=sensor;ct=60;anchor="coap://[2001:db8:3::123]:61616", + ;rt=sensor;ct=60;anchor="coap://[2001:db8:3::123]:61616", + ;rt=sensor;ct=60;anchor="coap://[2001:db8:3::123]:61616", + ;rt=sensor;ct=60;anchor="coap://[2001:db8:3::123]:61616", + ;rt=sensor;ct=60;anchor="coap://[2001:db8:3::123]:61616" + + The following example shows a client performing a lookup of all + resources from endpoints of a given endpoint type. It assumes that + two endpoints (with endpoint names "sensor1" and "sensor2") have + previously registered with their respective addresses + "coap://sensor1.example.com" and "coap://sensor2.example.com", and + posted the very payload of the 6th request of section 5 of [RFC6690]. + + It demonstrates how the link targets stay unmodified, but the anchors + get constructed by the resource directory: + + Req: GET /rd-lookup/res?et=sensor-node + + ;ct=40;title="Sensor Index"; + anchor="coap://sensor1.example.com", + ;rt="temperature-c";if="sensor"; + anchor="coap://sensor1.example.com", + ;rt="light-lux";if="sensor"; + anchor="coap://sensor1.example.com", + ;rel="describedby"; + anchor="coap://sensor1.example.com/sensors/temp", + ;rel="alternate";anchor="coap://sensor1.example.com/sensors/temp", + ;ct=40;title="Sensor Index"; + 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" 8. Security Considerations The security considerations as described in Section 7 of [RFC5988] 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 is determined to be unique by an RD by the Endpoint - identifier parameter included during Registration, and any associated - TLS or DTLS security bindings. An Endpoint MUST NOT be identified by - its protocol, port or IP address as these may change over the - lifetime of an Endpoint. + An Endpoint is determined to be unique within (the domain of) an RD + by the Endpoint identifier parameter included during Registration, + and any associated TLS or DTLS security bindings. 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 or Client on a resource directory SHOULD be mutually authenticated using Pre-Shared Key, Raw - Public Key or Certificate based security. Endpoints using a - Certificate MUST include the Endpoint identifier as the Subject of - the Certificate, and this identifier MUST be checked by a resource - directory to match the Endpoint identifier included in the - Registration message. + Public Key or Certificate based security. + + Consider te following threat: two devices A and B are managed by a + single server. Both devices have unique, per-device credentials for + use with DTLS to make sure that only parties with authorization to + access A or B can do so. + + Now, imagine that a malicious device A wants to sabotage the device + B. It uses its credentials during the TLS exchange. Then, it puts + the endpoint name of device B. If the server does not check whether + the identifier provided in the DTLS handshake matches the identifier + used at the CoAP layer then it may be inclined to use the endpoint + name for looking up what information to provision to the malicious + device. + + Therfore, Endpoints MUST include the Endpoint identifier in the + message, and this identifier MUST be checked by a resource directory + to match the Endpoint identifier included in the Registration + message. 8.2. Access Control Access control SHOULD be performed separately for the RD registration, Lookup, and group API paths, as different endpoints may be authorized to register with an RD from those authorized to lookup endpoints from the RD. Such access control SHOULD be performed in as fine-grained a level as possible. For example access control for lookups could be performed either at the domain, endpoint or resource level. @@ -1680,76 +1815,155 @@ unprotected UDP, there is no return routability check, and they can have a large amplification factor. The responses from the NTP server were found to be 19 times larger than the request. A Resource Directory (RD) which responds to wild-card lookups is potentially vulnerable if run with CoAP over UDP. Since there is no return routability check and the responses can be significantly larger than requests, RDs can unknowingly become part of a DDoS amplification attack. 9. IANA Considerations - 9.1. Resource Types "core.rd", "core.rd-group", "core.rd-lookup-ep", "core.rd-lookup- - res", "core.rd-lookup-d", and "core.rd-lookup-gp" resource types need - to be registered with the resource type registry defined by - [RFC6690]. + res", and "core.rd-lookup-gp" resource types need to be registered + with the resource type registry defined by [RFC6690]. 9.2. IPv6 ND Resource Directory Address Option This document registers one new ND option type under the subregistry "IPv6 Neighbor Discovery Option Formats": o Resource Directory address Option (38) 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 the human readable name of - the parameter, the query parameter, validity requirements if any and - a description. The query parameter MUST be a valid URI query key - [RFC3986]. + Each entry in the registry must include * the human readable name of + the parameter, * the short name as used in query parameters or link + attributes, * indication of whether it can be passed as a query + parameter at registration of endpoints or groups, as a query + parameter in lookups, or be expressed as a link attribute, * validity + requirements if any, and * a description. + + The query parameter MUST be both a valid URI query key [RFC3986] and + a parmname as used in [RFC5988]. + + The description must give details on which registrations they apply + to (Endpoint, group registrations or both? Can they be updated?), + and how they are 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 + for keeping it confidential at the discovery step.) Initial entries in this sub-registry are as follows: - +----------+-------+---------------+--------------------------------+ - | Name | Query | Validity | Description | - +----------+-------+---------------+--------------------------------+ - | Endpoint | ep | | Name of the endpoint, max 63 | - | Name | | | bytes | - | Lifetime | lt | 60-4294967295 | Lifetime of the registration | - | | | | in seconds | - | Domain | d | | Domain to which this endpoint | - | | | | belongs | - | Endpoint | et | | Semantic name of the endpoint | - | Type | | | | - | Context | con | URI | The scheme, address and port | - | | | | and path at which this server | - | | | | is available | - | Resource | res | | Name of the resource | - | Name | | | | - | Group | gp | | Name of a group in the RD | - | Name | | | | - | Page | page | Integer | Used for pagination | - | Count | count | Integer | Used for pagination | - +----------+-------+---------------+--------------------------------+ + +----------+-------+---------------+-----+--------------------------+ + | Full | Short | Validity | Use | Description | + | name | | | | | + +----------+-------+---------------+-----+--------------------------+ + | Endpoint | ep | | RLA | Name of the endpoint, | + | Name | | | | max 63 bytes | + | Lifetime | lt | 60-4294967295 | RLA | Lifetime of the | + | | | | | registration in seconds | + | Domain | d | | RLA | Domain to which this | + | | | | | endpoint belongs | + | Context | con | URI | RLA | The scheme, address and | + | | | | | port and path at which | + | | | | | this server is available | + | Group | gp | | RLA | Name of a group in the | + | Name | | | | RD | + | 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 + + 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 [RFC5226]. + 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 (Eg. 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 + 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 + 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 + subregistry. Endpoint types can be passed in the "et" query + parameter as part of extra-attrs at the Registration step, are shown + on endpoint lookups using the "et" target attribute, and can be + filtered for using "et" as a search criterion in resource and + endpoint lookup. Multiple endpoint types are given as separate query + parameters or link attributes. + + Note that Endpoint Type differs from Resource Type in that it uses + multiple attributes rather than space separated values. As a result, + Resource Directory implementations automatically support correct + filtering in the lookup interfaces from the rules for unknown + endpoint attributes. + +9.4. "Endpoint Type" (et=) RD Parameter values + + This specification establishes a new sub-registry under "CoRE + Parameters" called '"Endpoint Type" (et=) RD Parameter values'. The + registry properties (required policy, requirements, template) are + identical to those of the Resource Type parameters in [RFC6690], in + short: + + The review policy is IETF Review for values starting with "core", and + Specification Required for others. + + The requirements to be enforced are: + + o The values MUST be related to the purpose described in + 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 is initially empty. 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 @@ -1790,28 +2004,28 @@ Before commissioning by the lighting manager, the network is installed and access to the interfaces is proven to work by the network manager. At the moment of installation, the network under installation is not necessarily connected to the DNS infra structure. Therefore, SLAAC IPv6 addresses are assigned to CT, RD, luminaries and sensor shown in Table 3 below: - +--------------------+--------------+ + +--------------------+----------------+ | Name | IPv6 address | - +--------------------+--------------+ - | luminary1 | FDFD::ABCD:1 | - | luminary2 | FDFD::ABCD:2 | - | Presence sensor | FDFD::ABCD:3 | - | Resource directory | FDFD::ABCD:0 | - +--------------------+--------------+ + +--------------------+----------------+ + | luminary1 | 2001:db8:4::1 | + | luminary2 | 2001:db8:4::2 | + | Presence sensor | 2001:db8:4::3 | + | Resource directory | 2001:db8:4::ff | + +--------------------+----------------+ Table 3: interface SLAAC addresses In Section 10.1.2 the use of resource directory during installation is presented. 10.1.2. RD entries It is assumed that access to the DNS infrastructure is not always possible during installation. Therefore, the SLAAC addresses are @@ -1845,105 +2059,105 @@ Table 4: Resource Directory identifiers It is assumed that the CT knows of the RD's address, and has performed URI discovery on it that gave a response like the one in the Section 5.2 example. The CT inserts the endpoints of the luminaries and the sensor in the RD using the Context parameter (con) to specify the interface address: - Req: POST coap://[FDFD::ABCD:0]/rd - ?ep=lm_R2-4-015_wndw&con=coap://[FDFD::ABCD:1]&d=R2-4-015 + Req: POST coap://[2001:db8:4::ff]/rd + ?ep=lm_R2-4-015_wndw&con=coap://[2001:db8:4::1]&d=R2-4-015 Payload: ;rt="light", ;rt="light", ;rt="light" Res: 2.01 Created Location: /rd/4521 - Req: POST coap://[FDFD::ABCD:0]/rd - ?ep=lm_R2-4-015_door&con=coap://[FDFD::ABCD:2]&d=R2-4-015 + Req: POST coap://[2001:db8:4::ff]/rd + ?ep=lm_R2-4-015_door&con=coap://[2001:db8:4::2]&d=R2-4-015 Payload: ;rt="light", ;rt="light", ;rt="light" Res: 2.01 Created Location: /rd/4522 - Req: POST coap://[FDFD::ABCD:0]/rd - ?ep=ps_R2-4-015_door&con=coap://[FDFD::ABCD:3]d&d=R2-4-015 + Req: POST coap://[2001:db8:4::ff]/rd + ?ep=ps_R2-4-015_door&con=coap://[2001:db8:4::3]d&d=R2-4-015 Payload: ;rt="p-sensor" Res: 2.01 Created Location: /rd/4523 The domain name d=R2-4-015 has been added for an efficient lookup because filtering on "ep" name is more awkward. The same domain name is communicated to the two luminaries and the presence sensor by the CT. The group is specified in the RD. The Context parameter is set to the site-local multicast address allocated to the group. In the POST in the example below, these two endpoints and the endpoint of the presence sensor are registered as members of the group. - Req: POST coap://[FDFD::ABCD:0]/rd-group - ?gp=grp_R2-4-015&con=coap://[FF05::1] + Req: POST coap://[2001:db8:4::ff]/rd-group + ?gp=grp_R2-4-015&con=coap://[ff05::1] Payload: - <>;ep=lm_R2-4-015_wndw, - <>;ep=lm_R2-4-015_door, - <>;ep=ps_R2-4-015_door + , + , + Res: 2.01 Created Location: /rd-group/501 After the filling of the RD by the CT, the application in the luminaries can learn to which groups they belong, and enable their interface for the multicast address. The luminary, knowing its domain, queries the RD for the endpoint with rt=light and d=R2-4-015. The RD returns all endpoints in the domain. - Req: GET coap://[FDFD::ABCD:0]/rd-lookup/ep + Req: GET coap://[2001:db8:4::ff]/rd-lookup/ep ?d=R2-4-015;rt=light Res: 2.05 Content - ; + ;con="coap://[2001:db8:4::1]", ep="lm_R2-4-015_wndw", - ; + ;con="coap://[2001:db8:4::2]", ep="lm_R2-4-015_door" Knowing its own IPv6 address, the luminary discovers its endpoint name. With the endpoint name the luminary queries the RD for all groups to which the endpoint belongs. - Req: GET coap://[FDFD::ABCD:0]/rd-lookup/gp + Req: GET coap://[2001:db8:4::ff]/rd-lookup/gp ?ep=lm_R2-4-015_wndw Res: 2.05 Content - ;gp="grp_R2-4-015" + ;gp="grp_R2-4-015";con="coap://[ff05::1]" From the context 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 //[FDFD::ABCD:1]/coap-group + Req: POST //[2001:db8:4::1]/coap-group Content-Format: application/coap-group+json - { "a": "[FF05::1]", + { "a": "[ff05::1]", "n": "grp_R2-4-015"} Res: 2.01 Created Location-Path: /coap-group/1 Dependent on the situation, only the address, "a", or the name, "n", is specified in the coap-group resource. 10.2. OMA Lightweight M2M (LWM2M) Example @@ -2056,36 +2270,38 @@ When an LWM2M object or instance is registered, this indicates to the LWM2M server that the object and its resources are available for management and service enablement (REST API) operations. LWM2M endpoints may use the following RD registration parameters as defined in Table 2 : ep - Endpoint Name lt - registration lifetime - Endpoint Name is mandatory, all other registration parameters are + Endpoint Name, Lifetime, and LWM2M Version are mandatory parameters + for the register operation, all other registration parameters are optional. Additional optional LWM2M registration parameters are defined: - +------------+-------+-------------------------------+--------------+ + +-----------+-------+-------------------------------+---------------+ | Name | Query | Validity | Description | - +------------+-------+-------------------------------+--------------+ - | Protocol | b | {"U",UQ","S","SQ","US","UQS"} | Available | - | Binding | | | Protocols | + +-----------+-------+-------------------------------+---------------+ + | Binding | b | {"U",UQ","S","SQ","US","UQS"} | Available | + | Mode | | | Protocols | | | | | | | LWM2M | ver | 1.0 | Spec Version | | Version | | | | | | | | | - | SMS Number | sms | | MSISDN | - +------------+-------+-------------------------------+--------------+ + | SMS | sms | | MSISDN | + | Number | | | | + +-----------+-------+-------------------------------+---------------+ Table 5: LWM2M Additional Registration Parameters The following RD registration parameters are not currently specified for use in LWM2M: et - Endpoint Type con - Context The endpoint registration must include a payload containing links to @@ -2097,28 +2313,30 @@ ,,, 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 - An LWM2M Registration update proceeds as described in Section 5.4.1, - and adds some optional parameter updates: + The LwM2M update is really very similar to the registration update as + 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 Section 5.4.2. @@ -2118,29 +2336,65 @@ 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 Section 5.4.2. 11. Acknowledgments Oscar Novo, Srdjan Krco, Szymon Sasin, Kerry Lynn, Esko Dijk, Anders - Brandt, Matthieu Vial, Mohit Sethi, Sampo Ukkola, Linyi Tian, - Chistian Amsuss, 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. + 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 -11 to -12 + + o added Content Model section, including ER diagram + + o removed domain lookup interface; domains are now plain attributes + of groups and endpoints + + o updated chapter "Finding a Resource Directory"; now distinguishes + configuration-provided, network-provided and heuristic sources + + o improved text on: atomicity, idempotency, lookup with multiple + parameters, endpoint removal, simple registration + + o updated LWM2M description + + o clarified where relative references are resolved, and how context + and anchor interact + + o new appendix on the interaction with RFCs 6690, 5988 and 3986 + + o lookup interface: group and endpoint lookup return group and + registration resources as link targets + + o lookup interface: search parameters work the same across all + entities + + o removed all methods that modify links in an existing registration + (POST with payload, PATCH and iPATCH) + + o removed plurality definition (was only needed for link + modification) + + o enhanced IANA registry text + + o More examples and improved text + changes from -09 to -10 o removed "ins" and "exp" link-format extensions. o removed all text concerning DNS-SD. o removed inconsistency in RDAO text. o suggestions taken over from various sources @@ -2319,93 +2572,360 @@ 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-08 (work in - progress), April 2017. + JSON and CBOR", draft-ietf-core-links-json-09 (work in + progress), July 2017. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, - DOI 10.17487/RFC2119, March 1997, - . + 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, - . - - [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an - IANA Considerations Section in RFCs", RFC 5226, - DOI 10.17487/RFC5226, May 2008, - . + . [RFC5988] Nottingham, M., "Web Linking", RFC 5988, - DOI 10.17487/RFC5988, October 2010, - . + 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, - . + DOI 10.17487/RFC6570, March 2012, . [RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link Format", RFC 6690, DOI 10.17487/RFC6690, August 2012, - . + . - [RFC7396] Hoffman, P. and J. Snell, "JSON Merge Patch", RFC 7396, - DOI 10.17487/RFC7396, October 2014, - . + [RFC6763] Cheshire, S. and M. Krochmal, "DNS-Based Service + Discovery", RFC 6763, DOI 10.17487/RFC6763, February 2013, + . + + [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for + Writing an IANA Considerations Section in RFCs", BCP 26, + RFC 8126, DOI 10.17487/RFC8126, June 2017, + . [RFC8132] van der Stok, P., Bormann, C., and A. Sehgal, "PATCH and FETCH Methods for the Constrained Application Protocol (CoAP)", RFC 8132, DOI 10.17487/RFC8132, April 2017, - . + . 13.2. Informative References + [ER] Chen, P., "The entity-relationship model---toward a + unified view of data", ACM Transactions on Database + Systems Vol. 1, pp. 9-36, DOI 10.1145/320434.320440, March + 1976. + + [I-D.arkko-core-dev-urn] + Arkko, J., Jennings, C., and Z. Shelby, "Uniform Resource + Names for Device Identifiers", draft-arkko-core-dev-urn-04 + (work in progress), July 2017. + + [I-D.nottingham-rfc5988bis] + Nottingham, M., "Web Linking", draft-nottingham- + rfc5988bis-08 (work in progress), August 2017. + + [I-D.silverajan-core-coap-protocol-negotiation] + Silverajan, B. and M. Ocak, "CoAP Protocol Negotiation", + draft-silverajan-core-coap-protocol-negotiation-07 (work + in progress), October 2017. + [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, - . + 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, - . + . [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, - . + DOI 10.17487/RFC7252, June 2014, . [RFC7390] Rahman, A., Ed. and E. Dijk, Ed., "Group Communication for the Constrained Application Protocol (CoAP)", RFC 7390, - DOI 10.17487/RFC7390, October 2014, - . + DOI 10.17487/RFC7390, October 2014, . [RFC7641] Hartke, K., "Observing Resources in the Constrained Application Protocol (CoAP)", RFC 7641, - DOI 10.17487/RFC7641, September 2015, - . + DOI 10.17487/RFC7641, September 2015, . + +Appendix A. 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 + [RFC5988] 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. + +A.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: + + GET coap://[ff02::fd]:5683/.well-known/core?rt=temperature + + RES 2.05 Content + ;rt=temperature;ct=0 + + where the response is sent by the server, "[2001:db8:f0::1]:5683". + + While the client - on the practical or implementation side - can just + go ahead and create a new request to "[2001:db8:f0::1]:5683" with + Uri-Path: "temp", the full resolution steps without any shortcuts + are: + +A.1.1. Resolving the URIs + + The client parses the single returned record. The link's target + (sometimes called "href") is ""/temp"", which is a relative URI that + needs resolving. The Base URI to resolve that against is, in absence + of an "anchor" parameter, the URI of the requested resource as + described in [RFC6690] Section 2.1. + + The URI of the requested resource can be composed by following the + steps of [RFC7252] section 6.5 (with an addition at the end of 8.2) + into ""coap://[2001:db8:f0::1]/.well-known/core"". + + The record's target is resolved by replacing the path ""/.well-known/ + core"" from the Base URI (section 5.2 [RFC3986]) with the relative + target URI ""/temp"" into ""coap://[2001:db8:f0::1]/temp"". + +A.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 the context + resource has a named relation to the target resource, like "_This + page_ has _its table of contents_ at _/toc.html_". In [RFC6690] + link-format documents, there is an implicit "host relation" specified + with default parameter: rel="hosts". + + In our example, the context of the link is the URI of the requested + document itself. 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.' + +A.2. A slightly more complex example + + Omitting the "rt=temperature" filter, the discovery query would have + given some more records in the payload: + + ;rt=temperature;ct=0, + ;rt=light-lux;ct=0, + ;anchor="/sensors/temp";rel=alternate, + ;anchor="/sensors/temp"; + rel=describedby, + ;rel=alternate;ct=65001; + anchor="http://www.example.com/sensors/t123" + + Parsing the third record, the client encounters the "anchor" + parameter. It is a URI relative to the document's Base URI and is + thus resolved to ""coap://[2001:db8:f0::1]/sensors/temp"". That is + the context resource of the link, so the "rel" statement is not about + the target and the document Base URI any more, but about the target + and that address. + + Thus, the third record could be read as + ""coap://[2001:db8:f0::1]/sensors/temp" has an alternate + representation at "coap://[2001:db8:f0::1]/t"". + + The fourth record can be read as ""coap://[2001:db8:f0::1]/sensors/ + temp" is described by "http://www.example.com/sensors/t123"" + + In the last example the anchor is absolute, where a ""t123.pdf"" is + resolved relative to ""http://www.example.com/sensors/t123"", which + gives a statement that ""http://www.example.com/sensors/t123/ + t123.pdf" is an alternate representation to + ""http://www.example.com/sensors/t123" of which the content type is + PDF". + +A.3. Enter the Resource Directory + + The resource directory tries to carry the semantics obtainable by + classical CoAP discovery over to the resource lookup interface as + faithfully as possible. + + For the following queries, we will assume that the simple host has + used Simple Registration to register at the resource directory that + was announced to it, sending this request from its UDP port + "[2001:db8:f0::1]:6553": + + POST coap://[2001:db8:f01::ff]/.well-known/core?ep-simple-host1 + + The resource directory would have accepted the registration, and + queried the simple host's ".well-known/core" by itself. As a result, + the host is registered as an endpoint in the RD with the name + "simple-host1". The registration is active for 86400 seconds, and + the endpoint registration Base URI is ""coap://[2001:db8:f0::1]/"" + because that is the address the registration was sent from (and no + explicit "con=" was given). + + If the client now queries the RD as it would previously have issued a + multicast request, it would go through the RD discovery steps by + fetching "coap://[2001:db8:f0::ff]/.well-known/core?rt=core.rd- + lookup-res", obtain "coap://[2001:db8:f0::ff]/rd-lookup/res" as the + resource lookup endpoint, and issue a request to + "coap://[2001:db8:f0::ff]/rd-lookup/res?rt=temperature" to receive + the following data: + + ;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 would contain the (almost) same + 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 subject of ongoing discussion about RFC6690). + + 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]", + ;anchor="coap://[2001:db8:f0::1]/sensors/temp";rel=alternate, + ; + anchor="coap://[2001:db8:f0::1]/sensors/temp";rel=describedby, + ;rel=alternate;ct=65001; + anchor="http://www.example.com/sensors/t123" + + Note that the last link was not modified at all because its anchor + was already an absolute reference. + + Had the simple host registered with an explicit context (eg. + "?ep=simple-host1&con=coap+tcp://simple-host1.example.com"), that + context would have been used to resolve the relative anchor values + instead, giving + +;rt=temperature;ct=0;anchor="coap+tcp://simple-host1.example.com" + and analogous records. + +A.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] that should be kept in mind when using or + implementing a Resource Directory: + + 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 explictly when required. + + For example, while a Link header in a page about a Swedish city + might read + + "Link: ;rel="live-environment-data"" + + a link-format document from the same source might describe the + link as + + ";rel="live-environment-data"" + + o In a link-format document, if the anchor attribute is present, the + link target reference is resolved by using the the (resolved) + anchor value as Base URI for that link, while in Link headers, it + is resolved against the URI of the requested document. + + This is explicit in [RFC6690] section 2.1 for link-format, and + spelled out in section B.2 of [I-D.nottingham-rfc5988bis] , which + obsoletes the older [RFC5988]. [RFC6690] is based on [RFC5988] + and has not been updated with clarifications from + [I-D.nottingham-rfc5988bis]. + +Appendix B. 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: + + Req: POST coap://rd.example.com/rd?ep=node1 + &at=coap+tcp://[2001:db8:f1::2] + &at=coap://[2001:db8:f1::2] + Content-Format: 40 + Payload: + ;ct=0;rt="temperature";if="core.s" + + Res: 2.01 Created + Location: /rd/1234 + + A UDP client would then query: + + 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]" Authors' Addresses Zach Shelby ARM 150 Rose Orchard San Jose 95134 USA Phone: +1-408-203-9434