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Versions: (draft-loffredo-regext-rdap-sorting-and-paging) 00 01 02 03 04 05 06

Registration Protocols Extensions                            M. Loffredo
Internet-Draft                                             M. Martinelli
Intended status: Standards Track                     IIT-CNR/Registro.it
Expires: December 14, 2019                                 S. Hollenbeck
                                                           Verisign Labs
                                                           June 12, 2019


  Registration Data Access Protocol (RDAP) Query Parameters for Result
                           Sorting and Paging
              draft-ietf-regext-rdap-sorting-and-paging-03

Abstract

   The Registration Data Access Protocol (RDAP) does not include core
   functionality for clients to provide sorting and paging parameters
   for control of large result sets.  This omission can lead to
   unpredictable server processing of queries and client processing of
   responses.  This unpredictability can be greatly reduced if clients
   can provide servers with their preferences for managing large
   responses.  This document describes RDAP query extensions that allow
   clients to specify their preferences for sorting and paging result
   sets.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on December 14, 2019.

Copyright Notice

   Copyright (c) 2019 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



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   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   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  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Conventions Used in This Document . . . . . . . . . . . .   4
   2.  RDAP Query Parameter Specification  . . . . . . . . . . . . .   4
     2.1.  Sorting and Paging Metadata . . . . . . . . . . . . . . .   4
     2.2.  "count" Parameter . . . . . . . . . . . . . . . . . . . .   6
     2.3.  "sort" Parameter  . . . . . . . . . . . . . . . . . . . .   7
       2.3.1.  Sorting Properties Declaration  . . . . . . . . . . .   7
       2.3.2.  Representing Sorting Links  . . . . . . . . . . . . .  11
     2.4.  "cursor" Parameter  . . . . . . . . . . . . . . . . . . .  12
       2.4.1.  Representing Paging Links . . . . . . . . . . . . . .  15
   3.  Negative Answers  . . . . . . . . . . . . . . . . . . . . . .  16
   4.  RDAP Conformance  . . . . . . . . . . . . . . . . . . . . . .  17
   5.  Implementation Considerations . . . . . . . . . . . . . . . .  17
   6.  Implementation Status . . . . . . . . . . . . . . . . . . . .  17
     6.1.  IIT-CNR/Registro.it . . . . . . . . . . . . . . . . . . .  18
     6.2.  Google Registry . . . . . . . . . . . . . . . . . . . . .  18
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  18
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  19
   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  19
   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  19
     10.1.  Normative References . . . . . . . . . . . . . . . . . .  19
     10.2.  Informative References . . . . . . . . . . . . . . . . .  21
   Appendix A.  Change Log . . . . . . . . . . . . . . . . . . . . .  22
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  22

1.  Introduction

   The availability of functionality for result sorting and paging
   provides benefits to both clients and servers in the implementation
   of RESTful services [REST].  These benefits include:

   o  reducing the server response bandwidth requirements;
   o  improving server response time;
   o  improving query precision and, consequently, obtaining more
      reliable results;
   o  decreasing server query processing load;
   o  reducing client response processing time.




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   Approaches to implementing features for result sorting and paging can
   be grouped into two main categories:

   1.  Sorting and paging are implemented through the introduction of
       additional parameters in the query string (i.e.  ODATA protocol
       [OData-Part1]);

   2.  Information related to the number of results and the specific
       portion of the result set to be returned, in addition to a set of
       ready-made links for the result set scrolling, are inserted in
       the HTTP header of the request/response.

   However, there are some drawbacks associated with use of the HTTP
   header.  First, the header properties cannot be set directly from a
   web browser.  Moreover, in an HTTP session, the information on the
   status (i.e. the session identifier) is usually inserted in the
   header or in the cookies, while the information on the resource
   identification or the search type is included in the query string.
   The second approach is therefore not compliant with the HTTP standard
   [RFC7230].  As a result, this document describes a specification
   based on use of query parameters.

   Currently the RDAP protocol [RFC7482] defines two query types:

   o  lookup: the server returns only one object;
   o  search: the server returns a collection of objects.

   While the lookup query does not raise issues in the response
   management, the search query can potentially generate a large result
   set that could be truncated according to the server limits.  In
   addition, it is not possible to obtain the total number of the
   objects found that might be returned in a search query response
   [RFC7483].  Lastly, there is no way to specify sort criteria to
   return the most relevant objects at the beginning of the result set.
   Therefore, the client might traverse the whole result set to find the
   relevant objects or, due to truncation, could not find them at all.

   The specification described in this document extends RDAP query
   capabilities to enable result sorting and paging, by adding new query
   parameters that can be applied to RDAP search path segments.  The
   service is implemented using the Hypertext Transfer Protocol (HTTP)
   [RFC7230] and the conventions described in RFC 7480 [RFC7480].

   The implementation of the new parameters is technically feasible, as
   operators for counting, sorting and paging rows are currently
   supported by the major RDBMSs.





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1.1.  Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

2.  RDAP Query Parameter Specification

   The new query parameters are OPTIONAL extensions of path segments
   defined in RFC 7482 [RFC7482].  They are as follows:

   o  "count": a boolean value that allows a client to request the total
      number of objects found (that due to truncation can be different
      from the number of returned objects);

   o  "sort": a string value that allows a client to request a specific
      sort order for the result set;

   o  "cursor": a string value representing a pointer to a specific
      fixed size portion of the result set.

   Augmented Backus-Naur Form (ABNF) [RFC5234] is used in the following
   sections to describe the formal syntax of these new parameters.

2.1.  Sorting and Paging Metadata

   According to most advanced principles in REST design, collectively
   known as HATEOAS (Hypermedia as the Engine of Application State)
   ([HATEOAS]), a client entering a REST application through an initial
   URI should use the server-provided links to dynamically discover
   available actions and access the resources it needs.  In this way,
   the client is not requested to have prior knowledge of the service
   and, consequently, to hard code the URIs of different resources.
   This would allow the server to make URI changes as the API evolves
   without breaking the clients.  Definitively, a REST service should be
   as self-descriptive as possible.

   Therefore, servers implementing the query parameters described in
   this specification SHOULD provide additional information in their
   responses about both the available sorting criteria and the possible
   pagination.  Such information is collected in two new data structures
   named, respectively, "sorting_metadata" and "paging_metadata".

   Obviously, both the new data structures are OPTIONAL because their
   presence in the response not only depends on the implementation of
   sorting and paging query capabilities but also on some situations
   related to the results.  For example, it is quite natural to expect




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   that the "paging_metadata" element will not be present at the last
   result page when the server implements only the forward pagination.

   The "sorting_metadata" structure contains the following properties:

   o  "currentSort": "String" (OPTIONAL) either the value of sort
      "parameter" as specified in the query string or the sort applied
      by default, if any;

   o  "availableSorts": "AvailableSort[]" (OPTIONAL) an array of objects
      each one describing an alternate available sorting criterion.
      Members are:

      *  "property": "String" (REQUIRED) the name that can be used by
         the client to request the sorting criterion;
      *  "default": "Boolean" (REQUIRED) whether the sorting criterion
         is applied by default;
      *  "jsonPath": "String" (OPTIONAL) the JSON Path of the RDAP field
         corresponding to the property;
      *  "links": "Link[]" (OPTIONAL) an array of links as described in
         RFC 8288 [RFC8288] containing the query string that applies the
         sorting criterion.

   At least one between "currentSort" and "availableSorts" MUST be
   present.

   The "paging_metadata" structure contains the following fields:

   o  "totalCount": "Numeric" (OPTIONAL) a numeric value representing
      the total number of objects found.  It is provided if the query
      string contains the "count" parameter;

   o  "pageCount": "Numeric" (OPTIONAL) a numeric value representing the
      number of objects returned in the current page.  It is provided
      when the total number of objects exceeds the page size.  This
      property is redundant for clients because the page size can be
      derived from the length of the search results array but it can be
      helpful if the end user interacts with the server through a web
      browser;

   o  "links": "Link[]" (OPTIONAL) an array of links as described in RFC
      8288 [RFC8288] containing the reference to next page.  In this
      specification, only the forward pagination is dealt because it is
      considered satisfactory in order to traverse the result set.
      Examples of additional references are to: the previous page, the
      first page, the last page.

   At least one between "totalCount" and "links" MUST be present.



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2.2.  "count" Parameter

   Currently the RDAP protocol does not allow a client to determine the
   total number of the results in a query response when the result set
   is truncated.  This is rather inefficient because the user cannot
   evaluate the query precision and, at the same time, cannot receive
   information that could be relevant.

   The "count" parameter provides additional functionality (Figure 1)
   that allows a client to request information from the server that
   specifies the total number of elements matching the search pattern.


   https://example.com/rdap/domains?name=*nr.com&count=true

      Figure 1: Example of RDAP query reporting the "count" parameter

   The ABNF syntax is the following:

      count = "count=" ( trueValue / falseValue )
      trueValue = ("true" / "yes" / "1")
      falseValue = ("false" / "no" / "0")

   A trueValue means that the server MUST provide the total number of
   the objects in the "totalCount" field of the "paging_metadata"
   element (Figure 2).  A falseValue means that the server MUST NOT
   provide this number.


   {
     "rdapConformance": [
           "rdap_level_0",
           "paging_level_0"
     ],
     ...
     "paging_metadata": {
       "totalCount": 73
     },
     "domainSearchResults": [
       ...
     ]
   }

     Figure 2: Example of RDAP response with "paging_metadata" element
                     containing the "totalCount" field






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2.3.  "sort" Parameter

   The RDAP protocol does not provide any capability to specify results
   sort criteria.  A server could implement a default sorting scheme
   according to the object class, but this feature is not mandatory and
   might not meet user requirements.  Sorting can be addressed by the
   client, but this solution is rather inefficient.  Sorting features
   provided by the RDAP server could help avoid truncation of relevant
   results.

   The "sort" parameter allows the client to ask the server to sort the
   results according to the values of one or more properties and
   according to the sort direction of each property.  The ABNF syntax is
   the following:

      sort = "sort=" sortItem *( "," sortItem )
      sortItem = property-ref [":" ( "a" / "d" ) ]
      property-ref = ALPHA *( ALPHA / DIGIT / "_" )

   "a" means that the ascending sort MUST be applied, "d" means that the
   descending sort MUST be applied.  If the sort direction is absent, an
   ascending sort MUST be applied (Figure 3).


   https://example.com/rdap/domains?name=*nr.com&sort=ldhName

   https://example.com/rdap/domains?name=*nr.com&sort=registrationDate:d

   https://example.com/rdap/domains?name=*nr.com&sort=lockedDate,ldhName

      Figure 3: Examples of RDAP query reporting the "sort" parameter

   If the "sort" parameter reports an allowed sorting property, it MUST
   be provided in the "currentSort" field of the "sorting_metadata"
   element.

2.3.1.  Sorting Properties Declaration

   In the "sort" parameter ABNF syntax, property-ref represents a
   reference to a property of an RDAP object.  Such a reference could be
   expressed by using a JSON Path.  The JSON Path in a JSON document
   [RFC8259] is equivalent to the XPath [W3C.CR-xpath-31-20161213] in a
   XML document.  For example, the JSON Path to select the value of the
   ASCII name inside an RDAP domain object is "$.ldhName", where $
   identifies the root of the document (DOM).  Another way to select a
   value inside a JSON document is the JSON Pointer [RFC6901].  While
   JSON Path or JSON Pointer are both standard ways to select any value
   inside JSON data, neither is particularly easy to use (e.g.



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   "$.events[?(@.eventAction='registration')].eventDate" is the JSON
   Path expression of the registration date in an RDAP domain object).

   Therefore, this specification provides a definition of property-ref
   in terms of RDAP properties.  However, not all the RDAP properties
   are suitable to be used in sort criteria, such as:

   o  properties providing service information (e.g. links, notices,
      remarks, etc.);

   o  multivalued properties (e.g. status, roles, variants, etc.);

   o  properties modeling relationships to other objects (e.g.
      entities).

   On the contrary, some properties expressed as values of other
   properties (e.g. registration date) could be used in such a context.

   In the following, a list of properties an RDAP server MAY implement
   is presented.  The properties are divided in two groups: object
   common properties and object specific properties.

   o  Object common properties.  Object common properties are derived
      from the merge of the "eventAction" and the "eventDate"
      properties.  The following values of the "sort" parameter are
      defined:

      *  registrationDate
      *  reregistrationDate
      *  lastChangedDate
      *  expirationDate
      *  deletionDate
      *  reinstantiationDate
      *  transferDate
      *  lockedDate
      *  unlockedDate

   o  Object specific properties.  With regard to the specific
      properties, some of them are already defined among the query
      paths.  In the following a list of possible sorting properties,
      grouped by objects, is shown:

      *  Domain: ldhName
      *  Nameserver: ldhName, ipV4, ipV6.
      *  Entity: fn, handle, org, email, voice, country, cc, city.

   The correspondence between the sorting properties and the RDAP fields
   is shown in Table 1:



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   +-----------+-----------+-------------+---------+---------+---------+
   | Object    | Sorting   | RDAP        | RFC7483 | RFC6350 | RFC8605 |
   | class     | property  | property    |         |         |         |
   +-----------+-----------+-------------+---------+---------+---------+
   | Searchabl | Common pr | eventAction | 4.5.    |         |         |
   | e objects | operties  | values      |         |         |         |
   |           |           | suffixed by |         |         |         |
   |           |           | "Date"      |         |         |         |
   |           |           |             |         |         |         |
   | Domain    | ldhName   | ldhName     | 5.3.    |         |         |
   |           |           |             |         |         |         |
   | Nameserve | ldhName   | ldhName     | 5.2.    |         |         |
   | r         |           |             |         |         |         |
   |           | ipV4      | v4          | 5.2.    |         |         |
   |           |           | ipAddress   |         |         |         |
   |           | ipV6      | v6          | 5.2.    |         |         |
   |           |           | ipAddress   |         |         |         |
   |           |           |             |         |         |         |
   | Entity    | handle    | handle      | 5.1.    |         |         |
   |           | fn        | vcard fn    | 5.1.    | 6.2.1   |         |
   |           | org       | vcard org   | 5.1.    | 6.6.4   |         |
   |           | voice     | vcard tel   | 5.1.    | 6.4.1   |         |
   |           |           | with type=" |         |         |         |
   |           |           | voice"      |         |         |         |
   |           | email     | vcard email | 5.1.    | 6.4.2   |         |
   |           | country   | country     | 5.1.    | 6.3.1   |         |
   |           |           | name in     |         |         |         |
   |           |           | vcard adr   |         |         |         |
   |           | cc        | country     | 5.1.    |         | 3.1     |
   |           |           | code in     |         |         |         |
   |           |           | vcard adr   |         |         |         |
   |           | city      | locality in | 5.1.    | 6.3.1   |         |
   |           |           | vcard adr   |         |         |         |
   +-----------+-----------+-------------+---------+---------+---------+

                  Table 1: Sorting properties definition

   With regard to the definitions in Table 1, some further
   considerations must be made to disambiguate cases where the RDAP
   property is multivalued:

   o  even if a nameserver can have multiple IPv4 and IPv6 addresses,
      the most common configuration includes one address for each IP
      version.  Therefore, the assumption of having a single IPv4 and/or
      IPv6 value for a nameserver cannot be considered too stringent;

   o  with the exception of handle values, all the sorting properties
      defined for entity objects can be multivalued according to the



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      definition of vCard as given in RFC6350 [RFC6350].  When more than
      a value is reported, sorting can be applied to the preferred value
      identified by the parameter pref="1".

   Each RDAP provider MAY define other sorting properties than those
   shown in this document.

   The "jsonPath" field in the "sorting_metadata" element is used to
   clarify the RDAP field the sorting property refers to.  The mapping
   between the sorting properties and the JSON Paths of the RDAP fields
   is shown in Table 2.  The JSON Paths are provided according to the
   Goessner v.0.8.0 specification ([GOESSNER-JSON-PATH]):

   +-------+-------------+---------------------------------------------+
   | Objec | Sorting     | JSON Path                                   |
   | t     | property    |                                             |
   | class |             |                                             |
   +-------+-------------+---------------------------------------------+
   | Searc | registratio | "$.domainSearchResults[*].events[?(@.eventA |
   | hable | nDate       | ction=="registration")].eventDate           |
   | objec |             |                                             |
   | ts    |             |                                             |
   |       | reregistrat | "$.domainSearchResults[*].events[?(@.eventA |
   |       | ionDate     | ction=="reregistration")].eventDate         |
   |       | lastChanged | "$.domainSearchResults[*].events[?(@.eventA |
   |       | Date        | ction=="lastChanged")].eventDate            |
   |       | expirationD | "$.domainSearchResults[*].events[?(@.eventA |
   |       | ate         | ction=="expiration")].eventDate             |
   |       | deletionDat | "$.domainSearchResults[*].events[?(@.eventA |
   |       | e           | ction=="deletion")].eventDate               |
   |       | reinstantia | "$.domainSearchResults[*].events[?(@.eventA |
   |       | tionDate    | ction=="reinstantiation")].eventDate        |
   |       | transferDat | "$.domainSearchResults[*].events[?(@.eventA |
   |       | e           | ction=="transfer")].eventDate               |
   |       | lockedDate  | "$.domainSearchResults[*].events[?(@.eventA |
   |       |             | ction=="locked")].eventDate                 |
   |       | unlockedDat | "$.domainSearchResults[*].events[?(@.eventA |
   |       | e           | ction=="unlocked")].eventDate               |
   |       |             |                                             |
   | Domai | ldhName     | $.domainSearchResults[*].ldhName            |
   | n     |             |                                             |
   |       |             |                                             |
   | Names | ldhName     | $.nameserverSearchResults[*].ldhName        |
   | erver |             |                                             |
   |       | ipV4        | $.nameserverSearchResults[*].ipAddresses.v4 |
   |       |             | [0]                                         |
   |       | ipV6        | $.nameserverSearchResults[*].ipAddresses.v6 |
   |       |             | [0]                                         |



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   |       |             |                                             |
   | Entit | handle      | $.entitySearchResults[*].handle             |
   | y     |             |                                             |
   |       | fn          | $.entitySearchResults[*].vcardArray[1][?(@[ |
   |       |             | 0]="fn")][3]                                |
   |       | org         | $.entitySearchResults[*].vcardArray[1][?(@[ |
   |       |             | 0]="org")][3]                               |
   |       | voice       | $.entitySearchResults[*].vcardArray[1][?(@[ |
   |       |             | 0]=="tel" && @[1].type=="voice")][3]        |
   |       | email       | $.entitySearchResults[*].vcardArray[1][?(@[ |
   |       |             | 0]=="email")][3]                            |
   |       | country     | $.entitySearchResults[*].vcardArray[1][?(@[ |
   |       |             | 0]=="adr")][3][6]                           |
   |       | cc          | $.entitySearchResults[*].vcardArray[1][?(@[ |
   |       |             | 0]=="adr")][1].cc                           |
   |       | city        | $.entitySearchResults[*].vcardArray[1][?(@[ |
   |       |             | 0]=="adr")][3][3]                           |
   +-------+-------------+---------------------------------------------+

              Table 2: Sorting properties - JSON Path Mapping

2.3.2.  Representing Sorting Links

   An RDAP server MAY use the "links" array of the "sorting_metadata"
   element to provide ready-made references [RFC8288] to the available
   sort criteria (Figure 4).  Each link represents a reference to an
   alternate view of the results.
























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   {
     "rdapConformance": [
       "rdap_level_0",
       "sorting_level_0"
     ],
     ...
     "sorting_metadata": {
        "currentSort": "ldhName",
        "availableSorts": [
        {
        "property": "registrationDate",
        "jsonPath": "$.domainSearchResults[*]
           .events[?(@.eventAction==\"registration\")].eventDate",
        "default": false,
        "links": [
           {
           "value": "https://example.com/rdap/domains?name=*nr.com
                     &sort=ldhName",
           "rel": "alternate",
           "href": "https://example.com/rdap/domains?name=*nr.com
                    &sort=registrationDate",
           "title": "Result Ascending Sort Link",
           "type": "application/rdap+json"
           },
           {
           "value": "https://example.com/rdap/domains?name=*nr.com
                     &sort=ldhName",
           "rel": "alternate",
           "href": "https://example.com/rdap/domains?name=*nr.com
                    &sort=registrationDate:d",
           "title": "Result Descending Sort Link",
           "type": "application/rdap+json"
           }
        ]
     },
     "domainSearchResults": [
       ...
     ]
   }

      Figure 4: Example of a "sorting_metadata" instance to implement
                              result sorting

2.4.  "cursor" Parameter

   An RDAP query could return a response with hundreds, even thousands,
   of objects, especially when partial matching is used.  For that




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   reason, the cursor parameter addressing result pagination is defined
   to make responses easier to handle.

   Using limit and offset operators represents the most common way to
   implement results pagination.  Both of them can be used individually:

   o  "limit": means that the server must return the first N objects of
      the result set;

   o  "offset": means that the server must skip the first N objects and
      must return objects starting from position N+1.

   When limit and offset are used together, they allow to identify a
   specific portion of the result set.  For example, the pair
   "offset=100,limit=50" returns first 50 objects starting from position
   101 of the result set.

   However, offset pagination raises some well known drawbacks:

   o  when offset has a very high value, scrolling the result set could
      take some time;

   o  it always requires to fetch all the rows before dropping as many
      rows as specified by offset;

   o  it may return inconsistent pages when data are frequently updated
      (i.e. real-time data) but this doesn't seem the case of
      registration data.

   An alternative approach to offset pagination is keyset pagination
   [SEEK] which consists in adding a query condition that enables the
   seletion of the only data not yet returned.  This method has been
   taken as the basis for the implementation of a "cursor" parameter
   [CURSOR] by some REST API providers (e.g.
   [CURSOR-API1],[CURSOR-API2]).  The cursor is an opaque URL-safe
   string representing a logical pointer to the first result of the next
   page (Figure 5).  Basically, the cursor is the encryption of the key
   value identifying the last row of the current page.  For example, the
   cursor value "a2V5PXRoZWxhc3Rkb21haW5vZnRoZXBhZ2UuY29t=" is the mere
   Base64 encoding of "key=thelastdomainofthepage.com".

   The ABNF syntax is the following:

      cursor = "cursor=" ( ALPHA / DIGIT / "/" / "=" / "-" / "_" )







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   https://example.com/rdap/domains?name=*nr.com
   &cursor=wJlCDLIl6KTWypN7T6vc6nWEmEYe99Hjf1XY1xmqV-M=

    Figure 5: An example of RDAP query reporting the "cursor" parameter

   Nevertheless, even cursor pagination can be troublesome:

   o  it needs at least one key field;

   o  it does not allow to sort just by any field because the sorting
      criterion must contain a key;

   o  it works best with full composite values support by DBMS (i.e.
      [x,y]>[a,b]), emulation is possible but ugly and less performant;

   o  it does not allow to directly navigate to arbitrary pages because
      the result set must be scrolled in sequential order starting from
      the initial page;

   o  implementing the bi-directional navigation is tedious because all
      comparison and sort operations have to be reversed.

   Furthermore, in the RDAP context, some additional considerations can
   be made:

   o  an RDAP object is a conceptual aggregation of information
      generally collected from more than one data structure (e.g. table)
      and this makes even harder for the developers the implementation
      of the keyset pagination that is already quite difficult.  For
      example, the entity object can gather information from different
      data structures (registrars, registrants, contacts, resellers, and
      so on), each one with its own key field mapping the RDAP entity
      handle;

   o  depending on the number of the page results as well as the number
      and the complexity of the properties of each RDAP object in the
      response, the time required by offset pagination to skip the
      previous pages could be much faster than the processing time
      needed to build the current page.  In fact, RDAP objects are
      usually formed by information belonging to multiple data
      structures and containing multivalued properties (i.e. arrays)
      and, therefore, data selection might be a time consuming process.
      This situation occurs even though the selection is supported by
      indexes;

   o  depending on the access levels defined by each RDAP operator, the
      increase of complexity and the decrease of flexibility of cursor




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      pagination with respect to the offset pagination could be
      considered impractical.

   Ultimately, both pagination methods have benefits and drawbacks.
   That said, the cursor parameter can be used to encode not only the
   key value but also the information about offset pagination.  For
   example, the cursor value "b2Zmc2V0PTEwMCxsaW1pdD01MAo=" is the mere
   Base64 encoding of "offset=100,limit=50".  This solution lets RDAP
   providers to implement a pagination method according to their needs,
   the user access levels, the submitted queries.  In addition, servers
   can change the method over time without announcing anything to the
   clients.

2.4.1.  Representing Paging Links

   An RDAP server SHOULD use the "links" array of the "paging_metadata"
   element to provide a ready-made reference [RFC8288] to the next page
   of the result set (Figure 6).  Examples of additional "rel" values a
   server MAY implements are "first", "last", "prev".
































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   {
     "rdapConformance": [
       "rdap_level_0",
       "paging_level_0"
     ],
     ...
     "notices": [
       {
         "title": "Search query limits",
         "type": "result set truncated due to excessive load",
         "description": [
         "search results for domains are limited to 10"
         ]
       }
     ],
     "paging_metadata": {
       "totalCount": 73,
       "pageCount": 10,
       "links": [
         {
         "value": "https://example.com/rdap/domains?name=*nr.com",
         "rel": "next",
         "href": "https://example.com/rdap/domains?name=*nr.com
                 &cursor=wJlCDLIl6KTWypN7T6vc6nWEmEYe99Hjf1XY1xmqV-M=",
         "title": "Result Pagination Link",
         "type": "application/rdap+json"
         }
       ]
     },
     "domainSearchResults": [
       ...
     ]
   }

   Figure 6: Example of a "paging_metadata" instance to implement cursor
                                pagination

3.  Negative Answers

   The value constraints for the parameters are defined by their ABNF
   syntax.  Therefore, each request including an invalid value for a
   parameter SHOULD obtain an HTTP 400 (Bad Request) response code.  The
   same response SHOULD be returned in the following cases:

   o  if the client provides an unsupported value for the "sort"
      parameter in both single and multi sort;

   o  if the client submits an invalid value for the "cursor" parameter.



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   Optionally, the response MAY include additional information regarding
   the negative answer in the HTTP entity body.

4.  RDAP Conformance

   Servers returning the "paging_metadata" element in their response
   MUST include "paging_level_0" in the rdapConformance array as well as
   servers returning the "sorting_metadata" element MUST include
   "sorting_level_0".

5.  Implementation Considerations

   The implementation of the new parameters is technically feasible, as
   operators for counting, sorting and paging are currently supported by
   the major RDBMSs.

   Similar operators are completely or partially supported by the most
   known NoSQL databases (MongoDB, CouchDB, HBase, Cassandra, Hadoop) so
   the implementation of the new parameters seems to be practicable by
   servers working without the use of an RDBMS.

   Furthermore, both two pagination methods don't require the server to
   handle the result set in a storage area across the requests since a
   new result set is generated each time a request is submitted.

6.  Implementation Status

   NOTE: Please remove this section and the reference to RFC 7942 prior
   to publication as an RFC.

   This section records the status of known implementations of the
   protocol defined by this specification at the time of posting of this
   Internet-Draft, and is based on a proposal described in RFC 7942
   [RFC7942].  The description of implementations in this section is
   intended to assist the IETF in its decision processes in progressing
   drafts to RFCs.  Please note that the listing of any individual
   implementation here does not imply endorsement by the IETF.
   Furthermore, no effort has been spent to verify the information
   presented here that was supplied by IETF contributors.  This is not
   intended as, and must not be construed to be, a catalog of available
   implementations or their features.  Readers are advised to note that
   other implementations may exist.

   According to RFC 7942, "this will allow reviewers and working groups
   to assign due consideration to documents that have the benefit of
   running code, which may serve as evidence of valuable experimentation
   and feedback that have made the implemented protocols more mature.




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   It is up to the individual working groups to use this information as
   they see fit".

6.1.  IIT-CNR/Registro.it

      Responsible Organization: Institute of Informatics and Telematics
      of National Research Council (IIT-CNR)/Registro.it
      Location: https://rdap.pubtest.nic.it/
      Description: This implementation includes support for RDAP queries
      using data from .it public test environment.
      Level of Maturity: This is a "proof of concept" research
      implementation.
      Coverage: This implementation includes all of the features
      described in this specification.
      Contact Information: Mario Loffredo, mario.loffredo@iit.cnr.it

6.2.  Google Registry

      Responsible Organization: Google Registry
      Location: https://www.registry.google/rdap/
      Description: This implementation includes support for RDAP queries
      for TLDs such as .google, .how, .soy, and .xn--q9jyb4c . The RDAP
      server implements cursor pagination.  The link used to request the
      next page is included in the notice section of the response.
      Level of Maturity: Production.
      Coverage: This implementation includes the "cursor" parameter
      described in this specification.
      Contact Information: Brian Mountford, mountford@google.com

7.  IANA Considerations

   IANA is requested to register the following values in the RDAP
   Extensions Registry:

      Extension identifier: paging
      Registry operator: Any
      Published specification: This document.
      Contact: IESG <iesg@ietf.org>
      Intended usage: This extension describes a best practice for
      result set paging.

      Extension identifier: sorting
      Registry operator: Any
      Published specification: This document.
      Contact: IESG <iesg@ietf.org>
      Intended usage: This extension describes a best practice for
      result set sorting.




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8.  Security Considerations

   Security services for the operations specified in this document are
   described in RFC 7481 [RFC7481].

   Search query typically requires more server resources (such as
   memory, CPU cycles, and network bandwidth) when compared to lookup
   query.  This increases the risk of server resource exhaustion and
   subsequent denial of service due to abuse.  This risk can be
   mitigated by either restricting search functionality and limiting the
   rate of search requests.  Servers can also reduce their load by
   truncating the results in the response.  However, this last security
   policy can result in a higher inefficiency if the RDAP server does
   not provide any functionality to return the truncated results.

   The new parameters presented in this document provide the RDAP
   operators with a way to implement a secure server without penalizing
   its efficiency.  The "count" parameter gives the user a measure to
   evaluate the query precision and, at the same time, returns a
   significant information.  The "sort" parameter allows the user to
   obtain the most relevant information at the beginning of the result
   set.  In both cases, the user doesn't need to submit further
   unnecessary search requests.  Finally, the "cursor" parameter enables
   the user to scroll the result set by submitting a sequence of
   sustainable queries according to the server limits.

9.  Acknowledgements

   The authors would like to acknowledge Brian Mountford for his
   contribution to the development of this document.

10.  References

10.1.  Normative References

   [ISO.3166.1988]
              International Organization for Standardization, "Codes for
              the representation of names of countries, 3rd edition",
              ISO Standard 3166, August 1988.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.







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   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", RFC 5226,
              DOI 10.17487/RFC5226, May 2008,
              <https://www.rfc-editor.org/info/rfc5226>.

   [RFC5234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234,
              DOI 10.17487/RFC5234, January 2008,
              <https://www.rfc-editor.org/info/rfc5234>.

   [RFC6350]  Perreault, S., "vCard Format Specification", RFC 6350,
              DOI 10.17487/RFC6350, August 2011,
              <https://www.rfc-editor.org/info/rfc6350>.

   [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,
              <https://www.rfc-editor.org/info/rfc7230>.

   [RFC7480]  Newton, A., Ellacott, B., and N. Kong, "HTTP Usage in the
              Registration Data Access Protocol (RDAP)", RFC 7480,
              DOI 10.17487/RFC7480, March 2015,
              <https://www.rfc-editor.org/info/rfc7480>.

   [RFC7481]  Hollenbeck, S. and N. Kong, "Security Services for the
              Registration Data Access Protocol (RDAP)", RFC 7481,
              DOI 10.17487/RFC7481, March 2015,
              <https://www.rfc-editor.org/info/rfc7481>.

   [RFC7482]  Newton, A. and S. Hollenbeck, "Registration Data Access
              Protocol (RDAP) Query Format", RFC 7482,
              DOI 10.17487/RFC7482, March 2015,
              <https://www.rfc-editor.org/info/rfc7482>.

   [RFC7483]  Newton, A. and S. Hollenbeck, "JSON Responses for the
              Registration Data Access Protocol (RDAP)", RFC 7483,
              DOI 10.17487/RFC7483, March 2015,
              <https://www.rfc-editor.org/info/rfc7483>.

   [RFC8259]  Bray, T., Ed., "The JavaScript Object Notation (JSON) Data
              Interchange Format", STD 90, RFC 8259,
              DOI 10.17487/RFC8259, December 2017,
              <https://www.rfc-editor.org/info/rfc8259>.

   [RFC8288]  Nottingham, M., "Web Linking", RFC 8288,
              DOI 10.17487/RFC8288, October 2017,
              <https://www.rfc-editor.org/info/rfc8288>.




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   [RFC8605]  Hollenbeck, S. and R. Carney, "vCard Format Extensions:
              ICANN Extensions for the Registration Data Access Protocol
              (RDAP)", RFC 8605, DOI 10.17487/RFC8605, May 2019,
              <https://www.rfc-editor.org/info/rfc8605>.

10.2.  Informative References

   [CURSOR]   Nimesh, R., "Paginating Real-Time Data with Keyset
              Pagination", July 2014, <https://www.sitepoint.com/
              paginating-real-time-data-cursor-based-pagination/>.

   [CURSOR-API1]
              facebook.com, "facebook for developers - Using the Graph
              API", July 2017, <https://developers.facebook.com/docs/
              graph-api/using-graph-api>.

   [CURSOR-API2]
              twitter.com, "Pagination", 2017,
              <https://developer.twitter.com/en/docs/ads/general/guides/
              pagination.html>.

   [GOESSNER-JSON-PATH]
              Goessner, S., "JSONPath - XPath for JSON", 2007,
              <http://goessner.net/articles/JsonPath/>.

   [HATEOAS]  Jedrzejewski, B., "HATEOAS - a simple explanation", 2018,
              <https://www.e4developer.com/2018/02/16/
              hateoas-simple-explanation/>.

   [OData-Part1]
              Pizzo, M., Handl, R., and M. Zurmuehl, "OData Version 4.0.
              Part 1: Protocol Plus Errata 03", June 2016,
              <http://docs.oasis-
              open.org/odata/odata/v4.0/errata03/os/complete/part1-
              protocol/
              odata-v4.0-errata03-os-part1-protocol-complete.pdf>.

   [REST]     Fredrich, T., "RESTful Service Best Practices,
              Recommendations for Creating Web Services", April 2012,
              <http://www.restapitutorial.com/media/
              RESTful_Best_Practices-v1_1.pdf>.

   [RFC6901]  Bryan, P., Ed., Zyp, K., and M. Nottingham, Ed.,
              "JavaScript Object Notation (JSON) Pointer", RFC 6901,
              DOI 10.17487/RFC6901, April 2013,
              <https://www.rfc-editor.org/info/rfc6901>.





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   [RFC7942]  Sheffer, Y. and A. Farrel, "Improving Awareness of Running
              Code: The Implementation Status Section", BCP 205,
              RFC 7942, DOI 10.17487/RFC7942, July 2016,
              <https://www.rfc-editor.org/info/rfc7942>.

   [SEEK]     EverSQL.com, "Faster Pagination in Mysql - Why Order By
              With Limit and Offset is Slow?", July 2017,
              <https://www.eversql.com/faster-pagination-in-mysql-why-
              order-by-with-limit-and-offset-is-slow/>.

   [W3C.CR-xpath-31-20161213]
              Robie, J., Dyck, M., and J. Spiegel, "XML Path Language
              (XPath) 3.1", World Wide Web Consortium CR CR-xpath-
              31-20161213, December 2016,
              <https://www.w3.org/TR/2016/CR-xpath-31-20161213>.

Appendix A.  Change Log

   00:  Initial working group version ported from draft-loffredo-regext-
      rdap-sorting-and-paging-05
   01:  Removed both "offset" and "nextOffset" to keep "paging_metadata"
      consistent between the pagination methods.  Renamed
      "Considerations about Paging Implementation" section in ""cursor"
      Parameter".  Removed "FOR DISCUSSION" items.  Provided a more
      detailed description of both "sorting_metadata" and
      "paging_metadata" objects.
   02:  Removed both "offset" and "limit" parameters.  Added ABNF syntax
      of cursor parameter.  Rearranged the layout of some sections.
      Removed some items from "Informative References" section.  Changed
      "IANA Considerations" section.
   03:  Added "cc" to the list of sorting properties in "Sorting
      Properties Declaration" section.  Added RFC8605 to the list of
      "Informative References".

Authors' Addresses

   Mario Loffredo
   IIT-CNR/Registro.it
   Via Moruzzi,1
   Pisa  56124
   IT

   Email: mario.loffredo@iit.cnr.it
   URI:   http://www.iit.cnr.it







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   Maurizio Martinelli
   IIT-CNR/Registro.it
   Via Moruzzi,1
   Pisa  56124
   IT

   Email: maurizio.martinelli@iit.cnr.it
   URI:   http://www.iit.cnr.it


   Scott Hollenbeck
   Verisign Labs
   12061 Bluemont Way
   Reston, VA  20190
   USA

   Email: shollenbeck@verisign.com
   URI:   https://www.verisignlabs.com/

































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