Registration Protocols Extensions M. Loffredo
Internet-Draft M. Martinelli
Intended status: Standards Track IIT-CNR/Registro.it
Expires: November 30, 2020 S. Hollenbeck
Verisign Labs
May 29, 2020
Registration Data Access Protocol (RDAP) Query Parameters for Result
Sorting and Paging
draft-ietf-regext-rdap-sorting-and-paging-13
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 November 30, 2020.
Copyright Notice
Copyright (c) 2020 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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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
2.1.1. RDAP Conformance . . . . . . . . . . . . . . . . . . 6
2.2. "count" Parameter . . . . . . . . . . . . . . . . . . . . 6
2.3. "sort" Parameter . . . . . . . . . . . . . . . . . . . . 7
2.3.1. Sorting Properties Declaration . . . . . . . . . . . 8
2.3.2. Representing Sorting Links . . . . . . . . . . . . . 13
2.4. "cursor" Parameter . . . . . . . . . . . . . . . . . . . 15
2.4.1. Representing Paging Links . . . . . . . . . . . . . . 15
3. Negative Answers . . . . . . . . . . . . . . . . . . . . . . 16
4. Implementation Considerations . . . . . . . . . . . . . . . . 17
5. Implementation Status . . . . . . . . . . . . . . . . . . . . 17
5.1. IIT-CNR/Registro.it . . . . . . . . . . . . . . . . . . . 17
5.2. APNIC . . . . . . . . . . . . . . . . . . . . . . . . . . 18
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 18
7. Security Considerations . . . . . . . . . . . . . . . . . . . 18
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 19
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 19
9.1. Normative References . . . . . . . . . . . . . . . . . . 19
9.2. Informative References . . . . . . . . . . . . . . . . . 21
Appendix A. JSONPath operators . . . . . . . . . . . . . . . . . 22
Appendix B. Approaches to Result Pagination . . . . . . . . . . 23
B.1. Specific Issues Raised by RDAP . . . . . . . . . . . . . 24
Appendix C. Change Log . . . . . . . . . . . . . . . . . . . . . 25
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 26
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;
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o decreasing server query processing load;
o reducing client response processing time.
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 the 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 a cookie, 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 the 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 response size
management, the search query can potentially generate a large result
set that could be truncated according to server limits. In addition,
it is not possible to obtain the total number of 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, might 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].
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The implementation of the new parameters is technically feasible, as
operators for counting, sorting and paging rows are currently
supported by the major RDBMSs.
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 BCP 14 [RFC2119]
[RFC8174] when, and only when, they appear in all capitals, as shown
here.
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 return of
the total number of objects found;
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 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 allows the server to make URI changes as the API evolves without
breaking 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 possible
pagination. Such information is collected in two OPTIONAL response
elements named, respectively, "sorting_metadata" and
"paging_metadata".
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The "sorting_metadata" element 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, with each element describing an available sort criterion.
Members are:
* "property": "String" (REQUIRED) the name that can be used by
the client to request the sort criterion;
* "default": "Boolean" (REQUIRED) whether the sort criterion is
applied by default;
* "jsonPath": "String" (OPTIONAL) the JSONPath 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
sort criterion.
At least one of the "currentSort" and "availableSorts" properties
MUST be present.
The "paging_metadata" element contains the following fields:
o "totalCount": "Numeric" (OPTIONAL) a numeric value representing
the total number of objects found. It MUST be provided if the
query string contains the "count" parameter;
o "pageSize": "Numeric" (OPTIONAL) a numeric value representing the
number of objects returned in the current page. It MUST be
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 "pageNumber": "Numeric" (OPTIONAL) a numeric value representing
the number of the current page in the result set. It MUST be
provided when the total number of objects found exceeds the page
size;
o "links": "Link[]" (OPTIONAL) an array of links as described in RFC
8288 [RFC8288] containing the reference to the next page. In this
specification, only forward pagination is described because it is
all that is necessary to traverse the result set.
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2.1.1. RDAP Conformance
Servers returning the "paging_metadata" element in their response
MUST include the string literal "paging" in the rdapConformance
array. Servers returning the "sorting_metadata" element MUST include
the string literal "sorting".
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 inefficient because the user cannot determine
if the result set is complete.
The "count" parameter provides additional functionality (Figure 1)
that allows a client to request information from the server that
specifies the total number of objects 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.
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{
"rdapConformance": [
"rdap_level_0",
"paging"
],
...
"paging_metadata": {
"totalCount": 43
},
"domainSearchResults": [
...
]
}
Figure 2: Example of RDAP response with "paging_metadata" element
containing the "totalCount" field
2.3. "sort" Parameter
The RDAP protocol does not provide any capability to specify result
set 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 an ascending sort MUST be applied, "d" means that a
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=name
https://example.com/rdap/domains?name=*nr.com&sort=registrationDate:d
https://example.com/rdap/domains?name=*nr.com&sort=lockedDate,name
Figure 3: Examples of RDAP query reporting the "sort" parameter
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With the exception of sorting IP addresses, servers MUST implement
sorting according to the JSON value type of the RDAP field the
sorting property refers to. That is, JSON strings MUST be sorted
lexicographically and JSON numbers MUST be sorted numerically. If IP
addresses are represented as JSON strings, they MUST be sorted based
on their numeric conversion.
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 JSONPath. The JSONPath in a JSON document
[RFC8259] is equivalent to the XPath [W3C.CR-xpath-31-20161213] in a
XML document. For example, the JSONPath 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
JSONPath or JSON Pointer are both standard ways to select any value
inside JSON data, neither is particularly easy to use (e.g.
"$.events[?(@.eventAction='registration')].eventDate" is the JSONPath
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, properties expressed as values of other properties
(e.g. registration date) could be used in such a context. The list
of properties an RDAP server MAY implement are divided into 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:
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* registrationDate
* reregistrationDate
* lastChangedDate
* expirationDate
* deletionDate
* reinstantiationDate
* transferDate
* lockedDate
* unlockedDate
o Note that some of the object specific properties are also defined
as query paths. The object specific properties include:
* Domain: name
* Nameserver: name, ipV4, ipV6.
* Entity: fn, handle, org, email, voice, country, cc, city.
The correspondence between these sorting properties and the RDAP
object classes is shown in Table 1:
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+-----------+-----------+---------------------+------+-------+------+
| Object | Sorting | RDAP property | RFC | RFC | RFC |
| class | property | | 7483 | 6350 | 8605 |
+-----------+-----------+---------------------+------+-------+------+
| Searchabl | Common pr | eventAction values | 4.5. | | |
| e objects | operties | suffixed by "Date" | | | |
| | | | | | |
| Domain | name | unicodeName/ldhName | 5.3. | | |
| | | | | | |
| Nameserve | name | unicodeName/ldhName | 5.2. | | |
| r | | | | | |
| | ipV4 | v4 ipAddress | 5.2. | | |
| | ipV6 | v6 ipAddress | 5.2. | | |
| | | | | | |
| Entity | handle | handle | 5.1. | | |
| | fn | vcard fn | 5.1. | 6.2.1 | |
| | org | vcard org | 5.1. | 6.6.4 | |
| | voice | vcard tel with | 5.1. | 6.4.1 | |
| | | type="voice" | | | |
| | email | vcard email | 5.1. | 6.4.2 | |
| | country | country name in | 5.1. | 6.3.1 | |
| | | vcard adr | | | |
| | cc | country code in | 5.1. | | 3.1 |
| | | vcard adr | | | |
| | city | locality in vcard | 5.1. | 6.3.1 | |
| | | adr | | | |
+-----------+-----------+---------------------+------+-------+------+
Table 1: Sorting properties definition
With regard to the definitions in Table 1, some further
considerations are needed to disambiguate some cases:
o Since the response to a search on either domains or nameservers
might include both A-labels and U-labels ([RFC5890]) in general, a
consistent sorting policy MUST treat the unicodeName and ldhName
as two representations of the same value. By default, the
unicodeName value MUST be used while sorting. When unicodeName is
unavailable, the value of ldhName MUST be used instead;
o The jCard "sort-as" parameter MUST be ignored for the purpose of
the sorting capability described in this document;
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.
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When more than one address per IP version is reported, sorting
MUST be applied to the first value;
o Multiple events with a given action on an object might be
returned. If this occurs, sorting MUST be applied to the most
recent event;
o With the exception of handle values, all the sorting properties
defined for entity objects can be multivalued according to the
definition of vCard as given in RFC 6350 [RFC6350]. When more
than one value is reported, sorting MUST be applied to the
preferred value identified by the parameter pref="1". If the pref
parameter is missing, sorting MUST be applied to the first value.
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 JSONPaths of the RDAP fields
is shown in Table 2. The JSONPaths are provided according to the
Goessner v.0.8.0 specification ([GOESSNER-JSON-PATH]). Further
documentation about JSONPath operators used in Table 2 is included in
Appendix A.
+-------+-------------+---------------------------------------------+
| Objec | Sorting | JSONPath |
| t | property | |
| class | | |
+-------+-------------+---------------------------------------------+
| Searc | registratio | $.domainSearchResults[*].events[?(@.eventAc |
| hable | nDate | tion=="registration")].eventDate |
| objec | | |
| ts | | |
| | reregistrat | $.domainSearchResults[*].events[?(@.eventAc |
| | ionDate | tion=="reregistration")].eventDate |
| | lastChanged | $.domainSearchResults[*].events[?(@.eventAc |
| | Date | tion=="last changed")].eventDate |
| | expirationD | $.domainSearchResults[*].events[?(@.eventAc |
| | ate | tion=="expiration")].eventDate |
| | deletionDat | $.domainSearchResults[*].events[?(@.eventAc |
| | e | tion=="deletion")].eventDate |
| | reinstantia | $.domainSearchResults[*].events[?(@.eventAc |
| | tionDate | tion=="reinstantiation")].eventDate |
| | transferDat | $.domainSearchResults[*].events[?(@.eventAc |
| | e | tion=="transfer")].eventDate |
| | lockedDate | $.domainSearchResults[*].events[?(@.eventAc |
| | | tion=="locked")].eventDate |
| | unlockedDat | $.domainSearchResults[*].events[?(@.eventAc |
| | e | tion=="unlocked")].eventDate |
| | | |
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| Domai | name | $.domainSearchResults[*].unicodeName |
| n | | |
| | | |
| Names | name | $.nameserverSearchResults[*].unicodeName |
| erver | | |
| | ipV4 | $.nameserverSearchResults[*].ipAddresses.v4 |
| | | [0] |
| | ipV6 | $.nameserverSearchResults[*].ipAddresses.v6 |
| | | [0] |
| | | |
| 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 - JSONPath Mapping
Table 2 JSONPath notes:
o Those related to the event dates are defined only for the "domain"
object. To obtain the equivalent JSONPaths for "entity" and
"nameserver", the path segment "domainSearchResults" must be
replaced with "entitySearchResults" and "nameserverSearchResults"
respectively;
o Those related to vCard elements are specified without taking into
account the "pref" parameter. Servers that sort those values
identified by the pref parameter SHOULD update a JSONPath by
adding an appropriate filter. For example, if the email values
identified by pref="1" are considered for sorting, the JSONPath of
the "email" sorting property should be:
$.entitySearchResults[*].vcardArray[1][?(@[0]=="email" &&
@[1].pref=="1")][3]
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2.3.2. Representing Sorting Links
An RDAP server MAY use the "links" array of the "sorting_metadata"
element to provide ready-made references [RFC8288] to the available
sort criteria (Figure 4). Each link represents a reference to an
alternate view of the results.
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{
"rdapConformance": [
"rdap_level_0",
"sorting"
],
...
"sorting_metadata": {
"currentSort": "name",
"availableSorts": [
{
"property": "registrationDate",
"jsonPath": "$.domainSearchResults[*]
.events[?(@.eventAction==\"registration\")].eventDate",
"default": false,
"links": [
{
"value": "https://example.com/rdap/domains?name=*nr.com
&sort=name",
"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=name",
"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
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2.4. "cursor" Parameter
The cursor parameter defined in this specification can be used to
encode information about any pagination method. For example, in the
case of a simple implementation of the cursor parameter to represent
offset pagination information, the cursor value
"b2Zmc2V0PTEwMCxsaW1pdD01MAo=" is the Base64 encoding of
"offset=100,limit=50". Likewise, in a simple implementation to
represent keyset pagination information, the cursor value
"a2V5PXRoZWxhc3Rkb21haW5vZnRoZXBhZ2UuY29t=" represents the Base64
encoding of "key=thelastdomainofthepage.com" whereby the key value
identifies the last row of the current page.
This solution lets RDAP providers implement a pagination method
according to their needs, a user's access level, and the submitted
query. In addition, servers can change the method over time without
announcing anything to clients. The considerations that has led to
this solution are reported in more detail in Appendix B.
The ABNF syntax of the cursor paramter is the following:
cursor = "cursor=" 1*( ALPHA / DIGIT / "/" / "=" / "-" / "_" )
https://example.com/rdap/domains?name=*nr.com
&cursor=wJlCDLIl6KTWypN7T6vc6nWEmEYe99Hjf1XY1xmqV-M=
Figure 5: An example of RDAP query reporting the "cursor" parameter
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 implement are "first", "last", and "prev".
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{
"rdapConformance": [
"rdap_level_0",
"paging"
],
...
"notices": [
{
"title": "Search query limits",
"type": "result set truncated due to excessive load",
"description": [
"search results for domains are limited to 50"
]
}
],
"paging_metadata": {
"totalCount": 73,
"pageSize": 50,
"pageNumber": 1,
"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 that includes an invalid value for a
parameter SHOULD produce an HTTP 400 (Bad Request) response code.
The same response SHOULD be returned in the following cases:
o If in both single and multi sort the client provides an
unsupported value for the "sort" parameter, as well as a value
related to an object property not included in the response;
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o If the client submits an invalid value for the "cursor" parameter.
Optionally, the response MAY include additional information regarding
the negative answer in the HTTP entity body.
4. Implementation Considerations
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).
5. 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.
It is up to the individual working groups to use this information as
they see fit".
5.1. 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 an "alpha" test implementation.
Coverage: This implementation includes all of the features
described in this specification.
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Contact Information: Mario Loffredo, mario.loffredo@iit.cnr.it
5.2. APNIC
Responsible Organization: Asia-Pacific Network Information Centre
Location: https://github.com/APNIC-net/rdap-rmp-demo/tree/sorting-
and-paging
Description: A proof-of-concept for RDAP mirroring.
Level of Maturity: This is a proof-of-concept implementation.
Coverage: This implementation includes all of the features
described in the specification except for nameserver sorting and
unicodeName sorting.
Contact Information: Tom Harrison, tomh@apnic.net
6. 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.
7. Security Considerations
Security services for the operations specified in this document are
described in RFC 7481 [RFC7481].
A search query typically requires more server resources (such as
memory, CPU cycles, and network bandwidth) when compared to a 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 or limiting the
rate of search requests. Servers can also reduce their load by
truncating the results in a 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.
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The new parameters presented in this document provide RDAP operators
with a way to implement a server that reduces inefficiency risks.
The "count" parameter gives the client te ability to evaluate the
completeness of a response. The "sort" parameter allows the client
to obtain the most relevant information at the beginning of the
result set. This can reduce the amount of unnecessary search
requests. Finally, the "cursor" parameter enables the user to scroll
the result set by submitting a sequence of sustainable queries within
server-acceptable limits.
8. Acknowledgements
The authors would like to acknowledge Brian Mountford, Tom Harrison,
Karl Heinz Wolf and Jasdip Singh for their contribution to the
development of this document.
9. References
9.1. Normative References
[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>.
[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>.
[RFC5890] Klensin, J., "Internationalized Domain Names for
Applications (IDNA): Definitions and Document Framework",
RFC 5890, DOI 10.17487/RFC5890, August 2010,
<https://www.rfc-editor.org/info/rfc5890>.
[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>.
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[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>.
[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>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[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>.
[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>.
[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>.
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9.2. 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>.
[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/>.
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Appendix A. JSONPath operators
A JSONPath expression represents a path to find an element (or a set
of elements) in a JSON content.
The base JSONPath specification requires that implementations support
a set of "basic operators". These operators are used to access the
elements of a JSON structure like objects and arrays, and their
subelements, respectively, object members and array items. No
operations are defined for retrieving parent or sibling elements of a
given element. The root element is always referred to as $
regardless of it being an object or array.
Additionally, the specification permits implementations to support
arbitrary script expressions. These can be used to index into an
object or an array, or to filter elements from an array. While
script expression behaviour is implementation-defined, most
implementations support the basic relational and logical operators,
as well as both object member and array item access, sufficiently
similarly for the purposes of this document. Commonly-supported
operators/functions divided into "top-level operators" and "filter
operators" are documented in Table 3 and Table 4 respectively.
+-------------------+-----------------------------------------+
| Operator | Descritpion |
+-------------------+-----------------------------------------+
| $ | Root element |
| .<name> | Object member access (dot-notation) |
| ['<name>'] | Object member access (bracket-notation) |
| [<number>] | Array item access |
| * | All elements within the specified scope |
| [?(<expression>)] | Filter expression |
+-------------------+-----------------------------------------+
Table 3: JSONPath Top-Level Operators
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+------------+----------------------------------------+
| Operator | Descritpion |
+------------+----------------------------------------+
| @ | Current element being processed |
| .<name> | Object member access |
| [<number>] | Array item access |
| == | Left is equal to right |
| != | Left is not equal to right |
| < | Left is less than right |
| <= | Left is less than or equal to right |
| > | Left is greater than right |
| >= | Left is greater than or equal to right |
| && | Logical conjunction |
| || | Logical disjunction |
+------------+----------------------------------------+
Table 4: JSONPath Filter Operators
Appendix B. Approaches to Result Pagination
An RDAP query could return a response with hundreds, even thousands,
of objects, especially when partial matching is used. For that
reason, the cursor parameter addressing result pagination is defined
to make responses easier to handle.
Presently, the most popular methods to implement pagination in a REST
API include offset pagination and keyset pagination. Neither
pagination method requires the server to handle the result set in a
storage area across multiple requests since a new result set is
generated each time a request is submitted. Therefore, they are
preferred in comparison to any other method requiring the management
of a REST session.
Using limit and offset operators represents the traditionally used
method 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 provide the ability to
identify a specific portion of the result set. For example, the pair
"offset=100,limit=50" returns the first 50 objects starting from
position 101 of the result set.
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Though easy to implement, offset pagination also includes drawbacks:
o When offset has a very high value, scrolling the result set could
take some time;
o It always requires fetching all 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).
Keyset pagination [SEEK] adds a query condition that enables the
selection 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).
Nevertheless, even keyset 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 direct navigation to arbitrary pages because the
result set must be scrolled in sequential order starting from the
initial page;
o Implementing bi-directional navigation is tedious because all
comparison and sort operations have to be reversed.
B.1. Specific Issues Raised by RDAP
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 it even harder to implement keyset pagination, a
task that is already quite difficult. For example, the entity
object can include information from different data structures
(registrars, registrants, contacts, resellers, and so on), each
one with its own key field mapping the RDAP entity handle;
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o Depending on the number of 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 keyset
pagination with respect to offset pagination could be considered
impractical.
Ultimately, both pagination methods have benefits and drawbacks.
Appendix C. 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".
04: Replaced "ldhName" with "name" in the "Sorting Properties
Declaration" section. Clarified the sorting logic with respect to
the JSON value types and the sorting policy for multivalued
fields.
05: Clarified the logic of sorting on IP addresses. Clarified the
mapping between the sorting properties and the RDAP fields.
Updated "Acknowledgements" section.
06: Renamed "pageCount" to "pageSize" and added "pageNumber" in the
"paging_metadata" object.
07: Added "Paging Responses to POST Requests" section.
08: Added "Approaches to Result Pagination" section to appendix.
Added the case of requesting a sort on a property not included in
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the response to the errors listed in the "Negative Answers"
section.
09: Updated the "Implementation Status" section to include APNIC
implementation. Moved the "RDAP Conformance" section up in the
document. Removed the "Paging Responses to POST Requests"
section. Updated the "Acknowledgements" section. Removed unused
references. In the "Sorting Properties Declaration" section:
* clarified the logic of sorting on events;
* corrected the JSONPath of the "lastChanged" sorting property;
* provided a JSONPath example taking into account the vCard
"pref" parameter.
10: Corrected the JSONPaths of both "fn" and "org" sorting
properties in Table 2. Corrected JSON content in Figure 4. Moved
[W3C.CR-xpath-31-20161213] and [RFC7942] to the "Normative
References". Changed the rdapConformance tags "sorting_level_0"
and "paging_level_0" to "sorting" and "paging" respectively.
11: Added the "JSONPath operators" section to appendix.
12: Changed the content of "JSONPath operators" section.
13: Minor pre-AD review edits.
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
Maurizio Martinelli
IIT-CNR/Registro.it
Via Moruzzi,1
Pisa 56124
IT
Email: maurizio.martinelli@iit.cnr.it
URI: http://www.iit.cnr.it
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Scott Hollenbeck
Verisign Labs
12061 Bluemont Way
Reston, VA 20190
USA
Email: shollenbeck@verisign.com
URI: https://www.verisignlabs.com/
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