NETCONF Working Group K. Watsen Internet-Draft Watsen Networks Intended status: Standards Track Q. Wu Expires: 2 September 2024 Huawei Technologies P. Andersson Cisco Systems O. Hagsand SUNET H. Li Hewlett Packard Enterprise 1 March 2024 List Pagination for YANG-driven Protocols draft-ietf-netconf-list-pagination-03 Abstract In some circumstances, instances of YANG modeled "list" and "leaf- list" nodes may contain numerous entries. Retrieval of all the entries can lead to inefficiencies in the server, the client, and the network in between. This document defines a model for list pagination that can be implemented by YANG-driven management protocols such as NETCONF and RESTCONF. The model supports paging over optionally filtered and/or sorted entries. The solution additionally enables servers to constrain query expressions on some "config false" lists or leaf- lists. 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 2 September 2024. Watsen, et al. Expires 2 September 2024 [Page 1] Internet-Draft List Pagination March 2024 Copyright Notice Copyright (c) 2024 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/ license-info) in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4 1.2. Conventions . . . . . . . . . . . . . . . . . . . . . . . 4 1.3. Adherence to the NMDA . . . . . . . . . . . . . . . . . . 4 2. Solution Overview . . . . . . . . . . . . . . . . . . . . . . 4 3. Solution Details . . . . . . . . . . . . . . . . . . . . . . 5 3.1. Query Parameters for a Targeted List or Leaf-List . . . . 5 3.2. Query Parameter for Descendant Lists and Leaf-Lists . . . 10 3.3. Constraints on "where" and "sort-by" for "config false" Lists . . . . . . . . . . . . . . . . . . . . . . . . . . 11 3.3.1. Identifying Constrained "config false" Lists and Leaf-Lists . . . . . . . . . . . . . . . . . . . . . 11 3.3.2. Indicating the Constraints for "where" Filters and "sort-by" Expressions . . . . . . . . . . . . . . . . 12 4. The "ietf-list-pagination" Module . . . . . . . . . . . . . . 13 4.1. Data Model Overview . . . . . . . . . . . . . . . . . . . 13 4.2. Example Usage . . . . . . . . . . . . . . . . . . . . . . 13 4.2.1. Constraining a "config false" list . . . . . . . . . 13 4.2.2. Indicating number remaining in a limited list . . . . 14 4.3. YANG Module . . . . . . . . . . . . . . . . . . . . . . . 14 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23 5.1. The "IETF XML" Registry . . . . . . . . . . . . . . . . . 23 5.2. The "YANG Module Names" Registry . . . . . . . . . . . . 23 6. Security Considerations . . . . . . . . . . . . . . . . . . . 23 6.1. Considerations for the "ietf-list-pagination" YANG Module . . . . . . . . . . . . . . . . . . . . . . . . . 23 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 24 7.1. Normative References . . . . . . . . . . . . . . . . . . 24 7.2. Informative References . . . . . . . . . . . . . . . . . 25 Appendix A. Vector Tests . . . . . . . . . . . . . . . . . . . . 26 A.1. Example YANG Module . . . . . . . . . . . . . . . . . . . 27 A.2. Example Data Set . . . . . . . . . . . . . . . . . . . . 34 Watsen, et al. Expires 2 September 2024 [Page 2] Internet-Draft List Pagination March 2024 A.3. Example Queries . . . . . . . . . . . . . . . . . . . . . 39 A.3.1. The "limit" Parameter . . . . . . . . . . . . . . . . 39 A.3.2. The "offset" Parameter . . . . . . . . . . . . . . . 42 A.3.3. The "cursor" Parameter . . . . . . . . . . . . . . . 44 A.3.4. The "direction" Parameter . . . . . . . . . . . . . . 49 A.3.5. The "sort-by" Parameter . . . . . . . . . . . . . . . 50 A.3.6. The "where" Parameter . . . . . . . . . . . . . . . . 54 A.3.7. The "locale" Parameter . . . . . . . . . . . . . . . 56 A.3.8. The "sublist-limit" Parameter . . . . . . . . . . . . 58 A.3.9. Combinations of Parameters . . . . . . . . . . . . . 62 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 64 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 64 1. Introduction YANG modeled "list" and "leaf-list" nodes may contain a large number of entries. For instance, there may be thousands of entries in the configuration for network interfaces or access control lists. And time-driven logging mechanisms, such as an audit log or a traffic log, can contain millions of entries. Retrieval of all the entries can lead to inefficiencies in the server, the client, and the network in between. For instance, consider the following: * A client may need to filter and/or sort list entries in order to, e.g., present the view requested by a user. * A server may need to iterate over many more list entries than needed by a client. * A network may need to convey more data than needed by a client. Optimal global resource utilization is obtained when clients are able to cherry-pick just that which is needed to support the application- level business logic. This document defines a generic model for list pagination that can be implemented by YANG-driven management protocols such as NETCONF [RFC6241] and RESTCONF [RFC8040]. Details for how such protocols are updated are outside the scope of this document. The model presented in this document supports paging over optionally filtered and/or sorted entries. Server-side filtering and sorting is ideal as servers can leverage indexes maintained by a backend storage layer to accelerate queries. Watsen, et al. Expires 2 September 2024 [Page 3] Internet-Draft List Pagination March 2024 1.1. Terminology The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here. The following terms are defined in [RFC7950] and are not redefined here: client, data model, data tree, feature, extension, module, leaf, leaf-list, and server. 1.2. Conventions Various examples in this document use "BASE64VALUE=" as a placeholder value for binary data that has been base64 encoded (per Section 9.8 of [RFC7950]). This placeholder value is used because real base64 encoded structures are often many lines long and hence distracting to the example being presented. 1.3. Adherence to the NMDA This document is compliant with the Network Management Datastore Architecture (NMDA) [RFC8342]. The "ietf-list-pagination" module only defines a YANG extension and augments a couple leafs into a "config false" node defined by the "ietf-system-capabilities" module. 2. Solution Overview The solution presented in this document broadly entails a client sending a query to a server targeting a specific list or leaf-list including optional parameters guiding which entries should be returned. A secondary aspect of this solution entails a client sending a query parameter to a server guiding how descendent lists and leaf-lists should be returned. This parameter may be used on any target node, not just "list" and "leaf-list" nodes. Clients detect a server's support for list pagination via an entry for the "ietf-list-pagination" module (defined in Section 4) in the server's YANG Library [RFC8525] response. Relying on client-provided query parameters ensures servers remain backward compatible with legacy clients. Watsen, et al. Expires 2 September 2024 [Page 4] Internet-Draft List Pagination March 2024 3. Solution Details This section is composed of the following subsections: * Section 3.1 defines five query parameters clients may use to page through the entries of a single list or leaf-list in a data tree. * Section 3.2 defines one query parameter that clients may use to affect the content returned for descendant lists and leaf-lists. * Section 3.3 defines per schema-node tags enabling servers to indicate which "config false" lists are constrained and how they may be interacted with. 3.1. Query Parameters for a Targeted List or Leaf-List The five query parameters presented this section are listed in processing order. This processing order is logical, efficient, and matches the processing order implemented by database systems, such as SQL. The order is as follows: a server first processes the "where" parameter (see Section 3.1.1), then the "sort-by" parameter (see Section 3.1.2), then the "direction" parameter (see Section 3.1.4), and either a combination of the "offset" parameter (see Section 3.1.5) or the "cursor" parameter (see Section 3.1.6), and lastly "the "limit" parameter (see Section 3.1.7). The sorting can furthermore be configured with a locale for collation. This is done by setting the "locale" parameter (see Section 3.1.3). 3.1.1. The "where" Query Parameter Description The "where" query parameter specifies a filter expression that result-set entries must match. Default Value If this query parameter is unspecified, then no entries are filtered from the working result-set. Watsen, et al. Expires 2 September 2024 [Page 5] Internet-Draft List Pagination March 2024 Allowed Values The allowed values are XPath 1.0 expressions. It is an error if the XPath expression references a node identifier that does not exist in the schema, is optional or conditional in the schema or, for constrained "config false" lists and leaf-lists (see Section 3.3), if the node identifier does not point to a node having the "indexed" extension statement applied to it (see Section 3.3.2). Conformance The "where" query parameter MUST be supported for all "config true" lists and leaf-lists and SHOULD be supported for "config false" lists and leaf-lists. Servers MAY disable the support for some or all "config false" lists and leaf-lists as described in Section 3.3.2. 3.1.2. The "sort-by" Query Parameter Description The "sort-by" query parameter indicates the node in the working result-set (i.e., after the "where" parameter has been applied) that entries should be sorted by. Sorts are in ascending order (e.g., '1' before '9', 'a' before 'z', etc.). Missing values are sorted to the end (e.g., after all nodes having values). Sub- sorts are not supported. Default Value If this query parameter is unspecified, then the list or leaf- list's default order is used, per the YANG "ordered-by" statement (see Section 7.7.7 of [RFC7950]). Allowed Values The allowed values are node identifiers. It is an error if the specified node identifier does not exist in the schema, is optional or conditional in the schema or, for constrained "config false" lists and leaf-lists (see Section 3.3), if the node identifier does not point to a node having the "indexed" extension statement applied to it (see Section 3.3.2). Conformance The "sort-by" query parameter MUST be supported for all "config true" lists and leaf-lists and SHOULD be supported for "config false" lists and leaf-lists. Servers MAY disable the support for some or all "config false" lists and leaf-lists as described in Section 3.3.2. Watsen, et al. Expires 2 September 2024 [Page 6] Internet-Draft List Pagination March 2024 3.1.3. The "locale" Query Parameter Description The "locale" query parameter indicates what locale is used when collating the result-set. Default Value If this query parameter is unspecified, it is up to the server select a locale for collation. How the server chooses the locale used is out of scope for this document. The result-set includes the locale used by the server for collation with a metadata value [RFC7952] called "locale". Allowed Values The format is a free form string but SHOULD follow the language sub-tag format defined in [RFC5646]. An example is 'sv_SE'. If a supplied locale is unknown to the server, the "locale-unavailable" SHOULD be produced in the error-app-tag in the error output. Note that all locales are assumed to be UTF-8, since character encoding for YANG strings and all known YANG modelled encodings and protocols are required to be UTF-8 [RFC6241] [RFC7950] [RFC7951] [RFC8040]. A server MUST accept a known encoding with or without trailing ".UTF-8" and MAY emit an encoding with or without trailing ".UTF-8". This means a server must handle both e.g. "sv_SE" and "sv_SE.UTF-8" equally as output, and chooses how to emit used locale as output. Conformance The "locale" query parameter MUST be supported for all "config true" lists and leaf-lists and SHOULD be supported for "config false" lists and leaf-lists. Servers MAY disable the support for some or all "config false" lists and leaf-lists as described in Section 3.3.2. 3.1.4. The "direction" Query Parameter Description The "direction" query parameter indicates how the entries in the working result-set (i.e., after the "sort-by" parameter has been applied) should be traversed. Default Value If this query parameter is unspecified, the default value is "forwards". Allowed Values The allowed values are: Watsen, et al. Expires 2 September 2024 [Page 7] Internet-Draft List Pagination March 2024 forwards Return entries in the forwards direction. Also known as the "default" or "ascending" direction. backwards Return entries in the backwards direction. Also known as the "reverse" or "descending" direction Conformance The "direction" query parameter MUST be supported for all lists and leaf-lists. 3.1.5. The "offset" Query Parameter Description The "offset" query parameter indicates the number of entries in the working result-set (i.e., after the "direction" parameter has been applied) that should be skipped over when preparing the response. Default Value If this query parameter is unspecified, then no entries in the result-set are skipped, same as when the offset value '0' is specified. Allowed Values The allowed values are unsigned integers. It is an error for the offset value to exceed the number of entries in the working result-set, and the "offset-out-of-range" identity SHOULD be produced in the error-app-tag in the error output when this occurs. Conformance The "offset" query parameter MUST be supported for all lists and leaf-lists. 3.1.6. The "cursor" Query Parameter Description The "cursor" query parameter indicates where to start the working result-set (i.e., after the "direction" parameter has been applied), the elements before the cursor are skipped over when preparing the response. Furthermore, a result set constrained with the "limit" query parameter includes metadata values [RFC7952] called "next" and "previous", which contains cursor values to the next and previous result-sets. These next and previous cursor values are opaque index values for the underlying system's database, e.g. a key or other information needed to Watsen, et al. Expires 2 September 2024 [Page 8] Internet-Draft List Pagination March 2024 efficiently access the selected result-set. These "next" and "previous" metadata values work as Hypermedia as the Engine of Application State (HATEOAS) links [REST-Dissertation]. This means that the server does not keep any stateful information about the "next" and "previous" cursor or the current page. Due to their ephemeral nature, cursor values are never cached. Default Value If this query parameter is unspecified, then no entries in the result-set are skipped. Allowed Values The allowed values are base64 encoded positions interpreted by the server to index an element in the list, e.g. a list key or other information to efficiently access the selected result-set. It is an error to supply an unkown cursor for the working result-set, and the "cursor-not-found" identity SHOULD be produced in the error-app-tag in the error output when this occurs. Conformance The "cursor" query parameter MUST be supported for all "config true" lists and SHOULD be supported for all "config false" lists. It is however optional to support the "cursor" query parameter for "config false" lists and the support must be signaled by the server per list. Servers indicate that they support the "cursor" query parameter for a "config false" list node by having the "cursor-supported" extension statement applied to it in the "per-node-capabilities" node in the "ietf-system-capabilities" model. Since leaf-lists might not have any unique values that can be indexed, the "cursor" query parameter is not relevant for the leaf-lists. Consider the following leaf-list [1,1,2,3,5], which contains elements without uniquely indexable values. It would be possible to use the position, but then the solution would be equal to using the "offset" query parameter. 3.1.7. The "limit" Query Parameter Description The "limit" query parameter limits the number of entries returned from the working result-set (i.e., after the "offset" parameter has been applied). Any list or leaf-list that is limited includes, somewhere in its encoding, a metadata value [RFC7952] called "remaining", a positive integer indicating the number of elements that were not included in the result-set by the "limit" operation, or the value "unknown" in case, e.g., the server Watsen, et al. Expires 2 September 2024 [Page 9] Internet-Draft List Pagination March 2024 determines that counting would be prohibitively expensive. Default Value If this query parameter is unspecified, the number of entries that may be returned is unbounded. Allowed Values The allowed values are positive integers. Conformance The "limit" query parameter MUST be supported for all lists and leaf-lists. 3.2. Query Parameter for Descendant Lists and Leaf-Lists Whilst this document primarily regards pagination for a list or leaf- list, it begs the question for how descendant lists and leaf-lists should be handled, which is addressed by the "sublist-limit" query parameter described in this section. 3.2.1. The "sublist-limit" Query Parameter Description The "sublist-limit" parameter limits the number of entries returned for descendent lists and leaf-lists. Any descendent list or leaf-list limited by the "sublist-limit" parameter includes, somewhere in its encoding, a metadata value [RFC7952] called "remaining", a positive integer indicating the number of elements that were not included by the "sublist-limit" parameter, or the value "unknown" in case, e.g., the server determines that counting would be prohibitively expensive. When used on a list node, it only affects the list's descendant nodes, not the list itself, which is only affected by the parameters presented in Section 3.1. Default Value If this query parameter is unspecified, the number of entries that may be returned for descendent lists and leaf-lists is unbounded. Allowed Values The allowed values are positive integers. Conformance The "sublist-limit" query parameter MUST be supported for all conventional nodes, including a datastore's top-level node (i.e., '/'). Watsen, et al. Expires 2 September 2024 [Page 10] Internet-Draft List Pagination March 2024 3.3. Constraints on "where" and "sort-by" for "config false" Lists Some "config false" lists and leaf-lists may contain an enormous number of entries. For instance, a time-driven logging mechanism, such as an audit log or a traffic log, can contain millions of entries. In such cases, "where" and "sort-by" expressions will not perform well if the server must bring each entry into memory in order to process it. The server's best option is to leverage query-optimizing features (e.g., indexes) built into the backend database holding the dataset. However, arbitrary "where" expressions and "sort-by" node identifiers into syntax supported by the backend database and/or query-optimizers may prove challenging, if not impossible, to implement. Thusly this section introduces mechanisms whereby a server can: 1. Identify which "config false" lists and leaf-lists are constrained. 2. Identify what node-identifiers and expressions are allowed for the constrained lists and leaf-lists. | Note: The pagination performance for "config true" lists and | leaf-lists is not considered as already servers must be able to | process them as configuration. Whilst some "config true' lists | and leaf-lists may contain thousands of entries, they are well | within the capability of server-side processing. 3.3.1. Identifying Constrained "config false" Lists and Leaf-Lists Identification of which lists and leaf-lists are constrained occurs in the schema tree, not the data tree. However, as server abilities vary, it is not possible to define constraints in YANG modules defining generic data models. In order to enable servers to identify which lists and leaf-lists are constrained, the solution presented in this document augments the data model defined by the "ietf-system-capabilities" module presented in [RFC9196]. Specifically, the "ietf-list-pagination" module (see Section 4) augments an empty leaf node called "constrained" into the "per-node- capabilities" node defined in the "ietf-system-capabilities" module. Watsen, et al. Expires 2 September 2024 [Page 11] Internet-Draft List Pagination March 2024 The "constrained" leaf MAY be specified for any "config false" list or leaf-list. When a list or leaf-list is constrained: * All parts of XPath 1.0 expressions are disabled unless explicitly enabled by Section 3.3.2. * Node-identifiers used in "where" expressions and "sort-by" filters MUST have the "indexed" leaf applied to it (see Section 3.3.2). * For lists only, node-identifiers used in "where" expressions and "sort-by" filters MUST NOT descend past any descendent lists. This ensures that only indexes relative to the targeted list are used. Further constraints on node identifiers MAY be applied in Section 3.3.2. 3.3.2. Indicating the Constraints for "where" Filters and "sort-by" Expressions This section identifies how constraints for "where" filters and "sort-by" expressions are specified. These constraints are valid only if the "constrained" leaf described in the previous section Section 3.3.1 has been set on the immediate ancestor "list" node or, for "leaf-list" nodes, on itself. 3.3.2.1. Indicating Filterable/Sortable Nodes For "where" filters, an unconstrained XPath expressions may use any node in comparisons. However, efficient mappings to backend databases may support only a subset of the nodes. Similarly, for "sort-by" expressions, efficient sorts may only support a subset of the nodes. In order to enable servers to identify which nodes may be used in comparisons (for both "where" and "sort-by" expressions), the "ietf- list-pagination" module (see Section 4) augments an empty leaf node called "indexed" into the "per-node-capabilities" node defined in the "ietf-system-capabilities" module (see [RFC9196]). When a "list" or "leaf-list" node has the "constrained" leaf, only nodes having the "indexed" node may be used in "where" and/or "sort- by" expressions. If no nodes have the "indexed" leaf, when the "constrained" leaf is present, then "where" and "sort-by" expressions are disabled for that list or leaf-list. Watsen, et al. Expires 2 September 2024 [Page 12] Internet-Draft List Pagination March 2024 4. The "ietf-list-pagination" Module The "ietf-list-pagination" module is used by servers to indicate that they support pagination on YANG "list" and "leaf-list" nodes, and to provide an ability to indicate which "config false" list and/or "leaf-list" nodes are constrained and, if so, which nodes may be used in "where" and "sort-by" expressions. 4.1. Data Model Overview The following tree diagram [RFC8340] illustrates the "ietf-list- pagination" module: module: ietf-list-pagination augment /sysc:system-capabilities/sysc:datastore-capabilities /sysc:per-node-capabilities: +--ro constrained? empty +--ro indexed? empty +--ro cursor-supported? empty Comments: * As shown, this module augments three optional leafs into the "per- node-capabilities" node of the "ietf-system-capabilities" module. * Not shown is that the module also defines an "md:annotation" statement named "remaining". This annotation may be present in a server's response to a client request containing either the "limit" (Section 3.1.7) or "sublist-limit" parameters (Appendix A.3.8). 4.2. Example Usage 4.2.1. Constraining a "config false" list The following example illustrates the "ietf-list-pagination" module's augmentations of the "system-capabilities" data tree. This example assumes the "example-social" module defined in the Appendix A.1 is implemented. Watsen, et al. Expires 2 September 2024 [Page 13] Internet-Draft List Pagination March 2024 =============== NOTE: '\' line wrapping per RFC 8792 ================ ds:operational /es:audit-logs/es:audit-log /es:audit-logs/es:audit-log/es:timestamp /es:audit-logs/es:audit-log/es:member-id /es:audit-logs/es:audit-log/es:outcome 4.2.2. Indicating number remaining in a limited list FIXME: valid syntax for 'where'? 4.3. YANG Module This YANG module has normative references to [RFC7952] and [RFC9196]. file "ietf-list-pagination@2024-03-01.yang" module ietf-list-pagination { yang-version 1.1; namespace "urn:ietf:params:xml:ns:yang:ietf-list-pagination"; prefix lpg; import ietf-datastores { Watsen, et al. Expires 2 September 2024 [Page 14] Internet-Draft List Pagination March 2024 prefix ds; reference "RFC 8342: Network Management Datastore Architecture (NMDA)"; } import ietf-yang-types { prefix yang; reference "RFC 6991: Common YANG Data Types"; } import ietf-yang-metadata { prefix md; reference "RFC 7952: Defining and Using Metadata with YANG"; } import ietf-system-capabilities { prefix sysc; reference "RFC 9196: YANG Modules Describing Capabilities for Systems and Datastore Update Notifications"; } organization "IETF NETCONF (Network Configuration) Working Group"; contact "WG Web: https://datatracker.ietf.org/wg/netconf WG List: NETCONF WG list "; description "This module is used by servers to 1) indicate they support pagination on 'list' and 'leaf-list' resources, 2) define a grouping for each list-pagination parameter, and 3) indicate which 'config false' lists have constrained 'where' and 'sort-by' parameters and how they may be used, if at all. Copyright (c) 2024 IETF Trust and the persons identified as authors of the code. All rights reserved. Redistribution and use in source and binary forms, with or without modification, is permitted pursuant to, and subject to the license terms contained in, the Revised BSD License set forth in Section 4.c of the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info). Watsen, et al. Expires 2 September 2024 [Page 15] Internet-Draft List Pagination March 2024 This version of this YANG module is part of RFC XXXX (https://www.rfc-editor.org/info/rfcXXXX); see the RFC itself for full legal notices. The key words 'MUST', 'MUST NOT', 'REQUIRED', 'SHALL', 'SHALL NOT', 'SHOULD', 'SHOULD NOT', 'RECOMMENDED', 'NOT RECOMMENDED', 'MAY', and 'OPTIONAL' in this document are to be interpreted as described in BCP 14 (RFC 2119) (RFC 8174) when, and only when, they appear in all capitals, as shown here."; revision 2024-03-01 { description "Initial revision."; reference "RFC XXXX: List Pagination for YANG-driven Protocols"; } // Annotations md:annotation remaining { type union { type uint32; type enumeration { enum "unknown" { description "Indicates that number of remaining entries is unknown to the server in case, e.g., the server has determined that counting would be prohibitively expensive."; } } } description "This annotation contains the number of elements not included in the result set (a positive value) due to a 'limit' or 'sublist-limit' operation. If no elements were removed, this annotation MUST NOT appear. The minimum value (0), which never occurs in normal operation, is reserved to represent 'unknown'. The maximum value (2^32-1) is reserved to represent any value greater than or equal to 2^32-1 elements."; } md:annotation next { type string; description "This annotation contains the base64 encoded value of the next Watsen, et al. Expires 2 September 2024 [Page 16] Internet-Draft List Pagination March 2024 cursor in the pagination."; } md:annotation previous { type string; description "This annotation contains the base64 encoded value of the previous cursor in the pagination."; } md:annotation locale { type string; description "This annotation contains the locale used when sorting. The format is a free form string but SHOULD follow the language sub-tag format defined in RFC 5646. An example is 'sv_SE'. For further details see references: RFC 5646: Tags for identifying Languages RFC 6365: Technology Used in Internationalization in the IETF"; } // Identities identity list-pagination-error { description "Base identity for list-pagination errors."; } identity offset-out-of-range { base list-pagination-error; description "The 'offset' query parameter value is greater than the number of instances in the target list or leaf-list resource."; } identity cursor-not-found { base list-pagination-error; description "The 'cursor' query parameter value is unknown for the target list."; } identity locale-unavailable { base list-pagination-error; Watsen, et al. Expires 2 September 2024 [Page 17] Internet-Draft List Pagination March 2024 description "The 'locale' query parameter input is not a valid locale or the locale is not available on the system."; } // Groupings grouping where-param-grouping { description "This grouping may be used by protocol-specific YANG modules to define a protocol-specific query parameter."; leaf where { type union { type yang:xpath1.0; type enumeration { enum "unfiltered" { description "Indicates that no entries are to be filtered from the working result-set."; } } } default "unfiltered"; description "The 'where' parameter specifies a boolean expression that result-set entries must match. It is an error if the XPath expression references a node identifier that does not exist in the schema, is optional or conditional in the schema or, for constrained 'config false' lists and leaf-lists, if the node identifier does not point to a node having the 'indexed' extension statement applied to it (see RFC XXXX)."; } } grouping locale-param-grouping { description "The grouping may be used by protocol-specific YANG modules to define a protocol-specific query parameter."; leaf locale { type string; description "The 'locale' parameter indicates the locale which the entries in the working result-set should be collated."; } } Watsen, et al. Expires 2 September 2024 [Page 18] Internet-Draft List Pagination March 2024 grouping sort-by-param-grouping { description "This grouping may be used by protocol-specific YANG modules to define a protocol-specific query parameter."; leaf sort-by { type union { type string { // An RFC 7950 'descendant-schema-nodeid'. pattern '([0-9a-fA-F]*:)?[0-9a-fA-F]*' + '(/([0-9a-fA-F]*:)?[0-9a-fA-F]*)*'; } type enumeration { enum "none" { description "Indicates that the list or leaf-list's default order is to be used, per the YANG 'ordered-by' statement."; } } } default "none"; description "The 'sort-by' parameter indicates the node in the working result-set (i.e., after the 'where' parameter has been applied) that entries should be sorted by. Sorts are in ascending order (e.g., '1' before '9', 'a' before 'z', etc.). Missing values are sorted to the end (e.g., after all nodes having values)."; } } grouping direction-param-grouping { description "This grouping may be used by protocol-specific YANG modules to define a protocol-specific query parameter."; leaf direction { type enumeration { enum forwards { description "Indicates that entries should be traversed from the first to last item in the working result set."; } enum backwards { description "Indicates that entries should be traversed from the last to first item in the working result set."; } Watsen, et al. Expires 2 September 2024 [Page 19] Internet-Draft List Pagination March 2024 } default "forwards"; description "The 'direction' parameter indicates how the entries in the working result-set (i.e., after the 'sort-by' parameter has been applied) should be traversed."; } } grouping cursor-param-grouping { description "This grouping may be used by protocol-specific YANG modules to define a protocol-specific query parameter."; leaf cursor { type string; description "The 'cursor' parameter indicates where to start the working result-set (i.e. after the 'direction' parameter has been applied), the elements before the cursor are skipped over when preparing the response. Furthermare the result-set is annotated with attributes for the next and previous cursors following a result-set constrained with the 'limit' query parameter."; } } grouping offset-param-grouping { description "This grouping may be used by protocol-specific YANG modules to define a protocol-specific query parameter."; leaf offset { type uint32; default 0; description "The 'offset' parameter indicates the number of entries in the working result-set (i.e., after the 'direction' parameter has been applied) that should be skipped over when preparing the response."; } } grouping limit-param-grouping { description "This grouping may be used by protocol-specific YANG modules to define a protocol-specific query parameter."; leaf limit { type union { type uint32 { Watsen, et al. Expires 2 September 2024 [Page 20] Internet-Draft List Pagination March 2024 range "1..max"; } type enumeration { enum "unbounded" { description "Indicates that the number of entries that may be returned is unbounded."; } } } default "unbounded"; description "The 'limit' parameter limits the number of entries returned from the working result-set (i.e., after the 'offset' parameter has been applied). Any result-set that is limited includes, somewhere in its encoding, the metadata value 'remaining' to indicate the number entries not included in the result set."; } } grouping sublist-limit-param-grouping { description "This grouping may be used by protocol-specific YANG modules to define a protocol-specific query parameter."; leaf sublist-limit { type union { type uint32 { range "1..max"; } type enumeration { enum "unbounded" { description "Indicates that the number of entries that may be returned is unbounded."; } } } default "unbounded"; description "The 'sublist-limit' parameter limits the number of entries for descendent lists and leaf-lists. Any result-set that is limited includes, somewhere in its encoding, the metadata value 'remaining' to indicate the number entries not included in the result set."; } Watsen, et al. Expires 2 September 2024 [Page 21] Internet-Draft List Pagination March 2024 } // Protocol-accessible nodes augment "/sysc:system-capabilities/sysc:datastore-capabilities" + "/sysc:per-node-capabilities" { // Ensure the following nodes are only used for the // datastore. when "/sysc:system-capabilities/sysc:datastore-capabilities" + "/sysc:datastore = 'ds:operational'"; description "Defines some leafs that MAY be used by the server to describe constraints imposed of the 'where' filters and 'sort-by' parameters used in list pagination queries."; leaf constrained { type empty; description "Indicates that 'where' filters and 'sort-by' parameters on the targeted 'config false' list node are constrained. If a list is not 'constrained', then full XPath 1.0 expressions may be used in 'where' filters and all node identifiers are usable by 'sort-by'."; } leaf indexed { type empty; description "Indicates that the targeted descendent node of a 'constrained' list (see the 'constrained' leaf) may be used in 'where' filters and/or 'sort-by' parameters. If a descendent node of a 'constrained' list is not 'indexed', then it MUST NOT be used in 'where' filters or 'sort-by' parameters."; } leaf cursor-supported { type empty; description "Indicates that the targeted list node supports the 'cursor' parameter."; } } } Watsen, et al. Expires 2 September 2024 [Page 22] Internet-Draft List Pagination March 2024 5. IANA Considerations 5.1. The "IETF XML" Registry This document registers one URI in the "ns" subregistry of the IETF XML Registry [RFC3688] maintained at https://www.iana.org/assignments/xml-registry/xml-registry.xhtml#ns. Following the format in [RFC3688], the following registration is requested: URI: urn:ietf:params:xml:ns:yang:ietf-list-pagination Registrant Contact: The IESG. XML: N/A, the requested URI is an XML namespace. 5.2. The "YANG Module Names" Registry This document registers one YANG module in the YANG Module Names registry [RFC6020] maintained at https://www.iana.org/assignments/ yang-parameters/yang-parameters.xhtml. Following the format defined in [RFC6020], the below registration is requested: name: ietf-list-pagination namespace: urn:ietf:params:xml:ns:yang:ietf-list-pagination prefix: lpg RFC: XXXX 6. Security Considerations 6.1. Considerations for the "ietf-list-pagination" YANG Module This section follows the template defined in Section 3.7.1 of [RFC8407]. The YANG module specified in this document defines a schema for data that is designed to be accessed via network management protocols such as NETCONF [RFC6241] or RESTCONF [RFC8040]. The lowest NETCONF layer is the secure transport layer, and the mandatory-to-implement secure transport is Secure Shell (SSH) [RFC6242]. The lowest RESTCONF layer is HTTPS, and the mandatory-to-implement secure transport is TLS [RFC8446]. The Network Configuration Access Control Model (NACM) [RFC8341] provides the means to restrict access for particular NETCONF or RESTCONF users to a preconfigured subset of all available NETCONF or RESTCONF protocol operations and content. Watsen, et al. Expires 2 September 2024 [Page 23] Internet-Draft List Pagination March 2024 All protocol-accessible data nodes in this module are read-only and cannot be modified. Access control may be configured to avoid exposing any read-only data that is defined by the augmenting module documentation as being security sensitive. Since this module also defines groupings, these considerations are primarily for the designers of other modules that use these groupings. None of the readable data nodes defined in this YANG module are considered sensitive or vulnerable in network environments. The NACM "default-deny-all" extension has not been set for any data nodes defined in this module. This module does not define any RPCs or actions or notifications, and thus the security consideration for such is not provided here. 7. References 7.1. 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, . [RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, DOI 10.17487/RFC3688, January 2004, . [RFC5646] Phillips, A., Ed. and M. Davis, Ed., "Tags for Identifying Languages", BCP 47, RFC 5646, DOI 10.17487/RFC5646, September 2009, . [RFC6241] Enns, R., Ed., Bjorklund, M., Ed., Schoenwaelder, J., Ed., and A. Bierman, Ed., "Network Configuration Protocol (NETCONF)", RFC 6241, DOI 10.17487/RFC6241, June 2011, . [RFC6242] Wasserman, M., "Using the NETCONF Protocol over Secure Shell (SSH)", RFC 6242, DOI 10.17487/RFC6242, June 2011, . [RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language", RFC 7950, DOI 10.17487/RFC7950, August 2016, . Watsen, et al. Expires 2 September 2024 [Page 24] Internet-Draft List Pagination March 2024 [RFC7951] Lhotka, L., "JSON Encoding of Data Modeled with YANG", RFC 7951, DOI 10.17487/RFC7951, August 2016, . [RFC7952] Lhotka, L., "Defining and Using Metadata with YANG", RFC 7952, DOI 10.17487/RFC7952, August 2016, . [RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC8341] Bierman, A. and M. Bjorklund, "Network Configuration Access Control Model", STD 91, RFC 8341, DOI 10.17487/RFC8341, March 2018, . [RFC8407] Bierman, A., "Guidelines for Authors and Reviewers of Documents Containing YANG Data Models", BCP 216, RFC 8407, DOI 10.17487/RFC8407, October 2018, . [RFC8446] Rescorla, E., "The Transport Layer Security (TLS) Protocol Version 1.3", RFC 8446, DOI 10.17487/RFC8446, August 2018, . [RFC9196] Lengyel, B., Clemm, A., and B. Claise, "YANG Modules Describing Capabilities for Systems and Datastore Update Notifications", RFC 9196, DOI 10.17487/RFC9196, February 2022, . 7.2. Informative References [I-D.ietf-netconf-list-pagination-nc] Watsen, K., Wu, Q., Hagsand, O., Li, H., and P. Andersson, "NETCONF Extensions to Support List Pagination", Work in Progress, Internet-Draft, draft-ietf-netconf-list- pagination-nc-02, 22 October 2023, . [I-D.ietf-netconf-list-pagination-rc] Watsen, K., Wu, Q., Hagsand, O., Li, H., and P. Andersson, "RESTCONF Extensions to Support List Pagination", Work in Watsen, et al. Expires 2 September 2024 [Page 25] Internet-Draft List Pagination March 2024 Progress, Internet-Draft, draft-ietf-netconf-list- pagination-rc-02, 22 October 2023, . [I-D.ietf-netconf-restconf-collection] Bierman, A., Björklund, M., and K. Watsen, "RESTCONF Collection Resource", Work in Progress, Internet-Draft, draft-ietf-netconf-restconf-collection-00, 30 January 2015, . [REST-Dissertation] Fielding, R., "Architectural Styles and the Design of Network-based Software Architectures", 2000, . [RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for the Network Configuration Protocol (NETCONF)", RFC 6020, DOI 10.17487/RFC6020, October 2010, . [RFC6365] Hoffman, P. and J. Klensin, "Terminology Used in Internationalization in the IETF", BCP 166, RFC 6365, DOI 10.17487/RFC6365, September 2011, . [RFC8340] Bjorklund, M. and L. Berger, Ed., "YANG Tree Diagrams", BCP 215, RFC 8340, DOI 10.17487/RFC8340, March 2018, . [RFC8342] Bjorklund, M., Schoenwaelder, J., Shafer, P., Watsen, K., and R. Wilton, "Network Management Datastore Architecture (NMDA)", RFC 8342, DOI 10.17487/RFC8342, March 2018, . [RFC8525] Bierman, A., Bjorklund, M., Schoenwaelder, J., Watsen, K., and R. Wilton, "YANG Library", RFC 8525, DOI 10.17487/RFC8525, March 2019, . Appendix A. Vector Tests This normative appendix section illustrates every notable edge condition conceived during this document's production. Watsen, et al. Expires 2 September 2024 [Page 26] Internet-Draft List Pagination March 2024 Test inputs and outputs are provided in a manner that is both generic and concise. Management protocol specific documents need only reproduce as many of these tests as necessary to convey pecularities presented by the protocol. Implementations are RECOMMENDED to implement the tests presented in this document, in addition to any tests that may be presented in protocol specific documents. A.1. Example YANG Module The vector tests assume the "example-social" YANG module defined in this section. This module has been specially crafted to cover every notable edge condition, especially with regards to the types of the data nodes. Following is the tree diagram [RFC8340] for the "example-social" module: Watsen, et al. Expires 2 September 2024 [Page 27] Internet-Draft List Pagination March 2024 module: example-social +--rw members | +--rw member* [member-id] | +--rw member-id string | +--rw email-address inet:email-address | +--rw password ianach:crypt-hash | +--rw avatar? binary | +--rw tagline? string | +--rw privacy-settings | | +--rw hide-network? boolean | | +--rw post-visibility? enumeration | +--rw following* -> /members/member/member-id | +--rw posts | | +--rw post* [timestamp] | | +--rw timestamp yang:date-and-time | | +--rw title? string | | +--rw body string | +--rw favorites | | +--rw uint8-numbers* uint8 | | +--rw uint64-numbers* uint64 | | +--rw int8-numbers* int8 | | +--rw int64-numbers* int64 | | +--rw decimal64-numbers* decimal64 | | +--rw bits* bits | +--ro stats | +--ro joined yang:date-and-time | +--ro membership-level enumeration | +--ro last-activity? yang:date-and-time +--ro audit-logs +--ro audit-log* [] +--ro timestamp yang:date-and-time +--ro member-id string +--ro source-ip inet:ip-address +--ro request string +--ro outcome boolean Following is the YANG [RFC7950] for the "example-social" module: module example-social { yang-version 1.1; namespace "https://example.com/ns/example-social"; prefix es; import ietf-yang-types { prefix yang; reference "RFC 6991: Common YANG Data Types"; } Watsen, et al. Expires 2 September 2024 [Page 28] Internet-Draft List Pagination March 2024 import ietf-inet-types { prefix inet; reference "RFC 6991: Common YANG Data Types"; } import iana-crypt-hash { prefix ianach; reference "RFC 7317: A YANG Data Model for System Management"; } organization "Example, Inc."; contact "support@example.com"; description "Example Social Data Model."; revision YYYY-MM-DD { description "Initial version."; reference "RFC XXXX: Example social module."; } container members { description "Container for list of members."; list member { key "member-id"; description "List of members."; leaf member-id { type string { length "1..80"; pattern '.*[\n].*' { modifier invert-match; } } description "The member's identifier."; } leaf email-address { type inet:email-address; mandatory true; description "The member's email address."; } Watsen, et al. Expires 2 September 2024 [Page 29] Internet-Draft List Pagination March 2024 leaf password { type ianach:crypt-hash; mandatory true; description "The member's hashed-password."; } leaf avatar { type binary; description "An binary image file."; } leaf tagline { type string { length "1..80"; pattern '.*[\n].*' { modifier invert-match; } } description "The member's tagline."; } container privacy-settings { leaf hide-network { type boolean; description "Hide who you follow and who follows you."; } leaf post-visibility { type enumeration { enum public { description "Posts are public."; } enum unlisted { description "Posts are unlisted, though visable to all."; } enum followers-only { description "Posts only visible to followers."; } } default public; description "The post privacy setting."; Watsen, et al. Expires 2 September 2024 [Page 30] Internet-Draft List Pagination March 2024 } description "Preferences for the member."; } leaf-list following { type leafref { path "/members/member/member-id"; } description "Other members this members is following."; } container posts { description "The member's posts."; list post { key timestamp; leaf timestamp { type yang:date-and-time; description "The timestamp for the member's post."; } leaf title { type string { length "1..80"; pattern '.*[\n].*' { modifier invert-match; } } description "A one-line title."; } leaf body { type string; mandatory true; description "The body of the post."; } description "A list of posts."; } } container favorites { description "The member's favorites."; leaf-list uint8-numbers { Watsen, et al. Expires 2 September 2024 [Page 31] Internet-Draft List Pagination March 2024 type uint8; ordered-by user; description "The member's favorite uint8 numbers."; } leaf-list uint64-numbers { type uint64; ordered-by user; description "The member's favorite uint64 numbers."; } leaf-list int8-numbers { type int8; ordered-by user; description "The member's favorite int8 numbers."; } leaf-list int64-numbers { type int64; ordered-by user; description "The member's favorite uint64 numbers."; } leaf-list decimal64-numbers { type decimal64 { fraction-digits 5; } ordered-by user; description "The member's favorite decimal64 numbers."; } leaf-list bits { type bits { bit zero { position 0; description "zero"; } bit one { position 1; description "one"; } bit two { position 2; description "two"; } } ordered-by user; description Watsen, et al. Expires 2 September 2024 [Page 32] Internet-Draft List Pagination March 2024 "The member's favorite bits."; } } container stats { config false; description "Operational state members values."; leaf joined { type yang:date-and-time; mandatory true; description "Timestamp when member joined."; } leaf membership-level { type enumeration { enum admin { description "Site administrator."; } enum standard { description "Standard membership level."; } enum pro { description "Professional membership level."; } } mandatory true; description "The membership level for this member."; } leaf last-activity { type yang:date-and-time; description "Timestamp of member's last activity."; } } } } container audit-logs { config false; description "Audit log configuration"; list audit-log { description Watsen, et al. Expires 2 September 2024 [Page 33] Internet-Draft List Pagination March 2024 "List of audit logs."; leaf timestamp { type yang:date-and-time; mandatory true; description "The timestamp for the event."; } leaf member-id { type string; mandatory true; description "The 'member-id' of the member."; } leaf source-ip { type inet:ip-address; mandatory true; description "The apparent IP address the member used."; } leaf request { type string; mandatory true; description "The member's request."; } leaf outcome { type boolean; mandatory true; description "Indicate if request was permitted."; } } } } A.2. Example Data Set The examples assume the server's operational state as follows. The data is provided in JSON only for convenience and, in particular, has no bearing on the "generic" nature of the tests themselves. { "example-social:members": { "member": [ { "member-id": "bob", "email-address": "bob@example.com", Watsen, et al. Expires 2 September 2024 [Page 34] Internet-Draft List Pagination March 2024 "password": "$0$1543", "avatar": "BASE64VALUE=", "tagline": "Here and now, like never before.", "posts": { "post": [ { "timestamp": "2020-08-14T03:32:25Z", "body": "Just got in." }, { "timestamp": "2020-08-14T03:33:55Z", "body": "What's new?" }, { "timestamp": "2020-08-14T03:34:30Z", "body": "I'm bored..." } ] }, "favorites": { "decimal64-numbers": ["3.14159", "2.71828"] }, "stats": { "joined": "2020-08-14T03:30:00Z", "membership-level": "standard", "last-activity": "2020-08-14T03:34:30Z" } }, { "member-id": "eric", "email-address": "eric@example.com", "password": "$0$1543", "avatar": "BASE64VALUE=", "tagline": "Go to bed with dreams; wake up with a purpose.", "following": ["alice"], "posts": { "post": [ { "timestamp": "2020-09-17T18:02:04Z", "title": "Son, brother, husband, father", "body": "What's your story?" } ] }, "favorites": { "bits": ["two", "one", "zero"] }, "stats": { Watsen, et al. Expires 2 September 2024 [Page 35] Internet-Draft List Pagination March 2024 "joined": "2020-09-17T19:38:32Z", "membership-level": "pro", "last-activity": "2020-09-17T18:02:04Z" } }, { "member-id": "alice", "email-address": "alice@example.com", "password": "$0$1543", "avatar": "BASE64VALUE=", "tagline": "Every day is a new day", "privacy-settings": { "hide-network": false, "post-visibility": "public" }, "following": ["bob", "eric", "lin"], "posts": { "post": [ { "timestamp": "2020-07-08T13:12:45Z", "title": "My first post", "body": "Hiya all!" }, { "timestamp": "2020-07-09T01:32:23Z", "title": "Sleepy...", "body": "Catch y'all tomorrow." } ] }, "favorites": { "uint8-numbers": [17, 13, 11, 7, 5, 3], "int8-numbers": [-5, -3, -1, 1, 3, 5] }, "stats": { "joined": "2020-07-08T12:38:32Z", "membership-level": "admin", "last-activity": "2021-04-01T02:51:11Z" } }, { "member-id": "lin", "email-address": "lin@example.com", "password": "$0$1543", "privacy-settings": { "hide-network": true, "post-visibility": "followers-only" }, Watsen, et al. Expires 2 September 2024 [Page 36] Internet-Draft List Pagination March 2024 "following": ["joe", "eric", "alice"], "stats": { "joined": "2020-07-09T12:38:32Z", "membership-level": "standard", "last-activity": "2021-04-01T02:51:11Z" } }, { "member-id": "joe", "email-address": "joe@example.com", "password": "$0$1543", "avatar": "BASE64VALUE=", "tagline": "Greatness is measured by courage and heart.", "privacy-settings": { "post-visibility": "unlisted" }, "following": ["bob"], "posts": { "post": [ { "timestamp": "2020-10-17T18:02:04Z", "body": "What's your status?" } ] }, "stats": { "joined": "2020-10-08T12:38:32Z", "membership-level": "pro", "last-activity": "2021-04-01T02:51:11Z" } }, { "member-id": "åsa", "email-address": "asa@example.com", "password": "$0$1543", "avatar": "BASE64VALUE=", "privacy-settings": { "post-visibility": "unlisted" }, "following": ["alice", "bob"], "stats": { "joined": "2022-02-19T13:12:00Z", "membership-level": "standard", "last-activity": "2022-04-19T13:12:59Z" } } ] }, Watsen, et al. Expires 2 September 2024 [Page 37] Internet-Draft List Pagination March 2024 "example-social:audit-logs": { "audit-log": [ { "timestamp": "2020-10-11T06:47:59Z", "member-id": "alice", "source-ip": "192.168.0.92", "request": "POST /groups/group/2043", "outcome": true }, { "timestamp": "2020-11-01T15:22:01Z", "member-id": "bob", "source-ip": "192.168.2.16", "request": "POST /groups/group/123", "outcome": false }, { "timestamp": "2020-12-12T21:00:28Z", "member-id": "eric", "source-ip": "192.168.254.1", "request": "POST /groups/group/10", "outcome": true }, { "timestamp": "2021-01-03T06:47:59Z", "member-id": "alice", "source-ip": "192.168.0.92", "request": "POST /groups/group/333", "outcome": true }, { "timestamp": "2021-01-21T10:00:00Z", "member-id": "bob", "source-ip": "192.168.2.16", "request": "POST /groups/group/42", "outcome": true }, { "timestamp": "2020-02-07T09:06:21Z", "member-id": "alice", "source-ip": "192.168.0.92", "request": "POST /groups/group/1202", "outcome": true }, { "timestamp": "2020-02-28T02:48:11Z", "member-id": "bob", "source-ip": "192.168.2.16", Watsen, et al. Expires 2 September 2024 [Page 38] Internet-Draft List Pagination March 2024 "request": "POST /groups/group/345", "outcome": true } ] } } A.3. Example Queries The following sections are presented in reverse query-parameters processing order. Starting with the simplest (limit) and ending with the most complex (where). All the vector tests are presented in a protocol-independent manner. JSON is used only for its conciseness. A.3.1. The "limit" Parameter Noting that "limit" must be a positive number, the edge condition values are '1', '2', num-elements-1, num-elements, and num- elements+1. | If '0' were a valid limit value, it would always return an | empty result set. Any value greater than or equal to num- | elements results the entire result set, same as when "limit" is | unspecified. These vector tests assume the target "/example- social:members/member=alice/favorites/uint8-numbers", which has six values, thus the edge condition "limit" values are: '1', '2', '5', '6', and '7'. A.3.1.1. limit=1 REQUEST Target: /example-social:members/member=alice/favorites/uint8-numbers Pagination Parameters: Where: - Sort-by: - Direction: - Offset: - Limit: 1 RESPONSE Watsen, et al. Expires 2 September 2024 [Page 39] Internet-Draft List Pagination March 2024 { "example-social:uint8-numbers": [17], "@example-social:uint8-numbers": [ { "ietf-list-pagination:remaining": 5 } ] } A.3.1.2. limit=2 REQUEST Target: /example-social:members/member=alice/favorites/uint8-numbers Pagination Parameters: Where: - Sort-by: - Direction: - Offset: - Limit: 2 RESPONSE { "example-social:uint8-numbers": [17, 13], "@example-social:uint8-numbers": [ { "ietf-list-pagination:remaining": 4 } ] } A.3.1.3. limit=5 REQUEST Target: /example-social:members/member=alice/favorites/uint8-numbers Pagination Parameters: Where: - Sort-by: - Direction: - Offset: - Limit: 5 RESPONSE Watsen, et al. Expires 2 September 2024 [Page 40] Internet-Draft List Pagination March 2024 { "example-social:uint8-numbers": [17, 13, 11, 7, 5], "@example-social:uint8-numbers": [ { "ietf-list-pagination:remaining": 1 } ] } A.3.1.4. limit=6 REQUEST Target: /example-social:members/member=alice/favorites/uint8-numbers Pagination Parameters: Where: - Sort-by: - Direction: - Offset: - Limit: 6 RESPONSE { "example-social:uint8-numbers": [17, 13, 11, 7, 5, 3] } A.3.1.5. limit=7 REQUEST Target: /example-social:members/member=alice/favorites/uint8-numbers Pagination Parameters: Where: - Sort-by: - Direction: - Offset: - Limit: 7 RESPONSE { "example-social:uint8-numbers": [17, 13, 11, 7, 5, 3] } Watsen, et al. Expires 2 September 2024 [Page 41] Internet-Draft List Pagination March 2024 A.3.2. The "offset" Parameter Noting that "offset" must be an unsigned number less than or equal to the num-elements, the edge condition values are '0', '1', '2', num- elements-1, num-elements, and num-elements+1. These vector tests again assume the target "/example- social:members/member=alice/favorites/uint8-numbers", which has six values, thus the edge condition "limit" values are: '0', '1', '2', '5', '6', and '7'. A.3.2.1. offset=0 REQUEST Target: /example-social:members/member=alice/favorites/uint8-numbers Pagination Parameters: Where: - Sort-by: - Direction: - Offset: 0 Limit: - RESPONSE { "example-social:uint8-numbers": [17, 13, 11, 7, 5, 3] } A.3.2.2. offset=1 REQUEST Target: /example-social:members/member=alice/favorites/uint8-numbers Pagination Parameters: Where: - Sort-by: - Direction: - Offset: 1 Limit: - RESPONSE { "example-social:uint8-numbers": [13, 11, 7, 5, 3] } Watsen, et al. Expires 2 September 2024 [Page 42] Internet-Draft List Pagination March 2024 A.3.2.3. offset=2 REQUEST Target: /example-social:members/member=alice/favorites/uint8-numbers Pagination Parameters: Where: - Sort-by: - Direction: - Offset: 2 Limit: - RESPONSE { "example-social:uint8-numbers": [11, 7, 5, 3] } A.3.2.4. offset=5 REQUEST Target: /example-social:members/member=alice/favorites/uint8-numbers Pagination Parameters: Where: - Sort-by: - Direction: - Offset: 5 Limit: - RESPONSE { "example-social:uint8-numbers": [3] } A.3.2.5. offset=6 REQUEST Target: /example-social:members/member=alice/favorites/uint8-numbers Pagination Parameters: Where: - Sort-by: - Direction: - Offset: 6 Limit: - Watsen, et al. Expires 2 September 2024 [Page 43] Internet-Draft List Pagination March 2024 RESPONSE { "example-social:uint8-numbers": [] } A.3.2.6. offset=7 REQUEST Target: /example-social:members/member=alice/favorites/uint8-numbers Pagination Parameters: Where: - Sort-by: - Direction: - Offset: 7 Limit: - RESPONSE ERROR A.3.3. The "cursor" Parameter Noting that "cursor" must be an base64 encoded opaque value which addresses an element in a list. | The default value is empty, which is the same as supplying the | cursor value for the first element in the list. These vector tests assume the target "/example-social:members/member" which has five members. | Note that response has added attributes describing the result | set and position in pagination. A.3.3.1. cursor=&limit=2 REQUEST Target: /example-social:members/member Pagination Parameters: Where: - Sort-by: - Direction: - Offset: - Limit: 2 Cursor: - Watsen, et al. Expires 2 September 2024 [Page 44] Internet-Draft List Pagination March 2024 RESPONSE { "example-social:member": [ { "member-id": "bob", "email-address": "bob@example.com", "password": "$0$1543", "avatar": "BASE64VALUE=", "tagline": "Here and now, like never before.", "posts": { "post": [ { "timestamp": "2020-08-14T03:32:25Z", "body": "Just got in." }, { "timestamp": "2020-08-14T03:33:55Z", "body": "What's new?" }, { "timestamp": "2020-08-14T03:34:30Z", "body": "I'm bored..." } ] }, "favorites": { "decimal64-numbers": ["3.14159", "2.71828"] }, "stats": { "joined": "2020-08-14T03:30:00Z", "membership-level": "standard", "last-activity": "2020-08-14T03:34:30Z" } }, { "member-id": "eric", "email-address": "eric@example.com", "password": "$0$1543", "avatar": "BASE64VALUE=", "tagline": "Go to bed with dreams; wake up with a purpose.", "following": ["alice"], "posts": { "post": [ { "timestamp": "2020-09-17T18:02:04Z", "title": "Son, brother, husband, father", "body": "What's your story?" Watsen, et al. Expires 2 September 2024 [Page 45] Internet-Draft List Pagination March 2024 } ] }, "favorites": { "bits": ["two", "one", "zero"] }, "stats": { "joined": "2020-09-17T19:38:32Z", "membership-level": "pro", "last-activity": "2020-09-17T18:02:04Z" } } ], "@example-social:member": [ { "ietf-list-pagination:remaining": 3, "ietf-list-pagination:previous": "", "ietf-list-pagination:next": "YWxpY2U=" // alice } ] } A.3.3.2. cursor="YWxpY2U="&limit=2 REQUEST Target: /example-social:members/member Pagination Parameters: Where: - Sort-by: - Direction: - Offset: - Limit: 2 Cursor: YWxpY2U= RESPONSE { "example-social:member": [ { "member-id": "alice", "email-address": "alice@example.com", "password": "$0$1543", "avatar": "BASE64VALUE=", "tagline": "Every day is a new day", "privacy-settings": { "hide-network": false, "post-visibility": "public" Watsen, et al. Expires 2 September 2024 [Page 46] Internet-Draft List Pagination March 2024 }, "following": ["bob", "eric", "lin"], "posts": { "post": [ { "timestamp": "2020-07-08T13:12:45Z", "title": "My first post", "body": "Hiya all!" }, { "timestamp": "2020-07-09T01:32:23Z", "title": "Sleepy...", "body": "Catch y'all tomorrow." } ] }, "favorites": { "uint8-numbers": [17, 13, 11, 7, 5, 3], "int8-numbers": [-5, -3, -1, 1, 3, 5] }, "stats": { "joined": "2020-07-08T12:38:32Z", "membership-level": "admin", "last-activity": "2021-04-01T02:51:11Z" } }, { "member-id": "lin", "email-address": "lin@example.com", "password": "$0$1543", "privacy-settings": { "hide-network": true, "post-visibility": "followers-only" }, "following": ["joe", "eric", "alice"], "stats": { "joined": "2020-07-09T12:38:32Z", "membership-level": "standard", "last-activity": "2021-04-01T02:51:11Z" } } ], "@example-social:member": [ { "ietf-list-pagination:remaining": 1, "ietf-list-pagination:previous": "ZXJpYw==", // eric "ietf-list-pagination:next": "am9l" // joe } Watsen, et al. Expires 2 September 2024 [Page 47] Internet-Draft List Pagination March 2024 ] } A.3.3.3. cursor="am9l"&limit=2 REQUEST Target: /example-social:members/member Pagination Parameters: Where: - Sort-by: - Direction: - Offset: - Limit: 2 Cursor: am9l RESPONSE Watsen, et al. Expires 2 September 2024 [Page 48] Internet-Draft List Pagination March 2024 { "example-social:member": [ { "member-id": "joe", "email-address": "joe@example.com", "password": "$0$1543", "avatar": "BASE64VALUE=", "tagline": "Greatness is measured by courage and heart.", "privacy-settings": { "post-visibility": "unlisted" }, "following": ["bob"], "posts": { "post": [ { "timestamp": "2020-10-17T18:02:04Z", "body": "What's your status?" } ] }, "stats": { "joined": "2020-10-08T12:38:32Z", "membership-level": "pro", "last-activity": "2021-04-01T02:51:11Z" } } ], "@example-social:member": [ { "ietf-list-pagination:remaining": 0, "ietf-list-pagination:previous": "bGlu", // lin "ietf-list-pagination:next": "" } ] } A.3.4. The "direction" Parameter Noting that "direction" is an enumeration with two values, the edge condition values are each defined enumeration. | The value "forwards" is sometimes known as the "default" value, | as it produces the same result set as when "direction" is | unspecified. These vector tests again assume the target "/example- social:members/member=alice/favorites/uint8-numbers". The number of elements is relevant to the edge condition values. Watsen, et al. Expires 2 September 2024 [Page 49] Internet-Draft List Pagination March 2024 | It is notable that "uint8-numbers" is an "ordered-by" user | leaf-list. Traversals are over the user-specified order, not | the numerically-sorted order, which is what the "sort-by" | parameter addresses. If this were an "ordered-by system" leaf- | list, then the traversals would be over the system-specified | order, again not a numerically-sorted order. A.3.4.1. direction=forwards REQUEST Target: /example-social:members/member=alice/favorites/uint8-numbers Pagination Parameters: Where: - Sort-by: - Direction: forwards Offset: - Limit: - RESPONSE { "example-social:uint8-numbers": [17, 13, 11, 7, 5, 3] } A.3.4.2. direction=backwards REQUEST Target: /example-social:members/member=alice/favorites/uint8-numbers Pagination Parameters: Where: - Sort-by: - Direction: backwards Offset: - Limit: - RESPONSE { "example-social:uint8-numbers": [3, 5, 7, 11, 13, 17] } A.3.5. The "sort-by" Parameter Noting that the "sort-by" parameter is a node identifier, there is not so much "edge conditions" as there are "interesting conditions". This section provides examples for some interesting conditions. Watsen, et al. Expires 2 September 2024 [Page 50] Internet-Draft List Pagination March 2024 A.3.5.1. the target node's type The section provides three examples, one for a "leaf-list" and two for a "list", with one using a direct descendent and the other using an indirect descendent. A.3.5.1.1. type is a "leaf-list" This example illustrates when the target node's type is a "leaf- list". Note that a single period (i.e., '.') is used to represent the nodes to be sorted. This test again uses the target "/example- social:members/member=alice/favorites/uint8-numbers", which is a leaf-list. REQUEST Target: /example-social:members/member=alice/favorites/uint8-numbers Pagination Parameters: Where: - Sort-by: . Direction: - Offset: - Limit: - RESPONSE { "example-social:uint8-numbers": [3, 5, 7, 11, 13, 17] } A.3.5.1.2. type is a "list" and sort-by node is a direct descendent This example illustrates when the target node's type is a "list" and a direct descendent is the "sort-by" node. This vector test uses the target "/example-social:members/member", which is a "list", and the sort-by descendent node "member-id", which is the "key" for the list. REQUEST Watsen, et al. Expires 2 September 2024 [Page 51] Internet-Draft List Pagination March 2024 Target: /example-social:members/member Pagination Parameters: Where: - Sort-by: member-id Direction: - Offset: - Limit: - RESPONSE | To make the example more understandable, an ellipse (i.e., | "...") is used to represent a missing subtree of data. { "example-social:member": [ { "member-id": "alice", ... }, { "member-id": "bob", ... }, { "member-id": "eric", ... }, { "member-id": "joe", ... }, { "member-id": "lin", ... } ] } A.3.5.1.3. type is a "list" and sort-by node is an indirect descendent This example illustrates when the target node's type is a "list" and an indirect descendent is the "sort-by" node. This vector test uses the target "/example-social:members/member", which is a "list", and the sort-by descendent node "stats/joined", which is a "config false" descendent leaf. Due to "joined" being a "config false" node, this request would have to target the "member" node in the datastore. Watsen, et al. Expires 2 September 2024 [Page 52] Internet-Draft List Pagination March 2024 REQUEST Target: /example-social:members/member Pagination Parameters: Where: - Sort-by: stats/joined Direction: - Offset: - Limit: - RESPONSE | To make the example more understandable, an elipse (i.e., | "...") is used to represent a missing subtree of data. { "example-social:member": [ { "member-id": "alice", ... }, { "member-id": "lin", ... }, { "member-id": "bob", ... }, { "member-id": "eric", ... }, { "member-id": "joe", ... } ] } A.3.5.2. handling missing entries The section provides one example for when the "sort-by" node is not present in the data set. FIXME: need to finish this section... Watsen, et al. Expires 2 September 2024 [Page 53] Internet-Draft List Pagination March 2024 A.3.6. The "where" Parameter The "where" is an XPath 1.0 expression, there are numerous edge conditions to consider, e.g., the types of the nodes that are targeted by the expression. A.3.6.1. match of leaf-list's values FIXME A.3.6.2. match on descendent string containing a substring This example selects members that have an email address containing "@example.com". REQUEST Target: /example-social:members/member Pagination Parameters: Where: //.[contains (@email-address,'@example.com')] Sort-by: - Direction: - Offset: - Limit: - RESPONSE | To make the example more understandable, an elipse (i.e., | "...") is used to represent a missing subtree of data. Watsen, et al. Expires 2 September 2024 [Page 54] Internet-Draft List Pagination March 2024 { "example-social:member": [ { "member-id": "bob", ... }, { "member-id": "eric", ... }, { "member-id": "alice", ... }, { "member-id": "joe", ... }, { "member-id": "lin", ... } ] } A.3.6.3. match on decendent timestamp starting with a substring This example selects members that have a posting whose timestamp begins with the string "2020". REQUEST Target: /example-social:members/member Pagination Parameters: Where: //posts//post[starts-with(@timestamp,'2020')] Sort-by: - Direction: - Offset: - Limit: - RESPONSE | To make the example more understandable, an elipse (i.e., | "...") is used to represent a missing subtree of data. Watsen, et al. Expires 2 September 2024 [Page 55] Internet-Draft List Pagination March 2024 { "example-social:member": [ { "member-id": "bob", ... }, { "member-id": "eric", ... }, { "member-id": "alice", ... }, { "member-id": "joe", ... } ] } A.3.7. The "locale" Parameter The "locale" parameter may be used on any target node. | If this parameter is omitted, there is no default value it is | up to the server chooses a locale. This locale is then | reported in the result-set as the "locale" metadata value. REQUEST Target: /example-social:members/member Pagination Parameters: Where: - Sort-by: - Direction: - Offset: - Limit: - Sort-locale: sv_SE RESPONSE Watsen, et al. Expires 2 September 2024 [Page 56] Internet-Draft List Pagination March 2024 { "example-social:member": [ { "member-id": "alice", ... }, { "member-id": "bob", ... }, { "member-id": "eric", ... }, { "member-id": "joe", ... }, { "member-id": "lin", ... }, { "member-id": "åsa", ... } ], "@example-social:member": [ { "ietf-list-pagination:locale": "sv_SE" } ] } REQUEST Target: /example-social:members/member Pagination Parameters: Where: - Sort-by: - Direction: - Offset: - Limit: - Sort-locale: en_US RESPONSE Watsen, et al. Expires 2 September 2024 [Page 57] Internet-Draft List Pagination March 2024 { "example-social:member": [ { "member-id": "alice", ... }, { "member-id": "åsa", ... }, { "member-id": "bob", ... }, { "member-id": "eric", ... }, { "member-id": "joe", ... }, { "member-id": "lin", ... } ], "@example-social:member": [ { "ietf-list-pagination:locale": "en_US" } ] } A.3.8. The "sublist-limit" Parameter The "sublist-limit" parameter may be used on any target node. A.3.8.1. target is a list entry This example uses the target node '/example-social:members/ member=alice' in the datastore. | The target node is a specific list entry/element node, not the | YANG "list" node. This example sets the sublist-limit value '1', which returns just the first entry for all descendent lists and leaf-lists. Watsen, et al. Expires 2 September 2024 [Page 58] Internet-Draft List Pagination March 2024 Note that, in the response, the "remaining" metadata value is set on the first element of each descendent list and leaf-list having more than one value. REQUEST Datastore: Target: /example-social:members/member=alice Sublist-limit: 1 Pagination Parameters: Where: - Sort-by: - Direction: - Offset: - Limit: - RESPONSE Watsen, et al. Expires 2 September 2024 [Page 59] Internet-Draft List Pagination March 2024 { "example-social:member": [ { "member-id": "alice", "email-address": "alice@example.com", "password": "$0$1543", "avatar": "BASE64VALUE=", "tagline": "Every day is a new day", "privacy-settings": { "hide-network": "false", "post-visibility": "public" }, "following": ["bob"], "@following": [ { "ietf-list-pagination:remaining": "2" } ], "posts": { "post": [ { "@": { "ietf-list-pagination:remaining": "1" }, "timestamp": "2020-07-08T13:12:45Z", "title": "My first post", "body": "Hiya all!" } ] }, "favorites": { "uint8-numbers": [17], "int8-numbers": [-5], "@uint8-numbers": [ { "ietf-list-pagination:remaining": "5" } ], "@int8-numbers": [ { "ietf-list-pagination:remaining": "5" } ] } } ] } Watsen, et al. Expires 2 September 2024 [Page 60] Internet-Draft List Pagination March 2024 A.3.8.2. target is a datastore This example uses the target node . This example sets the sublist-limit value '1', which returns just the first entry for all descendent lists and leaf-lists. Note that, in the response, the "remaining" metadata value is set on the first element of each descendent list and leaf-list having more than one value. REQUEST Datastore: Target: / Sublist-limit: 1 Pagination Parameters: Where: - Sort-by: - Direction: - Offset: - Limit: - RESPONSE Watsen, et al. Expires 2 September 2024 [Page 61] Internet-Draft List Pagination March 2024 { "example-social:members": { "member": [ { "@": { "ietf-list-pagination:remaining": "4" }, "member-id": "bob", "email-address": "bob@example.com", "password": "$0$1543", "avatar": "BASE64VALUE=", "tagline": "Here and now, like never before.", "posts": { "post": [ { "@": { "ietf-list-pagination:remaining": "2" }, "timestamp": "2020-08-14T03:32:25Z", "body": "Just got in." } ] }, "favorites": { "decimal64-numbers": ["3.14159"], "@decimal64-numbers": [ { "ietf-list-pagination:remaining": "1" } ] } } ] } } A.3.9. Combinations of Parameters A.3.9.1. All six parameters at once REQUEST Watsen, et al. Expires 2 September 2024 [Page 62] Internet-Draft List Pagination March 2024 Datastore: Target: /example-social:members/member Sublist-limit: 1 Pagination Parameters: Where: //stats//joined[starts-with(@timestamp,'2020')] Sort-by: member-id Direction: backwards Offset: 2 Limit: 2 RESPONSE { "example-social:member": [ { "@": { "ietf-list-pagination:remaining": "1" }, "member-id": "eric", "email-address": "eric@example.com", "password": "$0$1543", "avatar": "BASE64VALUE=", "tagline": "Go to bed with dreams; wake up with a purpose.", "following": ["alice"], "posts": { "post": [ { "timestamp": "2020-09-17T18:02:04Z", "title": "Son, brother, husband, father", "body": "What's your story?" } ] }, "favorites": { "bits": ["two"], "@bits": [ { "ietf-list-pagination:remaining": "2" } ] }, "stats": { "joined": "2020-09-17T19:38:32Z", "membership-level": "pro", "last-activity": "2020-09-17T18:02:04Z" } }, { Watsen, et al. Expires 2 September 2024 [Page 63] Internet-Draft List Pagination March 2024 "member-id": "bob", "email-address": "bob@example.com", "password": "$0$1543", "avatar": "BASE64VALUE=", "tagline": "Here and now, like never before.", "posts": { "post": [ { "@": { "ietf-list-pagination:remaining": "2" }, "timestamp": "2020-08-14T03:32:25Z", "body": "Just got in." } ] }, "favorites": { "decimal64-numbers": ["3.14159"], "@decimal64-numbers": [ { "ietf-list-pagination:remaining": "1" } ] }, "stats": { "joined": "2020-08-14T03:30:00Z", "membership-level": "standard", "last-activity": "2020-08-14T03:34:30Z" } } } } Acknowledgements The authors would like to thank the following for lively discussions on list (ordered by first name): Andy Bierman, Martin Björklund, and Robert Varga. Authors' Addresses Kent Watsen Watsen Networks Email: kent+ietf@watsen.net Qin Wu Huawei Technologies Watsen, et al. Expires 2 September 2024 [Page 64] Internet-Draft List Pagination March 2024 Email: bill.wu@huawei.com Per Andersson Cisco Systems Email: perander@cisco.com Olof Hagsand SUNET Email: olof@hagsand.se Hongwei Li Hewlett Packard Enterprise Email: flycoolman@gmail.com Watsen, et al. Expires 2 September 2024 [Page 65]