NETCONF Working Group K. Watsen Internet-Draft Watsen Networks Intended status: Standards Track Q. Wu Expires: 28 April 2022 Huawei Technologies O. Hagsand Netgate H. Li Hewlett Packard Enterprise P. Andersson Cisco Systems 25 October 2021 List Pagination for YANG-driven Protocols draft-wwlh-netconf-list-pagination-00 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 28 April 2022. Watsen, et al. Expires 28 April 2022 [Page 1] Internet-Draft List Pagination October 2021 Copyright Notice Copyright (c) 2021 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 Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3 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 . . . 8 3.3. Constraints on "where" and "sort-by" for "config false" Lists . . . . . . . . . . . . . . . . . . . . . . . . . . 9 3.3.1. Identifying Constrained "config false" Lists and Leaf-Lists . . . . . . . . . . . . . . . . . . . . . 10 3.3.2. Indicating the Constraints for "where" Filters and "sort-by" Expressions . . . . . . . . . . . . . . . . 10 4. The "ietf-list-pagination" Module . . . . . . . . . . . . . . 11 4.1. Data Model Overview . . . . . . . . . . . . . . . . . . . 11 4.2. Example Usage . . . . . . . . . . . . . . . . . . . . . . 12 4.2.1. Constraining a "config false" list . . . . . . . . . 12 4.2.2. Indicating number remaining in a limited list . . . . 12 4.3. YANG Module . . . . . . . . . . . . . . . . . . . . . . . 12 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19 5.1. The "IETF XML" Registry . . . . . . . . . . . . . . . . . 19 5.2. The "YANG Module Names" Registry . . . . . . . . . . . . 19 6. Security Considerations . . . . . . . . . . . . . . . . . . . 19 6.1. Regarding the "ietf-list-pagination" YANG Module . . . . 19 7. References . . . . . . . . . . . . . . . . . . . . . . . . . 19 7.1. Normative References . . . . . . . . . . . . . . . . . . 20 7.2. Informative References . . . . . . . . . . . . . . . . . 20 Appendix A. Vector Tests . . . . . . . . . . . . . . . . . . . . 21 A.1. Example YANG Module . . . . . . . . . . . . . . . . . . . 21 A.2. Example Data Set . . . . . . . . . . . . . . . . . . . . 28 A.3. Example Queries . . . . . . . . . . . . . . . . . . . . . 32 Watsen, et al. Expires 28 April 2022 [Page 2] Internet-Draft List Pagination October 2021 A.3.1. The "limit" Parameter . . . . . . . . . . . . . . . . 33 A.3.2. The "offset" Parameter . . . . . . . . . . . . . . . 35 A.3.3. The "direction" Parameter . . . . . . . . . . . . . . 38 A.3.4. The "sort-by" Parameter . . . . . . . . . . . . . . . 39 A.3.5. The "where" Parameter . . . . . . . . . . . . . . . . 42 A.3.6. The "sublist-limit" Parameter . . . . . . . . . . . . 44 A.3.7. Combinations of Parameters . . . . . . . . . . . . . 48 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 50 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 50 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 28 April 2022 [Page 3] Internet-Draft List Pagination October 2021 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 used in this document use a placeholder value for binary data that has been base64 encoded (e.g., "BASE64VALUE="). This placeholder value is used as 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 28 April 2022 [Page 4] Internet-Draft List Pagination October 2021 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 3.1.3), then the "offset" parameter (see Section 3.1.4), and lastly the "limit" parameter (see Section 3.1.5). 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. 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). Watsen, et al. Expires 28 April 2022 [Page 5] Internet-Draft List Pagination October 2021 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. 3.1.3. 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". Watsen, et al. Expires 28 April 2022 [Page 6] Internet-Draft List Pagination October 2021 Allowed Values The allowed values are: 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. 3.1.4. 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 output when this occurs. Conformance The "offset" query parameter MUST be supported for all lists and leaf-lists. Watsen, et al. Expires 28 April 2022 [Page 7] Internet-Draft List Pagination October 2021 3.1.5. 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 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. Watsen, et al. Expires 28 April 2022 [Page 8] Internet-Draft List Pagination October 2021 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., '/'). 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. Watsen, et al. Expires 28 April 2022 [Page 9] Internet-Draft List Pagination October 2021 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 [I-D.ietf-netconf-notification-capabilities]. 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. 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. Watsen, et al. Expires 28 April 2022 [Page 10] Internet-Draft List Pagination October 2021 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 [I-D.ietf-netconf-notification-capabilities]). 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. 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 Comments: * As shown, this module augments two optional leaves into the "node- selector" 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 3.1.5) or "sublist-limit" parameters (Appendix A.3.6). Watsen, et al. Expires 28 April 2022 [Page 11] Internet-Draft List Pagination October 2021 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. =============== 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 [I-D.ietf-netconf-notification-capabilities]. Watsen, et al. Expires 28 April 2022 [Page 12] Internet-Draft List Pagination October 2021 file "ietf-list-pagination@2021-10-25.yang" module ietf-list-pagination { yang-version 1.1; namespace "urn:ietf:params:xml:ns:yang:ietf-list-pagination"; prefix lpg; 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 "draft-ietf-netconf-notification-capabilities: YANG Modules describing Capabilities for Systems and Datastore Update Notifications"; } organization "IETF NETCONF (Network Configuration) Working Group"; contact "WG Web: 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) 2021 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 Simplified Watsen, et al. Expires 28 April 2022 [Page 13] Internet-Draft List Pagination October 2021 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). 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 2021-10-25 { 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."; } Watsen, et al. Expires 28 April 2022 [Page 14] Internet-Draft List Pagination October 2021 // 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."; } // 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 sort-by-param-grouping { description "This grouping may be used by protocol-specific YANG modules Watsen, et al. Expires 28 April 2022 [Page 15] Internet-Draft List Pagination October 2021 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."; } } default "forwards"; description Watsen, et al. Expires 28 April 2022 [Page 16] Internet-Draft List Pagination October 2021 "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 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 { 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."; } Watsen, et al. Expires 28 April 2022 [Page 17] Internet-Draft List Pagination October 2021 } 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."; } } // Protocol-accessible nodes augment // FIXME: ensure datastore == "/sysc:system-capabilities/sysc:datastore-capabilities" + "/sysc:per-node-capabilities" { 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'."; } Watsen, et al. Expires 28 April 2022 [Page 18] Internet-Draft List Pagination October 2021 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."; } } } 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. Regarding the "ietf-list-pagination" YANG Module Pursuant the template defined in ...FIXME 7. References Watsen, et al. Expires 28 April 2022 [Page 19] Internet-Draft List Pagination October 2021 7.1. Normative References [I-D.ietf-netconf-notification-capabilities] Lengyel, B., Clemm, A., and B. Claise, "YANG Modules describing Capabilities for Systems and Datastore Update Notifications", Work in Progress, Internet-Draft, draft- ietf-netconf-notification-capabilities-21, 15 October 2021, . [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, . [RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language", RFC 7950, DOI 10.17487/RFC7950, August 2016, . [RFC7952] Lhotka, L., "Defining and Using Metadata with YANG", RFC 7952, DOI 10.17487/RFC7952, August 2016, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . 7.2. Informative References [RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for the Network Configuration Protocol (NETCONF)", RFC 6020, DOI 10.17487/RFC6020, October 2010, . [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, . [RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017, . Watsen, et al. Expires 28 April 2022 [Page 20] Internet-Draft List Pagination October 2021 [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. 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 28 April 2022 [Page 21] Internet-Draft List Pagination October 2021 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 "http://example.com/ns/example-social"; prefix es; import ietf-yang-types { prefix yang; reference "RFC 6991: Common YANG Data Types"; } Watsen, et al. Expires 28 April 2022 [Page 22] Internet-Draft List Pagination October 2021 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 28 April 2022 [Page 23] Internet-Draft List Pagination October 2021 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 28 April 2022 [Page 24] Internet-Draft List Pagination October 2021 } 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 28 April 2022 [Page 25] Internet-Draft List Pagination October 2021 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 28 April 2022 [Page 26] Internet-Draft List Pagination October 2021 "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 28 April 2022 [Page 27] Internet-Draft List Pagination October 2021 "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 28 April 2022 [Page 28] Internet-Draft List Pagination October 2021 "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 28 April 2022 [Page 29] Internet-Draft List Pagination October 2021 "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 28 April 2022 [Page 30] Internet-Draft List Pagination October 2021 "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" } } ] }, "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 Watsen, et al. Expires 28 April 2022 [Page 31] Internet-Draft List Pagination October 2021 }, { "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", "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. Watsen, et al. Expires 28 April 2022 [Page 32] Internet-Draft List Pagination October 2021 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 { "example-social:uint8-numbers": [17], "@example-social:uint8-numbers": [ { "ietf-list-pagination:remaining": 5 } ] } A.3.1.2. limit=2 REQUEST Watsen, et al. Expires 28 April 2022 [Page 33] Internet-Draft List Pagination October 2021 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 { "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 Watsen, et al. Expires 28 April 2022 [Page 34] Internet-Draft List Pagination October 2021 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] } 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 Watsen, et al. Expires 28 April 2022 [Page 35] Internet-Draft List Pagination October 2021 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] } 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 Watsen, et al. Expires 28 April 2022 [Page 36] Internet-Draft List Pagination October 2021 { "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: - RESPONSE { "example-social:uint8-numbers": [] } A.3.2.6. offset=7 REQUEST Watsen, et al. Expires 28 April 2022 [Page 37] Internet-Draft List Pagination October 2021 Target: /example-social:members/member=alice/favorites/uint8-numbers Pagination Parameters: Where: - Sort-by: - Direction: - Offset: 7 Limit: - RESPONSE ERROR A.3.3. 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. | 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.3.3.1. direction=forwards REQUEST Target: /example-social:members/member=alice/favorites/uint8-numbers Pagination Parameters: Where: - Sort-by: - Direction: forwards Offset: - Limit: - RESPONSE Watsen, et al. Expires 28 April 2022 [Page 38] Internet-Draft List Pagination October 2021 { "example-social:uint8-numbers": [17, 13, 11, 7, 5, 3] } A.3.3.2. 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.3.4. 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. A.3.4.1. 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.3.4.1.1. 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 Watsen, et al. Expires 28 April 2022 [Page 39] Internet-Draft List Pagination October 2021 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.3.4.1.2. 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 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. Watsen, et al. Expires 28 April 2022 [Page 40] Internet-Draft List Pagination October 2021 { "example-social:member": [ { "member-id": "alice", ... }, { "member-id": "bob", ... }, { "member-id": "eric", ... }, { "member-id": "joe", ... }, { "member-id": "lin", ... } ] } A.3.4.1.3. 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. REQUEST Target: /example-social:members/member Pagination Parameters: Where: - Sort-by: stats/joined Direction: - Offset: - Limit: - RESPONSE Watsen, et al. Expires 28 April 2022 [Page 41] Internet-Draft List Pagination October 2021 | 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.3.4.2. 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... A.3.5. 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.3.5.1. match of leaf-list's values FIXME Watsen, et al. Expires 28 April 2022 [Page 42] Internet-Draft List Pagination October 2021 A.3.5.2. 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. { "example-social:member": [ { "member-id": "bob", ... }, { "member-id": "eric", ... }, { "member-id": "alice", ... }, { "member-id": "joe", ... }, { "member-id": "lin", ... } ] } Watsen, et al. Expires 28 April 2022 [Page 43] Internet-Draft List Pagination October 2021 A.3.5.3. 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. { "example-social:member": [ { "member-id": "bob", ... }, { "member-id": "eric", ... }, { "member-id": "alice", ... }, { "member-id": "joe", ... } ] } A.3.6. The "sublist-limit" Parameter The "sublist-limit" parameter may be used on any target node. Watsen, et al. Expires 28 April 2022 [Page 44] Internet-Draft List Pagination October 2021 A.3.6.1. 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. 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 28 April 2022 [Page 45] Internet-Draft List Pagination October 2021 { "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 28 April 2022 [Page 46] Internet-Draft List Pagination October 2021 A.3.6.2. 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 28 April 2022 [Page 47] Internet-Draft List Pagination October 2021 { "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.3.7. Combinations of Parameters A.3.7.1. All six parameters at once REQUEST Watsen, et al. Expires 28 April 2022 [Page 48] Internet-Draft List Pagination October 2021 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 28 April 2022 [Page 49] Internet-Draft List Pagination October 2021 "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 Bjoerklund, and Robert Varga. Authors' Addresses Kent Watsen Watsen Networks Email: kent+ietf@watsen.net Watsen, et al. Expires 28 April 2022 [Page 50] Internet-Draft List Pagination October 2021 Qin Wu Huawei Technologies Email: bill.wu@huawei.com Olof Hagsand Netgate Email: olof@hagsand.se Hongwei Li Hewlett Packard Enterprise Email: flycoolman@gmail.com Per Andersson Cisco Systems Email: perander@cisco.com Watsen, et al. Expires 28 April 2022 [Page 51]