RFC 8072

YANG Patch Media Type

📅 published February 2017, from ietf

RFC 8072: YANG Patch Media Type 🎀

okay bestie, let's get into it 💖 this one came out in February 2017 and it was written by three people: A. Bierman (YumaWorks), M. Bjorklund (Tail-f Systems), and K. Watsen (Juniper Networks). it's a Standards Track document from the IETF, published under ISSN 2070-1721. the title block doesn't list anything it obsoletes or updates ✨

Abstract 🦋

okay so the abstract is short and sweet 🍓 it's basically saying this doc describes a way to apply patches to configuration datastores, using data that's defined with the YANG data modeling language. that's the whole vibe!

Status of This Memo 🌸

this is an Internet Standards Track document 💅

it's a product of the Internet Engineering Task Force (IETF), so it represents the consensus of the IETF community. it got public review and was approved for publication by the Internet Engineering Steering Group (IESG). if you want more info on Internet Standards, check out Section 2 of RFC 7841 🫶

info about the current status of this doc, any errata, and how to give feedback on it lives at http://www.rfc-editor.org/info/rfc8072 🔥

Copyright (c) 2017 IETF Trust and the persons identified as the document authors. All rights reserved. legal stuff, but it's important 💜

this document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info) as they were in effect on the date of publication. please actually review those documents carefully, because 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. they're provided without warranty, as described in the Simplified BSD License 🙈

Table of Contents 🧚

   1. Introduction ....................................................3
      1.1. Terminology ................................................3
           1.1.1. NETCONF .............................................3
           1.1.2. HTTP ................................................4
           1.1.3. YANG ................................................4
           1.1.4. RESTCONF ............................................4
           1.1.5. YANG Patch ..........................................5
           1.1.6. Examples ............................................5
           1.1.7. Tree Diagram Notations ..............................6
   2. YANG Patch ......................................................6
      2.1. Target Resource ............................................7
      2.2. yang-patch Request .........................................8
      2.3. yang-patch-status Response .................................9
      2.4. Target Data Node ..........................................10
      2.5. Edit Operations ...........................................11
      2.6. Successful Edit Response Handling .........................11
      2.7. Error Handling ............................................12
      2.8. ":yang-patch" RESTCONF Capability .........................12
   3. YANG Module ....................................................13
   4. IANA Considerations ............................................22
      4.1. Registrations for New URI and YANG Module .................22
      4.2. Media Types ...............................................23
           4.2.1. Media Type "application/yang-patch+xml" ............23
           4.2.2. Media Type "application/yang-patch+json" ...........24
      4.3. RESTCONF Capability URNs ..................................25
   5. Security Considerations ........................................25
   6. References .....................................................26
      6.1. Normative References ......................................26
      6.2. Informative References ....................................27
   Appendix A. Example YANG Module ...................................28
     A.1. YANG Patch Examples ........................................29
       A.1.1. Add Resources: Error ...................................29
       A.1.2. Add Resources: Success .................................33
       A.1.3. Insert List Entry ......................................35
       A.1.4. Move List Entry ........................................36
       A.1.5. Edit Datastore Resource ................................37
   Acknowledgements ..................................................39
   Authors' Addresses ................................................39

1. Introduction ✨

okay so here's the problem this is solving 💅 there's a need for standard ways to patch datastores defined in [RFC6241], which hold conceptual data that conforms to a schema written in YANG [RFC7950]. the idea is an "ordered 'edit' list" approach, which gives RESTCONF client developers way more precise control over the edit procedure than the "plain patch" mechanism you get in [RFC8040]. it's giving control freak energy, in the best way 🎀

this document defines a media type for a YANG-based editing mechanism that can be used with the HTTP PATCH method [RFC5789]. YANG Patch is designed to support the RESTCONF protocol, defined in [RFC8040]. this document only specifies how to use the YANG Patch media type with RESTCONF 🦋

it may be possible to use YANG Patch with other protocols besides RESTCONF, but that's outside the scope of this doc. for any protocol that supports the YANG Patch media type, if the entire patch document can't be successfully applied, then the server MUST NOT apply any of the changes. no partial messes, periodt 💀 it may also be possible to use YANG Patch with datastore types other than a configuration datastore, and that's also outside the scope of this doc 🌸

1.1. Terminology 🍓

the key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC2119]. these are the official requirement words, so they hit different 💜

1.1.1. NETCONF 🧚

the following terms are defined in [RFC6241]:

  • configuration data
  • datastore
  • configuration datastore
  • protocol operation
  • running configuration datastore
  • state data
  • user

1.1.2. HTTP 🌈

the following terms are defined in [RFC7230]:

  • header field
  • message-body
  • query
  • request URI

the following terms are defined in [RFC7231]:

  • method
  • request
  • resource

1.1.3. YANG ⭐

the following terms are defined in [RFC7950]:

  • container
  • data node
  • leaf
  • leaf-list
  • list

1.1.4. RESTCONF 👑

the following terms are defined in [RFC8040]:

  • application/yang-data+xml
  • application/yang-data+json
  • data resource
  • datastore resource
  • patch
  • RESTCONF capability
  • target resource
  • YANG data template

1.1.5. YANG Patch 💖

these terms are used within this document:

  • RESTCONF client: a client that implements the RESTCONF protocol.
  • RESTCONF server: a server that implements the RESTCONF protocol.
  • YANG Patch: a conceptual edit request using the "yang-patch" YANG Patch template, defined in Section 3. in HTTP, it refers to a PATCH method where a representation uses either the media type "application/yang-patch+xml" or "application/yang-patch+json".
  • YANG Patch Status: a conceptual edit status response using the YANG "yang-patch-status" YANG data template, defined in Section 3. in HTTP, it refers to a response message for a PATCH method, where it has a representation with either the media type "application/yang-data+xml" or "application/yang-data+json".
  • YANG Patch template: similar to a YANG data template, except that it has a representation with the media type "application/yang-patch+xml" or "application/yang-patch+json".

1.1.6. Examples 🙈

some protocol message lines in the examples throughout this document are split across multiple lines just for display purposes. when a line ends with a backslash (\) as its last character, the line is wrapped for display. you treat it as joined to the next line by deleting the backslash, the following line break, and the leading whitespace of the next line 🫶

1.1.7. Tree Diagram Notations 🎀

this document uses a simplified graphical representation of the data model. here's what the symbols in those diagrams mean:

  • Brackets [ and ] enclose list keys.
  • Abbreviations before data node names: rw means configuration data (read-write), ro means state data (read-only), and x means operation resource (executable).
  • Symbols after data node names: ? means an optional node, and * denotes a list and leaf-list.
  • Parentheses enclose choice and case nodes, and case nodes are also marked with a colon (:).
  • Ellipsis (...) stands for contents of subtrees that are not shown.

2. YANG Patch 💅

a "YANG Patch" is an ordered list of edits that get applied to the target datastore by the RESTCONF server. the specific fields are defined in the YANG module in Section 3 🌸

the RESTCONF client invokes the YANG Patch operation by sending a PATCH method request with a representation that uses either the media type "application/yang-patch+xml" or "application/yang-patch+json". this message-body, which represents the YANG Patch input parameters, MUST be present. no body, no patch, bestie 🙅

YANG Patch can do some things that the "plain-patch" mechanism in RESTCONF [RFC8040] can't:

  • YANG Patch allows multiple sub-resources to be edited within the same PATCH method. main character energy 👑
  • YANG Patch allows a more precise edit operation than the "plain patch" mechanism found in [RFC8040]. there are seven operations supported: "create", "delete", "insert", "merge", "move", "replace", and "remove" 🔥
  • YANG Patch uses an "edit" list with an explicit processing order. the edits are processed in the client-specified order, and error processing can be precise even when multiple errors happen in the same YANG Patch request 🧚

the YANG Patch "patch-id" may be useful for debugging, and it SHOULD be present in any audit logging records the RESTCONF server generates for a patch 🍓

the RESTCONF server MUST return the "Accept-Patch" header field in an OPTIONS response, as specified in [RFC5789], and that header includes the media type for YANG Patch. a client needs this to figure out which message-encoding formats the server supports (for example XML, JSON, or both). here's an example of an "Accept-Patch" header:
    Accept-Patch: application/yang-patch+xml,application/yang-patch+json

note that YANG Patch can only edit data resources. the PATCH method can't be used to replace the datastore resource 🙈 also, even though the "ietf-yang-patch" YANG module is written using YANG version 1.1 [RFC7950], an implementation of YANG Patch can be used with content defined in YANG version 1 [RFC6020] as well 🌈

a YANG Patch can be encoded in XML format according to [W3C.REC-xml-20081126]. it can also be encoded in JSON according to "JSON Encoding of Data Modeled with YANG" [RFC7951]. and if any metadata needs to be sent in a JSON message, it gets encoded according to "Defining and Using Metadata with YANG" [RFC7952] 💖

2.1. Target Resource 🎯

okay so the YANG Patch operation uses the RESTCONF target resource URI to figure out exactly which resource is getting patched 💅 This can be the datastore resource itself, i.e., "{+restconf}/data", if you wanna edit top-level configuration data resources 🌸 or it can be a configuration data resource inside the datastore, e.g., "{+restconf}/data/ietf-interfaces:interfaces", if you only want to edit sub-resources inside a top-level config data resource 🧚

The target resource MUST identify exactly one resource instance. If more than one resource instance is identified, then the request MUST NOT be processed and a "400 Bad Request" error response MUST be sent by the server. If the target resource does not identify any existing resource instance, then the request MUST NOT be processed and a "404 Not Found" error response MUST be sent by the server. 😭 no vague targets allowed, bestie!

Each edit with a YANG Patch identifies a target data node for the associated edit. This is described in Section 2.4. 🦋

2.2. yang-patch Request

okay so a YANG Patch is identified by a unique "patch-id", and it can have an optional comment 💜 A patch is an ordered collection of edits. Each edit is identified by an "edit-id", and it has an edit operation ("create", "delete", "insert", "merge", "move", "replace", or "remove") that gets applied to the target resource 🔥 Each edit can be applied to a sub-resource "target" within the target resource. If the operation is "insert" or "move", then the "where" parameter tells you how the node gets inserted or moved. For values "before" and "after", the "point" parameter specifies the data node insertion point. the way that this is so precise 😩🎀

The "merge", "replace", "create", "delete", and "remove" edit operations have exactly the same meanings as those defined for the "operation" attribute described in Section 7.2 of [RFC6241]. ✨

Each edit within a YANG Patch MUST identify exactly one data resource instance. If an edit represents more than one resource instance, then the request MUST NOT be processed and a "400 Bad Request" error response MUST be sent by the server. If the edit does not identify any existing resource instance and the operation for the edit is not "create", then the request MUST NOT be processed and a "404 Not Found" error response MUST be sent by the server. A "yang-patch-status" response MUST be sent by the server identifying the edit or edits that are not valid. 💀 rude but fair

YANG Patch does not provide any access to specific datastores. How a server processes an edit if it is co-located with a Network Configuration Protocol (NETCONF) server that does provide access to individual datastores is left up to the implementation 🧚 A complete datastore cannot be replaced in the same manner as that provided by the <copy-config> operation defined in Section 7.3 of [RFC6241]. Only the specified nodes in a YANG Patch are affected. no whole-datastore wipeouts here, periodt 🙅‍♀️

A message-body representing the YANG Patch is sent by the RESTCONF client to specify the edit operation request. When used with the HTTP PATCH method, this data is identified by the YANG Patch media type. 🌈

YANG tree diagram for "yang-patch" container:

  +---- yang-patch
        +---- patch-id    string
        +---- comment?    string
        +---- edit* [edit-id]
           +---- edit-id      string
           +---- operation    enumeration
           +---- target       target-resource-offset
           +---- point?       target-resource-offset
           +---- where?       enumeration
           +---- value?

2.3. yang-patch-status Response

okay so a message-body representing the YANG Patch Status gets sent back to the RESTCONF client to report the detailed status of the edit operation 🦋 When used with the HTTP PATCH method, this data is identified by the YANG Patch Status media type. The syntax specification is defined in Section 3 ✨

YANG tree diagram for "yang-patch-status" container:

  +---- yang-patch-status
        +---- patch-id       string
        +---- (global-status)?
        |  +--:(global-errors)
        |  |  +---- errors
        |  |     +---- error*
        |  |        +---- error-type       enumeration
        |  |        +---- error-tag        string
        |  |        +---- error-app-tag?   string
        |  |        +---- error-path?      instance-identifier
        |  |        +---- error-message?   string
        |  |        +---- error-info?
        |  +--:(ok)
        |     +---- ok?            empty
        +---- edit-status
           +---- edit* [edit-id]
              +---- edit-id    string
              +---- (edit-status-choice)?
                 +--:(ok)
                 |  +---- ok?        empty
                 +--:(errors)
                    +---- errors
                       +---- error*
                          +---- error-type       enumeration
                          +---- error-tag        string
                          +---- error-app-tag?   string
                          +---- error-path?      instance-identifier
                          +---- error-message?   string
                          +---- error-info?

2.4. Target Data Node

the target data node for each edit operation is decided by two things: the value of the target resource in the request, and the "target" leaf inside each "edit" entry 💖

If the target resource specified in the request URI identifies a datastore resource, then the path string in the "target" leaf is treated as an absolute path expression identifying the target data node for the corresponding edit. The first node specified in the "target" leaf is a top-level data node defined within a YANG module. The "target" leaf MUST NOT contain a single forward slash ("/"), since this would identify the datastore resource, not a data resource. 🙈 that one's a hard no

If the target resource specified in the request URI identifies a configuration data resource, then the path string in the "target" leaf is treated as a relative path expression. The first node specified in the "target" leaf is a child configuration data node of the data node associated with the target resource. If the "target" leaf contains a single forward slash ("/"), then the target data node is the target resource data node. 🧚‍♀️ the slash flips the meaning depending on context, iconic

2.5. Edit Operations

each YANG Patch edit specifies one edit operation on the target data node. The set of operations lines up with the NETCONF edit operations, but it also includes some new ones 🎀 Here's the lineup:

  +-----------+-------------------------------------------------------+
  | Operation | Description                                           |
  +-----------+-------------------------------------------------------+
  | create    | create a new data resource if it does not already     |
  |           | exist; if it already exists, return an error          |
  |           |                                                       |
  | delete    | delete a data resource if it already exists; if it    |
  |           | does not exist, return an error                       |
  |           |                                                       |
  | insert    | insert a new user-ordered data resource               |
  |           |                                                       |
  | merge     | merge the edit value with the target data resource;   |
  |           | create if it does not already exist                   |
  |           |                                                       |
  | move      | reorder the target data resource                      |
  |           |                                                       |
  | replace   | replace the target data resource with the edit value  |
  |           |                                                       |
  | remove    | remove a data resource if it already exists           |
  +-----------+-------------------------------------------------------+

YANG Patch Edit Operations 📊

2.6. Successful Edit Response Handling

okay so if a YANG Patch gets completed without errors, the RESTCONF server MUST return a "yang-patch-status" message with a "global-status" choice set to "ok" 🥳✨

Refer to Appendix A.1.2 for an example of a successful YANG Patch response. 🫶

2.7. Error Handling

if a well-formed, schema-valid YANG Patch message is received, then the RESTCONF server will process the supplied edits in ascending order 🍓 The following error modes apply to the processing of this "edit" list:

If a YANG Patch is completed with errors, the RESTCONF server SHOULD return a "yang-patch-status" message. It is possible (e.g., within a distributed implementation) that an invalid request will be rejected before the YANG Patch edits are processed. In this case, the server MUST send the appropriate HTTP error response instead. 😬 the server gets a choice, but also no escape from the error response

Refer to Appendix A.1.1 for an example of an error YANG Patch response. 💅

2.8. ":yang-patch" RESTCONF Capability

a URI is defined to identify the YANG Patch extension to the base RESTCONF protocol 🌸 If the RESTCONF server supports the YANG Patch media type, then the ":yang-patch" RESTCONF capability defined in Section 4.3 MUST be present in the "capability" leaf-list in the "ietf-restconf-monitoring" module defined in [RFC8040]. 🔥 main character capability energy

3. YANG Module ✨

the "ietf-yang-patch" module defines conceptual definitions with the "yang-data" extension statements. These are not meant to be implemented as datastore contents by a RESTCONF server 🧚

The "ietf-restconf" module from [RFC8040] is used by this module for the "yang-data" extension definition. 💜

<CODE BEGINS>

file "ietf-yang-patch@2017-02-22.yang"

module ietf-yang-patch { yang-version 1.1; namespace "urn:ietf:params:xml:ns:yang:ietf-yang-patch"; prefix "ypatch";

import ietf-restconf { prefix rc; }

organization "IETF NETCONF (Network Configuration) Working Group";

contact "WG Web: <https://datatracker.ietf.org/wg/netconf/> WG List: <mailto:netconf@ietf.org>

Author: Andy Bierman <mailto:andy@yumaworks.com>

Author: Martin Bjorklund <mailto:mbj@tail-f.com>

Author: Kent Watsen <mailto:kwatsen@juniper.net>";

description "This module contains conceptual YANG specifications for the YANG Patch and YANG Patch Status data structures.

Note that the YANG definitions within this module do not represent configuration data of any kind. The YANG grouping statements provide a normative syntax for XML and JSON message-encoding purposes.

Copyright (c) 2017 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 BSD License set forth in Section 4.c of the IETF Trust's Legal Provisions Relating to IETF Documents (http://trustee.ietf.org/license-info).

This version of this YANG module is part of RFC 8072; see the RFC itself for full legal notices.";

revision 2017-02-22 { description "Initial revision."; reference "RFC 8072: YANG Patch Media Type."; }

typedef target-resource-offset { type string; description "Contains a data resource identifier string representing a sub-resource within the target resource. The document root for this expression is the target resource that is specified in the protocol operation (e.g., the URI for the PATCH request).


okay so we're still deep in the YANG module and it's giving *serious* structure 🎀 the first thing to clock is that `rc:yang-data` stanzas that wrap the two main containers, so RESTCONF can carry them as data 💖

This string is encoded according to the same rules as those for a data resource identifier in a RESTCONF request URI."; reference "RFC 8040, Section 3.5.3."; }

rc:yang-data "yang-patch" { uses yang-patch; }

rc:yang-data "yang-patch-status" { uses yang-patch-status; }


---

now the `yang-patch` grouping, which is the request side of the whole thing 💅 the container starts with the patch-level rules, and bestie, the big one is that every edit gets applied in ascending order and if anything goes wrong the datastore stays untouched 😭🫶

grouping yang-patch {

description "A grouping that contains a YANG container representing the syntax and semantics of a YANG Patch edit request message.";

container yang-patch { description "Represents a conceptual sequence of datastore edits, called a patch. Each patch is given a client-assigned patch identifier. Each edit MUST be applied in ascending order, and all edits MUST be applied. If any errors occur, then the target datastore MUST NOT be changed by the YANG Patch operation.

It is possible for a datastore constraint violation to occur due to any node in the datastore, including nodes not included in the 'edit' list. Any validation errors MUST be reported in the reply message.";

reference "RFC 7950, Section 8.3.";

leaf patch-id { type string; mandatory true; description "An arbitrary string provided by the client to identify the entire patch. Error messages returned by the server that pertain to this patch will be identified by this 'patch-id' value. A client SHOULD attempt to generate unique 'patch-id' values to distinguish between transactions from multiple clients in any audit logs maintained by the server."; }

leaf comment { type string; description "An arbitrary string provided by the client to describe the entire patch. This value SHOULD be present in any audit logging records generated by the server for the patch."; }


the `patch-id` is the client's little name tag for the whole patch, so error messages can point back to it 🦋 and `comment` is just a note that should show up in the audit logs 📝

---

next up is the `edit` list, which is where the actual work happens ✨ it's ordered by the user (so the order you write it in is the order it runs), and each edit gets its own `edit-id` tag 🌸

list edit { key edit-id; ordered-by user;

description "Represents one edit within the YANG Patch request message. The 'edit' list is applied in the following manner:

  • The first edit is conceptually applied to a copy of the existing target datastore, e.g., the running configuration datastore.
  • Each ascending edit is conceptually applied to the result of the previous edit(s).
  • After all edits have been successfully processed, the result is validated according to YANG constraints.
  • If successful, the server will attempt to apply the result to the target datastore.";

leaf edit-id { type string; description "Arbitrary string index for the edit. Error messages returned by the server that pertain to a specific edit will be identified by this value."; }


the whole flow is basically: start with a copy, stack each edit on top of the last, validate the final result, and only then try to apply it for real 💜 very careful, very iconic 👑

---

now the `operation` leaf, which has seven different moods 🍓 `create` only makes something that doesn't exist yet, `delete` needs the thing to already be there, and `merge`, `replace`, and `remove` each handle existing data in their own way 🧚

leaf operation { type enumeration { enum create { description "The target data node is created using the supplied value, only if it does not already exist. The 'target' leaf identifies the data node to be created, not the parent data node."; } enum delete { description "Delete the target node, only if the data resource currently exists; otherwise, return an error."; } enum insert { description "Insert the supplied value into a user-ordered list or leaf-list entry. The target node must represent a new data resource. If the 'where' parameter is set to 'before' or 'after', then the 'point' parameter identifies the insertion point for the target node."; } enum merge { description "The supplied value is merged with the target data node."; } enum move { description "Move the target node. Reorder a user-ordered list or leaf-list. The target node must represent an existing data resource. If the 'where' parameter is set to 'before' or 'after', then the 'point' parameter identifies the insertion point to move the target node."; } enum replace { description "The supplied value is used to replace the target data node."; } enum remove { description "Delete the target node if it currently exists."; } } mandatory true; description "The datastore operation requested for the associated 'edit' entry."; } leaf target { type target-resource-offset; mandatory true; description "Identifies the target data node for the edit operation. If the target has the value '/', then the target data node is the target resource. The target node MUST identify a data resource, not the datastore resource."; }


`delete` and `remove` look like twins but they're not 🙈 `delete` errors out if the node isn't there, while `remove` just shrugs and moves on. and `target` is the address of the node you're editing, with `/` meaning the target resource itself 🌈

---

the `point` and `where` leaves are the insertion and ordering crew 🧚‍♀️ `point` only shows up when you're doing an `insert` or a `move` and you're placing things before or after something, and `where` picks the spot, with `last` as the default

leaf point { when "(../operation = 'insert' or ../operation = 'move')"

  • "and (../where = 'before' or ../where = 'after')" { description "This leaf only applies for 'insert' or 'move' operations, before or after an existing entry."; } type target-resource-offset; description "The absolute URL path for the data node that is being used as the insertion point or move point for the target of this 'edit' entry."; }

leaf where { when "../operation = 'insert' or ../operation = 'move'" { description "This leaf only applies for 'insert' or 'move' operations."; } type enumeration { enum before { description "Insert or move a data node before the data resource identified by the 'point' parameter."; } enum after { description "Insert or move a data node after the data resource identified by the 'point' parameter."; } enum first { description "Insert or move a data node so it becomes ordered as the first entry."; } enum last { description "Insert or move a data node so it becomes ordered as the last entry."; } } default last; description "Identifies where a data resource will be inserted or moved. YANG only allows these operations for list and leaf-list data nodes that are 'ordered-by user'."; }


so `where` is basically "front, back, or next to this specific buddy," and YANG only lets you do this stuff on lists and leaf-lists that are `ordered-by user` 💅

---

last bit for this part is the `value` leaf, which is the payload that carries the actual data 🫶 it only gets used for `create`, `merge`, `replace`, and `insert`, and the example shows a container called `foo` wrapped up nicely in a `<value>` element 🍓

anydata value { when "../operation = 'create' "

  • "or ../operation = 'merge' "
  • "or ../operation = 'replace' "
  • "or ../operation = 'insert'" { description "The anydata 'value' is only used for 'create', 'merge', 'replace', and 'insert' operations."; } description "Value used for this edit operation. The anydata 'value' contains the target resource associated with the 'target' leaf.

For example, suppose the target node is a YANG container named foo:

container foo { leaf a { type string; } leaf b { type int32; } }

The 'value' node contains one instance of foo:

<value> <foo xmlns='example-foo-namespace'> <a>some value</a> <b>42</b> </foo> </value> "; } } }

} // grouping yang-patch


that wraps up the request side, and honestly the whole design is giving main character energy ✨ next up is the status grouping, which is the reply that tells the client how everything went 🎀

grouping yang-patch-status {

description "A grouping that contains a YANG container representing the syntax and semantics of a YANG Patch Status response message.";

container yang-patch-status { description "A container representing the response message sent by the server after a YANG Patch edit request message has been processed.";

leaf patch-id { type string; mandatory true; description "The 'patch-id' value used in the request."; }

choice global-status { description "Report global errors or complete success. If there is no case selected, then errors are reported in the 'edit-status' container.";

case global-errors { uses rc:errors; description "This container will be present if global errors that are unrelated to a specific edit occurred."; } leaf ok { type empty; description "This leaf will be present if the request succeeded and there are no errors reported in the 'edit-status' container."; } }

container edit-status { description "This container will be present if there are edit-specific status responses to report. If all edits succeeded and the 'global-status' returned is 'ok', then a server MAY omit this container.";

list edit { key edit-id;

description "Represents a list of status responses, corresponding to edits in the YANG Patch request message. If an 'edit' entry was skipped or not reached by the server, then this list will not contain a corresponding entry for that edit.";

leaf edit-id { type string; description "Response status is for the 'edit' list entry with this 'edit-id' value."; } choice edit-status-choice { description "A choice between different types of status responses for each 'edit' entry."; leaf ok { type empty; description "This 'edit' entry was invoked without any errors detected by the server associated with this edit."; } case errors { uses rc:errors; description "The server detected errors associated with the edit identified by the same 'edit-id' value."; } } } } } } // grouping yang-patch-status

}

<CODE ENDS>


# 4. IANA Considerations ✨

## 4.1. Registrations for New URI and YANG Module

Okay so IANA time 🎀 This document registers one URI as a namespace in the "IETF XML Registry" [RFC3688]. It follows the format in RFC 3688 💅

URI: urn:ietf:params:xml:ns:yang:ietf-yang-patch Registrant Contact: The IESG. XML: N/A; the requested URI is an XML namespace.


This document also registers one YANG module in the "YANG Module Names" registry [RFC6020] 🌸

name: ietf-yang-patch namespace: urn:ietf:params:xml:ns:yang:ietf-yang-patch prefix: ypatch reference: RFC 8072


## 4.2. Media Types

### 4.2.1. Media Type "application/yang-patch+xml"

- **Type name:** `application`
- **Subtype name:** `yang-patch+xml`
- **Required parameters:** None
- **Optional parameters:** None
- **Encoding considerations:** `8-bit` 🫶 The `utf-8` charset is always used for this type. Each conceptual YANG data node gets encoded according to the XML Encoding Rules and Canonical Format for its specific YANG data node type, as defined in [RFC7950]. On top of that, the "yang-patch" YANG Patch template found in RFC 8072 defines the structure of a YANG Patch request, so it's giving very organized energy ✨
- **Security considerations:** Security considerations related to generating and consuming RESTCONF messages are discussed in Section 5 of RFC 8072. Extra security considerations are specific to the semantics of particular YANG data models 🔥 Each YANG module is expected to spell out security considerations for the YANG data defined in that module.
- **Interoperability considerations:** RFC 8072 specifies the format of conforming messages and how they're interpreted 💜
- **Published specification:** RFC 8072
- **Applications that use this media type:** Instance document data parsers used within a protocol or automation tool that use the YANG Patch data structure.
- **Fragment identifier considerations:** The syntax and semantics of fragment identifiers are the same as the syntax and semantics specified for the `application/xml` media type.
- **Additional information:**
  - **Deprecated alias names for this type:** N/A
  - **Magic number(s):** N/A
  - **File extension(s):** None
  - **Macintosh file type code(s):** `"TEXT"`
- **Person & email address to contact for further information:** See the Authors' Addresses section of RFC 8072 📮
- **Intended usage:** COMMON
- **Restrictions on usage:** N/A
- **Author:** See the Authors' Addresses section of RFC 8072.
- **Change controller:** Internet Engineering Task Force (`mailto:iesg@ietf.org`).
- **Provisional registration? (standards tree only):** no

### 4.2.2. Media Type "application/yang-patch+json"

- **Type name:** `application`
- **Subtype name:** `yang-patch+json`
- **Required parameters:** None
- **Optional parameters:** None
- **Encoding considerations:** `8-bit` 💖 The `utf-8` charset is always used for this type. Each conceptual YANG data node is encoded according to RFC 7951. A metadata annotation is encoded according to RFC 7952. And again, the "yang-patch" YANG Patch template found in RFC 8072 defines the structure of a YANG Patch request 🧚
- **Security considerations:** Security considerations related to generating and consuming RESTCONF messages are discussed in Section 5 of RFC 8072. Extra security considerations are specific to the semantics of particular YANG data models 🙈 Each YANG module is expected to spell out security considerations for the YANG data defined in that module.
- **Interoperability considerations:** RFC 8072 specifies the format of conforming messages and how they're interpreted 💜
- **Published specification:** RFC 8072
- **Applications that use this media type:** Instance document data parsers used within a protocol or automation tool that use the YANG Patch data structure.
- **Fragment identifier considerations:** The syntax and semantics of fragment identifiers are the same as the syntax and semantics specified for the `application/json` media type.
- **Additional information:**
  - **Deprecated alias names for this type:** N/A
  - **Magic number(s):** N/A
  - **File extension(s):** None
  - **Macintosh file type code(s):** `"TEXT"`
- **Person & email address to contact for further information:** See the Authors' Addresses section of RFC 8072 📮
- **Intended usage:** COMMON
- **Restrictions on usage:** N/A
- **Author:** See the Authors' Addresses section of RFC 8072.
- **Change controller:** Internet Engineering Task Force (`mailto:iesg@ietf.org`).
- **Provisional registration? (standards tree only):** no

## 4.3. RESTCONF Capability URNs

Next up 🦋 This document registers one capability identifier in the "RESTCONF Capability URNs" registry [RFC8040]. The review policy for this registry is "IETF Review" [RFC5226].

Index Capability Identifier

:yang-patch urn:ietf:params:restconf:capability:yang-patch:1.0


# 5. Security Considerations

Okay, this section is the serious one, bestie 🥺 The YANG Patch media type does not introduce any significant new security threats beyond what is described in [RFC8040]. This document defines edit processing instructions for a variant of the PATCH method, as used within the RESTCONF protocol. Message integrity is provided by the RESTCONF protocol. There is no additional capability to validate that a patch has not been altered.

It may be possible to use YANG Patch with protocols other than RESTCONF, but that topic is outside the scope of this document 🌈

For RESTCONF, both the client and server MUST be authenticated according to Section 2 of [RFC8040]. It is super important for RESTCONF server implementations to carefully validate all the edit request parameters in some manner 🚨 If the entire YANG Patch request cannot be completed, then no configuration changes to the system are done. A PATCH request MUST be applied atomically, as specified in Section 2 of [RFC5789] 🔒

A RESTCONF server implementation SHOULD attempt to prevent system disruption caused by incremental processing of the YANG Patch "edit" list 💀 It may be possible to construct an attack on such a RESTCONF server that relies on the edit processing order mandated by YANG Patch. A server SHOULD apply only the fully validated configuration to the underlying system. For example, an "edit" list that deleted an interface and then recreated it could cause system disruption if the "edit" list was incrementally applied 😭

A RESTCONF server implementation SHOULD attempt to prevent system disruption caused by excessive resource consumption required to fulfill YANG Patch edit requests 🫠 On such an implementation, it may be possible to construct an attack that tries to consume all available memory or other resource types.

# 6. References

## 6.1. 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, <http://www.rfc-editor.org/info/rfc2119>.

[RFC3688] Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688, DOI 10.17487/RFC3688, January 2004, <http://www.rfc-editor.org/info/rfc3688>.

[RFC5789] Dusseault, L. and J. Snell, "PATCH Method for HTTP", RFC 5789, DOI 10.17487/RFC5789, March 2010, <http://www.rfc-editor.org/info/rfc5789>.

[RFC6020] Bjorklund, M., Ed., "YANG - A Data Modeling Language for the Network Configuration Protocol (NETCONF)", RFC 6020, DOI 10.17487/RFC6020, October 2010, <http://www.rfc-editor.org/info/rfc6020>.

[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, <http://www.rfc-editor.org/info/rfc6241>.

[RFC7159] Bray, T., Ed., "The JavaScript Object Notation (JSON) Data Interchange Format", RFC 7159, DOI 10.17487/RFC7159, March 2014, <http://www.rfc-editor.org/info/rfc7159>.

[RFC7230] Fielding, R., Ed., and J. Reschke, Ed., "Hypertext Transfer Protocol (HTTP/1.1): Message Syntax and Routing", RFC 7230, DOI 10.17487/RFC7230, June 2014, <http://www.rfc-editor.org/info/rfc7230>.

[RFC7231] Fielding, R., Ed., and J. Reschke, Ed., "Hypertext Transfer Protocol (HTTP/1.1): Semantics and Content", RFC 7231, DOI 10.17487/RFC7231, June 2014, <http://www.rfc-editor.org/info/rfc7231>.

[RFC7950] Bjorklund, M., Ed., "The YANG 1.1 Data Modeling Language", RFC 7950, DOI 10.17487/RFC7950, August 2016, <http://www.rfc-editor.org/info/rfc7950>.

[RFC7951] Lhotka, L., "JSON Encoding of Data Modeled with YANG", RFC 7951, DOI 10.17487/RFC7951, August 2016, <http://www.rfc-editor.org/info/rfc7951>.

[RFC7952] Lhotka, L., "Defining and Using Metadata with YANG", RFC 7952, DOI 10.17487/RFC7952, August 2016, <http://www.rfc-editor.org/info/rfc7952>.

[RFC8040] Bierman, A., Bjorklund, M., and K. Watsen, "RESTCONF Protocol", RFC 8040, DOI 10.17487/RFC8040, January 2017, <http://www.rfc-editor.org/info/rfc8040>.

[W3C.REC-xml-20081126] Bray, T., Paoli, J., Sperberg-McQueen, M., Maler, E., and F. Yergeau, "Extensible Markup Language (XML) 1.0 (Fifth Edition)", World Wide Web Consortium Recommendation REC-xml-20081126, November 2008, <http://www.w3.org/TR/2008/REC-xml-20081126>.


## 6.2. Informative References

[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 5226, DOI 10.17487/RFC5226, May 2008, <http://www.rfc-editor.org/info/rfc5226>.


Okay bestie, let's pick up right where we left off with the example jukebox! 🎀✨

---

# Appendix A. Example YANG Module 🎶

okay so the example YANG module used in this doc is basically a simple media jukebox interface, and it's giving very cute little music-app energy 💖 The "example-jukebox" module is defined in [RFC8040].

Here's the YANG tree diagram for "example-jukebox" (look at that nested library, it's so organized 😭🫶):

+--rw jukebox! +--rw library

+--rw artist* [name]
+--rw name string
+--rw album* [name]
+--rw name string
+--rw genre? identityref
+--rw year? uint16
+--rw admin
+--rw label? string
+--rw catalogue-number? string
+--rw song* [name]
+--rw name string
+--rw location string
+--rw format? string
+--rw length? uint32
+--ro artist-count? uint32
+--ro album-count? uint32
+--ro song-count? uint32

+--rw playlist* [name]

+--rw name string
+--rw description? string
+--rw song* [index]
+--rw index uint32
+--rw id instance-identifier

+--rw player +--rw gap? decimal64

rpcs:

+---x play +--ro input +--ro playlist string +--ro song-number uint32


## A.1. YANG Patch Examples 🩰

this section has RESTCONF examples, and they're mostly in JSON encoding [RFC7159], with some in XML encoding [W3C.REC-xml-20081126] 🌸

### A.1.1. Add Resources: Error 🙈

the following example shows several songs being added to an existing album. Each edit has one song. The first song already exists, so an error gets reported for that edit. The rest of the edits were not attempted, since the first edit failed. XML encoding is used here 🫶

Request from the RESTCONF client:

PATCH /restconf/data/example-jukebox:jukebox/\ library/artist=Foo%20Fighters/album=Wasting%20Light HTTP/1.1 Host: example.com Accept: application/yang-data+xml Content-Type: application/yang-patch+xml

<yang-patch xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-patch"> <patch-id>add-songs-patch</patch-id> <edit> <edit-id>edit1</edit-id> <operation>create</operation> <target>/song=Bridge%20Burning</target> <value> <song xmlns="http://example.com/ns/example-jukebox"> <name>Bridge Burning</name> <location>/media/bridge_burning.mp3</location> <format>MP3</format> <length>288</length> </song> </value> </edit> <edit> <edit-id>edit2</edit-id> <operation>create</operation> <target>/song=Rope</target> <value> <song xmlns="http://example.com/ns/example-jukebox"> <name>Rope</name> <location>/media/rope.mp3</location> <format>MP3</format> <length>259</length> </song> </value> </edit> <edit> <edit-id>edit3</edit-id> <operation>create</operation> <target>/song=Dear%20Rosemary</target> <value> <song xmlns="http://example.com/ns/example-jukebox"> <name>Dear Rosemary</name> <location>/media/dear_rosemary.mp3</location> <format>MP3</format> <length>269</length> </song> </value> </edit> </yang-patch>


XML response from the RESTCONF server:

HTTP/1.1 409 Conflict Date: Thu, 26 Jan 2017 20:56:30 GMT Server: example-server Last-Modified: Thu, 26 Jan 2017 20:56:30 GMT Content-Type: application/yang-data+xml

<yang-patch-status xmlns="urn:ietf:params:xml:ns:yang:ietf-yang-patch"> <patch-id>add-songs-patch</patch-id> <edit-status> <edit> <edit-id>edit1</edit-id> <errors> <error> <error-type>application</error-type> <error-tag>data-exists</error-tag> <error-path xmlns:jb="http://example.com/ns/example-jukebox"> /jb:jukebox/jb:library /jb:artist[jb:name='Foo Fighters'] /jb:album[jb:name='Wasting Light'] /jb:song[jb:name='Bridge Burning'] </error-path> <error-message> Data already exists; cannot be created </error-message> </error> </errors> </edit> </edit-status> </yang-patch-status>


JSON response from the RESTCONF server:

the following response is in JSON to show off the different "error-path" object encoding 💅 For JSON, the instance-identifier encoding specified in [RFC7951] is used.

HTTP/1.1 409 Conflict Date: Thu, 26 Jan 2017 20:56:30 GMT Server: example-server Last-Modified: Thu, 26 Jan 2017 20:56:30 GMT Content-Type: application/yang-data+json

{ "ietf-yang-patch:yang-patch-status" : { "patch-id" : "add-songs-patch", "edit-status" : { "edit" : [ { "edit-id" : "edit1", "errors" : { "error" : [ { "error-type": "application", "error-tag": "data-exists", "error-path": "/example-jukebox:jukebox/library\ /artist[name='Foo Fighters']\ /album[name='Wasting Light']\ /song[name='Bridge Burning']", "error-message": "Data already exists; cannot be created" } ] } } ] } } }


### A.1.2. Add Resources: Success 🎉

the following example shows several songs being added to an existing album, and it's so satisfying 🥹

- Each of two edits contains one song.
- Both edits succeed, and new sub-resources are created.

Request from the RESTCONF client:

PATCH /restconf/data/example-jukebox:jukebox/\ library/artist=Foo%20Fighters/album=Wasting%20Light \ HTTP/1.1 Host: example.com Accept: application/yang-data+json Content-Type: application/yang-patch+json

{ "ietf-yang-patch:yang-patch" : { "patch-id" : "add-songs-patch-2", "edit" : [ { "edit-id" : "edit1", "operation" : "create", "target" : "/song=Rope", "value" : { "song" : [ { "name" : "Rope", "location" : "/media/rope.mp3", "format" : "MP3", "length" : 259 } ] } }, { "edit-id" : "edit2", "operation" : "create", "target" : "/song=Dear%20Rosemary", "value" : { "song" : [ { "name" : "Dear Rosemary", "location" : "/media/dear_rosemary.mp3", "format" : "MP3", "length" : 269 } ] } } ] } }


Response from the RESTCONF server:

HTTP/1.1 200 OK Date: Thu, 26 Jan 2017 20:56:30 GMT Server: example-server Last-Modified: Thu, 26 Jan 2017 20:56:30 GMT Content-Type: application/yang-data+json

{ "ietf-yang-patch:yang-patch-status" : { "patch-id" : "add-songs-patch-2", "ok" : [null] } }


### A.1.3. Insert List Entry 🧚

the following example shows a song being inserted within an existing playlist. Song "6" in playlist "Foo-One" is being inserted after song "5" in the playlist. The operation succeeds, so a non-error reply can be provided 🍓

Request from the RESTCONF client:

PATCH /restconf/data/example-jukebox:jukebox/\ playlist=Foo-One HTTP/1.1 Host: example.com Accept: application/yang-data+json Content-Type: application/yang-patch+json

{ "ietf-yang-patch:yang-patch" : { "patch-id" : "insert-song-patch", "comment" : "Insert song 6 after song 5", "edit" : [ { "edit-id" : "edit1", "operation" : "insert", "target" : "/song=6", "point" : "/song=5", "where" : "after", "value" : { "example-jukebox:song" : [ { "index" : 6, "id" : "/example-jukebox:jukebox/library\ /artist[name='Foo Fighters']\ /album[name='Wasting Light']\ /song[name='Bridge Burning']" } ] } } ] }


Response from the RESTCONF server:

HTTP/1.1 200 OK Date: Thu, 26 Jan 2017 20:56:30 GMT Server: example-server Last-Modified: Thu, 26 Jan 2017 20:56:30 GMT Content-Type: application/yang-data+json

{ "ietf-yang-patch:yang-patch-status" : { "patch-id" : "insert-song-patch", "ok" : [null] } }


### A.1.4. Move List Entry 🦋

the following example shows a song being moved within an existing playlist. Song "1" in playlist "Foo-One" is being moved after song "3" in the playlist. Note that no "value" parameter is needed for a "move" operation. The operation succeeds, so a non-error reply can be provided ✨

Request from the RESTCONF client:

PATCH /restconf/data/example-jukebox:jukebox/\ playlist=Foo-One HTTP/1.1 Host: example.com Accept: application/yang-data+json Content-Type: application/yang-patch+json

{ "ietf-yang-patch:yang-patch" : { "patch-id" : "move-song-patch", "comment" : "Move song 1 after song 3", "edit" : [ { "edit-id" : "edit1", "operation" : "move", "target" : "/song=1", "point" : "/song=3", "where" : "after" } ] } }


Response from the RESTCONF server:

HTTP/1.1 200 OK Date: Thu, 26 Jan 2017 20:56:30 GMT Server: example-server Last-Modified: Thu, 26 Jan 2017 20:56:30 GMT Content-Type: application/yang-data+json

{ "ietf-restconf:yang-patch-status" : { "patch-id" : "move-song-patch", "ok" : [null] } }


### A.1.5. Edit Datastore Resource ✨

Okay bestie, this one is a total showstopper 💅 It shows how **three top-level data nodes from different modules** can get edited all in one go. Multitasking, but make it protocol 🦋

Here's the cast of characters:

- Example module "foo" defines leaf X.
- Example module "bar" defines container Y, with child leafs A and B.
- Example module "baz" defines list Z, with key C and child leafs D and E.

**Request from the RESTCONF client:**

PATCH /restconf/data HTTP/1.1 Host: example.com Accept: application/yang-data+json Content-Type: application/yang-patch+json

{ "ietf-yang-patch:yang-patch" : { "patch-id" : "datastore-patch-1", "comment" : "Edit 3 top-level data nodes at once", "edit" : [ { "edit-id" : "edit1", "operation" : "create", "target" : "/foo:X", "value" : { "foo:X" : 42 } }, { "edit-id" : "edit2", "operation" : "merge", "target" : "/bar:Y", "value" : { "bar:Y" : { "A" : "test1", "B" : 99 } } }, { "edit-id" : "edit3", "operation" : "replace", "target" : "/baz:Z=2", "value" : { "baz:Z" : [ { "C" : 2, "D" : 100, "E" : false } ] } } ] } }


**Response from the RESTCONF server:**

HTTP/1.1 200 OK Date: Thu, 26 Jan 2017 20:56:30 GMT Server: example-server Last-Modified: Thu, 26 Jan 2017 20:55:30 GMT Content-Type: application/yang-data+json

{ "ietf-yang-patch:yang-patch-status" : { "patch-id" : "datastore-patch-1", "ok" : [null] } }


---

# Acknowledgements

The authors would like to give a huge shoutout to Rex Fernando 🫶 for his contributions to this document. Thank you, Rex, you're iconic ✨

Andy Bierman's contributions to this material were based on work supported by the United States Army, Space & Terrestrial Communications Directorate (S&TCD) under Contract No. W15P7T-13-C-A616. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the S&TCD 🎀

---

# Authors' Addresses

Andy Bierman YumaWorks

Email: andy@yumaworks.com

Martin Bjorklund Tail-f Systems

Email: mbj@tail-f.com

Kent Watsen Juniper Networks

Email: kwatsen@juniper.net

📦 where this page comes from