Merge pull request sonic-net#165 from BRCM-SONIC/faraaz_cyrus

Added requirements HLD for YANG PATCH feature in RESTCONF server

manageability/mgmt-framework/Yang_Patch_HLD.md

@@ -0,0 +1,124 @@
+# Feature Name
+YANG Patch Media Type
+# High Level Requirements Document
+#### Rev 0.1
+
+# Table of Contents
+  * [List of Tables](#list-of-tables)
+  * [Revision](#revision)
+  * [About This Manual](#about-this-manual)
+  * [Scope](#scope)
+  * [Feature Overview](#feature-overview)
+  * [Requirements](#requirements)
+  * [Limitations](#limitations) 
+  * [Example](#example) 
+
+# Revision
+| Rev |     Date    |       Author       | Change Description                |
+|:---:|:-----------:|:------------------:|-----------------------------------|
+| 0.1 | 04/23/2021  |   Mohammed Faraaz  | Initial version                   |
+
+# About this Manual
+This document provides general information about the YANG Patch Media Type feature implementation in SONiC mgmt-framework's RESTCONF server.
+# Scope
+This document describes the high level design of YANG Patch Media Type feature. Describing RESTCONF and other related information are beyond the scope of this document.
+
+# Feature Overview
+A "YANG Patch" is an ordered list of edits that are applied to the target configuration datastore by the RESTCONF server.
+The YANG Patch operation is invoked by the RESTCONF client by sending a PATCH method request with a representation using 
+"application/yang-patch+json". The message-body representing the YANG Patch input parameters MUST be present.
+
+## Requirements
+
+### Functional Requirements
+
+1. The RESTCONF server should implement the "YANG PATCH" feature as described in the [RFC8072](https://tools.ietf.org/html/rfc8072)
+2. The RESTCONF server should allow multiple sub-resources to be edited within the same PATCH method.
+3. The RESTCONF server should allow a more precise edit operation than the "plain patch" mechanism found in [RFC8040](https://tools.ietf.org/html/rfc8040). i.e. edits operations can be heterogenuous.
+4. The RESTCONF server should support "create", "delete", "merge", "replace", and "remove" operations.
+5. The RESTCONF server should process "edits" in the explicit order. i.e. The edits are processed in client-specified order.
+6. The RESTCONF server should process errors precisely even when multiple errors occur in the same YANG Patch request.
+7. The YANG Patch request should be an atomic operation. i.e. All the edits must be succeded, otherwise an error will be thrown.
+8. The RESTCONF server should log the YANG Patch's "patch-id" in the audit-log, this is useful for debugging.
+9. The RESTCONF server MUST return the "Accept-Patch" header field in an OPTIONS response, as specified in [RFC5789], which includes the media type for YANG Patch.  This is needed by a client to determine the message-encoding formats supported by the server (e.g., XML, JSON, or both).
+   The following is an example of an "Accept-Patch" header:
+   Accept-Patch: application/yang-patch+json
+
+# Limitations
+
+1. Does not support “insert” and “move” operations because SONiC does not support order by user.
+2. Does not support YANG patch for data store resource i.e. The target resource cannot be '/' (top-level).
+
+# Example
+
+```
+   The following example shows several songs being added to an existing
+   album.
+
+   o  Each of two edits contains one song.
+
+   o  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]
+        }
+      }            
+```
+