Inconsistencies with CPS Core API's

Owned by Arpit Singh
Last updated: Oct 16, 2024
7 min read

Issues/Decisions

Introduction

There are few inconsistencies and missing features found within the CPS core APIs. This proposal aims to discuss these problems and suggest appropriate solutions for the same. The following list of APIs are found to be impacted by the findings:

  • Get a node

  • Update node leaves

  • Replace a node with descendants

Detailed Analysis

Get a Node

Problem Description:

When a list is fetched using Get a node API then instead of returning one list containing n-number of list items, the API returns n-JSON objects where each object contains one list item each.

For example: if there is a list named "Items" containing 10 items named Item 1, Item 2, ......, Item 10. Then when this list is fetched using get a node API a total of 10 individual JSON objects are returned where each object contains one Item.

Data Originally Stored
{ "book-store:bookstore": { "bookstore-name": "Easons", "categories": [ { "code": "1", "name": "Children", "books": [ { "title": "Matilda", "lang": "English", "price": 20 }, { "title": "The Gruffalo", "lang": "English", "price": 15 } ] } ] } }

 

Response when querying the list directly
[ { "books": { "title": "Matilda", "lang": "English", "price": 20 } }, { "books": { "title": "The Gruffalo", "lang": "English", "price": 15 } } ]

 

Expected Result
[ { "books": [ { "title": "Matilda", "lang": "English", "price": 20 }, { "title": "The Gruffalo", "lang": "English", "price": 15 } ] } ]

 

Initial setup to try the sample requests up ahead

To tryout the sample curl requests below please create a simple bookstore entry in your local CPS deployment. Or just execute the following curl request

curl --location 'http://localhost:8883/cps/api/v2/dataspaces/my-dataspace/anchors/bookstore-example/nodes?xpath=%2F' --header 'Content-Type: application/json' --header 'Accept: application/json' --header 'Authorization: ••••••' --data '{ "bookstore": { "bookstore-name": "Easons", "premises": { "addresses": [ { "house-number": 2, "street": "Main Street", "town": "Maynooth", "county": "Kildare" } ] }, "categories": [ { "code": 1, "name": "Children", "books" : [ { "title": "Matilda", "lang": "English", "authors": ["Roald Dahl"], "editions": [1988, 2000], "price": 20 }, { "title": "The Gruffalo", "lang": "English", "authors": ["Julia Donaldson"], "editions": [1999], "price": 15 } ] }, { "code": 2, "name": "Thriller", "books" : [ { "title": "Annihilation", "lang": "English", "authors": ["Jeff VanderMeer"], "editions": [2014], "price": 15 } ] } ] } } '

Update node leaves

Problem Description

When updating any data node, it's parent node xpath is provided as part of the update request. And the JSON payload contains the data of child node to be updated.

But due to a user error the parent nodes data can be sent as part of the JSON payload and even then, instead of failing the request is successfully executed with partial update Where only the child data node is updated, and the parent data node is not updated.

Original JSON data:
JSON with updates
JSON data after update

Notes

Original JSON data:
JSON with updates
JSON data after update

Notes

{ "code": 1, "name": "Children", "books": [ { "title": "Matilda", "lang": "English", "authors": ["Roald Dahl"], "editions": [1988, 2000], "price": 20 } ] }

 

 

{ "code": 1, "name": "Kids", "books": [ { "title": "Matilda", "editions": [1988, 2000, 2024], "price": 25 } ] }

 

{ "code": "1", "name": "Children", "books": [ { "title": "Matilda", "lang": "English", "authors": ["Roald Dahl"], "editions": [1988, 2000, 2024], "price": 25       } ] }

 

  • The expected behavior should be to throw an exception as the Update a node API requires parent node xpath to update any child data. Which in this case should be "/bookstore" because the request is also updating the node with key "code=1"

  • This situation can mainly occur due to user error, where user provides updated parent data along with parent node xpath as part of the request.

Curl request to replicate the scenario
curl --location --globoff --request PATCH 'http://localhost:8883/cps/api/v2/dataspaces/my-dataspace/anchors/bookstore/nodes?xpath=%2Fbookstore%2Fcategories[%40code%3D1]' --header 'Content-Type: application/json' --header 'Accept: application/json' --header 'Authorization: ••••••' --data '{ "code": 1, "name": "Kids", "books": [ { "title": "Matilda", "editions": [1988, 2000, 2024], "price": 25 } ] }'

Problem Description 2

Update operation can only be done on one node at a time and when trying to update parent child in one request, then only the parent node is updated.

Original JSON data
JSON to be updated
Updated JSON data

Notes

Original JSON data
JSON to be updated
Updated JSON data

Notes

{ "categories": { "code": "1", "name": "Children", "books": [ { "title": "Matilda",       "lang": "English", "price": 200, "authors":["Roald Dahl"], "editions": [1988,2000] } ] } }

 

{ "categories": { "code": 1, "name": "Kids", "books": [ { "title": "Matilda", "price": 20, "editions": [1988, 2000, 2022] } ] } }

 

{ "categories": { "code": "1", "name": "Kids", "books": [ { "title": "Matilda",     "lang": "English", "price": 200, "authors": ["Roald Dahl"], "editions": [1988,2000]        } ] } }

 

  • So, either the API should reject any request containing multiple nodes or support updating multiple nodes at once.

Curl request to replicate the scenario
curl --location --request PATCH 'http://localhost:8883/cps/api/v2/dataspaces/my-dataspace/anchors/bookstore/nodes?xpath=%2Fbookstore' --header 'Content-Type: application/json' --header 'Accept: application/json' --header 'Authorization: ••••••' --data '{ "categories": { "code": 1, "name": "Kids", "books": [ { "title": "Matilda", "price": 20, "editions": [1988, 2000, 2022] } ] } }'

Replace a node with descendants

Problem Description

If a replace operation is performed on a list, where a new list item is also added to the list, then it results in a 200-response code, with a partial replace operation.

Original JSON data
Data to replace
Result after Replace operation

Notes

Original JSON data
Data to replace
Result after Replace operation

Notes

[ { "book-store:books": { "title": "Matilda", "lang": "English", "price": 20, "authors": ["Roald Dahl"], "editions": [1988,2000] } } ]

 

{ "books": [ { "title": "Matilda", "lang": "English", "authors": ["Roald Dahl"], "editions": [2024] }, { "title": "The Gruffalo", "lang": "English", "authors": ["Julia Donaldson"], "editions": [1999], "price": 15 } ] }

 

[ { "book-store:books": { "title": "Matilda", "lang": "English", "authors": ["Roald Dahl"], "editions": [2024] } } ]

 

  • This is a user error as request here is itself wrong, because it tries to add a new list element.

  • CPS provides a separate endpoint to Add a list element

  • So, such a scenario should be handled by the API instead of returning a successful response.

Curel request to replicate the scenario
curl --location --globoff --request PUT 'http://localhost:8883/cps/api/v2/dataspaces/my-dataspace/anchors/bookstore/nodes?xpath=%2Fbookstore%2Fcategories[%40code%3D1]' --header 'Content-Type: application/json' --header 'Accept: application/json' --header 'Authorization: ••••••' --data '{ "books": [ { "title": "Matilda", "lang": "English", "authors": ["Roald Dahl"], "editions": [2024] }, { "title": "The Gruffalo", "lang": "English", "authors": ["Julia Donaldson"], "editions": [1999], "price": 15 } ] }'