[PR] Detect per-field diffs inside of the changed containers

[kopf-archiver]

A pull request by nolar at 2019-09-25 20:51:24+00:00
Original URL: zalando-incubator/kopf#191
Merged by nolar at 2019-09-26 10:34:42+00:00

Fix the issue with no calling the field-handlers if the change is too big/generic.

Issue : fixes #190

Description

import kopf

@kopf.on.field('zalando.org', 'v1', 'kopfexamples', field='spec.field')
def fn(**kwargs):
    pass

Example original object (note the absence of spec!):

apiVersion: zalando.org/v1
kind: KopfExample
metadata:
  name: kopf-example-1

Changed object:

apiVersion: zalando.org/v1
kind: KopfExample
metadata:
  name: kopf-example-1
spec:
  field: value

Caused by the diff detection and reduction algorithms:

• The addition of the whole spec field is detected, so that the diff equals to [('add', ('spec',), None, {'field': 'value'})].
• The reduction algorithm for spec.field scans the whole diff for all records starting with field-prefix ('spec', 'field'), and finds nothing — ('spec',) does not start with ('spec', 'field').
• The handler is not selected for execution.

In addition to the fix, the types of diff structures were clarified and restricted, so that later the diffs can be extended with diff-specific DSL (e.g. diff-slicing, etc).

Types of Changes

• Bug fix (non-breaking change which fixes an issue)
• Refactoring (types).

Review

List of tasks the reviewer must do to review the PR

• Tests
• Documentation