feat(translator): JsonPath in PatchPolicy

[denniskniep]

JsonPath can be utilized to select elements for JSONPatch in EnvoyPatchPolicy

Fixes #1686

EnvoyPatchPolicy API Changes:

• Added jsonPath
• path is optional

These changes are backwards compatible

Change Summary:
jsonPath is evaluated based on the json and the patch is done for all found items (pointers)

We can only "find" existing items in the json with jsonPath. Therefore we need a way to extend the found items (pointers). This enables us to add not existing properties. This is implemented by adding the string of the path to the end of the found items (pointers)

Example:
jsonPath: "filter_chains[*].filters[*].typed_config"
path: "/preserve_external_request_id"

will find following items (pointers):
/filter_chains/0/filters/0/typed_config
/filter_chains/0/filters/1/typed_config

Final jsonPointers which are used withing the JSONPatch:
/filter_chains/0/filters/0/typed_config/preserve_external_request_id
/filter_chains/0/filters/1/typed_config/preserve_external_request_id

[denniskniep]

@arkodg can you plz have a quick look if this is the right direction?
If yes, I will start working on the docs or should that be handled by a different PR?

[codecov]

Codecov Report

Attention: Patch coverage is 59.30233% with 70 lines in your changes missing coverage. Please review.

Project coverage is 67.64%. Comparing base (866a6ce) to head (72b8113).
Report is 11 commits behind head on main.

Files	Patch %	Lines
internal/xds/translator/jsonpatch.go	33.33%	52 Missing and 16 partials ⚠️
internal/xds/translator/jsonpathtopointer.go	97.10%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##             main    #3757    +/-   ##
========================================
  Coverage   67.64%   67.64%            
========================================
  Files         185      187     +2     
  Lines       22578    22859   +281     
========================================
+ Hits        15272    15464   +192     
- Misses       6213     6282    +69     
- Partials     1093     1113    +20     

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[arkodg]

can we add examples with filters, which is the real value prop for using jsonpatch over path since its hard to figure out index

[denniskniep]

Will add this test. It makes clear, that you do not need to go through all parent nested properties and you can select explicitly the route by name, which is much more reliable then selecting via index:

  - type: "type.googleapis.com/envoy.config.route.v3.RouteConfiguration"
    name: "first-listener"
    operation:
      op: "replace"
      jsonPath: "..routes[?(@.name=='second-route')].route.upgrade_configs"
      value:
      - upgrade_type: CONNECT
        connect_config:
          {}

but there is already this scenario:
jsonPath: "..endpoints[*].load_balancing_weight"
which addresses ALL endpoints, which is not possible right now

[arkodg]

to maintain uniformity, can these tests be represented in this

gateway/internal/ir/xds_test.go

Line 533 in eeb62c8

tests := []struct {

format ? (moving the struct def inside the test itself)

[arkodg]

hey @denniskniep sorry for the delay in review, the diff looks good !
added a few minor comments

[denniskniep]

hey @denniskniep sorry for the delay in review, the diff looks good ! added a few minor comments

cool, thx

@arkodg addressed your comments

[arkodg]

LGTM thanks for adding this feature !
hopefully this makes it easier to author EnvoyPatchPolicies for modifying elements within a list