jsonnet-modifiers - A new Jsonnet library for conveniently modifying nested values

[Stanisław Barzowski]

Inspired by some questions on Stack Overflow, I was thinking about a better way of changing deep nested structures.

For example take a look at these cases:

https://stackoverflow.com/questions/54886373/overwrite-a-nested-list-element-using-jsonnet

https://stackoverflow.com/questions/54880959/make-changes-to-json-string-using-jsonnet

I wrote a tiny library which allows to do this sort of thing more easily. It's also pretty extensible - it's basically a pattern of doing deep modifications and a few convenience functions.

It could perhaps be a good fit for stdlib one day, but I want to collect some feedback and ideas for improving the API before proposing including it.

Please let me know what you think. Here's the link: https://github.com/sbarzowski/jsonnet-modifiers

[Brett Viren]

Stanisław Barzowski <stanislaw...@gmail.com> writes:

> Please let me know what you think. Here's the link: https://github.com/sbarzowski/jsonnet-modifiers

Just last week I was wishing for something exactly like this. Thanks!

-Brett.

[Dan Compton]

This is an extremely useful contribution and should be included in the standard library.  One example I can provide where
it's useful is for the modification of attributes of an ECS Task Definition JSON (e.g. the envoy container) in the snippet below.

{ 
      "containerDefinitions": [
      {
         "dockerLabels": {
            "SERVICE_80_NAME": "someService-api-http",
            "SERVICE_80_TAGS": "service=someService-api-http"
         },
         "environment": [
            {
               "name": "DEST_DB",
               "value": "db.service.consul:27000"
            }
         ],
         "essential": true,
         "image": "someRepo/someServiced:0.4.2",
         "links": [
            "envoy:db.service.consul"
         ],
         "memory": 218,
         "mountPoints": [ ],
         "name": "someService",
         "portMappings": [
            {
               "containerPort": 80,
               "hostPort": 0,
               "protocol": "tcp"
            }
         ]
      },
      {
         "dockerLabels": {
            "SERVICE_9901_NAME": "envoy",
            "SERVICE_9901_TAGS": "service=someService-api-http"
         },
         "environment": [
                 ...
         ],
         "essential": true,
         "image": "someRepo/mongoproxy-envoy:versio",
         "memory": 100,
         "name": "envoy",
         "portMappings": [
            {
               "containerPort": 9901,
               "hostPort": 0,
               "protocol": "tcp"
            }
         ],
         "volumesFrom": [ ]
      }
   ],
   "family": "someService-someENV",
   "placementConstraints": [ ],
   "volumes": [ ]
}

Related: It would also be useful to have functions to test existence of deeply nested fields as well as retrieve deeply nested values including those nested in objects in arrays nested within objects -- for example, if I wanted to obtain the value of the
envoy container or to determine if the envoy container exists given the json above.   The following does not cover the array case, but does not require nested std.objectHas statements. (please let me know if there's a better way to do this in jsonet -- it's possible

via the jsonPath query $.containerDefinitions[?(@.name=='envoy']  if we had something similar then perhaps we could perform the query, patch the object, and subsequently patch the original object)

  // Returns value at path or default, if path does not
  // exist in the specified obj.
  objectValueAtPath(obj, path, default=null)::
    assert std.isObject(obj) == true;
    assert std.isArray(path) == true;
    if std.length(path) <= 0 then
      default
    else if std.length(path) == 1 then
      if std.objectHas(obj, path[0]) then
        obj[path[0]]
      else
        default
    else
      if !std.objectHas(obj, path[0]) then
        default
      else
        zstd.objectValueAtPath(obj[path[0]], path[1:], default) tailstrict,

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