Recursively replace all JSON `$ref`s with the code that they refer to

One approach would be preprocessing the JSON with a JS/TS library like json-schema-ref-parser to de-reference/resolve the references before decoding it in Elixir.

If you really wanted to do this in Elixir, I’d take a look at how the JS libraries handle tree traversal and re-implement it in Elixir. I imagine there would be opportunities for recursion.

Off the top of my head, Elixir’s built-in get_in/2 and update_in/3 functions in the Kernel module paired with the Access module will be helpful. There’s also a Pathex library that could be a good alternative for working with nested data structures.

Edit to add: this github issue might be relevant
https://github.com/open-api-spex/open_api_spex/issues/517

Both of the examples you linked to are specifically about embedding references in schemas (either YAML- or JSON-formatted) to reduce duplication; I don’t believe a normal application decoding plain JSON would ever encounter a $ref outside of that context.

If you are expecting input like this, make sure to be careful about which URLs you follow and when. For instance, if you wrote a JSON parser that loaded these references before validating the shape of the data you could accidentally create a denial-of-service reflector. For instance, imagine a malicious payload like:

{
  "foo1": {
    "$ref": "http://example.com/oh_no1#foo"
  },
  "foo2": {
    "$ref": "http://example.com/oh_no2#foo"
  },
  "foo3": {
    "$ref": "http://example.com/oh_no3#foo"
  },
  "foo4": {
    "$ref": "http://example.com/oh_no4#foo"
  },
  ...etc for thousands of times
}

A single request to an API that tries to “follow” all those refs would be multiplied into thousands pointed at example.com.