[ML] Delete Forecast : REST JSON inconsistency

[codebrain]

The documentation (https://www.elastic.co/guide/en/elasticsearch/reference/6.5/ml-delete-forecast.html) indicates that <forecast_id> is optional, and the REST JSON specification indicates this too (

elasticsearch/x-pack/plugin/src/test/resources/rest-api-spec/api/ml.delete_forecast.json

Line 19 in 9e8cfbb

"required": false,

).

The issue is, however, is that the RestDeleteForecastAction registration only registers URLs that contain the <forecastid> parameter (

elasticsearch/x-pack/plugin/ml/src/main/java/org/elasticsearch/xpack/ml/rest/job/RestDeleteForecastAction.java

Line 24 in fc76bcb

public RestDeleteForecastAction(Settings settings, RestController controller) {

).

The .NET client, when calling a URL without the <forecastid> defaults to a DELETE verb on _xpack/ml/anomaly_detectors/<job_id>/_forecast. The server then responds with a 405 error and that the endpoint accepts a POST - at this point the server likely assumes this request was intended to post a record - albeit an incorrect assumption.

In the meantime I have patched the REST JSON spec locally to make <forecastid> a required field and everything then works as expected: https://github.com/elastic/elasticsearch-net/blob/4aa8ad121cd4830afe98f1dbcdcc3790fd2e291d/src/CodeGeneration/ApiGenerator/RestSpecification/XPack/MachineLearning/xpack.ml.delete_forecast.patch.json

---

Can a fix be considered along the lines of:

• Register correct REST endpoint url for DELETE action.
  or
• Make <forecastid> required.

[elasticmachine]

Pinging @elastic/ml-core

[droberts195]

• Register correct REST endpoint url for DELETE action

This should be the fix, as the docs are clear that not specifying <forecastid> is permitted.

We should also check that the HLRC is works when no forecast ID is supplied.