REST handlers silently ignore request body if unexpected

[DaveCTurner]

In https://discuss.elastic.co/t/ilm-retry-api-not-honoring-timeouts/281772 a user reported confusion over the way that Elasticsearch ignored the parameters in this request:

POST */_ilm/retry
{
  "timeout": "30m",
  "master_timeout": "30m"
}

The immediate solution was to move the parameters into the URL where they belong, but the question highlights a broader problem: if an API endpoint expects a request body then we parse the body fairly strictly and reject requests that contain unexpected things, but if the endpoint doesn't expect a body at all then we seem to leniently accept requests with a body anyway. Silently ignoring input like this is confusing, and I think we should have rejected this request with a 400 Bad request instead.

[elasticmachine]

Pinging @elastic/es-core-infra (Team:Core/Infra)

[rjernst]

What version was this on? That should have been fixed already in 7.0: #37504

[DaveCTurner]

Bah sorry for the noise, I guess they must have been using 6.8.x. It does look to be fixed indeed.