Aliases: Throw exception if index is null when creating alias

[polyfractal]

Fixes a bug where alias creation would allow null for index name, which thereby applied the alias to all indices. This patch makes the validator throw an exception if the index is null.

Fixes #7863

POST /_aliases
{
   "actions": [
      {
         "add": {
            "alias": "empty-alias",
            "index": null
         }
      }
   ]
}

{
   "error": "ActionRequestValidationException[Validation Failed: 1: Alias action [add]: [index] may not be null;]",
   "status": 400
}

Edit:

The reason this bug wasn't caught by the existing tests is because the old test for nullness only validated against a cluster which had zero indices. The null index is translated into "_all", and since there are no indices, this fails because the index doesn't exist. So the test passes.

However, as soon as you add an index, "_all" resolves and you get the situation described in the original bug report: null index is accepted by the alias, resolves to "_all" and gets applied to everything.

[rjernst]

What is here looks good, but I think we should do more. Right now not passing any index at all results in using _all, which I think is very dangerous?

Ryans-MacBook-Pro:~ rjernst$ curl -i -XPOST 'http://localhost:9200/_aliases' -d '{"actions":[{"add":{"alias":"myalias"}}]}'
HTTP/1.1 200 OK
Content-Type: application/json; charset=UTF-8
Content-Length: 21

{"acknowledged":true}

[polyfractal]

@rjernst Just looked into this, and it appears the patch will also protect against complete omission of the field.

The indices() method ensures that the array of indices is always initialized (even if empty), which means the new else clause introduced in the patch will throw an exception if indices is omitted entirely.

$ curl -XPOST "http://localhost:9200/_aliases" -d'
{
   "actions":[
      {
         "add":{
            "alias":"empty-alias"
         }
      }
   ]
}'

{
   "error": "ActionRequestValidationException[Validation Failed: 1: Alias action [add]: [index] may not be null;]",
   "status": 400
}

[rjernst]

Cool! LGTM.

My only thought is maybe the error message should be more generic, since it could be a missing "index" key, or index set to null?

[s1monw]

LGTM too agreed with @rjernst