ClassCastException when settings set to [] during index creation

[thewunder]

Elasticsearch version: 6.8.2

Plugins installed: repository-s3

JVM version:
openjdk version "1.8.0_222"
OpenJDK Runtime Environment (build 1.8.0_222-8u222-b10-1ubuntu1~16.04.1-b10)

OS version:
Linux ip-172-31-37-249 4.4.0-59-generic #80-Ubuntu SMP Fri Jan 6 17:47:47 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux

Description of the problem including expected versus actual behavior:
Passing an a

Steps to reproduce:

curl -X PUT "localhost:9200/myindex" -H 'Content-Type: application/json' -d'
{
   "settings" : []
}                  
'

Stack Trace:

java.lang.ClassCastException: java.util.ArrayList cannot be cast to java.util.Map
        at org.elasticsearch.action.admin.indices.create.CreateIndexRequest.source(CreateIndexRequest.java:386) ~[elasticsearch-6.8.2.jar:6.8.2]
        at org.elasticsearch.rest.action.admin.indices.RestCreateIndexAction.prepareRequest(RestCreateIndexAction.java:71) ~[elasticsearch-6.8.2.jar:6.8.2]
        at org.elasticsearch.rest.BaseRestHandler.handleRequest(BaseRestHandler.java:91) ~[elasticsearch-6.8.2.jar:6.8.2]
        at org.elasticsearch.xpack.security.rest.SecurityRestFilter.handleRequest(SecurityRestFilter.java:87) ~[?:?]
        at org.elasticsearch.rest.RestController.dispatchRequest(RestController.java:240) [elasticsearch-6.8.2.jar:6.8.2]
        at org.elasticsearch.rest.RestController.tryAllHandlers(RestController.java:336) [elasticsearch-6.8.2.jar:6.8.2]
        at org.elasticsearch.rest.RestController.dispatchRequest(RestController.java:174) [elasticsearch-6.8.2.jar:6.8.2]
        at org.elasticsearch.http.netty4.Netty4HttpServerTransport.dispatchRequest(Netty4HttpServerTransport.java:551) [transport-netty4-client-6.8.2.jar:6.8.2]

[elasticmachine]

Pinging @elastic/es-core-infra

[DaveCTurner]

What exactly do you think is wrong with this behaviour @thewunder? The request isn't valid so throwing some kind of exception is the right thing to do.

[DaveCTurner]

Closing this for want of feedback. We can always reopen it if we hear back from @thewunder.

[thewunder]

@DaveCTurner

org.elasticsearch.ElasticsearchParseException or org.elasticsearch.action.ActionRequestValidationException?

To me as a user, if I am passing invalid input I would expect to see something Validation or parse related and tell me the error made. Internal java exceptions are the least informative type of error.

[rjernst]

@thewunder I agree with you, a ClassCastException can be confusing for users that don't understand the connection between Map in the sent request needing to contain a json object, nor where the error occurred within the request body. I've opened #45588 to address this.

[thewunder]

Thanks @rjernst looks good!