[BUG] OpenSearchIndicesClient#getAlias throws UnexpectedJsonEventException when the alias doesn't exist

[luontola]

What is the bug?

When specifying the name of an alias with org.opensearch.client.opensearch.indices.GetAliasRequest.Builder#name and the alias doesn't exist on the server, the client will throw a JSON parsing exception instead of indicating that the alias doesn't exist.

How can one reproduce the bug?

Run the following code when the foo alias doesn't exist.

        OpenSearchClient client = new OpenSearchClient(
                new RestClientTransport(
                        RestClient.builder(HttpHost.create("http://127.0.0.1:9200"))
                                .build(),
                        new JacksonJsonpMapper()));

        try (var ignored = client._transport()) {
            GetAliasResponse response = client.indices().getAlias(
                    builder -> builder.name("foo")
            );
            System.out.println(response.result());
        }

The client will make the request GET /_alias/foo and the server will response with http status 404 and the body {"error":"alias [foo] missing","status":404}.

This causes the client to throw the exception:

org.opensearch.client.json.UnexpectedJsonEventException: Unexpected JSON event 'VALUE_STRING' instead of '[START_OBJECT, KEY_NAME]'
	at org.opensearch.client.json.JsonpUtils.ensureAccepts(JsonpUtils.java:81)
	at org.opensearch.client.json.JsonpDeserializer.deserialize(JsonpDeserializer.java:87)
	at org.opensearch.client.json.ObjectBuilderDeserializer.deserialize(ObjectBuilderDeserializer.java:92)
	at org.opensearch.client.json.DelegatingDeserializer$SameType.deserialize(DelegatingDeserializer.java:56)
	at org.opensearch.client.json.ObjectDeserializer$FieldObjectDeserializer.deserialize(ObjectDeserializer.java:85)
	at org.opensearch.client.json.ObjectDeserializer.deserialize(ObjectDeserializer.java:189)
	at org.opensearch.client.json.ObjectDeserializer.deserialize(ObjectDeserializer.java:150)
	at org.opensearch.client.json.JsonpDeserializer.deserialize(JsonpDeserializer.java:88)
	at org.opensearch.client.json.ObjectBuilderDeserializer.deserialize(ObjectBuilderDeserializer.java:92)
	at org.opensearch.client.json.DelegatingDeserializer$SameType.deserialize(DelegatingDeserializer.java:56)
	at org.opensearch.client.transport.rest_client.RestClientTransport.getHighLevelResponse(RestClientTransport.java:271)
	at org.opensearch.client.transport.rest_client.RestClientTransport.performRequest(RestClientTransport.java:143)
	at org.opensearch.client.opensearch.indices.OpenSearchIndicesClient.getAlias(OpenSearchIndicesClient.java:671)
	at org.opensearch.client.opensearch.indices.OpenSearchIndicesClient.getAlias(OpenSearchIndicesClient.java:685)
	at example.Example.main(Example.java:30)

What is the expected behavior?

It would return a result that says the alias doesn't exist. I suppose with the current Java client the style is to throw an OpenSearchException with status 404.

What is your host/environment?

opensearch server 2.3.0
opensearch-java 2.1.0
opensearch-rest-client 2.4.0

[wbeckler]

This is a good catch. Would you be up for writing a PR to fix this, or at least a failing test?