Abcd.java

public class Abcd {

    public static void main(String[] args) throws Exception {
        Settings settings = Settings.builder()
            .put("http.enabled", "false")
            .put("transport.type", "local")
            .put("discovery.type", "local")
            .put("path.home", "/home/mvg/temp")
            .put("cluster.name", "bwc_index_5.0.0")
            .put("repositories.url.allowed_urls", "http://snapshot.test*")
            .build();
        Node node = new N(settings);
        node.start();
        Client client = node.client();

        client.admin().cluster().preparePutRepository("repo")
            .setType("url")
            .setSettings(Settings.builder().put("url", "http://snapshot.test"))
            .get();

        client.admin().cluster().preparePutStoredScript()
            .setScriptLang(MockScriptEngine.NAME)
            .setId("key")
            .setSource(new BytesArray("{\"script\": \"key\""))
            .get();

        client.admin().cluster().preparePutPipeline("id", new BytesArray("{\"processors\": []}"))
            .get();

        client.admin().indices().prepareCreate("test")
            .addCustom(new TestPlugin.IMDC("value"))
            .get();
        client.admin().cluster().prepareHealth().setWaitForYellowStatus().get();

        client.close();
        node.close();
    }

    static class N extends Node {

        public N(Settings settings) {
            super(InternalSettingsPreparer.prepareEnvironment(settings, null), Arrays.asList(TestPlugin.class, S.class));
        }
    }

    public static class TestPlugin extends Plugin {

        static {
            IndexMetaData.registerPrototype("custom", TestPlugin.IMDC.PROTO);
        }

        public static class IMDC implements IndexMetaData.Custom {

            public static final TestPlugin.IMDC PROTO = new TestPlugin.IMDC(null);

            private final String field;

            public IMDC(String field) {
                this.field = field;
            }

            @Override
            public Diff<IndexMetaData.Custom> diff(IndexMetaData.Custom previousState) {
                return new TestPlugin.IMDC.IMDCDiff((TestPlugin.IMDC) previousState);
            }

            @Override
            public Diff<IndexMetaData.Custom> readDiffFrom(StreamInput in) throws IOException {
                return new TestPlugin.IMDC.IMDCDiff(new TestPlugin.IMDC(in.readString()));
            }

            @Override
            public IndexMetaData.Custom readFrom(StreamInput in) throws IOException {
                return new TestPlugin.IMDC(in.readString());
            }

            @Override
            public void writeTo(StreamOutput out) throws IOException {
                out.writeString(field);
            }

            @Override
            public XContentBuilder toXContent(XContentBuilder builder, Params params) throws IOException {
                builder.field("field", field);
                return builder;
            }

            @Override
            public String type() {
                return "custom";
            }

            @Override
            public IndexMetaData.Custom fromMap(Map<String, Object> map) throws IOException {
                return new TestPlugin.IMDC((String) map.get("field"));
            }

            @Override
            public IndexMetaData.Custom fromXContent(XContentParser parser) throws IOException {
                return new TestPlugin.IMDC(parser.text());
            }

            @Override
            public IndexMetaData.Custom mergeWith(IndexMetaData.Custom another) {
                TestPlugin.IMDC other = (TestPlugin.IMDC) another;
                return new TestPlugin.IMDC(field + other.field);
            }

            static class IMDCDiff implements Diff<IndexMetaData.Custom> {

                private final TestPlugin.IMDC previous;

                IMDCDiff(TestPlugin.IMDC previous) {
                    this.previous = previous;
                }

                @Override
                public IndexMetaData.Custom apply(IndexMetaData.Custom part) {
                    return new TestPlugin.IMDC(((TestPlugin.IMDC) part).field);
                }

                @Override
                public void writeTo(StreamOutput out) throws IOException {
                    out.writeString(previous.field);
                }
            }
        }
    }

    public static class S extends MockScriptPlugin {

        @Override
        protected Map<String, Function<Map<String, Object>, Object>> pluginScripts() {
            return Collections.singletonMap("key", params -> "value");
        }
    }

}