Allow YamlTemplateRegistry to fallback to TemplateResources

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/template/ResourceUtils.java

@@ -7,12 +7,15 @@
 
 package org.elasticsearch.xpack.core.template;
 
+import org.elasticsearch.xpack.core.template.resources.TemplateResources;
+
 import java.io.IOException;
 import java.io.InputStream;
 import java.nio.charset.StandardCharsets;
 import java.util.Map;
 
 public class ResourceUtils {
+
     static byte[] loadVersionedResourceUTF8(Class<?> clazz, String name, int version, String versionProperty) {
         return loadVersionedResourceUTF8(clazz, name, version, versionProperty, Map.of());
     }
@@ -25,16 +28,33 @@ static byte[] loadVersionedResourceUTF8(
         Map<String, String> variables
     ) {
         try {
-            String content = loadResource(clazz, name);
+            String content = loadResourceWithFallback(clazz, name);
             content = TemplateUtils.replaceVariables(content, String.valueOf(version), versionProperty, variables);
             return content.getBytes(StandardCharsets.UTF_8);
         } catch (IOException e) {
             throw new RuntimeException(e);
         }
     }
 
-    public static String loadResource(Class<?> clazz, String name) throws IOException {
-        InputStream is = clazz.getResourceAsStream(name);
+    /**
+     * loadResourceWithFallback loads template resources from TemplateResource class. It expects
+     * the loader to be a named Java module and the template resources to contain required templates
+     * with a folder named with the module name. If the specified resource name is not found in
+     * template resource then the plugin's resources is used as a fallback.
+     *
+     * @param clazz the runtime class of the source plugin
+     * @param name the relative path of the resource with leading `/`
+     * @return the loaded resource as string
+     * @throws IOException
+     */
+    static String loadResourceWithFallback(Class<?> clazz, String name) throws IOException {
+        InputStream is = null;
+        if (clazz.getModule().isNamed()) {
+            is = TemplateResources.class.getResourceAsStream("/" + clazz.getModule().getName() + name);
+        }
+        if (is == null) {
+            is = clazz.getResourceAsStream(name);
+        }
         if (is == null) {
             throw new IOException("Resource [" + name + "] not found in classpath.");
         }

x-pack/plugin/core/src/main/java/org/elasticsearch/xpack/core/template/YamlTemplateRegistry.java

@@ -31,7 +31,7 @@
 import java.util.Optional;
 import java.util.stream.Collectors;
 
-import static org.elasticsearch.xpack.core.template.ResourceUtils.loadResource;
+import static org.elasticsearch.xpack.core.template.ResourceUtils.loadResourceWithFallback;
 import static org.elasticsearch.xpack.core.template.ResourceUtils.loadVersionedResourceUTF8;
 
 /**
@@ -64,7 +64,7 @@ public YamlTemplateRegistry(
         try {
             final Map<String, Object> resources = XContentHelper.convertToMap(
                 YamlXContent.yamlXContent,
-                loadResource(this.getClass(), "/resources.yaml"),
+                loadResourceWithFallback(this.getClass(), "/resources.yaml"),
                 false
             );
             version = (((Number) resources.get("version")).intValue());