Add ConfigResource

Closes #31

src/main/java/org/kiwiproject/dropwizard/util/resource/ConfigResource.java

@@ -0,0 +1,46 @@
+package org.kiwiproject.dropwizard.util.resource;
+
+import static javax.ws.rs.core.MediaType.APPLICATION_JSON;
+import static org.kiwiproject.json.KiwiJacksonSerializers.buildPropertyMaskingSafeSerializerModule;
+
+import com.codahale.metrics.annotation.ExceptionMetered;
+import com.codahale.metrics.annotation.Timed;
+import io.dropwizard.Configuration;
+import lombok.extern.slf4j.Slf4j;
+import org.kiwiproject.json.JsonHelper;
+
+import javax.ws.rs.GET;
+import javax.ws.rs.Path;
+import javax.ws.rs.Produces;
+import javax.ws.rs.core.Response;
+import java.util.List;
+
+/**
+ * JAX-RS resource that enables the retrieval of the current runtime configuration of the service.
+ * <p>
+ * A list of regex patterns can be given in order to mask secrets in the configuration.
+ */
+@Slf4j
+@Path("app/config")
+public class ConfigResource<T extends Configuration> {
+
+    // Intentionally creating a separate JsonHelper to allow customizations
+    private final JsonHelper jsonHelper;
+    private final T config;
+
+    public ConfigResource(T config, List<String> hiddenRegex) {
+        this.config = config;
+        this.jsonHelper = JsonHelper.newDropwizardJsonHelper();
+
+        jsonHelper.getObjectMapper().registerModule(buildPropertyMaskingSafeSerializerModule(hiddenRegex));
+    }
+
+    @GET
+    @Timed
+    @ExceptionMetered
+    @Produces(APPLICATION_JSON)
+    public Response getCurrentConfiguration() {
+        var json = jsonHelper.toJson(config);
+        return Response.ok(json).build();
+    }
+}

src/test/java/org/kiwiproject/dropwizard/util/resource/ConfigResourceTest.java

@@ -0,0 +1,58 @@
+package org.kiwiproject.dropwizard.util.resource;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+import io.dropwizard.Application;
+import io.dropwizard.Configuration;
+import io.dropwizard.setup.Environment;
+import io.dropwizard.testing.junit5.DropwizardAppExtension;
+import io.dropwizard.testing.junit5.DropwizardExtensionsSupport;
+import lombok.AllArgsConstructor;
+import lombok.Getter;
+import lombok.Setter;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.extension.ExtendWith;
+
+import javax.ws.rs.core.GenericType;
+import java.util.List;
+import java.util.Map;
+
+@DisplayName("ConfigResource")
+@ExtendWith(DropwizardExtensionsSupport.class)
+class ConfigResourceTest {
+
+    @Getter
+    @Setter
+    @AllArgsConstructor
+    static class TestConfig extends Configuration {
+        private String someNeededProperty;
+        private String someHiddenPassword;
+    }
+
+    public static class TestApp extends Application<TestConfig> {
+
+        public TestApp() {}
+
+        @Override
+        public void run(TestConfig config, Environment environment) {
+            environment.jersey().register(new ConfigResource<>(config, List.of(".*Password")));
+        }
+    }
+
+    private static final TestConfig CONFIG = new TestConfig("foo", "secret");
+    private static final DropwizardAppExtension<TestConfig> APP = new DropwizardAppExtension<>(TestApp.class, CONFIG);
+
+    @Test
+    void shouldReturnConfigAndMaskSecrets() {
+        var response = APP.client().target("http://localhost:" + APP.getLocalPort() + "/app/config")
+                .request()
+                .get();
+
+        var configData = response.readEntity(new GenericType<Map<String, Object>>(){});
+
+        assertThat(configData)
+                .containsEntry("someNeededProperty", "foo")
+                .containsEntry("someHiddenPassword", "********");
+    }
+}