Revert "Revert "feat: health checks""

Author: sladkoff

src/main/java/de/sldk/mc/HealthController.java

@@ -0,0 +1,28 @@
+package de.sldk.mc;
+
+import de.sldk.mc.health.HealthChecks;
+import org.eclipse.jetty.http.HttpStatus;
+import org.eclipse.jetty.server.Handler;
+import org.eclipse.jetty.server.Request;
+import org.eclipse.jetty.server.Response;
+import org.eclipse.jetty.util.Callback;
+
+public class HealthController extends Handler.Abstract {
+
+    private final HealthChecks checks;
+
+    private HealthController(final HealthChecks checks) {
+        this.checks = checks;
+    }
+
+    public static Handler create(final HealthChecks checks) {
+        return new HealthController(checks);
+    }
+
+    @Override
+    public boolean handle(Request request, Response response, Callback callback) throws Exception {
+        response.setStatus(checks.isHealthy() ? HttpStatus.OK_200 : HttpStatus.SERVICE_UNAVAILABLE_503);
+        callback.succeeded();
+        return true;
+    }
+}

src/main/java/de/sldk/mc/MetricsController.java

@@ -19,10 +19,13 @@ public class MetricsController extends Handler.Abstract {
     private final MetricRegistry metricRegistry = MetricRegistry.getInstance();
     private final PrometheusExporter exporter;
 
-    public MetricsController(PrometheusExporter exporter) {
+    private MetricsController(PrometheusExporter exporter) {
         this.exporter = exporter;
     }
 
+    public static Handler create(final PrometheusExporter exporter) {
+        return new MetricsController(exporter);
+    }
 
     @Override
     public boolean handle(Request request, Response response, Callback callback) throws Exception {

src/main/java/de/sldk/mc/MetricsServer.java

@@ -1,6 +1,7 @@
 package de.sldk.mc;
 
 import org.eclipse.jetty.http.pathmap.PathSpec;
+import de.sldk.mc.health.HealthChecks;
 import org.eclipse.jetty.server.Server;
 import org.eclipse.jetty.server.handler.PathMappingsHandler;
 import org.eclipse.jetty.server.handler.gzip.GzipHandler;
@@ -12,20 +13,23 @@ public class MetricsServer {
     private final String host;
     private final int port;
     private final PrometheusExporter prometheusExporter;
+	private final HealthChecks healthChecks;
 
     private Server server;
 
-    public MetricsServer(String host, int port, PrometheusExporter prometheusExporter) {
+    public MetricsServer(String host, int port, PrometheusExporter prometheusExporter, HealthChecks healthChecks) {
         this.host = host;
         this.port = port;
         this.prometheusExporter = prometheusExporter;
-    }
+    this.healthChecks = healthChecks;
+	}
 
     public void start() throws Exception {
         GzipHandler gzipHandler = new GzipHandler();
 
         var pathMappings = new PathMappingsHandler();
-        pathMappings.addMapping(PathSpec.from("/metrics"), new MetricsController(prometheusExporter));
+        pathMappings.addMapping(PathSpec.from("/metrics"), MetricsController.create(prometheusExporter));
+        pathMappings.addMapping(PathSpec.from("/health"), HealthController.create(healthChecks));
 
         gzipHandler.setHandler(pathMappings);
 

src/main/java/de/sldk/mc/health/ConcurrentHealthChecks.java

@@ -0,0 +1,33 @@
+package de.sldk.mc.health;
+
+import java.util.Set;
+import java.util.concurrent.ConcurrentHashMap;
+
+public final class ConcurrentHealthChecks implements HealthChecks {
+
+    private final Set<HealthCheck> checks;
+
+    private ConcurrentHealthChecks(final Set<HealthCheck> checks) {
+        this.checks = checks;
+    }
+
+    public static HealthChecks create() {
+        return new ConcurrentHealthChecks(ConcurrentHashMap.newKeySet());
+    }
+
+    @Override
+    public boolean isHealthy() {
+        for (final HealthCheck check : checks) if (!check.isHealthy()) return false;
+        return true;
+    }
+
+    @Override
+    public void add(final HealthCheck check) {
+        checks.add(check);
+    }
+
+    @Override
+    public void remove(final HealthCheck check) {
+        checks.remove(check);
+    }
+}

src/main/java/de/sldk/mc/health/HealthCheck.java

@@ -0,0 +1,64 @@
+package de.sldk.mc.health;
+
+/**
+ * Health check.
+ */
+public interface HealthCheck {
+
+    /**
+     * Checks if the current state is healthy.
+     *
+     * @return {@code true} if the state is healthy and {@code false} otherwise
+     */
+    boolean isHealthy();
+
+    /**
+     * Creates a health compound check from the provided ones reporting healthy status if all the checks report it.
+     *
+     * @param checks merged health checks
+     * @return compound health check
+     */
+    static HealthCheck allOf(final HealthCheck... checks) {
+        return new AllOf(checks);
+    }
+
+    /**
+     * Creates a compound health check from the provided ones reporting healthy status if any check reports it.
+     *
+     * @param checks merged health checks
+     * @return compound health check
+     */
+    static HealthCheck anyOf(final HealthCheck... checks) {
+        return new AnyOf(checks);
+    }
+
+    final class AllOf implements HealthCheck {
+        private final HealthCheck[] checks;
+
+        private AllOf(final HealthCheck[] checks) {
+            this.checks = checks;
+        }
+
+        @Override
+        public boolean isHealthy() {
+            for (final HealthCheck check : checks) if (!check.isHealthy()) return false;
+
+            return true;
+        }
+    }
+
+    final class AnyOf implements HealthCheck {
+        private final HealthCheck[] checks;
+
+        private AnyOf(final HealthCheck[] checks) {
+            this.checks = checks;
+        }
+
+        @Override
+        public boolean isHealthy() {
+            for (final HealthCheck check : checks) if (check.isHealthy()) return true;
+
+            return false;
+        }
+    }
+}

src/main/java/de/sldk/mc/health/HealthChecks.java

@@ -0,0 +1,21 @@
+package de.sldk.mc.health;
+
+/**
+ * Dynamic compound health checks.
+ */
+public interface HealthChecks extends HealthCheck {
+
+    /**
+     * Adds the provided health check to this one.
+     *
+     * @param check added health check
+     */
+    void add(HealthCheck check);
+
+    /**
+     * Removes the provided health check from this one.
+     *
+     * @param check removed health check
+     */
+    void remove(HealthCheck check);
+}

src/main/kotlin/de/sldk/mc/PrometheusExporter.kt

@@ -3,9 +3,13 @@
 package de.sldk.mc
 
 import de.sldk.mc.config.PrometheusExporterConfig
+import de.sldk.mc.health.ConcurrentHealthChecks
+import de.sldk.mc.health.HealthChecks
+import org.bukkit.plugin.ServicePriority
 import org.bukkit.plugin.java.JavaPlugin
 import java.util.logging.Level
 
+
 class PrometheusExporter : JavaPlugin() {
     private val config: PrometheusExporterConfig = PrometheusExporterConfig(this)
     private var server: MetricsServer? = null
@@ -14,14 +18,18 @@ class PrometheusExporter : JavaPlugin() {
     override fun onEnable() {
         config.loadDefaultsAndSave()
         config.enableConfiguredMetrics()
-        startMetricsServer()
+
+        val healthChecks = ConcurrentHealthChecks.create()
+        getServer().servicesManager.register(HealthChecks::class.java, healthChecks, this, ServicePriority.Normal)
+
+        startMetricsServer(healthChecks)
     }
 
-    private fun startMetricsServer() {
+    private fun startMetricsServer(healthChecks: HealthChecks) {
         val host = config[PrometheusExporterConfig.HOST]
         val port = config[PrometheusExporterConfig.PORT]
 
-        server = MetricsServer(host, port, this)
+        server = MetricsServer(host, port, this, healthChecks)
 
         try {
             server?.start()

src/test/java/de/sldk/mc/exporter/PrometheusExporterTest.java

@@ -1,10 +1,9 @@
 package de.sldk.mc.exporter;
 
 
-import static org.assertj.core.api.Assertions.assertThat;
-
 import de.sldk.mc.MetricsServer;
 import de.sldk.mc.PrometheusExporter;
+import de.sldk.mc.health.ConcurrentHealthChecks;
 import io.prometheus.client.CollectorRegistry;
 import io.prometheus.client.Counter;
 import io.prometheus.client.exporter.common.TextFormat;
@@ -21,6 +20,8 @@
 import java.io.IOException;
 import java.net.ServerSocket;
 
+import static org.assertj.core.api.Assertions.assertThat;
+
 @ExtendWith(MockitoExtension.class)
 public class PrometheusExporterTest {
 
@@ -34,7 +35,9 @@ public class PrometheusExporterTest {
 	void setup() throws Exception {
 		CollectorRegistry.defaultRegistry.clear();
 		metricsServerPort = getRandomFreePort();
-		metricsServer = new MetricsServer("localhost", metricsServerPort, exporterMock);
+		metricsServer = new MetricsServer(
+                "localhost", metricsServerPort, exporterMock, ConcurrentHealthChecks.create()
+        );
 		metricsServer.start();
 	}
 
@@ -83,4 +86,14 @@ void metrics_server_should_return_404_on_unknown_paths() {
 				.statusCode(HttpStatus.NOT_FOUND_404);
 	}
 
+	@Test
+	void metrics_server_should_return_200_on_health_check() {
+		String requestPath = URIUtil.newURI("http", "localhost", metricsServerPort, "/health", null);
+
+		RestAssured.when()
+				.get(requestPath)
+				.then()
+				.statusCode(HttpStatus.OK_200);
+	}
+
 }