Use log4j2 Plugin framework

Observed in downstream projects that other Log4j2 configurations were
"winning" over our manual configuration, so we choose a very high
priority (1e6) to force logging to match Barista's desired configuration.

Unfortunately the approaach we're taking now won't allow any kind of
tweaking or customization, so we might have to revisit down the road.

barista/build.gradle.kts

@@ -22,6 +22,9 @@ dependencies {
     // users of this library should have access to the slf4j api for their own logging
     api("org.slf4j:slf4j-api")
 
+    // register @Plugin annotation processor
+    annotationProcessor("org.apache.logging.log4j:log4j-core")
+
     testImplementation(platform("org.junit:junit-bom"))
     testImplementation("org.junit.jupiter:junit-jupiter-engine")
     testImplementation("org.assertj:assertj-core")

barista/src/main/java/barista/Logging.java

@@ -1,49 +1,63 @@
 package barista;
 
+import java.net.URI;
 import org.apache.logging.log4j.Level;
-import org.apache.logging.log4j.core.Filter.Result;
+import org.apache.logging.log4j.core.LoggerContext;
 import org.apache.logging.log4j.core.appender.ConsoleAppender;
-import org.apache.logging.log4j.core.config.Configurator;
+import org.apache.logging.log4j.core.config.Configuration;
+import org.apache.logging.log4j.core.config.ConfigurationFactory;
+import org.apache.logging.log4j.core.config.ConfigurationSource;
+import org.apache.logging.log4j.core.config.Order;
 import org.apache.logging.log4j.core.config.builder.api.AppenderComponentBuilder;
 import org.apache.logging.log4j.core.config.builder.api.ConfigurationBuilder;
-import org.apache.logging.log4j.core.config.builder.api.ConfigurationBuilderFactory;
-import org.apache.logging.log4j.core.config.builder.api.FilterComponentBuilder;
 import org.apache.logging.log4j.core.config.builder.api.LayoutComponentBuilder;
-import org.apache.logging.log4j.core.config.builder.api.LoggerComponentBuilder;
 import org.apache.logging.log4j.core.config.builder.impl.BuiltConfiguration;
+import org.apache.logging.log4j.core.config.plugins.Plugin;
+
+@Plugin(name = "BaristaLogging", category = ConfigurationFactory.CATEGORY)
+@Order(1_000_000)
+final class Logging extends ConfigurationFactory {
 
-final class Logging {
     private static final String STDOUT = "stdout";
+    public static final String[] SUPPORTED_TYPES = {"*"};
 
-    public static void configure() {
-        ConfigurationBuilder<BuiltConfiguration> builder =
-                ConfigurationBuilderFactory.newConfigurationBuilder()
-                        .setStatusLevel(Level.ERROR)
-                        .setConfigurationName("barista");
+    static BuiltConfiguration createConfiguration(
+            String name, ConfigurationBuilder<BuiltConfiguration> builder) {
+        builder.setStatusLevel(Level.ERROR);
+        builder.setConfigurationName(name);
 
         LayoutComponentBuilder layout =
                 builder.newLayout("PatternLayout")
                         .addAttribute("pattern", "%d [%t] %-5level: %msg%n%throwable");
-        FilterComponentBuilder filter =
-                builder.newFilter("MarkerFilter", Result.DENY, Result.NEUTRAL)
-                        .addAttribute("marker", "FLOW");
 
         AppenderComponentBuilder appenderBuilder =
                 builder.newAppender(STDOUT, "CONSOLE")
                         .addAttribute("target", ConsoleAppender.Target.SYSTEM_OUT)
-                        .add(layout)
-                        .add(filter);
+                        .add(layout);
+
+        builder.add(appenderBuilder);
+        builder.add(
+                builder.newRootLogger(Level.INFO)
+                        .add(builder.newAppenderRef(appenderBuilder.getName())));
+
+        return builder.build();
+    }
 
-        LoggerComponentBuilder logger =
-                builder.newLogger("org.apache.logging.log4j", Level.DEBUG)
-                        .add(builder.newAppenderRef(STDOUT))
-                        .addAttribute("additivity", false);
+    @Override
+    public Configuration getConfiguration(
+            final LoggerContext loggerContext, final ConfigurationSource source) {
+        return getConfiguration(loggerContext, source.toString(), null);
+    }
 
-        builder.add(appenderBuilder)
-                .add(logger)
-                .add(builder.newRootLogger(Level.INFO).add(builder.newAppenderRef(STDOUT)));
+    @Override
+    public Configuration getConfiguration(
+            final LoggerContext loggerContext, final String name, final URI configLocation) {
+        ConfigurationBuilder<BuiltConfiguration> builder = newConfigurationBuilder();
+        return createConfiguration(name, builder);
+    }
 
-        Configurator.initialize(builder.build());
-        // TODO(markelliot): we may want to stop the logging context on server shutdown
+    @Override
+    protected String[] getSupportedTypes() {
+        return SUPPORTED_TYPES;
     }
 }

barista/src/main/java/barista/Server.java

@@ -98,8 +98,6 @@ public Builder disableTls() {
         }
 
         public Server start() {
-            Logging.configure();
-
             Preconditions.checkNotNull(authz);
 
             EndpointHandlerBuilder handler = new EndpointHandlerBuilder(serde, authz);