Support micrometer context-propagation : Skeleton code

reactor3/build.gradle

@@ -1,3 +1,4 @@
 dependencies {
     api libs.reactor.core
+    implementation 'io.micrometer:context-propagation:1.1.1'
 }

reactor3/src/main/java/com/linecorp/armeria/common/reactor3/RequestContextAccessor.java

@@ -0,0 +1,55 @@
+package com.linecorp.armeria.common.reactor3;
+
+import java.util.Objects;
+
+import com.linecorp.armeria.common.RequestContext;
+import com.linecorp.armeria.internal.common.RequestContextUtil;
+
+import io.micrometer.context.ThreadLocalAccessor;
+
+public class RequestContextAccessor implements ThreadLocalAccessor<RequestContext> {
+
+    private static final String KEY = "ARMERIA_REQUEST_CONTEXT";
+    private static final RequestContextAccessor instance = createInstance();
+
+    private static RequestContextAccessor createInstance() {
+        return new RequestContextAccessor();
+    }
+
+    public static RequestContextAccessor getInstance() {
+        return instance;
+    }
+
+    private RequestContextAccessor() {
+    }
+
+    @Override
+    public Object key() {
+        return KEY;
+    }
+
+    @Override
+    public RequestContext getValue() {
+        return RequestContextUtil.get();
+    }
+
+    @Override
+    public void setValue(RequestContext value) {
+        RequestContextUtil.getAndSet(value);
+    }
+
+    @Override
+    public void setValue() {
+        // NO Operation.
+    }
+
+    @Override
+    public void restore(RequestContext previousValue) {
+        RequestContextUtil.getAndSet(previousValue);
+    }
+
+    @Override
+    public void restore() {
+        RequestContextUtil.pop();
+    }
+}

reactor3/src/main/java/com/linecorp/armeria/common/reactor3/RequestContextPropagationHook.java

@@ -0,0 +1,33 @@
+package com.linecorp.armeria.common.reactor3;
+
+
+import io.micrometer.context.ContextRegistry;
+import reactor.core.publisher.Hooks;
+
+public class RequestContextPropagationHook {
+
+    private static boolean enabled;
+
+    public static synchronized void enable() {
+        if (enabled) {
+            return;
+        }
+        ContextRegistry.getInstance().registerThreadLocalAccessor(RequestContextAccessor.getInstance());
+        Hooks.enableAutomaticContextPropagation();
+
+        enabled = true;
+    }
+
+    public static boolean isEnable() {
+        return enabled;
+    }
+
+    public static synchronized void disable() {
+        if (!enabled) {
+            return;
+        }
+
+        Hooks.disableAutomaticContextPropagation();
+        enabled = false;
+    }
+}