Add time-limited logs to Epp Login flow to test increased latency (#2810)

util/src/main/java/google/registry/util/StopwatchLogger.java

@@ -0,0 +1,45 @@
+// Copyright 2025 The Nomulus Authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package google.registry.util;
+
+import com.google.common.flogger.FluentLogger;
+import java.time.Duration;
+
+/**
+ * A helper class to log only if the time elapsed between calls is more than a specified threshold.
+ */
+public final class StopwatchLogger {
+  private static final FluentLogger logger = FluentLogger.forEnclosingClass();
+  Duration threshold = Duration.ofMillis(400);
+  private final long thresholdNanos;
+  private long lastTickNanos;
+
+  public StopwatchLogger() {
+    this.thresholdNanos = threshold.toNanos();
+    this.lastTickNanos = System.nanoTime();
+  }
+
+  public void tick(String message) {
+    long currentNanos = System.nanoTime();
+    long elapsedNanos = currentNanos - lastTickNanos;
+
+    // Only log if the elapsed time is over the threshold.
+    if (elapsedNanos > thresholdNanos) {
+      logger.atInfo().log("%s (took %d ms)", message, Duration.ofNanos(elapsedNanos).toMillis());
+    }
+
+    this.lastTickNanos = currentNanos;
+  }
+}