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Spring Framework on Google Cloud Stackdriver Logging

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/*
 * Copyright 2017-2019 the original author or authors.
 *
 * 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
 *
 *      https://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 com.google.cloud.spring.logging.extensions;

import ch.qos.logback.classic.spi.ILoggingEvent;
import com.google.cloud.logging.LogEntry;
import com.google.cloud.logging.logback.LoggingEventEnhancer;
import com.google.cloud.spring.logging.JsonLoggingEventEnhancer;
import java.util.Iterator;
import java.util.List;
import java.util.Map;
import java.util.function.Consumer;
import net.logstash.logback.marker.ObjectAppendingMarker;
import org.slf4j.Marker;

/**
 * Logging enhancer which adds Logstash markers to Logging API calls and JSON log entries.
 *
 * Supported Markers: - ObjectAppendingMarker: key-value pairs are added to the log entries.
 *
 * This can be used by specifying this class in a {@code } element for your
 * {@link com.google.cloud.logging.logback.LoggingAppender} or {@link
 * com.google.cloud.spring.logging.StackdriverJsonLayout} definitions in logback.xml.
 */
public class LogstashLoggingEventEnhancer
    implements LoggingEventEnhancer, JsonLoggingEventEnhancer {

  @Override
  public void enhanceLogEntry(LogEntry.Builder builder, ILoggingEvent event) {
    addLogstashMarkerIfNecessary(
        getFirstMarker(event.getMarkerList()),
        marker -> builder.addLabel(marker.getFieldName(), marker.getFieldValue().toString()));
  }

  @Override
  public void enhanceJsonLogEntry(Map jsonMap, ILoggingEvent event) {
    addLogstashMarkerIfNecessary(
        getFirstMarker(event.getMarkerList()),
        marker -> jsonMap.put(marker.getFieldName(), marker.getFieldValue()));
  }

  private Marker getFirstMarker(List markers) {
    return markers == null || markers.isEmpty() ? null : markers.get(0);
  }

  private void addLogstashMarkerIfNecessary(
      Marker marker, Consumer markerAdderFunction) {
    if (marker == null) {
      return;
    }

    if (marker instanceof ObjectAppendingMarker objectAppendingMarker) {
      markerAdderFunction.accept(objectAppendingMarker);
    }

    if (marker.hasReferences()) {
      for (Iterator i = marker.iterator(); i.hasNext(); ) {
        Marker next = (Marker) i.next();
        addLogstashMarkerIfNecessary(next, markerAdderFunction);
      }
    }
  }
}