Ability to instrument logs before OTel injection into OTel appenders

instrumentation/log4j/log4j-appender-2.17/javaagent/src/main/java/io/opentelemetry/javaagent/instrumentation/log4j/appender/v2_17/Log4jHelper.java

@@ -27,10 +27,12 @@ public final class Log4jHelper {
 
   private static final LogEventMapper<Map<String, String>> mapper;
 
+  private static final boolean captureExperimentalAttributes;
+
   static {
     InstrumentationConfig config = InstrumentationConfig.get();
 
-    boolean captureExperimentalAttributes =
+    captureExperimentalAttributes =
         config.getBoolean("otel.instrumentation.log4j-appender.experimental-log-attributes", false);
     boolean captureMapMessageAttributes =
         config.getBoolean(
@@ -66,7 +68,16 @@ public static void capture(
             .build()
             .logRecordBuilder();
     Map<String, String> contextData = ThreadContext.getImmutableContext();
-    mapper.mapLogEvent(builder, message, level, marker, throwable, contextData);
+
+    String threadName = null;
+    long threadId = -1;
+    if (captureExperimentalAttributes) {
+      Thread currentThread = Thread.currentThread();
+      threadName = currentThread.getName();
+      threadId = currentThread.getId();
+    }
+    mapper.mapLogEvent(
+        builder, message, level, marker, throwable, contextData, threadName, threadId);
     builder.setTimestamp(Instant.now());
     builder.emit();
   }

instrumentation/log4j/log4j-appender-2.17/library/README.md

@@ -93,11 +93,12 @@ Setting can be configured as XML attributes, for example:
 
 The available settings are:
 
-| XML Attribute                   | Type    | Default | Description                                                                                                           |
-| ------------------------------- | ------- | ------- | --------------------------------------------------------------------------------------------------------------------- |
-| `captureExperimentalAttributes` | Boolean | `false` | Enable the capture of experimental span attributes `thread.name` and `thread.id`.                                     |
-| `captureMapMessageAttributes`   | Boolean | `false` | Enable the capture of `MapMessage` attributes.                                                                        |
-| `captureMarkerAttribute;`       | Boolean | `false` | Enable the capture of Log4j markers as attributes.                                                                    |
-| `captureContextDataAttributes`  | String  |         | Comma separated list of context data attributes to capture. Use the wildcard character `*` to capture all attributes. |
+| XML Attribute                   | Type    | Default | Description                                                                                                                                                                                                |
+|---------------------------------|---------|---------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
+| `captureExperimentalAttributes` | Boolean | `false` | Enable the capture of experimental span attributes `thread.name` and `thread.id`.                                                                                                                          |
+| `captureMapMessageAttributes`   | Boolean | `false` | Enable the capture of `MapMessage` attributes.                                                                                                                                                             |
+| `captureMarkerAttribute;`       | Boolean | `false` | Enable the capture of Log4j markers as attributes.                                                                                                                                                         |
+| `captureContextDataAttributes`  | String  |         | Comma separated list of context data attributes to capture. Use the wildcard character `*` to capture all attributes.                                                                                      |
+| `numLogsCapturedBeforeOtelInstall`            | Integer | 1000    | Log telemetry is emitted after the initialization of the OpenTelemetry Log4j appender with an OpenTelemetry object. This setting allows you to modify the size of the cache used to replay the first logs. |
 
 [source code attributes]: https://github.com/open-telemetry/semantic-conventions/blob/main/docs/general/attributes.md#source-code-attributes

instrumentation/log4j/log4j-appender-2.17/library/src/main/java/io/opentelemetry/instrumentation/log4j/appender/v2_17/LogEventToReplay.java

@@ -0,0 +1,210 @@
+/*
+ * Copyright The OpenTelemetry Authors
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+package io.opentelemetry.instrumentation.log4j.appender.v2_17;
+
+import java.util.Collections;
+import java.util.Map;
+import javax.annotation.Nullable;
+import org.apache.logging.log4j.Level;
+import org.apache.logging.log4j.Marker;
+import org.apache.logging.log4j.ThreadContext;
+import org.apache.logging.log4j.core.LogEvent;
+import org.apache.logging.log4j.core.impl.ThrowableProxy;
+import org.apache.logging.log4j.core.time.Instant;
+import org.apache.logging.log4j.message.Message;
+import org.apache.logging.log4j.message.StringMapMessage;
+import org.apache.logging.log4j.message.StructuredDataMessage;
+import org.apache.logging.log4j.util.ReadOnlyStringMap;
+
+class LogEventToReplay implements LogEvent {
+
+  private static final long serialVersionUID = 1L;
+
+  // Log4j 2 reuses LogEvent object, so we make a copy of all the fields that are used during export
+  // in order to be able to replay the log event later.
+
+  private final String loggerName;
+  private final Message message;
+  private final Level level;
+  private final Instant instant;
+  private final Throwable thrown;
+  private final Marker marker;
+  private final ReadOnlyStringMap contextData;
+  private final String threadName;
+  private final long threadId;
+
+  LogEventToReplay(LogEvent logEvent) {
+    this.loggerName = logEvent.getLoggerName();
+    Message messageOrigin = logEvent.getMessage();
+    if (messageOrigin instanceof StructuredDataMessage) {
+      StructuredDataMessage structuredDataMessage = (StructuredDataMessage) messageOrigin;
+      this.message =
+          // Log4j 2 reuses StructuredDataMessage object
+          new StructuredDataMessage(
+              structuredDataMessage.getId(),
+              structuredDataMessage.getFormat(),
+              structuredDataMessage.getType(),
+              structuredDataMessage.getData());
+    } else if (messageOrigin instanceof StringMapMessage) {
+      // StringMapMessage objects are not reused by Log4j 2
+      this.message = messageOrigin;
+    } else {
+      this.message = new MessageCopy(logEvent.getMessage());
+    }
+
+    this.level = logEvent.getLevel();
+    this.instant = logEvent.getInstant();
+    this.thrown = logEvent.getThrown();
+    this.marker = logEvent.getMarker();
+    this.contextData = logEvent.getContextData();
+    this.threadName = logEvent.getThreadName();
+    this.threadId = logEvent.getThreadId();
+  }
+
+  @Override
+  public LogEvent toImmutable() {
+    return null;
+  }
+
+  @SuppressWarnings("deprecation") // Override
+  @Override
+  public Map<String, String> getContextMap() {
+    return Collections.emptyMap();
+  }
+
+  @Override
+  public ReadOnlyStringMap getContextData() {
+    return contextData;
+  }
+
+  @Nullable
+  @Override
+  public ThreadContext.ContextStack getContextStack() {
+    return null;
+  }
+
+  @Override
+  public String getLoggerFqcn() {
+    return null;
+  }
+
+  @Override
+  public Level getLevel() {
+    return level;
+  }
+
+  @Override
+  public String getLoggerName() {
+    return loggerName;
+  }
+
+  @Override
+  public Marker getMarker() {
+    return marker;
+  }
+
+  @Override
+  public Message getMessage() {
+    return message;
+  }
+
+  @Override
+  public long getTimeMillis() {
+    return 0;
+  }
+
+  @Override
+  public Instant getInstant() {
+    return instant;
+  }
+
+  @Override
+  public StackTraceElement getSource() {
+    return null;
+  }
+
+  @Override
+  public String getThreadName() {
+    return threadName;
+  }
+
+  @Override
+  public long getThreadId() {
+    return threadId;
+  }
+
+  @Override
+  public int getThreadPriority() {
+    return 0;
+  }
+
+  @Override
+  public Throwable getThrown() {
+    return thrown;
+  }
+
+  @Override
+  public ThrowableProxy getThrownProxy() {
+    return null;
+  }
+
+  @Override
+  public boolean isEndOfBatch() {
+    return false;
+  }
+
+  @Override
+  public boolean isIncludeLocation() {
+    return false;
+  }
+
+  @Override
+  public void setEndOfBatch(boolean endOfBatch) {}
+
+  @Override
+  public void setIncludeLocation(boolean locationRequired) {}
+
+  @Override
+  public long getNanoTime() {
+    return 0;
+  }
+
+  private static class MessageCopy implements Message {
+
+    private static final long serialVersionUID = 1L;
+    private final String formattedMessage;
+    private final String format;
+    private final Object[] parameters;
+    private final Throwable throwable;
+
+    public MessageCopy(Message message) {
+      this.formattedMessage = message.getFormattedMessage();
+      this.format = message.getFormat();
+      this.parameters = message.getParameters();
+      this.throwable = message.getThrowable();
+    }
+
+    @Override
+    public String getFormattedMessage() {
+      return formattedMessage;
+    }
+
+    @Override
+    public String getFormat() {
+      return format;
+    }
+
+    @Override
+    public Object[] getParameters() {
+      return parameters;
+    }
+
+    @Override
+    public Throwable getThrowable() {
+      return throwable;
+    }
+  }
+}