only create a mutable copy of the BsonDocument when needed

Author: na-ji

dd-java-agent/instrumentation/mongo/common/src/main/java/datadog/trace/instrumentation/mongo/MongoCommentInjector.java

@@ -28,10 +28,13 @@ public static BsonDocument injectComment(String dbmComment, BsonDocument origina
       return originalBsonDocument;
     }
 
-    // Create a mutable copy by constructing a new BsonDocument and copying all entries
-    // This handles both regular BsonDocument and immutable RawBsonDocument/ByteBufBsonDocument
-    BsonDocument command = new BsonDocument();
-    command.putAll(originalBsonDocument);
+    BsonDocument command = originalBsonDocument;
+    if (!originalBsonDocument.getClass().equals(BsonDocument.class)) {
+      // Create a mutable copy by constructing a new BsonDocument and copying all entries
+      // This handles both regular BsonDocument and immutable RawBsonDocument/ByteBufBsonDocument
+      command = new BsonDocument();
+      command.putAll(originalBsonDocument);
+    }
 
     try {
       for (String commentKey : new String[] {"comment", "$comment"}) {

dd-java-agent/instrumentation/mongo/common/src/test/groovy/MongoCommentInjectorTest.groovy

@@ -5,6 +5,7 @@ import datadog.trace.instrumentation.mongo.MongoCommentInjector
 import org.bson.BsonDocument
 import org.bson.BsonString
 import org.bson.RawBsonDocument
+import org.bson.codecs.BsonDocumentCodec
 
 abstract class BaseMongoCommentInjectorTest extends InstrumentationSpecification {
   @Override
@@ -113,7 +114,7 @@ class MongoCommentInjectorServiceModeForkedTest extends BaseMongoCommentInjector
 
     // Create a RawBsonDocument (immutable) by encoding a regular BsonDocument
     def mutableDoc = new BsonDocument("find", new BsonString("collection"))
-    def rawDoc = new RawBsonDocument(mutableDoc, new org.bson.codecs.BsonDocumentCodec())
+    def rawDoc = new RawBsonDocument(mutableDoc, new BsonDocumentCodec())
     def dbmComment = "dddbs='test-service',dde='test'"
 
     // Verify RawBsonDocument.clone() returns immutable document
@@ -151,6 +152,6 @@ class MongoCommentInjectorServiceModeForkedTest extends BaseMongoCommentInjector
     result != null
     result.containsKey("comment")
     result.get("comment").asString().getValue() == dbmComment
-    !result.is(originalCommand)
+    result.is(originalCommand)
   }
 }