code: protected void writeMessagePrologue(final BsonOutput bsonOutput) {
          bsonOutput.writeInt32(0); // length: will set this later
          bsonOutput.writeInt32(id);
          bsonOutput.writeInt32(0); // response to
          bsonOutput.writeInt32(opCode.getValue());
      }
docs: Writes the message prologue to the given output.
  
  @param bsonOutput the output