[jira] [Created] (LOG4J2-2118) MutableLogEvent does not retain the Message format string

[Zack Slayton (JIRA)]

Zack Slayton created LOG4J2-2118:
------------------------------------

             Summary: MutableLogEvent does not retain the Message format string
                 Key: LOG4J2-2118
                 URL: https://issues.apache.org/jira/browse/LOG4J2-2118
             Project: Log4j 2
          Issue Type: Bug
          Components: Layouts
    Affects Versions: 2.8
         Environment: Mac OS X 10.11.6
Java 1.8.0_141
            Reporter: Zack Slayton


I'm attempting to create a custom binary Layout that stores the provided format 
string separate from the parameters rather than eagerly formatting them all 
into a single piece of text. However, when I went to implement 
`Layout::toByteArray`, I discovered that the `Message::getFormat` method always 
returns null.

{code:java}
import org.apache.logging.log4j.LogManager;
import org.apache.logging.log4j.Logger;
import org.apache.logging.log4j.core.LogEvent;
import org.apache.logging.log4j.core.config.plugins.Plugin;
import org.apache.logging.log4j.core.config.plugins.PluginFactory;
import org.apache.logging.log4j.core.layout.AbstractLayout;

import java.io.Serializable;
import java.util.Arrays;

@Plugin(name = "MyLayout", category = "Core", elementType = "layout", 
printObject = true)
public class MyLayout extends AbstractLayout {

    public MyLayout() {
        super(null, null, null);
    }

    @PluginFactory
    public static MyLayout createLayout(){
        return new MyLayout();
    }

    public static void main(String[] args) {
        Logger log = LogManager.getLogger(MyLayout.class);
        log.info("Here's a thing: {}. And another: {}", 75, "walrus");
    }

    @Override
    public byte[] toByteArray(LogEvent event) {
        System.out.println("Format: " + event.getMessage().getFormat());
        System.out.println("Parameters: " + 
Arrays.toString(event.getMessage().getParameters()));
        return new byte[0];
    }

    @Override
    public Serializable toSerializable(LogEvent event) {
        return null;
    }

    @Override
    public String getContentType() {
        return null;
    }

    @Override
    public byte[] getFooter() {
        return new byte[0];
    }

    @Override
    public byte[] getHeader() {
        return new byte[0];
    }
}
{code}

If I run `main` (with an extra `PatternLayout`+`Console` appender in my 
config), I see the following output:

{code}
17:55:28.524 [main] INFO  com.example.logging.plugins.MyLayout - Here's a 
thing: 75. And another: walrus
Format: null
Parameters: [75, walrus]
{code}

I had expected to be able to see the format string and the array of parameters, 
but instead I can only see the parameters. The format string is always null.

This appears to be due to the implementation of `MutableLogEvent::setMessage` 
highlighted [in LOG4J2-1510|https://issues.apache.org/jira/browse/LOG4J2-1510]. 
Because the messages are reusable, they appear to be eagerly formatted and the 
format string itself is discarded. The `getFormat` method is hardcoded to 
return `null`.

Is this by design? If so, what is the prescribed approach to getting the format 
string in my layout? (Preferably one that does not disable the performance 
optimizations offered by enabling threadlocals.)

Thanks!



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