[JIRA] (SLF4J-397) Bridge can still call underlying logging system with a null message.

7 Mar 2017

      Joern Huxhorn created SLF4J-397:
-----------------------------------

             Summary: Bridge can still call underlying logging system with a null message.
                 Key: SLF4J-397
                 URL: https://jira.qos.ch/browse/SLF4J-397
             Project: SLF4J
          Issue Type: Bug
          Components: jul-to-slf4j
    Affects Versions: 1.7.24
         Environment: any
            Reporter: Joern Huxhorn
            Assignee: SLF4J developers list

I just found a bug while preparing SLF4J-396.

{code:java}
private String getMessageI18N(LogRecord record) {
    String message = record.getMessage();

    if (message == null) {
        return null;
    }
    // [..]
}
{code}

should be changed to
{code:java}
private String getMessageI18N(LogRecord record) {
    String message = record.getMessage(); // can be null!
    // this is a check to avoid calling the underlying logging system
    // with a null message. While it is legitimate to invoke j.u.l. with
    // a null message, other logging frameworks do not support this.
    // see also http://jira.qos.ch/browse/SLF4J-99

    if (message == null) {
        return "";
    }
    // [..]
}
{code}

and

{code:java}
public void publish(LogRecord record) {
    // Silently ignore null records.
    if (record == null) {
        return;
    }

    Logger slf4jLogger = getSLF4JLogger(record);
    String message = record.getMessage(); // can be null!
    // this is a check to avoid calling the underlying logging system
    // with a null message. While it is legitimate to invoke j.u.l. with
    // a null message, other logging frameworks do not support this.
    // see also http://jira.qos.ch/browse/SLF4J-99
    if (message == null) {
        message = "";
    }
    if (slf4jLogger instanceof LocationAwareLogger) {
        callLocationAwareLogger((LocationAwareLogger) slf4jLogger, record);
    } else {
        callPlainSLF4JLogger(slf4jLogger, record);
    }
}
{code}

should be changed to

{code:java}
public void publish(LogRecord record) {
    // Silently ignore null records.
    if (record == null) {
        return;
    }

    Logger slf4jLogger = getSLF4JLogger(record);
    if (slf4jLogger instanceof LocationAwareLogger) {
        callLocationAwareLogger((LocationAwareLogger) slf4jLogger, record);
    } else {
        callPlainSLF4JLogger(slf4jLogger, record);
    }
}
{code}

The local {{message}} variable was assigned but never used. I suspect some refactoring sneakily reintroduced the problematic case where the underlying logging system is called with a {{null}} message.
{{getMessageI18N}} is called by both {{callLocationAwareLogger}} and {{callPlainSLF4JLogger}} so this fix should be fine.

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