i am experimenting with KLogging a bit is there an...

# kotlin-logging

[Nikky]

i am experimenting with KLogging a bit is there any way to get filename + linenumber in the console/stdout output ?
i want to make use of the fact that idea converts .(Main.kt:23) into a clickable link

i eneded up making a custom renderer and ${level}F overloads that throws and catches to get the stacktrace.. its not clean.. but timing measurements show it only costs 100us on average.. good enough for me

[Michael Strasser]

Hey @Nikky thanks for trying Klogging!

I have not implemented filename + line number but will look at it if there is demand. Do you have some code you can share?

—Michael (creator of Klogging)

[Nikky]

i use this function to grab the info fro mthe stacktrace:

fun getLocation(): String? {
    if (!scanStacktrace) return null
    return try {
        throw Exception()
    } catch (e: Exception) {
        val firstElement = e.stackTrace.first()
        e.stackTrace.firstOrNull { element ->
            element.fileName != firstElement.fileName
                    && element.lineNumber > 0
                    && element.className.startsWith("moe.nikky.")
        }?.let { element ->
            "${element.fileName}:${element.lineNumber}"
        }.also {
            if (it == null) e.printStackTrace()
        }
    }
}

[Nikky]

would probably be better to just add a callsite: StackTraceElement? to LogEvent
and a flag in the log configuration whether to grab the stacktraces or not.. creating sand catching stacktraces is (relatively) expensive

currently i store in in the log context and remove it before printing the items, not so clean.. but i did not want to fork Klogging (yet)

val CUSTOM_RENDERER: RenderString = { e: LogEvent ->
    val loggerOrFile = e.items["file"]?.let { ".($it)" } ?: e.logger
    val time = e.timestamp.localString.padEnd(29, '0')
    val message = "$time ${e.level} $loggerOrFile : ${e.evalTemplate()}"
    val cleanedItems = e.items - "file"
    val maybeItems = if (cleanedItems.isNotEmpty()) " : $cleanedItems" else ""
    val maybeStackTrace = if (e.stackTrace != null) "\n${e.stackTrace}" else ""
    message + maybeItems + maybeStackTrace
}

[charleskorn]

Something slightly less expensive and a bit more intention-revealing than throwing an exception to get the stack trace would be using Thread.getStackTrace() (this will only work on the JVM though)

[Oliver.O]

log4j and logback both use the stack trace of a newly created Throwable() in combination with the fully qualified caller class name for location information:
• log4j source
• logback source
As logback is supposedly better at figuring out line numbers, it might be worth a look.

Browsers offer a similar capability via the Error() object: https://stackoverflow.com/a/2343382/2529022. However, as such stack traces normally refer to minified code they will require further decoding via source maps.

[Oliver.O]

For performant logging with line numbers, a compiler plugin would be ideal, which would also probably be the only option available for native platforms.

[Nikky]

i think i'd rather wait for those to be documented, although i guess it might help with a lot of other things that are limiting on native and js

[Nikky]

also.. thanks for the hint about thread.getStrackTrace()

fun getLocation(): String? {
    if (!scanStacktrace) return null
    val stackTrace = Thread.currentThread().stackTrace.drop(1)
    val firstElement = stackTrace.first()
    return stackTrace.firstOrNull { element ->
        element.fileName != firstElement.fileName
                && element.lineNumber > 0
                && element.className.startsWith("moe.nikky.")
    }?.let { element ->
        "${element.fileName}:${element.lineNumber}"
    }.also {
        if (it == null) System.err.println(stackTrace.joinToString("\n  at "))
    }
}

this code seems to be more performant

[Oliver.O]

I'd also be hesitant with plugin development, though I feel it's good to know that the option is on the table. 🙂