Debugging

Logging

JVM

For JVM targets, the Kotlin SDK uses the slf4j logger. The build configuration can be updated to enable log output.

While any slf4j-compatible log library may be used, here is an example to enable log output from the SDK in JVM programs via Log4j2:

Gradle dependencies

Add the following dependencies via Gradle:

implementation("org.apache.logging.log4j:log4j-slf4j-impl:2.17.2")
implementation("org.apache.logging.log4j:log4j-core:2.17.2")
implementation("org.apache.logging.log4j:log4j-api:2.17.2")

Log4j2 configuration file

Create a file named log4j2.xml in your resources directory (e.g., <project-dir>/src/main/resources). Add the following XML configuration to the file:

<Configuration status="ERROR">
    <Appenders>
        <Console name="Out">
            <PatternLayout pattern="%d{YYYY-MM-dd HH:mm:ss} %-5p %c:%L - %encode{%m}{CRLF}%n"/>
        </Console>
    </Appenders>
    <Loggers>
        <Root level="info">
            <AppenderRef ref="Out"/>
        </Root>
    </Loggers>
</Configuration>

For more information on how to customize logging, see Log4j2's Configuration guide.

To view low-level request and response log output and the time of the log entry, change the appender level to trace:

<Root level="trace">

Unit Tests

To enable or customize logging in JVM unit tests, add a log4j2-test.xml file to the resources directory.

CRT Logs

JVM system properties for CRT related logs

Property	Description
aws.crt.log.level	Specify log level None, Fatal, Error, Warn, Info, Debug, Trace
aws.crt.log.destination	The destination to log to None, Stdout, Stderr, File. By default when level is not None stderr is used
aws.crt.log.filename	Redirect logs to a file

Error Metadata

The raw protocol response is usually available on exceptions if you need access to additional response details (headers, status code, etc).

try {
    ...
} catch(ex: AwsServiceException) {
    val httpResp = ex.sdkErrorMetadata.protocolResponse as? HttpResponse
    if (httpResp != null) {
        println(httpResp.headers)
        println(httpResp.body.readAll()?.decodeToString())
    }
}