jitsi-metaconfig

jitsi-metaconfig is not a config library. jitsi-metaconfig helps solve the problems around the evolution of configuration properties, such as:

1. Property names changing
2. Changing property file locations or formats
3. The value type of a property key changing (e.g. it was a number of milliseconds but is now a Duration)

jitsi-metaconfig allows defining properties in code in such a way that names, locations and types can all be changed while still supporting the old format so deployments which use old keys/types/files won't break. It also supports marking old properties as deprecated to ease the transition to removing support for them.

Example config properties:

class Foo {
    // A simple property with just a key and a source
    val enabled: Boolean by config("app.enabled".from(myConfigSource))

    // Optional property
    val optionalParam: String? by optionalconfig("app.client.optional-param".from(myConfigSource))

    // Convert the type (retrieve as a Long, convert to a Duration)
    val interval: Duration by config {
        "app.interval-ms".from(myConfigSource).convertFrom<Long>(Duration::ofMillis)
    }

    // Transform the value (invert the retrieved boolean value)
    val enabled: Boolean by config {
        "app.disabled".from(myConfigSource).andTransformBy { !it }
    }

    // Search for value in a legacy config file and then the new one
    val enabled: Boolean by config {
        "old.path.app.enabled".from(legacyConfigSource)
        "new.path.app.enabled".from(newConfigSource)
    }

    // Search for value in a legacy config file and then the new one, mark the old one as deprecated
    val enabled: Boolean by config {
        "old.path.app.enabled".from(legacyConfigSource).softDeprecated("use 'new.path.app.enabled' in new config source")
        "new.path.app.enabled".from(newConfigSource)
    }

    // Use the result of a lambda as a value
    val port: Int by config {
        "path.to.port".from(newConfigSource)
        "default" { 8080 }
    }

    // Only allow access to port if 'enabled' is true (throws an exception otherwise)
    val port: Int by config {
        onlyIf("Server is enabled", ::enabled) {
            "path.to.port".from(newConfigSource)
        }
    }
}

Read more:

• Implementing a ConfigSource
• Using property delegates to define properties in code
• SupplierTypes
• Debugging