mdc-util

A tiny clojure library wrapping the MDC functionality in slf4j.

Usage

Provides two simple macros to set up a logging context that will be used for all nested logging calls. The logging context is expected to be a Map<String,String>.

(with-context {"key-a" "value-a"
               "key-b" "value-b"}
			   ...
			   (log/info "hello with values")
			   ...)

This will make the map available for downstream processing (eg in the case of logstash-logback-encoder add the map to the emitted JSON map, see here: https://github.com/logstash/logstash-logback-encoder#loggingevent_mdc).

For other types of appenders, configuration is required to integrate selected values into log messages (see logback documentation here: http://logback.qos.ch/manual/mdc.html).

Bonus feature: with-safe-context

This enables proper shadowing of context members, ie nested calls with different values assigned to key-a in each nesting are scoped as would be expected with a lexical binding. The unsafe version clears up all keys it has set, potentially removing keys that were present in an outer context.

The drawback of with-safe-context is that currently a backup of the current context is being held and recovered at the end of the form. These maps, unfortunately, have to be copied every time, which might result in a quite noticable performance overhead in some scenarios.

Bonus feature: with-weak-context

This will only add the specified keys if they're not already present in the MDC (ie shadowing properties are reversed) - cleans up keys that were set.