Logging

Logview is an optional dependency of CIDER Log Mode. We recommend using it, since it is responsible for coloring the log events and it provides other useful features, such as syntax highlighting, filtering and more. It is used automatically when available and its use can be customized via cider-log-use-logview.

To use CIDER Log Mode, type C-c M-l l or M-x cider-log in any buffer that has a CIDER Sesman session attached to it. The first time you run the command, it will prompt you to select a log framework to use, and then attach a log appender to the root logger of the selected framework. After the log appender has been attached, the cider-log command will show a Transient menu, from which you can take further actions, like managing the log framework, appenders, consumers and events.

To view log events and stream them to your client, type es (Search log events) followed by s. This will open the *cider-log* buffer showing any log events captured thus far. It will also add a log consumer to this buffer, which receives newly-arriving log events.

CIDER Log Mode supports log frameworks that allow reconfiguration at run time. More specifically the framework should support attaching log appenders to loggers, in order to capture events.

At the moment the following log frameworks are supported:

There is some work in progress to support Log4j as well, but there are some difficulties with configuration changes made at runtime, which are wiped out by the Log4j2 reconfiguration mechanism.

In order to capture log events, a log appender needs to be attached to a logger of a framework. Once an appender is attached to a logger it captures the log events emitted by the framework in an in-memory atom. A log appender can be configured to have a certain size (default: 100000) and a threshold in percentage (default: 10). Log events are cleared from the appender when threshold (appender size plus threshold) is reached. Additionally an appender can be configured to only capture events that match a set of filters.

Log events can be streamed to a client by attaching a log consumer to an appender. Once a log consumer has been attached to an appender, it will receive events from the appender. Similar to log appenders, consumers can also be configured with a set of filters to only receive certain events.

Log events can be searched, streamed to a client or viewed in CIDER’s Inspector and Stacktrace Mode. When searching log events the user can specify a set of filters. Events that match the filters are shown in the *cider-log* buffer. Additionally a log consumer will be attached to the appender to receive log events matching the search criteria after the search command has been issued. The log appender will be removed automatically once a new search has been submitted or when the *cider-log* buffer gets killed.

Filters for log events can be attached to log appenders and consumers. They also take effect when searching events or streaming them to clients. If multiple filters are chosen they are combined using logical AND condition. The following filters are available: