Crate log4rs [−] [src]

log4rs is a highly configurable logging framework modeled after Java's Logback and log4j libraries.

Architecture

The basic units of configuration are appenders, encoders, filters, and loggers.

Appenders

An appender takes a log record and logs it somewhere, for example, to a file, the console, or the syslog.

Encoders

An encoder is responsible for taking a log record, transforming it into the appropriate output format, and writing it out. An appender will normally use an encoder internally.

Filters

Filters are associated with appenders and, like the name would suggest, filter log events coming into that appender.

Loggers

A log event is targeted at a specific logger, which are identified by string names. The logging macros built in to the log crate set the logger of a log event to the one identified by the module containing the invocation location.

Loggers form a heirarchy: logger names are divided into components by "::". One logger is the ancestor of another if the first logger's component list is a prefix of the second logger's component list.

Loggers are associated with a maximum log level. Log events for that logger with a level above the maximum will be ignored. The maximum log level for any logger can be configured manually; if it is not, the level will be inherited from the logger's parent.

Loggers are also associated with a set of appenders. Appenders can be associated directly with a logger. In addition, the appenders of the logger's parent will be associated with the logger unless the logger has its additivity set to false. Log events sent to the logger that are not filtered out by the logger's maximum log level will be sent to all associated appenders.

The "root" logger is the ancestor of all other loggers. Since it has no ancestors, its additivity cannot be configured.

Configuration

log4rs can be configured programmatically by using the builders in the config module to construct a log4rs Config object, which can be passed to the init_config function.

The more common configuration method, however, is via a separate config file. The init_file function takes the path to a config file as well as a Deserializers object which is responsible for instantiating the various objects specified by the config file. The file module documentation covers the exact configuration syntax, but an example in the YAML format is provided below.

Examples

# Scan this file for changes every 30 seconds
refresh_rate: 30 seconds

appenders:
  # An appender named "stdout" that writes to stdout
  stdout:
    kind: console

  # An appender named "requests" that writes to a file with a custom pattern encoder
  requests:
    kind: file
    path: "log/requests.log"
    encoder:
      pattern: "{d} - {m}{n}"

# Set the default logging level to "warn" and attach the "stdout" appender to the root
root:
  level: warn
  appenders:
    - stdout

loggers:
  # Raise the maximum log level for events sent to the "app::backend::db" logger to "info"
  app::backend::db:
    level: info

  # Route log events sent to the "app::requests" logger to the "requests" appender,
  # and *not* the normal appenders installed at the root
  app::requests:
    level: info
    appenders:
      - requests
    additive: false

Modules

append

Appenders
config

log4rs configuration
encode

Encoders
file

Support for log4rs configuration from files.
filter

Filters

Structs

Handle

A handle to the active logger.

Enums

Error

An error initializing the logging framework from a file.

Functions

init_config

Initializes the global logger as a log4rs logger with the provided config.
init_file

Initializes the global logger as a log4rs logger configured via a file.