Crate flexi_logger

A flexible and easy-to-use logger that writes logs to stderr and/or to files or other output streams.

To read the log specification from an environment variable and get the log written to stderr, start flexi_logger e.g. like this:

flexi_logger::Logger::try_with_env().unwrap().start().unwrap();

See

• The builder Logger for a full description of all configuration options,
• module code_examples for various concrete examples of flexi_logger initialization
• the module writers for the usage of additional log writers,
• and the README for how to get started.

There are configuration options to e.g.

• decide whether you want to write your logs to stderr or to a file,
• configure the path and the filenames of the log files,
• use file rotation,
• specify the line format for the log lines,
• apply a stateful filter before log lines are really written,
• define additional log output streams, e.g for alert or security messages,
• support changing the log specification while the program is running,

flexi_logger uses a similar syntax as env_logger for specifying which logs should really be written (but is more graceful with the syntax, and can provide error information).

By default, i.e. if feature colors is not switched off, the log lines that appear on your terminal are coloured. In case the chosen colors don’t fit to your terminal’s color theme, you can adapt the colors to improve readability. See the documentation of method Logger::set_palette for a description how this can be done.

Modules

code_examples

Here are some examples for the flexi_logger initialization.

error_info

Error codes of flexi_logger.

filter

This module contains two traits which allow adding a stateful filter using Logger::filter.

trctrc

Use flexi_logger functionality with tracing.

writers

Contains the trait LogWriter for extending flexi_logger with additional log writers, and two concrete implementations for writing to files (FileLogWriter) or to the syslog (SyslogWriter). You can also use your own implementations of LogWriter.

Structs

DeferredNow

Deferred timestamp creation.

FileSpec

Builder object for specifying the name and path of the log output file.

LogSpecBuilder

Builder for LogSpecification.

LogSpecification

Immutable struct that defines which loglines are to be written, based on the module, the log level, and the text.

Logger

The entry-point for using flexi_logger.

LoggerHandle

Shuts down the logger when its last instance is dropped (in case you use LoggerHandle::clone() you can have multiple instances), and allows reconfiguring the logger programmatically.

ModuleFilter

Defines which loglevel filter to use for the specified module.

Record

Re-exports from log crate The “payload” of a log message.

Enums

AdaptiveFormatatty

Can be used in Logger::adaptive_format_for_stderr and Logger::adaptive_format_for_stdout to use coloring only if the output goes to a tty.

Age

The age after which a log file rotation will be triggered, when Criterion::Age is chosen.

Cleanup

Defines the strategy for handling older log files.

Criterion

Criterion when to rotate the log file.

Duplicate

Used to control which messages are to be duplicated to stderr, when log_to_file() is used.

ErrorChannel

Enum for defining the output channel for flexi_logger’s own error messages.

FlexiLoggerError

Describes errors in the initialization of flexi_logger.

Level

Re-exports from log crate An enum representing the available verbosity levels of the logger.

LevelFilter

Re-exports from log crate An enum representing the available verbosity level filters of the logger.

Naming

The naming convention for rotated log files.

WriteMode

Describes whether the log output should be written synchronously or asynchronously, and if and how I/O should be buffered and flushed.

Constants

DEFAULT_BUFFER_CAPACITY

Default buffer capacity (8k), when buffering is used.

DEFAULT_FLUSH_INTERVAL

Default flush interval (1s), when flushing is used.

DEFAULT_MESSAGE_CAPAasync

Default capacity for the message buffers; a higher value reduces allocations when longer log lines are used.

DEFAULT_POOL_CAPAasync

Default size of the message pool; a higher value could further reduce allocations during log file rotation and cleanup.

TS_DASHES_BLANK_COLONS_DOT_BLANK

Time stamp format that is used by the provided format functions.

Functions

colored_default_formatcolors

A colored version of the logline-formatter default_format that produces log lines like
ERROR [my_prog::some_submodule] File not found

colored_detailed_formatcolors

A colored version of the logline-formatter detailed_format.

colored_opt_formatcolors

A colored version of the logline-formatter opt_format.

colored_with_threadcolors

A colored version of the logline-formatter with_thread.

default_format

A logline-formatter that produces log lines like
INFO [my_prog::some_submodule] Task successfully read from conf.json

detailed_format

A logline-formatter that produces log lines like
[2016-01-13 15:25:01.640870 +01:00] INFO [foo::bar] src/foo/bar.rs:26: Task successfully read from conf.json
i.e. with timestamp, module path and file location.

opt_format

A logline-formatter that produces log lines with timestamp and file location, like
[2016-01-13 15:25:01.640870 +01:00] INFO [src/foo/bar:26] Task successfully read from conf.json

stylecolors

Helper function that is used in the provided coloring format functions to apply colors based on the log level and the effective color palette.

with_thread

A logline-formatter that produces log lines like
[2016-01-13 15:25:01.640870 +01:00] T[taskreader] INFO [src/foo/bar:26] Task successfully read from conf.json
i.e. with timestamp, thread name and file location.

Type Definitions

FormatFunction

Function type for format functions.