Struct flexi_logger::Logger

pub struct Logger { /* fields omitted */ }

The standard entry-point for using flexi_logger.

Create a Logger with your desired (initial) loglevel-specification

• by specifying it programmatically as a String, using Logger::with_str(),
• or by expecting a String in the environment, using Logger::with_env(),
• or by combining both options, using Logger::with_env_or_str(),
• or by providing an explicitly built LogSpecification, using Logger::with(),

then use Logger's configuration methods, and finally call start(), or start_reconfigurable(), or start_with_specfile().

Examples

Use defaults only

If you initialize flexi_logger like this, it behaves like env_logger:

use flexi_logger::Logger;

Logger::with_env().start().unwrap();

Write to files, use a detailed log-line format that contains the module and line number

Here we configure flexi_logger to write log entries with time and location info into a log file in folder "log_files", and we provide the loglevel-specification programmatically, as String, but allow it to be overridden by the environment variable RUST_LOG:

use flexi_logger::{Logger,opt_format};

Logger::with_env_or_str("myprog=debug, mylib=warn")
            .log_to_file()
            .directory("log_files")
            .format(opt_format)
            .start()
            .unwrap_or_else(|e|{panic!("Logger initialization failed with {}",e)});

Methods

impl Logger

Simple methods for influencing the behavior of the Logger.

pub fn with(logspec: LogSpecification) -> Logger

Creates a Logger that you provide with an explicit LogSpecification. By default, logs are written with default_format to stderr.

pub fn with_str<S: AsRef<str>>(s: S) -> Logger

Creates a Logger that reads the LogSpecification from a String or &str. See LogSpecification for the syntax.

pub fn with_env() -> Logger

Creates a Logger that reads the LogSpecification from the environment variable RUST_LOG.

pub fn with_env_or_str<S: AsRef<str>>(s: S) -> Logger

Creates a Logger that reads the LogSpecification from the environment variable RUST_LOG, or derives it from the given String, if RUST_LOG is not set.

pub fn log_to_file(self) -> Logger

Makes the logger write all logs to a file, rather than to stderr.

The default pattern for the filename is '<program_name>_<date>_<time>.<suffix>', e.g. myprog_2015-07-08_10-44-11.log.

pub fn print_message(self) -> Logger

Makes the logger print an info message to stdout with the name of the logfile when a logfile is opened for writing.

pub fn duplicate_error(self) -> Logger

Makes the logger write all logged error messages additionally to stdout.

pub fn duplicate_info(self) -> Logger

Makes the logger write all logged error, warning, and info messages additionally to stdout.

pub fn format(self, format: FormatFunction) -> Logger

Makes the logger use the provided format function for the log entries, rather than formats::default_format.

You can either choose between some predefined variants, default_format, opt_format, detailed_format, with_thread, or you create and use your own format function with the signature fn(&Record) -> String.

pub fn directory<S: Into<String>>(self, directory: S) -> Logger

Specifies a folder for the log files.

This parameter only has an effect if log_to_file is set to true. If the specified folder does not exist, the initialization will fail. By default, the log files are created in the folder where the program was started.

pub fn suffix<S: Into<String>>(self, suffix: S) -> Logger

Specifies a suffix for the log files.

This parameter only has an effect if log_to_file is set to true.

pub fn suppress_timestamp(self) -> Logger

Makes the logger not include a timestamp into the names of the log files.

This option only has an effect if log_to_file is used, too.

pub fn rotate_over_size(self, rotate_over_size: usize) -> Logger

By default, the log file will grow indefinitely. With this option, when the log file reaches or exceeds the specified file size, the file will be closed and a new file will be opened. Also the filename pattern changes - instead of the timestamp, a serial number is included into the filename.

This option only has an effect if log_to_file is used, too.

pub fn discriminant<S: Into<String>>(self, discriminant: S) -> Logger

The specified String is added to the log file name after the program name.

This option only has an effect if log_to_file is used, too.

pub fn create_symlink<S: Into<String>>(self, symlink: S) -> Logger

The specified String will be used on linux systems to create in the current folder a symbolic link to the current log file.

This option only has an effect if log_to_file is used, too.

pub fn add_writer<S: Into<String>>(
    self,
    name: S,
    writer: Box<LogWriter>
) -> Logger

Registers a LogWriter implementation under the given target name.

The target name should not start with an underscore.

See the module documentation of writers.

pub fn start(self) -> Result<(), FlexiLoggerError>

Consumes the Logger object and initializes the flexi_logger. If started this way, the logger cannot be influenced anymore while the program is running.

pub fn start_reconfigurable(
    self
) -> Result<ReconfigurationHandle, FlexiLoggerError>

Consumes the Logger object and initializes the flexi_logger in a way that subsequently the log specification can be exchanged dynamically.

The resulting logger is still fast, but measurable slower for those log-calls (trace!() etc) that are on a deeper level than the deepest level in the LogSpecification. This is because the Log crate has an optimization for returning very fast from deep-level log calls, but the deepest level needs be given at initialization and cannot be updated later.

Here is the output from a benchmark test, runnning on a windows laptop:

 1  PS C:\projects\flexi_logger> cargo bench --bench bench_standard -- --nocapture
 2      Finished release [optimized] target(s) in 0.4 secs
 3       Running target\release\deps\bench_standard-20539c2be6d4f2e0.exe
 4
 5  running 4 tests
 6  test b10_no_logger_active  ... bench:         118 ns/iter (+/- 19)
 7  test b20_initialize_logger ... bench:           0 ns/iter (+/- 0)
 8  test b30_relevant_logs     ... bench:     291,436 ns/iter (+/- 44,658)
 9  test b40_suppressed_logs   ... bench:         123 ns/iter (+/- 5)
10
11  test result: ok. 0 passed; 0 failed; 0 ignored; 4 measured; 0 filtered out
12
13  PS C:\projects\flexi_logger> cargo bench --bench bench_reconfigurable -- --nocapture
14      Finished release [optimized] target(s) in 0.4 secs
15       Running target\release\deps\bench_reconfigurable-2e292a8d5c887d0d.exe
16
17  running 4 tests
18  test b10_no_logger_active  ... bench:         130 ns/iter (+/- 37)
19  test b20_initialize_logger ... bench:           0 ns/iter (+/- 0)
20  test b30_relevant_logs     ... bench:     301,092 ns/iter (+/- 87,452)
21  test b40_suppressed_logs   ... bench:       3,482 ns/iter (+/- 339)
22
23  test result: ok. 0 passed; 0 failed; 0 ignored; 4 measured; 0 filtered out

It shows that logging is fastest when no logger is active (lines 6 and 18). And it is just as fast when the above-mentioned optimization kicks in (line 9).

Logging has measurable costs when logs are really written (line 8 and 20), independent of the reconfigurability feature of the flexi_logger.

The measurable, but still in most cases not important, price for reconfigurability can be seen by comparing lines 9 and 21.

impl Logger

Alternative set of methods to control the behavior of the Logger. Use these methods when you want to control the settings flexibly, e.g. with commandline arguments via docopts or clap.

pub fn o_log_to_file(self, log_to_file: bool) -> Logger

With true, makes the logger write all logs to a file, otherwise to stderr.

pub fn o_print_message(self, print_message: bool) -> Logger

With true, makes the logger print an info message to stdout, each time when a new file is used for log-output.

pub fn o_duplicate_error(self, duplicate_error: bool) -> Logger

With true, makes the logger write all logged error messages additionally to stdout.

pub fn o_duplicate_info(self, duplicate_info: bool) -> Logger

With true, makes the logger write all logged error, warning, and info messages additionally to stdout.

pub fn o_directory<S: Into<String>>(self, directory: Option<S>) -> Logger

Specifies a folder for the log files.

This parameter only has an effect if log_to_file is set to true. If the specified folder does not exist, the initialization will fail. With None, the log files are created in the folder where the program was started.

pub fn o_timestamp(self, timestamp: bool) -> Logger

With true, makes the logger include a timestamp into the names of the log files. (log_to_file must be chosen, too).

pub fn o_rotate_over_size(self, rotate_over_size: Option<usize>) -> Logger

This option only has an effect if log_to_file is used, too.

By default, and with None, the log file will grow indefinitely. If a size is set, when the log file reaches or exceeds the specified size, the file will be closed and a new file will be opened. Also the filename pattern changes - instead of the timestamp a serial number is included into the filename.

pub fn o_discriminant<S: Into<String>>(self, discriminant: Option<S>) -> Logger

This option only has an effect if log_to_file is used, too.

The specified String is added to the log file name.

pub fn o_create_symlink<S: Into<String>>(self, symlink: Option<S>) -> Logger

This option only has an effect if log_to_file is used, too.

If a String is specified, it will be used on linux systems to create in the current folder a symbolic link with this name to the current log file.

Trait Implementations