Struct Builder 

pub struct Builder { /* private fields */ }

A builder for configuring RollingFileAppenders.

Implementations

impl Builder

pub const fn new() -> Builder

Returns a new Builder for configuring a RollingFileAppender, with the default parameters.

Default Values

The default values for the builder are:

Parameter	Default Value	Notes
rotation	Rotation::NEVER	By default, log files will never be rotated.
filename_prefix	""	By default, log file names will not have a prefix.
filename_suffix	""	By default, log file names will not have a suffix.
max_log_files	None	By default, there is no limit for maximum log file count.

pub fn rotation(self, rotation: Rotation) -> Builder

Sets the rotation strategy for log files.

By default, this is Rotation::NEVER.

Examples

use tracing_appender::rolling::{Rotation, RollingFileAppender};

let appender = RollingFileAppender::builder()
    .rotation(Rotation::HOURLY) // rotate log files once every hour
    // ...
    .build("/var/log")
    .expect("failed to initialize rolling file appender");

pub fn filename_prefix(self, prefix: impl Into<String>) -> Builder

Sets the prefix for log filenames. The prefix is output before the timestamp in the file name, and if it is non-empty, it is followed by a dot (.).

By default, log files do not have a prefix.

Examples

Setting a prefix:

use tracing_appender::rolling::RollingFileAppender;

let appender = RollingFileAppender::builder()
    .filename_prefix("myapp.log") // log files will have names like "myapp.log.2019-01-01"
    // ...
    .build("/var/log")
    .expect("failed to initialize rolling file appender");

No prefix:

use tracing_appender::rolling::RollingFileAppender;

let appender = RollingFileAppender::builder()
    .filename_prefix("") // log files will have names like "2019-01-01"
    // ...
    .build("/var/log")
    .expect("failed to initialize rolling file appender");

pub fn filename_suffix(self, suffix: impl Into<String>) -> Builder

Sets the suffix for log filenames. The suffix is output after the timestamp in the file name, and if it is non-empty, it is preceded by a dot (.).

By default, log files do not have a suffix.

Examples

Setting a suffix:

use tracing_appender::rolling::RollingFileAppender;

let appender = RollingFileAppender::builder()
    .filename_suffix("myapp.log") // log files will have names like "2019-01-01.myapp.log"
    // ...
    .build("/var/log")
    .expect("failed to initialize rolling file appender");

No suffix:

use tracing_appender::rolling::RollingFileAppender;

let appender = RollingFileAppender::builder()
    .filename_suffix("") // log files will have names like "2019-01-01"
    // ...
    .build("/var/log")
    .expect("failed to initialize rolling file appender");

pub fn max_log_files(self, n: usize) -> Builder

Keeps the last n log files on disk.

When constructing a RollingFileAppender or starting a new log file, the appender will delete the oldest matching log files until at most n files remain. The exact number of retained files can sometimes dip below the maximum, so if you need to retain m log files, specify a max of m + 1.

If 0 is supplied, the RollingAppender will not remove any files.

Files are considered candidates for deletion based on the following criteria:

• The file must not be a directory or symbolic link.
• If the appender is configured with a filename_prefix, the file name must start with that prefix.
• If the appender is configured with a filename_suffix, the file name must end with that suffix.
• If the appender has neither a filename prefix nor a suffix, then the file name must parse as a valid date based on the appender’s date format.

Files matching these criteria may be deleted if the maximum number of log files in the directory has been reached.

Examples

use tracing_appender::rolling::RollingFileAppender;

let appender = RollingFileAppender::builder()
    .max_log_files(5) // only the most recent 5 log files will be kept
    // ...
    .build("/var/log")
    .expect("failed to initialize rolling file appender");

pub fn build( &self, directory: impl AsRef<Path>, ) -> Result<RollingFileAppender, InitError>

Builds a new RollingFileAppender with the configured parameters, emitting log files to the provided directory.

Unlike RollingFileAppender::new, this returns a Result rather than panicking when the appender cannot be initialized.

Examples

use tracing_appender::rolling::{Rotation, RollingFileAppender};

let appender = RollingFileAppender::builder()
    .rotation(Rotation::DAILY) // rotate log files once per day
    .filename_prefix("myapp.log") // log files will have names like "myapp.log.2019-01-01"
    .build("/var/log/myapp") // write log files to the '/var/log/myapp' directory
    .expect("failed to initialize rolling file appender");

This is equivalent to

let appender = tracing_appender::rolling::daily("myapp.log", "/var/log/myapp");

Trait Implementations

impl Debug for Builder

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.

impl Default for Builder

fn default() -> Builder

Returns the “default value” for a type.