flexi_logger 0.20.1

An easy-to-configure and flexible logger that writes logs to stderr or stdout and/or to files. It allows custom logline formats, and it allows changing the log specification at runtime. It also allows defining additional log streams, e.g. for alert or security messages.
Documentation 
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use crate::{DeferredNow, FormatFunction};
use log::Record;

/// Writes to a single log output stream.
///
/// Boxed instances of `LogWriter` can be used as additional log targets
/// (see [writers](crate::writers) for more details).
pub trait LogWriter: Sync + Send {
    /// Writes out a log line.
    ///
    /// # Errors
    ///
    /// [`std::io::Error`]
    fn write(&self, now: &mut DeferredNow, record: &Record) -> std::io::Result<()>;

    /// Flushes any buffered records.
    ///
    /// # Errors
    ///
    /// [`std::io::Error`]
    fn flush(&self) -> std::io::Result<()>;

    /// Provides the maximum log level that is to be written.
    fn max_log_level(&self) -> log::LevelFilter {
        log::LevelFilter::Trace
    }

    /// Sets the format function.
    ///
    /// Defaults to [`default_format`](crate::default_format),
    /// but can be changed with a call to
    /// [`Logger::format_for_writer`](crate::Logger::format_for_writer).
    ///
    /// The default implementation is a no-op.
    fn format(&mut self, format: FormatFunction) {
        let _ = format;
    }

    /// Cleanup open resources, if necessary.
    fn shutdown(&self) {}

    /// Takes a vec with three patterns per line that represent the log out,
    /// compares the written log with the expected lines,
    /// and asserts that both are in sync.
    ///
    /// This function is not meant for productive code, only for tests.
    #[doc(hidden)]
    fn validate_logs(&self, _expected: &[(&'static str, &'static str, &'static str)]) {
        unimplemented!("only useful for tests");
    }
}