Module flexi_logger::writers

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Expand description

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.

Such log writers can be used in two ways:

  • You can influence to which output stream normal log messages will be written, i.e. those from normal log macro calls without explicit target specification. By default, the logs are sent to stderr. With one of the methods

    you can specify a different log target. See there for more details.

    Normal log calls will only be written to the chosen output channel if they match the current log specification.

  • You can register additional log writers under a target name with Logger::add_writer(), and address these log writers by specifying the target name in calls to the log macros.

    A log call with a target value that has the form {Name1,Name2,...}, i.e., a comma-separated list of target names, within braces, is not sent to the default logger, but to the loggers specified explicitly in the list. In such a list you can again specify the default logger with the target name _Default.

    These log calls will not be affected by the value of flexi_logger’s log specification; they will always be written, as you might want it for alerts or auditing.

    In the following example we define an alert writer, and a macro to facilitate using it (and avoid using the explicit target specification in the macro call), and show some example calls.

    use log::*;

use flexi_logger::{FileSpec,Logger};
use flexi_logger::writers::FileLogWriter;

// Configure a FileLogWriter for alert messages
pub fn alert_logger() -> Box<FileLogWriter> {
    Box::new(FileLogWriter::builder(
        FileSpec::default()
            .discriminant("Alert")
            .suffix("alerts")
        )
        .print_message()
        .try_build()
        .unwrap())
}

// Define a macro for writing messages to the alert log and to the normal log
#[macro_use]
mod macros {
    #[macro_export]
    macro_rules! alert_error {
        ($($arg:tt)*) => (
            error!(target: "{Alert,_Default}", $($arg)*);
        )
    }
}

fn main() {
    Logger::try_with_env_or_str("info")
        .expect("LogSpecification String has errors")
        .print_message()
        .log_to_file(FileSpec::default())
        .add_writer("Alert", alert_logger())
        .start()
        .unwrap_or_else(|e| panic!("Logger initialization failed with {}", e));


    // Explicitly send logs to different loggers
    error!(target : "{Alert}", "This is only an alert");
    error!(target : "{Alert,_Default}", "This is an alert and log message");

    // Nicer: use the explicit macro
    alert_error!("This is another alert and log message");

    // Standard log macros write only to the normal log
    error!("This is a normal error message");
    warn!("This is a warning");
    info!("This is an info message");
    debug!("This is a debug message - you will not see it");
    trace!("This is a trace message - you will not see it");
}

Structs

Traits

  • LogWriter
    Writes to a single log output stream.