Struct fern::Output

pub struct Output(_);

Configuration for a logger output.

Methods

impl Output

pub fn file<T: Into<Cow<'static, str>>>(file: File, line_sep: T) -> Self

Returns a file logger using a custom separator.

If the default separator of \n is acceptable, an fs::File instance can be passed into Dispatch::chain directly.

fern::Dispatch::new()
    .chain(std::fs::File::create("log")?)

fern::Dispatch::new()
    .chain(fern::log_file("log")?)

Example usage (using fern::log_file):

fern::Dispatch::new()
    .chain(fern::Output::file(fern::log_file("log")?, "\r\n"))

pub fn writer<T: Into<Cow<'static, str>>>(
    writer: Box<dyn Write + Send>,
    line_sep: T
) -> Self

Returns a logger using arbitrary write object and custom separator.

If the default separator of \n is acceptable, an Box<Write + Send> instance can be passed into Dispatch::chain directly.

// Anything implementing 'Write' works.
let mut writer = std::io::Cursor::new(Vec::<u8>::new());

fern::Dispatch::new()
    // as long as we explicitly cast into a type-erased Box
    .chain(Box::new(writer) as Box<std::io::Write + Send>)

Example usage:

let writer = Box::new(std::io::Cursor::new(Vec::<u8>::new()));

fern::Dispatch::new()
    .chain(fern::Output::writer(writer, "\r\n"))

pub fn stdout<T: Into<Cow<'static, str>>>(line_sep: T) -> Self

Returns an stdout logger using a custom separator.

If the default separator of \n is acceptable, an io::Stdout instance can be passed into Dispatch::chain() directly.

fern::Dispatch::new()
    .chain(std::io::stdout())

Example usage:

fern::Dispatch::new()
    // some unix tools use null bytes as message terminators so
    // newlines in messages can be treated differently.
    .chain(fern::Output::stdout("\0"))

pub fn stderr<T: Into<Cow<'static, str>>>(line_sep: T) -> Self

Returns an stderr logger using a custom separator.

If the default separator of \n is acceptable, an io::Stderr instance can be passed into Dispatch::chain() directly.

fern::Dispatch::new()
    .chain(std::io::stderr())

Example usage:

fern::Dispatch::new()
    .chain(fern::Output::stderr("\n\n\n"))

pub fn sender<T: Into<Cow<'static, str>>>(
    sender: Sender<String>,
    line_sep: T
) -> Self

Returns a mpsc::Sender logger using a custom separator.

If the default separator of \n is acceptable, an mpsc::Sender<String> instance can be passed into Dispatch:: chain() directly.

Each log message will be suffixed with the separator, then sent as a single String to the given sender.

use std::sync::mpsc::channel;

let (tx, rx) = channel();
fern::Dispatch::new()
    .chain(tx)

pub fn syslog_5424<F>(
    logger: Logger<LoggerBackend, (i32, HashMap<String, HashMap<String, String>>, String), Formatter5424>,
    transform: F
) -> Self where
    F: Fn(&Record) -> (i32, HashMap<String, HashMap<String, String>>, String) + Sync + Send + 'static, 

Returns a logger which logs into an RFC5424 syslog.

This method takes an additional transform method to turn the log data into RFC5424 data.

I've honestly got no clue what the expected keys and values are for this kind of logging, so I'm just going to link the rfc instead.

If you're an expert on syslog logging and would like to contribute an example to put here, it would be gladly accepted!

This requires the "syslog-4" feature.

pub fn call<F>(func: F) -> Self where
    F: Fn(&Record) + Sync + Send + 'static, 

Returns a logger which simply calls the given function with each message.

The function will be called inline in the thread the log occurs on.

Example usage:

fern::Dispatch::new()
    .chain(fern::Output::call(|record| {
        // this is mundane, but you can do anything here.
        println!("{}", record.args());
    }))

Trait Implementations

impl From<Dispatch> for Output

fn from(log: Dispatch) -> Self

Creates an output logger forwarding all messages to the dispatch.

impl From<Box<dyn Log + 'static>> for Output

fn from(log: Box<dyn Log>) -> Self

Creates an output logger forwarding all messages to the custom logger.

impl From<&'static (dyn Log + 'static)> for Output

fn from(log: &'static dyn Log) -> Self

Creates an output logger forwarding all messages to the custom logger.

impl From<File> for Output

fn from(file: File) -> Self

Creates an output logger which writes all messages to the file with \n as the separator.

File writes are buffered and flushed once per log record.

impl From<Box<dyn Write + 'static + Send>> for Output

fn from(writer: Box<dyn Write + Send>) -> Self

Creates an output logger which writes all messages to the writer with \n as the separator.

This does no buffering and it is up to the writer to do buffering as needed (eg. wrap it in BufWriter). However, flush is called after each log record.

impl From<Stdout> for Output

fn from(stream: Stdout) -> Self

Creates an output logger which writes all messages to stdout with the given handle and \n as the separator.

impl From<Stderr> for Output

fn from(stream: Stderr) -> Self

Creates an output logger which writes all messages to stderr with the given handle and \n as the separator.

impl From<Sender<String>> for Output

fn from(stream: Sender<String>) -> Self

Creates an output logger which writes all messages to the given mpsc::Sender with '\n' as the separator.

All messages sent to the mpsc channel are suffixed with '\n'.

impl From<Logger> for Output

fn from(log: Logger) -> Self

Creates an output logger which writes all messages to the given syslog output.

Log levels are translated trace => debug, debug => debug, info => informational, warn => warning, and error => error.

This requires the "syslog-3" feature.

impl From<Box<Logger>> for Output

fn from(log: Box<Logger>) -> Self

Creates an output logger which writes all messages to the given syslog output.

Log levels are translated trace => debug, debug => debug, info => informational, warn => warning, and error => error.

Note that while this takes a Box for convenience (syslog methods return Boxes), it will be immediately unboxed upon storage in the configuration structure. This will create a configuration identical to that created by passing a raw syslog::Logger.

This requires the "syslog-3" feature.

impl From<Logger<LoggerBackend, String, Formatter3164>> for Output

fn from(log: Logger<LoggerBackend, String, Formatter3164>) -> Self

Creates an output logger which writes all messages to the given syslog.

Log levels are translated trace => debug, debug => debug, info => informational, warn => warning, and error => error.

Note that due to https://github.com/Geal/rust-syslog/issues/41, logging to this backend requires one allocation per log call.

This is for RFC 3164 loggers. To use an RFC 5424 logger, use the Output::syslog_5424 helper method.

This requires the "syslog-4" feature.

impl From<Panic> for Output

fn from(_: Panic) -> Self

Creates an output logger which will panic with message text for all messages.

impl Debug for Output

fn fmt(&self, f: &mut Formatter) -> Result

Formats the value using the given formatter.