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#![deny(missing_docs)] #![doc(html_root_url = "https://dabo.guru/rust/fern/")] //! Efficient, configurable logging in Rust. //! //! With Fern, you can: //! //! - Configure logging at runtime; make changes based off of user arguments or configuration //! - Format log records without allocating intermediate results //! - Output to stdout, stderr, log files and custom destinations //! - Apply a blanket level filter and per-crate/per-module overrides //! - Intuitively apply filters and formats to groups of loggers via builder chaining //! - Log using the standard `log` crate macros //! //! # Depending on `fern` //! //! First, depend on the `fern` and `log` crates in your project's `Cargo.toml`: //! //! ```toml //! [dependencies] //! log = "0.3" //! fern = "0.4" //! ``` //! //! Then declare both in your program's `main.rs` or `lib.rs`: //! //! ``` //! #[macro_use] //! extern crate log; //! extern crate fern; //! # fn main() {} //! ``` //! //! # Example setup: //! //! In fern 0.4, creating, configuring, and establishing a logger as the global logger are all merged //! into builder methods on the `Dispatch` struct. //! //! Here's an example logger which formats messages, limits to Debug level, and puts everything into both stdout and //! an output.log file. //! //! ```no_run //! extern crate chrono; //! # extern crate fern; //! # #[macro_use] //! # extern crate log; //! //! # fn setup_logger() -> Result<(), fern::InitError> { //! fern::Dispatch::new() //! .format(|out, message, record| { //! out.finish(format_args!( //! "{}[{}][{}] {}", //! chrono::Local::now().format("[%Y-%m-%d][%H:%M:%S]"), //! record.target(), //! record.level(), //! message //! )) //! }) //! .level(log::LogLevelFilter::Debug) //! .chain(std::io::stdout()) //! .chain(fern::log_file("output.log")?) //! .apply()?; //! # Ok(()) //! # } //! # fn main() { //! # setup_logger().expect("failed to set up logger") //! # } //! ``` //! //! Let's unwrap the above example: //! //! --- //! //! [`fern::Dispatch::new()`] //! //! Create an empty logger config. //! //! --- //! //! [`.format(|...| ...)`] //! //! Add a formatter to the logger, modifying all messages sent through. //! //! ___ //! //! [`chrono::Local::now()`] //! //! Get the current time in the local timezone using the [`chrono`] library. See the [time-and-date docs]. //! //! ___ //! //! [`.format(`]`"[%Y-%m-%d][%H:%M:%S]`[`")`] //! //! Use chrono's lazy format specifier to turn the time into a readable string. //! //! --- //! //! [`out.finish(format_args!(...))`] //! //! Call the `fern::FormattingCallback` to submit the formatted message. //! //! Fern uses this callback style to allow usage of [`std::fmt`] formatting without the allocation that would //! be needed to return the formatted result. //! //! [`format_args!()`] has the same arguments as [`println!()`] or any other [`std::fmt`]-based macro. //! //! The final output of this formatter will be: //! //! ```text //! [2017-01-20][12:55:04][crate-name][INFO] Something happened. //! ``` //! //! --- //! //! [`.level(log::LogLevelFilter::Debug)`] //! //! Set the minimum level needed to output to `Debug`. //! //! This accepts `Debug`, `Info`, `Warn` and `Error` level messages, and denies the lowest level, `Trace`. //! //! --- //! //! [`.chain(std::io::stdout())`] //! //! Add a child to the logger; send all messages to stdout. //! //! [`Dispatch::chain`] accepts [`Stdout`], [`Stderr`], [`File`]s and other [`Dispatch`] instances. //! //! --- //! //! [`.chain(fern::log_file(...)?)`] //! //! Add a second child; send all messages to the file "output.log". //! //! See [`fern::log_file()`] for more info on file output. //! //! --- //! //! [`.apply()`][`.apply`] //! //! Consume the configuration and instantiate it as the current runtime global logger. //! //! This will fail if and only if another fern or [`log`] logger has already been set as the global logger. //! //! Since it's really up to the binary-producing crate to set up logging, the [`apply`] result can be reasonably //! unwrapped or ignored. //! //! # Logging //! //! Once the logger has been set using [`apply`] it will pick up all [`log`] macro calls from your //! crate and all your libraries. //! //! ```rust //! #[macro_use] //! extern crate log; //! extern crate fern; //! //! # fn setup_logger() -> Result<(), fern::InitError> { //! fern::Dispatch::new() //! // ... //! .apply()?; //! # Ok(()) //! # } //! //! # fn main() { //! # setup_logger().ok(); // we're ok with this not succeeding. //! trace!("Trace message"); //! debug!("Debug message"); //! info!("Info message"); //! warn!("Warning message"); //! error!("Error message"); //! # } //! ``` //! //! # More configuration //! //! Check out the [`Dispatch` documentation] and the [full example program] for more usages. //! //! [`fern::Dispatch::new()`]: struct.Dispatch.html#method.new //! [`.format(|...| ...)`]: struct.Dispatch.html#method.format //! [`chrono::Local::now()`]: https://docs.rs/chrono/0.4/chrono/offset/local/struct.Local.html#method.now //! [`.format(`]: https://docs.rs/chrono/0.4/chrono/datetime/struct.DateTime.html#method.format //! [`")`]: https://docs.rs/chrono/0.4/chrono/datetime/struct.DateTime.html#method.format //! [`out.finish(format_args!(...))`]: struct.FormatCallback.html#method.finish //! [`.level(log::LogLevelFilter::Debug)`]: struct.Dispatch.html#method.level //! [`Dispatch::chain`]: struct.Dispatch.html#method.chain //! [`.chain(std::io::stdout())`]: struct.Dispatch.html#method.chain //! [`Stdout`]: https://doc.rust-lang.org/std/io/struct.Stdout.html //! [`Stderr`]: https://doc.rust-lang.org/std/io/struct.Stderr.html //! [`File`]: https://doc.rust-lang.org/std/fs/struct.File.html //! [`Dispatch`]: struct.Dispatch.html //! [`.chain(fern::log_file(...)?)`]: struct.Dispatch.html#method.chain //! [`fern::log_file()`]: fn.log_file.html //! [`.apply`]: struct.Dispatch.html#method.apply //! [`format_args!()`]: https://doc.rust-lang.org/std/macro.format_args.html //! [`println!()`]: https://doc.rust-lang.org/std/macro.println.html //! [`std::fmt`]: https://doc.rust-lang.org/std/fmt/ //! [`chrono`]: https://github.com/chronotope/chrono //! [time-and-date docs]: https://docs.rs/chrono/0.4/chrono/index.html#date-and-time //! [the format specifier docs]: https://docs.rs/chrono/0.4/chrono/format/strftime/index.html#specifiers //! [`Dispatch` documentation]: struct.Dispatch.html //! [full example program]: https://github.com/daboross/fern/tree/master/examples/cmd-program.rs //! [`apply`]: struct.Dispatch.html#method.apply //! [`log`]: doc.rust-lang.org/log/ #[cfg(feature = "colored")] extern crate colored; extern crate log; use std::convert::AsRef; use std::path::Path; use std::fs::{File, OpenOptions}; use std::{fmt, io}; pub use builders::{Dispatch, Output}; pub use log_impl::FormatCallback; pub use errors::InitError; mod builders; mod log_impl; mod errors; #[cfg(feature = "colored")] pub mod colors; /// A type alias for a log formatter. pub type Formatter = Fn(FormatCallback, &fmt::Arguments, &log::LogRecord) + Sync + Send + 'static; /// A type alias for a log filter. Returning true means the record should succeed - false means it should fail. pub type Filter = Fn(&log::LogMetadata) -> bool + Send + Sync + 'static; /// Fern logging trait. This is necessary in order to allow for custom loggers taking in arguments that have already had /// a custom format applied to them. /// /// The original `log::Log` trait's `log` method only accepts messages that were created using the log macros - this /// trait also accepts records which have had additional formatting applied to them. pub trait FernLog: Sync + Send { /// Logs a log record, but with the given fmt::Arguments instead of the one contained in the LogRecord. /// /// This has access to the original record, but _should ignore_ the original `record.args()` and instead /// use the passed in payload. fn log_args(&self, payload: &fmt::Arguments, record: &log::LogRecord); } /// Convenience method for opening a log file with common options. /// /// Equivalent to: /// /// ```no_run /// std::fs::OpenOptions::new() /// .write(true) /// .create(true) /// .append(true) /// .open("filename") /// # ; /// ``` /// /// See [`OpenOptions`] for more information. /// /// [`OpenOptions`]: https://doc.rust-lang.org/std/fs/struct.OpenOptions.html #[inline] pub fn log_file<P: AsRef<Path>>(path: P) -> io::Result<File> { OpenOptions::new() .write(true) .create(true) .append(true) .open(path) }