lib.rs

// Copyright 2014 The Rust Project Developers. See the COPYRIGHT
// file at the top-level directory of this distribution and at
// http://rust-lang.org/COPYRIGHT.
//
// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
// option. This file may not be copied, modified, or distributed
// except according to those terms.

//! Utilities for program-wide and customizable logging
//!
//! # Examples
//!
//! ```
//! #[macro_use] extern crate log;
//!
//! fn main() {
//!     debug!("this is a debug {:?}", "message");
//!     error!("this is printed by default");
//!
//!     if log_enabled!(log::INFO) {
//!         let x = 3 * 4; // expensive computation
//!         info!("the answer was: {:?}", x);
//!     }
//! }
//! ```
//!
//! Assumes the binary is `main`:
//!
//! ```{.bash}
//! $ RUST_LOG=error ./main
//! ERROR:main: this is printed by default
//! ```
//!
//! ```{.bash}
//! $ RUST_LOG=info ./main
//! ERROR:main: this is printed by default
//! INFO:main: the answer was: 12
//! ```
//!
//! ```{.bash}
//! $ RUST_LOG=debug ./main
//! DEBUG:main: this is a debug message
//! ERROR:main: this is printed by default
//! INFO:main: the answer was: 12
//! ```
//!
//! You can also set the log level on a per module basis:
//!
//! ```{.bash}
//! $ RUST_LOG=main=info ./main
//! ERROR:main: this is printed by default
//! INFO:main: the answer was: 12
//! ```
//!
//! And enable all logging:
//!
//! ```{.bash}
//! $ RUST_LOG=main ./main
//! DEBUG:main: this is a debug message
//! ERROR:main: this is printed by default
//! INFO:main: the answer was: 12
//! ```
//!
//! # Logging Macros
//!
//! There are five macros that the logging subsystem uses:
//!
//! * `log!(level, ...)` - the generic logging macro, takes a level as a u32 and any
//!                        related `format!` arguments
//! * `debug!(...)` - a macro hard-wired to the log level of `DEBUG`
//! * `info!(...)` - a macro hard-wired to the log level of `INFO`
//! * `warn!(...)` - a macro hard-wired to the log level of `WARN`
//! * `error!(...)` - a macro hard-wired to the log level of `ERROR`
//!
//! All of these macros use the same style of syntax as the `format!` syntax
//! extension. Details about the syntax can be found in the documentation of
//! `std::fmt` along with the Rust tutorial/manual.
//!
//! If you want to check at runtime if a given logging level is enabled (e.g. if the
//! information you would want to log is expensive to produce), you can use the
//! following macro:
//!
//! * `log_enabled!(level)` - returns true if logging of the given level is enabled
//!
//! # Enabling logging
//!
//! Log levels are controlled on a per-module basis, and by default all logging is
//! disabled except for `error!` (a log level of 1). Logging is controlled via the
//! `RUST_LOG` environment variable. The value of this environment variable is a
//! comma-separated list of logging directives. A logging directive is of the form:
//!
//! ```text
//! path::to::module=log_level
//! ```
//!
//! The path to the module is rooted in the name of the crate it was compiled for,
//! so if your program is contained in a file `hello.rs`, for example, to turn on
//! logging for this file you would use a value of `RUST_LOG=hello`.
//! Furthermore, this path is a prefix-search, so all modules nested in the
//! specified module will also have logging enabled.
//!
//! The actual `log_level` is optional to specify. If omitted, all logging will be
//! enabled. If specified, the it must be either a numeric in the range of 1-255, or
//! it must be one of the strings `debug`, `error`, `info`, or `warn`. If a numeric
//! is specified, then all logging less than or equal to that numeral is enabled.
//! For example, if logging level 3 is active, error, warn, and info logs will be
//! printed, but debug will be omitted.
//!
//! As the log level for a module is optional, the module to enable logging for is
//! also optional. If only a `log_level` is provided, then the global log level for
//! all modules is set to this value.
//!
//! Some examples of valid values of `RUST_LOG` are:
//!
//! * `hello` turns on all logging for the 'hello' module
//! * `info` turns on all info logging
//! * `hello=debug` turns on debug logging for 'hello'
//! * `hello=3` turns on info logging for 'hello'
//! * `hello,std::option` turns on hello, and std's option logging
//! * `error,hello=warn` turn on global error logging and also warn for hello
//!
//! # Filtering results
//!
//! A RUST_LOG directive may include a string filter. The syntax is to append
//! `/` followed by a string. Each message is checked against the string and is
//! only logged if it contains the string. Note that the matching is done after
//! formatting the log string but before adding any logging meta-data. There is
//! a single filter for all modules.
//!
//! Some examples:
//!
//! * `hello/foo` turns on all logging for the 'hello' module where the log message
//! includes 'foo'.
//! * `info/f.o` turns on all info logging where the log message includes 'foo',
//! 'f1o', 'fao', etc.
//! * `hello=debug/foo*foo` turns on debug logging for 'hello' where the log
//! message includes 'foofoo' or 'fofoo' or 'fooooooofoo', etc.
//! * `error,hello=warn/[0-9] scopes` turn on global error logging and also warn for
//!  hello. In both cases the log message must include a single digit number
//!  followed by 'scopes'
//!
//! # Performance and Side Effects
//!
//! Each of these macros will expand to code similar to:
//!
//! ```rust,ignore
//! if log_level <= my_module_log_level() {
//!     ::log::log(log_level, format!(...));
//! }
//! ```
//!
//! What this means is that each of these macros are very cheap at runtime if
//! they're turned off (just a load and an integer comparison). This also means that
//! if logging is disabled, none of the components of the log will be executed.

// Do not remove on snapshot creation. Needed for bootstrap. (Issue #22364)
#![cfg_attr(stage0, feature(custom_attribute))]
#![crate_name = "log"]
#![unstable(feature = "rustc_private",
            reason = "use the crates.io `log` library instead")]
#![staged_api]
#![crate_type = "rlib"]
#![crate_type = "dylib"]
#![doc(html_logo_url = "http://www.rust-lang.org/logos/rust-logo-128x128-blk-v2.png",
       html_favicon_url = "https://doc.rust-lang.org/favicon.ico",
       html_root_url = "http://doc.rust-lang.org/nightly/",
       html_playground_url = "http://play.rust-lang.org/")]
#![deny(missing_docs)]

#![feature(box_raw)]
#![feature(box_syntax)]
#![feature(const_fn)]
#![feature(iter_cmp)]
#![feature(rt)]
#![feature(staged_api)]
#![feature(static_mutex)]

use std::cell::RefCell;
use std::fmt;
use std::io::{self, Stderr};
use std::io::prelude::*;
use std::mem;
use std::env;
use std::rt;
use std::slice;
use std::sync::{Once, StaticMutex};

use directive::LOG_LEVEL_NAMES;

#[macro_use]
pub mod macros;

mod directive;

/// Maximum logging level of a module that can be specified. Common logging
/// levels are found in the DEBUG/INFO/WARN/ERROR constants.
pub const MAX_LOG_LEVEL: u32 = 255;

/// The default logging level of a crate if no other is specified.
const DEFAULT_LOG_LEVEL: u32 = 1;

static LOCK: StaticMutex = StaticMutex::new();

/// An unsafe constant that is the maximum logging level of any module
/// specified. This is the first line of defense to determining whether a
/// logging statement should be run.
static mut LOG_LEVEL: u32 = MAX_LOG_LEVEL;

static mut DIRECTIVES: *mut Vec<directive::LogDirective> =
    0 as *mut Vec<directive::LogDirective>;

/// Optional filter.
static mut FILTER: *mut String = 0 as *mut _;

/// Debug log level
pub const DEBUG: u32 = 4;
/// Info log level
pub const INFO: u32 = 3;
/// Warn log level
pub const WARN: u32 = 2;
/// Error log level
pub const ERROR: u32 = 1;

thread_local! {
    static LOCAL_LOGGER: RefCell<Option<Box<Logger + Send>>> = {
        RefCell::new(None)
    }
}

/// A trait used to represent an interface to a thread-local logger. Each thread
/// can have its own custom logger which can respond to logging messages
/// however it likes.
pub trait Logger {
    /// Logs a single message described by the `record`.
    fn log(&mut self, record: &LogRecord);
}

struct DefaultLogger { handle: Stderr }

/// Wraps the log level with fmt implementations.
#[derive(Copy, Clone, PartialEq, PartialOrd, Debug)]
pub struct LogLevel(pub u32);

impl fmt::Display for LogLevel {
    fn fmt(&self, fmt: &mut fmt::Formatter) -> fmt::Result {
        let LogLevel(level) = *self;
        match LOG_LEVEL_NAMES.get(level as usize - 1) {
            Some(ref name) => fmt::Display::fmt(name, fmt),
            None => fmt::Display::fmt(&level, fmt)
        }
    }
}

impl Logger for DefaultLogger {
    fn log(&mut self, record: &LogRecord) {
        match writeln!(&mut self.handle,
                       "{}:{}: {}",
                       record.level,
                       record.module_path,
                       record.args) {
            Err(e) => panic!("failed to log: {:?}", e),
            Ok(()) => {}
        }
    }
}

impl Drop for DefaultLogger {
    fn drop(&mut self) {
        // FIXME(#12628): is panicking the right thing to do?
        match self.handle.flush() {
            Err(e) => panic!("failed to flush a logger: {:?}", e),
            Ok(()) => {}
        }
    }
}

/// This function is called directly by the compiler when using the logging
/// macros. This function does not take into account whether the log level
/// specified is active or not, it will always log something if this method is
/// called.
///
/// It is not recommended to call this function directly, rather it should be
/// invoked through the logging family of macros.
#[doc(hidden)]
pub fn log(level: u32, loc: &'static LogLocation, args: fmt::Arguments) {
    // Test the literal string from args against the current filter, if there
    // is one.
    unsafe {
        let _g = LOCK.lock();
        match FILTER as usize {
            0 => {}
            1 => panic!("cannot log after main thread has exited"),
            n => {
                let filter = mem::transmute::<_, &String>(n);
                if !args.to_string().contains(&filter[..]) {
                    return
                }
            }
        }
    }

    // Completely remove the local logger from TLS in case anyone attempts to
    // frob the slot while we're doing the logging. This will destroy any logger
    // set during logging.
    let mut logger: Box<Logger + Send> = LOCAL_LOGGER.with(|s| {
        s.borrow_mut().take()
    }).unwrap_or_else(|| {
        box DefaultLogger { handle: io::stderr() }
    });
    logger.log(&LogRecord {
        level: LogLevel(level),
        args: args,
        file: loc.file,
        module_path: loc.module_path,
        line: loc.line,
    });
    set_logger(logger);
}

/// Getter for the global log level. This is a function so that it can be called
/// safely
#[doc(hidden)]
#[inline(always)]
pub fn log_level() -> u32 { unsafe { LOG_LEVEL } }

/// Replaces the thread-local logger with the specified logger, returning the old
/// logger.
pub fn set_logger(logger: Box<Logger + Send>) -> Option<Box<Logger + Send>> {
    let mut l = Some(logger);
    LOCAL_LOGGER.with(|slot| {
        mem::replace(&mut *slot.borrow_mut(), l.take())
    })
}

/// A LogRecord is created by the logging macros, and passed as the only
/// argument to Loggers.
#[derive(Debug)]
pub struct LogRecord<'a> {

    /// The module path of where the LogRecord originated.
    pub module_path: &'a str,

    /// The LogLevel of this record.
    pub level: LogLevel,

    /// The arguments from the log line.
    pub args: fmt::Arguments<'a>,

    /// The file of where the LogRecord originated.
    pub file: &'a str,

    /// The line number of where the LogRecord originated.
    pub line: u32,
}

#[doc(hidden)]
#[derive(Copy, Clone)]
pub struct LogLocation {
    pub module_path: &'static str,
    pub file: &'static str,
    pub line: u32,
}

/// Tests whether a given module's name is enabled for a particular level of
/// logging. This is the second layer of defense about determining whether a
/// module's log statement should be emitted or not.
#[doc(hidden)]
pub fn mod_enabled(level: u32, module: &str) -> bool {
    static INIT: Once = Once::new();
    INIT.call_once(init);

    // It's possible for many threads are in this function, only one of them
    // will perform the global initialization, but all of them will need to check
    // again to whether they should really be here or not. Hence, despite this
    // check being expanded manually in the logging macro, this function checks
    // the log level again.
    if level > unsafe { LOG_LEVEL } { return false }

    // This assertion should never get tripped unless we're in an at_exit
    // handler after logging has been torn down and a logging attempt was made.

    let _g = LOCK.lock();
    unsafe {
        assert!(DIRECTIVES as usize != 0);
        assert!(DIRECTIVES as usize != 1,
                "cannot log after the main thread has exited");

        enabled(level, module, (*DIRECTIVES).iter())
    }
}

fn enabled(level: u32,
           module: &str,
           iter: slice::Iter<directive::LogDirective>)
           -> bool {
    // Search for the longest match, the vector is assumed to be pre-sorted.
    for directive in iter.rev() {
        match directive.name {
            Some(ref name) if !module.starts_with(&name[..]) => {},
            Some(..) | None => {
                return level <= directive.level
            }
        }
    }
    level <= DEFAULT_LOG_LEVEL
}

/// Initialize logging for the current process.
///
/// This is not threadsafe at all, so initialization is performed through a
/// `Once` primitive (and this function is called from that primitive).
fn init() {
    let (mut directives, filter) = match env::var("RUST_LOG") {
        Ok(spec) => directive::parse_logging_spec(&spec[..]),
        Err(..) => (Vec::new(), None),
    };

    // Sort the provided directives by length of their name, this allows a
    // little more efficient lookup at runtime.
    directives.sort_by(|a, b| {
        let alen = a.name.as_ref().map(|a| a.len()).unwrap_or(0);
        let blen = b.name.as_ref().map(|b| b.len()).unwrap_or(0);
        alen.cmp(&blen)
    });

    let max_level = {
        let max = directives.iter().max_by(|d| d.level);
        max.map(|d| d.level).unwrap_or(DEFAULT_LOG_LEVEL)
    };

    unsafe {
        LOG_LEVEL = max_level;

        assert!(FILTER.is_null());
        match filter {
            Some(f) => FILTER = Box::into_raw(box f),
            None => {}
        }

        assert!(DIRECTIVES.is_null());
        DIRECTIVES = Box::into_raw(box directives);

        // Schedule the cleanup for the globals for when the runtime exits.
        let _ = rt::at_exit(move || {
            let _g = LOCK.lock();
            assert!(!DIRECTIVES.is_null());
            let _directives = Box::from_raw(DIRECTIVES);
            DIRECTIVES = 1 as *mut _;

            if !FILTER.is_null() {
                let _filter = Box::from_raw(FILTER);
                FILTER = 1 as *mut _;
            }
        });
    }
}

#[cfg(test)]
mod tests {
    use super::enabled;
    use directive::LogDirective;

    #[test]
    fn match_full_path() {
        let dirs = [
            LogDirective {
                name: Some("crate2".to_string()),
                level: 3
            },
            LogDirective {
                name: Some("crate1::mod1".to_string()),
                level: 2
            }
        ];
        assert!(enabled(2, "crate1::mod1", dirs.iter()));
        assert!(!enabled(3, "crate1::mod1", dirs.iter()));
        assert!(enabled(3, "crate2", dirs.iter()));
        assert!(!enabled(4, "crate2", dirs.iter()));
    }

    #[test]
    fn no_match() {
        let dirs = [
            LogDirective { name: Some("crate2".to_string()), level: 3 },
            LogDirective { name: Some("crate1::mod1".to_string()), level: 2 }
        ];
        assert!(!enabled(2, "crate3", dirs.iter()));
    }

    #[test]
    fn match_beginning() {
        let dirs = [
            LogDirective { name: Some("crate2".to_string()), level: 3 },
            LogDirective { name: Some("crate1::mod1".to_string()), level: 2 }
        ];
        assert!(enabled(3, "crate2::mod1", dirs.iter()));
    }

    #[test]
    fn match_beginning_longest_match() {
        let dirs = [
            LogDirective { name: Some("crate2".to_string()), level: 3 },
            LogDirective { name: Some("crate2::mod".to_string()), level: 4 },
            LogDirective { name: Some("crate1::mod1".to_string()), level: 2 }
        ];
        assert!(enabled(4, "crate2::mod1", dirs.iter()));
        assert!(!enabled(4, "crate2", dirs.iter()));
    }

    #[test]
    fn match_default() {
        let dirs = [
            LogDirective { name: None, level: 3 },
            LogDirective { name: Some("crate1::mod1".to_string()), level: 2 }
        ];
        assert!(enabled(2, "crate1::mod1", dirs.iter()));
        assert!(enabled(3, "crate2::mod2", dirs.iter()));
    }

    #[test]
    fn zero_level() {
        let dirs = [
            LogDirective { name: None, level: 3 },
            LogDirective { name: Some("crate1::mod1".to_string()), level: 0 }
        ];
        assert!(!enabled(1, "crate1::mod1", dirs.iter()));
        assert!(enabled(3, "crate2::mod2", dirs.iter()));
    }
}