fern_logger/
lib.rs

1// Copyright 2020-2022 IOTA Stiftung
2// SPDX-License-Identifier: Apache-2.0
3
4//! Convenient multi-output backend for the `log` crate.
5
6mod config;
7
8pub use config::{LoggerConfig, LoggerConfigBuilder, LoggerOutputConfig, LoggerOutputConfigBuilder};
9
10use fern::{
11    colors::{Color, ColoredLevelConfig},
12    Dispatch,
13};
14use thiserror::Error;
15
16/// Name of the standard output.
17pub const LOGGER_STDOUT_NAME: &str = "stdout";
18
19/// Error occuring when initializing a logger backend.
20#[derive(Error, Debug)]
21#[non_exhaustive]
22pub enum Error {
23    /// Creating output file failed.
24    #[error("Creating output file failed.")]
25    CreatingFileFailed,
26    /// Initializing the logger backend failed.
27    #[error("Initializing the logger backend failed.")]
28    InitializationFailed,
29}
30
31macro_rules! log_format {
32    ($target:expr, $level:expr, $message:expr, $target_width:expr, $level_width:expr) => {
33        format_args!(
34            "{} {:target_width$} {:level_width$} {}",
35            time_helper::format(&time_helper::now_utc()),
36            $target,
37            $level,
38            $message,
39            target_width = $target_width,
40            level_width = $level_width
41        )
42    };
43}
44
45/// Initializes a `fern` logger backend for the `log` crate.
46///
47/// # Arguments
48///
49/// * `config`  -   Logger configuration
50pub fn logger_init(config: LoggerConfig) -> Result<(), Error> {
51    let target_width = config.target_width;
52    let level_width = config.level_width;
53
54    let mut logger = Dispatch::new();
55
56    for output in config.outputs {
57        // Creates a logger dispatch for each output of the configuration.
58        let mut dispatch = if output.color_enabled {
59            let colors = ColoredLevelConfig::new()
60                .trace(Color::BrightMagenta)
61                .debug(Color::BrightBlue)
62                .info(Color::BrightGreen)
63                .warn(Color::BrightYellow)
64                .error(Color::BrightRed);
65
66            // Creates a logger dispatch with color support.
67            Dispatch::new().format(move |out, message, record| {
68                out.finish(log_format!(
69                    record.target(),
70                    colors.color(record.level()),
71                    message,
72                    target_width,
73                    level_width
74                ))
75            })
76        } else {
77            // Creates a logger dispatch without color support.
78            Dispatch::new().format(move |out, message, record| {
79                out.finish(log_format!(
80                    record.target(),
81                    record.level(),
82                    message,
83                    target_width,
84                    level_width
85                ))
86            })
87        }
88        .level(output.level_filter);
89
90        if !output.target_filters.is_empty() {
91            let target_filters = output.target_filters;
92            dispatch = dispatch.filter(move |metadata| {
93                let target = metadata.target().to_lowercase();
94                target_filters.iter().any(|f| target.contains(f))
95            });
96        }
97
98        if !output.target_exclusions.is_empty() {
99            let target_exclusions = output.target_exclusions;
100            dispatch = dispatch.filter(move |metadata| {
101                let target = metadata.target().to_lowercase();
102                !target_exclusions.iter().any(|f| target.contains(f))
103            });
104        }
105
106        // Special case for the standard output.
107        dispatch = if output.name == LOGGER_STDOUT_NAME {
108            dispatch.chain(std::io::stdout())
109        } else {
110            dispatch.chain(fern::log_file(output.name).map_err(|_| Error::CreatingFileFailed)?)
111        };
112
113        logger = logger.chain(dispatch);
114    }
115
116    logger.apply().map_err(|_| Error::InitializationFailed)?;
117
118    Ok(())
119}
fern_logger/lib.rs

fern_logger/
lib.rs
