logform

A flexible log format library designed for chaining and composing log transformations in Rust.

use logform::{align, colorize, combine, printf, timestamp, LogInfo};

pub fn initialize_and_test_formats() {
    let aligned_with_colors_and_time = combine(vec![
        colorize(),
        timestamp(),
        align(),
        printf(|info| {
            format!(
                "{} {}: {}",
                info.meta_as_str("timestamp").unwrap_or(""), info.level, info.message
            )
        }),
    ]);

    let mut info = LogInfo::new("info", "hi");
    info = aligned_with_colors_and_time.transform(info, None).unwrap();
    println!("{}", info.message);
}

• LogInfo Objects
• Understanding Formats
  • Combining Formats
  • Filtering LogInfo Objects
• Formats
  • Align
  • CLI
  • Colorize
  • Combine
  • JSON
  • Label
  • Logstash
  • Metadata
  • PadLevels
  • PrettyPrint
  • Printf
  • Simple
  • Timestamp
  • Uncolorize

LogInfo Objects

The LogInfo struct represents a single log message.

 pub struct LogInfo {
    pub level: String,
    pub message: String,
    pub meta: HashMap<String, Value>,
}

let info = LogInfo {
    level: "info".into(),                  // Level of the logging message
    message: "Hey! Log something?".into(), // Descriptive message being logged
    meta: HashMap::new(),                   // Other properties
};

//OR
let info = LogInfo::new("info", "Hey! Log something?");

//add meta
let info = LogInfo::new("info", "Hey! Log something?").with_meta("key", "value");//you can chain more

//remove meta
info.without_meta("key");

//get meta
info.get_meta("key");

Several of the formats in logform itself add to the meta:

As a consumer, you may add whatever meta you wish

Understanding Formats

Formats in logform are structs that implement a transform method with the signature transform(info: LogInfo, opts: FormatOptions) -> Option<LogInfo>.

• info: The LogInfo struct representing the log message.
• opts: Settings(Options) specific to the current instance of the format.

They are expected to return one of two things:

• A LogInfo Object representing a new transformed version of the info argument. The LogInfo struct is treated as immutable, meaning a new instance is created and returned with the desired modifications.
• A None value indicating that the info argument should be ignored by the caller. (See: Filtering LogInfo Objects) below.

Creating formats is designed to be as simple as possible. To define a new format, use Format::new() and pass a closure that implements the transformation logic:transform(info: LogInfo, opts: FormatOptions).

The named Format returned can be used to create as many copies of the given Format as desired:

use logform::Format;

fn test_custom_format() {
    let volume = Format::new(|mut info: LogInfo, opts: FormatOptions| {
        if let Some(opts) = opts {
            if opts.get("yell").is_some() {
                info.message = info.message.to_uppercase();
            } else if opts.get("whisper").is_some() {
                info.message = info.message.to_lowercase();
            }
        }
        Some(info)
    });

    // `volume` is now a Format instance that can be used for transformations
    let mut scream_opts = HashMap::new();
    scream_opts.insert("yell".to_string(), "true".to_string());
    let scream = volume.clone();

    let info = LogInfo::new("info", "sorry for making you YELL in your head!");

    let result = scream.transform(info, Some(scream_opts)).unwrap();
    println!("{}", result.message);
    //SORRY FOR MAKING YOU YELL IN YOUR HEAD!

    // `volume` can be used multiple times with different options
    let mut whisper_opts = HashMap::new();
    whisper_opts.insert("whisper".to_string(), "true".to_string());
    let whisper = volume;

    let info2 = LogInfo::new("info", "WHY ARE THEY MAKING US YELL SO MUCH!");

    let result2 = whisper.transform(info2, Some(whisper_opts)).unwrap();
    println!("{}", result2.message);
    //why are they making us yell so much!
}

Combining Formats

Any number of formats may be combined into a single format using logform::combine. Since logform::combine takes no options, it returns a pre-created instance of the combined format.

use logform::{combine, simple, timestamp};

fn test_combine_formatters() {
    // Combine timestamp and simple
    let combined_formatter = combine(vec![timestamp(), simple()]);

    let info = LogInfo::new("info", "Test message").with_meta("key", "value");

    let result = combined_formatter.transform(info, None).unwrap();
    println!("{}", result.message);
}
//info: Test message {"key":"value","timestamp":"2024-08-27 02:39:15"}

Filtering LogInfo Objects

If you wish to filter out a given LogInfo Object completely, simply return None.

use logform::Format;

fn test_ignore_private() {
    let ignore_private = Format::new(|info: LogInfo, _opts: FormatOptions| {
        if let Some(private) = info.meta.get("private") {
            if private == "true" {
                return None;
            }
        }
        Some(info)
    });

    let format = ignore_private;

    let public_info = LogInfo::new("error", "Public error to share").with_meta("private", "false");

    let result = format.transform(public_info, None).unwrap();
    println!("{}", result.message);
    //Public error to share

    let private_info =
        LogInfo::new("error", "This is super secret - hide it.").with_meta("private", "true");

    let result = format.transform(private_info, None);
    println!("{:?}", result);
    // None
}

The use of logform::combine will respect any None values returned and stop the evaluation of later formats in the series. For example:

use logform::{combine, Format};

let will_never_panic = combine(vec![
    Format::new(|_info, _opts| None), // Ignores everything
    Format::new(|_info, _opts| {
        panic!("Never reached");
    }),
]);

let info = LogInfo::new("info", "wow such testing");

println!("{:?}", will_never_panic.transform(info, None));
// None

Formats

Align

The align format adds a tab character before the message.

let aligned_format = align();

CLI

The cli format is a combination of the colorize and pad_levels formats and accepts both of their options. It pads, colorize, and then formats the log message as level:message.

use std::collections::HashMap;
use crate::{Format, LogInfo, cli};

let cli_format = cli()
    .with_option("colors", &serde_json::to_string(&HashMap::from([("info", "blue")])).unwrap())
    .with_option("filler", "*")
    .with_option("all", "true");

let info = LogInfo::new("info", "my message");
let transformed_info = cli_format.transform(info, None);

println!("{:?}", transformed_info);
// Output: LogInfo { level: "\x1b[34minfo\x1b[39m", message: "\x1b[34m**my message\x1b[39m", meta: {} }

Colorize

The colorize format adds colors to log levels and messages.

let colorizer = colorize()
    .with_option("colors", r#"{"info": ["blue"], "error": ["red", "bold"]}"#)
    .with_option("all", "true");

Combine

The combine format allows you to chain multiple formats together.

let combined_format = combine(vec![
    timestamp(),
    json(),
    colorize().with_option("colors", r#"{"info": ["blue"]}"#),
]);

JSON

The json format converts the log info into a JSON string.

let json_format = json();

Label

The label format adds a specified label to the log message or metadata. It accepts the following options:

• label: The label to prepend to the message or store in the metadata.
• message (optional): Determines where the label is added.
  • true (default): Adds the label before the message.
  • false: Adds the label to the meta field instead of the message.

use std::collections::HashMap;
use crate::{Format, LogInfo, label};

let label_format = label();
let info = LogInfo::new("info", "Test message");

let mut opts = HashMap::new();
opts.insert("label".to_string(), "MY_LABEL".to_string());
opts.insert("message".to_string(), "true".to_string());

let result = label_format.transform(info, Some(opts)).unwrap();
println!("{:?}", result);
// Output: LogInfo { level: "info", message: "[MY_LABEL] Test message", meta: {} }

opts.insert("message".to_string(), "false".to_string());
let result_meta = label_format.transform(info, Some(opts)).unwrap();
println!("{:?}", result_meta);
// Output: LogInfo { level: "info", message: "Test message", meta: {"label": "MY_LABEL"} }

Logstash

The logstash format converts the log info into a Logstash-compatible JSON string.

use logform::{ combine, logstash, timestamp };

let logstash_format = combine(vec![timestamp(), logstash()]);

let mut info = LogInfo::new("info", "my message");

let formatted_info = logstash_format.transform(info, None).unwrap();

println!("{}", formatted_info.message);
// {"@message":"my message","@timestamp":"2025-01-12T13:10:05.202213+00:00","@fields":{"level":"info"}}

Metadata

The metadata format collects metadata from the log and adds it to the specified key. It defaults to using the key "metadata", and includes all the keys in info.meta unless exclusions are specified.

It accepts the following options:

• key (optional): Name of the key used for the metadata. Default is "metadata".
• fillExcept (optional): Comma-separated list of keys to exclude from the metadata object.
• fillWith (optional): Comma-separated list of keys to include in the metadata object.

By default, all keys in info.meta are collected into the metadata, except those specified in fillExcept.

use logform::{metadata, LogInfo};
use serde_json::json;
use std::collections::HashMap;

let metadata_format = metadata();

let mut info = LogInfo::new("info", "Test message");
info.meta.insert("key1".to_string(), "value1".into());
info.meta.insert("key2".to_string(), "value2".into());

// Example 1: Default behavior (no options given)
let result = metadata_format.transform(info.clone(), None).unwrap();
println!("{:?}", result);
// Output: LogInfo { level: "info", message: "Test message", meta: {"metadata": Object {"key1": String("value1"), "key2": String("value2")}} }


// Example 2: Only include `key1` in metadata
let mut opts = HashMap::new();
opts.insert("fillWith".to_string(), "key1".to_string());
let result = metadata_format.transform(info.clone(), Some(opts)).unwrap();
println!("{:?}", result);
// Output: LogInfo { level: "info", message: "Test message", meta: {"key2": String("value2"), "metadata": Object {"key1": String("value1")}} }

// Example 3: Exclude only `key1` from metadata
let mut opts = HashMap::new();
opts.insert("fillExcept".to_string(), "key1".to_string());
let result = metadata_format.transform(info, Some(opts)).unwrap();
println!("{:?}", result.meta);
// Output: LogInfo { level: "info", message: "Test message", meta: {"metadata": Object {"key2": String("value2")}, "key1": String("value1")} }

PadLevels

The pad_levels format pads levels to be the same length.

use std::collections::HashMap;
use crate::{Format, LogInfo, pad_levels};

let pad_levels_format = pad_levels();

let info = LogInfo::new("info", "my message");
let transformed_info = pad_levels_format.transform(info, None);

println!("{:?}", transformed_info);
// Output: LogInfo { level: "info", message: "  my message", meta: {} }

Ms

The ms format adds the time in milliseconds since the last log message.

let ms_format = ms();

PrettyPrint

The pretty_print format provides a more readable output of the log info.

let pretty_format = pretty_print().with_option("colorize", "true");

Printf

The printf format allows you to define a custom formatting function.

let printf_format = printf(|info| {
    format!("{} - {}: {}", info.meta_as_str("timestamp").unwrap_or(""), info.level, info.message)
});

Simple

The simple format provides a basic string representation of the log info.

let simple_format = simple();

Timestamp

The timestamp format adds a timestamp to the log info.

let timestamp_format = timestamp()
    .with_option("format", "%Y-%m-%d %H:%M:%S")
    .with_option("alias", "log_time");

Uncolorize

The uncolorize format removes ANSI color codes from the log info.

let uncolorize_format = uncolorize();

Usage

To use logform in your project, add it to your Cargo.toml:

[dependencies]
logform = "0.3"

or with

cargo add logform

Then, in your Rust code:

use logform::{LogInfo, combine, timestamp, json};

let format = combine(vec![
    timestamp(),
    json(),
]);

let info = LogInfo::new("info", "Test message");
let formatted_info = format.transform(info, None).unwrap();
println!("{}", formatted_info.message);

Testing

Run the tests using:

cargo test

License

This project is licensed under the MIT License.

Acknowledgements

This library is inspired by the logform package for Node.js.