nolog logger

Convenient and 'beautiful by default' logger for debugging your programs. Easy to use, you don't need to learn anything to start using it. Zero deps. No unsafe (by #![deny(unsafe_code)]).

nolog

See this example code

nolog features

In most cases nolog uses a std::format_args!() (that avoids heap allocations) and compile-time level filtering by Cargo features. If you use the default setup without additional features (like logmod, logonly, logcatch, tofile), then in most cases nolog will only work on compile-time macros without using functions, methods, if or loops. In fact it will expand into the string eprintln!("{}", format_args!("{}{}{}{}"," ", "CRIT⧽", "msg", "[34] src/main.rs"));. Nothing extra.
Filtering by module path (logmod feature).
Display messages only from a selected section of code (logonly feature).
Smart logging: hide all messages, show the previous Х messages if an error or crit level message was triggered (logcatch feature).
A custom indent can be added to the message, as well as a number of blank lines before and after it. You can use variables (eg loop counter) to set the indent for the selected message.
Easily adjust and disable all indents and newlines with features.
Сustomization: you can create your own color scheme for the logger.
Support for named format arguments: info!("{line_count} lines.");.
Support for key => value syntax: info!("{server}" => "{ip}");
Automatically disabled in the release build: cargo run --release. If you want the log to be enabled in the release build, then use release feature: nolog = {version = "*", features = ["release"]}.
All levels are disabled by default. Turning on the debug level also turns on the levels above it: info, warn, error, crit. Level can be enabled using the console: cargo run --features debug or in Cargo.toml: nolog = {version = "*", features = ["debug"]}. To enable all levels: cargo run --features trace.
By default, the log is writting to stderr. You can log to a file with tofile feature. You may set the buffer size. Automatic flush after each message will be used. If you want wait for the buffer to fill or to do it manually with logflush!() then use no_auto_flush feature.
Custom output redirection. For example, to a file and to stderr at the same time. An example is at the very bottom of the page.
You can add a timestamp like [2022-07-10 06:49:33.646361181 UTC] using a third party library you like. An example is below.
Support for chaining multiple messages into one (they must all be of the same type: usual or key-value): rust info!( "{server}" => "{ip}"; "Status" => "{server_check_result}"; );

Using nolog

Cargo.toml

```toml [dependencies] nolog = { version = "1", features = [] }

[features] nolog_setup = []

example `classic`

nologsetup = ["nolog/showlvlheaderkv", "nolog/indentignoreall", "nolog/newlineignore", "nolog/locationstyleclassic", "nolog/sepcolon"]

example `classic_plain`

nologsetup = ["nolog/plain", "nolog/showlvlheaderkv", "nolog/indentignoreall", "nolog/newlineignore", "nolog/locationstyleclassic", "nolog/sepcolon"]

trace = ["nolog/trace", "nologsetup"] debug = ["nolog/debug", "nologsetup"] info = ["nolog/info", "nologsetup"] warn = ["nolog/warn", "nologsetup"] error = ["nolog/error", "nologsetup"] crit = ["nolog/crit", "nologsetup"]

logonly = ["nolog/logonly"] logcatch = ["nolog/logcatch"] logmod = ["nolog/logmod"] ```

main.rs

```rust

[macro_use]

extern crate nolog;

fn main() { trace!("linecount: {}", 42); debug!("linecount: {}", 42); info!("linecount: {}", 42); warn!("linecount: {}", 42); error!("linecount: {}", 42); crit!("linecount: {}", 42); } ```

This example on GitHub.

nolog has the same syntax as most loggers based on the log crate. nolog extends the log crate syntax by adding new features. However, nolog is not based on log crate, it just has the same macro names.

Therefore, switching to nolog will require minimal changes in the code. In fact, this boils down to a change in Cargo.toml and line extern crate nolog;.

Then:

sh cargo run --features trace

Or, for example

```sh

The output will be empty because there are no logonly

blocks, etc. in the code.

This is just to demonstrate the use of several features.

cargo run --features trace,logonly,logcatch,logmod ```

It's the same but noisier

```sh

The output will be empty because there are no logonly

blocks, etc. in the code.

This is just to demonstrate the use of several features.

cargo run --features nolog/trace,nolog/logonly,nolog/logcatch,nolog/logmod ```

Result:

example

Tofile. Writing log entries to a file

Cargo.toml

```toml

...

[dependencies] nolog = { version = "1", features = ["tofile"] }

...

```

main.rs

```rust use std::fs::OpenOptions; use std::io::{self, Read}; use std::path::PathBuf;

[macro_use]

extern crate nolog;

fn main() -> io::Result<()> { let path = PathBuf::from("log.txt"); let file = OpenOptions::new() .read(true) .write(true) .create(true) .truncate(true) //^^^^^^^ truncate the file to 0 length if it already exists. //.append(true) .open(&path)?;

// Initialization
// Don't use macros like `debug!("msg");` before initialization.
logfile!(file);

trace!("Hello from file!");

let mut file = OpenOptions::new()
    .read(true)
    .open(&path)?;

let mut contents = String::new();
file.read_to_string(&mut contents)?;
println!("\n      -- In {path:?} --");
println!("{contents}");

Ok(())

} ```

This example on GitHub.

Optionally, you can set the buffer size.

rust // Buffer `std::io::BufWriter` with capacity: 8000 bytes. logfile!(8000, file);

The default is to automatically flush after each message. If you want wait for the buffer to fill or to do it manually with logflush!() then use no_auto_flush feature.

Cargo.toml

```toml

...

[dependencies] nolog = { version = "1", features = ["tofile", "noautoflush"] }

...

```

Then use logflush!() to flush the log manually.

main.rs

``rust ... // Initialization // Don't use macros likedebug!("msg");` before initialization. logfile!(8000, file);

trace!("Hello from file!");
logflush!();

... ```

How to add a timestamp

You can add a timestamp like [2022-07-10 06:49:33.646361181 UTC] using a third party library you like.

For this example, we will use chrono crate.

Cargo.toml

```toml

...

[dependencies] nolog = { version = "1", features = [] } chrono = "0.4"

[features] customleading = ["nolog/customleading"] customtrailing = ["nolog/customtrailing"] custombeforemsg = ["nolog/custombeforemsg"] customaftermsg = ["nolog/customaftermsg"]

nologsetup = ["customleading"]

...

```

We have 4 options here: - "customleading" - <TIMESTAMP>CRIT⧽ msg [5] src/main.rs - "customtrailing" - CRIT⧽ msg [5] src/main.rs<TIMESTAMP> - "custombeforemsg" - CRIT⧽ <TIMESTAMP>msg [5] src/main.rs - "customaftermsg" - CRIT⧽ msg<TIMESTAMP> [5] src/main.rs

Log entry structure:

usual: <indents><custom_leading><lvlheader><sep><custom_before_msg><msg><custom_after_msg><location><custom_trailing>

key-value: <indents><custom_leading><lvlheader><sep_kv><custom_before_msg><key><sep_key><value_indent><value><custom_after_msg><location><custom_trailing>

Here is an example:

main.rs

```rust

[macro_use]

extern crate nolog;

[macro_use]

pub mod loggersetup { #[macroexport] #[cfg(feature = "customleading")] macrorules! // ^^^^^^^^^^^^^^ customleading { // usual ( $level:tt, $indent:expr, $($msg:expr),* ) => { formatargs!("[{}] ", chrono::Utc::now())

    };
    // key-value
    ( $level:tt, $indent:expr, $($key:expr),* => $($value:expr),* ) => {
        format_args!("[{}] ", chrono::Local::now())
    };
}

}

mod other { pub fn fromothermod() -> () { crit!(->[0] "Other" => "Hello from other mod! This is key-value msg."); } }

fn main() { crit!("Hello from main! This is usual msg."); other::fromothermod();
} ```

This example on GitHub.

Output:

```sh [2022-09-07 09:22:09.150921578 UTC] CRIT⧽ Hello from main! This is usual msg. [34] src/main.rs [2022-09-07 12:22:09.150973037 +03:00] Other⧽ Hello from other mod! This is key-value msg. [29] src/main.rs

```

With classic style:

sh [2022-09-07 09:29:45.859185734 UTC] CRIT: Hello from main! This is usual msg. [src/main.rs 34:5] [2022-09-07 12:29:45.859225186 +03:00] CRIT: Other: Hello from other mod! This is key-value msg. [src/main.rs 29:9]

Styles

Default

toml nolog_setup = []

`classic`

toml nolog_setup = ["nolog/show_lvl_header_kv", "nolog/indent_ignore_all", "nolog/newline_ignore", "nolog/location_style_classic", "nolog/sep_colon"]

`classic_plain`

toml nolog_setup = ["nolog/plain", "nolog/show_lvl_header_kv", "nolog/indent_ignore_all", "nolog/newline_ignore", "nolog/location_style_classic", "nolog/sep_colon"]

styles

Chaining

Messages in a chain should all be of the same type: usual or key-value

ususal

rust debug!( "Planet {name} thinks..."; "Planet {name} thinks..."; );

key-value

rust debug!( "{server}" => "{ip}"; "Status" => "{server_check_result}"; );

Logmod. Filtering by module path

Add it as early as possible in the code:

rust logmod!( [ ] main, [!=] crate::other2, );

[] - Include a module and all its submodules.
[=] - the same (Include a module and all its submodules).
[!] - Exclude a module and all its submodules.
[==] - Include only this module without submodules.
[!=] - Exclude only this module without submodules.

Then

cargo run --features trace,logmod

Logonly. Display messages only from a selected section of code

This is useful for debugging to get messages from just a small piece of code.

rust logonly!( let universe = [0;3]; crit!("The Universe was created with a lifetime of {} days.", universe.len()); error!("Uncontrolled evolutionary processes have begun on the planet {planet_name}."); );

Then

cargo run --features trace,logonly

You can use any brackets

logonly!(), logonly!{}, logonly![].

You can use multiple logonly!() blocks. Messages will be displayed from all.

It won't break your code when the logger turns off in release build. So you can leave these blocks in the code.

When disabled, the definition of this macro will be replaced with the following:

rust logonly { ( $($a:tt)* ) => { $($a)* }; }

It simply writes down the code it received.

Logcatch. Smart logging

Hide all messages, show the previous Х messages if an error or crit level message was triggered.

By default X=10. You can change this anywhere in the code.

rust // This will take effect for the code below. logcatch!(2); // now X=2

To enable this feature, use:

cargo run --features trace,logcatch

Each new line created with newline!() or ->[_,1,1](about what it will be below) counts as a separate message.

Quick disable and enable messages

You can disable individual messages without removing them from the code. A macro like debug!([_]; "msg") will expand into an empty tuple ().

```rust // on info!([#]; "New {name} on planet {planet_name}.");

// off info!([_]; "{repr}" => "{name} says: {speech}"); ```

You can use any options you like:

On: [#], [x], [v], [+], [on], [true], [your_var]

Off: [ ], [_], [-], [off], [false], [your_var]

your_var should be bool.

To change states, you need to change only one character:

[_] --> [#].

This also works with chained messages, but disables the entire chain. You can't turn off a single message in a chain.

rust crit!([_]; "The answer is {answer}."; "Planet {planet_name} started watching TV."; );

You can turn off the action of block logonly. This will not affect the code, the effect is as if macro logonly was not in this place.

rust logonly!{[_]; crit!("The answer is {answer}."); let x = 42; }

This way you can leave logonly!() in the code and if it is required in the future just enable it.

Variables and expressions

If necessary, you can control messages using variables and expressions.

rust let my_log_enabled = true; crit!([my_log_enabled]; "The planet {} has been destroyed.", self.name);

rust let status = "ok"; crit!([(status == "ok")]; "The planet {} has been destroyed.", self.name); // ^ ^ // Add parentheses

rust fn is_message_show_fn () -> bool { false } ... crit!([(is_message_show_fn())]; "The planet {} has been destroyed.", self.name); // ^ ^ // Add parentheses

Indentation and new lines

new lines

newline!(2); - It will simply write the passed number of new lines to the log.

Indentation

Indents are of several types:

Base indent

Base indent will be added to every line. - Default for all: 6 indents. One indent equals one space.

You can change base indent with cargo features:

indent_base_zero
indent_base_one
indent_base_two
indent_base_three
indent_base_four
indent_base_five
indent_base_seven
indent_base_eight
indent_base_nine
indent_base_ten

For example in Cargo.toml:

```toml nologsetup = ["nolog/indentbase_zero"]

trace = ["nolog/trace", "nolog_setup"] ```

The indent of the selected message

Default for usual: 0
Default for key-value: 6

The default indentation is used if no value has been provided by the user.

You can specify indentation in the following way:

crit!(->[X,Y,Z] "msg");

X - Indents.
Y - Add Y blank lines before message (same effect as newline!(Y)).
Z - Add Z blank lines after message.

All of these arguments are optional:

rust crit!("msg"); crit!(->[1] "msg"); crit!(->[6,1] "msg"); crit!(->[1,2,3] "msg"); crit!([#]; ->[1,2,3] "msg");

If you want to add blank lines and leave the default indentation:

rust crit!(->[_,1] "msg"); crit!(->[_,_,2] "msg");

The same works for each message in the chain.

rust debug!( ->[2] "Planet {name} thinks..."; ->[_,1] "Planet {name} thinks..."; "Planet {name} thinks..."; );

key => value have an indentation of 6 by default, but you can reset it by setting it to zero.

rust error!(->[0] "{name}" => "{}!! Oh, yeaaaah!", 2*3*7);

Or you can do it via Cargo.toml for all messages.

indent_kv_default_zero
indent_kv_default_one
indent_kv_default_two
indent_kv_default_three
indent_kv_default_four
indent_kv_default_five
indent_kv_default_seven
indent_kv_default_eight
indent_kv_default_nine
indent_kv_default_ten

For example in Cargo.toml: ```toml nologsetup = ["nolog/indentkvdefaultzero"]

trace = ["nolog/trace", "nolog_setup"] ```

Key-values have the additional ability to set indentation not only for the key, but also for the value.

rust debug!( "{server}" => "{ip}"; "Status" => ->[3] "{server_check_result}"; );

This allows you to get nice aligned output if you want.

indent

Indent variables

You can use variables to set the indentation and add blank lines.

rust for i in 0..2 { warn!(->[i,i,i] "msg"); }

Ignore all indents

Ignore all types of indentation.

toml nolog_setup = ["nolog/indent_ignore_all"]

indent

Ignore all newlines

toml nolog_setup = ["nolog/newline_ignore"]

Colors

nolog colored by default, use this feature for plain output:

toml nolog_setup = ["nolog/plain"]

Level headers

toml nolog_setup = ["nolog/show_lvl_header_kv"]

Show level name for key-value: sh CRIT: Key: value [src/main.rs 90:5]` ^^^^

It's disabled by default: sh Key: value [src/main.rs 90:5]

Don't disable logger in release build

toml nolog = { version = "1", features = ["release"] }

Location

Don't show location (like [src/main.rs 155:9])

toml nolog_setup = ["nolog/location_hide"]

Style like this: [src/main.rs 155:9]

toml nolog_setup = ["nolog/location_style_classic"]

location

Separator

Default = "⧽ "

": "

toml nolog_setup = ["nolog/sep_colon"]

toml nolog_setup = ["nolog/sep_space"]

toml nolog_setup = ["nolog/sep_hide"]

Custom color scheme

You can create your own color scheme for the logger.

Cargo.toml

```toml

...

[dependencies] nolog = { version = "1", features = [] }

[features] customcolors = ["nolog/customcolors"] nologsetup = ["customcolors"]

...

```

Here is an example:

main.rs

```rust

[macro_use]

extern crate nolog;

[macro_use]

pub mod loggersetup { #[macroexport] #[cfg(feature = "customcolors")] macrorules! // ^^^^^^^^^^^^^ color { ( [trace] ) => { "\x1B[34m" }; ( [debug] ) => { "\x1B[36m" }; ( [info] ) => { "\x1B[32m" }; ( [warn] ) => { "\x1B[33m" }; ( [error] ) => { "\x1B[31m" }; ( [crit] ) => { "\x1B[35m" }; ( [sep] ) => { "\x1B[1m\x1B[2m" }; // +bold +dim ( [msg] ) => { "" }; // default term font color ( [from] ) => { "\x1B[90m\x1B[3m" }; // [src/main.rs 101:5] in location_style_classic ( [sep2] ) => { "\x1B[90m\x1B[2m" }; // sep2 in default style ( [sep3] ) => { "\x1B[90m\x1B[2m" }; // sep3 in default style ( [line] ) => { "\x1B[38;5;67m\x1B[1m\x1B[2m" }; // line number in default style ( [key] ) => { "\x1B[3m\x1B[1m" }; // +italic +bold ( [value] ) => { "\x1B[3m" }; // +italic ( [rm] ) => { "\x1B[0m" }; // remove previous colors } }

mod other { pub fn fromothermod() -> () { crit!(->[0] "Other" => "Hello from other mod! This is key-value msg."); } }

fn main(){ crit!("Hello from main! This is usual msg."); other::fromothermod();
} ```

This example on GitHub.

Custom output redirection

It is possible to redirect output. For example, we will redirect output to stderr and to a file at the same time. The limitation is that output to stderr will be the same as to a file, it will not be colorized.

Cargo.toml

```toml

...

[dependencies] nolog = { version = "1", features = [] }

[features] nologsetup = [ "customwriteloginner", "nolog/tofile" ] customwriteloginner = ["nolog/customwritelog_inner"]

...

```

Here is an example:

main.rs

```rust use std::fs::OpenOptions; use std::io::{self, Read}; use std::path::PathBuf;

[macro_use]

extern crate nolog;

// use cargo run --features trace

[macro_use]

pub mod loggersetup { #[macroexport] #[cfg(feature = "customwriteloginner")] macrorules! writeloginner { ( $msg:expr ) => { eprintln!("{}", $msg); // write to stderr tofilewriteloginner_helper!($msg); // write to a file } } }

mod other { pub fn fromothermod() -> () { crit!(->[0] "Other" => "Hello from other mod! This is key-value msg."); } }

// Initialization
// Don't use macros like `debug!("msg");` before initialization.
logfile!(file);

eprintln!("\n-- From eprintln: --");
crit!("Hello from main! This is usual msg.");
other::from_other_mod();

let mut file = OpenOptions::new()
    .read(true)
    .open(&path)?;

let mut contents = String::new();
file.read_to_string(&mut contents)?;
println!("\n-- In {path:?} --");
println!("{contents}");

Ok(())

} ```

This example on GitHub.

Output:

```sh -- From eprintln: -- CRIT: Hello from main! This is usual msg. [main.rs 54:5] CRIT: Other: Hello from other mod! This is key-value msg. [main.rs 34:9]

-- In "log.txt" -- CRIT: Hello from main! This is usual msg. [main.rs 54:5] CRIT: Other: Hello from other mod! This is key-value msg. [main.rs 34:9]

```

Other customization options

nolog has other customization options not described here, since it is unlikely that they will be in demand by a wide range of users. Their use is similar to that described above. You can see the full up-to-date list in Cargo.toml.

Logging in tests

Logging in tests works exactly the same, except that Rust test programs hide standard output of successful tests.

Use the following code to see the output of successful tests.

sh cargo test --features trace -- --nocapture

The output of failed tests will be displayed anyway.

sh cargo test --features trace

Changelog

1.0.12 - 1.0.14 – Small changes in Readme etc. Minor optimization fixes.
1.0.10 - 1.0.11 – Minor changes, an example with output redirection has been added.
1.0.1 - 1.0.9 – Small changes in Readme etc.
1.0.0 – Release. Completely rewritten.
0.1.1-0.2.3 – Early versions.

nolog logger

nolog features

Using nolog

example classic

nologsetup = ["nolog/showlvlheaderkv", "nolog/indentignoreall", "nolog/newlineignore", "nolog/locationstyleclassic", "nolog/sepcolon"]

example classic_plain

nologsetup = ["nolog/plain", "nolog/showlvlheaderkv", "nolog/indentignoreall", "nolog/newlineignore", "nolog/locationstyleclassic", "nolog/sepcolon"]

[macro_use]

The output will be empty because there are no logonly

blocks, etc. in the code.

This is just to demonstrate the use of several features.

The output will be empty because there are no logonly

blocks, etc. in the code.

This is just to demonstrate the use of several features.

Tofile. Writing log entries to a file

...

...

[macro_use]

...

...

How to add a timestamp

...

...

[macro_use]

[macro_use]

Styles

Default

classic

classic_plain

Chaining

Logmod. Filtering by module path

Logonly. Display messages only from a selected section of code

Logcatch. Smart logging

Quick disable and enable messages

Variables and expressions

Indentation and new lines

new lines

Indentation

Base indent

The indent of the selected message

Indent variables

Ignore all indents

Ignore all newlines

Colors

Level headers

Don't disable logger in release build

Location

Separator

Custom color scheme

...

...

[macro_use]

[macro_use]

Custom output redirection

...

...

[macro_use]

[macro_use]

Other customization options

Logging in tests

Changelog

example `classic`

example `classic_plain`

`classic`

`classic_plain`