path: root/readme.md

# micromark-rs

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A [`CommonMark`][commonmark-spec] compliant markdown parser in [Rust][] with
positional info, concrete tokens, and extensions.

## Feature highlights

- [x] **[compliant][commonmark]** (100% to CommonMark)
- [x] **[extensions][]** (GFM, directives, frontmatter, math)
- [x] **[safe][security]** (100% safe rust, also 100% safe HTML by default)
- [x] **[robust][test]** (1800+ tests, 100% coverage)

It’s also `#![no_std]` + `alloc`, has tons of docs, and has a single dependency
(for optional debug logging).

> 🐣 **Note**: extensions and coverage are currently within progress.

## When to use this

- If you _just_ want to turn markdown into HTML (with maybe a few extensions)
- If you want to do _really complex things_ with markdown

See [§ Comparison][comparison] for more info

## Intro

micromark is markdown parser in Rust.
It uses a state machine to parse the entirety of markdown into concrete
tokens.
Its API compiles to HTML, but its parts are made to be used separately, so as to
generate syntax trees or compile to other output formats.
`micromark-rs` has a sibling in JavaScript, [`micromark-js`][micromark-js].

<!-- To do: link to unified etc if this repo gets moved there? -->

- to learn markdown, see this [cheatsheet and tutorial][cheat]
- for questions, see [Discussions][chat]
- to help, see [contribute][] or [sponsor][] below

## Contents

<!-- To do: generate this? Use remark? -->

> 🚧 **To do**.

## Install

With [Rust][] (rust edition 2018+, ±version 1.56+), install with `cargo`:

```sh
cargo install micromark
```

## Use

```rs
extern crate micromark;
use micromark::micromark;

fn main() {
    println!("{}", micromark("## Hello, *world*!"));
}
```

Yields:

```html
<h2>Hello, <em>world</em>!</h2>
```

Extensions (in this case GFM):

```rs
extern crate micromark;
use micromark::{micromark_with_options, Constructs, Options};

fn main() {
    println!(
        "{}",
        micromark_with_options(
            "* [x] contact@example.com ~~strikethrough~~",
            &Options {
                constructs: Constructs::gfm(),
                ..Options::default()
            }
        )
    );
}
```

Yields:

```html
<ul>
  <li>
    <input checked="" disabled="" type="checkbox" />
    <a href="mailto:contact@example.com">contact@example.com</a>
    <del>strikethrough</del>
  </li>
</ul>
```

## API

`micromark` exposes
[`micromark`](https://wooorm.com/micromark-rs/micromark/fn.micromark.html),
[`micromark_with_options`](https://wooorm.com/micromark-rs/micromark/fn.micromark_with_options.html), and
[`Options`](https://wooorm.com/micromark-rs/micromark/struct.Options.html).
See [crate docs][docs] for more info.

## Extensions

micromark supports extensions.
These extensions are maintained in this project.
They are not enabled by default but can be turned on with `options.constructs`.

> 🐣 **Note**: extensions are currently within progress.

- [ ] directive
- [x] frontmatter
- [ ] gfm
  - [x] autolink literal
  - [ ] footnote
  - [ ] strikethrough
  - [ ] table
  - [ ] tagfilter
  - [ ] task list item
- [ ] math

It is not a goal of this project to support lots of different extensions.
It’s instead a goal to support incredibly common, somewhat standardized,
extensions.

## Architecture

micromark is maintained as a single monolithic package.

### Overview

The process to parse markdown looks like this:

```txt
                     micromark
+------------------------------------------------+
|            +-------+         +---------+       |
| -markdown->+ parse +-events->+ compile +-html- |
|            +-------+         +---------+       |
+------------------------------------------------+
```

### File structure

The files in `src/` are as follows:

- `construct/*.rs`
  — CommonMark, GFM, and other extension constructs used in micromark
- `util/*.rs`
  — helpers often needed when parsing markdown
- `compiler.rs`
  — turns events into a string of HTML
- `constants.rs`
  — magic numbers and sets used in markdown
- `event.rs`
  — things with meaning happening somewhere
- `lib.rs`
  — core module
- `parser.rs`
  — turn a string of markdown into events
- `resolve.rs`
  — steps to process events
- `state.rs`
  — steps of the state machine
- `subtokenize.rs`
  — handle content in other content
- `tokenizer.rs`
  — glue the states of the state machine together
- `unicode.rs`
  — info on unicode

## Examples

<!-- To do: example section with more full-fledges examples, on GFM, math, frontmatter, etc. -->

> 🚧 **To do**.

## Markdown

### CommonMark

The first definition of “Markdown” gave several examples of how it worked,
showing input Markdown and output HTML, and came with a reference implementation
(`Markdown.pl`).
When new implementations followed, they mostly followed the first definition,
but deviated from the first implementation, and added extensions, thus making
the format a family of formats.

Some years later, an attempt was made to standardize the differences between
implementations, by specifying how several edge cases should be handled, through
more input and output examples.
This is known as [CommonMark][commonmark-spec], and many implementations now
work towards some degree of CommonMark compliancy.
Still, CommonMark describes what the output in HTML should be given some
input, which leaves many edge cases up for debate, and does not answer what
should happen for other output formats.

micromark passes all tests from CommonMark and has many more tests to match the
CommonMark reference parsers.

### Grammar

The syntax of markdown can be described in Backus–Naur form (BNF) as:

```bnf
markdown = .*
```

No, that’s [not a typo](http://trevorjim.com/a-specification-for-markdown/):
markdown has no syntax errors; anything thrown at it renders _something_.

For more practical examples of how things roughly work in BNF, see the module docs of each `src/construct`.

## Project

### Comparison

> 🚧 **To do**.

<!-- To do. -->

### Test

micromark is tested with the \~650 CommonMark tests and more than 1.2k extra
tests confirmed with CM reference parsers.
Then there’s even more tests for GFM and other extensions.
These tests reach all branches in the code, which means that this project has
100% code coverage.

The following scripts are useful when working on this project:

- run examples:
  ```sh
  RUST_BACKTRACE=1 RUST_LOG=debug cargo run --example lib
  ```
- format:
  ```sh
  cargo fmt --all
  ```
- lint:
  ```sh
  cargo fmt --all --check && cargo clippy -- -D clippy::pedantic -D clippy::cargo -A clippy::doc_link_with_quotes
  ```
- test:
  ```sh
  RUST_BACKTRACE=1 cargo test
  ```
- docs:
  ```sh
  cargo doc --document-private-items
  ```

### Version

micromark adheres to [semver](https://semver.org).

### Security

The typical security aspect discussed for markdown is [cross-site scripting
(XSS)][xss] attacks.
Markdown itself is safe if it does not include embedded HTML or dangerous
protocols in links/images (such as `javascript:` or `data:`).
micromark makes any markdown safe by default, even if HTML is embedded or
dangerous protocols are used, as it encodes or drops them.
Turning on the `allow_dangerous_html` or `allow_dangerous_protocol` options for
user-provided markdown opens you up to XSS attacks.

Another security aspect is DDoS attacks.
For example, an attacker could throw a 100mb file at micromark, in which case
it’s going to take a long while to finish.
It is also possible to crash micromark with smaller payloads, notably when
thousands of links, images, emphasis, or strong are opened but not closed.
It is wise to cap the accepted size of input (500kb can hold a big book) and to
process content in a different thread so that it can be stopped when needed.

For more information on markdown sanitation, see
[`improper-markup-sanitization.md`][improper] by [**@chalker**][chalker].

### Contribute

> 🚧 **To do**.

<!-- To do: contrib. -->
<!-- See [`contributing.md`][contributing] for ways to get started.
See [`support.md`][support] for ways to get help. -->

<!-- To do: CoC. -->

### Sponsor

> 🚧 **To do**.

<!-- To do: mention Vercel. -->

Support this effort and give back by sponsoring:

- [GitHub Sponsors](https://github.com/sponsors/wooorm)
  (personal; monthly or one-time)
- [OpenCollective](https://opencollective.com/unified) or
  [GitHub Sponsors](https://github.com/sponsors/unifiedjs)
  (unified; monthly or one-time)

<!-- To do: origin story -->

### License

[MIT][license] © [Titus Wormer][author]

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[sponsors-badge]: https://opencollective.com/unified/sponsors/badge.svg
[backers-badge]: https://opencollective.com/unified/backers/badge.svg
[opencollective]: https://opencollective.com/unified
[docs]: https://wooorm.com/micromark-rs/micromark/
[chat-badge]: https://img.shields.io/badge/chat-discussions-success.svg
[chat]: https://github.com/wooorm/micromark-rs/discussions
[commonmark-spec]: https://spec.commonmark.org
[cheat]: https://commonmark.org/help/
[gfm-spec]: https://github.github.com/gfm/
[rust]: https://www.rust-lang.org
[cmsm]: https://github.com/micromark/common-markup-state-machine
[micromark-js]: https://github.com/micromark/micromark
[xss]: https://en.wikipedia.org/wiki/Cross-site_scripting
[improper]: https://github.com/ChALkeR/notes/blob/master/Improper-markup-sanitization.md
[chalker]: https://github.com/ChALkeR
[license]: https://github.com/micromark/micromark/blob/main/license
[author]: https://wooorm.com
[contribute]: #contribute
[sponsor]: #sponsor
[commonmark]: #commonmark
[extensions]: #extensions
[security]: #security
[test]: #test
[comparison]: #comparison