pulldown-cmark guide

Normalizes wikilinks as they pass through the parser.

The resulting destination url of the wikilink is normalized closely to how MediaWiki links are normalized. Use this example to customize this behavior for your use cases.

use pulldown_cmark::{html, CowStr, Event, LinkType, Options, Parser, Tag};
use regex::RegexBuilder;
use std::io::Write;

/// This example demonstrates how to normalize the href of a wikilink. The
/// details of this implementation can be tweaked for different use cases.
fn main() {
    let markdown_input: &str = r#"
Example provided by [[https://example.org/]].
Some people might prefer the wikilink syntax for autolinks.

Wanna go for a [[Wiki Walk]]?"#;

    let parser = Parser::new_ext(markdown_input, Options::ENABLE_WIKILINKS).map(|event| {
        if let Event::Start(Tag::Link {
            link_type: LinkType::WikiLink { has_pothole },
            dest_url,
            title,
            id,
        }) = event
        {
            let new_link = normalize_wikilink(dest_url);
            Event::Start(Tag::Link {
                link_type: LinkType::WikiLink { has_pothole },
                dest_url: new_link,
                title,
                id,
            })
        } else {
            event
        }
    });

    // Write to anything implementing the `Write` trait. This could also be a file
    // or network socket.
    let stdout = std::io::stdout();
    let mut handle = stdout.lock();
    handle.write_all(b"\nHTML output:\n").unwrap();
    html::write_html_io(&mut handle, parser).unwrap();
}

/// Performs wikilink normalization.
fn normalize_wikilink(link: CowStr) -> CowStr {
    // your wiki is stored at "/wiki"
    let prefix: &str = "/wiki";
    if link.is_empty() {
        return link;
    }

    // check if the link is absolute, if it is, return as is
    // according to RFC 3986; https://www.rfc-editor.org/rfc/rfc3986
    let is_absolute = RegexBuilder::new("^(?:[a-z][a-z0-9+\\-.]*:)?//")
        .case_insensitive(true)
        .build()
        .expect("valid regex");

    if is_absolute.is_match(&link) {
        return link;
    }

    let mut result = String::with_capacity(link.len() + 2);
    let mut i = 0;
    let mut mark = 0;
    let mut in_whitespace = false;

    result.push_str(prefix);

    if !link.starts_with('/') {
        result.push('/');
    }

    while i < link.len() {
        if !in_whitespace && link.as_bytes()[i].is_ascii_whitespace() {
            in_whitespace = true;
            result.push_str(&link[mark..i]);
        } else if in_whitespace && !link.as_bytes()[i].is_ascii_whitespace() {
            result.push('_');
            mark = i;
            in_whitespace = false;
        }

        i += 1;
    }

    if !in_whitespace {
        result.push_str(&link[mark..]);
    }
    if !result.ends_with('/') {
        result.push('/');
    }
    result.into()
}