LOL HTML

Low Output Latency streaming HTML rewriter/parser with CSS-selector based API.

It is designed to modify HTML on the fly with minimal buffering. It can quickly handle very large documents, and operate in environments with limited memory resources. More details can be found in the blog post.

The crate serves as a back-end for the HTML rewriting functionality of Cloudflare Workers, but can be used as a standalone library with a convenient API for a wide variety of HTML rewriting/analysis tasks.

Documentation

https://docs.rs/lol_html/

Bindings for other programming languages

C
Lua
Go (unofficial, not coming from Cloudflare)
Ruby (unofficial, not coming from Cloudflare)

Example

Rewrite insecure hyperlinks:

use lol_html::{element, HtmlRewriter, Settings};

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let mut output = vec![];

    let mut rewriter = HtmlRewriter::new(
        Settings {
            element_content_handlers: vec![
                element!("a[href]", |el| {
                    let href = el
                        .get_attribute("href")
                        .expect("href was required")
                        .replace("http:", "https:");

                    el.set_attribute("href", &href)?;

                    Ok(())
                })
            ],
            ..Settings::new()
        },
        |c: &[u8]| output.extend_from_slice(c)
    );

    rewriter.write(b"<div><a href=")?;
    rewriter.write(b"http://example.com>")?;
    rewriter.write(b"</a></div>")?;
    rewriter.end()?;

    assert_eq!(
        String::from_utf8(output)?,
        r#"<div><a href="https://example.com"></a></div>"#
    );
    Ok(())
}