css-inline

css_inline is a high-performance library for inlining CSS into HTML 'style' attributes.

This library is designed for scenarios such as preparing HTML emails or embedding HTML into third-party web pages.

For instance, the crate transforms HTML like this:

<html>
    <head>
        <style>h1 { color:blue; }</style>
    </head>
    <body>
        <h1>Big Text</h1>
    </body>
</html>

into:

<html>
    <head></head>
    <body>
        <h1 style="color:blue;">Big Text</h1>
    </body>
</html>

Uses reliable components from Mozilla's Servo project
Inlines CSS from style and link tags
Removes style and link tags
Resolves external stylesheets (including local files)
Works on Linux, Windows, and macOS
Supports HTML5 & CSS3

Installation

To include it in your project, add the following line to the dependencies section in your project's Cargo.toml file:

[dependencies]
css-inline = "0.11"

The Minimum Supported Rust Version is 1.63.

Usage

const HTML: &str = r#"<html>
<head>
    <style>h1 { color:blue; }</style>
</head>
<body>
    <h1>Big Text</h1>
</body>
</html>"#;

fn main() -> Result<(), css_inline::InlineError> {
    let inlined = css_inline::inline(HTML)?;
    // Do something with inlined HTML, e.g. send an email
    Ok(())
}

Configuration

css-inline can be configured by using CSSInliner::options() that implements the Builder pattern:

const HTML: &str = "...";

fn main() -> Result<(), css_inline::InlineError> {
    let inliner = css_inline::CSSInliner::options()
        .load_remote_stylesheets(false)
        .build();
    let inlined = inliner.inline(HTML);
    // Do something with inlined HTML, e.g. send an email
    Ok(())
}

inline_style_tags. Specifies whether to inline CSS from "style" tags. Default: true
keep_style_tags. Specifies whether to keep "style" tags after inlining. Default: false
keep_link_tags. Specifies whether to keep "link" tags after inlining. Default: false
base_url. The base URL used to resolve relative URLs. If you'd like to load stylesheets from your filesystem, use the file:// scheme. Default: None
load_remote_stylesheets. Specifies whether remote stylesheets should be loaded. Default: true
extra_css. Extra CSS to be inlined. Default: None
preallocate_node_capacity. Advanced. Preallocates capacity for HTML nodes during parsing. This can improve performance when you have an estimate of the number of nodes in your HTML document. Default: 32

You can also skip CSS inlining for an HTML tag by adding the data-css-inline="ignore" attribute to it:

<head>
    <style>h1 { color:blue; }</style>
</head>
<body>
    <!-- The tag below won't receive additional styles -->
    <h1 data-css-inline="ignore">Big Text</h1>
</body>

The data-css-inline="ignore" attribute also allows you to skip link and style tags:

<head>
    <!-- Styles below are ignored -->
    <style data-css-inline="ignore">h1 { color:blue; }</style>
</head>
<body>
    <h1>Big Text</h1>
</body>

If you'd like to load stylesheets from your filesystem, use the file:// scheme:

const HTML: &str = "...";

fn main() -> Result<(), css_inline::InlineError> {
    let base_url = css_inline::Url::parse("file://styles/email/").expect("Invalid URL");
    let inliner = css_inline::CSSInliner::options()
        .base_url(Some(base_url))
        .build();
    let inlined = inliner.inline(HTML);
    // Do something with inlined HTML, e.g. send an email
    Ok(())
}

Performance

css-inline typically inlines HTML emails within hundreds of microseconds, though results may vary with input complexity.

Benchmarks for css-inline==0.10.5:

Basic: 6.40 µs, 230 bytes
Realistic-1: 140.19 µs, 8.58 KB
Realistic-2: 86.21 µs, 4.3 KB
GitHub page: 263.33 ms, 1.81 MB

These benchmarks, conducted using rustc 1.71.1, can be found in css-inline/benches/inliner.rs.

Bindings

css-inline is primarily a Rust library, but we also provide bindings for several other languages:

Command Line Interface

Installation

Install with cargo:

cargo install css-inline

Usage

The following command inlines CSS in multiple documents in parallel. Resulting files will be saved as inlined.email1.html and inlined.email2.html:

css-inline email1.html email2.html

For full details of the options available, you can use the --help flag:

css-inline --help

Further reading

If you're interested in learning how this library was created and how it works internally, check out these articles:

Support

If you have any questions or discussions related to this library, please join our gitter!

License

This project is licensed under the terms of the MIT license.

License

synapticarbors/css-inline

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