SsKaTeX

Server-side KaTeX for Ruby

This is a TeX-to-HTML+MathML+CSS converter class using the Javascript-based KaTeX, interpreted by one of the Javascript engines supported by ExecJS. The intended purpose is to eliminate the need for math-rendering Javascript in the client's HTML browser. Therefore the name: SsKaTeX means server-side KaTeX.

Javascript execution context initialization can be done once and then reused for formula renderings with the same general configuration. As a result, the performance is reasonable. Consider this a fast and lightweight alternative to mathjax-node-cli.

Requirements for using SsKaTeX:

• Ruby gem ExecJS,
• A Javascript engine supported by ExecJS, e.g. via one of
  • Ruby gem therubyracer,
  • Ruby gem therubyrhino,
  • Ruby gem duktape.rb,
  • Node.js,
• katex.min.js from KaTeX.

Although the converter only needs katex.min.js, you may need to serve the rest of the KaTeX package, that is, CSS and fonts, as resources to the targeted web browsers. The upside is that your HTML templates need no longer include Javascripts for Math (neither katex.js nor any search-and-replace script). Your HTML templates should continue referencing the KaTeX CSS. If you host your own copy of the CSS, also keep hosting the fonts.

Minimal usage example:

tex_to_html = SsKaTeX.new(katex_js: 'path-to-katex/katex.min.js')
# Here you could verify contents of tex_to_html.js_source for security...

body_html = '<p>By Pythagoras, %s. Furthermore:</p>' %
  tex_to_html.call('a^2 + b^2 = c^2', false)  # inline math
body_html <<                                  # block display
  tex_to_html.call('\frac{1}{2} + \frac{1}{3} + \frac{1}{6} = 1', true)
# etc, etc.

More configuration options are described in the Rdoc. Most options, with the notable exception of katex_opts, do not affect usage nor output, but may be needed to make SsKaTeX work with all the external parts (JS engine and KaTeX). Since KaTeX is distributed separately from the SsKaTeX gem, configuration of the latter must support the specification of Javascript file locations. This implies that execution of arbitrary Javascript code is possible. Specifically, options with js in their names should be accepted from trusted sources only. Applications using SsKaTeX need to check this.

Also included is a command-line interface to the SsKaTeX gem: A script called sskatex. It demonstrates basic functionality and options of the SsKaTeX gem. It only renders one TeX math expression per invocation; try sskatex -h for more information. If you want to see the SsKaTeX gem used more efficiently, look at kramdown v1.16 or later which can use SsKaTeX as a math engine. But do not make SsKaTeX available where kramdown is exposed to untrusted users; that would be insecure unless that process is sandboxed.