MDN/Archives/Kuma/Scripting

Overview

The mission of the Kuma wiki is to replace MindTouch. One of the advanced features of MindTouch is DekiScript, a Lua-based scripting environment for wiki authors.

We'd like to replace this feature with something secure, capable, modern, and convenient. We'd also like it if we could carry over the existing body of DekiScript with minimal manual changes. Let's see what's feasible.

DekiScript highlights

• Lua-based dynamic scripting language
• XML/HTML literals for easier construction of well-formed markup
• Inline { { script expressions } } in wiki page content
• Long-form Template: scripts callable with parameters from inline expressions
• Local API with access to Wiki data queries (eg. custom tables of contents, etc)
• Network API with access to external web services (eg. RSS feeds, bugzilla, etc)
• Safe for use by wiki content authors
  • (Not entirely sure what makes it safe, need more research)
    • Seems like long-form Template: scripts are editable only by elevated-permission users?
    • Normal content editors can make calls to Template: scripts, but not employ all scripting features?

Code samples

Here's some inline script excerpted from en/Firefox_9_for_developers:

    <li>The <code>value</code> attribute of {{HTMLElement("li")}} now can be
    negative as specified in HTML5. Previously negative values were converted
    to 0.</li>

Here's the source of Template:HTMLElement, a commonly used script:

    /* accepts as input one required parameter: HTML element to create a xref to */
    var uri = uri.parts(Page.uri);
    var lang = string.tolower(uri.path[0]);
    if (string.contains(lang, "project") || string.contains(lang, "Project")) {
      let lang = string.substr(lang, 8);
    }
    /* fall back to page.language on a user page */
    else if (string.StartsWith(lang, "user:")) {
      let lang = page.language;
    }
    var name = $0;
    var sectionname = "Element";

    if (!string.compare("es", string.tolower(lang))) {
      let sectionname = "Elemento";
    }

    if (args.title) {
      let name = args.title;
    }
    var dest = lang .. '/' .. 'HTML/' .. sectionname .. '/' .. name;
    var destEng = 'en/HTML/Element/' .. name;
    if (wiki.pageExists(dest)) { /* the page exists */
      <code>(web.link(wiki.uri(dest), '<' .. name .. '>'))</code>;
    } else if (lang == 'zh_tw' && wiki.pageExists(destEng)){
      /* the MozTW community consider links to English pages better than red ones. 
         I'll write about this to mozilla.dev.mdc later */   
      <code>(web.link(wiki.uri(destEng), '<' .. name .. '>'))</code>;
    } else { /* the page doesn't exist */
      var targeturi = "https://developer.mozilla.org/Article_not_found?uri=" .. dest;
      <code><a rel=('internal') href=(targeturi) class=('new')>web.text('<' .. name .. '>')</a></code>
    }

Miscellaneous notes

• Use standalone embedded JS templates instead of literals embedded in script?
  • Employs code-in-markup instead of markup-in-code, and avoids the need for fancy compiler hijinx
• Might js-xml-literals come in handy?
  • I failed on my first attempt to install, so haven't seen this in action.
• Should we get a compiler / language expert in on this for opinions?
• Could we port DekiScript directly? (It's open source, right?)

Proposed solution #1

Considering this from a high-level view of off-the-shelf parts that could be glued together:

• Kuma wiki CMS (Django/Python)
• Sandboxed server-side JavaScript filter proxy (node.js)
• Convenience methods to perform wiki content queries and utility functions
• Plentiful and intelligent HTTP-based caching

Sandboxed eval with node.js

• Can this be done in a way that restricts file, network, memory, and CPU usage?
• Host configuration vs node.js env construction?
  • That is, configure the server host in a restrictive way and/or redefine node.js globals
• No filesystem access at all (chroot?)
• Whitelisted network access (firewall rules?)
• Limited execution time (kill the process after 30 sec?)
• Limited memory usage (kill the process after 10MB consumed?)
• Auto-disable script if abuse detected?
• Anything else dangerous to expose?