From: "mdalessio (Mike Dalessio) via ruby-core" <ruby-core@...>
Date: 2026-08-05T13:40:55+00:00
Subject: [ruby-core:126271] [Ruby Feature#22229] Allow GCI.escapeHTML to take a custom escape table

Issue #22229 has been updated by mdalessio (Mike Dalessio).


I would also like to have this feature. Loofah (used by Rails's sanitization stack) currently has this code to re-implement `escapeHTML` with a custom table: https://github.com/flavorjones/loofah/blob/main/lib/loofah/html5/scrub.rb#L275-L299, as does the Rouge gem (and probably others).

----------------------------------------
Feature #22229: Allow GCI.escapeHTML to take a custom escape table
https://bugs.ruby-lang.org/issues/22229#change-118360

* Author: byroot (Jean Boussier)
* Status: Open
----------------------------------------
### Use case

`CGI.escapeHTML` has a fixed escape table:

```c
    HTML_ESCAPE('\'', "&#39;"),
    HTML_ESCAPE('&', "&amp;"),
    HTML_ESCAPE('"', "&quot;"),
    HTML_ESCAPE('<', "&lt;"),
    HTML_ESCAPE('>', "&gt;"),
```

But in some context you may want to escape more or less characters than that, or escape them differently.

One example of this is Active Support JSON serialization, which by defaults escape `<>&` as  `\u003e\u003c\u0026`, to ensure that the generated
JSON can safely be interpolated inside a `<script>` tag without causing XSS vulnerabilities.

There's likely other use case as evidenced by the popularity of the `htmlentities` gem, which support several more escape tables.

### Why not `gsub` ?

Today, this sort of escaping is performed using `gsub`, it works but is very noticeably slower than `CGI.escapeHTML` (see benchmarks on the PoC PR).
This is because the only way to use `gsub` with an escape table is to craft a regexp:

```ruby
def escape(string, table)
  pattern = Regexp.union(table.keys)
  string.gsub(pattern, table)
end

puts escape("<script>", "<" => "&lt;", ">" => "&gt;")
```

If `gsub` could be used directly with the escape table it would certainly make it faster:

```ruby
puts "<script>".gsub("<" => "&lt;", ">" => "&gt;")
```

But compared to `CGI.escapeHTML` it would still need to deal with noticeably more scenarios (multi character search, etc), so would always be slower than a dedicated escaping method.

`CGI.escapeHTML` can be more restrictive (single character search, etc).

### Specification

```ruby
GCI.escapeHTML("</script>", "<" => "&lt;", ">" => "&gt;")
```

- The escape table keys must be single characters (currently ASCII only, but could be muti-byte characters if deemed necessary).

### Implementation

Pull Request: https://github.com/ruby/cgi/pull/55 (NB: it's at proof of concept / demo stage, if the feature is accepted I can polish it).



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