Ruby bindings for Boa — what we built and how we'd like to contribute back

[rubys]

Title: Ruby bindings for Boa — what we built and how we'd like to contribute back

I've been experimenting with embedding Boa in Ruby via Rust (using magnus/rb-sys for the FFI layer). The result is boax, a proof of concept that lets Ruby call JavaScript through proxy objects:

intl = Boax.import('Intl')
nf = intl.NumberFormat.new('en-US', { style: 'currency', currency: 'USD' })
nf.format(1234.56)  # => "$1,234.56"

Boax.init(root: __dir__)
_ = Boax.import('lodash-es')
_.chunk([1, 2, 3, 4, 5, 6], 2).to_ruby  # => [[1, 2], [3, 4], [5, 6]]

It supports ES module loading (via oxc_resolver against node_modules/), CommonJS require, and npm packages like lodash-es, date-fns, uuid, and chalk load and run correctly.

Along the way, we implemented several things that probably shouldn't live in a Ruby gem long-term, and I wanted to open a conversation about where they might belong.

Node.js built-in modules

We implemented 13 Node.js modules as Boa synthetic modules: path, fs, util, events, process, os, buffer, crypto, stream, querystring, string_decoder, assert, and url. These are pure Rust (or JS evaluated at init time), with no Ruby dependency. They exist so that npm packages that import Node built-ins don't fail at load time.

The implementations are pragmatic — fs wraps std::fs, crypto wraps sha2/hmac/getrandom, path wraps std::path, stream is an MVP without backpressure. They're not complete Node.js compatibility, but they cover the subset that popular npm packages actually use.

These feel like they'd be useful to anyone embedding Boa, not just Ruby. A boa_node crate (or additions to boa_runtime) would let Deno-like projects, CLI tools, or other embedders share the same implementations rather than each writing their own path.join.

Intl gaps

We hit the unimplemented error in NumberFormat for currency and percent styles. Rather than just polyfilling around it, I looked at the Boa source and submitted #5257 to fix percent formatting. It was a small change — multiply_pow10(2) and appending the percent sign — and it was a good way to learn how Boa's Intl code is structured.

Currency formatting looks similarly approachable: a currency_digits() lookup table to fix the constructor, plus symbol/placement wrapping around the existing DecimalFormatter output. I'd be happy to work on that as a follow-up PR if the percent one looks reasonable.

Web Crypto

We added crypto.getRandomValues as a global (wrapping getrandom) because packages like uuid expect it. This is a Web API in the same category as URL and TextEncoder that boa_runtime already provides. Would a PR adding it to boa_runtime be welcome?

No urgency

None of this is blocking us. The proof of concept works as-is, and the polyfills serve their purpose. This is more about wanting to contribute the generally-useful pieces back rather than maintaining them in a Ruby-specific gem. I'm happy to work at whatever pace makes sense for the project.

The boax source is available if anyone wants to see the full implementation. I wrote about the motivation in a blog post as well.