napi-rs-cn-font-split

A napi-rs binding for cn-font-split — a font subsetter/splitter that breaks large CJK fonts into many small, unicode-range-keyed woff2 chunks so the browser only downloads the glyphs a page actually renders.

Why this exists

Upstream cn-font-split ships a JS-only npm package and downloads its native Rust binary from GitHub Releases at install/first-use time. That download isn't pinned to the package version, isn't integrity-checked, and isn't atomic — a partial download silently breaks dlopen later.

This package wraps the same upstream Rust library with napi-rs instead, so the native binary is distributed the standard npm way: prebuilt per-platform .node addons published as optionalDependencies, version-locked to the JS package, integrity-hashed in your lockfile, and installed offline-cacheably. HarfBuzz is built from source and linked statically, so each addon is self-contained (no system libharfbuzz required).

Install

npm install napi-rs-cn-font-split

Prebuilt binaries are published for: macOS (arm64, x64), Linux gnu (arm64, x64), Windows msvc (arm64, x64).

Usage

The binding mirrors the upstream protobuf contract: pass a protobuf-encoded InputTemplate, receive each streamed EventMessage back as a protobuf-encoded Buffer, in emission order.

import { fontSplit } from 'napi-rs-cn-font-split'

// `input` is a protobuf-encoded cn-font InputTemplate (field 1 = the ttf/woff2 bytes).
const events: Buffer[] = fontSplit(input)
// Decode each Buffer as an EventMessage. OUTPUT_DATA events carry { message: filename, data }
// for each woff2 chunk / css / reporter; the final event is END.

See __test__/index.spec.ts for a minimal hand-rolled encode/decode example.

Development

yarn install
yarn build        # builds the .node addon (compiles bundled HarfBuzz on first run)
yarn test         # ava
yarn lint         # oxlint

The upstream Rust crates are pinned to a specific git rev in Cargo.toml. HARFBUZZ_SYS_NO_PKG_CONFIG is set in .cargo/config.toml so local builds bundle HarfBuzz the same way CI does.

Releasing

CI publishes to npm when the latest commit message is a bare semver (e.g. 1.0.0):

yarn version          # bumps version, runs `napi version`
git commit -am "1.0.0"
git push

Requires an NPM_TOKEN repository secret.