Support building for externally shared js builtins

Initial support for loading unbundled module in `AddExternalizedBuiltin`.

- Reduces downstream distribution package size (by not shipping wasm twice
  and not base64-encoding it)
- Provides a cleaner stacktrace
- Easier to patch

To enable this, pass `EXTERNAL_PATH=/path/to/global/node_modules/undici`
to `build/wasm.js`.
You shall also pass this path to `--shared-builtin-undici/undici-path`
in Node.js's `configure.py`.

Reference:

nodejs/node@ca5be26b318
nodejs/node#44376

Author: mochaaP

build/wasm.js

@@ -2,7 +2,7 @@
 
 const { execSync } = require('child_process')
 const { writeFileSync, readFileSync } = require('fs')
-const { join, resolve } = require('path')
+const { join, resolve, basename } = require('path')
 
 const ROOT = resolve(__dirname, '../')
 const WASM_SRC = resolve(__dirname, '../deps/llhttp')
@@ -15,6 +15,8 @@ let WASM_CFLAGS = process.env.WASM_CFLAGS || '--sysroot=/usr/share/wasi-sysroot
 let WASM_LDFLAGS = process.env.WASM_LDFLAGS || ''
 const WASM_LDLIBS = process.env.WASM_LDLIBS || ''
 
+const EXTERNAL_PATH = process.env.EXTERNAL_PATH
+
 // These are relevant for undici and should not be overridden
 WASM_CFLAGS += ' -Ofast -fno-exceptions -fvisibility=hidden -mexec-model=reactor'
 WASM_LDFLAGS += ' -Wl,-error-limit=0 -Wl,-O3 -Wl,--lto-O3 -Wl,--strip-all'
@@ -60,18 +62,27 @@ if (hasApk) {
   writeFileSync(join(WASM_OUT, 'wasm_build_env.txt'), buildInfo)
 }
 
+const writeWasmChunk = EXTERNAL_PATH
+  ? (path, dest) => {
+      const base64 = readFileSync(join(WASM_OUT, path)).toString('base64')
+      writeFileSync(join(WASM_OUT, dest), `module.exports = '${base64}'\n`)
+    }
+  : (path, dest) => {
+      writeFileSync(join(WASM_OUT, dest), `
+'use strict'
+
+module.exports = fs.readFileSync(require.resolve('./${basename(path)}'))
+`)
+    }
+
 // Build wasm binary
 execSync(`${WASM_CC} ${WASM_CFLAGS} ${WASM_LDFLAGS} \
  ${join(WASM_SRC, 'src')}/*.c \
  -I${join(WASM_SRC, 'include')} \
  -o ${join(WASM_OUT, 'llhttp.wasm')} \
  ${WASM_LDLIBS}`, { stdio: 'inherit' })
 
-const base64Wasm = readFileSync(join(WASM_OUT, 'llhttp.wasm')).toString('base64')
-writeFileSync(
-  join(WASM_OUT, 'llhttp-wasm.js'),
-  `module.exports = '${base64Wasm}'\n`
-)
+writeWasmChunk('llhttp.wasm', 'llhttp-wasm.js')
 
 // Build wasm simd binary
 execSync(`${WASM_CC} ${WASM_CFLAGS} -msimd128 ${WASM_LDFLAGS} \
@@ -80,8 +91,12 @@ execSync(`${WASM_CC} ${WASM_CFLAGS} -msimd128 ${WASM_LDFLAGS} \
  -o ${join(WASM_OUT, 'llhttp_simd.wasm')} \
  ${WASM_LDLIBS}`, { stdio: 'inherit' })
 
-const base64WasmSimd = readFileSync(join(WASM_OUT, 'llhttp_simd.wasm')).toString('base64')
-writeFileSync(
-  join(WASM_OUT, 'llhttp_simd-wasm.js'),
-  `module.exports = '${base64WasmSimd}'\n`
-)
+writeWasmChunk('llhttp_simd.wasm', 'llhttp_simd-wasm.js')
+
+if (EXTERNAL_PATH) {
+  writeFileSync(join(ROOT, 'loader.js'), `
+'use strict'
+
+module.exports = require('node:module').createRequire('${EXTERNAL_PATH}/loader.js')('./index-fetch.js')
+`)
+}

package.json

@@ -65,6 +65,7 @@
     "*.d.ts",
     "index.js",
     "index-fetch.js",
+    "loader.js",
     "lib",
     "types",
     "docs"