build.mjs

#!/usr/bin/env node
/**
 * Build script: esbuild + post-process patches for onnxruntime-web in Cloudflare Workers.
 *
 * Root problem: workerd (the Cloudflare Workers runtime) blocks WebAssembly.compile()
 * and leaves import.meta.url empty, breaking both WASM loading paths in onnxruntime-web.
 *
 * Solution: three patches applied after esbuild bundles the code:
 *
 *   Patch 1 — static WASM + model imports (preamble)
 *     Add `import __ORT_WASM__ from "./ort-wasm-simd-threaded.wasm"` at bundle top.
 *     Wrangler [[rules]] type="CompiledWasm" makes this resolve to a WebAssembly.Module
 *     that was compiled at *deploy time* (not at runtime), bypassing the runtime block.
 *     Same for the .onnx model (type="Data" → ArrayBuffer).
 *
 *   Patch 2 — instantiateWasm callback
 *     ORT's Emscripten-compiled JS checks for `config.instantiateWasm` before trying
 *     WebAssembly.compile(). We inject this callback onto the Emscripten Module config
 *     variable (the one with `numThreads`) right before the factory call.
 *     The callback calls `new WebAssembly.Instance(module, imports)` directly —
 *     this works in workerd because the module is *already compiled*.
 *
 *   Patch 3 — kill dynamic import()
 *     ORT contains `await import(variable)` for proxy worker loading. workerd rejects
 *     dynamic import specifiers at module analysis time (not runtime), so the entire
 *     Worker script would fail to load. We replace it with a rejected promise.
 *
 * Size budget (gzip):
 *   ort.wasm.bundle.min.mjs   ~0.43 MB
 *   ort-wasm-simd-threaded.wasm  ~2.98 MB
 *   silero_vad.onnx (2.3 MB)  ~1.85 MB
 *   Total: ~5.26 MB (well under 10 MB Worker limit)
 */

import esbuild from "esbuild";
import { cpSync, readFileSync, writeFileSync, mkdirSync, rmSync, existsSync } from "node:fs";
import { resolve, dirname } from "node:path";
import { fileURLToPath } from "node:url";

const __dirname = dirname(fileURLToPath(import.meta.url));
const OUT_DIR = resolve(__dirname, ".worker");
const ORT_DIST = resolve(__dirname, "node_modules/onnxruntime-web/dist");

// ── Cleanup ──────────────────────────────────────────────────────────────────
rmSync(OUT_DIR, { recursive: true, force: true });
mkdirSync(OUT_DIR, { recursive: true });

// ── 1. esbuild ──────────────────────────────────────────────────────────────
console.log("[build] esbuild …");
await esbuild.build({
  entryPoints: [resolve(__dirname, "src/index.ts")],
  bundle: true,
  format: "esm",
  target: "es2022",
  platform: "browser",
  outfile: resolve(OUT_DIR, "index.js"),
  sourcemap: true,
  minify: false,  // keep readable for patching; wrangler can minify after
  external: ["node:async_hooks", "cloudflare:workers"],
  alias: {
    // Use the bundle variant: ORT's Emscripten glue + JS inlined, no external loader .mjs
    "onnxruntime-web": resolve(ORT_DIST, "ort.wasm.bundle.min.mjs"),
  },
});

// ── 2. Copy assets ──────────────────────────────────────────────────────────
console.log("[build] copying assets …");
cpSync(resolve(ORT_DIST, "ort-wasm-simd-threaded.wasm"), resolve(OUT_DIR, "ort-wasm-simd-threaded.wasm"));
cpSync(resolve(__dirname, "model.onnx"), resolve(OUT_DIR, "model.onnx"));

// ── 3. Post-process patches ──────────────────────────────────────────────────
console.log("[build] patching bundle …");
let code = readFileSync(resolve(OUT_DIR, "index.js"), "utf8");

// Patch 1: preamble — static imports for WASM module + model bytes
const preamble = [
  `import __ORT_WASM__ from "./ort-wasm-simd-threaded.wasm";`,
  `import __MODEL_BYTES__ from "./model.onnx";`,
  `globalThis.__ORT_WASM__ = __ORT_WASM__;`,
  `globalThis.__MODEL_BYTES__ = __MODEL_BYTES__;`,
].join("\n") + "\n";
code = preamble + code;

// Patch 2: inject instantiateWasm on Emscripten Module config
//
// esbuild preserves the ORT pattern: let CONFIG = { numThreads: N }
// ... (locateFile assignments) ...
// FACTORY(CONFIG).then(
//
// We inject instantiateWasm right before the FACTORY(CONFIG) call.
const configMatch = code.match(/let\s+(\w+)\s*=\s*\{\s*numThreads:\s*(\w+)\s*\}/);
if (!configMatch) {
  throw new Error("Could not find Emscripten config `let X = { numThreads: Y }` — ORT version changed?");
}
const configVar = configMatch[1];

const factoryCallRe = new RegExp(`(\\w+)\\(${configVar}\\)\\.then\\(`);
const factoryMatch = code.match(factoryCallRe);
if (!factoryMatch) {
  throw new Error(`Could not find factory call FUNC(${configVar}).then( — ORT version changed?`);
}

const instantiateWasmSnippet =
  `${configVar}.instantiateWasm = (imports, cb) => {` +
  ` var inst = new WebAssembly.Instance(__ORT_WASM__, imports);` +
  ` cb(inst, __ORT_WASM__);` +
  ` return inst.exports; };`;

code = code.replace(factoryMatch[0], instantiateWasmSnippet + " " + factoryMatch[0]);
console.log(`[build]   injected instantiateWasm on config var "${configVar}"`);

// Patch 3: kill variable dynamic import() — workerd rejects at module analysis time
let dynamicImportCount = 0;
code = code.replace(/await import\([\s\S]*?\)/g, (match) => {
  if (/await import\(\s*["'`]/.test(match)) return match; // keep static string imports
  dynamicImportCount++;
  return 'await Promise.reject(new Error("dynamic import disabled in workerd"))';
});
console.log(`[build]   patched ${dynamicImportCount} dynamic import() call(s)`);

// ── 4. Write + verify ────────────────────────────────────────────────────────
writeFileSync(resolve(OUT_DIR, "index.js"), code);
console.log(`[build] done — .worker/index.js (${(code.length / 1024).toFixed(0)} KB)`);

for (const f of ["index.js", "ort-wasm-simd-threaded.wasm", "model.onnx"]) {
  if (!existsSync(resolve(OUT_DIR, f))) throw new Error(`Missing ${f} in .worker/`);
}
console.log("[build] all assets verified ✓");
console.log("\nDeploy with:");
console.log("  wrangler deploy .worker/index.js --no-bundle");