feat(bundler): lazy-externalize undici + urllib by default for snapshots

Add `undici` and `urllib` to DEFAULT_SNAPSHOT_LAZY_MODULES so an app gets a
serializable V8 startup snapshot without listing them in
`egg.snapshot.lazyModules`. Egg builds its HttpClient (urllib -> undici) during
boot, and undici instantiates an llhttp WebAssembly module (disabled under
--build-snapshot) + an HTTPParser that cannot be snapshot-serialized.

As npm packages, urllib/undici would otherwise be inlined into the bundle and
evaluated at build time; listing them here forces them external so the prelude's
member-proxy stub is used at build and the real module is required on restore.
The member-proxy (eggjs#6003) already replays the recorded access path, so egg's
`class HttpClient extends urllib.HttpClient` keeps working across the
build->restore boundary.

Adds a unit assertion for the default list and a real @utoo/pack build test that
exercises `class Sub extends pkg.Base` for a forced-external npm package across
the build-stub / restore-real boundary (upstream only covered the node:http
builtin).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: killagu

tools/egg-bundler/src/lib/prelude.ts

@@ -36,9 +36,9 @@ const debug = debuglog('egg/bundler/snapshot-prelude');
 export const SNAPSHOT_PRELUDE_MARKER = '@eggjs/egg-bundler:snapshot-prelude';
 
 /**
- * Node built-in modules that produce non-serializable native bindings when loaded
- * inside a V8 startup snapshot builder. They are kept as lazy externals: build time
- * returns a member-proxy stub; restore time forwards to the real module via
+ * Modules that produce non-serializable native bindings when loaded inside a V8
+ * startup snapshot builder. They are kept as lazy externals: build time returns a
+ * member-proxy stub; restore time forwards to the real module via
  * `globalThis.__RUNTIME_REQUIRE`.
  *
  * - network stack (HTTPParser, nghttp2, SecureContext, ChannelWrap):
@@ -50,6 +50,16 @@ export const SNAPSHOT_PRELUDE_MARKER = '@eggjs/egg-bundler:snapshot-prelude';
  *   (readline/repl + http2 nghttp2 native), making the heap unserializable. Keep
  *   it lazy so the build-time stub is used; the live process gets the real module
  *   on restore.
+ * - `undici` / `urllib`: egg's HTTP client stack, built during boot
+ *   (`class HttpClient extends urllib.HttpClient`, and urllib's own
+ *   `class BaseAgent extends undici.Agent`). undici instantiates an llhttp
+ *   `WebAssembly` module (disabled under `--build-snapshot`) + an `HTTPParser`, so
+ *   it must not be evaluated at build. Unlike the builtins above these are npm
+ *   packages that would otherwise be **inlined** into the bundle and evaluated at
+ *   build; listing them here forces them external (see {@link Bundler}) so the
+ *   member-proxy stub is used at build and the real module is required on restore.
+ *   Listing them by default means an app gets a serializable snapshot without
+ *   adding them to `egg.snapshot.lazyModules` itself.
  */
 export const DEFAULT_SNAPSHOT_LAZY_MODULES: readonly string[] = [
   'http',
@@ -64,6 +74,8 @@ export const DEFAULT_SNAPSHOT_LAZY_MODULES: readonly string[] = [
   'node:dns',
   'inspector',
   'node:inspector',
+  'undici',
+  'urllib',
 ];
 
 /**

tools/egg-bundler/test/snapshot-lazy-external.test.ts

@@ -31,6 +31,18 @@ describe('snapshot lazy-external', () => {
       expect(result).toContain('node:dns');
     });
 
+    it("lazy-externalizes egg's HTTP client stack (undici + urllib) by default", async () => {
+      // Egg builds its HttpClient (urllib -> undici) during boot; undici's llhttp
+      // WebAssembly + HTTPParser cannot be snapshot-serialized. As npm packages they
+      // would otherwise be inlined, so they must be forced external (this list) to get
+      // the member-proxy stub at build — without an app listing them itself.
+      expect(DEFAULT_SNAPSHOT_LAZY_MODULES).toContain('undici');
+      expect(DEFAULT_SNAPSHOT_LAZY_MODULES).toContain('urllib');
+      const result = await resolveSnapshotLazyModules(tmp);
+      expect(result).toContain('undici');
+      expect(result).toContain('urllib');
+    });
+
     it('returns the default list when package.json has no egg.snapshot.lazyModules', async () => {
       await fs.writeFile(path.join(tmp, 'package.json'), JSON.stringify({ name: 'app', egg: {} }));
       expect(await resolveSnapshotLazyModules(tmp)).toEqual([...DEFAULT_SNAPSHOT_LAZY_MODULES]);

tools/egg-bundler/test/snapshot-lazy.realbuild.test.ts

@@ -232,4 +232,141 @@ describe('snapshot lazy-external — real @utoo/pack build', () => {
     expect(probe.BlobType).toBe('function');
     expect(probe.blobText).toBe('z'); // real node:buffer Blob
   }, 60_000);
+
+  it('forced-external npm package: class extends pkg.Base is a stub at build, real base after restore', async () => {
+    // The scenario this PR's undici/urllib defaults enable: a bundled module extends a
+    // class exported by a forced-external npm package (egg's
+    // `class HttpClient extends urllib.HttpClient`). The `extends` clause is evaluated
+    // at BUILD time against the member-proxy stub; at RESTORE the member-proxy replays
+    // the access path against the real module, so `super(...)` and inherited methods
+    // resolve to the real base class. A local `lazy-base` package stands in for urllib
+    // so the test stays hermetic (ExternalsResolver is mocked, so it is forced external
+    // only via egg.snapshot.lazyModules).
+    await fs.writeFile(
+      path.join(baseDir, 'package.json'),
+      JSON.stringify({ name: 'snaplazy-extends-app', egg: { snapshot: { lazyModules: ['lazy-base'] } } }),
+    );
+    const basePkgDir = path.join(baseDir, 'node_modules', 'lazy-base');
+    await fs.mkdir(basePkgDir, { recursive: true });
+    await fs.writeFile(path.join(basePkgDir, 'package.json'), JSON.stringify({ name: 'lazy-base', main: 'index.js' }));
+    await fs.writeFile(
+      path.join(basePkgDir, 'index.js'),
+      [
+        // Module-eval load counter: lets the runners prove WHEN the real package is
+        // actually loaded (it must be never at build, and only at restore once the
+        // member-proxy resolves through the lazy hook — not via native resolution).
+        'globalThis.__LAZY_BASE_LOADS = (globalThis.__LAZY_BASE_LOADS || 0) + 1;',
+        'class Base {',
+        '  constructor(opt) { this.opt = opt; }',
+        "  greet() { return 'base#' + this.opt; }",
+        '}',
+        'module.exports = { Base };',
+        '',
+      ].join('\n'),
+    );
+
+    const entryDir = path.join(baseDir, '.egg-bundle', 'entries');
+    await fs.mkdir(entryDir, { recursive: true });
+    const entry = path.join(entryDir, 'worker.entry.ts');
+    await fs.writeFile(
+      entry,
+      [
+        '// @ts-nocheck',
+        // captured at module-eval; the `extends` link freezes against whatever this is
+        "const { Base } = require('lazy-base');",
+        'class Sub extends Base {',
+        '  constructor(opt) { super(opt); this.tag = "sub"; }',
+        '  describe() { return this.tag + ":" + this.greet(); }',
+        '}',
+        // defer instantiation so the runner controls the build/restore boundary
+        'globalThis.__makeSub = (n) => new Sub(n);',
+        'process.stdout.write("ENTRY_OK");',
+        '',
+      ].join('\n'),
+    );
+    mocks.workerEntry = entry;
+    mocks.entryDir = entryDir;
+
+    const outputDir = path.join(baseDir, 'dist');
+    await bundle({ baseDir, outputDir, snapshot: true });
+
+    const workerPath = path.join(outputDir, 'worker.js');
+    const worker = await fs.readFile(workerPath, 'utf8');
+    expect(worker).toContain(SNAPSHOT_PRELUDE_MARKER);
+    expect(worker).toMatch(/function\s+externalRequire\s*\(/);
+    await execFileAsync(process.execPath, ['--check', workerPath]);
+
+    const basePathLiteral = JSON.stringify(basePkgDir);
+
+    // BUILD context: define + construct the subclass with no __RUNTIME_REQUIRE. The base
+    // is the member-proxy stub, so the instance is not a real lazy-base instance, nothing
+    // throws, and crucially the real lazy-base module is NEVER loaded (realLoads === 0) —
+    // proving the bundle used the build-time stub rather than resolving the package.
+    const buildRunner = path.join(outputDir, 'build-runner.cjs');
+    await fs.writeFile(
+      buildRunner,
+      [
+        'const probe = { phase: "build" };',
+        'try {',
+        '  require("./worker.js");',
+        '  globalThis.__makeSub(7);',
+        '  probe.restored = !!globalThis.__RUNTIME_REQUIRE;',
+        '  probe.realLoads = globalThis.__LAZY_BASE_LOADS || 0;',
+        '  probe.threw = false;',
+        '} catch (e) { probe.threw = true; probe.err = e.message; }',
+        'process.stdout.write("\\n" + JSON.stringify(probe));',
+        '',
+      ].join('\n'),
+    );
+    const built = await execFileAsync(process.execPath, [buildRunner], { cwd: outputDir });
+    expect(JSON.parse(built.stdout.split('\n').pop() ?? '')).toMatchObject({
+      restored: false,
+      threw: false,
+      realLoads: 0, // real lazy-base never loaded at build
+    });
+
+    // RESTORE context (cross-phase, one process): require worker.js with __RUNTIME_REQUIRE
+    // still unset (freezing `extends` against the stub), THEN install it, THEN instantiate.
+    // The load counters prove the real lazy-base is pulled in ONLY when the member-proxy
+    // resolves through the `__RUNTIME_REQUIRE` hook (loadedBeforeMakeSub === 0,
+    // loadedAfterMakeSub === 1) — i.e. via the lazy hook, not native pre-resolution.
+    //
+    // `instanceof Base` is intentionally NOT asserted: makeMember's `protoProxy` exposes
+    // only a `get` trap (no `getPrototypeOf`), so inherited methods forward to the real
+    // prototype but the snapshot-frozen subclass's prototype chain does not literally
+    // contain the real `Base.prototype` — identity-by-prototype is a known non-goal of the
+    // upstream member-proxy.
+    const restoreRunner = path.join(outputDir, 'restore-runner.cjs');
+    await fs.writeFile(
+      restoreRunner,
+      [
+        'require("./worker.js");',
+        'const loadedBeforeRT = globalThis.__LAZY_BASE_LOADS || 0;',
+        `globalThis.__RUNTIME_REQUIRE = (id) => id === "lazy-base" ? require(${basePathLiteral}) : require(id);`,
+        'const loadedBeforeMakeSub = globalThis.__LAZY_BASE_LOADS || 0;',
+        'const inst = globalThis.__makeSub(7);',
+        'const probe = {',
+        '  restored: true,',
+        '  loadedBeforeRT,',
+        '  loadedBeforeMakeSub,',
+        '  loadedAfterMakeSub: globalThis.__LAZY_BASE_LOADS || 0,',
+        '  tag: inst.tag,',
+        '  greet: inst.greet(),',
+        '  describe: inst.describe(),',
+        '};',
+        'process.stdout.write("\\n" + JSON.stringify(probe));',
+        '',
+      ].join('\n'),
+    );
+    const restored = await execFileAsync(process.execPath, [restoreRunner], { cwd: outputDir });
+    expect(JSON.parse(restored.stdout.split('\n').pop() ?? '')).toEqual({
+      restored: true,
+      loadedBeforeRT: 0, // building the worker did not load the real module
+      loadedBeforeMakeSub: 0, // installing __RUNTIME_REQUIRE does not eagerly load it
+      loadedAfterMakeSub: 1, // loaded exactly once, when the member-proxy resolved via the hook
+      tag: 'sub', // subclass constructor ran
+      greet: 'base#7', // inherited real method + real field (opt=7) — real base constructed
+      describe: 'sub:base#7', // subclass method invoking the inherited one
+    });
+  }, 60_000);
 });

wiki/log.md

@@ -2,6 +2,15 @@
 
 Dates use the workspace-local Asia/Shanghai calendar date.
 
+## [2026-06-28] package | snapshot bundler lazy-externalizes undici + urllib by default (PR #6011)
+
+- sources touched: `tools/egg-bundler/src/lib/prelude.ts`, `tools/egg-bundler/test/snapshot-lazy-external.test.ts`, `tools/egg-bundler/test/snapshot-lazy.realbuild.test.ts`
+- pages updated: `wiki/packages/egg-bundler.md`, `wiki/log.md`
+- branch: `feat/snapshot-default-lazy-undici-urllib` (off `next`)
+- change: Added `undici` + `urllib` to `DEFAULT_SNAPSHOT_LAZY_MODULES` so an app gets a serializable V8 snapshot without listing them in `egg.snapshot.lazyModules`. Egg builds its HttpClient (urllib → undici) during boot, and undici's llhttp `WebAssembly` + `HTTPParser` cannot be snapshot-serialized. As npm packages they would be inlined; listing them forces them external (`Bundler` adds lazy ids to the externals map) so the prelude member-proxy stub is used at build and the real module is required on restore.
+- history note: the PR originally (off the older `next`) shipped a bespoke per-export forwarder in `__makeLazyExt` to make `class HttpClient extends urllib.HttpClient` survive the build→restore boundary. While the PR was open, #6003 landed on `next` and rewrote `__makeLazyExt` into a general **access-path-recording member-proxy** (`makeMember`) that already handles `class X extends pkg.Klass` / `DataTypes.INTEGER(11).UNSIGNED` plus `ownKeys`/`getOwnPropertyDescriptor` via `__EXTERNAL_EXPORTS`. The PR was rebased onto that and **reduced to just the default-list addition** (forwarder dropped as superseded). Note `makeMember`'s `protoProxy` has only a `get` trap (no `getPrototypeOf`), so `instanceof RealBase` on a snapshot-frozen subclass is `false` — methods/fields/super() work, identity-by-prototype does not.
+- verification: unit test asserts undici+urllib in the default list; new real `@utoo/pack` build test exercises a **forced-external npm package** `class Sub extends pkg.Base` across the build-stub / restore-real boundary in one process (upstream only realbuild-tested the `node:http` builtin). 28 lazy/realbuild tests green; tsgo + oxlint clean. Pre-existing macOS `ManifestLoader`/`EntryGenerator` tmpdir-symlink failures unrelated.
+
 ## [2026-06-27] concept | fix concurrent-import race in multi-app boot (oxc-node PR #5965)
 
 - sources touched: `packages/utils/src/import.ts`

wiki/packages/egg-bundler.md

@@ -7,9 +7,10 @@ source_files:
   - tools/egg-bundler/src/lib/Bundler.ts
   - tools/egg-bundler/src/lib/EntryGenerator.ts
   - tools/egg-bundler/src/lib/ExternalsResolver.ts
+  - tools/egg-bundler/src/lib/prelude.ts
   - tools/egg-bin/src/commands/bundle.ts
   - tools/egg-bundler/docs/output-structure.md
-updated_at: 2026-05-06
+updated_at: 2026-06-28
 status: active
 ---
 
@@ -66,3 +67,28 @@ CommonJS artifact from an Egg application.
   external.
 - `BundlerConfig.tegg` is accepted but intentionally not wired into the current
   implementation yet.
+
+### Snapshot lazy-external defaults
+
+In `snapshot: true` mode the bundler keeps a set of modules **lazy-external** so a
+V8 startup snapshot stays serializable: each is emitted as an `externalRequire`,
+left out of the build-time heap (a member-proxy stub from the prelude's
+`__makeLazyExt`), and forwarded to the real module at restore via
+`globalThis.__RUNTIME_REQUIRE`. The injected hook also lazy-stubs any **non-builtin**
+external at build (`!__isBuiltin(id)`); the explicit list mainly exists to (a) cover
+builtins the `!isBuiltin` rule skips and (b) **force npm packages external** that
+would otherwise be inlined.
+
+- `DEFAULT_SNAPSHOT_LAZY_MODULES` (in `src/lib/prelude.ts`) covers the Node network
+  stack (`http`/`https`/`http2`/`tls`/`dns`), `inspector`, **and egg's HTTP client
+  stack `undici` + `urllib`**. Egg builds its `HttpClient` (urllib → undici) during
+  boot, and undici instantiates an llhttp `WebAssembly` (disabled under
+  `--build-snapshot`) + `HTTPParser` that cannot be serialized. As npm packages
+  urllib/undici would be inlined; listing them forces them external (`Bundler` adds
+  the lazy ids to the externals map) so the member-proxy stub is used at build — an
+  app gets a serializable snapshot without listing them in `egg.snapshot.lazyModules`.
+- The member-proxy records the build-time access path (`get`/`apply`/`construct`) and
+  replays it against the real module on restore, so `class HttpClient extends
+urllib.HttpClient` (and urllib's own `class BaseAgent extends undici.Agent`) keep
+  working: the `extends` is evaluated against the build stub, then `super(...)` /
+  inherited methods resolve to the real base class after deserialization.