fix(core): bound ASCII folding allocations for large HTML (#5098)

* fix(core): bound ASCII folding allocations for large HTML

* chore(core): consolidate ASCII folding rationale

* fix(core): preserve unchanged spans during ASCII folding

Author: miguel-heygen

packages/core/src/compiler/htmlDocument.test.ts

@@ -1,3 +1,6 @@
+import { spawnSync } from "node:child_process";
+import { resolve } from "node:path";
+import { pathToFileURL } from "node:url";
 import { describe, expect, it } from "vitest";
 import {
   findStartTags,
@@ -60,6 +63,65 @@ const workGrowth = (scan: (n: number) => void) =>
   scannedChars(() => scan(20_000)) / scannedChars(() => scan(10_000));
 
 describe("htmlDocument helpers", () => {
+  it("strips runtimes from large mixed-case base64 HTML within a bounded heap", () => {
+    const moduleUrl = pathToFileURL(resolve(__dirname, "htmlDocument.ts")).href;
+    const result = spawnSync(
+      process.execPath,
+      [
+        "--max-old-space-size=256",
+        "--import=tsx",
+        "--input-type=module",
+        "--eval",
+        `
+          import { strict as assert } from "node:assert";
+          import { stripEmbeddedRuntimeScripts } from ${JSON.stringify(moduleUrl)};
+          const media = '<img src="data:image/png;base64,' + 'Aa0/'.repeat(8 * 1024 * 1024) + '">';
+          const runtime = '<SCRIPT src="HYPERFRAME.RUNTIME.IIFE.JS"></SCRIPT>';
+          assert.equal(stripEmbeddedRuntimeScripts(media + runtime), media);
+          console.log("large HTML preserved; runtime removed");
+        `,
+      ],
+      { encoding: "utf8", timeout: 60_000 },
+    );
+    expect(result.error).toBeUndefined();
+    expect(result.status, result.stderr).toBe(0);
+    expect(result.stdout).toContain("large HTML preserved; runtime removed");
+  }, 65_000);
+
+  it.each([
+    { first: "a", oldSpace: 96 },
+    { first: "A", oldSpace: 128 },
+  ])(
+    "preserves a large authored script starting with $first within $oldSpace MiB old-space",
+    ({ first, oldSpace }) => {
+      const moduleUrl = pathToFileURL(resolve(__dirname, "htmlDocument.ts")).href;
+      const result = spawnSync(
+        process.execPath,
+        [
+          `--max-old-space-size=${oldSpace}`,
+          "--max-semi-space-size=4",
+          "--import=tsx",
+          "--input-type=module",
+          "--eval",
+          `
+        import { strict as assert } from "node:assert";
+        import { stripEmbeddedRuntimeScripts } from ${JSON.stringify(moduleUrl)};
+        const data = ${JSON.stringify(first)} + "a".repeat(48 * 1024 * 1024 - 1);
+        const html = '<!doctype html><html><head></head><body><script>const embeddeddata="' + data + '";</script></body></html>';
+        assert.ok(stripEmbeddedRuntimeScripts(html) === html);
+        assert.equal(data.length, 48 * 1024 * 1024);
+        console.log("authored script preserved");
+      `,
+        ],
+        { encoding: "utf8", timeout: 60_000 },
+      );
+      expect(result.error).toBeUndefined();
+      expect(result.status, result.stderr).toBe(0);
+      expect(result.stdout).toContain("authored script preserved");
+    },
+    65_000,
+  );
+
   it("keeps a document's <html> attributes when a comment comes before the doctype", () => {
     const doc = parseHTMLContent(
       '<!-- hyperframes-registry-item: blk -->\n<!doctype html>\n<html lang="en" data-composition-variables="[]"><body></body></html>',
@@ -301,6 +363,15 @@ describe("htmlDocument helpers", () => {
 });
 
 describe("findStartTags", () => {
+  it("preserves Unicode offsets and mixed-case tags across chunk boundaries", () => {
+    const prefix = "Aİ" + "a".repeat(65_533) + "😀İ";
+    const html = prefix + "<ImG src=x>" + "A".repeat(65_524) + "<IMG src=y>";
+    expect(findStartTags(html, "iMg")).toEqual([65_538, 131_073]);
+    expect(
+      stripEmbeddedRuntimeScripts(prefix + '<SCRIPT src="HYPERFRAME.RUNTIME.IIFE.JS"></SCRIPT>'),
+    ).toBe(prefix);
+  });
+
   const at = (html: string, name: string) =>
     findStartTags(html, name).map((i) => html.slice(i, html.indexOf(">", i) + 1));
 

packages/core/src/compiler/htmlDocument.ts

@@ -30,9 +30,11 @@ export function parseHTMLContent(html: string): Document {
   return parseHTML(`<!DOCTYPE html><html><head></head><body>${html}</body></html>`).document;
 }
 
-/** Lowercases A-Z only, so indexes found in the result are valid in the input ("İ" lowercases to two chars). */
+/** ASCII-only chunks bound match arrays; starting at uppercase preserves unchanged spans. */
 function lowerAscii(text: string): string {
-  return text.replace(/[A-Z]+/g, (letters) => letters.toLowerCase());
+  return text.replace(/[A-Z][\s\S]{0,65535}/g, (chunk) =>
+    chunk.replace(/[A-Z]+/g, (letters) => letters.toLowerCase()),
+  );
 }
 
 export function stripEmbeddedRuntimeScripts(html: string): string {