fixes

AGENTS.md

@@ -0,0 +1,205 @@
+# Agent notes for local-page-archiver
+
+## Project overview
+
+This tool renders web pages in Chromium (via Playwright) and saves them as fully self-contained HTML files. All external assets (images, fonts, stylesheets) are inlined as data URIs so the resulting file works offline.
+
+The pipeline is:
+
+```
+URL ──► Playwright render ──► inject privacy filters ──► inline assets ──► write HTML
+```
+
+## Source layout
+
+- `src/cli.mjs` — CLI entrypoint. Supports `archive` and `help`. Accepts `--archive-path`, `--id`, and `--headful` flags.
+- `src/archiver.mjs` — Core archiving logic. Loads privacy filters, steers the browser, injects adblockers/userscripts, and calls the inliner.
+- `src/asset-inliner.mjs` — Fetches and inlines external resources (images, CSS, iframes). Also strips `<script>` and `<noscript>` tags for a static archive.
+- `privacy-filters/` — Third-party filter lists and userscripts used to strip paywalls, trackers, and ad banners before the snapshot is taken.
+
+## Privacy filters (`privacy-filters/`)
+
+### `bpc-paywall-filter.txt`
+
+An AdBlock Plus / uBlock Origin filter list. It contains three kinds of rules:
+
+1. **Network rules** (`||tracker.com^`, `/regex/`) — block specific third-party paywall / tracking scripts.
+2. **Exception rules** (`@@||example.com^`) — whitelist requests that a global block rule would otherwise hit.
+3. **Cosmetic rules** (`example.com##.paywall`) — inject CSS to hide DOM elements (e.g. subscription banners, blurred overlays).
+
+At module load time `archiver.mjs` parses this file into three arrays (`blockRules`, `allowRules`, `cosmeticRules`). Network rules are enforced at the Playwright level with `page.route(...)`. Cosmetic rules are injected as a `<style>` tag after the page reaches `domcontentloaded`.
+
+#### Cosmetic rule caveats
+
+Some advanced cosmetic syntax is unsupported and is silently discarded:
+
+- `:remove()` — we can't actually remove DOM nodes from the CSS layer; only hide them.
+- `:style(...)` — converted to real CSS `display: none`.
+- `:xpath(...)`, `:upward(...)`, `:matches-css(...)` — discarded during parsing.
+
+### `userscript/` directory
+
+Contains Greasemonkey-style userscripts (`bpc.*.user.js`) plus a shared library `bpc_func.js`. They do heavy lifting: decrypt paywalls, reconstruct article text from JSON data embedded in the page, remove blur overlays, etc.
+
+#### Selective injection (important)
+
+Each userscript declares `@match` and `@exclude` metadata. **Only matching scripts are injected.** For example, on `bloomberg.com` only `bpc.en.user.js` is injected. Injecting all scripts into every page caused literal JavaScript source expressions to leak into DOM attributes, which the asset inliner then tried to fetch as URLs, producing garbage `HTTP 403` warnings.
+
+The matching logic is a simple glob parser for userscript `@match` patterns:
+- `*://*.com/*` matches any `.com` domain
+- `*://example.com/path/*` matches that path prefix
+- `@exclude` patterns take precedence and skip the script
+
+#### `GM.xmlHttpRequest` mock
+
+The userscripts rely on `GM.xmlHttpRequest` to fetch article text from archive mirrors or API endpoints. In a Playwright context this doesn't exist, so we inject a tiny mock that wraps the browser's native `fetch()` and presents the same callback interface (`onload`, `onerror`).
+
+#### Timing
+
+Userscripts are injected **after** `domcontentloaded` but **before** `networkidle`. We then wait an extra 2 s (`page.waitForTimeout`) so any `setTimeout(..., 1000)` callbacks inside the scripts have time to fire before we snapshot the DOM.
+
+## Stealth / anti-detection
+
+### The `playwright-extra` stealth packages are broken
+
+The common recommendation is:
+
+```bash
+npm install playwright-extra playwright-extra-plugin-stealth
+```
+
+**This does not work.** All three packages on npm (`playwright-extra-plugin-stealth`, `playwright-extra-stealth`, `playwright-stealth`) are **placeholder packages** (version `0.0.1`) that literally throw on `require()`:
+
+```
+Error: Wrong package, please see this:
+https://github.com/berstend/puppeteer-extra/issues/454
+```
+
+No functional Playwright stealth plugin exists in those package names. We therefore removed them from `package.json`.
+
+### Manual stealth evasions
+
+Instead we apply the same core evasions manually via `context.addInitScript()` and browser launch flags.
+
+**Launch flags:**
+- `--disable-blink-features=AutomationControlled`
+- `--disable-infobars`
+- `--disable-web-security`
+- `--no-sandbox`, `--disable-setuid-sandbox`
+- `--disable-dev-shm-usage`
+- Removed `--enable-automation` via `ignoreDefaultArgs`
+
+**Init script (injected into every page before any scripts run):**
+```js
+Object.defineProperty(navigator, 'webdriver',
+  { get: () => undefined, configurable: true, enumerable: true });
+window.chrome = window.chrome || { runtime: {} };
+window.navigator.permissions.query = (/* patched for notifications */);
+```
+
+#### CRITICAL: Avoid `delete navigator.webdriver` + iframe trick
+
+An earlier version used a more elaborate stealth snippet that did `delete navigator.webdriver` and then created an `<iframe>` to steal the real navigator descriptor. **This crashed the Chromium renderer process on tab creation** with:
+
+```
+Protocol error (Page.addScriptToEvaluateOnNewDocument): Target crashed
+```
+
+The current init script is minimal and safe — it only overrides the getter via `Object.defineProperty` and avoids DOM mutation during page init.
+
+## Browser context & headful mode
+
+`renderPage()` auto-detects whether a display is available (`$DISPLAY` / `$WAYLAND_DISPLAY`). If neither is set it defaults to headless. The caller can override via `options.headless`.
+
+- **ViewPort:** 1366×768 (standard laptop resolution, not the default Playwright 1280×720)
+- **Locale:** `en-US`
+- **Timezone:** `America/New_York`
+- **User-Agent:** macOS Chrome 130 (matches the Playwright image's Chromium version)
+
+## Docker / Podman support
+
+### Dockerfile
+
+- Base: `mcr.microsoft.com/playwright:v1.60.0` (must stay in sync with the `playwright` npm version)
+- Installs Node 22 (the base image may ship an older Node)
+- Runs `npx playwright install chromium` so the browser binary is baked into the image
+
+### `podman-run.sh`
+
+Helper for local runs. Two modes:
+
+1. **`./podman-run.sh archive <URL>`** — headless, mounts `./archives`
+2. **`./podman-run.sh headful-archive <URL>`** — headful with internal VNC
+
+**Headful mode details:**
+The container's `ENTRYPOINT` is `node src/cli.mjs`. To run a shell command inside the container (setting up Xvfb + x11vnc) we must override the entrypoint:
+
+```bash
+podman run --rm --entrypoint sh <image> -c "...setup Xvfb... && node src/cli.mjs archive <URL>"
+```
+
+Port `5900` inside the container maps to `5901` on the host to avoid conflicts with macOS's built-in VNC.
+
+### `docker-compose.yml`
+
+Includes a `headful` profile that can be run with:
+
+```bash
+docker compose --profile headful up archiver-headful
+```
+
+## Known limitations
+
+### Bloomberg bot wall
+
+Bloomberg detects our requests as automated. Both headless and headful mode return **"Are you a robot?"** from this IP. We verified the same page text is returned by `curl` with identical headers, confirming the block is network-level (IP / TLS fingerprint / rate-limit reputation), not browser-fingerprint-level. To archive Bloomberg you currently need a residential proxy or to use an archive mirror service.
+
+### Unsupported adblock syntax
+
+- Advanced procedural cosmetic filters (`:remove()`, `:upward()`, `:xpath()`) are silently ignored.
+- Scriptlet injection (`##+js(...)`) is not supported — only cosmetic CSS injection works.
+- Preprocessor directives (`!#if`) are skipped.
+
+## Adding a new site to privacy filters
+
+If you add a new filter rule or userscript:
+
+1. **Filter rules:** Edit `privacy-filters/bpc-paywall-filter.txt`. `archiver.mjs` reloads the file on every process start, so no code changes are needed.
+2. **Userscripts:** Drop a new `.user.js` into `privacy-filters/userscript/` and add its filename to the `userScriptFiles` array inside `loadPrivacyFilters()` in `archiver.mjs`.
+3. Test with `node src/cli.mjs archive <URL>` and inspect the generated HTML.
+
+## Rebuilding the Docker image
+
+Playwright npm version image tags must match:
+
+```bash
+# Check what npm installed
+node -e "console.log(require('playwright/package.json').version)"
+
+# Update the FROM line in Dockerfile if needed
+# Then rebuild
+podman build -t local-page-archiver .
+```
+
+## Development quick reference
+
+```bash
+# Install deps
+npm install
+
+# Install browser binaries
+npm run install-browsers
+
+# Archive a page (headless)
+node src/cli.mjs archive https://example.com
+
+# Archive a page (headful on macOS)
+node src/cli.mjs archive https://example.com --headful
+
+# Archive inside container (headless)
+./podman-run.sh archive https://example.com
+
+# Archive inside container (headful + VNC)
+./podman-run.sh headful-archive https://example.com
+# Then open vnc://localhost:5901
+```

package.json

@@ -9,6 +9,7 @@
   },
   "scripts": {
     "archive": "node src/cli.mjs archive",
+    "test": "node --test test/*.test.mjs",
     "install-browsers": "playwright install chromium"
   },
   "dependencies": {

src/archiver.mjs

@@ -32,6 +32,7 @@ const PRIVACY_FILTERS_DIR = path.join(__dirname, "..", "privacy-filters");
 let privacyFiltersAvailable = false;
 let filterRules = { blockRules: [], allowRules: [], cosmeticRules: [] };
 let userScriptData = []; // { file, content, matches, excludes }
+let userScriptRequireContent = "";
 
 async function loadPrivacyFilters() {
   try {
@@ -40,6 +41,7 @@ async function loadPrivacyFilters() {
     filterRules = parseFilterRules(filterContent);
 
     const userscriptDir = path.join(PRIVACY_FILTERS_DIR, "userscript");
+    userScriptRequireContent = await fs.readFile(path.join(userscriptDir, "bpc_func.js"), "utf8");
     const userScriptFiles = [
       "bpc.en.user.js",
       "bpc.de.user.js",
@@ -126,7 +128,7 @@ function parseNetworkRule(line) {
   const lastDollar = line.lastIndexOf("$");
   if (lastDollar > 0) {
     const optsStr = line.slice(lastDollar + 1);
-    if (/^[a-z,=~\-|0-9]+$/i.test(optsStr)) {
+    if (/^[a-z,=~_.\-|0-9]+$/i.test(optsStr)) {
       options = optsStr.split(",");
       pattern = line.slice(0, lastDollar);
     }
@@ -134,8 +136,20 @@ function parseNetworkRule(line) {
 
   if (!pattern) return null;
 
-  const type = options.find((o) =>
+  const types = options.filter((o) =>
-    ["script", "stylesheet", "image", "media", "xmlhttprequest", "other", "inline-script"].includes(o)
+    [
+      "document",
+      "font",
+      "image",
+      "inline-script",
+      "media",
+      "object",
+      "other",
+      "script",
+      "stylesheet",
+      "subdocument",
+      "xmlhttprequest"
+    ].includes(o)
   );
   const isThirdParty = options.includes("third-party");
   const isFirstParty = options.includes("~third-party");
@@ -162,7 +176,7 @@ function parseNetworkRule(line) {
       kind: "domain",
       domain,
       path,
-      type,
+      types,
       isThirdParty,
       isFirstParty,
       includeDomains,
@@ -171,14 +185,12 @@ function parseNetworkRule(line) {
     };
   }
 
-  if (pattern.startsWith("/")) {
+  if (pattern.startsWith("/") && pattern.endsWith("/") && pattern.length > 1) {
-    const lastSlash = pattern.lastIndexOf("/");
+    const regex = pattern.slice(1, -1);
-    if (lastSlash > 0) {
-      const regex = pattern.slice(1, lastSlash);
     return {
       kind: "regex",
       regex,
-        type,
+      types,
       isThirdParty,
       isFirstParty,
       includeDomains,
@@ -186,12 +198,25 @@ function parseNetworkRule(line) {
       important
     };
   }
-  }
 
-  return null;
+  return {
+    kind: "pattern",
+    regex: adblockPatternToRegex(pattern),
+    types,
+    isThirdParty,
+    isFirstParty,
+    includeDomains,
+    excludeDomains,
+    important
+  };
 }
 
 function cosmeticSelectorToCss(selector) {
+  if (selector.endsWith(":remove()")) {
+    const baseSelector = selector.slice(0, -":remove()".length);
+    return baseSelector ? `${baseSelector} { display: none !important; }` : null;
+  }
+
   const styleMatch = selector.match(/:style\((.+)\)$/);
   if (styleMatch) {
     const baseSelector = selector.slice(0, selector.lastIndexOf(":style("));
@@ -246,17 +271,8 @@ function matchesNetworkRule(url, urlObj, hostname, resourceType, sourceHostname,
     if (blocked) return false;
   }
 
-  if (rule.type) {
+  if (rule.types.length > 0) {
-    const typeMap = {
+    if (!rule.types.some((type) => resourceTypeMatches(type, resourceType))) {
-      script: "script",
-      stylesheet: "stylesheet",
-      image: "image",
-      media: "media",
-      xmlhttprequest: "xhr",
-      other: "other",
-      "inline-script": "script"
-    };
-    if (typeMap[rule.type] && resourceType !== typeMap[rule.type]) {
       return false;
     }
   }
@@ -271,18 +287,11 @@ function matchesNetworkRule(url, urlObj, hostname, resourceType, sourceHostname,
   }
 
   if (rule.kind === "domain") {
-    const domainRe = new RegExp(
+    if (!domainPatternMatches(hostname, rule.domain)) return false;
-      "^" + rule.domain.replace(/\./g, "\\.").replace(/\*/g, "[^.]*") + "$",
-      "i"
-    );
-    if (!domainRe.test(hostname)) return false;
 
     if (rule.path) {
-      const pathRe = new RegExp(
+      const pathRe = new RegExp("^" + adblockPatternToRegex(rule.path), "i");
-        "^" + rule.path.replace(/\./g, "\\.").replace(/\*/g, ".*").replace(/\?/g, "\\?").replace(/\^/g, ""),
+      if (!pathRe.test(urlObj.pathname + urlObj.search)) return false;
-        "i"
-      );
-      if (!pathRe.test(urlObj.pathname)) return false;
     }
     return true;
   }
@@ -296,8 +305,83 @@ function matchesNetworkRule(url, urlObj, hostname, resourceType, sourceHostname,
     }
   }
 
+  if (rule.kind === "pattern") {
+    try {
+      const re = new RegExp(rule.regex, "i");
+      return re.test(url);
+    } catch {
       return false;
     }
+  }
+
+  return false;
+}
+
+function resourceTypeMatches(filterType, resourceType) {
+  const typeMap = {
+    document: ["document"],
+    font: ["font"],
+    image: ["image"],
+    "inline-script": ["script"],
+    media: ["media"],
+    object: ["object"],
+    other: ["other"],
+    script: ["script"],
+    stylesheet: ["stylesheet"],
+    subdocument: ["document"],
+    xmlhttprequest: ["fetch", "xhr"]
+  };
+  const mapped = typeMap[filterType];
+  return mapped ? mapped.includes(resourceType) : false;
+}
+
+function domainPatternMatches(hostname, pattern) {
+  const normalized = pattern.replace(/\^$/, "").toLowerCase();
+  if (!normalized) return false;
+
+  if (!normalized.includes("*")) {
+    return hostname === normalized || hostname.endsWith("." + normalized);
+  }
+
+  const re = new RegExp(
+    "^" +
+      normalized
+        .split("*")
+        .map((part) => part.replace(/[|\\{}()[\]^$+?.]/g, "\\$&"))
+        .join("[^.]*") +
+      "$",
+    "i"
+  );
+  return re.test(hostname);
+}
+
+function adblockPatternToRegex(pattern) {
+  let source = "";
+  let remaining = pattern;
+  let anchoredStart = false;
+  let anchoredEnd = false;
+
+  if (remaining.startsWith("|")) {
+    anchoredStart = true;
+    remaining = remaining.slice(1);
+  }
+  if (remaining.endsWith("|")) {
+    anchoredEnd = true;
+    remaining = remaining.slice(0, -1);
+  }
+
+  for (const ch of remaining) {
+    if (ch === "*") {
+      source += ".*";
+    } else if (ch === "^") {
+      source += "(?:[^A-Za-z0-9_.%-]|$)";
+    } else {
+      source += ch.replace(/[|\\{}()[\]^$+?.]/g, "\\$&");
+    }
+  }
+
+  return `${anchoredStart ? "^" : ""}${source}${anchoredEnd ? "$" : ""}`;
+}
 
 function shouldBlockRequest(url, resourceType, sourceHostname) {
   if (url === sourceHostname || url.startsWith(sourceHostname + "/")) {
@@ -512,7 +596,7 @@ async function setupRequestBlocking(page, sourceHostname) {
   await page.route("**/*", (route) => {
     try {
       const request = route.request();
-      if (request.isNavigationRequest()) {
+      if (request.isNavigationRequest() && request.frame() === page.mainFrame()) {
         route.continue();
         return;
       }
@@ -584,6 +668,9 @@ async function injectPrivacyUserScripts(page, sourceUrl) {
   // Inject GM API mock first.
   try {
     await page.addScriptTag({ content: GM_MOCK });
+    if (userScriptRequireContent) {
+      await page.addScriptTag({ content: userScriptRequireContent });
+    }
   } catch {
     return;
   }
@@ -731,18 +818,22 @@ function addArchiveComment(html, sourceUrl) {
 
 export function findExternalAssetRefs(html) {
   const refs = new Set();
-  const attrPattern = /\s(?:src|srcset|poster|data)\s*=\s*(["'])([\s\S]*?)\1/gi;
+  const assetTagPattern = /<(?:img|source|audio|video|track|embed|object|input|iframe)\b[^>]*>/gi;
-  for (const match of html.matchAll(attrPattern)) {
+  for (const match of html.matchAll(assetTagPattern)) {
-    if (isSelfContainedAssetRef(match[2])) {
+    const tag = match[0];
+    for (const attr of ["src", "srcset", "poster", "data"]) {
+      const value = readAttribute(tag, attr);
+      if (!value || isSelfContainedAssetRef(value)) {
         continue;
       }
-    for (const part of match[2].split(",")) {
+      for (const part of value.split(",")) {
         const candidate = part.trim().split(/\s+/)[0];
         if (candidate && !isSelfContainedAssetRef(candidate)) {
           refs.add(candidate);
         }
       }
     }
+  }
 
   const linkPattern = /<link\b[^>]*>/gi;
   for (const match of html.matchAll(linkPattern)) {
@@ -779,8 +870,8 @@ function isSelfContainedAssetRef(value) {
 }
 
 function readAttribute(tag, attr) {
-  const match = tag.match(new RegExp(`\\b${attr}\\s*=\\s*("([^"]*)"|'([^']*)'|([^\\s>]+))`, "i"));
+  const match = findAttribute(tag, attr);
-  return match ? match[2] ?? match[3] ?? match[4] ?? "" : "";
+  return match ? match.value : "";
 }
 
 function cleanCssUrl(value) {
@@ -796,3 +887,61 @@ function cleanCssUrl(value) {
   }
   return decoded;
 }
+
+function findAttribute(openingTag, attr) {
+  const attrLower = attr.toLowerCase();
+  const nameMatch = openingTag.match(/^<[^\s/>]+/);
+  let index = nameMatch ? nameMatch[0].length : 1;
+
+  while (index < openingTag.length) {
+    while (index < openingTag.length && /\s/.test(openingTag[index])) {
+      index += 1;
+    }
+    if (index >= openingTag.length || openingTag[index] === ">" || openingTag[index] === "/") {
+      return null;
+    }
+
+    const start = index;
+    while (index < openingTag.length && !/[\s=/>]/.test(openingTag[index])) {
+      index += 1;
+    }
+    const name = openingTag.slice(start, index);
+
+    while (index < openingTag.length && /\s/.test(openingTag[index])) {
+      index += 1;
+    }
+
+    let value = "";
+    if (openingTag[index] === "=") {
+      index += 1;
+      while (index < openingTag.length && /\s/.test(openingTag[index])) {
+        index += 1;
+      }
+
+      const quote = openingTag[index];
+      if (quote === '"' || quote === "'") {
+        index += 1;
+        const valueStart = index;
+        while (index < openingTag.length && openingTag[index] !== quote) {
+          index += 1;
+        }
+        value = openingTag.slice(valueStart, index);
+        if (openingTag[index] === quote) {
+          index += 1;
+        }
+      } else {
+        const valueStart = index;
+        while (index < openingTag.length && !/[\s>]/.test(openingTag[index])) {
+          index += 1;
+        }
+        value = openingTag.slice(valueStart, index);
+      }
+    }
+
+    if (name.toLowerCase() === attrLower) {
+      return { start, end: index, value };
+    }
+  }
+
+  return null;
+}

src/asset-inliner.mjs

@@ -197,11 +197,6 @@ export class AssetInliner {
       async (match) => this.rewriteMediaAttributes(match[0], effectiveBase)
     );
 
-    output = await replaceAsync(output, /srcset=(["'])([\s\S]*?)\1/gi, async (match) => {
-      const rewritten = await this.inlineSrcset(match[2], effectiveBase);
-      return `srcset=${match[1]}${htmlEscape(rewritten)}${match[1]}`;
-    });
-
     return output;
   }
 
@@ -259,12 +254,28 @@ export class AssetInliner {
         output = replaceMissingMediaAttribute(output, attr);
       }
     }
+    const srcset = getAttribute(output, "srcset");
+    if (srcset) {
+      const rewritten = await this.inlineSrcset(srcset, baseUrl);
+      output = setAttribute(output, "srcset", rewritten);
+    }
     return output;
   }
 
   async rewriteIframeTag(tag, baseUrl, depth) {
+    const srcdoc = getAttribute(tag, "srcdoc");
+    if (srcdoc) {
+      let rewritten = removeAttribute(tag, "src");
+      if (depth >= 2) {
+        return rewritten;
+      }
+      const inlined = await this.inlineHtml(srcdoc, baseUrl, { depth: depth + 1 });
+      rewritten = setAttribute(rewritten, "srcdoc", inlined);
+      return rewritten;
+    }
+
     const src = getAttribute(tag, "src");
-    if (!src || getAttribute(tag, "srcdoc")) {
+    if (!src) {
       return this.rewriteMediaAttributes(tag, baseUrl);
     }
     const absolute = resolveUrl(src, baseUrl);
@@ -425,24 +436,42 @@ function mimeFromUrl(rawUrl) {
 }
 
 function getAttribute(tag, attr) {
-  const match = tag.match(new RegExp(`\\b${attr}\\s*=\\s*("([^"]*)"|'([^']*)'|([^\\s>]+))`, "i"));
+  const openingTag = getOpeningTag(tag);
-  if (!match) {
+  if (!openingTag) {
     return null;
   }
-  return htmlDecode(match[2] ?? match[3] ?? match[4] ?? "");
+  const match = findAttribute(openingTag, attr);
+  return match ? htmlDecode(match.value) : null;
 }
 
 function setAttribute(tag, attr, value) {
   const escaped = htmlEscape(value);
-  const attrRegex = new RegExp(`\\b${attr}\\s*=\\s*("([^"]*)"|'([^']*)'|([^\\s>]+))`, "i");
+  return replaceOpeningTag(tag, (openingTag) => {
-  if (attrRegex.test(tag)) {
+    const match = findAttribute(openingTag, attr);
-    return tag.replace(attrRegex, `${attr}="${escaped}"`);
+    if (match) {
+      return `${openingTag.slice(0, match.start)}${attr}="${escaped}"${openingTag.slice(match.end)}`;
     }
-  return tag.replace(/^<[^>]*>/, (openingTag) => openingTag.replace(/\/?>$/, (end) => ` ${attr}="${escaped}"${end}`));
+
+    const selfClosing = /\/\s*>$/.test(openingTag);
+    const closeIndex = openingTag.lastIndexOf(">");
+    const beforeClose = openingTag.slice(0, closeIndex).replace(/\s*\/\s*$/, "");
+    return `${beforeClose} ${attr}="${escaped}"${selfClosing ? " /" : ""}>`;
+  });
 }
 
 function removeAttribute(tag, attr) {
-  return tag.replace(new RegExp(`\\s+${attr}\\s*=\\s*("([^"]*)"|'([^']*)'|([^\\s>]+))`, "i"), "");
+  return replaceOpeningTag(tag, (openingTag) => {
+    const match = findAttribute(openingTag, attr);
+    if (!match) {
+      return openingTag;
+    }
+
+    let start = match.start;
+    while (start > 0 && /\s/.test(openingTag[start - 1])) {
+      start -= 1;
+    }
+    return `${openingTag.slice(0, start)}${openingTag.slice(match.end)}`;
+  });
 }
 
 function replaceMissingMediaAttribute(tag, attr) {
@@ -474,3 +503,95 @@ function cleanCssUrl(value) {
   }
   return decoded;
 }
+
+function getOpeningTag(markup) {
+  const end = openingTagEndIndex(markup);
+  return end >= 0 ? markup.slice(0, end + 1) : null;
+}
+
+function replaceOpeningTag(markup, replacer) {
+  const end = openingTagEndIndex(markup);
+  if (end < 0) {
+    return markup;
+  }
+  return `${replacer(markup.slice(0, end + 1))}${markup.slice(end + 1)}`;
+}
+
+function openingTagEndIndex(markup) {
+  let quote = "";
+  for (let i = 0; i < markup.length; i += 1) {
+    const ch = markup[i];
+    if (quote) {
+      if (ch === quote) {
+        quote = "";
+      }
+      continue;
+    }
+    if (ch === '"' || ch === "'") {
+      quote = ch;
+      continue;
+    }
+    if (ch === ">") {
+      return i;
+    }
+  }
+  return -1;
+}
+
+function findAttribute(openingTag, attr) {
+  const attrLower = attr.toLowerCase();
+  const nameMatch = openingTag.match(/^<[^\s/>]+/);
+  let index = nameMatch ? nameMatch[0].length : 1;
+
+  while (index < openingTag.length) {
+    while (index < openingTag.length && /\s/.test(openingTag[index])) {
+      index += 1;
+    }
+    if (index >= openingTag.length || openingTag[index] === ">" || openingTag[index] === "/") {
+      return null;
+    }
+
+    const start = index;
+    while (index < openingTag.length && !/[\s=/>]/.test(openingTag[index])) {
+      index += 1;
+    }
+    const name = openingTag.slice(start, index);
+
+    while (index < openingTag.length && /\s/.test(openingTag[index])) {
+      index += 1;
+    }
+
+    let value = "";
+    if (openingTag[index] === "=") {
+      index += 1;
+      while (index < openingTag.length && /\s/.test(openingTag[index])) {
+        index += 1;
+      }
+
+      const quote = openingTag[index];
+      if (quote === '"' || quote === "'") {
+        index += 1;
+        const valueStart = index;
+        while (index < openingTag.length && openingTag[index] !== quote) {
+          index += 1;
+        }
+        value = openingTag.slice(valueStart, index);
+        if (openingTag[index] === quote) {
+          index += 1;
+        }
+      } else {
+        const valueStart = index;
+        while (index < openingTag.length && !/[\s>]/.test(openingTag[index])) {
+          index += 1;
+        }
+        value = openingTag.slice(valueStart, index);
+      }
+    }
+
+    if (name.toLowerCase() === attrLower) {
+      return { start, end: index, value };
+    }
+  }
+
+  return null;
+}