XSS-WebGuard/script.js at main · SagarBiswas-MultiHAT/XSS-WebGuard · GitHub

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(() => {
  const THEME_KEY = "input-sanitizer-theme";
  let domPurifyHookInstalled = false;

  const byId = (id) => {
    const element = document.getElementById(id);
    if (!element) throw new Error(`Missing element: #${id}`);
    return element;
  };

  const elements = {
    input: byId("input"),
    output: byId("output"),
    preview: byId("preview"),
    mode: byId("mode"),
    allowStyles: byId("allowStyles"),
    autoSanitize: byId("autoSanitize"),
    sanitizeButton: byId("sanitizeButton"),
    clearButton: byId("clearButton"),
    copyButton: byId("copyButton"),
    downloadButton: byId("downloadButton"),
    inputCharCount: byId("inputCharCount"),
    outputCharCount: byId("outputCharCount"),
    suggestionsList: byId("suggestionsList"),
    status: byId("status"),
    themeToggle: byId("themeToggle"),
  };

  function setStatus(message, kind = "info") {
    elements.status.textContent = message;
    elements.status.classList.toggle("error", kind === "error");
  }

  function escapeHtml(text) {
    return String(text)
      .replaceAll("&", "&amp;")
      .replaceAll("<", "&lt;")
      .replaceAll(">", "&gt;")
      .replaceAll('"', "&quot;")
      .replaceAll("'", "&#39;");
  }

  function installDomPurifyHooksOnce() {
    if (domPurifyHookInstalled) return;
    if (!window.DOMPurify) return;

    window.DOMPurify.addHook("afterSanitizeAttributes", (node) => {
      if (
        node &&
        node.tagName === "A" &&
        node.getAttribute("target") === "_blank"
      ) {
        const existingRel = (node.getAttribute("rel") || "").trim();
        const relParts = new Set(existingRel.split(/\s+/).filter(Boolean));
        relParts.add("noopener");
        relParts.add("noreferrer");
        node.setAttribute("rel", Array.from(relParts).join(" "));
      }
    });

    window.DOMPurify.addHook("uponSanitizeAttribute", (_node, data) => {
      if (data.attrName === "style") {
        const value = String(data.attrValue || "");
        if (/javascript\s*:/i.test(value) || /expression\s*\(/i.test(value)) {
          data.keepAttr = false;
        }
      }
    });

    domPurifyHookInstalled = true;
  }

  function sanitizeHtml(input, { allowStyles }) {
    if (!window.DOMPurify) {
      setStatus(
        "DOMPurify failed to load. Falling back to basic escaping (safe but changes meaning).",
        "error",
      );
      return escapeHtml(input);
    }

    installDomPurifyHooksOnce();

    const forbidTags = [
      "script",
      "iframe",
      "object",
      "embed",
      "link",
      "meta",
      "base",
    ];
    const forbidAttrs = [];

    if (!allowStyles) {
      forbidTags.push("style");
      forbidAttrs.push("style");
    }

    const config = {
      USE_PROFILES: { html: true },
      FORBID_TAGS: forbidTags,
      FORBID_ATTR: forbidAttrs,
      ALLOWED_URI_REGEXP:
        /^(?:(?:https?|mailto|tel):|data:image\/(?:png|jpeg|gif|webp);base64,)/i,
    };

    return window.DOMPurify.sanitize(input, config);
  }

  function buildPreviewSrcDoc(mode, sanitized) {
    const bodyContent =
      mode === "html"
        ? sanitized
        : `<pre style="white-space: pre-wrap; word-wrap: break-word;">${sanitized}</pre>`;

    const csp =
      "default-src 'none'; base-uri 'none'; script-src 'none'; connect-src 'none'; img-src https: data:; style-src 'unsafe-inline'; font-src https: data:;";

    return `<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8" />
  <meta http-equiv="Content-Security-Policy" content="${csp}">
  <meta name="viewport" content="width=device-width, initial-scale=1" />
  <title>Preview</title>
  <style>
    :root { color-scheme: light dark; }
    body { font-family: system-ui, -apple-system, Segoe UI, Roboto, Arial, sans-serif; padding: 12px; }
  </style>
</head>
<body>${bodyContent}</body>
</html>`;
  }

  function generateSuggestions(rawInput, mode) {
    const suggestions = [];
    const input = String(rawInput);

    if (mode === "text") {
      if (/<\w+[^>]*>/i.test(input)) {
        suggestions.push(
          "You selected plain text mode; HTML is being escaped, not “cleaned”.",
        );
      }
      suggestions.push(
        "If you are inserting untrusted content into the DOM, prefer textContent/innerText instead of innerHTML.",
      );
      return suggestions;
    }

    if (/<script\b/i.test(input))
      suggestions.push("Avoid <script> in untrusted input (XSS).");
    if (/\son\w+\s*=\s*(['"]).*?\1/i.test(input))
      suggestions.push("Avoid inline event handlers (onclick/onerror/etc.).");
    if (/javascript\s*:/i.test(input))
      suggestions.push(
        "Avoid javascript: URLs; browsers may execute them when clicked.",
      );
    if (/<iframe\b|<object\b|<embed\b/i.test(input))
      suggestions.push(
        "Avoid embedding active content (iframe/object/embed) from untrusted sources.",
      );
    if (/<style\b/i.test(input) || /\sstyle\s*=\s*/i.test(input)) {
      suggestions.push(
        "Untrusted CSS can be risky (tracking/visual spoofing). Keep CSS disabled unless you really need it.",
      );
    }
    if (/(src|href)\s*=\s*(['"])https?:\/\//i.test(input)) {
      suggestions.push(
        "External URLs may load remote resources in the preview; treat them as untrusted.",
      );
    }
    if (/data\s*:/i.test(input))
      suggestions.push(
        "Be cautious with data: URLs; they can hide unexpected content.",
      );

    if (suggestions.length === 0)
      suggestions.push("No obvious issues detected for this mode.");
    return suggestions;
  }

  function renderSuggestions(items) {
    elements.suggestionsList.innerHTML = "";
    for (const item of items) {
      const li = document.createElement("li");
      li.textContent = item;
      elements.suggestionsList.appendChild(li);
    }
  }

  function updateCounts(inputValue, outputValue) {
    elements.inputCharCount.textContent = String(inputValue.length);
    elements.outputCharCount.textContent = String(outputValue.length);
  }

  function sanitizeAndRender() {
    const input = elements.input.value;
    const mode = elements.mode.value;
    const allowStyles = elements.allowStyles.checked;

    let output = "";
    if (mode === "html") {
      output = sanitizeHtml(input, { allowStyles });
      setStatus(
        window.DOMPurify
          ? "Sanitized with DOMPurify."
          : "Sanitized with fallback escaping (DOMPurify missing).",
        window.DOMPurify ? "info" : "error",
      );
    } else {
      output = escapeHtml(input);
      setStatus("Escaped as plain text (safe for HTML insertion).");
    }

    elements.output.value = output;
    updateCounts(input, output);
    elements.preview.srcdoc = buildPreviewSrcDoc(mode, output);
    renderSuggestions(generateSuggestions(input, mode));
  }

  function debounce(fn, delayMs) {
    let timeoutId;
    return (...args) => {
      window.clearTimeout(timeoutId);
      timeoutId = window.setTimeout(() => fn(...args), delayMs);
    };
  }

  async function copyOutput() {
    const text = elements.output.value;
    if (!text) return;

    try {
      if (navigator.clipboard?.writeText) {
        await navigator.clipboard.writeText(text);
        setStatus("Copied to clipboard.");
        return;
      }
    } catch {
      // Fall back below
    }

    elements.output.focus();
    elements.output.select();
    try {
      document.execCommand("copy");
      setStatus("Copied to clipboard (fallback).", "info");
    } catch {
      setStatus(
        "Copy failed. Tip: the Clipboard API needs HTTPS. Please copy manually.",
        "error",
      );
    }
    window.getSelection()?.removeAllRanges?.();
  }

  function downloadOutput() {
    const output = elements.output.value;
    const blob = new Blob([output], { type: "text/plain" });
    const a = document.createElement("a");
    a.href = URL.createObjectURL(blob);
    a.download = "sanitized_output.txt";
    a.click();
    URL.revokeObjectURL(a.href);
  }

  function clearAll() {
    elements.input.value = "";
    elements.output.value = "";
    elements.preview.srcdoc = buildPreviewSrcDoc(elements.mode.value, "");
    elements.suggestionsList.innerHTML = "";
    updateCounts("", "");
    setStatus("Cleared.");
  }

  function setTheme(isDark) {
    document.body.classList.toggle("dark-mode", isDark);
    elements.themeToggle.setAttribute("aria-pressed", String(isDark));
    elements.themeToggle.textContent = isDark ? "Light mode" : "Dark mode";
    localStorage.setItem(THEME_KEY, isDark ? "dark" : "light");
  }

  function initTheme() {
    const saved = localStorage.getItem(THEME_KEY);
    if (saved === "dark") {
      setTheme(true);
    } else if (saved === "light") {
      setTheme(false);
    } else {
      const prefersDark = window.matchMedia?.(
        "(prefers-color-scheme: dark)",
      )?.matches;
      setTheme(Boolean(prefersDark));
    }
  }

  function syncModeUi() {
    const isHtml = elements.mode.value === "html";
    elements.allowStyles.disabled = !isHtml;
    if (!isHtml) elements.allowStyles.checked = false;
    sanitizeAndRender();
  }

  const debouncedAutoSanitize = debounce(() => {
    if (elements.autoSanitize.checked) sanitizeAndRender();
    else updateCounts(elements.input.value, elements.output.value);
  }, 180);

  function init() {
    initTheme();

    elements.themeToggle.addEventListener("click", () => {
      const isDark = document.body.classList.contains("dark-mode");
      setTheme(!isDark);
    });

    elements.sanitizeButton.addEventListener("click", sanitizeAndRender);
    elements.clearButton.addEventListener("click", clearAll);
    elements.copyButton.addEventListener("click", copyOutput);
    elements.downloadButton.addEventListener("click", downloadOutput);

    elements.input.addEventListener("input", debouncedAutoSanitize);
    elements.mode.addEventListener("change", syncModeUi);
    elements.allowStyles.addEventListener("change", () => sanitizeAndRender());
    elements.autoSanitize.addEventListener("change", () => {
      if (elements.autoSanitize.checked) sanitizeAndRender();
    });

    elements.input.addEventListener("keydown", (e) => {
      if ((e.ctrlKey || e.metaKey) && e.key === "Enter") sanitizeAndRender();
    });

    syncModeUi();
    setStatus(
      window.DOMPurify
        ? "Ready."
        : "Ready (DOMPurify still loading or blocked).",
    );
  }

  if (document.readyState === "loading") {
    document.addEventListener("DOMContentLoaded", init);
  } else {
    init();
  }
})();