fix: strip XML-illegal control characters from generated documents (#5760)

* fix: strip XML-illegal control characters from generated documents

OOXML documents (.docx/.xlsx/.pptx) embed their text directly into
internal XML parts (e.g. word/document.xml). XML 1.0 §2.2 forbids every
C0 control character except tab, line feed, and carriage return. When an
LLM emits LaTeX such as `\frac`, the `\f` decodes (via the tool-call JSON
escape) to a form feed (U+000C) which lands in the content unchanged. The
generated file is a valid ZIP but Office refuses to open it ("Word
experienced an error trying to open the file.").

Add a shared `stripInvalidXmlChars` helper to the create-files manager
that removes the illegal characters from a string or, recursively, from
every string in a nested array/object. Apply it to the user/LLM-supplied
content in the docx, pdf, xlsx, and pptx handlers before generation.
Plain-text output is left untouched since control characters are legal
there.

Resolves #5756

* unset binary format

* update test suite to catch drifts

* lint

---------

Co-authored-by: Timothy Carambat <rambat1010@gmail.com>

server/__tests__/utils/agents/aibitat/plugins/create-files/lib.test.js

@@ -0,0 +1,86 @@
+/* eslint-env jest */
+const createFilesLib = require("../../../../../../utils/agents/aibitat/plugins/create-files/lib.js");
+
+describe("CreateFilesManager.stripInvalidXmlChars", () => {
+  test("removes the form feed produced by a LaTeX backslash sequence", () => {
+    // `\frac` arrives as a JSON "\f" escape that decodes to U+000C (form feed),
+    // which is illegal in XML 1.0 and corrupts OOXML documents.
+    const content = "En la fracción $\x0Crac{3}{5}$";
+    const cleaned = createFilesLib.stripInvalidXmlChars(content);
+    expect(cleaned).toBe("En la fracción $rac{3}{5}$");
+    expect(cleaned).not.toMatch(/[\x00-\x08\x0B\x0C\x0E-\x1F]/);
+  });
+
+  test("strips every disallowed C0 control character", () => {
+    const dirty = "a\x00b\x08c\x0Bd\x0Ce\x1Ff";
+    expect(createFilesLib.stripInvalidXmlChars(dirty)).toBe("abcdef");
+  });
+
+  test("preserves tab, line feed, and carriage return (the legal C0 chars)", () => {
+    const content = "line1\tcol2\nline2\r\nline3";
+    expect(createFilesLib.stripInvalidXmlChars(content)).toBe(content);
+  });
+
+  test("leaves clean strings unchanged", () => {
+    const content = "# Title\n\nA normal paragraph with **bold** text.";
+    expect(createFilesLib.stripInvalidXmlChars(content)).toBe(content);
+  });
+
+  test("preserves typical markdown document content", () => {
+    const content = [
+      "# Quarterly Report\n",
+      "## Summary\n",
+      "Revenue grew **15%** year-over-year.\n",
+      "- Item 1: $1,200\n- Item 2: $3,400\n",
+      "| Column A | Column B |\n|----------|----------|\n| value    | value    |",
+    ].join("\n");
+    expect(createFilesLib.stripInvalidXmlChars(content)).toBe(content);
+  });
+
+  test("preserves unicode, accented characters, and emoji", () => {
+    const content = "Ñoño résumé naïve — «quotes» 日本語 🎉👍";
+    expect(createFilesLib.stripInvalidXmlChars(content)).toBe(content);
+  });
+
+  test("preserves HTML tags that appear in rich content", () => {
+    const content =
+      '<h1>Title</h1>\n<p style="color:red">Hello &amp; goodbye</p>';
+    expect(createFilesLib.stripInvalidXmlChars(content)).toBe(content);
+  });
+
+  test("preserves code blocks and special syntax", () => {
+    const content =
+      "```javascript\nconst x = () => { return 42; };\n```\n\n$E = mc^2$";
+    expect(createFilesLib.stripInvalidXmlChars(content)).toBe(content);
+  });
+
+  test("preserves backslash sequences that are NOT control characters", () => {
+    const content =
+      "Use \\textbf{bold} and \\newline and C:\\Users\\file.txt";
+    expect(createFilesLib.stripInvalidXmlChars(content)).toBe(content);
+  });
+
+  test("recursively cleans arrays and nested objects", () => {
+    const sheets = [
+      {
+        name: "Sheet\x0C1",
+        csvData: "a,b\n1\x00,2",
+        options: { headerStyle: true, autoFit: 1 },
+      },
+    ];
+    expect(createFilesLib.stripInvalidXmlChars(sheets)).toEqual([
+      {
+        name: "Sheet1",
+        csvData: "a,b\n1,2",
+        options: { headerStyle: true, autoFit: 1 },
+      },
+    ]);
+  });
+
+  test("returns non-string scalars untouched", () => {
+    expect(createFilesLib.stripInvalidXmlChars(null)).toBeNull();
+    expect(createFilesLib.stripInvalidXmlChars(undefined)).toBeUndefined();
+    expect(createFilesLib.stripInvalidXmlChars(42)).toBe(42);
+    expect(createFilesLib.stripInvalidXmlChars(true)).toBe(true);
+  });
+});

server/utils/agents/aibitat/plugins/create-files/docx/create-docx-file.js

@@ -122,6 +122,13 @@ module.exports.CreateDocxFile = {
             try {
               this.super.handlerProps.log(`Using the create-docx-file tool.`);
 
+              // Strip XML 1.0 illegal control characters (e.g. the form feed a
+              // LaTeX `\frac` decodes to) so Word can open the generated file.
+              content = createFilesLib.stripInvalidXmlChars(content);
+              title = createFilesLib.stripInvalidXmlChars(title);
+              subtitle = createFilesLib.stripInvalidXmlChars(subtitle);
+              author = createFilesLib.stripInvalidXmlChars(author);
+
               const hasExtension = /\.docx$/i.test(filename);
               if (!hasExtension) filename = `${filename}.docx`;
               const displayFilename = filename.split("/").pop();

server/utils/agents/aibitat/plugins/create-files/lib.js

@@ -268,6 +268,39 @@ class CreateFilesManager {
       .substring(0, 255);
   }
 
+  /**
+   * Removes characters that are illegal in XML 1.0 from a string, or - when
+   * given an array/object - recursively from every string it contains.
+   *
+   * OOXML documents (.docx/.xlsx/.pptx) embed their text directly into internal
+   * XML parts (e.g. word/document.xml). XML 1.0 §2.2 forbids every C0 control
+   * character except tab (U+0009), line feed (U+000A) and carriage return
+   * (U+000D). When one of the forbidden characters reaches the content the file
+   * is still a valid ZIP, but Office refuses to open it ("Word experienced an
+   * error trying to open the file."). The most common offender is a form feed
+   * (U+000C): an LLM that emits LaTeX such as `\frac` produces a `\f` JSON
+   * escape that decodes to U+000C before it ever reaches the generator.
+   *
+   * Stripping these characters yields a readable document instead of a corrupt
+   * one. Non-string scalars are returned untouched.
+   * @param {*} value - A string, or an array/object that may contain strings.
+   * @returns {*} The value with all invalid XML characters removed.
+   */
+  stripInvalidXmlChars(value) {
+    if (typeof value === "string")
+      // eslint-disable-next-line no-control-regex
+      return value.replace(/[\x00-\x08\x0B\x0C\x0E-\x1F]/g, "");
+    if (Array.isArray(value))
+      return value.map((item) => this.stripInvalidXmlChars(item));
+    if (value && typeof value === "object") {
+      const cleaned = {};
+      for (const [key, val] of Object.entries(value))
+        cleaned[key] = this.stripInvalidXmlChars(val);
+      return cleaned;
+    }
+    return value;
+  }
+
   /**
    * Gets the AnythingLLM logo for branding.
    * @param {Object} options

server/utils/agents/aibitat/plugins/create-files/pptx/create-presentation.js

@@ -169,6 +169,11 @@ module.exports.CreatePptxPresentation = {
                 `Using the create-pptx-presentation tool.`
               );
 
+              // Strip XML 1.0 illegal control characters so PowerPoint can open
+              // the generated deck (slide content is sanitized after assembly).
+              title = createFilesLib.stripInvalidXmlChars(title);
+              author = createFilesLib.stripInvalidXmlChars(author);
+
               if (!filename.toLowerCase().endsWith(".pptx"))
                 filename += ".pptx";
 
@@ -250,12 +255,18 @@ module.exports.CreatePptxPresentation = {
 
               const totalSlideCount = allSlides.length;
 
+              // Sub-agent output can carry XML 1.0 illegal control characters
+              // (e.g. a form feed from a LaTeX `\frac`); strip them recursively
+              // from every slide so PowerPoint can open the generated deck.
+              const cleanSlides =
+                createFilesLib.stripInvalidXmlChars(allSlides);
+
               // Title slide
               const titleSlide = pptx.addSlide();
               renderTitleSlide(titleSlide, pptx, { title, author }, theme);
 
               // Render every slide produced by the section agents
-              allSlides.forEach((slideData, index) => {
+              cleanSlides.forEach((slideData, index) => {
                 const slide = pptx.addSlide();
                 const slideNumber = index + 1;
                 const layout = slideData.layout || "content";

server/utils/agents/aibitat/plugins/create-files/xlsx/create-excel-file.js

@@ -167,6 +167,11 @@ module.exports.CreateExcelFile = {
             try {
               this.super.handlerProps.log(`Using the create-excel-file tool.`);
 
+              // Strip XML 1.0 illegal control characters from all cell content
+              // and sheet names so Excel can open the generated workbook.
+              csvData = createFilesLib.stripInvalidXmlChars(csvData);
+              sheets = createFilesLib.stripInvalidXmlChars(sheets);
+
               const hasExtension = /\.xlsx$/i.test(filename);
               if (!hasExtension) filename = `${filename}.xlsx`;