Fix the regex used to normalize css fonts in XFA

The regex was quadratic in the number of consecutive spaces,
which caused performance issues when normalizing fonts with
a large number of spaces.

src/core/core_utils.js

@@ -574,6 +574,18 @@ function validateFontName(fontFamily, mustWarn = false) {
   return true;
 }
 
+// Strip the spaces preceding a digit, since e.g. "Wingdings 3" is not a valid
+// font name in the css specs.
+// The optional trailing digit is matched as part of the space run, so that a
+// failing match cannot backtrack over the spaces; otherwise the replacement
+// would be quadratic in the number of consecutive spaces.
+function normalizeCSSFontFamily(fontFamily) {
+  return fontFamily.replaceAll(
+    /( +)(\d)?/g,
+    (_, spaces, digit) => digit ?? " "
+  );
+}
+
 function validateCSSFont(cssFontInfo) {
   // See https://developer.mozilla.org/en-US/docs/Web/CSS/font-style.
   const DEFAULT_CSS_FONT_OBLIQUE = "14";
@@ -750,6 +762,7 @@ export {
   lookupRect,
   MAX_INT_32,
   MissingDataException,
+  normalizeCSSFontFamily,
   numberToString,
   ParserEOFException,
   parseXFAPath,

src/core/document.js

@@ -42,6 +42,7 @@ import {
   isWhiteSpace,
   lookupNormalRect,
   MissingDataException,
+  normalizeCSSFontFamily,
   PDF_VERSION_REGEXP,
   RESOURCES_KEYS_OPERATOR_LIST,
   RESOURCES_KEYS_TEXT_CONTENT,
@@ -1396,9 +1397,7 @@ class PDFDocument {
       if (!(descriptor instanceof Dict)) {
         continue;
       }
-      let fontFamily = descriptor.get("FontFamily");
-      // For example, "Wingdings 3" is not a valid font name in the css specs.
-      fontFamily = fontFamily.replaceAll(/ +(\d)/g, "$1");
+      const fontFamily = normalizeCSSFontFamily(descriptor.get("FontFamily"));
       const fontWeight = descriptor.get("FontWeight");
 
       // Angle is expressed in degrees counterclockwise in PDF

test/unit/core_utils_spec.js

@@ -24,6 +24,7 @@ import {
   getRotationMatrix,
   getSizeInBytes,
   isWhiteSpace,
+  normalizeCSSFontFamily,
   numberToString,
   parseXFAPath,
   recoverJsURL,
@@ -325,6 +326,41 @@ describe("core_utils", function () {
     });
   });
 
+  describe("normalizeCSSFontFamily", function () {
+    it("should strip the spaces preceding a digit", function () {
+      expect(normalizeCSSFontFamily("Wingdings 3")).toEqual("Wingdings3");
+      expect(normalizeCSSFontFamily("Wingdings   3")).toEqual("Wingdings3");
+      expect(normalizeCSSFontFamily(" 1 2 3")).toEqual("123");
+      expect(normalizeCSSFontFamily("MS Gothic 2 Bold 7")).toEqual(
+        "MS Gothic2 Bold7"
+      );
+    });
+
+    it("should keep the spaces which don't precede a digit", function () {
+      expect(normalizeCSSFontFamily("")).toEqual("");
+      expect(normalizeCSSFontFamily("Times New Roman")).toEqual(
+        "Times New Roman"
+      );
+      // The runs of spaces must be preserved as-is.
+      expect(normalizeCSSFontFamily("  Times   New Roman ")).toEqual(
+        " Times New Roman "
+      );
+      // A digit which isn't preceded by a space is left alone.
+      expect(normalizeCSSFontFamily("Wingdings3")).toEqual("Wingdings3");
+    });
+
+    it("should handle long runs of spaces efficiently", function () {
+      // Guard against a regular expression that backtracks over the spaces,
+      // which makes the replacement quadratic: that needs several seconds
+      // here, whereas a linear one needs well under a millisecond.
+      const fontFamily = `Wingdings${" ".repeat(100000)}`;
+
+      const startTime = performance.now();
+      expect(normalizeCSSFontFamily(fontFamily)).toEqual("Wingdings ");
+      expect(performance.now() - startTime).toBeLessThan(1000);
+    });
+  });
+
   describe("validateCSSFont", function () {
     it("Check font family", function () {
       const cssFontInfo = {