feat(viewer): add self-hosted PDFium font fallback and eager WASM streaming fallback

frontend/editor/src/core/components/viewer/LocalEmbedPDF.tsx

@@ -100,6 +100,7 @@ import { DocumentPermissionsAPIBridge } from "@app/components/viewer/DocumentPer
 import { DocumentReadyWrapper } from "@app/components/viewer/DocumentReadyWrapper";
 import { ActiveDocumentProvider } from "@app/components/viewer/ActiveDocumentContext";
 import { pdfiumWasmUrl } from "@app/services/wasmPrecompiler";
+import { getLocalFontFallbackConfig } from "@app/services/pdfiumFontFallback";
 import { FormFieldOverlay } from "@app/tools/formFill/FormFieldOverlay";
 import { FormCreationInteractionLock } from "@app/tools/formFill/FormCreationInteractionLock";
 import { FormFieldCreationOverlay } from "@app/tools/formFill/FormFieldCreationOverlay";
@@ -437,9 +438,12 @@ export function LocalEmbedPDF({
     ];
   }, [pdfUrl, enableAnnotations, exportFileName]);
 
+  const fontFallbackConfig = useMemo(() => getLocalFontFallbackConfig(), []);
+
   // Initialize the engine with the React hook - use local WASM for offline support
   const { engine, isLoading, error } = usePdfiumEngine({
     wasmUrl: pdfiumWasmUrl,
+    fontFallback: fontFallbackConfig,
   });
 
   // Early return if no file or URL provided

frontend/editor/src/core/services/pdfiumFontFallback.test.ts

@@ -0,0 +1,30 @@
+import { describe, expect, it } from "vitest";
+import { FontCharset } from "@embedpdf/models";
+import { getLocalFontFallbackConfig } from "@app/services/pdfiumFontFallback";
+
+describe("pdfiumFontFallback", () => {
+  it("generates a self-hosted font fallback configuration without external CDN URLs", () => {
+    const config = getLocalFontFallbackConfig();
+
+    expect(config.baseUrl).toContain("/fonts");
+    expect(config.defaultFont).toBe("NotoSans-Regular.ttf");
+
+    expect(config.fonts[FontCharset.ANSI]).toBe("NotoSans-Regular.ttf");
+    expect(config.fonts[FontCharset.DEFAULT]).toBe("NotoSans-Regular.ttf");
+    expect(config.fonts[FontCharset.SHIFTJIS]).toBe("NotoSansJP-Regular.ttf");
+    expect(config.fonts[FontCharset.HANGEUL]).toBe("NotoSansKR-Regular.ttf");
+    expect(config.fonts[FontCharset.GB2312]).toBe("NotoSansSC-Regular.ttf");
+    expect(config.fonts[FontCharset.CHINESEBIG5]).toBe(
+      "NotoSansTC-Regular.ttf",
+    );
+    expect(config.fonts[FontCharset.ARABIC]).toBe("NotoSansArabic-Regular.ttf");
+    expect(config.fonts[FontCharset.THAI]).toBe("NotoSansThai-Regular.ttf");
+
+    expect(config.baseUrl).not.toContain("jsdelivr");
+    for (const fontVal of Object.values(config.fonts)) {
+      expect(String(fontVal)).not.toContain("http://");
+      expect(String(fontVal)).not.toContain("https://");
+      expect(String(fontVal)).not.toContain("jsdelivr");
+    }
+  });
+});

frontend/editor/src/core/services/pdfiumFontFallback.ts

@@ -0,0 +1,27 @@
+import { BASE_PATH } from "@app/constants/app";
+import type { FontFallbackConfig } from "@embedpdf/engines";
+import { FontCharset } from "@embedpdf/models";
+
+export function getLocalFontFallbackConfig(): FontFallbackConfig {
+  const origin = typeof window !== "undefined" ? window.location.origin : "";
+  const baseUrl = `${origin}${BASE_PATH}/fonts`;
+
+  return {
+    baseUrl,
+    defaultFont: "NotoSans-Regular.ttf",
+    fonts: {
+      [FontCharset.ANSI]: "NotoSans-Regular.ttf",
+      [FontCharset.DEFAULT]: "NotoSans-Regular.ttf",
+      [FontCharset.CYRILLIC]: "NotoSans-Regular.ttf",
+      [FontCharset.GREEK]: "NotoSans-Regular.ttf",
+      [FontCharset.VIETNAMESE]: "NotoSans-Regular.ttf",
+      [FontCharset.EASTERNEUROPEAN]: "NotoSans-Regular.ttf",
+      [FontCharset.ARABIC]: "NotoSansArabic-Regular.ttf",
+      [FontCharset.THAI]: "NotoSansThai-Regular.ttf",
+      [FontCharset.SHIFTJIS]: "NotoSansJP-Regular.ttf",
+      [FontCharset.HANGEUL]: "NotoSansKR-Regular.ttf",
+      [FontCharset.GB2312]: "NotoSansSC-Regular.ttf",
+      [FontCharset.CHINESEBIG5]: "NotoSansTC-Regular.ttf",
+    },
+  };
+}

frontend/editor/src/core/services/wasmPrecompiler.ts

@@ -32,20 +32,40 @@ export function startEagerWasmCompilation(): void {
   if (compilationStarted) return;
   compilationStarted = true;
 
-  if (
-    typeof WebAssembly === "object" &&
-    typeof WebAssembly.compileStreaming === "function"
-  ) {
-    WebAssembly.compileStreaming(fetch(pdfiumWasmUrl))
-      .then(resolvePromise)
-      .catch((err) => {
-        console.warn(
-          "Eager WASM compilation failed or not supported in this environment:",
-          err,
-        );
-        resolvePromise(null);
-      });
-  } else {
+  if (typeof WebAssembly !== "object") {
     resolvePromise(null);
+    return;
   }
+
+  const compileWithFallback = async (): Promise<WebAssembly.Module | null> => {
+    try {
+      if (typeof WebAssembly.compileStreaming === "function") {
+        try {
+          return await WebAssembly.compileStreaming(fetch(pdfiumWasmUrl));
+        } catch (streamingErr) {
+          console.warn(
+            "WASM compileStreaming failed, falling back to ArrayBuffer:",
+            streamingErr,
+          );
+        }
+      }
+
+      // compileStreaming requires application/wasm MIME; fall back to ArrayBuffer if the server or proxy serves octet-stream.
+      const res = await fetch(pdfiumWasmUrl);
+      if (!res.ok) {
+        throw new Error(
+          `Failed to fetch WASM: ${res.status} ${res.statusText}`,
+        );
+      }
+      const buffer = await res.arrayBuffer();
+      return await WebAssembly.compile(buffer);
+    } catch (err) {
+      console.warn("WASM compilation failed:", err);
+      return null;
+    }
+  };
+
+  compileWithFallback()
+    .then(resolvePromise)
+    .catch(() => resolvePromise(null));
 }

frontend/editor/vite.config.ts

@@ -256,6 +256,7 @@ export default defineConfig(async ({ mode, command }) => {
           "/login/saml2": backendProxy,
           "/swagger-ui": backendProxy,
           "/v1/api-docs": backendProxy,
+          "/fonts": backendProxy,
         };
 
   return {
@@ -340,6 +341,11 @@ export default defineConfig(async ({ mode, command }) => {
             src: "src/core/assets/brand/modern-logo/*",
             dest: "modern-logo",
           },
+          {
+            // Fallback TrueType fonts for PDFium (Noto Sans, CJK, Arabic, etc.)
+            src: "../../app/core/src/main/resources/static/fonts/*.ttf",
+            dest: "fonts",
+          },
         ],
       }),
       compressStaticCopyPlugin(),