snapshot of https://github.com/excalidraw/excalidraw.git (master, 2026-09-16; blobs > 131072B omitted)

packages/excalidraw/subset/subset-main.ts

@@ -0,0 +1,130 @@
+import { isServerEnv, promiseTry } from "@excalidraw/common";
+
+import { WorkerInTheMainChunkError, WorkerUrlNotDefinedError } from "../errors";
+import { WorkerPool } from "../workers";
+
+import type { Commands } from "./subset-shared.chunk";
+
+let shouldUseWorkers = typeof Worker !== "undefined";
+
+/**
+ * Tries to subset glyphs in a font based on the used codepoints, returning the font as dataurl.
+ * Under the hood utilizes worker threads (Web Workers, if available), otherwise fallbacks to the main thread.
+ *
+ * Check the following diagram for details: link.excalidraw.com/readonly/MbbnWPSWXgadXdtmzgeO
+ *
+ * @param arrayBuffer font data buffer in the woff2 format
+ * @param codePoints codepoints used to subset the glyphs
+ *
+ * @returns font with subsetted glyphs (all glyphs in case of errors) converted into a dataurl
+ */
+export const subsetWoff2GlyphsByCodepoints = async (
+  arrayBuffer: ArrayBuffer,
+  codePoints: Array<number>,
+): Promise<string> => {
+  const { Commands, subsetToBase64, toBase64 } =
+    await lazyLoadSharedSubsetChunk();
+
+  if (!shouldUseWorkers) {
+    return subsetToBase64(arrayBuffer, codePoints);
+  }
+
+  return promiseTry(async () => {
+    try {
+      const workerPool = await getOrCreateWorkerPool();
+      // copy the buffer to avoid working on top of the detached array buffer in the fallback
+      // i.e. in case the worker throws, the array buffer does not get automatically detached, even if the worker is terminated
+      const arrayBufferCopy = arrayBuffer.slice(0);
+      const result = await workerPool.postMessage(
+        {
+          command: Commands.Subset,
+          arrayBuffer: arrayBufferCopy,
+          codePoints,
+        } as const,
+        { transfer: [arrayBufferCopy] },
+      );
+
+      // encode on the main thread to avoid copying large binary strings (as dataurl) between threads
+      return toBase64(result);
+    } catch (e) {
+      // don't use workers if they are failing
+      shouldUseWorkers = false;
+
+      if (
+        // don't log the expected errors server-side
+        !(
+          isServerEnv() &&
+          (e instanceof WorkerUrlNotDefinedError ||
+            e instanceof WorkerInTheMainChunkError)
+        )
+      ) {
+        // eslint-disable-next-line no-console
+        console.error(
+          "Failed to use workers for subsetting, falling back to the main thread.",
+          e,
+        );
+      }
+
+      // fallback to the main thread
+      return subsetToBase64(arrayBuffer, codePoints);
+    }
+  });
+};
+
+// lazy-loaded and cached chunks
+let subsetWorker: Promise<typeof import("./subset-worker.chunk")> | null = null;
+let subsetShared: Promise<typeof import("./subset-shared.chunk")> | null = null;
+
+const lazyLoadWorkerSubsetChunk = async () => {
+  if (!subsetWorker) {
+    subsetWorker = import("./subset-worker.chunk");
+  }
+
+  return subsetWorker;
+};
+
+const lazyLoadSharedSubsetChunk = async () => {
+  if (!subsetShared) {
+    // load dynamically to force create a shared chunk reused between main thread and the worker thread
+    subsetShared = import("./subset-shared.chunk");
+  }
+
+  return subsetShared;
+};
+
+// could be extended with multiple commands in the future
+type SubsetWorkerData = {
+  command: typeof Commands.Subset;
+  arrayBuffer: ArrayBuffer;
+  codePoints: Array<number>;
+};
+
+type SubsetWorkerResult<T extends SubsetWorkerData["command"]> =
+  T extends typeof Commands.Subset ? ArrayBuffer : never;
+
+let workerPool: Promise<
+  WorkerPool<SubsetWorkerData, SubsetWorkerResult<SubsetWorkerData["command"]>>
+> | null = null;
+
+/**
+ * Lazy initialize or get the worker pool singleton.
+ *
+ * @throws implicitly if anything goes wrong - worker pool creation, loading wasm, initializing worker, etc.
+ */
+const getOrCreateWorkerPool = () => {
+  if (!workerPool) {
+    // immediate concurrent-friendly return, to ensure we have only one pool instance
+    workerPool = promiseTry(async () => {
+      const { WorkerUrl } = await lazyLoadWorkerSubsetChunk();
+
+      const pool = WorkerPool.create<
+        SubsetWorkerData,
+        SubsetWorkerResult<SubsetWorkerData["command"]>
+      >(WorkerUrl);
+
+      return pool;
+    });
+  }
+
+  return workerPool;
+};