1 files changed, 69 insertions, 0 deletions
diff --git a/packages/excalidraw/data/image.ts b/packages/excalidraw/data/image.ts
new file mode 100644
index 0000000..0359a9c
--- /dev/null
+++ b/packages/excalidraw/data/image.ts
@@ -0,0 +1,69 @@
+import decodePng from "png-chunks-extract";
+import tEXt from "png-chunk-text";
+import encodePng from "png-chunks-encode";
+import { encode, decode } from "./encode";
+import { EXPORT_DATA_TYPES, MIME_TYPES } from "../constants";
+import { blobToArrayBuffer } from "./blob";
+
+// -----------------------------------------------------------------------------
+// PNG
+// -----------------------------------------------------------------------------
+
+export const getTEXtChunk = async (
+  blob: Blob,
+): Promise<{ keyword: string; text: string } | null> => {
+  const chunks = decodePng(new Uint8Array(await blobToArrayBuffer(blob)));
+  const metadataChunk = chunks.find((chunk) => chunk.name === "tEXt");
+  if (metadataChunk) {
+    return tEXt.decode(metadataChunk.data);
+  }
+  return null;
+};
+
+export const encodePngMetadata = async ({
+  blob,
+  metadata,
+}: {
+  blob: Blob;
+  metadata: string;
+}) => {
+  const chunks = decodePng(new Uint8Array(await blobToArrayBuffer(blob)));
+
+  const metadataChunk = tEXt.encode(
+    MIME_TYPES.excalidraw,
+    JSON.stringify(
+      encode({
+        text: metadata,
+        compress: true,
+      }),
+    ),
+  );
+  // insert metadata before last chunk (iEND)
+  chunks.splice(-1, 0, metadataChunk);
+
+  return new Blob([encodePng(chunks)], { type: MIME_TYPES.png });
+};
+
+export const decodePngMetadata = async (blob: Blob) => {
+  const metadata = await getTEXtChunk(blob);
+  if (metadata?.keyword === MIME_TYPES.excalidraw) {
+    try {
+      const encodedData = JSON.parse(metadata.text);
+      if (!("encoded" in encodedData)) {
+        // legacy, un-encoded scene JSON
+        if (
+          "type" in encodedData &&
+          encodedData.type === EXPORT_DATA_TYPES.excalidraw
+        ) {
+          return metadata.text;
+        }
+        throw new Error("FAILED");
+      }
+      return decode(encodedData);
+    } catch (error: any) {
+      console.error(error);
+      throw new Error("FAILED");
+    }
+  }
+  throw new Error("INVALID");
+};