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@@ -0,0 +1,130 @@
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+import decodePng from "png-chunks-extract";
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+import tEXt from "png-chunk-text";
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+import encodePng from "png-chunks-encode";
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+import { stringToBase64, encode, decode, base64ToString } from "./encode";
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+import { MIME_TYPES } from "../constants";
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+
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+// -----------------------------------------------------------------------------
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+// PNG
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+// -----------------------------------------------------------------------------
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+
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+const blobToArrayBuffer = (blob: Blob): Promise<ArrayBuffer> => {
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+ if ("arrayBuffer" in blob) {
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+ return blob.arrayBuffer();
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+ }
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+ // Safari
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+ return new Promise((resolve, reject) => {
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+ const reader = new FileReader();
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+ reader.onload = (event) => {
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+ if (!event.target?.result) {
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+ return reject(new Error("couldn't convert blob to ArrayBuffer"));
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+ }
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+ resolve(event.target.result as ArrayBuffer);
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+ };
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+ reader.readAsArrayBuffer(blob);
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+ });
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+};
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+
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+export const getTEXtChunk = async (
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+ blob: Blob,
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+): Promise<{ keyword: string; text: string } | null> => {
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+ const chunks = decodePng(new Uint8Array(await blobToArrayBuffer(blob)));
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+ const metadataChunk = chunks.find((chunk) => chunk.name === "tEXt");
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+ if (metadataChunk) {
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+ return tEXt.decode(metadataChunk.data);
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+ }
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+ return null;
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+};
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+
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+export const encodePngMetadata = async ({
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+ blob,
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+ metadata,
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+}: {
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+ blob: Blob;
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+ metadata: string;
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+}) => {
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+ const chunks = decodePng(new Uint8Array(await blobToArrayBuffer(blob)));
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+
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+ const metadataChunk = tEXt.encode(
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+ MIME_TYPES.excalidraw,
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+ JSON.stringify(
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+ await encode({
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+ text: metadata,
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+ compress: true,
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+ }),
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+ ),
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+ );
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+ // insert metadata before last chunk (iEND)
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+ chunks.splice(-1, 0, metadataChunk);
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+
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+ return new Blob([encodePng(chunks)], { type: "image/png" });
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+};
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+
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+export const decodePngMetadata = async (blob: Blob) => {
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+ const metadata = await getTEXtChunk(blob);
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+ if (metadata?.keyword === MIME_TYPES.excalidraw) {
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+ try {
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+ const encodedData = JSON.parse(metadata.text);
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+ if (!("encoded" in encodedData)) {
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+ // legacy, un-encoded scene JSON
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+ if ("type" in encodedData && encodedData.type === "excalidraw") {
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+ return metadata.text;
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+ }
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+ throw new Error("FAILED");
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+ }
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+ return await decode(encodedData);
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+ } catch (error) {
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+ console.error(error);
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+ throw new Error("FAILED");
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+ }
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+ }
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+ throw new Error("INVALID");
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+};
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+
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+// -----------------------------------------------------------------------------
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+// SVG
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+// -----------------------------------------------------------------------------
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+
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+export const encodeSvgMetadata = async ({ text }: { text: string }) => {
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+ const base64 = await stringToBase64(
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+ JSON.stringify(await encode({ text })),
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+ true /* is already byte string */,
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+ );
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+
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+ let metadata = "";
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+ metadata += `<!-- payload-type:${MIME_TYPES.excalidraw} -->`;
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+ metadata += `<!-- payload-version:2 -->`;
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+ metadata += "<!-- payload-start -->";
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+ metadata += base64;
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+ metadata += "<!-- payload-end -->";
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+ return metadata;
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+};
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+
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+export const decodeSvgMetadata = async ({ svg }: { svg: string }) => {
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+ if (svg.includes(`payload-type:${MIME_TYPES.excalidraw}`)) {
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+ const match = svg.match(/<!-- payload-start -->(.+?)<!-- payload-end -->/);
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+ if (!match) {
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+ throw new Error("INVALID");
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+ }
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+ const versionMatch = svg.match(/<!-- payload-version:(\d+) -->/);
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+ const version = versionMatch?.[1] || "1";
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+ const isByteString = version !== "1";
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+
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+ try {
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+ const json = await base64ToString(match[1], isByteString);
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+ const encodedData = JSON.parse(json);
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+ if (!("encoded" in encodedData)) {
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+ // legacy, un-encoded scene JSON
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+ if ("type" in encodedData && encodedData.type === "excalidraw") {
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+ return json;
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+ }
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+ throw new Error("FAILED");
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+ }
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+ return await decode(encodedData);
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+ } catch (error) {
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+ console.error(error);
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+ throw new Error("FAILED");
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+ }
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+ }
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+ throw new Error("INVALID");
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+};
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