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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");
};
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