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