signal-desktop/ts/util/trimPadding.ts

52 lines
1.4 KiB
TypeScript

// Copyright 2024 Signal Messenger, LLC
// SPDX-License-Identifier: AGPL-3.0-only
import { Transform } from 'node:stream';
import { strictAssert } from './assert';
/**
* Truncates the stream to the target size and analyzes padding type.
*/
export function trimPadding(
size: number,
onPaddingAnalyzed: ({
isPaddingAllZeros,
}: {
isPaddingAllZeros: boolean;
}) => void
): Transform {
let total = 0;
let seenNonZeroPadding = false;
return new Transform({
transform(chunk, _encoding, callback) {
strictAssert(chunk instanceof Uint8Array, 'chunk must be Uint8Array');
const chunkSize = chunk.byteLength;
const sizeLeft = size - total;
let paddingInThisChunk: Uint8Array | undefined;
if (sizeLeft >= chunkSize) {
total += chunkSize;
callback(null, chunk);
} else if (sizeLeft > 0) {
total += sizeLeft;
const data = chunk.subarray(0, sizeLeft);
paddingInThisChunk = chunk.subarray(sizeLeft);
callback(null, data);
} else {
paddingInThisChunk = chunk;
callback(null, null);
}
if (
paddingInThisChunk &&
!seenNonZeroPadding &&
!paddingInThisChunk.every(el => el === 0)
) {
seenNonZeroPadding = true;
}
},
flush(callback) {
onPaddingAnalyzed({ isPaddingAllZeros: !seenNonZeroPadding });
callback();
},
});
}