ts-mls/dist/src/codec/variableLength.js

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import { CodecError } from "../mlsError";
export const encodeVarLenData = (data) => {
    const lenBytes = encodeLength(data.length);
    const result = new Uint8Array(lenBytes.length + data.length);
    result.set(lenBytes, 0);
    result.set(data, lenBytes.length);
    return result;
};
export function encodeLength(len) {
    if (len < 64) {
        // 1-byte length: 00xxxxxx
        return new Uint8Array([len & 0b00111111]);
    }
    else if (len < 16384) {
        // 2-byte length: 01xxxxxx xxxxxxxx
        return new Uint8Array([((len >> 8) & 0b00111111) | 0b01000000, len & 0xff]);
    }
    else if (len < 0x40000000) {
        // 4-byte length: 10xxxxxx xxxxxxxx xxxxxxxx xxxxxxxx
        return new Uint8Array([((len >> 24) & 0b00111111) | 0b10000000, (len >> 16) & 0xff, (len >> 8) & 0xff, len & 0xff]);
    }
    else {
        throw new CodecError("Length too large to encode (max is 2^30 - 1)");
    }
}
export function determineLength(data, offset = 0) {
    if (offset >= data.length) {
        throw new CodecError("Offset beyond buffer");
    }
    const firstByte = data[offset];
    const prefix = firstByte >> 6;
    if (prefix === 0) {
        return { length: firstByte & 0b00111111, lengthFieldSize: 1 };
    }
    else if (prefix === 1) {
        if (offset + 2 > data.length)
            throw new CodecError("Incomplete 2-byte length");
        return { length: ((firstByte & 0b00111111) << 8) | data[offset + 1], lengthFieldSize: 2 };
    }
    else if (prefix === 2) {
        if (offset + 4 > data.length)
            throw new CodecError("Incomplete 4-byte length");
        return {
            length: ((firstByte & 0b00111111) << 24) |
                (data[offset + 1] << 16) |
                (data[offset + 2] << 8) |
                data[offset + 3],
            lengthFieldSize: 4,
        };
    }
    else {
        throw new CodecError("8-byte length not supported in this implementation");
    }
}
export const decodeVarLenData = (buf, offset) => {
    if (offset >= buf.length) {
        throw new CodecError("Offset beyond buffer");
    }
    const { length, lengthFieldSize } = determineLength(buf, offset);
    const totalBytes = lengthFieldSize + length;
    if (offset + totalBytes > buf.length) {
        throw new CodecError("Data length exceeds buffer");
    }
    const data = buf.subarray(offset + lengthFieldSize, offset + totalBytes);
    return [data, totalBytes];
};
export function encodeVarLenType(enc) {
    return (data) => {
        let x = new Uint8Array();
        for (const t of data) {
            x = new Uint8Array([...x, ...enc(t)]);
        }
        return encodeVarLenData(x);
    };
}
export function decodeVarLenType(dec) {
    return (b, offset) => {
        const d = decodeVarLenData(b, offset);
        if (d === undefined)
            return;
        const [totalBytes, totalLength] = d;
        let cursor = 0;
        const result = [];
        while (cursor < totalBytes.length) {
            const item = dec(totalBytes, cursor);
            if (item === undefined)
                return undefined;
            const [value, len] = item;
            result.push(value);
            cursor += len;
        }
        return [result, totalLength];
    };
}
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