@ledgerhq/devices/lib-es/hid-framing.js

Ledger devices

import { TransportError } from "@ledgerhq/errors";
const Tag = 0x05;
function asUInt16BE(value) {
    const b = Buffer.alloc(2);
    b.writeUInt16BE(value, 0);
    return b;
}
const initialAcc = {
    data: Buffer.alloc(0),
    dataLength: 0,
    sequence: 0,
};
/**
 * Object to handle HID frames (encoding and decoding)
 *
 * @param channel
 * @param packetSize The HID protocol packet size in bytes (usually 64)
 */
const createHIDframing = (channel, packetSize) => {
    return {
        /**
         * Frames/encodes an APDU message into HID USB packets/frames
         *
         * @param apdu The APDU message to send, in a Buffer containing [cla, ins, p1, p2, data length, data(if not empty)]
         * @returns an array of HID USB frames ready to be sent
         */
        makeBlocks(apdu) {
            // Encodes the APDU length in 2 bytes before the APDU itself.
            // The length is measured as the number of bytes.
            // As the size of the APDU `data` should have been added in 1 byte just before `data`,
            // the minimum size of an APDU is 5 bytes.
            let data = Buffer.concat([asUInt16BE(apdu.length), apdu]);
            const blockSize = packetSize - 5;
            const nbBlocks = Math.ceil(data.length / blockSize);
            // Fills data with 0-padding
            data = Buffer.concat([data, Buffer.alloc(nbBlocks * blockSize - data.length + 1).fill(0)]);
            const blocks = [];
            for (let i = 0; i < nbBlocks; i++) {
                const head = Buffer.alloc(5);
                head.writeUInt16BE(channel, 0);
                head.writeUInt8(Tag, 2);
                head.writeUInt16BE(i, 3);
                // `slice` and not `subarray`: this might not be a Node Buffer, but probably only a Uint8Array
                const chunk = data.slice(i * blockSize, (i + 1) * blockSize);
                blocks.push(Buffer.concat([head, chunk]));
            }
            return blocks;
        },
        /**
         * Reduces HID USB packets/frames to one response.
         *
         * @param acc The value resulting from (accumulating) the previous call of reduceResponse.
         *   On first call initialized to `initialAcc`. The accumulator enables handling multi-frames messages.
         * @param chunk Current chunk to reduce into accumulator
         * @returns An accumulator value updated with the current chunk
         */
        reduceResponse(acc, chunk) {
            let { data, dataLength, sequence } = acc || initialAcc;
            if (chunk.readUInt16BE(0) !== channel) {
                throw new TransportError("Invalid channel", "InvalidChannel");
            }
            if (chunk.readUInt8(2) !== Tag) {
                throw new TransportError("Invalid tag", "InvalidTag");
            }
            if (chunk.readUInt16BE(3) !== sequence) {
                throw new TransportError("Invalid sequence", "InvalidSequence");
            }
            // Gets the total length of the response from the 1st frame
            if (!acc) {
                dataLength = chunk.readUInt16BE(5);
            }
            sequence++;
            // The total length on the 1st frame takes 2 more bytes
            const chunkData = chunk.slice(acc ? 5 : 7);
            data = Buffer.concat([data, chunkData]);
            // Removes any 0 padding
            if (data.length > dataLength) {
                data = data.slice(0, dataLength);
            }
            return {
                data,
                dataLength,
                sequence,
            };
        },
        /**
         * Returns the response message that has been reduced from the HID USB frames
         *
         * @param acc The accumulator
         * @returns A Buffer containing the cleaned response message, or null if no response message, or undefined if the
         *   accumulator is incorrect (message length is not valid)
         */
        getReducedResult(acc) {
            if (acc && acc.dataLength === acc.data.length) {
                return acc.data;
            }
        },
    };
};
export default createHIDframing;
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