@hpke/ohttp/esm/src/bhttp/varint.js

Oblivious HTTP (RFC 9458) client and server using HPKE

/**
 * QUIC variable-length integer encoding (RFC 9000 Section 16), used by
 * Binary HTTP (RFC 9292) for all length and integer fields.
 *
 * Values are limited to `Number.MAX_SAFE_INTEGER` since they are handled as
 * JavaScript numbers.
 *
 * @module
 */
import { OhttpError } from "../errors.js";
const MAX_1 = 0x3f;
const MAX_2 = 0x3fff;
const MAX_4 = 0x3fffffff;
const TWO_POW_32 = 0x100000000;
/**
 * Returns the number of bytes needed to encode `v` as a varint.
 */
export function varintLength(v) {
    if (!Number.isSafeInteger(v) || v < 0) {
        throw new OhttpError(`Invalid varint value: ${v}`);
    }
    if (v <= MAX_1)
        return 1;
    if (v <= MAX_2)
        return 2;
    if (v <= MAX_4)
        return 4;
    return 8;
}
/**
 * Writes `v` as a varint into `buf` at `offset`.
 *
 * @returns The offset just after the written varint.
 */
export function writeVarint(buf, offset, v) {
    switch (varintLength(v)) {
        case 1:
            buf[offset] = v;
            return offset + 1;
        case 2:
            buf[offset] = 0x40 | (v >>> 8);
            buf[offset + 1] = v & 0xff;
            return offset + 2;
        case 4:
            buf[offset] = 0x80 | (v >>> 24);
            buf[offset + 1] = (v >>> 16) & 0xff;
            buf[offset + 2] = (v >>> 8) & 0xff;
            buf[offset + 3] = v & 0xff;
            return offset + 4;
        default: {
            const hi = Math.floor(v / TWO_POW_32);
            const lo = v >>> 0;
            buf[offset] = 0xc0 | (hi >>> 24);
            buf[offset + 1] = (hi >>> 16) & 0xff;
            buf[offset + 2] = (hi >>> 8) & 0xff;
            buf[offset + 3] = hi & 0xff;
            buf[offset + 4] = lo >>> 24;
            buf[offset + 5] = (lo >>> 16) & 0xff;
            buf[offset + 6] = (lo >>> 8) & 0xff;
            buf[offset + 7] = lo & 0xff;
            return offset + 8;
        }
    }
}
/**
 * Encodes `v` as a varint.
 */
export function encodeVarint(v) {
    const buf = new Uint8Array(varintLength(v));
    writeVarint(buf, 0, v);
    return buf;
}
/**
 * Reads a varint from `buf` at `offset`.
 *
 * @returns A tuple of the decoded value and the offset just after it.
 */
export function readVarint(buf, offset) {
    if (offset >= buf.byteLength) {
        throw new OhttpError("Invalid binary HTTP message: truncated varint");
    }
    const len = 1 << (buf[offset] >>> 6);
    if (offset + len > buf.byteLength) {
        throw new OhttpError("Invalid binary HTTP message: truncated varint");
    }
    const first = buf[offset] & 0x3f;
    switch (len) {
        case 1:
            return [first, offset + 1];
        case 2:
            return [(first << 8) | buf[offset + 1], offset + 2];
        case 4:
            return [
                ((first << 24) | (buf[offset + 1] << 16) | (buf[offset + 2] << 8) |
                    buf[offset + 3]) >>> 0,
                offset + 4,
            ];
        default: {
            const hi = ((first << 24) | (buf[offset + 1] << 16) |
                (buf[offset + 2] << 8) | buf[offset + 3]) >>> 0;
            const lo = ((buf[offset + 4] << 24) | (buf[offset + 5] << 16) |
                (buf[offset + 6] << 8) | buf[offset + 7]) >>> 0;
            const v = hi * TWO_POW_32 + lo;
            if (!Number.isSafeInteger(v)) {
                throw new OhttpError("Invalid binary HTTP message: varint exceeds Number.MAX_SAFE_INTEGER");
            }
            return [v, offset + 8];
        }
    }
}