micro-eth-signer/src/rlp.ts

Minimal library for Ethereum transactions, addresses and smart contracts

import { numberToVarBytesBE } from '@noble/curves/abstract/utils';
import * as P from 'micro-packed';
import { isBytes } from './utils.ts';

// Spec-compliant RLP in 100 lines of code.
export type RLPInput = string | number | Uint8Array | bigint | RLPInput[] | null;
// length: first 3 bit !== 111 ? 6 bit length : 3bit lenlen
const RLPLength = P.wrap({
  encodeStream(w: P.Writer, value: number) {
    if (value < 56) return w.bits(value, 6);
    w.bits(0b111, 3);
    const length = P.U32BE.encode(value);
    let pos = 0;
    for (; pos < length.length; pos++) if (length[pos] !== 0) break;
    w.bits(4 - pos - 1, 3);
    w.bytes(length.slice(pos));
  },
  decodeStream(r: P.Reader): number {
    const start = r.bits(3);
    if (start !== 0b111) return (start << 3) | r.bits(3);
    const len = r.bytes(r.bits(3) + 1);
    for (let i = 0; i < len.length; i++) {
      if (len[i]) break;
      throw new Error('Wrong length encoding with leading zeros');
    }
    const res = P.int(len.length).decode(len);
    if (res <= 55) throw new Error('RLPLength: less than 55, but used multi-byte flag');
    return res;
  },
});

// Recursive struct definition
export type InternalRLP =
  | { TAG: 'byte'; data: number }
  | {
      TAG: 'complex';
      data: { TAG: 'string'; data: Uint8Array } | { TAG: 'list'; data: InternalRLP[] };
    };

const rlpInner = P.tag(P.map(P.bits(1), { byte: 0, complex: 1 }), {
  byte: P.bits(7),
  complex: P.tag(P.map(P.bits(1), { string: 0, list: 1 }), {
    string: P.bytes(RLPLength),
    list: P.prefix(
      RLPLength,
      P.array(
        null,
        P.lazy((): P.CoderType<InternalRLP> => rlpInner)
      )
    ),
  }),
});

const phex = P.hex(null);
const pstr = P.string(null);
const empty = Uint8Array.of();

/**
 * RLP parser.
 * Real type of rlp is `Item = Uint8Array | Item[]`.
 * Strings/number encoded to Uint8Array, but not decoded back: type information is lost.
 */
export const RLP: P.CoderType<RLPInput> = P.apply(rlpInner, {
  encode(from: InternalRLP): RLPInput {
    if (from.TAG === 'byte') return new Uint8Array([from.data]);
    if (from.TAG !== 'complex') throw new Error('RLP.encode: unexpected type');
    const complex = from.data;
    if (complex.TAG === 'string') {
      if (complex.data.length === 1 && complex.data[0] < 128)
        throw new Error('RLP.encode: wrong string length encoding, should use single byte mode');
      return complex.data;
    }
    if (complex.TAG === 'list') return complex.data.map((i) => this.encode(i));
    throw new Error('RLP.encode: unknown TAG');
  },
  decode(data: RLPInput): InternalRLP {
    if (data == null) return this.decode(empty);
    switch (typeof data) {
      case 'object':
        if (isBytes(data)) {
          if (data.length === 1) {
            const head = data[0];
            if (head < 128) return { TAG: 'byte', data: head };
          }
          return { TAG: 'complex', data: { TAG: 'string', data: data } };
        }
        if (Array.isArray(data))
          return { TAG: 'complex', data: { TAG: 'list', data: data.map((i) => this.decode(i)) } };
        throw new Error('RLP.encode: unknown type');
      case 'number':
        if (data < 0) throw new Error('RLP.encode: invalid integer as argument, must be unsigned');
        if (data === 0) return this.decode(empty);
        return this.decode(numberToVarBytesBE(data));
      case 'bigint':
        if (data < BigInt(0))
          throw new Error('RLP.encode: invalid integer as argument, must be unsigned');
        return this.decode(numberToVarBytesBE(data));
      case 'string':
        return this.decode(data.startsWith('0x') ? phex.encode(data) : pstr.encode(data));
      default:
        throw new Error('RLP.encode: unknown type');
    }
  },
});