bitcoinjs-lib/src/push_data.js

Client-side Bitcoin JavaScript library

'use strict';
Object.defineProperty(exports, '__esModule', { value: true });
exports.decode = exports.encode = exports.encodingLength = void 0;
const ops_1 = require('./ops');
/**
 * Calculates the encoding length of a number used for push data in Bitcoin transactions.
 * @param i The number to calculate the encoding length for.
 * @returns The encoding length of the number.
 */
function encodingLength(i) {
  return i < ops_1.OPS.OP_PUSHDATA1 ? 1 : i <= 0xff ? 2 : i <= 0xffff ? 3 : 5;
}
exports.encodingLength = encodingLength;
/**
 * Encodes a number into a buffer using a variable-length encoding scheme.
 * The encoded buffer is written starting at the specified offset.
 * Returns the size of the encoded buffer.
 *
 * @param buffer - The buffer to write the encoded data into.
 * @param num - The number to encode.
 * @param offset - The offset at which to start writing the encoded buffer.
 * @returns The size of the encoded buffer.
 */
function encode(buffer, num, offset) {
  const size = encodingLength(num);
  // ~6 bit
  if (size === 1) {
    buffer.writeUInt8(num, offset);
    // 8 bit
  } else if (size === 2) {
    buffer.writeUInt8(ops_1.OPS.OP_PUSHDATA1, offset);
    buffer.writeUInt8(num, offset + 1);
    // 16 bit
  } else if (size === 3) {
    buffer.writeUInt8(ops_1.OPS.OP_PUSHDATA2, offset);
    buffer.writeUInt16LE(num, offset + 1);
    // 32 bit
  } else {
    buffer.writeUInt8(ops_1.OPS.OP_PUSHDATA4, offset);
    buffer.writeUInt32LE(num, offset + 1);
  }
  return size;
}
exports.encode = encode;
/**
 * Decodes a buffer and returns information about the opcode, number, and size.
 * @param buffer - The buffer to decode.
 * @param offset - The offset within the buffer to start decoding.
 * @returns An object containing the opcode, number, and size, or null if decoding fails.
 */
function decode(buffer, offset) {
  const opcode = buffer.readUInt8(offset);
  let num;
  let size;
  // ~6 bit
  if (opcode < ops_1.OPS.OP_PUSHDATA1) {
    num = opcode;
    size = 1;
    // 8 bit
  } else if (opcode === ops_1.OPS.OP_PUSHDATA1) {
    if (offset + 2 > buffer.length) return null;
    num = buffer.readUInt8(offset + 1);
    size = 2;
    // 16 bit
  } else if (opcode === ops_1.OPS.OP_PUSHDATA2) {
    if (offset + 3 > buffer.length) return null;
    num = buffer.readUInt16LE(offset + 1);
    size = 3;
    // 32 bit
  } else {
    if (offset + 5 > buffer.length) return null;
    if (opcode !== ops_1.OPS.OP_PUSHDATA4) throw new Error('Unexpected opcode');
    num = buffer.readUInt32LE(offset + 1);
    size = 5;
  }
  return {
    opcode,
    number: num,
    size,
  };
}
exports.decode = decode;