minimaldata-b4bcoin/index.js

A module to check b4bcoin policy: SCRIPT_VERIFY_MINIMALDATA

var OPS = require('b4bcoin-ops')
var pushData = require('pushdata-b4bcoin')

// https://github.com/bitcoin/bitcoin/blob/master/src/script/script.h#L22
var MAX_SCRIPT_ELEMENT_SIZE = 520

// https://github.com/bitcoin/bitcoin/blob/d612837814020ae832499d18e6ee5eb919a87907/src/script/interpreter.cpp#L209
function checkMinimalPush (opcode, data) {
  // Could have used OP_0.
  if (data.length === 0) {
    return opcode === OPS.OP_0

  // Could have used OP_1 .. OP_16.
  } else if (data.length === 1 && data[0] >= 1 && data[0] <= 16) {
    return opcode === OPS.OP_1 + (opcode - 1)

  // Could have used OP_1NEGATE.
  } else if (data.length === 1 && opcode === 0x81) {
    return opcode === OPS.OP_1NEGATE

  // Could have used a direct push (opcode indicating number of bytes pushed + those bytes).
  } else if (data.length <= 75) {
    return opcode === data.length

  // Could have used OP_PUSHDATA1.
  } else if (data.length <= 255) {
    return opcode === OPS.OP_PUSHDATA1

  // Could have used OP_PUSHDATA2.
  } else if (data.length <= 65535) {
    return opcode === OPS.OP_PUSHDATA2
  }

  return false
}

// https://github.com/bitcoin/bips/blob/master/bip-0062.mediawiki
module.exports = function bip62 (buffer) {
  var i = 0

  while (i < buffer.length) {
    var opcode = buffer[i]

    // is this a data PUSH?
    if (opcode >= 0 && opcode <= OPS.OP_PUSHDATA4) {
      var d = pushData.decode(buffer, i)

      // did reading a pushDataInt fail? empty script
      if (d === null) return false
      i += d.size

      // attempt to read too much data? empty script
      if (i + d.number > buffer.length) return false

      var data = buffer.slice(i, i + d.number)
      i += d.number

      if (d.number > MAX_SCRIPT_ELEMENT_SIZE) return false
      if (!checkMinimalPush(opcode, data)) return false

    // opcode
    } else {
      ++i
    }
  }

  return true
}