Class: Bitcoin::Script

Inherits:
Object show all
Includes:
Opcodes
Defined in:
lib/bitcoin/script/script.rb

Overview

bitcoin script

Constant Summary

Constants included from Opcodes

Opcodes::DUPLICATE_KEY, Opcodes::NAME_MAP, Opcodes::OPCODES_MAP, Opcodes::OP_0, Opcodes::OP_0NOTEQUAL, Opcodes::OP_1, Opcodes::OP_10, Opcodes::OP_11, Opcodes::OP_12, Opcodes::OP_13, Opcodes::OP_14, Opcodes::OP_15, Opcodes::OP_16, Opcodes::OP_1ADD, Opcodes::OP_1NEGATE, Opcodes::OP_1SUB, Opcodes::OP_2, Opcodes::OP_2DIV, Opcodes::OP_2DROP, Opcodes::OP_2DUP, Opcodes::OP_2MUL, Opcodes::OP_2OVER, Opcodes::OP_2ROT, Opcodes::OP_2SWAP, Opcodes::OP_3, Opcodes::OP_3DUP, Opcodes::OP_4, Opcodes::OP_5, Opcodes::OP_6, Opcodes::OP_7, Opcodes::OP_8, Opcodes::OP_9, Opcodes::OP_ABS, Opcodes::OP_ADD, Opcodes::OP_AND, Opcodes::OP_BOOLAND, Opcodes::OP_BOOLOR, Opcodes::OP_CAT, Opcodes::OP_CHECKMULTISIG, Opcodes::OP_CHECKMULTISIGVERIFY, Opcodes::OP_CHECKSIG, Opcodes::OP_CHECKSIGVERIFY, Opcodes::OP_CODESEPARATOR, Opcodes::OP_DEPTH, Opcodes::OP_DIV, Opcodes::OP_DROP, Opcodes::OP_DUP, Opcodes::OP_ELSE, Opcodes::OP_ENDIF, Opcodes::OP_EQUAL, Opcodes::OP_EQUALVERIFY, Opcodes::OP_FROMALTSTACK, Opcodes::OP_GREATERTHAN, Opcodes::OP_GREATERTHANOREQUAL, Opcodes::OP_HASH160, Opcodes::OP_HASH256, Opcodes::OP_IF, Opcodes::OP_IFDUP, Opcodes::OP_INVALIDOPCODE, Opcodes::OP_INVERT, Opcodes::OP_LEFT, Opcodes::OP_LESSTHAN, Opcodes::OP_LESSTHANOREQUAL, Opcodes::OP_LSHIFT, Opcodes::OP_MAX, Opcodes::OP_MIN, Opcodes::OP_MOD, Opcodes::OP_MUL, Opcodes::OP_NEGATE, Opcodes::OP_NIP, Opcodes::OP_NOP, Opcodes::OP_NOP1, Opcodes::OP_NOP10, Opcodes::OP_NOP2, Opcodes::OP_NOP3, Opcodes::OP_NOP4, Opcodes::OP_NOP5, Opcodes::OP_NOP6, Opcodes::OP_NOP7, Opcodes::OP_NOP8, Opcodes::OP_NOP9, Opcodes::OP_NOT, Opcodes::OP_NOTIF, Opcodes::OP_NUMEQUAL, Opcodes::OP_NUMEQUALVERIFY, Opcodes::OP_NUMNOTEQUAL, Opcodes::OP_OR, Opcodes::OP_OVER, Opcodes::OP_PICK, Opcodes::OP_PUBKEY, Opcodes::OP_PUBKEYHASH, Opcodes::OP_PUSHDATA1, Opcodes::OP_PUSHDATA2, Opcodes::OP_PUSHDATA4, Opcodes::OP_RESERVED, Opcodes::OP_RESERVED1, Opcodes::OP_RESERVED2, Opcodes::OP_RETURN, Opcodes::OP_RIGHT, Opcodes::OP_RIPEMD160, Opcodes::OP_ROLL, Opcodes::OP_ROT, Opcodes::OP_RSHIFT, Opcodes::OP_SHA1, Opcodes::OP_SHA256, Opcodes::OP_SIZE, Opcodes::OP_SUB, Opcodes::OP_SUBSTR, Opcodes::OP_SWAP, Opcodes::OP_TOALTSTACK, Opcodes::OP_TUCK, Opcodes::OP_VER, Opcodes::OP_VERIF, Opcodes::OP_VERIFY, Opcodes::OP_VERNOTIF, Opcodes::OP_WITHIN, Opcodes::OP_XOR

Instance Attribute Summary collapse

Class Method Summary collapse

Instance Method Summary collapse

Methods included from Opcodes

defined?, name_to_opcode, opcode_to_name, opcode_to_small_int, small_int_to_opcode

Constructor Details

#initialize ⇒ Script

Returns a new instance of Script.



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# File 'lib/bitcoin/script/script.rb', line 12

def initialize
  @chunks = []
end

Instance Attribute Details

#chunks ⇒ Object

Returns the value of attribute chunks.



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# File 'lib/bitcoin/script/script.rb', line 10

def chunks
  @chunks
end

Class Method Details

.decode_number(s) ⇒ Object

decode script number hex to int value



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# File 'lib/bitcoin/script/script.rb', line 388

def self.decode_number(s)
  v = s.htb.reverse
  return 0 if v.length.zero?
  mbs = v[0].unpack('C').first
  v[0] = [mbs - 0x80].pack('C') unless (mbs & 0x80) == 0
  result = v.bth.to_i(16)
  result = -result unless (mbs & 0x80) == 0
  result
end

.encode_number(i) ⇒ Object

encode int value to script number hex. The stacks hold byte vectors. When used as numbers, byte vectors are interpreted as little-endian variable-length integers with the most significant bit determining the sign of the integer. Thus 0x81 represents -1. 0x80 is another representation of zero (so called negative 0). Positive 0 is represented by a null-length vector. Byte vectors are interpreted as Booleans where False is represented by any representation of zero, and True is represented by any representation of non-zero.



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# File 'lib/bitcoin/script/script.rb', line 374

def self.encode_number(i)
  return '' if i == 0
  negative = i < 0

  hex = i.abs.to_even_length_hex
  hex = '0' + hex unless (hex.length % 2).zero?
  v = hex.htb.reverse # change endian

  v = v << (negative ? 0x80 : 0x00) unless (v[-1].unpack('C').first & 0x80) == 0
  v[-1] = [v[-1].unpack('C').first | 0x80].pack('C') if negative
  v.bth
end

.from_string(string) ⇒ Object

generate script from string.



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# File 'lib/bitcoin/script/script.rb', line 69

def self.from_string(string)
  script = new
  string.split(' ').each do |v|
    opcode = Opcodes.name_to_opcode(v)
    if opcode
      script << (v =~ /^\d/ && Opcodes.small_int_to_opcode(v.ord) ? v.ord : opcode)
    else
      script << (v =~ /^[0-9]+$/ ? v.to_i : v)
    end
  end
  script
end

.pack_pushdata(data) ⇒ Object

binary data convert pushdata which contains data length and append PUSHDATA opcode if necessary.



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# File 'lib/bitcoin/script/script.rb', line 399

def self.pack_pushdata(data)
  size = data.bytesize
  header = if size < OP_PUSHDATA1
             [size].pack('C')
           elsif size < 0xff
             [OP_PUSHDATA1, size].pack('CC')
           elsif size < 0xffff
             [OP_PUSHDATA2, size].pack('Cv')
           elsif size < 0xffffffff
             [OP_PUSHDATA4, size].pack('CV')
           else
             raise ArgumentError, 'data size is too big.'
           end
  header + data
end

.parse_from_addr(addr) ⇒ Bitcoin::Script

generate script from addr.

Parameters:

Returns:



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# File 'lib/bitcoin/script/script.rb', line 85

def self.parse_from_addr(addr)
  begin
    segwit_addr = Bech32::SegwitAddr.new(addr)
    raise 'Invalid hrp.' unless Bitcoin.chain_params.bech32_hrp == segwit_addr.hrp
    Bitcoin::Script.parse_from_payload(segwit_addr.to_script_pubkey.htb)
  rescue Exception => e
    hex, addr_version = Bitcoin.decode_base58_address(addr)
    case addr_version
    when Bitcoin.chain_params.address_version
      Bitcoin::Script.to_p2pkh(hex)
    when Bitcoin.chain_params.p2sh_version
      Bitcoin::Script.to_p2sh(hex)
    else
      throw e
    end
  end
end

.parse_from_payload(payload) ⇒ Object 



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# File 'lib/bitcoin/script/script.rb', line 103

def self.parse_from_payload(payload)
  s = new
  buf = StringIO.new(payload)
  until buf.eof?
    opcode = buf.read(1)
    if opcode.pushdata?
      pushcode = opcode.ord
      packed_size = nil
      len = case pushcode
              when OP_PUSHDATA1
                packed_size = buf.read(1)
                packed_size.unpack('C').first
              when OP_PUSHDATA2
                packed_size = buf.read(2)
                packed_size.unpack('v').first
              when OP_PUSHDATA4
                packed_size = buf.read(4)
                packed_size.unpack('V').first
              else
                pushcode if pushcode < OP_PUSHDATA1
            end
      if len
        s.chunks << [len].pack('C') if buf.eof?
        unless buf.eof?
          chunk = (packed_size ? (opcode + packed_size) : (opcode)) + buf.read(len)
          s.chunks << chunk
        end
      end
    else
      if Opcodes.defined?(opcode.ord)
        s << opcode.ord
      else
        s.chunks << (opcode + buf.read) # If opcode is invalid, put all remaining data in last chunk.
      end
    end
  end
  s
end

.to_multisig_script(m, pubkeys) ⇒ Script

generate m of n multisig script

Parameters:

  • m (String) —

    the number of signatures required for multisig

  • pubkeys (Array) —

    array of public keys that compose multisig

Returns:

  • (Script) —

    multisig script.



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# File 'lib/bitcoin/script/script.rb', line 57

def self.to_multisig_script(m, pubkeys)
  new << m << pubkeys << pubkeys.size << OP_CHECKMULTISIG
end

.to_p2pkh(pubkey_hash) ⇒ Object

generate P2PKH script



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# File 'lib/bitcoin/script/script.rb', line 17

def self.to_p2pkh(pubkey_hash)
  new << OP_DUP << OP_HASH160 << pubkey_hash << OP_EQUALVERIFY << OP_CHECKSIG
end

.to_p2sh(script_hash) ⇒ Script

generate p2sh script.

Parameters:

  • script_hash (String) —

    script hash for P2SH

Returns:



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# File 'lib/bitcoin/script/script.rb', line 38

def self.to_p2sh(script_hash)
  Script.new << OP_HASH160 << script_hash << OP_EQUAL
end

.to_p2sh_multisig_script(m, pubkeys) ⇒ Script

generate m of n multisig p2sh script

Parameters:

  • m (String) —

    the number of signatures required for multisig

  • pubkeys (Array) —

    array of public keys that compose multisig

Returns:

  • (Script, Script) —

    first element is p2sh script, second one is redeem script.



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# File 'lib/bitcoin/script/script.rb', line 30

def self.to_p2sh_multisig_script(m, pubkeys)
  redeem_script = to_multisig_script(m, pubkeys)
  [redeem_script.to_p2sh, redeem_script]
end

.to_p2wpkh(pubkey_hash) ⇒ Object

generate P2WPKH script



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# File 'lib/bitcoin/script/script.rb', line 22

def self.to_p2wpkh(pubkey_hash)
  new << WITNESS_VERSION << pubkey_hash
end

.to_p2wsh(redeem_script) ⇒ Object

generate p2wsh script for redeem_script

Parameters:

  • redeem_script (Script) —

    target redeem script

  • p2wsh (Script) —

    script



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# File 'lib/bitcoin/script/script.rb', line 64

def self.to_p2wsh(redeem_script)
  new << WITNESS_VERSION << redeem_script.to_sha256
end

Instance Method Details

#<<(obj) ⇒ Object

append object to payload



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# File 'lib/bitcoin/script/script.rb', line 268

def <<(obj)
  if obj.is_a?(Integer)
    push_int(obj)
  elsif obj.is_a?(String)
    append_data(obj)
  elsif obj.is_a?(Array)
    obj.each { |o| self.<< o}
    self
  end
end

#==(other) ⇒ Object 



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# File 'lib/bitcoin/script/script.rb', line 475

def ==(other)
  return false unless other
  chunks == other.chunks
end

#addresses ⇒ Object 



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# File 'lib/bitcoin/script/script.rb', line 150

def addresses
  return [p2pkh_addr] if p2pkh?
  return [p2sh_addr] if p2sh?
  return [bech32_addr] if witness_program?
  return get_multisig_pubkeys.map{|pubkey| Bitcoin::Key.new(pubkey: pubkey.bth).to_p2pkh} if multisig?
  []
end

#append_data(data) ⇒ Script

append data to payload with pushdata opcode

Parameters:

  • data (String) —

    append data. this data is not binary

Returns:



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# File 'lib/bitcoin/script/script.rb', line 302

def append_data(data)
  data = Encoding::ASCII_8BIT == data.encoding ? data : data.htb
  chunks << Bitcoin::Script.pack_pushdata(data)
  self
end

#append_opcode(opcode) ⇒ Script

append opcode to payload

Parameters:

  • opcode (Integer) —

    append opcode which defined by Bitcoin::Opcodes

Returns:

Raises:

  • (ArgumentError) 


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# File 'lib/bitcoin/script/script.rb', line 292

def append_opcode(opcode)
  opcode = Opcodes.small_int_to_opcode(opcode) if -1 <= opcode && opcode <= 16
  raise ArgumentError, "specified invalid opcode #{opcode}." unless Opcodes.defined?(opcode)
  chunks << opcode.chr
  self
end

#delete_opcode(opcode) ⇒ Object

remove all occurences of opcode. Typically it’s OP_CODESEPARATOR.



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# File 'lib/bitcoin/script/script.rb', line 457

def delete_opcode(opcode)
  @chunks = chunks.select{|chunk| chunk.ord != opcode}
  self
end

#empty? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/bitcoin/script/script.rb', line 146

def empty?
  chunks.size == 0
end

#find_and_delete(subscript) ⇒ Object

removes chunks matching subscript byte-for-byte and returns as a new object.

Raises:

  • (ArgumentError) 


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# File 'lib/bitcoin/script/script.rb', line 423

def find_and_delete(subscript)
  raise ArgumentError, 'subscript must be Bitcoin::Script' unless subscript.is_a?(Script)
  return self if subscript.chunks.empty?
  buf = []
  i = 0
  result = Script.new
  chunks.each do |chunk|
    sub_chunk = subscript.chunks[i]
    if chunk.start_with?(sub_chunk)
      if chunk == sub_chunk
        buf << chunk
        i += 1
        (i = 0; buf.clear) if i == subscript.chunks.size # matched the whole subscript
      else # matched the part of head
        i = 0
        tmp = chunk.dup
        tmp.slice!(sub_chunk)
        result.chunks << tmp
      end
    else
      result.chunks << buf.join unless buf.empty?
      if buf.first == chunk
        i = 1
        buf = [chunk]
      else
        i = 0
        result.chunks << chunk
      end
    end
  end
  result
end

#get_multisig_pubkeys ⇒ Object 



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# File 'lib/bitcoin/script/script.rb', line 48

def get_multisig_pubkeys
  num = Bitcoin::Opcodes.opcode_to_small_int(chunks[-2].bth.to_i(16))
  (1..num).map{ |i| chunks[i].pushed_data }
end

#get_pubkeys ⇒ Object

get public keys in the stack. @return[Array] an array of the pubkeys with hex format.



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# File 'lib/bitcoin/script/script.rb', line 219

def get_pubkeys
  chunks.select{|c|c.pushdata? && [33, 65].include?(c.pushed_data.bytesize) && [2, 3, 4, 6, 7].include?(c.pushed_data[0].bth.to_i(16))}.map{|c|c.pushed_data.bth}
end

#include?(item) ⇒ Boolean

Check the item is in the chunk of the script.

Returns:

  • (Boolean) 


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# File 'lib/bitcoin/script/script.rb', line 309

def include?(item)
  chunk_item = if item.is_a?(Integer)
                 item.chr
               elsif item.is_a?(String)
                 data = Encoding::ASCII_8BIT == item.encoding ? item : item.htb
                 Bitcoin::Script.pack_pushdata(data)
               end
  return false unless chunk_item
  chunks.include?(chunk_item)
end

#multisig? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/bitcoin/script/script.rb', line 186

def multisig?
  return false if chunks.size < 4 || chunks.last.ord != OP_CHECKMULTISIG
  pubkey_count = Opcodes.opcode_to_small_int(chunks[-2].opcode)
  sig_count = Opcodes.opcode_to_small_int(chunks[0].opcode)
  return false unless pubkey_count || sig_count
  sig_count <= pubkey_count
end

#op_return? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/bitcoin/script/script.rb', line 194

def op_return?
  chunks.size >= 1 && chunks[0].ord == OP_RETURN
end

#op_return_data ⇒ Object 



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# File 'lib/bitcoin/script/script.rb', line 203

def op_return_data
  return nil unless op_return?
  return nil if chunks.size == 1
  chunks[1].pushed_data
end

#p2pkh? ⇒ Boolean

whether this script is a P2PKH format script.

Returns:

  • (Boolean) 


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# File 'lib/bitcoin/script/script.rb', line 164

def p2pkh?
  return false unless chunks.size == 5
  [OP_DUP, OP_HASH160, OP_EQUALVERIFY, OP_CHECKSIG] ==
      (chunks[0..1]+ chunks[3..4]).map(&:ord) && chunks[2].bytesize == 21
end

#p2sh? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/bitcoin/script/script.rb', line 181

def p2sh?
  return false unless chunks.size == 3
  OP_HASH160 == chunks[0].ord && OP_EQUAL == chunks[2].ord && chunks[1].bytesize == 21
end

#p2wpkh? ⇒ Boolean

whether this script is a P2WPKH format script.

Returns:

  • (Boolean) 


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# File 'lib/bitcoin/script/script.rb', line 171

def p2wpkh?
  return false unless chunks.size == 2
  chunks[0].ord == WITNESS_VERSION && chunks[1].bytesize == 21
end

#p2wsh? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/bitcoin/script/script.rb', line 176

def p2wsh?
  return false unless chunks.size == 2
  chunks[0].ord == WITNESS_VERSION && chunks[1].bytesize == 33
end

#push_int(n) ⇒ Object

push integer to stack.



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# File 'lib/bitcoin/script/script.rb', line 280

def push_int(n)
  begin
    append_opcode(n)
  rescue ArgumentError
    append_data(Script.encode_number(n))
  end
  self
end

#push_only? ⇒ Boolean

whether data push only script which dose not include other opcode

Returns:

  • (Boolean) 


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# File 'lib/bitcoin/script/script.rb', line 210

def push_only?
  chunks.each do |c|
    return false if !c.opcode.nil? && c.opcode > OP_16
  end
  true
end

#run ⇒ Object

execute script interpreter using this script for development.



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# File 'lib/bitcoin/script/script.rb', line 362

def run
  Bitcoin::ScriptInterpreter.eval(Bitcoin::Script.new, self.dup)
end

#size ⇒ Object

script size



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# File 'lib/bitcoin/script/script.rb', line 357

def size
  to_payload.bytesize
end

#standard? ⇒ Boolean

check whether standard script.

Returns:

  • (Boolean) 


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# File 'lib/bitcoin/script/script.rb', line 159

def standard?
  p2pkh? | p2sh? | p2wpkh? | p2wsh? | multisig? | standard_op_return?
end

#standard_op_return? ⇒ Boolean

Returns:

  • (Boolean) 


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# File 'lib/bitcoin/script/script.rb', line 198

def standard_op_return?
  op_return? && size <= MAX_OP_RETURN_RELAY &&
      (chunks.size == 1 || chunks[1].opcode <= OP_16)
end

#subscript(*args) ⇒ Object

subscript this script to the specified range.



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# File 'lib/bitcoin/script/script.rb', line 416

def subscript(*args)
  s = self.class.new
  s.chunks = chunks[*args]
  s
end

#subscript_codeseparator(separator_index) ⇒ Object

Returns a script that deleted the script before the index specified by separator_index.



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# File 'lib/bitcoin/script/script.rb', line 463

def subscript_codeseparator(separator_index)
  buf = []
  process_separator_index = 0
  chunks.each{|chunk|
    buf << chunk if process_separator_index == separator_index
    if chunk.ord == OP_CODESEPARATOR && process_separator_index < separator_index
      process_separator_index += 1
    end
  }
  buf.join
end

#to_h ⇒ Object 



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# File 'lib/bitcoin/script/script.rb', line 489

def to_h
  h = {asm: to_s, hex: to_payload.bth, type: type}
  addrs = addresses
  unless addrs.empty?
    h[:req_sigs] = multisig? ? Bitcoin::Opcodes.opcode_to_small_int(chunks[0].bth.to_i(16)) :addrs.size
    h[:addresses] = addrs
  end
  h
end

#to_hash160 ⇒ Object

generate hash160 hash for payload



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# File 'lib/bitcoin/script/script.rb', line 352

def to_hash160
  Bitcoin.hash160(to_payload.bth)
end

#to_hex ⇒ String

convert payload to hex data.

Returns:

  • (String) —

    script with hex format.



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# File 'lib/bitcoin/script/script.rb', line 508

def to_hex
  to_payload.bth
end

#to_p2sh ⇒ Script

generate p2sh script with this as a redeem script

Returns:



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# File 'lib/bitcoin/script/script.rb', line 44

def to_p2sh
  Script.to_p2sh(to_hash160)
end

#to_payload ⇒ Object 



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# File 'lib/bitcoin/script/script.rb', line 142

def to_payload
  chunks.join
end

#to_s ⇒ Object 



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# File 'lib/bitcoin/script/script.rb', line 320

def to_s
  chunks.map { |c|
    case c
    when Integer
      opcode_to_name(c)
    when String
      if c.pushdata?
        v = Opcodes.opcode_to_small_int(c.ord)
        if v
          v
        else
          data = c.pushed_data
          if data.bytesize <= 4
            Script.decode_number(data.bth) # for scriptnum
          else
            data.bth
          end
        end
      else
        opcode = Opcodes.opcode_to_name(c.ord)
        opcode ? opcode : 'OP_UNKNOWN [error]'
      end
    end
  }.join(' ')
end

#to_script_code(skip_separator_index = 0) ⇒ Object

If this script is witness program, return its script code, otherwise returns the self payload. ScriptInterpreter does not use this.



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# File 'lib/bitcoin/script/script.rb', line 250

def to_script_code(skip_separator_index = 0)
  payload = to_payload
  if p2wpkh?
    payload = Script.to_p2pkh(chunks[1].pushed_data.bth).to_payload
  elsif skip_separator_index > 0
    payload = subscript_codeseparator(skip_separator_index)
  end
  Bitcoin.pack_var_string(payload)
end

#to_sha256 ⇒ Object

generate sha-256 hash for payload



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# File 'lib/bitcoin/script/script.rb', line 347

def to_sha256
  Bitcoin.sha256(to_payload).bth
end

#type ⇒ Object 



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# File 'lib/bitcoin/script/script.rb', line 480

def type
  return 'pubkeyhash' if p2pkh?
  return 'scripthash' if p2sh?
  return 'multisig' if multisig?
  return 'witness_v0_keyhash' if p2wpkh?
  return 'witness_v0_scripthash' if p2wsh?
  'nonstandard'
end

#unspendable? ⇒ Boolean

Returns whether the script is guaranteed to fail at execution, regardless of the initial stack. This allows outputs to be pruned instantly when entering the UTXO set.

Returns:

  • (Boolean) —

    whether the script is guaranteed to fail at execution



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# File 'lib/bitcoin/script/script.rb', line 502

def unspendable?
  (size > 0 && op_return?) || size > Bitcoin::MAX_SCRIPT_SIZE
end

#witness_commitment ⇒ Object

get witness commitment



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# File 'lib/bitcoin/script/script.rb', line 241

def witness_commitment
  return nil if !op_return? || op_return_data.bytesize < 36
  buf = StringIO.new(op_return_data)
  return nil unless buf.read(4).bth == WITNESS_COMMITMENT_HEADER
  buf.read(32).bth
end

#witness_data ⇒ Object

get witness version and witness program



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# File 'lib/bitcoin/script/script.rb', line 261

def witness_data
  version = opcode_to_small_int(chunks[0].opcode)
  program = chunks[1].pushed_data
  [version, program]
end

#witness_program? ⇒ Boolean

A witness program is any valid Script that consists of a 1-byte push opcode followed by a data push between 2 and 40 bytes.

Returns:

  • (Boolean) 


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# File 'lib/bitcoin/script/script.rb', line 224

def witness_program?
  return false if size < 4 || size > 42 || chunks.size < 2

  opcode = chunks[0].opcode

  return false if opcode != OP_0 && (opcode < OP_1 || opcode > OP_16)
  return false unless chunks[1].pushdata?

  if size == (chunks[1][0].unpack('C').first + 2)
    program_size = chunks[1].pushed_data.bytesize
    return program_size >= 2 && program_size <= 40
  end

  false
end