604 lines
22 KiB
Go
604 lines
22 KiB
Go
// Copyright (c) 2015-2016 The btcsuite developers
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// Use of this source code is governed by an ISC
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// license that can be found in the LICENSE file.
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package blockchain
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import (
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"github.com/btcsuite/btcd/btcec"
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"github.com/btcsuite/btcd/txscript"
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)
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// -----------------------------------------------------------------------------
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// A variable length quantity (VLQ) is an encoding that uses an arbitrary number
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// of binary octets to represent an arbitrarily large integer. The scheme
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// employs a most significant byte (MSB) base-128 encoding where the high bit in
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// each byte indicates whether or not the byte is the final one. In addition,
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// to ensure there are no redundant encodings, an offset is subtracted every
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// time a group of 7 bits is shifted out. Therefore each integer can be
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// represented in exactly one way, and each representation stands for exactly
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// one integer.
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//
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// Another nice property of this encoding is that it provides a compact
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// representation of values that are typically used to indicate sizes. For
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// example, the values 0 - 127 are represented with a single byte, 128 - 16511
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// with two bytes, and 16512 - 2113663 with three bytes.
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//
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// While the encoding allows arbitrarily large integers, it is artificially
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// limited in this code to an unsigned 64-bit integer for efficiency purposes.
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//
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// Example encodings:
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// 0 -> [0x00]
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// 127 -> [0x7f] * Max 1-byte value
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// 128 -> [0x80 0x00]
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// 129 -> [0x80 0x01]
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// 255 -> [0x80 0x7f]
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// 256 -> [0x81 0x00]
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// 16511 -> [0xff 0x7f] * Max 2-byte value
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// 16512 -> [0x80 0x80 0x00]
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// 32895 -> [0x80 0xff 0x7f]
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// 2113663 -> [0xff 0xff 0x7f] * Max 3-byte value
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// 270549119 -> [0xff 0xff 0xff 0x7f] * Max 4-byte value
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// 2^64-1 -> [0x80 0xfe 0xfe 0xfe 0xfe 0xfe 0xfe 0xfe 0xfe 0x7f]
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//
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// References:
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// https://en.wikipedia.org/wiki/Variable-length_quantity
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// http://www.codecodex.com/wiki/Variable-Length_Integers
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// -----------------------------------------------------------------------------
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// serializeSizeVLQ returns the number of bytes it would take to serialize the
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// passed number as a variable-length quantity according to the format described
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// above.
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func serializeSizeVLQ(n uint64) int {
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size := 1
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for ; n > 0x7f; n = (n >> 7) - 1 {
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size++
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}
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return size
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}
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// putVLQ serializes the provided number to a variable-length quantity according
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// to the format described above and returns the number of bytes of the encoded
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// value. The result is placed directly into the passed byte slice which must
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// be at least large enough to handle the number of bytes returned by the
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// serializeSizeVLQ function or it will panic.
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func putVLQ(target []byte, n uint64) int {
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offset := 0
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for ; ; offset++ {
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// The high bit is set when another byte follows.
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highBitMask := byte(0x80)
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if offset == 0 {
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highBitMask = 0x00
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}
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target[offset] = byte(n&0x7f) | highBitMask
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if n <= 0x7f {
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break
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}
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n = (n >> 7) - 1
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}
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// Reverse the bytes so it is MSB-encoded.
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for i, j := 0, offset; i < j; i, j = i+1, j-1 {
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target[i], target[j] = target[j], target[i]
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}
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return offset + 1
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}
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// deserializeVLQ deserializes the provided variable-length quantity according
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// to the format described above. It also returns the number of bytes
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// deserialized.
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func deserializeVLQ(serialized []byte) (uint64, int) {
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var n uint64
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var size int
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for _, val := range serialized {
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size++
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n = (n << 7) | uint64(val&0x7f)
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if val&0x80 != 0x80 {
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break
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}
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n++
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}
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return n, size
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}
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// -----------------------------------------------------------------------------
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// In order to reduce the size of stored scripts, a domain specific compression
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// algorithm is used which recognizes standard scripts and stores them using
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// less bytes than the original script. The compression algorithm used here was
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// obtained from Bitcoin Core, so all credits for the algorithm go to it.
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//
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// The general serialized format is:
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//
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// <script size or type><script data>
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//
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// Field Type Size
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// script size or type VLQ variable
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// script data []byte variable
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//
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// The specific serialized format for each recognized standard script is:
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//
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// - Pay-to-pubkey-hash: (21 bytes) - <0><20-byte pubkey hash>
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// - Pay-to-script-hash: (21 bytes) - <1><20-byte script hash>
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// - Pay-to-pubkey**: (33 bytes) - <2, 3, 4, or 5><32-byte pubkey X value>
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// 2, 3 = compressed pubkey with bit 0 specifying the y coordinate to use
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// 4, 5 = uncompressed pubkey with bit 0 specifying the y coordinate to use
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// ** Only valid public keys starting with 0x02, 0x03, and 0x04 are supported.
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//
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// Any scripts which are not recognized as one of the aforementioned standard
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// scripts are encoded using the general serialized format and encode the script
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// size as the sum of the actual size of the script and the number of special
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// cases.
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// -----------------------------------------------------------------------------
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// The following constants specify the special constants used to identify a
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// special script type in the domain-specific compressed script encoding.
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//
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// NOTE: This section specifically does not use iota since these values are
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// serialized and must be stable for long-term storage.
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const (
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// cstPayToPubKeyHash identifies a compressed pay-to-pubkey-hash script.
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cstPayToPubKeyHash = 0
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// cstPayToScriptHash identifies a compressed pay-to-script-hash script.
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cstPayToScriptHash = 1
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// cstPayToPubKeyComp2 identifies a compressed pay-to-pubkey script to
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// a compressed pubkey. Bit 0 specifies which y-coordinate to use
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// to reconstruct the full uncompressed pubkey.
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cstPayToPubKeyComp2 = 2
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// cstPayToPubKeyComp3 identifies a compressed pay-to-pubkey script to
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// a compressed pubkey. Bit 0 specifies which y-coordinate to use
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// to reconstruct the full uncompressed pubkey.
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cstPayToPubKeyComp3 = 3
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// cstPayToPubKeyUncomp4 identifies a compressed pay-to-pubkey script to
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// an uncompressed pubkey. Bit 0 specifies which y-coordinate to use
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// to reconstruct the full uncompressed pubkey.
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cstPayToPubKeyUncomp4 = 4
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// cstPayToPubKeyUncomp5 identifies a compressed pay-to-pubkey script to
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// an uncompressed pubkey. Bit 0 specifies which y-coordinate to use
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// to reconstruct the full uncompressed pubkey.
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cstPayToPubKeyUncomp5 = 5
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// numSpecialScripts is the number of special scripts recognized by the
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// domain-specific script compression algorithm.
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numSpecialScripts = 6
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)
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// isPubKeyHash returns whether or not the passed public key script is a
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// standard pay-to-pubkey-hash script along with the pubkey hash it is paying to
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// if it is.
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func isPubKeyHash(script []byte) (bool, []byte) {
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if len(script) == 25 && script[0] == txscript.OP_DUP &&
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script[1] == txscript.OP_HASH160 &&
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script[2] == txscript.OP_DATA_20 &&
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script[23] == txscript.OP_EQUALVERIFY &&
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script[24] == txscript.OP_CHECKSIG {
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return true, script[3:23]
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}
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return false, nil
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}
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// isScriptHash returns whether or not the passed public key script is a
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// standard pay-to-script-hash script along with the script hash it is paying to
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// if it is.
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func isScriptHash(script []byte) (bool, []byte) {
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if len(script) == 23 && script[0] == txscript.OP_HASH160 &&
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script[1] == txscript.OP_DATA_20 &&
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script[22] == txscript.OP_EQUAL {
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return true, script[2:22]
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}
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return false, nil
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}
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// isPubKey returns whether or not the passed public key script is a standard
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// pay-to-pubkey script that pays to a valid compressed or uncompressed public
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// key along with the serialized pubkey it is paying to if it is.
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//
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// NOTE: This function ensures the public key is actually valid since the
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// compression algorithm requires valid pubkeys. It does not support hybrid
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// pubkeys. This means that even if the script has the correct form for a
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// pay-to-pubkey script, this function will only return true when it is paying
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// to a valid compressed or uncompressed pubkey.
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func isPubKey(script []byte) (bool, []byte) {
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// Pay-to-compressed-pubkey script.
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if len(script) == 35 && script[0] == txscript.OP_DATA_33 &&
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script[34] == txscript.OP_CHECKSIG && (script[1] == 0x02 ||
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script[1] == 0x03) {
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// Ensure the public key is valid.
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serializedPubKey := script[1:34]
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_, err := btcec.ParsePubKey(serializedPubKey, btcec.S256())
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if err == nil {
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return true, serializedPubKey
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}
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}
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// Pay-to-uncompressed-pubkey script.
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if len(script) == 67 && script[0] == txscript.OP_DATA_65 &&
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script[66] == txscript.OP_CHECKSIG && script[1] == 0x04 {
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// Ensure the public key is valid.
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serializedPubKey := script[1:66]
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_, err := btcec.ParsePubKey(serializedPubKey, btcec.S256())
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if err == nil {
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return true, serializedPubKey
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}
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}
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return false, nil
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}
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// compressedScriptSize returns the number of bytes the passed script would take
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// when encoded with the domain specific compression algorithm described above.
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func compressedScriptSize(pkScript []byte, version int32) int {
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// Pay-to-pubkey-hash script.
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if valid, _ := isPubKeyHash(pkScript); valid {
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return 21
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}
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// Pay-to-script-hash script.
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if valid, _ := isScriptHash(pkScript); valid {
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return 21
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}
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// Pay-to-pubkey (compressed or uncompressed) script.
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if valid, _ := isPubKey(pkScript); valid {
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return 33
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}
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// When none of the above special cases apply, encode the script as is
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// preceded by the sum of its size and the number of special cases
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// encoded as a variable length quantity.
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return serializeSizeVLQ(uint64(len(pkScript)+numSpecialScripts)) +
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len(pkScript)
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}
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// decodeCompressedScriptSize treats the passed serialized bytes as a compressed
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// script, possibly followed by other data, and returns the number of bytes it
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// occupies taking into account the special encoding of the script size by the
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// domain specific compression algorithm described above.
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func decodeCompressedScriptSize(serialized []byte, version int32) int {
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scriptSize, bytesRead := deserializeVLQ(serialized)
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if bytesRead == 0 {
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return 0
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}
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switch scriptSize {
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case cstPayToPubKeyHash:
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return 21
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case cstPayToScriptHash:
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return 21
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case cstPayToPubKeyComp2, cstPayToPubKeyComp3, cstPayToPubKeyUncomp4,
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cstPayToPubKeyUncomp5:
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return 33
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}
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scriptSize -= numSpecialScripts
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scriptSize += uint64(bytesRead)
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return int(scriptSize)
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}
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// putCompressedScript compresses the passed script according to the domain
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// specific compression algorithm described above directly into the passed
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// target byte slice. The target byte slice must be at least large enough to
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// handle the number of bytes returned by the compressedScriptSize function or
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// it will panic.
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func putCompressedScript(target, pkScript []byte, version int32) int {
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// Pay-to-pubkey-hash script.
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if valid, hash := isPubKeyHash(pkScript); valid {
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target[0] = cstPayToPubKeyHash
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copy(target[1:21], hash)
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return 21
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}
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// Pay-to-script-hash script.
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if valid, hash := isScriptHash(pkScript); valid {
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target[0] = cstPayToScriptHash
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copy(target[1:21], hash)
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return 21
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}
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// Pay-to-pubkey (compressed or uncompressed) script.
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if valid, serializedPubKey := isPubKey(pkScript); valid {
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pubKeyFormat := serializedPubKey[0]
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switch pubKeyFormat {
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case 0x02, 0x03:
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target[0] = pubKeyFormat
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copy(target[1:33], serializedPubKey[1:33])
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return 33
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case 0x04:
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// Encode the oddness of the serialized pubkey into the
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// compressed script type.
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target[0] = pubKeyFormat | (serializedPubKey[64] & 0x01)
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copy(target[1:33], serializedPubKey[1:33])
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return 33
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}
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}
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// When none of the above special cases apply, encode the unmodified
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// script preceded by the sum of its size and the number of special
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// cases encoded as a variable length quantity.
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encodedSize := uint64(len(pkScript) + numSpecialScripts)
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vlqSizeLen := putVLQ(target, encodedSize)
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copy(target[vlqSizeLen:], pkScript)
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return vlqSizeLen + len(pkScript)
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}
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// decompressScript returns the original script obtained by decompressing the
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// passed compressed script according to the domain specific compression
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// algorithm described above.
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//
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// NOTE: The script parameter must already have been proven to be long enough
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// to contain the number of bytes returned by decodeCompressedScriptSize or it
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// will panic. This is acceptable since it is only an internal function.
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func decompressScript(compressedPkScript []byte, version int32) []byte {
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// In practice this function will not be called with a zero-length or
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// nil script since the nil script encoding includes the length, however
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// the code below assumes the length exists, so just return nil now if
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// the function ever ends up being called with a nil script in the
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// future.
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if len(compressedPkScript) == 0 {
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return nil
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}
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// Decode the script size and examine it for the special cases.
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encodedScriptSize, bytesRead := deserializeVLQ(compressedPkScript)
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switch encodedScriptSize {
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// Pay-to-pubkey-hash script. The resulting script is:
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// <OP_DUP><OP_HASH160><20 byte hash><OP_EQUALVERIFY><OP_CHECKSIG>
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case cstPayToPubKeyHash:
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pkScript := make([]byte, 25)
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pkScript[0] = txscript.OP_DUP
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pkScript[1] = txscript.OP_HASH160
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pkScript[2] = txscript.OP_DATA_20
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copy(pkScript[3:], compressedPkScript[bytesRead:bytesRead+20])
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pkScript[23] = txscript.OP_EQUALVERIFY
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pkScript[24] = txscript.OP_CHECKSIG
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return pkScript
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// Pay-to-script-hash script. The resulting script is:
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// <OP_HASH160><20 byte script hash><OP_EQUAL>
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case cstPayToScriptHash:
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pkScript := make([]byte, 23)
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pkScript[0] = txscript.OP_HASH160
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pkScript[1] = txscript.OP_DATA_20
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copy(pkScript[2:], compressedPkScript[bytesRead:bytesRead+20])
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pkScript[22] = txscript.OP_EQUAL
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return pkScript
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// Pay-to-compressed-pubkey script. The resulting script is:
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// <OP_DATA_33><33 byte compressed pubkey><OP_CHECKSIG>
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case cstPayToPubKeyComp2, cstPayToPubKeyComp3:
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pkScript := make([]byte, 35)
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pkScript[0] = txscript.OP_DATA_33
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pkScript[1] = byte(encodedScriptSize)
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copy(pkScript[2:], compressedPkScript[bytesRead:bytesRead+32])
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pkScript[34] = txscript.OP_CHECKSIG
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return pkScript
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// Pay-to-uncompressed-pubkey script. The resulting script is:
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// <OP_DATA_65><65 byte uncompressed pubkey><OP_CHECKSIG>
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case cstPayToPubKeyUncomp4, cstPayToPubKeyUncomp5:
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// Change the leading byte to the appropriate compressed pubkey
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// identifier (0x02 or 0x03) so it can be decoded as a
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// compressed pubkey. This really should never fail since the
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// encoding ensures it is valid before compressing to this type.
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compressedKey := make([]byte, 33)
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compressedKey[0] = byte(encodedScriptSize - 2)
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copy(compressedKey[1:], compressedPkScript[1:])
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key, err := btcec.ParsePubKey(compressedKey, btcec.S256())
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if err != nil {
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return nil
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}
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pkScript := make([]byte, 67)
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pkScript[0] = txscript.OP_DATA_65
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copy(pkScript[1:], key.SerializeUncompressed())
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pkScript[66] = txscript.OP_CHECKSIG
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return pkScript
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}
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// When none of the special cases apply, the script was encoded using
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// the general format, so reduce the script size by the number of
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// special cases and return the unmodified script.
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scriptSize := int(encodedScriptSize - numSpecialScripts)
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pkScript := make([]byte, scriptSize)
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copy(pkScript, compressedPkScript[bytesRead:bytesRead+scriptSize])
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return pkScript
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}
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// -----------------------------------------------------------------------------
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// In order to reduce the size of stored amounts, a domain specific compression
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// algorithm is used which relies on there typically being a lot of zeroes at
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// end of the amounts. The compression algorithm used here was obtained from
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// Bitcoin Core, so all credits for the algorithm go to it.
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//
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// While this is simply exchanging one uint64 for another, the resulting value
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// for typical amounts has a much smaller magnitude which results in fewer bytes
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// when encoded as variable length quantity. For example, consider the amount
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// of 0.1 BTC which is 10000000 satoshi. Encoding 10000000 as a VLQ would take
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// 4 bytes while encoding the compressed value of 8 as a VLQ only takes 1 byte.
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//
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// Essentially the compression is achieved by splitting the value into an
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// exponent in the range [0-9] and a digit in the range [1-9], when possible,
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// and encoding them in a way that can be decoded. More specifically, the
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// encoding is as follows:
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// - 0 is 0
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// - Find the exponent, e, as the largest power of 10 that evenly divides the
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// value up to a maximum of 9
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// - When e < 9, the final digit can't be 0 so store it as d and remove it by
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// dividing the value by 10 (call the result n). The encoded value is thus:
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// 1 + 10*(9*n + d-1) + e
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// - When e==9, the only thing known is the amount is not 0. The encoded value
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// is thus:
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// 1 + 10*(n-1) + e == 10 + 10*(n-1)
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//
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// Example encodings:
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// (The numbers in parenthesis are the number of bytes when serialized as a VLQ)
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// 0 (1) -> 0 (1) * 0.00000000 BTC
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// 1000 (2) -> 4 (1) * 0.00001000 BTC
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// 10000 (2) -> 5 (1) * 0.00010000 BTC
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// 12345678 (4) -> 111111101(4) * 0.12345678 BTC
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// 50000000 (4) -> 47 (1) * 0.50000000 BTC
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// 100000000 (4) -> 9 (1) * 1.00000000 BTC
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// 500000000 (5) -> 49 (1) * 5.00000000 BTC
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// 1000000000 (5) -> 10 (1) * 10.00000000 BTC
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// -----------------------------------------------------------------------------
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// compressTxOutAmount compresses the passed amount according to the domain
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// specific compression algorithm described above.
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func compressTxOutAmount(amount uint64) uint64 {
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// No need to do any work if it's zero.
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if amount == 0 {
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|
return 0
|
|
}
|
|
|
|
// Find the largest power of 10 (max of 9) that evenly divides the
|
|
// value.
|
|
exponent := uint64(0)
|
|
for amount%10 == 0 && exponent < 9 {
|
|
amount /= 10
|
|
exponent++
|
|
}
|
|
|
|
// The compressed result for exponents less than 9 is:
|
|
// 1 + 10*(9*n + d-1) + e
|
|
if exponent < 9 {
|
|
lastDigit := amount % 10
|
|
amount /= 10
|
|
return 1 + 10*(9*amount+lastDigit-1) + exponent
|
|
}
|
|
|
|
// The compressed result for an exponent of 9 is:
|
|
// 1 + 10*(n-1) + e == 10 + 10*(n-1)
|
|
return 10 + 10*(amount-1)
|
|
}
|
|
|
|
// decompressTxOutAmount returns the original amount the passed compressed
|
|
// amount represents according to the domain specific compression algorithm
|
|
// described above.
|
|
func decompressTxOutAmount(amount uint64) uint64 {
|
|
// No need to do any work if it's zero.
|
|
if amount == 0 {
|
|
return 0
|
|
}
|
|
|
|
// The decompressed amount is either of the following two equations:
|
|
// x = 1 + 10*(9*n + d - 1) + e
|
|
// x = 1 + 10*(n - 1) + 9
|
|
amount--
|
|
|
|
// The decompressed amount is now one of the following two equations:
|
|
// x = 10*(9*n + d - 1) + e
|
|
// x = 10*(n - 1) + 9
|
|
exponent := amount % 10
|
|
amount /= 10
|
|
|
|
// The decompressed amount is now one of the following two equations:
|
|
// x = 9*n + d - 1 | where e < 9
|
|
// x = n - 1 | where e = 9
|
|
n := uint64(0)
|
|
if exponent < 9 {
|
|
lastDigit := amount%9 + 1
|
|
amount /= 9
|
|
n = amount*10 + lastDigit
|
|
} else {
|
|
n = amount + 1
|
|
}
|
|
|
|
// Apply the exponent.
|
|
for ; exponent > 0; exponent-- {
|
|
n *= 10
|
|
}
|
|
|
|
return n
|
|
}
|
|
|
|
// -----------------------------------------------------------------------------
|
|
// Compressed transaction outputs consist of an amount and a public key script
|
|
// both compressed using the domain specific compression algorithms previously
|
|
// described.
|
|
//
|
|
// The serialized format is:
|
|
//
|
|
// <compressed amount><compressed script>
|
|
//
|
|
// Field Type Size
|
|
// compressed amount VLQ variable
|
|
// compressed script []byte variable
|
|
// -----------------------------------------------------------------------------
|
|
|
|
// compressedTxOutSize returns the number of bytes the passed transaction output
|
|
// fields would take when encoded with the format described above. The
|
|
// preCompressed flag indicates the provided amount and script are already
|
|
// compressed. This is useful since loaded utxo entries are not decompressed
|
|
// until the output is accessed.
|
|
func compressedTxOutSize(amount uint64, pkScript []byte, version int32, preCompressed bool) int {
|
|
if preCompressed {
|
|
return serializeSizeVLQ(amount) + len(pkScript)
|
|
}
|
|
|
|
return serializeSizeVLQ(compressTxOutAmount(amount)) +
|
|
compressedScriptSize(pkScript, version)
|
|
}
|
|
|
|
// putCompressedTxOut potentially compresses the passed amount and script
|
|
// according to their domain specific compression algorithms and encodes them
|
|
// directly into the passed target byte slice with the format described above.
|
|
// The preCompressed flag indicates the provided amount and script are already
|
|
// compressed in which case the values are not modified. This is useful since
|
|
// loaded utxo entries are not decompressed until the output is accessed. The
|
|
// target byte slice must be at least large enough to handle the number of bytes
|
|
// returned by the compressedTxOutSize function or it will panic.
|
|
func putCompressedTxOut(target []byte, amount uint64, pkScript []byte, version int32, preCompressed bool) int {
|
|
if preCompressed {
|
|
offset := putVLQ(target, amount)
|
|
copy(target[offset:], pkScript)
|
|
return offset + len(pkScript)
|
|
}
|
|
|
|
offset := putVLQ(target, compressTxOutAmount(amount))
|
|
offset += putCompressedScript(target[offset:], pkScript, version)
|
|
return offset
|
|
}
|
|
|
|
// decodeCompressedTxOut decodes the passed compressed txout, possibly followed
|
|
// by other data, into its compressed amount and compressed script and returns
|
|
// them along with the number of bytes they occupied.
|
|
func decodeCompressedTxOut(serialized []byte, version int32) (uint64, []byte, int, error) {
|
|
// Deserialize the compressed amount and ensure there are bytes
|
|
// remaining for the compressed script.
|
|
compressedAmount, bytesRead := deserializeVLQ(serialized)
|
|
if bytesRead >= len(serialized) {
|
|
return 0, nil, bytesRead, errDeserialize("unexpected end of " +
|
|
"data after compressed amount")
|
|
}
|
|
|
|
// Decode the compressed script size and ensure there are enough bytes
|
|
// left in the slice for it.
|
|
scriptSize := decodeCompressedScriptSize(serialized[bytesRead:], version)
|
|
if len(serialized[bytesRead:]) < scriptSize {
|
|
return 0, nil, bytesRead, errDeserialize("unexpected end of " +
|
|
"data after script size")
|
|
}
|
|
|
|
// Make a copy of the compressed script so the original serialized data
|
|
// can be released as soon as possible.
|
|
compressedScript := make([]byte, scriptSize)
|
|
copy(compressedScript, serialized[bytesRead:bytesRead+scriptSize])
|
|
return compressedAmount, compressedScript, bytesRead + scriptSize, nil
|
|
}
|