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SizeEstimation.php
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SizeEstimation.php
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<?php
namespace Blocktrail\SDK;
use BitWasp\Bitcoin\Script\ScriptFactory;
use BitWasp\Bitcoin\Script\ScriptType;
use BitWasp\Bitcoin\Crypto\EcAdapter\Key\PublicKeyInterface;
use \BitWasp\Bitcoin\Script\ScriptInfo\Multisig;
use \BitWasp\Bitcoin\Script\ScriptInfo\PayToPubKey;
use \BitWasp\Bitcoin\Script\Classifier\OutputClassifier;
use BitWasp\Bitcoin\Script\ScriptInterface;
use BitWasp\Bitcoin\Transaction\TransactionOutputInterface;
class SizeEstimation
{
const SIZE_DER_SIGNATURE = 72;
const SIZE_V0_P2WSH = 36;
/**
* @param bool $compressed
* @return int
*/
public static function getPublicKeySize($compressed = true) {
return $compressed ? PublicKeyInterface::LENGTH_COMPRESSED : PublicKeyInterface::LENGTH_UNCOMPRESSED;
}
/**
* @param int $length
* @return int
*/
public static function getLengthOfScriptLengthElement($length) {
if ($length < 75) {
return 1;
} else if ($length <= 0xff) {
return 2;
} else if ($length <= 0xffff) {
return 3;
} else if ($length <= 0xffffffff) {
return 5;
} else {
throw new \RuntimeException('Size of pushdata too large');
}
}
/**
* @param int $length
* @return int
*/
public static function getLengthOfVarInt($length) {
if ($length < 253) {
return 1;
} else if ($length < 65535) {
$num_bytes = 2;
} else if ($length < 4294967295) {
$num_bytes = 4;
} else if ($length < 18446744073709551615) {
$num_bytes = 8;
} else {
throw new \InvalidArgumentException("Invalid decimal");
}
return 1 + $num_bytes;
}
/**
* @param array $vectorSizes
* @return int|mixed
*/
public static function getLengthOfVector(array $vectorSizes) {
$vectorSize = self::getLengthOfVarInt(count($vectorSizes));
foreach ($vectorSizes as $size) {
$vectorSize += self::getLengthOfVarInt($size) + $size;
}
return $vectorSize;
}
/**
* @param Multisig $multisig
* @return array - first is array of stack sizes, second is script len
*/
public static function estimateMultisigStackSize(Multisig $multisig) {
$stackSizes = [0];
for ($i = 0; $i < $multisig->getRequiredSigCount(); $i++) {
$stackSizes[] = self::SIZE_DER_SIGNATURE;
}
$scriptSize = 1; // OP_$m
$keys = $multisig->getKeyBuffers();
for ($i = 0, $n = $multisig->getKeyCount(); $i < $n; $i++) {
$scriptSize += 1 + $keys[$i]->getSize();
}
$scriptSize += 1 + 1; // OP_$n OP_CHECKMULTISIG
return [$stackSizes, $scriptSize];
}
/**
* @param PayToPubKey $info
* @return array - first is array of stack sizes, second is script len
*/
public static function estimateP2PKStackSize(PayToPubKey $info) {
$stackSizes = [self::SIZE_DER_SIGNATURE];
$scriptSize = 1 + $info->getKeyBuffer()->getSize(); // PUSHDATA[<75] PUBLICKEY
$scriptSize += 1; // OP_CHECKSIG
return [$stackSizes, $scriptSize];
}
/**
* @param bool $isCompressed
* @return array - first is array of stack sizes, second is script len
*/
public static function estimateP2PKHStackSize($isCompressed = true) {
$pubKeySize = self::getPublicKeySize($isCompressed);
$stackSizes = [self::SIZE_DER_SIGNATURE, $pubKeySize];
$scriptSize = 1 + 1 + 1 + 20 + 1 + 1;
return [$stackSizes, $scriptSize];
}
/**
* @param array $stackSizes - array of integer size of a value (for scriptSig or witness)
* @param bool $isWitness
* @param ScriptInterface $redeemScript
* @param ScriptInterface $witnessScript
* @return array
*/
public static function estimateSizeForStack(array $stackSizes, $isWitness, ScriptInterface $redeemScript = null, ScriptInterface $witnessScript = null) {
assert(($witnessScript === null) || $isWitness);
if ($isWitness) {
$scriptSigSizes = [];
$witnessSizes = $stackSizes;
if ($witnessScript instanceof ScriptInterface) {
$witnessSizes[] = $witnessScript->getBuffer()->getSize();
}
} else {
$scriptSigSizes = $stackSizes;
$witnessSizes = [];
}
if ($redeemScript instanceof ScriptInterface) {
$scriptSigSizes[] = $redeemScript->getBuffer()->getSize();
}
$scriptSigSize = 0;
foreach ($scriptSigSizes as $size) {
$len = self::getLengthOfScriptLengthElement($size);
$scriptSigSize += $len;
$scriptSigSize += $size;
}
// Make sure to count the CScriptBase length prefix..
$scriptSigSize += self::getLengthOfVarInt($scriptSigSize);
// make sure this is set to 0 when not used.
// Summing WitnessSize is used in addition to $withWitness
// because a tx without witnesses _cannot_ use witness serialization
// total witnessSize = 0 means don't use that format
$witnessSize = 0;
if (count($witnessSizes) > 0) {
// witness has a prefix indicating `n` elements in vector
$witnessSize = self::getLengthOfVector($witnessSizes);
}
return [$scriptSigSize, $witnessSize];
}
/**
* @param ScriptInterface $script - not the scriptPubKey, might be SPK,RS,WS
* @param ScriptInterface|null $redeemScript
* @param ScriptInterface $witnessScript
* @param bool $isWitness
* @return array
*/
public static function estimateInputFromScripts(ScriptInterface $script, ScriptInterface $redeemScript = null, ScriptInterface $witnessScript = null, $isWitness) {
assert($witnessScript === null || $isWitness);
$classifier = new OutputClassifier();
if ($classifier->isMultisig($script)) {
list ($stackSizes, ) = SizeEstimation::estimateMultisigStackSize(new Multisig($script));
} else if ($classifier->isPayToPublicKey($script)) {
list ($stackSizes, ) = SizeEstimation::estimateP2PKStackSize(new PayToPubKey($script));
} else if ($classifier->isPayToPublicKeyHash($script)) {
// defaults to compressed, tough luck
list ($stackSizes, ) = SizeEstimation::estimateP2PKHStackSize();
} else {
throw new \InvalidArgumentException("Unsupported script type");
}
return self::estimateSizeForStack($stackSizes, $isWitness, $redeemScript, $witnessScript);
}
/**
* @param UTXO $utxo
* @return array
*/
public static function estimateUtxo(UTXO $utxo) {
return self::estimateUtxoFromScripts($utxo->scriptPubKey, $utxo->redeemScript, $utxo->witnessScript);
}
/**
* @param ScriptInterface $scriptPubKey
* @param ScriptInterface $redeemScript
* @param ScriptInterface $witnessScript
* @return array
*/
public static function estimateUtxoFromScripts(
ScriptInterface $scriptPubKey,
ScriptInterface $redeemScript = null,
ScriptInterface $witnessScript = null
) {
$classifier = new OutputClassifier();
$decodePK = $classifier->decode($scriptPubKey);
$witness = false;
if ($decodePK->getType() === ScriptType::P2SH) {
if (null === $redeemScript) {
throw new \RuntimeException("Can't estimate, missing redeem script");
}
$decodePK = $classifier->decode($redeemScript);
}
if ($decodePK->getType() === ScriptType::P2WKH) {
$scriptSitu = ScriptFactory::scriptPubKey()->p2pkh($decodePK->getSolution());
$decodePK = $classifier->decode($scriptSitu);
$witness = true;
} else if ($decodePK->getType() === ScriptType::P2WSH) {
if (null === $witnessScript) {
throw new \RuntimeException("Can't estimate, missing witness script");
}
$decodePK = $classifier->decode($witnessScript);
$witness = true;
}
if (!in_array($decodePK->getType(), [ScriptType::MULTISIG, ScriptType::P2PKH, ScriptType::P2PK])) {
throw new \RuntimeException("Unsupported script type");
}
$script = $decodePK->getScript();
list ($scriptSig, $witness) = SizeEstimation::estimateInputFromScripts($script, $redeemScript, $witnessScript, $witness);
return [
"scriptSig" => $scriptSig,
"witness" => $witness,
];
}
/**
* @param UTXO[] $utxos
* @param bool $withWitness
* @return integer
*/
public static function estimateInputsSize(array $utxos, $withWitness) {
$inputSize = 0;
$witnessSize = 0;
foreach ($utxos as $utxo) {
$estimate = SizeEstimation::estimateUtxo($utxo);
$inputSize += 32 + 4 + 4;
$inputSize += $estimate['scriptSig'];
if ($withWitness) {
$witnessSize += $estimate['witness'];
}
}
if ($withWitness && $witnessSize != 0) {
$inputSize += $witnessSize;
$inputSize += 2; // flag bytes
}
return $inputSize;
}
/**
* @param array $outputs
* @return int
*/
public static function estimateOutputsSize(array $outputs) {
$outputSize = 0;
foreach ($outputs as $output) {
$size = 8;
$scriptSize = null;
if ($output instanceof TransactionOutputInterface) {
$scriptSize = $output->getScript()->getBuffer()->getSize();
} else {
if (isset($output['scriptPubKey'])) {
if ($output['scriptPubKey'] instanceof ScriptInterface) {
$scriptSize = $output['scriptPubKey']->getBuffer()->getSize();
} else {
$scriptSize = strlen($output['scriptPubKey']) / 2;
}
} else {
$scriptSize = 25;
}
}
$size += SizeEstimation::getLengthOfVarInt($scriptSize) + $scriptSize;
$outputSize += $size;
}
return $outputSize;
}
/**
* @param UTXO[] $utxos
* @param array $outputs
* @return int
*/
public static function estimateVsize(array $utxos, array $outputs) {
return (int)ceil(self::estimateWeight($utxos, $outputs) / 4);
}
/**
* @param UTXO[] $utxos
* @param array $outputs
* @return int
*/
public static function estimateWeight(array $utxos, array $outputs) {
$outputsSize = SizeEstimation::estimateOutputsSize($outputs);
$outputsSize += SizeEstimation::getLengthOfVarInt(count($outputs));
$baseSize = 4 +
SizeEstimation::getLengthOfVarInt(count($utxos)) + SizeEstimation::estimateInputsSize($utxos, false) +
$outputsSize + 4;
$witnessSize = 4 +
SizeEstimation::getLengthOfVarInt(count($utxos)) + SizeEstimation::estimateInputsSize($utxos, true) +
$outputsSize + 4;
return ($baseSize * 3) + $witnessSize;
}
}