lbcd/txscript/example_test.go

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// Copyright (c) 2014-2016 The btcsuite developers
txscript: Introduce zero-alloc script tokenizer. This implements an efficient and zero-allocation script tokenizer that is exported to both provide a new capability to tokenize scripts to external consumers of the API as well as to serve as a base for refactoring the existing highly inefficient internal code. It is important to note that this tokenizer is intended to be used in consensus critical code in the future, so it must exactly follow the existing semantics. The current script parsing mechanism used throughout the txscript module is to fully tokenize the scripts into an array of internal parsed opcodes which are then examined and passed around in order to implement virtually everything related to scripts. While that approach does simplify the analysis of certain scripts and thus provide some nice properties in that regard, it is both extremely inefficient in many cases, and makes it impossible for external consumers of the API to implement any form of custom script analysis without manually implementing a bunch of error prone tokenizing code or, alternatively, the script engine exposing internal structures. For example, as shown by profiling the total memory allocations of an initial sync, the existing script parsing code allocates a total of around 295.12GB, which equates to around 50% of all allocations performed. The zero-alloc tokenizer this introduces will allow that to be reduced to virtually zero. The following is a before and after comparison of tokenizing a large script with a high opcode count using the existing code versus the tokenizer this introduces for both speed and memory allocations: benchmark old ns/op new ns/op delta BenchmarkScriptParsing-8 63464 677 -98.93% benchmark old allocs new allocs delta BenchmarkScriptParsing-8 1 0 -100.00% benchmark old bytes new bytes delta BenchmarkScriptParsing-8 311299 0 -100.00% The following is an overview of the changes: - Introduce new error code ErrUnsupportedScriptVersion - Implement zero-allocation script tokenizer - Add a full suite of tests to ensure the tokenizer works as intended and follows the required consensus semantics - Add an example of using the new tokenizer to count the number of opcodes in a script - Update README.md to include the new example - Update script parsing benchmark to use the new tokenizer
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// Copyright (c) 2015-2019 The Decred developers
// Use of this source code is governed by an ISC
// license that can be found in the LICENSE file.
package txscript_test
import (
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"encoding/hex"
"fmt"
"github.com/lbryio/lbcd/btcec"
"github.com/lbryio/lbcd/chaincfg"
"github.com/lbryio/lbcd/chaincfg/chainhash"
"github.com/lbryio/lbcd/txscript"
"github.com/lbryio/lbcd/wire"
btcutil "github.com/lbryio/lbcutil"
)
// This example demonstrates creating a script which pays to a bitcoin address.
// It also prints the created script hex and uses the DisasmString function to
// display the disassembled script.
func ExamplePayToAddrScript() {
// Parse the address to send the coins to into a btcutil.Address
// which is useful to ensure the accuracy of the address and determine
// the address type. It is also required for the upcoming call to
// PayToAddrScript.
addressStr := "bHW58d37s1hBjj3wPBkn5zpCX3F8ZW3uWf"
address, err := btcutil.DecodeAddress(addressStr, &chaincfg.MainNetParams)
if err != nil {
fmt.Println(err)
return
}
// Create a public key script that pays to the address.
script, err := txscript.PayToAddrScript(address)
if err != nil {
fmt.Println(err)
return
}
fmt.Printf("Script Hex: %x\n", script)
disasm, err := txscript.DisasmString(script)
if err != nil {
fmt.Println(err)
return
}
fmt.Println("Script Disassembly:", disasm)
// Output:
// Script Hex: 76a914345991dbf57bfb014b87006acdfafbfc5fe8292f88ac
// Script Disassembly: OP_DUP OP_HASH160 345991dbf57bfb014b87006acdfafbfc5fe8292f OP_EQUALVERIFY OP_CHECKSIG
}
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// This example demonstrates extracting information from a standard public key
// script.
func ExampleExtractPkScriptAddrs() {
// Start with a standard pay-to-pubkey-hash script.
scriptHex := "76a914128004ff2fcaf13b2b91eb654b1dc2b674f7ec6188ac"
script, err := hex.DecodeString(scriptHex)
if err != nil {
fmt.Println(err)
return
}
// Extract and print details from the script.
scriptClass, addresses, reqSigs, err := txscript.ExtractPkScriptAddrs(
script, &chaincfg.MainNetParams)
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if err != nil {
fmt.Println(err)
return
}
fmt.Println("Script Class:", scriptClass)
fmt.Println("Addresses:", addresses)
fmt.Println("Required Signatures:", reqSigs)
// Output:
// Script Class: pubkeyhash
// Addresses: [bER6Ddq6YfRKDJDmmdeaqrP8XHmDJcYSJQ]
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// Required Signatures: 1
}
// This example demonstrates manually creating and signing a redeem transaction.
func ExampleSignTxOutput() {
// Ordinarily the private key would come from whatever storage mechanism
// is being used, but for this example just hard code it.
privKeyBytes, err := hex.DecodeString("22a47fa09a223f2aa079edf85a7c2" +
"d4f8720ee63e502ee2869afab7de234b80c")
if err != nil {
fmt.Println(err)
return
}
privKey, pubKey := btcec.PrivKeyFromBytes(btcec.S256(), privKeyBytes)
pubKeyHash := btcutil.Hash160(pubKey.SerializeCompressed())
addr, err := btcutil.NewAddressPubKeyHash(pubKeyHash,
&chaincfg.MainNetParams)
if err != nil {
fmt.Println(err)
return
}
// For this example, create a fake transaction that represents what
// would ordinarily be the real transaction that is being spent. It
// contains a single output that pays to address in the amount of 1 BTC.
originTx := wire.NewMsgTx(wire.TxVersion)
prevOut := wire.NewOutPoint(&chainhash.Hash{}, ^uint32(0))
txIn := wire.NewTxIn(prevOut, []byte{txscript.OP_0, txscript.OP_0}, nil)
originTx.AddTxIn(txIn)
pkScript, err := txscript.PayToAddrScript(addr)
if err != nil {
fmt.Println(err)
return
}
txOut := wire.NewTxOut(100000000, pkScript)
originTx.AddTxOut(txOut)
originTxHash := originTx.TxHash()
// Create the transaction to redeem the fake transaction.
redeemTx := wire.NewMsgTx(wire.TxVersion)
// Add the input(s) the redeeming transaction will spend. There is no
// signature script at this point since it hasn't been created or signed
// yet, hence nil is provided for it.
prevOut = wire.NewOutPoint(&originTxHash, 0)
txIn = wire.NewTxIn(prevOut, nil, nil)
redeemTx.AddTxIn(txIn)
// Ordinarily this would contain that actual destination of the funds,
// but for this example don't bother.
txOut = wire.NewTxOut(0, nil)
redeemTx.AddTxOut(txOut)
// Sign the redeeming transaction.
lookupKey := func(a btcutil.Address) (*btcec.PrivateKey, bool, error) {
// Ordinarily this function would involve looking up the private
// key for the provided address, but since the only thing being
// signed in this example uses the address associated with the
// private key from above, simply return it with the compressed
// flag set since the address is using the associated compressed
// public key.
//
// NOTE: If you want to prove the code is actually signing the
// transaction properly, uncomment the following line which
// intentionally returns an invalid key to sign with, which in
// turn will result in a failure during the script execution
// when verifying the signature.
//
// privKey.D.SetInt64(12345)
//
return privKey, true, nil
}
// Notice that the script database parameter is nil here since it isn't
// used. It must be specified when pay-to-script-hash transactions are
// being signed.
sigScript, err := txscript.SignTxOutput(&chaincfg.MainNetParams,
redeemTx, 0, originTx.TxOut[0].PkScript, txscript.SigHashAll,
txscript.KeyClosure(lookupKey), nil, nil)
if err != nil {
fmt.Println(err)
return
}
redeemTx.TxIn[0].SignatureScript = sigScript
// Prove that the transaction has been validly signed by executing the
// script pair.
flags := txscript.ScriptBip16 | txscript.ScriptVerifyDERSignatures |
txscript.ScriptStrictMultiSig |
txscript.ScriptDiscourageUpgradableNops
vm, err := txscript.NewEngine(originTx.TxOut[0].PkScript, redeemTx, 0,
flags, nil, nil, -1)
if err != nil {
fmt.Println(err)
return
}
if err := vm.Execute(); err != nil {
fmt.Println(err)
return
}
fmt.Println("Transaction successfully signed")
// Output:
// Transaction successfully signed
}
txscript: Introduce zero-alloc script tokenizer. This implements an efficient and zero-allocation script tokenizer that is exported to both provide a new capability to tokenize scripts to external consumers of the API as well as to serve as a base for refactoring the existing highly inefficient internal code. It is important to note that this tokenizer is intended to be used in consensus critical code in the future, so it must exactly follow the existing semantics. The current script parsing mechanism used throughout the txscript module is to fully tokenize the scripts into an array of internal parsed opcodes which are then examined and passed around in order to implement virtually everything related to scripts. While that approach does simplify the analysis of certain scripts and thus provide some nice properties in that regard, it is both extremely inefficient in many cases, and makes it impossible for external consumers of the API to implement any form of custom script analysis without manually implementing a bunch of error prone tokenizing code or, alternatively, the script engine exposing internal structures. For example, as shown by profiling the total memory allocations of an initial sync, the existing script parsing code allocates a total of around 295.12GB, which equates to around 50% of all allocations performed. The zero-alloc tokenizer this introduces will allow that to be reduced to virtually zero. The following is a before and after comparison of tokenizing a large script with a high opcode count using the existing code versus the tokenizer this introduces for both speed and memory allocations: benchmark old ns/op new ns/op delta BenchmarkScriptParsing-8 63464 677 -98.93% benchmark old allocs new allocs delta BenchmarkScriptParsing-8 1 0 -100.00% benchmark old bytes new bytes delta BenchmarkScriptParsing-8 311299 0 -100.00% The following is an overview of the changes: - Introduce new error code ErrUnsupportedScriptVersion - Implement zero-allocation script tokenizer - Add a full suite of tests to ensure the tokenizer works as intended and follows the required consensus semantics - Add an example of using the new tokenizer to count the number of opcodes in a script - Update README.md to include the new example - Update script parsing benchmark to use the new tokenizer
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// This example demonstrates creating a script tokenizer instance and using it
// to count the number of opcodes a script contains.
func ExampleScriptTokenizer() {
// Create a script to use in the example. Ordinarily this would come from
// some other source.
hash160 := btcutil.Hash160([]byte("example"))
script, err := txscript.NewScriptBuilder().AddOp(txscript.OP_DUP).
AddOp(txscript.OP_HASH160).AddData(hash160).
AddOp(txscript.OP_EQUALVERIFY).AddOp(txscript.OP_CHECKSIG).Script()
if err != nil {
fmt.Printf("failed to build script: %v\n", err)
return
}
// Create a tokenizer to iterate the script and count the number of opcodes.
const scriptVersion = 0
var numOpcodes int
tokenizer := txscript.MakeScriptTokenizer(scriptVersion, script)
for tokenizer.Next() {
numOpcodes++
}
if tokenizer.Err() != nil {
fmt.Printf("script failed to parse: %v\n", err)
} else {
fmt.Printf("script contains %d opcode(s)\n", numOpcodes)
}
// Output:
// script contains 5 opcode(s)
}