// isNonstandardTransaction determines whether a transaction contains any
// scripts which are not one of the standard types.
func isNonstandardTransaction(tx *btcutil.Tx) bool {
// Check all of the output public key scripts for non-standard scripts.
for _, txOut := range tx.MsgTx().TxOut {
scriptClass := txscript.GetScriptClass(txOut.PkScript)
if scriptClass == txscript.NonStandardTy {
return true
}
}
return false
}
// IsDustOutput determines whether a transaction output is considered dust.
// Transactions with dust outputs are not standard and are rejected by mempools
// with default policies.
func IsDustOutput(output *wire.TxOut, relayFeePerKb btcutil.Amount) bool {
// Unspendable outputs which solely carry data are not checked for dust.
if txscript.GetScriptClass(output.PkScript) == txscript.NullDataTy {
return false
}
// All other unspendable outputs are considered dust.
if txscript.IsUnspendable(output.PkScript) {
return true
}
return IsDustAmount(btcutil.Amount(output.Value), len(output.PkScript),
relayFeePerKb)
}
// checkInputsStandard performs a series of checks on a transaction's inputs
// to ensure they are "standard". A standard transaction input within the
// context of this function is one whose referenced public key script is of a
// standard form and, for pay-to-script-hash, does not have more than
// maxStandardP2SHSigOps signature operations. However, it should also be noted
// that standard inputs also are those which have a clean stack after execution
// and only contain pushed data in their signature scripts. This function does
// not perform those checks because the script engine already does this more
// accurately and concisely via the txscript.ScriptVerifyCleanStack and
// txscript.ScriptVerifySigPushOnly flags.
func checkInputsStandard(tx *btcutil.Tx, utxoView *blockchain.UtxoViewpoint) error {
// NOTE: The reference implementation also does a coinbase check here,
// but coinbases have already been rejected prior to calling this
// function so no need to recheck.
for i, txIn := range tx.MsgTx().TxIn {
// It is safe to elide existence and index checks here since
// they have already been checked prior to calling this
// function.
prevOut := txIn.PreviousOutPoint
entry := utxoView.LookupEntry(&prevOut.Hash)
originPkScript := entry.PkScriptByIndex(prevOut.Index)
switch txscript.GetScriptClass(originPkScript) {
case txscript.NonStandardTy:
str := fmt.Sprintf("transaction input #%d has a "+
"non-standard script form", i)
return txRuleError(wire.RejectNonstandard, str)
}
}
return nil
}
// TestCheckPkScriptStandard tests the checkPkScriptStandard API.
func TestCheckPkScriptStandard(t *testing.T) {
var pubKeys [][]byte
for i := 0; i < 4; i++ {
pk, err := btcec.NewPrivateKey(btcec.S256())
if err != nil {
t.Fatalf("TestCheckPkScriptStandard NewPrivateKey failed: %v",
err)
return
}
pubKeys = append(pubKeys, pk.PubKey().SerializeCompressed())
}
tests := []struct {
name string // test description.
script *txscript.ScriptBuilder
isStandard bool
}{
{
"key1 and key2",
txscript.NewScriptBuilder().AddOp(txscript.OP_2).
AddData(pubKeys[0]).AddData(pubKeys[1]).
AddOp(txscript.OP_2).AddOp(txscript.OP_CHECKMULTISIG),
true,
},
{
"key1 or key2",
txscript.NewScriptBuilder().AddOp(txscript.OP_1).
AddData(pubKeys[0]).AddData(pubKeys[1]).
AddOp(txscript.OP_2).AddOp(txscript.OP_CHECKMULTISIG),
true,
},
{
"escrow",
txscript.NewScriptBuilder().AddOp(txscript.OP_2).
AddData(pubKeys[0]).AddData(pubKeys[1]).
AddData(pubKeys[2]).
AddOp(txscript.OP_3).AddOp(txscript.OP_CHECKMULTISIG),
true,
},
{
"one of four",
txscript.NewScriptBuilder().AddOp(txscript.OP_1).
AddData(pubKeys[0]).AddData(pubKeys[1]).
AddData(pubKeys[2]).AddData(pubKeys[3]).
AddOp(txscript.OP_4).AddOp(txscript.OP_CHECKMULTISIG),
false,
},
{
"malformed1",
txscript.NewScriptBuilder().AddOp(txscript.OP_3).
AddData(pubKeys[0]).AddData(pubKeys[1]).
AddOp(txscript.OP_2).AddOp(txscript.OP_CHECKMULTISIG),
false,
},
{
"malformed2",
txscript.NewScriptBuilder().AddOp(txscript.OP_2).
AddData(pubKeys[0]).AddData(pubKeys[1]).
AddOp(txscript.OP_3).AddOp(txscript.OP_CHECKMULTISIG),
false,
},
{
"malformed3",
txscript.NewScriptBuilder().AddOp(txscript.OP_0).
AddData(pubKeys[0]).AddData(pubKeys[1]).
AddOp(txscript.OP_2).AddOp(txscript.OP_CHECKMULTISIG),
false,
},
{
"malformed4",
txscript.NewScriptBuilder().AddOp(txscript.OP_1).
AddData(pubKeys[0]).AddData(pubKeys[1]).
AddOp(txscript.OP_0).AddOp(txscript.OP_CHECKMULTISIG),
false,
},
{
"malformed5",
txscript.NewScriptBuilder().AddOp(txscript.OP_1).
AddData(pubKeys[0]).AddData(pubKeys[1]).
AddOp(txscript.OP_CHECKMULTISIG),
false,
},
{
"malformed6",
txscript.NewScriptBuilder().AddOp(txscript.OP_1).
AddData(pubKeys[0]).AddData(pubKeys[1]),
false,
},
}
for _, test := range tests {
script, err := test.script.Script()
if err != nil {
t.Fatalf("TestCheckPkScriptStandard test '%s' "+
"failed: %v", test.name, err)
continue
}
scriptClass := txscript.GetScriptClass(script)
got := checkPkScriptStandard(script, scriptClass)
if (test.isStandard && got != nil) ||
(!test.isStandard && got == nil) {
t.Fatalf("TestCheckPkScriptStandard test '%s' failed",
test.name)
return
}
}
}
// checkTransactionStandard performs a series of checks on a transaction to
// ensure it is a "standard" transaction. A standard transaction is one that
// conforms to several additional limiting cases over what is considered a
// "sane" transaction such as having a version in the supported range, being
// finalized, conforming to more stringent size constraints, having scripts
// of recognized forms, and not containing "dust" outputs (those that are
// so small it costs more to process them than they are worth).
func checkTransactionStandard(tx *btcutil.Tx, height int32,
medianTimePast time.Time, minRelayTxFee btcutil.Amount,
maxTxVersion int32) error {
// The transaction must be a currently supported version.
msgTx := tx.MsgTx()
if msgTx.Version > maxTxVersion || msgTx.Version < 1 {
str := fmt.Sprintf("transaction version %d is not in the "+
"valid range of %d-%d", msgTx.Version, 1,
maxTxVersion)
return txRuleError(wire.RejectNonstandard, str)
}
// The transaction must be finalized to be standard and therefore
// considered for inclusion in a block.
if !blockchain.IsFinalizedTransaction(tx, height, medianTimePast) {
return txRuleError(wire.RejectNonstandard,
"transaction is not finalized")
}
// Since extremely large transactions with a lot of inputs can cost
// almost as much to process as the sender fees, limit the maximum
// size of a transaction. This also helps mitigate CPU exhaustion
// attacks.
txWeight := blockchain.GetTransactionWeight(tx)
if txWeight > maxStandardTxWeight {
str := fmt.Sprintf("weight of transaction %v is larger than max "+
"allowed weight of %v", txWeight, maxStandardTxWeight)
return txRuleError(wire.RejectNonstandard, str)
}
for i, txIn := range msgTx.TxIn {
// Each transaction input signature script must not exceed the
// maximum size allowed for a standard transaction. See
// the comment on maxStandardSigScriptSize for more details.
sigScriptLen := len(txIn.SignatureScript)
if sigScriptLen > maxStandardSigScriptSize {
str := fmt.Sprintf("transaction input %d: signature "+
"script size of %d bytes is large than max "+
"allowed size of %d bytes", i, sigScriptLen,
maxStandardSigScriptSize)
return txRuleError(wire.RejectNonstandard, str)
}
// Each transaction input signature script must only contain
// opcodes which push data onto the stack.
if !txscript.IsPushOnlyScript(txIn.SignatureScript) {
str := fmt.Sprintf("transaction input %d: signature "+
"script is not push only", i)
return txRuleError(wire.RejectNonstandard, str)
}
}
// None of the output public key scripts can be a non-standard script or
// be "dust" (except when the script is a null data script).
numNullDataOutputs := 0
for i, txOut := range msgTx.TxOut {
scriptClass := txscript.GetScriptClass(txOut.PkScript)
err := checkPkScriptStandard(txOut.PkScript, scriptClass)
if err != nil {
// Attempt to extract a reject code from the error so
// it can be retained. When not possible, fall back to
// a non standard error.
rejectCode := wire.RejectNonstandard
if rejCode, found := extractRejectCode(err); found {
rejectCode = rejCode
}
str := fmt.Sprintf("transaction output %d: %v", i, err)
return txRuleError(rejectCode, str)
}
// Accumulate the number of outputs which only carry data. For
// all other script types, ensure the output value is not
// "dust".
if scriptClass == txscript.NullDataTy {
numNullDataOutputs++
} else if isDust(txOut, minRelayTxFee) {
str := fmt.Sprintf("transaction output %d: payment "+
"of %d is dust", i, txOut.Value)
return txRuleError(wire.RejectDust, str)
}
}
// A standard transaction must not have more than one output script that
// only carries data.
if numNullDataOutputs > 1 {
str := "more than one transaction output in a nulldata script"
return txRuleError(wire.RejectNonstandard, str)
}
return nil
}