Add signedSize for inputs so fees can be predicted

peercoin · Nov 8, 2023 · 8ff580a · 8ff580a
1 parent e053348
commit 8ff580a
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Showing 6 changed files with 40 additions and 0 deletions.
diff --git a/coinlib/lib/src/tx/inputs/input.dart b/coinlib/lib/src/tx/inputs/input.dart
@@ -21,6 +21,12 @@ abstract class Input with Writable {
  /// True when the input is fully signed and ready for broadcast
  bool get complete;
 
+ /// The maximum total size when fully signed via the default hash type
+ /// including any witness data of the input. If this is unknown, this is
+ /// null. The actual signed size may be lower according to the data being
+ /// encoded.
+ int? get signedSize => null;
+
  Input();
 
  /// Given a [RawInput] and witness data, the specific [Input] subclass is

diff --git a/coinlib/lib/src/tx/inputs/p2pkh_input.dart b/coinlib/lib/src/tx/inputs/p2pkh_input.dart
@@ -23,6 +23,8 @@ class P2PKHInput extends LegacyInput with PKHInput {
  final ECPublicKey publicKey;
  @override
  final ECDSAInputSignature? insig;
+ @override
+ final int? signedSize = 147;
 
  P2PKHInput({
  required OutPoint prevOut,

diff --git a/coinlib/lib/src/tx/inputs/p2sh_multisig_input.dart b/coinlib/lib/src/tx/inputs/p2sh_multisig_input.dart
@@ -200,4 +200,17 @@ class P2SHMultisigInput extends LegacyInput {
  @override
  Script get script => super.script!;
 
+ int get _signedScriptSize
+ => 1 // Extra 0
+ + program.threshold*73 // Add 73 bytes per signature
+ // Determine the length of the program pushdata by actually compiling it.
+ // Not the most efficient but the simplest solution.
+ + ScriptPushData(program.script.compiled).compiled.length;
+
+ @override
+ int? get signedSize
+ => 40 // Outpoint plus sequence
+ + _signedScriptSize
+ + (_signedScriptSize < 0xfd ? 1 : 3); // Varint size
+
 }
diff --git a/coinlib/lib/src/tx/inputs/p2wpkh_input.dart b/coinlib/lib/src/tx/inputs/p2wpkh_input.dart
@@ -22,6 +22,8 @@ class P2WPKHInput extends LegacyWitnessInput with PKHInput {
  final ECPublicKey publicKey;
  @override
  final ECDSAInputSignature? insig;
+ @override
+ final int? signedSize = 147;
 
  P2WPKHInput({
  required OutPoint prevOut,

diff --git a/coinlib/lib/src/tx/inputs/taproot_key_input.dart b/coinlib/lib/src/tx/inputs/taproot_key_input.dart
@@ -16,6 +16,10 @@ class TaprootKeyInput extends TaprootInput {
 
  final SchnorrInputSignature? insig;
 
+ @override
+ // 64-bit sig plus varint with default sighash type
+ final int? signedSize = 41 + 65;
+
  TaprootKeyInput({
  required OutPoint prevOut,
  this.insig,

diff --git a/coinlib/test/tx/transaction_test.dart b/coinlib/test/tx/transaction_test.dart
@@ -40,6 +40,10 @@ void main() {
  expect(mapToHex(tx.outputs), mapToHex(vec.obj.outputs));
  }
 
+ expectInputSignedSize(Input input) => expect(
+ input.size, lessThanOrEqualTo(input.signedSize!),
+ );
+
  test("valid txs", () {
  for (final vec in validTxVecs) {
 
@@ -331,6 +335,7 @@ void main() {
  key: keyVec.privateObj,
  hashType: hashType,
  );
+ expectInputSignedSize(signed.inputs[i]);
  }
 
  expect(tx.complete, false);
@@ -426,6 +431,7 @@ void main() {
  inputN: 1, key: keyVec.privateObj, value: BigInt.from(3000000),
  );
  expect(signed.complete, true);
+ expectInputSignedSize(signed.inputs[1]);
 
  expect(
  signed.toHex(),
@@ -479,6 +485,9 @@ void main() {
  );
 
  expect(signed.complete, true);
+ for (final input in signed.inputs) {
+ expectInputSignedSize(input);
+ }
 
  expect(
  signed.toHex(),
@@ -602,6 +611,8 @@ void main() {
  outputs: [exampleOutput, exampleOutput],
  );
 
+ final signedSizeFromUnsigned = tx.inputs[1].signedSize;
+
  // Sign first P2PKH input
  var signed = tx.sign(inputN: 0, key: privkeys[0]);
  expect(signed.complete, false);
@@ -638,6 +649,8 @@ void main() {
 
  // Check final tx
  expect(signed.complete, true);
+ expectInputSignedSize(signed.inputs[1]);
+ expect(signed.inputs[1].signedSize, signedSizeFromUnsigned);
  expectMultisigSigs(
  signed, [
  SigHashType.single(),